A compound of formula (I), wherein R.sup.1 is H; R.sup.2 is aryl, het, C.sub.3-8cycloalkyl, C.sub.1-6alkyl, (CH.sub.2).sub.2aryl or R.sup.4, wherein each of the cycloalkyl, aryl, het and R.sup.4 groups is optionally substituted by at least one substituent independently selected from C.sub.1-6alkyl, C.sub.1-6alkoxy, OH, halo, CF.sub.3, OCF.sub.3, OCHF.sub.2, O(CH.sub.2).sub.yCF.sub.3, CN, CONH.sub.2, CON(H)C.sub.1-6alkyl, CON(C.sub.1-6alkyl).sub.2, hydroxy-C.sub.1-6alkyl, C.sub.1-4alkoxy-C.sub.1-6alkyl, C.sub.1-4alkoxy-C.sub.1-4alkoxy, SCF.sub.3, C.sub.1-6alkyISO.sub.2, C.sub.1-4alkyl-S-C.sub.1-4alkyl, C.sub.1-4alkyl-S--, C.sub.1-4alkyINR.sup.10R.sup.11 and NR.sup.10R.sup.11; or R.sup.1 and R.sup.2, together with the carbon atom to which they are bound, form a 5- or 6-membered carbocycle or a 5- or 6-membered heterocycle containing at least one N, O or S heteroatom; R.sup.3 is aryl, het or R.sup.4, each optionally substituted by at least one substituent independently selected from C.sub.1-6-alkyl, C.sub.1-6-alkoxy, het, OH, halo, CF.sub.3, OCF.sub.3, OCHF.sub.2, O(CH.sub.2).sub.yCF.sub.3, CN, CONH.sub.2, CON(H)C.sub.1-6alkyl, CON(C.sub.1-6alkyl).sub.2, hydroxy-C.sub.1-6alkyl, C.sub.1-4alkoxy-C.sub.1-6alkyl, C.sub.1-4alkoxy-C.sub.1-4alkoxy, SCF.sub.3, C.sub.1-6alkyISO.sub.2, C.sub.1-4alkyl-S-C.sub.1-4alkyl, C.sub.1-4alkyl-S--, C.sub.1-4alkylNR.sup.10R.sup.11and NR.sup.10R.sup.11; R.sup.4 is a phenyl group fused to a 5- or 6 membered carbocycle, or a phenyl group fused to a 5- or 6-membered heterocycle containing at least one N, O or S heteroatom; R.sup.5 is H or C.sub.1-6alkyl; R.sup.10 and R.sup.11 are the same or different and are independently H or C.sub.1-4alkyl; A is a C.sub.1-3alkylene chain which is optionally substituted by OH, C.sub.1-4alkyl or C.sub.1-4alkoxy; x is an integer from 1 to 3; y is 1 or 2; z is an integer from 1 to 3; aryl is phenyl, naphthyl, anthracyl or phenanthryl; and het is an aromatic or non-aromatic 4, 5- or 6-membered heterocycle which contains at least one N, O or S heteroatom, optionally fused to a 5- or 6-membered carbocycle or a second 4, 5- or 6-membered heterocycle which contains at least one N, O or S heteroatom.