Tetrahydrothiophene derivatives

A compound of the formula (I) and pharmaceutically acceptable salts thereof, ##STR11## wherein R.sup.1 is hydrogen or lower alkyl;

• R.sup.2 is hydrogen, lower alkyl, lower alkenyl, lower alkanoyl, phenyl lower alkyl, phenylcarbonyl, phenyl lower alkylcarbonyl, trityl or tetrahydropyranyl, and the phenyl ring of the said phenyl lower alkyl, phenylcarbonyl or phenyl lower alkylcarbonyl is unsubstituted or substituted by lower alkyl, lower alkoxy, halogen, carboxy or lower alkoxycarbonyl;
• R.sup.3 is hydroxy, lower alkoxy, lower alkenyloxy, phenyl lower alkoxy, N-succinimidoxy, amino or lower alkylamino, and the lower alkyl of the said lower alkylamino is unsubstituted or substituted by imidazolyl, carboxy, amino, lower alkylamino, lower alkoxycarbonylamino, phenyl lower alkoxycarbonylamino or hydroxy, and the phenyl ring of the said phenyl lower alkoxy or phenyl lower alkoxycarbonylamino is unsubstituted or substituted by lower alkyl, lower alkoxy, halogen, carboxy or lower alkoxycarbonyl, and
• A is straight or branched lower alkylene, and the sulfur atom in the side chain may be directly joined with --CO-- to form a thiolactone ring.