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Abstract:
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The labdane-type diterpene 15,16-epoxy-8(17),13(16),14-labdatrien-12??-ol (1) was isolated
together with 2'-hydroxy-4',6'-dimethoxychalcone and 2,3-dihydro-4',7-di-O-methylkaempferol from the
rhizomes of the endemic Vietnamese medicinal plant Alpinia tonkinensis Gagnep. (Zingiberaceae).
Although both diastereomers of the furanolabdane alcohol 1 provided by the chiral center at the 12-position
have already been reported as semisynthetic intermediates, the absolute configuration at the 12-position,
which affects the chemical shifts of the 17-exomethylene protons, remains to be clarified. In this study, the
natural furanolabdane 1, which possessed the same 1H- and 13C-NMR spectroscopic data as those of one of
the semisynthetic diastereoisomeric pair, was determined to be in the (12S)-form from spectroscopic data
and by applying the modified Mosher's method. |