Claims for Patent: 5,104,888

Summary for Patent: 5,104,888

Title:	Thiazolidine derivatives, their preparation and use
Abstract:	Compounds of formula (I): ##STR1## (in which R.sup.1 -R.sup.7 are hydrogen or various organic groups, n is 1-10, Ar is an aromatic group, U is CH.sub.2 or a carbon atom doubly bonded to either one of its adjacent carbons, and W is >CH.sub.2, >C.dbd.O, >CHOH, >C.dbd.NOH or various derivatives thereof) have the ability to lower the levels of blood lipid peroxides and blood sugars and to inhibit the activity of aldose reductase; they may be used therapeutically for these purposes.
Inventor(s):	Yoshioka; Takao (Hiromachi, JP), Kitazawa; Eiichi (Hiromachi, JP), Kurumada; Yomoyuki (Hiromachi, JP), Yamazaki; Mitsuo (Hiromachi, JP), Hasegawa; Kazuo (Hiromachi, JP), Fujita; Takashi (Hiromachi, JP)
Assignee:	Sankyo Company, Limited (Tokyo, JP)
Application Number:	07/560,466
Patent Claims:	1. A compound of formula (I): ##STR619## in which: R.sup.1 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group or a C.sub.7 -C.sub.13 aralkyl group; R.sup.2 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.23 alkanoyl group, a C.sub.3 -C.sub.23 alkenoyl group, a C.sub.3 -C.sub.23 alkynoyl group, a substituted C.sub.1 -C.sub.23 alkanoyl, C.sub.3 -C.sub.23 alkenoyl or C.sub.3 -C.sub.23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl, a 5 to 8-membered heterocyclic acyl group having 1 to 3 hetero atoms of N, S or O, a group of formula --SO.sub.3 R.sup.8 where R.sup.6 represents a hydrogen atom, an aralkyl group where the alkyl part is C.sub.1 -C.sub.3 alkyl, a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.5 alkyl group having at least one substituent selected from the group consisting of hydroxy groups and C.sub.1 -C.sub.5 alkoxy groups, a C.sub.1 -C.sub.10 alkyl group or a substituted C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (b); R.sup.4 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group or a C.sub.1 -C.sub.5 alkoxy group; R.sup.5 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.5 alkoxy group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.10 alkyl groups and substituted C.sub.1 -C.sub.10 alkyl groups having at least one substituent selected from the group consisting of substituents (b); Ar is a divalent group selected from the group consisting of divalent carbocyclic aromatic groups, and divalent heterocyclic aromatic groups formed from a pyridine, furan, thiophene or pyrrole ring; W represents a --CH.sub.2 -- group, a >C.dbd.O group, a group of formula >CH--OR.sup.11 wherein R.sup.11 represents a hydrogen atom, a C.sub.1 -C.sub.23 alkanoyl group, a C.sub.3 -C.sub.23 alkenoyl group, a C.sub.3 -C.sub.23 alkynoyl group, a substituted C.sub.1 -C.sub.23 alkanoyl, C.sub.3 -C.sub.23 alkenoyl or C.sub.3 -C.sub.23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and napthoyl, a 5-8 membered heterocyclia acyl having 1 to 3 heteroatoms of N, S, or O, A C.sub.1 -C.sub.10 alkyl group or a substituted C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (b), or a group of formula >C.dbd.N--O--R.sup.12 in which R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group, a C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (b), a C.sub.1 -C.sub.23 alkanoyl group, a C.sub.3 -C.sub.23 alkenoyl group, a C.sub.3 -C.sub.23 alkynoyl group, a substituted C.sub.1 -C.sub.23 alkanoyl, C.sub.3 -C.sub.23 alkenoyl or C.sub.3 -C.sub.23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl or a heterocyclic acyl group having 1 to 3 heteroatoms of N, S or O; U represents a --CH.sub.2 -- group; or W and U together represent a group of formula --CH.dbd.CH--; or when W represents a carbonyl group or said group of formula >C.dbd.N--OR.sup.12, U, R.sup.1 and the carbon atom to which R.sup.1 is attached together represent a group of formula --CH.dbd.C<; n is an integer of from 1 to 3; said aryl groups and the aryl parts of said aralkyl, aralkyloxycarbonyl, and aromatic acyloxy being C.sub.6 -C.sub.10 carbocyclic aryl groups which are unsubstituted or have at least one substituent selected from the group consisting of substituents (c); said heterocyclic groups, heterocyclic parts of said heterocyclic acyl and acyloxy groups have from 5 to 10 ring atoms, of which from 1 to 5 are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic groups being unsubstituted or having at least one substituent selected from the group consisting of substituents (d); said substituents (a) being selected from the group consisting of aryl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and aralkyloxycarbonyl groups; said substituents (b) being selected from the group consisting of hydroxy groups, C.sub.1 -C.sub.5 alkoxy groups, aryl groups, C.sub.1 -C.sub.23 alkanoyloxy groups, C.sub.3 -C.sub.23 alkenoyloxy groups, C.sub.3 -C.sub.23 alkynoyloxy groups, substituted C.sub.1 -C.sub.23 alkanoyloxy, C.sub.3 -C.sub.23 alkenoyloxy or C.sub.3 -C.sub.23 alkynoyloxy groups having at least one substituent selected from the group consisting of substituents (a), aromatic acyloxy groups, heterocyclic acyloxy groups, groups of formula --COOR.sup.8 where R.sup.8 is as defined above and groups of formula --CONR.sup.9 R.sup.10 where R.sup.9 and R.sup.10 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.5 alkyl groups or R.sup.9 and R.sup.10, together with the nitrogen atom to which they are attached, represent a heterocyclic group having from 5 to 7 ring atoms of which from 1 to 3 atoms, including nitrogen atom, are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted, or, where said ring atoms include an additional nitrogen hetero-atom, said additional nitrogen atom being unsubstituted or having a single substituent selected from the group consisting of substituents (e); said substituents (c) being selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups, C.sub.1 -C.sub.5 alkyl groups having at least one halogen substituent, halogen atoms, amino groups, C.sub.1 -C.sub.5 alkylamino groups, dialkylamino groups in which each alkyl part is C.sub.1 -C.sub.5, nitro groups, cyano groups, groups of formula --CONR.sub.2 where R represents a C.sub.1 -C.sub.5 alkyl group or an aryl group and hydroxy groups; and said substituents (d) being selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and doubly bonded oxygen atoms; said substituents (e) being selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkanoyl groups, C.sub.3 -C.sub.5 alkenoyl groups and C.sub.3 -C.sub.5 alkynoyl groups; provided that: (.alpha.) where: R.sup.3 represents said hydrogen atom, an unsubstituted C.sub.1 -C.sub.6 alkanoyl group, an unsubstituted C.sub.3 -C.sub.6 alkenoyl group, an unsubstituted C.sub.3 -C.sub.6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group; and