A pharmaceutical compound of the formula: ##STR1## in which R.sup.1 is C.sub.7-20 alkyl, C.sub.7-20 alkenyl or C.sub.7-20 alkynyl, the alkyl, alkenyl or alkynyl group being optionally substituted by phenyl or substituted phenyl and the alkenyl and alkynyl groups containing 1 to 3 unsaturated bonds, R.sup.2 is (i) optionally substituted phenyl, (ii) C.sub.1-10 alkyl optionally substituted by one or more substituents selected from optionally protected hydroxyl, optionally protected carboxyl, nitrile, optionally protected tetrazolyl, --COR.sup.4 where R.sup.4 is C.sub.1-14 alkyl, C.sub.1-4 alkoxy, an optionally protected amino acid residue or --NR.sub.2.sup.5 where each R.sup.5 is hydrogen or C.sub.1-4 alkyl, and --NHR.sup.6 where R.sup.6 is hydrogen, a protecting group, an optionally protected amino acid residue, C.sub.1-4 alkyl or --COR.sup.7 where R.sup.7 is C.sub.1-4 alkyl or C.sub.1-4 alkoxy, or (iii) C.sub.1-10 alkyl substituted with a group selected from ##STR2## where each R.sup.8 is hydrogen or C.sub.1-4 alkyl, and R.sup.3 is hydrogen, carboxyl, C.sub.2-5 alkoxycarbonyl, C.sub.1-4 alkyl, C.sub.1-4 alkoxy, hydroxyl, optionally protected tetrazolyl, halo, trifluoromethyl, nitrile, nitro and --CONR.sub.2.sup.9 where each R.sup.9 is hydrogen or C.sub.1-4 alkyl; and salts thereof.