Novel long-range isotope effects in a macrolide antibiotic: bafilomycin A1

Abstract

The ¹H and ¹³C NMR spectra of bafilomycin A₁(1), 21-O-trimethylsilylbafilomycin A₁(2) and 7-O-acetyl-21-O-t-butyldimethylsilylbafilomycin A₁(3) have been unambiguously solved in a variety of solvents by 1D and 2D NMR techniques. Partial deuteriation of the hydroxy groups of (1), (2), and (3) led to the observation of many novel and long-range isotope effects in the ¹H and ¹³C spectra of (1), (2), and (3). These experiments also confirmed the existence in solution of the hydrogen-bonding network involving 19-OH, 17-OH, and C(1)O for (1), (2), and (3), as was found in the crystalline state for (1). The possible mechanisms of the isotope effects are discussed.