R.sup.6 and R.sup.7 both represent hydrogen atoms; and Ar represents a p-phenylene group; and W represents a group of formula >CH.sub.2, >C.dbd.O or >CH--OR.sup.11x (wherein R.sup.11x represents a hydrogen atom, an unsubstituted C.sub.1 -C.sub.6 alkanoyl group, an unsubstituted C.sub.3 -C.sub.6 alkenoyl group, an unsubstituted C.sub.3 -C.sub.6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group); and U represents said group of formula >CH.sub.2, then (i) when R.sup.1 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group, R.sup.4 represents a C.sub.6 -C.sub.10 alkyl group, and (ii) when R.sup.4 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.5 alkoxy group, R.sup.1 represents a C.sub.6 -C.sub.10 alkyl group or said C.sub.7 -C.sub.13 aralkyl group; (.beta.) where: R.sup.1 and R.sup.2 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.5 alkyl groups; and R.sup.4 and R.sup.5 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.5 alkyl groups and C.sub.1 -C.sub.5 alkoxy groups; and Ar represents a p-phenylene group; and W is a group of formula >CH.sub.2, >C.dbd.O or >CH--OR.sup.11x (where R.sup.11x is as defined above); and U represents said group of formula >CH.sub.2 ; and n is an integer from 1 to 3, then at least one of R.sup.3, R.sup.6 and R.sup.7 represents said alkyl or substituted alkyl group; and pharmaceutically acceptable salts thereof. 2. A compound as claimed in claim 1, in which: R.sup.1 represents a hydrogen atom or a C.sub.1 -C.sub.10 alkyl group; R.sup.2 represents a hydrogen atom or a C.sub.1 -C.sub.3 alkyl group; R.sup.3 represents a hydrogen atom, a sulfo group, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C.sub.6 -C.sub.10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R.sup.13 --(CH.sub.2).sub.m --CO--, where R.sup.13 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (g), and m is an integer from 1 to 5, a group of formula Het--CO--, where Het represents a heterocyclic group having 5 to 6 ring atoms, of which from 1 to 3 are hetero-atoms selected from the group consisting of nitrogen oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted or having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a group of formula --COOR.sup.8a, where R.sup.8a represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or an alkoxyalkyl group were both the alkoxy part and the alkyl part are C.sub.1 -C.sub.5, a C.sub.2 -C.sub.5 hydroxyalkyl group, a C.sub.2 -C.sub.5 alkyl group substituted by a group of formula --O--CO--R.sup.53, where R.sup.53 represents a C.sub.1 -C.sub.10 alkyl group, a phenyl group, a phenyl group having at least one substituent selected from the group consisting of substituents (g) or a heterocyclic group Het, as defined above, or a C.sub.1 -C.sub.3 alkyl group substituted by a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (g) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, trifluoromethyl groups, C.sub.1 -C.sub.5 alkoxy groups, halogen atoms, nitro groups, amino groups, hydroxy groups and dialkylamino groups where each alkyl part is C.sub.1 -C.sub.5 ; said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C.sub.1 -C.sub.4, dialkylcarbamoyl groups where each alkyl part is C.sub.1 -C.sub.4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; R.sup.4 represents a C.sub.1 -C.sub.10 alkyl group or a methoxy group; R.sup.5 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a methoxy group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, C.sub.2 -C.sub.5 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a group of formula --O--CO--R.sup.53 where R.sup.53 is as defined above, and C.sub.1 -C.sub.3 alkyl groups having a single substituent selected from the group consisting of substituents (h); Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH.sub.2).sub.n --O-- at its 2-position and is attached to the --CH.sub.2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a C.sub.1 -C.sub.3 alkyl substituent; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH--OR.sup.11 or >C.dbd.N--OR.sup.12 where R.sup.11 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C.sub.6 -C.sub.10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R.sup.13 --(CH.sub.2).sub.m --CO-- where R.sup.13 and m are as defined above or a group of formula Het--CO-- where Het is as defined above, and R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (j), a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C.sub.6 -C.sub.10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), or said group of formula R.sup.13 --CH.sub.2).sub.m --CO-- or Het--CO--; and said substituents (j) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (g), C.sub.2 -C.sub.11 alkanoyloxy groups, C.sub.2 -C.sub.11 alkanoyloxy groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, C.sub.3 -C.sub.11 alkenoyloxy groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, phenylalkenoyloxy groups where the alkenyl part is C.sub.2 -C.sub.10 and the phenyl part is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (g), groups of formula --COOR.sup.8a where R.sup.8a is as defined above, benzyloxycarbonyl groups and groups of formula --COR.sup.9 R.sup.10 where R.sup.9 and R.sup.10 are as defined above; U represents (i) where W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH.sub.2 OR.sup.11 or >C.dbd.N--OR.sup.12, a group of formula --CH.sub.2 --, (ii) with W, a group of formula --CH.dbd.CH--, or (iii) where W represents a group of formula >C.dbd.O or >C.dbd.N--OR.sup.14, in which R.sup.14 represents any one of the acyl groups defined for R.sup.12, with R.sup.1 and the carbon atom to which R.sup.1 is attached, a group of formula --CH.dbd.C<. 3. A compound as claimed in claim 2, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are defined in claim 2; R.sup.6 and R.sup.7 both represent hydrogen atoms; R.sup.3 and R.sup.11 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.10 alkanoyl groups, C.sub.3 -C.sub.10 alkenoyl groups, C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 2, arylcarbonyl groups as defined in claim 2, and groups of formulae R.sup.13 --(CH.sub.2).sub.m --CO-- and Het--CO-- where R.sup.13, m and Het are as defined in claim 2; and R.sup.12 represents any one of the groups or atoms defined for R.sup.3 and R.sup.11 or a C.sub.1 -C.sub.5 alkyl group of a C.sub.1 -C.sub.3 alkyl group having at least one substituent selected from the group consisting of substituents (f) defined in claim 2. 