6S,8R-stereochemistry of the C-27- and C-29-alkane-6,8-diols isolated fromthree Compositae flowers

The Delta delta (delta(S)-delta(R)) values for the C-1 methyl H-1 signals i n the H-1-NMR spectroscopy of the bis-MTPA esters of four synthetic stereoi somers of alkane-6,8-diols, viz., bis-MTPA esters of (6S,8R)-C-27- (1a) and C-29- (3a) (Delta delta=-0.05 ppm), (6R,8S)-C-27- (2a) and C-29- (4a) (Del ta delta=+0.05 ppm), (6S,8S)-C-27- (5a) (Delta delta=-0.01 ppm), and (6R,8R )-C-27- (6a) (Delta delta=+0.01 ppm) alkane-6,8-diols, made it possible to differentiate unequivocally among the four stereoisomers. This allowed the determination of the (6S,8R)-stereochemistry (Delta delta=-0.05 ppm for the bis-MTPA esters) for the natural C-27- and C-29-alkane-6,8-diols isolated from the flowers of three Compositae plants, Carthamus tinctorius, Cynara c ardanclus, and Taraxacum platycarpum.