A nuclear magnetic resonance study of the degradation of penicillin G in acidic solution

N.m.r. methods have been used to study the degradation of benzylpenicillin at pH 2.5 and 37 °C. After 100 min three major reaction products, penamaldic acid, penillic acid, and penicilloic acid were detected. By measuring the extent of deuteriation at the C-6 position (the reaction was conducted in DCl–D2O solution) it was shown that most of the penillic acid (65%) and penicilloic acid (70%) had not been formed via a penicillenic acid type intermediate as previously suggested. Eventually the three initial products degraded into penilloic acid without any further deuteriation (estimated from the deuteriation at the C-6 position of penilloic acid): thus penillic acid and penicilloic acid do not degrade via a penicillenic acid intermediate. No penicillamine, benzylpenilloaldehyde, or related products were detected.