4. A compound as claimed in claim 2, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are as defined in claim 2; R.sup.3, R.sup.6, R.sup.7 and R.sup.12 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2, C.sub.2 -C.sub.5 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a group of formula --O--CO--R.sup.53 where R.sup.53 is as defined in claim 2 and C.sub.1 -C.sub.3 alkyl groups substituted by a single substituent selected from the group consisting of substituents (h) as defined in claim 2; and R.sup.11 represents a hydrogen atom, an acetyl group or a benzoyl group; or R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (k), a C.sub.2 -C.sub.6 alkanoyl group, a C.sub.2 -C.sub.10 alkanoyl group having at least one substituent selected from the group consisting of substituents (l), a C.sub.3 -C.sub.5 alkenoyl group, a C.sub.3 -C.sub.5 alkenoyl group having at least one substituent selected from the group consisting of substituents (l), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (m), a pyridinecarbonyl group, a furoyl group, a thenoyl group or a pyridinecarbonyl, furoyl or thenoyl group having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups; said substituents (k) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (m), C.sub.2 -C.sub.5 alkanoyloxy groups, C.sub.2 -C.sub.10 alkanoyloxy or C.sub.3 -C.sub.10 alkenoyloxy groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2, C.sub.3 -C.sub.10 alkenoyloxy groups substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (m), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (m), groups of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2 and substituents (h) as defined in claim 2; said substituents (l) are selected from the group consisting of phenyl groups, carboxy groups, alkoxycarbonyl groups where the alkoxy part is C.sub.1 -C.sub.5 and benzyloxycarbonyl groups; and said substituents (m) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups, halogen atoms and trifluoromethyl groups. 5. A compound as claimed in claim 1, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, ethyl, isobutyl, pentyl, hexyl, 3,3-dimethylbutyl, heptyl, 4,4-dimethylpentyl, octyl, 5,5-dimethylhexyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (n), an aralkanoyl group of formula R.sup.15 --(CH.sub.2).sub.m --CO-- where R.sup.15 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (n), and m is an integer from 1 to 5, a pyridinecarbonyl group, a furoyl group, a thenoyl group, a C.sub.1 -C.sub.3 alkyl group, a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C.sub.1 -C.sub.5, a C.sub.2 -C.sub.3 hydroxyalkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a C.sub.1 -C.sub.5 alkoxy group, a C.sub.2 -C.sub.5 alkyl group substituted by a C.sub.2 -C.sub.4 alkanoyloxy or a benzoyloxy group or a methyl group having a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (n) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and halogen atoms; R.sup.4 represents a C.sub.1 -C.sub.10 alkyl group; R.sup.5 represents a hydrogen atom or a C.sub.1 -C.sub.3 alkyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.3 alkyl groups, C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, C.sub.2 -C.sub.3 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a C.sub.2 -C.sub.4 alkanoyloxy of a benzoyloxy group, and methyl groups substituted by a single substituent selected from the group consisting of substituents (h); said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C.sub.1 -C.sub.4, dialkylcarbamoyl groups where each alkyl part is C.sub.1 -C.sub.4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH.sub.2).sub.n --O-- at its 2-position and is attached to the --CH.sub.2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a methyl substituent; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH--OR.sup.11 or >C.dbd.N--OR.sup.12, where: R.sup.11 represents a hydrogen atom or any one of the acyl groups defined above for R.sup.3 ; and R.sup.12 represents a benzyl group, any one of the groups or atoms defined above for R.sup.3, a pyridinecarbonyl group or a pyridinecarbonyl group having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups; and U represents (i) where W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH--OR.sup.11 or >C.dbd.N--OR.sup.12 , a group of formula --CH.sub.2 --, (ii) with W, a group of formula --CH.dbd.CH--, or (iii) where W represents a group of formula >C.dbd.O, with R.sup.1 and the carbon atom to which R.sup.1 is attached, a group of formula --CH.dbd.C<. 6. A compound as claimed in claim 5, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are as defined in claim 5; R.sup.6 and R.sup.7 are both hydrogen atoms; R.sup.3 and R.sup.11 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.10 alkanoyl groups, C.sub.3 -C.sub.10 alkenoyl groups, C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 5, benzoyl groups, benzoyl groups having at least one substituent selected from the group consisting of substituents (n) as defined in claim 5, groups of formula R.sup.15 --(CH.sub.2).sub.m --CO-- where R.sup.15 and m are as defined in claim 5, pyridinecarbonyl groups, furoyl groups and thenoyl groups; and R.sup.12 represents a hydrogen atom, a methyl group, a benzyl group, a t-butoxycarbonylmethyl group or any one of the acyl groups defined above for R.sup.3 and R.sup.11. 7. A compound as claimed in claim 5, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are as defined in claim 5; R.sup.3, R.sup.6 R.sup.7 are independently selected from the group consisting of C.sub.1 -C.sub.3 alkyl groups, C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 5, C.sub.2 -C.sub.3 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a C.sub.2 -C.sub.4 alkanoyloxy or a benzoyloxy group, and methyl groups having a single substituent selected from the group consisting of substituents (h) as defined in claim 5; R.sup.11 represents a hydrogen atom; R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.3 alkyl group having at least one substituent selected from the group consisting of substituents (o), a C.sub.2 -C.sub.4 alkanoyl group, a C.sub.2 -C.sub.4 alkanoyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 5, an acryloyl group, an acryloyl group having a .beta.-substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (q), a pyridinecarbonyl group, a pyridinecarbonyl group having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and benzyloxycarbonyl groups; and said substituents (o) are selected from the group consisting of carboxy groups and alkoxycarbonyl groups where the alkoxy part is C.sub.1 -C.sub.5 ; said substituents (q) are selected from the group consisting of methyl groups, ethyl groups, methoxy groups and ethoxy groups. 8. A compound as claimed in claim 1 in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.16 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C.sub.1 -C.sub.5 ; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >C.dbd.N--OH, >C.dbd.N--OCH.sub.2 COOH or >C.dbd.N--OCOR.sup.18 where R.sup.18 represents a C.sub.1 -C.sub.5 alkyl group; and U represents a group of formula --CH.sub.2 --. 