Nuclear magnetic resonance spectroscopy. Carbon-13 spectra of some macrolide antibiotics and derivatives. Substituent and conformational effects

Carbon-13(^(13)C NMR) chemical shifts are reported and assigned for a series of naturally occurring macrolide antibiotics, biosynthetic precursors, shunt metabolites, and derivatives. Besides the usual ^(13)C NMR substituent effects, the results are interpreted with reference to conformational models proposed for these compounds. A number of proposals are made concerning the conformations of the various derivatives, the differences between them, and the possibility of internal motion. The usefulness of ^(13)C NMR in ascertaining hydrogen bonding and in the structural analysis of these important cornpounds is demonstrated.