the dashed line joining A and C(R^a) is present and represents a bond and A is a —C(R^b)═ group;

R^a and R^b are both hydrogen;

X is —S—;

Y is —C(R¹⁰)═ in which R¹⁰ is —CONH₂, —CONHet¹, —CON(R¹²)Het², —CON(R¹²)Alk⁵Het² or —CO₂Alk⁶ wherein —NHet¹ is pyrrolidinyl, imidazolidinyl, pyrazolidinyl, piperazinyl, morpholinyl, thiomorpholinyl, piperidinyl or thiazolidinyl, R¹² is a hydrogen atom or a straight or branched C_1-6 alkyl group, -Het² is cyclopentyl, cyclohexyl, pyrrolidinyl, imidazolidinyl, pyrazolidinyl, piperazinyl, morpholinyl, thiomorpholinyl, piperidinyl or thiazolidinyl, Alk⁵ is a straight or branched C_1-6 alkylene, C_2-6 alkenylene or C_2-6 alkynylene chain, optionally interrupted by one, two or three —O— or —S— atoms or —S(O)—, —S(O)₂— or —N(R¹²)— groups, and Alk⁶ is C_1-4 alkyl;

n is zero or the integer 1;

Alk¹ is an aliphatic or heteroaliphatic chain optionally substituted with one, two, three or more substituents where each substituent may be the same or different and is selected from halogen atoms, —OH, —CO₂H, —CO₂R⁴ —CO₂CH₃, —CON(CH₃)₃, —CONHR⁴, —CON(R⁴)₂, —COR⁴, C_1-6 alkoxy, halo(C_1-6)alkoxy, —SH, —S(O)R⁴, —S(O)₂R⁴, C_1-6 alkylthio, NHR⁴, and —N(R⁴)₂, where R⁴ is an optionally substituted straight or branched C_1-6 alkyl group, and such that where two R⁴ groups are present they may be the same or different and, if attached to an N atom may be joined, together with the N atom to which they are attached, to form a heterocyclic ring, which heterocyclic ring may be optionally interrupted by a further heteroatom or heteroatom-containing group selected from —O—, —S—, —N(R⁴)—, —C(O)— or —C (S)—;

L¹ is a covalent bond or a linker atom or group, said linker atom or group being selected from —O—, —S—, —C(O)—,—C(O)O—, —OC(O)—, —C(S)—, —S(O)—, —S(O)₂—, —N(R³)—, —N(R³)O—, —N(R³)NH—, —CON(R³)—, —OC(O)N(R³)—, —CSN (R³)—, —N(R³)CO—, —(R³)C(O)O—, —N(R³)CS—, —S(O)₂N (R³)—, —N(R³)S(O)₂—, —N(R³)CON(R³)—, —N(R³)CSN(R³)— and —N(R³)SO₂N(R³)—, where R³ is a hydrogen atom or a straight or branched alkyl group, and such that where L¹ contains two R³ groups these may be the same or different;

Cy¹ is a hydrogen atom or an optionally substituted cycloaliphatic, polycycloaliphatic, heterocycloaliphatic, polyheterocycloaliphatic, aromatic or heteroaromatic group, said optional substituent being selected from halogen, C_1-6 alkyl, halo(C_1-6 alkyl), C_1-6 alkoxy, halo(C_1-6 alkoxy), cyano, —CO₂CH₃, —CO₂C(CH₃)₃, nitro, amino, —NHCH₃, —N(CH₃)₂, —COCH₃ and —NHCOCH₃;

L is an atom or chain —(CH₂)_pHet(CH₂)_q—;

p and q, which may be the same or different, are each zero or the integer 1;

Het is an —O— or —S— atom or a —C(R^3a)(R^3b)—, —C(O)—, —C(O)O—, —OC(O)—, —C(S)—, —S(O)—, —S(O)₂—, —N(R^3c)O—, —N(R^3c)NH—, —N(R^3c)C(R^3a)(R^3b)—, —CON(R^3c)—, —OC(O)N(R^3c)—, —CSN(R^3c)—, —N(R^3c)CO—, —N(R^3c)C(O)O—, —N(R^3c)CS—, —S(O)₂N(R^3c)—, —N(R^3c)S(O)₂—, —N(R^3c)CON(R^3d)—, —N(R^3c)CSN(R^3d)— or —N(R^3c)S(O)₂N(R^3d)— group and, when one or both of p and q is the integer 1, Het is additionally a —N(R^3c)— group;

R^3a and R^3b are each independently a hydrogen atom, —OH, or an optionally substituted C_1-6 alkyl group;

R^3c and R^3d are each independently a hydrogen atom or a straight or branched alkyl group;

Ar is an optionally substituted aromatic or heteroaromatic group;