Osami Aki

Electrochemical reduction of cephalosporanic acids

Electrochemical reduction of cephalosporanic acid derivatives (I) bearing various substituents at the 3-position gave the corresponding 3-methylenecepham derivatives (II), a new class of cephalosporins. Reductive opening of the 3-hydroxymethyl-3-cephem-4-carboxylic acid lactone (IV) was effected to give (II) by cathodic reaction. The 3-methylenecepham derivatives (II) were readily isomerized to the 3-methyl-3-cephem derivatives (III) providing a new synthesis of cephalexin [7-(D-2-amino-2-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid](IIIc). The reaction mechanism is discussed on the basis of deuteriation and polarography of the cephalosporins involved.

Reduction of cephalosporanic acids with chromium(II) salts : Synthesis of 3-methylenecepham derivatives☆

Abstract 7-Acylaminocephalosporanic acid derivatives (1) were converted into 7-acylamino-3-methylenecepham-4-carboxylic acids (2) by treatment with chromium(II) salts in aqueous media. The esters (4a or 4b) of 7-acylamino-3-methylenecepham compounds were readily isomerized to the 3-methyl-3-cephem compounds (5a or 5b) under basic conditions. The reaction mechanism is discussed.