Penicillin esters

A compound of formula (I) or a pharmaceutically acceptable acid addition salt thereof:

• ##SPC3##
• wherein R is hydrogen, methyl or phenyl;
• Ra and Rb are hydrogen or lower alkyl;
• and R.sup.1 is an acylamino group selected from phenylacetamido;
• p-hydroxyphenylacetamido;
• p-heptylphenylacetamido;
• phenoxyacetamido;
• .alpha.-phenoxypropionamido;
• .alpha.-phenoxybutyamido;
• 2,6-dimethoxyphenylacetamido;
• 3-phenyl-5-methyl-isoxazole-4-carbamido;
• 3-(2-chlorophenyl)-5-methyl-isoxazole-4-carbamido;
• 3-(2,6-dichlorophenyl)-5-methyl-isoxazole-4-carbamido;
• 3-(2-chloro-6-fluorophenyl)-5-methyl-isoxazole-4-carbamido;
• 2-ethoxynapthyl-1-carbamido;
• o, m or p-aminophenylacetamido;
• 3-carboxyquinoxalin-2-carbamido;
• 2-furylacetamido;
• 2-thienylacetamido;
• 3-thienylacetamido;
• 3-pyridylacetamido;
• isothiazolylacetamido;
• 3-hexenamido;
• 2-biphenylamido;
• n-hexanamido;
• n-octanamido;
• propionamido;
• .alpha.-aminophenylacetamido;
• .alpha.-amino-2-thienylacetamido;
• .alpha.-amino-3-thienylacetamido;
• .alpha.-methylaminoacetamido;
• .alpha.-amino-2- or -3- or -4-chlorophenylacetamido;
• .alpha.-amino-2-methoxyphenylacetamido;
• .alpha.-amino-2,4-dichlorophenylacetamido;
• .alpha.-amino-3,4-dichlorophenylacetamido;
• .alpha.-amino-.alpha.-methylphenylacetamido;
• .alpha.-amino-4-hydroxyphenylacetamido;
• .alpha.-amino-3-chloro-4-hydroxyphenylacetamido;
• .alpha.-methylphenylacetamido;
• .alpha.-hydroxyphenylacetamido;
• .alpha.-carboxyphenylacetamido;
• .alpha.-(5-tetrazolyl)phenylacetamido;
• .alpha.-guanidino-2-thienylacetamido;
• .alpha.-guanidino-4-hydroxyphenylacetamido;
• .alpha.-guanidino-4-hydroxy-2- or -3-methylphenylacetamido;
• .alpha.-carboxy-3-thienylacetamido;
• .alpha.-sulphaminophenylacetamido;
• .alpha.-sulphamino-3-thienylacetamido;
• .alpha.-(N-methylsulphamino)-phenylacetamido;
• .alpha. -azidophenylacetamido;
• 1-aminocyclohexylcarbamido;
• 1-aminocyclopentylcarbamido;
• 5-amino-5-carboxypentanamido;
• .alpha.-phenoxyphenylacetamido;
• .alpha.-phenyl-.beta.-sulphaminopropionamido;
• .alpha.-sulphophenylacetamido;
• .alpha.-guanidinophenylacetamido;
• .beta.-amino-.beta.-cyclohexylpropionamido and .alpha.-(benzyloxycarbonyl)phenylacetamido.