Abstract
Three step transformations of α-formylation, chlorination and hydrolysis starting from ethyl 4-thiazoleacetate (1) afforded a new cephem 7-side chain acid, (E)-3-chloro-2-(thiazol-4-yl)propenoic acid (4-(E)). The presence of the corresponding 4-(Z) derived from photoisomerization of 4-(E) was confirmed by nuclear magnetic resonance analysis. Acylation of several 7-aminocephalosporins was conducted by two routes involving the photoisomerization of 4-(E) to 4-(Z) (method A) or the isomerization of the activated intermediate (formula III) of the carboxylic acid 4-(E) with Vilsmeier reagent by heating (method B). The synthesis and the antibacterial activities of a new series of geometrical isomers of 7-[3-chloro-2-(thiazol-4-yl)propenamido] cephalosporins (formula II) are described.
