6S, 8R-Stereochemistry of the C₂₇- and C₂₉-Alkane-6, 8-diols Isolated from Three Compositae Flowers

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The Δδ(δ_S-δ_R) values for the C-1 methyl ¹H signals in the ¹H-NMR spectroscopy of the bis-MTPA esters of four synthetic stereoisomers of alkane-6, 8-diols, viz., bis-MTPA esters of (6S, 8R)-C₂₇- (1a) and C₂₉- (3a) (Δδ=-0.05 ppm), (6R, 8S)-C₂₇- (2a) and C₂₉- (4a) (Δδ=+0.05 ppm), (6S, 8S)-C₂₇- (5a) (Δδ=-0.01 ppm), and (6R, 8R)-C₂₇- (6a) (Δδ=+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 (Δδ=-0.05 ppm for the bis-MTPA esters) for the natural C₂₇- and C₂₉-alkane-6, 8-diols isolated from the flowers of three Compositae plants, Carthamus tinctorius, Cynara cardanclus, and Taraxacum platycarpum.