Abstract
Three novel spiroketals were prepared by a one-pot transformation of 6-O-methyl-9(E)-hydroxyiminoerythronolide A. We present the formation of a [4.5]spiroketal moiety within the macrolide lactone ring, but also the unexpected formation of a 10-C=11-C double bond and spontaneous change of stereochemistry at position 8-C. As a result, a thermodynamically stable structure was obtained. The structures of two new diastereomeric, unsaturated spiroketals, their configurations and conformations, were determined by means of NMR spectroscopy and molecular modelling. The reaction kinetics and mechanistic aspects of this transformation are discussed. These rearrangements provide a facile synthesis of novel macrolide scaffolds.
Highlights
Macrolide antibiotics are natural or semi-synthetic products of polyketide origin, containing one or more desoxy sugars attached to a macrocyclic lactone aglycon
We present the formation of a [4.5]spiroketal moiety within the macrolide lactone ring, and the unexpected formation of a 10-C=11-C double bond and spontaneous change of stereochemistry at position 8-C
In the latest revision of the reaction pathway Hassanzadeh et al showed that this macrolide spiroketal in acid media exists in equilibrium with the 9,12-hemiacetal of erythromycin A [47]
Summary
Macrolide antibiotics are natural or semi-synthetic products of polyketide origin, containing one or more desoxy sugars attached to a macrocyclic lactone aglycon. The structures of two new diastereomeric, unsaturated spiroketals, their configurations and conformations, were determined by means of NMR spectroscopy and molecular modelling.
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