Structure and conformational analysis of spiroketals from 6-O-methyl-9(E)-hydroxyiminoerythronolide A

• Ana Čikoš,
• Irena Ćaleta,
• Dinko Žiher,
• Mark B. Vine,
• Ivaylo J. Elenkov,
• Marko Dukši,
• Dubravka Gembarovski,
• Marina Ilijaš,
• Snježana Dragojević,
• Ivica Malnar and
• Sulejman Alihodžić

Beilstein J. Org. Chem. 2015, 11, 1447–1457, doi:10.3762/bjoc.11.157

• Park, Harlow, CM19 5AW, United Kingdom 10.3762/bjoc.11.157 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

• 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. Keywords: configuration; conformation; 6-O-methyl-9(E)-hydroxyiminoerythronolide A; reaction mechanism

• acid-promoted modification of 6-O-methyl-9(E)-hydroxyiminoerythronolide A into three rigid tricyclic spiroketal systems 2, 3 and 4. Compound 2 proved to be stable in non-acidic media. After acidic treatment two new dehydrated molecules are formed: compound 3 which with time spontaneously transforms