9. A compound as claimed in claim 8, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar and U are as defined in claim 8; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, a C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.16 and m are as defined in claim 8, a cis or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 is as defined in claim 8, or a 2-, 3- or 4-pyridinecarbonyl group; R.sup.6 and R.sup.7 are both hydrogen atoms; W represents a group of formula >C.dbd.NOR.sup.12 where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 8, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; and n is 1 or 2. 10. A compound as claimed in claim 8, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar and U are as defined in claim 8; R.sup.3, R.sup.6 and R.sup.7 are independently selected from the group consisting of C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 8; W represents a group of formula >CH.sub.2, >C.dbd.O or >C.dbd.NOR.sup.12 ; R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 8, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; and n is 1 or 2. 11. A compound as claimed in claim 2, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f) as defined in claim 2, an arylcarbonyl group as defined in claim 2, a group of formula R.sup.13 --(CH.sub.2).sub.m --CO-- or Het--CO-- where R.sup.13, m and Het are as defined in claim 2 or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 represents a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; R.sup.7 represents a hydrogen atom or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula >CH.sub.2, >C.dbd.O or >C.dbd.NOR.sup.12, where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 2, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; U represents a group of formula --CH.sub.2 --; and n is 1 or 2. 12. A compound as claimed in claim 2, in which: R.sup.1 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.14 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 represents a hydrogen atom, C.sub.1 -C.sub.5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O or >C.dbd.N--OR.sup.12, where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 2, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; said substituents (n) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and halogen atoms; and U represents a group of formula --CH.sub.2 --. 13. A compound as claimed in claim 2, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.16 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group of a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; R.sup.4 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 2; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O or >C.dbd.N--OR.sup.12 where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 2, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; said substituents (n) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and halogen atoms; and U represents a group of formula --CH.sub.2 --. 14. A compound as claimed in claim 2, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a, where R.sup.8a is as defined in claim 2; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >C.dbd.N--OH, or >C.dbd.N--O--(C.sub.1 -C.sub.3 alkyl)--COOR.sup.8a where R.sup.8a is as defined in claim 2; U represents a group of formula --CH.sub.2 --; and n is 1 or 2. 15. A compound as claimed in claim 2, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents --CH.sub.2 --COO(C.sub.1 -C.sub.5 alkyl) group; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >C.dbd.N--OH, or >C.dbd.N--O--(C.sub.1 -C.sub.3 alkyl)--COO(C.sub.1 -C.sub.5 alkyl); U represents a group of formula --CH.sub.2 --; and n is 1 or 2. 16. The compound as claimed in claim 1, which is 5-[4-(6-Hydroxy-5,7,8-trimethyl-2-octylchroman-2-ylmethoxy)benzyl]thiazoli dine-2,4-dione and pharmaceutically acceptable salts thereof. 17. The compound as claimed in claim 1, which is 5-{4-[6-Hydroxy-4-(E)-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy] benzyl}thiazolidine-2,4-dione and pharmaceutically acceptable salts thereof. 18. The compound as claimed in claim 1, which 5-{4-[6-Acetoxy-4-(E)-acetoxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy] benzyl}thiazolidine-2,4-dione and pharmaceutically acceptable salts thereof. 19. The compound as claimed in claim 1, which is .alpha.-{5-[4-(6-Carboxymethoxy-2,5,7,8-tetramethyl-4-oxochroman-2-ylmetho xy)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid and pharmaceutically acceptable salts thereof. 20. The compound as claimed in claim 1, which is .alpha.-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethylchroman- 2-ylmethoxy)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid and pharmaceutically acceptable salts thereof. 21. The compound as claimed in claim 1, which is .alpha.,.alpha.'-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethy lchroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidine-3,5-diyl}diacetic acid and pharmaceutically acceptable salts thereof. 22. A pharmaceutical composition for the treatment of hyperlipaemia or hyperglycaemia, comprising an effective amount of an active compound in combination with a pharmaceutically acceptable carrier or diluent, wherein the active compound is selected from the group consisting of compounds of formula (1): ##STR620## in which: R.sup.1 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group or a C.sub.7 -C.sub.13 aralkyl group; R.sup.2 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.23 alkanoyl group, a C.sub.3 -C.sub.23 alkenoyl group, a C.sub.3 -C.sub.23 alkynoyl group, a substituted C.sub.1 -C.sub.23 alkanoyl, C.sub.3 -C.sub.23 alkenoyl or C.sub.3 -C.sub.23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl, a 5 to 8-membered heterocyclic acyl group having 1 to 3 hetero atoms of N, S or O, a group of formula --SO.sub.3 R.sup.8 where R.sup.8 represents a hydrogen atom, an aralkyl group where the alkyl part is C.sub.1 -C.sub.3 alkyl, a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.5 alkyl group having at least one substituent selected from the group consisting of hydroxy groups and C.sub.1 -C.sub.5 alkoxy groups, a C.sub.1 -C.sub.10 alkyl group or a substituted C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (b); R.sup.4 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group or a C.sub.1 -C.sub.5 alkoxy group; R.sup.5 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.5 alkoxy group; R.sup.6 and R.sup.7 are independently selected for the group consisting of hydrogen atoms, C.sub.1 -C.sub.10 alkyl groups and substituted C.sub.1 -C.sub.10 alkyl groups having at least one substituent selected from the group consisting of substituents (b); Ar is a divalent group