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Anhydration of 8-hydroxyerythromycin A (1) in aqueous medium at pH about 1.5 afforded 69 12-spiroketal 4, an analogue of anhydroerythromycin A (3). Hydroxylation of erythromycin A 8, 9-anhydro-69-hemiketal (7) with m-chloroperbenzoic acid in chloroform solution yielded a mixture of the N-oxide of 8-hydroxyerythromycin A 69 12-spiroketal and the N-oxide of 8-hydroxyerythromycin A 69 11-spiroketal (8).
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Krowicki et al. (1973) studied this question.
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