Translactonization of erythromycin A during oximation: mixture analysis and reaction monitoring by NMR

Oximation of erythromycin A with hydroxylamine hydrochloride and sodium ace tate in methanol led to the formation of pseudoerythromycin A enol ether wi th erythromycin A oxime as analysed by detailed two-dimensional NMR spectro scopy in the mixture along with traces of 8,9-anhydroerythromycin A 6,9-hem iketal and erythromycin A 6,9:9,12-spiroketal. The formation of the degrade d products was established by performing in situ C-13 NMR spectroscopy. The analysis suggests that pseudoerythromycin A enol ether is formed by the tr anslactonization of erythromycin A enol ether which forms as a result of ac id degradation. Copyright (C) 2001 John Wiley & Sons, Ltd.