selected from the group consisting of divalent carbocyclic aromatic groups, and divalent heterocyclic aromatic groups formed from a pyridine, furan, thiophene or pyrrole ring; W represents a --CH.sub.2 -- group, a >C.dbd.O group, a group of formula >CH--OR.sup.11 where R.sup.11 represents a hydrogen atom, a C.sub.1 -C.sub.23 alkanoyl group, a C.sub.3 -C.sub.23 alkenoyl group, a C.sub.3 -C.sub.23 alkynoyl group, a substituted C.sub.1 -C.sub.23 alkanoyl, C.sub.3 -C.sub.23 alkenoyl or C.sub.3 -C.sub.23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and napthoyl, a 5-8 membered heterocyclia acyl having 1 to 3 heteroatoms of N, S, or O, A C.sub.1 -C.sub.10 alkyl group or a substituted C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (b), or a group of formula >C.dbd.N--O--R.sup.12 in which R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkyl group, a C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (b), a C.sub.1 -C.sub.23 alkanoyl group, a C.sub.3 -C.sub.23 alkenoyl group, a C.sub.3 -C.sub.23 alkynoyl group, a substituted C.sub.1 -C.sub.23 alkanoyl, C.sub.3 -C.sub.23 alkenoyl or C.sub.3 -C.sub.23 alkynoyl group having at least one substituent selected from the group consisting of substituents (a), an aromatic acyl group selected from the group consisting of benzoyl and naphthoyl or a heterocyclic acyl group having 1 to 3 heteroatoms of N, S or O; U represents a --CH.sub.2 -- group; or W and U together represent a group of formula --CH.dbd.CH--; or when W represents a carbonyl group of said group of formula >C.dbd.N--OR.sup.12, U, R.sup.1 and the carbon atom to which R.sup.1 is attached together represent a group of formula --CH.dbd.C<; n is an integer of from 1 to 3; said aryl groups and the aryl parts of said aralkyl, aralkyloxycarbonyl, and aromatic acyloxy being C.sub.6 -C.sub.10 carbocyclic aryl groups which are unsubstituted or have at least one substituent selected from the group consisting of substituents (c); said heterocyclic groups, heterocyclic parts of said heterocyclic acyl and acyloxy groups have from 5 to 10 ring atoms, of which 1 to 5 are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic groups being unsubstituted or having at least one substituent selected from the group consisting of substituents (d); said substituents (a) being selected from the group consisting of aryl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and aralkyloxycarbonyl groups; said substituents (b) being selected from the group consisting of hydroxy groups, C.sub.1 -C.sub.5 alkoxy groups, aryl groups, C.sub.1 -C.sub.23 alkanoyloxy groups, C.sub.3 -C.sub.23 alkenoyloxy groups, C.sub.3 -C.sub.23 alkynoyloxy groups, substituted C.sub.1 -C.sub.23 alkanoyloxy, C.sub.3 -C.sub.23 alkenoyloxy or C.sub.3 -C.sub.23 alkynoyloxy groups having at least one substituent selected from the group consisting of substituents (a), aromatic acyloxy groups, heterocyclic acyloxy groups, groups of formula --COOR.sup.8 where R.sup.8 is as defined above and groups of formula --CONR.sup.9 R.sup.10 where R.sup.9 and R.sup.10 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.5 alkyl groups or R.sup.9 and R.sup.10, together with the nitrogen atom to which they are attached, represent a heterocyclic group having from 5 to 7 ring atoms of which from 1 to 3 atoms, including said nitrogen atom, are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted, or, where said ring atoms include an additional nitrogen hetero-atom, said additional nitrogen atom being unsubstituted or having a single substituent selected from the group consisting of substituents (e); said substituents (c) being selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups, C.sub.1 -C.sub.5 alkyl groups having at least one halogen substituent, halogen atoms, amino groups, C.sub.1 -C.sub.5 alkylamino groups, dialkylamino groups in which each alkyl part is C.sub.1 -C.sub.5, nitro groups, cyano groups, groups of formula --CONR.sub.2 where R represents a C.sub.1 -C.sub.5 alkyl group or an aryl group and hydroxy groups; and said substituents (d) being selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and doubly bonded oxygen atoms; said substituents (e) being selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkanoyl groups, C.sub.3 -C.sub.5 alkenoykl groups and C.sub.3 -C.sub.5 alkynoyl groups; provided that: (.alpha.) where: R.sup.3 represents said hydrogen atom, an unsubstituted C.sub.1 -C.sub.6 alkanoyl group, an unsubstituted C.sub.3 -C.sub.6 alkenoyl group, an unsubstituted C.sub.3 -C.sub.6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group; and R.sup.6 and R.sup.7 both represent hydrogen atoms; and Ar represents a p-phenylene group; and W represents a group of formula >CH.sub.2, >C.dbd.O or >CH--OR.sup.11x (wherein R.sup.11x represents a hydrogen atom, an unsubstituted C.sub.1 -C.sub.6 alkanoyl group, an unsubstituted C.sub.3 -C.sub.6 alkenoyl group, an unsubstituted C.sub.3 -C.sub.6 alkynoyl group, said aromatic acyl group, said heterocyclic acyl group, an aralkanoyl group or an aralkenoyl group); and U represents said group of formula >CH.sub.2, then (i) when R.sup.1 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group, R.sup.4 represents a C.sub.6 -C.sub.10 alkyl group, and (ii) when R.sup.4 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.5 alkoxy group, R.sup.1 represents a C.sub.6 -C.sub.10 alkyl group or said C.sub.7 -C.sub.13 aralkyl group; or (.beta.) where: R.sup.1 and R.sup.2 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.5 alkyl groups; and R.sup.4 and R.sup.5 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.5 alkyl groups and C.sub.1 -C.sub.5 alkoxy groups; and Ar represents a p-phenylene group; and W is a group of formula >CH.sub.2, >C.dbd.O or >CH--OR.sup.11x (where R.sup.11x is as defined above); and U represents said group of formula >CH.sub.2 ; and n is an integer from 1 to 3, then at least one of R.sup.3, R.sup.6 and R.sup.7 represents said alkyl or substituted alkyl group; and pharmaceutically acceptable salts thereof. 