Dissolution of brefeldin-A in CDCl3 afforded two species in We ratio 13:3.
Vicinal proton-proton coupling constants and NOE intensity enhancement meas
urements showed that the 13-membered ring conformation found by x-ray cryst
allography in the solid state appears To be preferred also in the solution-
state major species. The observance of signals from a solution-state minor
species (e.g, for the C-15 methyl) shows that: at least one other 13-member
ed ring conformation exists in a small amount. While some degree of conform
ational flexibility for the major species cyclopentyl ring cannot be ruled
out, the O-13 hydroxyl group is clearly axially disposed in the solution st
ate as it is in the crystal. Comparison of the solution-state C-13 NMR chem
ical shifts of the major species with those values measured by solid-state
cross-polarization magic angle spinning show fairly good agreement with dif
ferences usually of 1 ppm, or less, with the exception of C-2,8,6,11,15 sig
nals where differences were ca 2-3 ppm. Copyright (C) 2000 John Wiley & Son
s, Ltd.