¹H- and ¹³C-NMR Spectroscopic Studies of Selected Quassinoids

Abstract

The ¹³C-NMR spectra of some selected C₂₀ quassinoids have been investigated. Unambiguous assignments were obtained through one-bond and long-range heteronuclear correlation spectroscopy. Some previous assignments have been corrected and ambiguities clarified. The usefulness of one-dimensional, long-range, proton-carbon correlation for the structure elucidation of the highly functionalized picrasan skeleton has been demonstrated. Proton homonuclear spectroscopy (COSY and delayed COSY) was useful for establishing the relative stereochemistry at C-1 and C-12, and several diagnostic, long-range couplings are reported for the first time for the picrasan skeleton.