23. A composition as claimed in claim 22, in which: R.sup.1 represents a hydrogen atom or a C.sub.1 -C.sub.10 alkyl group; R.sup.2 represents a hydrogen atom or a C.sub.1 -C.sub.3 alkyl group; R.sup.3 represents a hydrogen atom, a sulfo group, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C.sub.6 -C.sub.10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R.sup.13 --(CH.sub.2).sub.m --CO--, where R.sup.13 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (g), and m is an integer from 1 to 5, a group of formula Het--CO--, where Het represents a heterocyclic group having 5 to 6 ring atoms, of which from 1 to 3 are hetero-atoms selected from the group consisting of nitrogen, oxygen and sulfur hetero-atoms, said heterocyclic group being unsubstituted or having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a group of formula --COOR.sup.8a, where R.sup.8a represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C.sub.1 -C.sub.5, a C.sub.2 -C.sub.5 hydroxyalkyl group, a C.sub.2 -C.sub.5 alkyl group substituted by a group of formula --O--CO--R.sup.53, where R.sup.53 represents a C.sub.1 -C.sub.10 alkyl group, a phenyl group, a phenyl group having at least one substituent selected from the group consisting of substituents (g) or a heterocyclic group Het, as defined above, or a C.sub.1 -C.sub.3 alkyl group substituted by a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (g) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, trifluoromethyl groups, C.sub.1 -C.sub.5 alkoxy groups, halogen atoms, nitro groups, amino groups, hydroxy groups and dialkylamino groups where each alkyl part is C.sub.1 -C.sub.5 ; said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C.sub.1 -C.sub.4, dialkylcarbamoyl groups where each alkyl part is C.sub.1 -C.sub.4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; R.sup.4 represents a C.sub.1 -C.sub.10 alkyl group or a methoxy group; R.sup.5 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a methoxy group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, C.sub.2 -C.sub.5 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a group of formula --O--CO--R.sup.53 where R.sup.53 is as defined above, and C.sub.1 -C.sub.3 alkyl groups having a single substituent selected from the group consisting of substituents (h); Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH.sub.2).sub.n --O-- at its 2-position and is attached to the --CH.sub.2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a C.sub.1 -C.sub.3 alkyl substituent; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH--OR.sup.11 or >C.dbd.N--OR.sup.12 where R.sup.11 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C.sub.6 -C.sub.10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), a group of formula R.sup.13 --(CH.sub.2).sub.m --CO-- where R.sup.13 and m are as defined above or a group of formula Het--CO-- where Het is as defined above, and R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.10 alkyl group having at least one substituent selected from the group consisting of substituents (j), a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), an arylcarbonyl group wherein the aryl part is a C.sub.6 -C.sub.10 carbocyclic aryl group which is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), or said group of formula R.sup.13 --(CH.sub.2).sub.m --CO-- or Het--CO--; and said substituents (j) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (g), C.sub.2 -C.sub.11 alkanoyloxy groups, C.sub.2 -C.sub.11 alkanoyloxy groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, C.sub.3 -C.sub.11 alkenoyloxy groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, phenylalkenoyloxy groups where the alkenyl part is C.sub.2 -C.sub.10 and the phenyl part is unsubstituted or has at least one substituent selected from the group consisting of substituents (g), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (g), groups of formula --COOR.sup.8a where R.sup.8a is as defined above, benzyloxycarbonyl groups and groups of formula --COR.sup.9 R.sup.10 where R.sup.9 and R.sup.10 are as defined above; U represents (i) where W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH.sub.2 OR.sup.11 or >C.dbd.N--OR.sup.12, a group of formula --CH.sub.2 --, (ii) with W, a group of formula --CH.dbd.CH--, or (iii) where W represents a group of formula >C.dbd.O or >C.dbd.N--OR.sup.14, in which R.sup.14 represents any one of the acyl groups defined for R.sup.12, with R.sup.1 and the carbon atom to which R.sup.1 is attached, a group of formula --CH.dbd.C<. 24. A composition as claimed in claim 23, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are as defined in claim 23; R.sup.6 and R.sup.7 both represent hydrogen atoms; R.sup.3 and R.sup.11 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.10 alkanoyl groups, C.sub.3 -C.sub.10 alkenoyl groups, C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 23, arylcarbonyl groups as defined in claim 23, and groups of formulae R.sup.13 --(CH.sub.2).sub.m --CO-- and Het--CO-- where R.sup.13, m and Het are as defined in claim 23; and R.sup.12 represents any one of the groups or atoms defined for R.sup.3 and R.sup.11 or a C.sub.1 -C.sub.5 alkyl group or a C.sub.1 -C.sub.3 alkyl group having at least one substituent selected from the group consisting of substituents (f) defined in claim 23. 25. A composition as claimed in claim 23, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are as defined in claim 23; R.sup.3, R.sup.6, R.sup.7 and R.sup.12 are independently selected from the group consisting of hydrogen atom, C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23, C.sub.2 -C.sub.5 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a group of formula --O--CO--R.sup.53 where R.sup.53 is as defined in claim 23 and C.sub.1 -C.sub.3 alkyl groups substituted by a single substituent selected from the group consisting of substituents (h) as defined in claim 23; and R.sup.11 represents a hydrogen atom, an acetyl group or a benzoyl group; R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.10 alkly group having at least one substituent selected from the group consisting of substituents (k), a C.sub.2 -C.sub.6 alkanoyl group, a C.sub.2 -C.sub.10 alkanoyl group having at least one substituent selected from the group consisting of substituents (l), a C.sub.3 -C.sub.5 alkenoyl group, a C.sub.3 -C.sub.5 alkenoyl group having at least one substituent selected from the group consisting of substituents (l), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (m), a pyridinecarbonyl group, a furoyl group, a thenoyl group or a pyridinecarbonyl, furoyl or thenoyl group having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups; said substituents (k) are selected from the group consisting of hydroxy groups, phenyl groups, phenyl groups having at least one substituent selected from the group consisting of substituents (m), C.sub.2 -C.sub.5 alkanoyloxy groups, C.sub.2 -C.sub.10 alkanoyloxy or C.sub.3 -C.sub.10 alkenoyloxy groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23, C.sub.3 -C.sub.10 alkenoyloxy groups substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (m), benzoyloxy groups, benzoyloxy groups having at least one substituent selected from the group consisting of substituents (m), groups of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23 and substituents (h) as defined in claim 23; said substituents (l) are selected from the group consisting of phenyl groups, carboxy groups, alkoxycarbonyl groups where the alkoxy part is C.sub.1 -C.sub.5 and benzyloxycarbonyl groups; and said substituents (m) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups, halogen atoms and trifluoromethyl groups. 