Studies related to penicillins. Part VII. The structure of the epimers derived from 6β-substituted penicillanic acids

Abstract

Methoxymethyl 6β-(2-hydroxy-1-naphthylmethyleneamino)penicillanate (6) is equilibrated with an epimer when treated with 1,5-diazabicyclo[4,3,0]non-5-ene in dichloromethane. Acidic hydrolysis of the epimer yields methoxymethyl 6-aminopenicillanate, which reacts with N-ethoxycarbonylphthalimide to give methoxymethyl 6-phthalimidopenicillanate. This last substance is identical with the epimer derived from the base-catalysed isomerisation of methoxymethyl 6β-phthalimidopenicillanate (2).

Methoxymethyl 6β-aminopenicilanate (7) and its epimer react with sodium nitrite and dilute hydrochloric acid to give methoxymethyl 6α-chloropenicillanate (17). The epimers, therefore, possess the R-stereochemistry at position 5 and they are 6α-substituted penicillanic acid derivatives. Methoxymethyl 6-diazopenicillanate is implicated in the deamination of both amines.