A compound of formula (I) or a pharmaceutically acceptable salt thereof:
in which X represents R₁OOC- in which R₁ is C₁₋₄ alkyl, C₂₋₄ alkenyl or C₂₋₄ alkynyl; R₂O- in which R₂ is C₁₋₂ alkyl, C₁₋₂ alkylcarbonyl or aminocarbonyl optionally substituted by one or two methyl groups;
a group
in which Y represents a 3-membered divalent residue completing a 5-membered aromatic ring and comprises one or two heteroatoms selected from oxygen, nitrogen and sulphur, any amino nitrogen optionally substituted by a C₁₋₂ alkyl group, Y being optionally C-substituted by a methyl group; or a group
in which A₁ is oxygen or sulphur, one of A₂ and A₃ is CR₃ and the other is nitrogen or CR₄ where R₃ and R₄ are independently selected from hydrogen and methyl; and each of p and q independently represents an integer of 2 to 4.
A compound of formula (I) or a pharmaceutically acceptable salt thereof: ##STR1## in which X represents R.sub.1 OOC-- in which R.sub.1 is C.sub.1-4 alkyl, C.sub.2-4 alkenyl or C.sub.2-4 alkynyl; R.sub.2 O-- in which R.sub.2 is C.sub.1-2 alkyl, C.sub.1-2 alkylcarbonyl or aminocarbonyl optionally substituted by one or two methyl groups; a group ##STR2## in which Y represents a 3-membered divalent residue completing a 5-membered aromatic ring and comprises one or two heteroatoms selected from oxygen, nitrogen and sulphur, any amino nitrogen optionally substituted by a C.sub.1-2 alkyl group, Y being optionally C-substituted by a methyl group; or a group ##STR3## in which A.sub.1 is oxygen or sulphur, one of A.sub.2 and A.sub.3 is CR.sub.3 and the other is nitrogen or CR.sub.4 where R.sub.3 and R.sub.4 are independently selected from hydrogen and methyl; and each of p and q independently represents an integer of 2 to 4.