26. A composition as claimed in claim 22, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, ethyl, isobutyl, pentyl, hexyl, 3,3-dimethylbutyl, heptyl, 4,4-dimethylpentyl, octyl, 5,5-dimethylhexyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a substituted C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (n), an aralkanoyl group of formula R.sup.15 --(CH.sub.2).sub.m --CO-- where R.sup.15 represents a phenyl group or a phenyl group having at least one substituent selected from the group consisting of substituents (n), and m is an integer from 1 to 5, a pyridinecarbonyl group, a furoyl group, a thenoyl group, a C.sub.1 -C.sub.3 alkyl group, a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C.sub.1 -C.sub.5, a C.sub.2 -C.sub.3 hydroxyalkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a C.sub.1 -C.sub.5 alkoxy group, a C.sub.2 -C.sub.5 alkyl group substituted by a C.sub.2 -C.sub.4 alkanoyloxy or a benzoyloxy group or a methyl group having a single substituent selected from the group consisting of substituents (h); said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and benzyloxycarbonyl groups; said substituents (n) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and halogen atoms; R.sup.4 represents a C.sub.1 -C.sub.10 alkyl group; R.sup.5 represents a hydrogen atom or a C.sub.1 -C.sub.3 alkyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.3 alkyl groups, C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above, C.sub.2 -C.sub.3 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a C.sub.2 -C.sub.4 alkanoyloxy or a benzoyloxy group, and methyl groups substituted by a single substituent selected from the group consisting of substituents (h); said substituents (h) are selected from the group consisting of alkylcarbamoyl groups where the alkyl part is C.sub.1 -C.sub.4, dialkylcarbamoyl groups where each alkyl part is C.sub.1 -C.sub.4, 1-pyrrolidinylcarbonyl groups, piperidinocarbonyl groups and morpholinocarbonyl groups; Ar represents a o-phenylene, m-phenylene or p-phenylene group or a pyridine-diyl group which is attached to the part of said compound of formula (I) of formula --(CH.sub.2).sub.n --O-- at its 2-position and is attached to the --CH.sub.2 -thiazolidine group at its 5- or 6-position, said phenylene and pyridine-diyl groups being unsubstituted or having a methyl substituent; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH--OR.sup.11 or >C.dbd.N--OR.sup.12, where: R.sup.11 represents a hydrogen atom or any one of the acyl groups defined above for R.sup.3 ; and R.sup.12 represents a benzyl group, any one of the groups or atoms defined above for R.sup.3, a pyridinecarbonyl group or a pyridinecarbonyl group having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups; and U represents (i) where W represents a group of formula --CH.sub.2 --, >C.dbd.O, >CH--OR.sup.11 or >C.dbd.N--OR.sup.12, a group of formula --CH.sub.2 --, (ii) with W, a group of formula --CH.dbd.CH--, or (iii) where W represents a group of formula >C.dbd.O, with R.sup.1 and the carbon atom to which R.sup.1 is attached, a group of formula --CH.dbd.C<. 27. A composition as claimed in claim 26, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are as defined in claim 26; R.sup.6 and R.sup.7 are both hydrogen atoms; R.sup.3 and R.sup.11 are independently selected from the group consisting of hydrogen atoms, C.sub.1 -C.sub.10 alkanoyl groups, C.sub.3 -C.sub.10 alkenoyl groups, C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl groups having at least one substituent selected from the group consisting of substituents (f) as defined in claim 26, benzoyl groups, benzoyl groups having at least one substituent selected from the group consisting of substituents (n) as defined in claim 26, groups of formula R.sup.15 --(CH.sub.2).sub.m --CO-- where R.sup.15 and m are as defined in claim 26, pyridinecarbonyl groups, furoyl groups and thenoyl groups; and R.sup.12 represents a hydrogen atom, a methyl group, a benzyl group, a t-butoxycarbonylmethyl group or any one of the acyl groups defined above for R.sup.3 and R.sup.11. 28. A composition as claimed in claim 26, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar, W and U are as defined in claim 26; R.sup.3, R.sup.6 and R.sup.7 are independently selected from the group consisting of C.sub.1 -C.sub.3 alkyl groups, C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 26, C.sub.2 -C.sub.3 hydroxyalkyl groups, C.sub.1 -C.sub.5 alkyl groups substituted by a C.sub.1 -C.sub.5 alkoxy group, C.sub.2 -C.sub.5 alkyl groups substituted by a C.sub.2 -C.sub.4 alkanoyloxy or a benzoyloxy group, and methyl groups having a single substituent selected from the group consisting of substituents (h) as defined in claim 26; R.sup.11 represents a hydrogen atom; R.sup.12 represents a hydrogen atom, a C.sub.1 -C.sub.3 alkyl group having at least one substituent selected from the group consisting of substituents (o), a C.sub.2 -C.sub.4 alkanoyl group, a C.sub.2 -C.sub.4 alkanoyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 26, an acryloyl group, an acryloyl group having a .beta.-substituent selected from the group consisting of substituents (f), a benzoyl group, a benzoyl group having at least one substituent selected from the group consisting of substituents (q), a pyridinecarbonyl group, a pyridinecarbonyl group having at least one substituent selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; said substituents (f) are selected from the group consisting of phenyl groups, carboxy groups, C.sub.2 -C.sub.6 alkoxycarbonyl groups and benzyloxycarbonyl groups; and said substituents (o) are selected from the group consisting of carboxy groups and alkoxycarbonyl groups where the alkoxy part is C.sub.1 -C.sub.5 ; said substituents (g) are selected from the group consisting of methyl groups, ethyl groups, methoxy groups and ethoxy groups. 29. A composition as claimed in claim 22 in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.16 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or an alkoxyalkyl group where both the alkoxy part and the alkyl part are C.sub.1 -C.sub.5 ; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined above; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >C.dbd.N--OH, >C.dbd.N--OCH.sub.2 COOH or >C.dbd.N--OCOR.sup.18 where R.sup.18 represents a C.sub.1 -C.sub.5 alkyl group; and U represents a group of formula --CH.sub.2 --. 