2-Penem compounds

A 6-amino-2-penem-3-carboxylic acid compound of the formula ##STR30## in which R.sub.1.sup.a is hydrogen or a group R.sub.1.sup.A which denotes a conventional acyl radical of an organic carboxylic acid having up to 18 carbon atoms, a conventional triarylmethyl group or a conventional organic silyl or stannyl group, R.sub.1.sup.b is hydrogen or a conventional acyl radical or an organic carboxylic acid having up to 18 carbon atoms, R.sub.1.sup.a and R.sub.1.sup.b together is a conventional bivalent acyl radical of an organic dicarboxylic acid having up to 18 carbon atoms or the conventional acyl radical of an .alpha.-aminoacetic acid, which is substituted in .alpha.-position by an aromatic or heterocyclic group, and in which the amino group is bonded to the nitrogen atom via a methylene radical which is substituted by two lower alkyl groups, or R.sub.1.sup.a and R.sub.1.sup.b together represent a conventional aliphatic, cycloaliphatic, cycloaliphatic-aliphatic or araliphatic ylidene radical having up to 18 carbon atoms, R.sub.2 denotes hydroxyl or a radical R.sub.1.sup.A which, together with the carbonyl grouping --C(.dbd.O)--, forms a conventional protected carboxyl group, and R.sub.3 is hydrogen lower alkyl with up to 7 carbon atoms, cycloalkyl with 3 to 7 carbon atoms, cycloalkyl-lower alkyl with 4 to 7 carbon atoms, phenyl, naphthyl or phenyl-lower alkyl or such group substituted by hydroxyl, mercapto, lower alkoxy, lower alkanoyloxy, halogen, lower alkylmercapto, carboxyl, lower alkoxycarbonyl, carbamoyl, cyano, nitro, amino, lower alkylamino, di-lower alkylamino or lower alkylene-amino, or R.sub.3 is pyridyl, thienyl, furyl, pyridyl-lower alkyl, thienyl-lower alkyl or furyl-lower alkyl, the 1-oxide thereof and pharmaceutically acceptable salts thereof.