Studies on lactams. Part XIV. The synthesis of a structural isomer of penicillin

Abstract

5-Carboxy-2,2-dimethyl-6-phenoxyacetamidopenam, a structural isomer of penicillin V, was synthesized via an α-azido-β-lactam from t-butyl 5,5-dimethyl-2-thiazoline-2-carboxylate and azidoacetyl chloride. The 2-thiazoline was obtained from the readily synthesized t-butyl 5,5-dimethyl-3-thiazoline-2-carboxylate by isomerization under the influence of potassium t-butoxide. The α-azido-β-lactam t-butyl ester was catalytically reduced with hydrogen and acylated. The amido-ester was converted into the free acid on treatment with trifluoroacetic acid. Mainly from n.m.r. studies, the amido- and carboxy-groups were deduced to be cis to each other, and the penicillin sulphoxide type of conformation was suggested for the thiazolidine ring.