30. A composition as claimed in claim 29, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar and U are as defined in claim 29; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, a C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.16 and m are as defined in claim 29, a cis or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 is as defined in claim 29, or a 2-, 3- or 4-pyridinecarbonyl group; R.sup.6 and R.sup.7 are both hydrogen atoms; W represents a group of formula >C.dbd.NOR.sup.12 where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 29, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; and n is 1 or 2. 31. A composition as claimed in claim 29, in which: R.sup.1, R.sup.2, R.sup.4, R.sup.5, Ar and U are as defined in claim 29; R.sup.3, R.sup.6 and R.sup.7 are independently selected from the group consisting of C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 29; W represents a group of formula >CH.sub.2, >C.dbd.O or >C.dbd.NOR.sup.12 ; R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 29, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; and n is 1 or 2. 32. A composition as claimed in claim 23, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.10 alkanoyl group, a C.sub.3 -C.sub.10 alkenoyl group, a C.sub.1 -C.sub.10 alkanoyl or C.sub.3 -C.sub.10 alkenoyl group having at least one substituent selected from the group consisting of substituents (f) as defined in claim 23, an arylcarbonyl group as defined in claim 23, a group of formula R.sup.13 --(CH.sub.2).sub.m --CO-- of Het--CO-- where R.sup.13, m and Het are as defined in claim 23 or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 represents a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; R.sup.7 represents a hydrogen atom or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula >CH.sub.2, >C.dbd.O or >C.dbd.NOR.sup.12, where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 23, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; U represents a group of formula --CH.sub.2 --; and n is 1 or 2. 33. A composition as claimed in claim 23, in which: R.sup.1 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.16 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 represents a hydrogen atom, C.sub.1 -C.sub.5 alkyl group of a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O or >C.dbd.N--OR.sup.12, where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 23, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; said substituents (n) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and halogen atoms; and U represents a group of formula --CH.sub.2 --. 34. A composition as claimed in claim 23, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkanoyl group, C.sub.3 -C.sub.5 alkenoyl group, a cinnamoyl group, a group of formula R.sup.16 OOC(CH.sub.2).sub.m CO-- where R.sup.16 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group and m is an integer from 1 to 5, a cis- or trans- group of formula R.sup.17 OOC.CH.dbd.CH--CO-- where R.sup.17 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or a benzyl group, a 2-, 3- or 4-pyridinecarbonyl group or a C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; R.sup.4 represents an alkyl group selected from the group consisting of hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are independently selected from the group consisting of hydrogen atoms and C.sub.1 -C.sub.3 alkyl groups substituted by a group of formula --COOR.sup.8a where R.sup.8a is as defined in claim 23; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O or >C.dbd.N--OR.sup.12 where R.sup.12 represents a hydrogen atom, a group of formula --(CH.sub.2).sub.3 COOR.sup.8a, --CH.sub.2 COOR.sup.8a, --C(CH.sub.3).sub.2 COOR.sup.8a, --COCH.sub.2 CH.sub.2 COOR.sup.8a or --CO--CH.dbd.CH--COOR.sup.8a where R.sup.8a is as defined in claim 23, an acetyl group, a cinnamoyl group, a benzoyl group, a pyridinecarbonyl group, a C.sub.1 -C.sub.5 alkyl group, a C.sub.1 -C.sub.5 alkyl group substituted by a phenyl group where the phenyl group is unsubstituted or has at least one substituent selected from the group consisting of substituents (n), or any one of the groups defined above for R.sup.3, R.sup.6 and R.sup.7 ; said substituents (n) are selected from the group consisting of C.sub.1 -C.sub.5 alkyl groups, C.sub.1 -C.sub.5 alkoxy groups and halogen atoms; and U represents a group of formula --CH.sub.2 --. 35. A composition as claimed in claim 23, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents C.sub.1 -C.sub.3 alkyl group substituted by a group of formula --COOR.sup.8a, where R.sup.8a is as defined in claim 23; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >C.dbd.N--OH, or >C.dbd.N--O--(C.sub.1 -C.sub.3 alkyl)--COOR.sup.8a where R.sup.8a is as defined in claim 23; U represents a group of formula --CH.sub.2 --; and N is 1 to 2. 36. A composition as claimed in claim 23, in which: R.sup.1 represents an alkyl group selected from the group consisting of methyl, isobutyl, hexyl, heptyl, octyl, nonyl and 3,7-dimethyloctyl groups; R.sup.2 represents a hydrogen atom or a methyl group; R.sup.3 represents --CH.sub.2 --COO(C.sub.1 -C.sub.5 alkyl) group; R.sup.4 represents an alkyl group selected from the group consisting of methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, 1,1-dimethylbutyl and 1,1-dimethylpropyl groups; R.sup.5 represents a hydrogen atom or a methyl group; R.sup.6 and R.sup.7 are both hydrogen atoms; Ar represents a p-phenylene group, a m-phenylene group having a methyl group at the position ortho to the position of attachment to the group of formula --(CH.sub.2).sub.n --O-- or a pyridine-diyl group attached to said group of formula --(CH.sub.2).sub.n --O-- at the 2-position and to the --CH.sub.2 -thiazolidine group at the 5-position; W represents a group of formula --CH.sub.2 --, >C.dbd.O, >C.dbd.N--OH, or >C.dbd.N--O--(C.sub.1 -C.sub.3 alkyl)--COO(C.sub.1 -C.sub.5 alkyl); U represents a group of formula --CH.sub.2 --; and n is 1 to 2. 37. A composition as claimed in claim 22, wherein said active compound is selected from the group consisting of: 5-[4-(6-Hydroxy-5,7,8-trimethyl-2-octylchroman-2-ylmethoxy)benzyl]thiazolid ine-2,4-dione; 5-{4-[6-Hydroxy-4-(E)-hydroxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy]b enzyl}thiazolidine-2,4-dione; 5-{4-[6-Acetoxy-4-(E)-acetoxyimino-2,5,7,8-tetramethylchroman-2-ylmethoxy]b enzyl}thiazolidine-2,4-dione; .alpha.-{5-[4-(6-Carboxymethoxy-2,5,7,8-tetramethyl-4-oxochroman-2-ylmethox y)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid; .alpha.-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethylchroman-2 -ylmethoxy)benzyl]-2,4-dioxothiazolidin-3-yl}acetic acid; .alpha.,.alpha.'-{5-[4-(6-Carboxymethoxy-4-hydroxyimino-2,5,7,8-tetramethyl chroman-2-ylmethoxy)benzyl]-2,4-dioxothiazolidine-3,5-diyl}diacetic acid; and pharmaceutically acceptable salts thereof.