Proton NMR study of degradation mechanisms of oxacephem derivatives with various 3'-substituents in alkaline solution

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Abstract
The degradation process of oxacephams with various 3''-substituents (1-9) in alkaline solution was examined by 1H NMR spectroscopy, and the structures of two types of degradation products were determined: the hydrolysis products 10-14 having the cleaved .beta.-lactam ring and the remaining 3''-substituents, and the exo-methylene compounds 15 and 16 having the cleaved .beta.-lactam ring and the expelled 3''-substituents. The oxacephems were found to decompose, giving the former compounds that subsequently decomposed to the latter compound. Although the ratios of the formation of the exo-methylene compound 15 relative to the other degradation products depended on the leavability of the 3''-substituents, there was little correlation between the relative yields and the .beta.-lactam reactivity. Thus, the expulsion of the leaving group at the 3''-position was concluded to be not involved in the nucleophilic attack on the .beta.-lactam carbonyl.

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