Megastigmane glycosides are now an expanding class of compounds and their relatively wide distribution in plant kingdom has been reported. In a previous work, 1) a megastigmane was isolated as a non-glycosidic form from Euscaphis japonica and its absolute configuration was determined by the modified Mosher's method. Leaves of Turpinia ternate collected in Okinawa also afforded one megastigmane (1) and seven megastigmane glycosides (2-8). The structure of the megastigmane (1) was elucidated to be the same as that of that isolated from E. japonica, including absolute configurations. Compounds 2 and 3 were found to be known compounds, corchoionoside C 2) and icariside B 4 , 3) respectively. The structures of the remaining megastigmane glucosides were elucidated by NMR spectroscopic analyses and the absolute configurations of turpinionosides A-E (4-8) were elucidated in this work by the modified Mosher's method.
Results and DiscussionMegastigamane (1) and megastigamane glucosides (2-8) were isolated from the n-BuOH-soluble fraction of a MeOH extract of leaves of Turpinia ternata by means of a combination of several kinds of chromatographic methods, and details being given in the experimental section. The structures of other known compounds (2, 3) were identified by comparison of spectroscopic data with those reported.Compound 1, C 13 H 24 O 4 , was isolated as a syrup and its planar structure was elucidated to be the same as that of the megastigamane isolated from a related plant, Euscaphis japonica.1) On comparison of the optical rotation values of 1 from both sources, the absolute configurations were presumed to be the same. This was confirmed by that compound 1 from the title plant was also determined with the modified Mosher's method 4) to have the 3S, 5R, 6R and 9S configurations (Fig. 1).Turpenionoside A (4), [a] D 22 Ϫ38.4°, was isolated as an amorphous powder and its elemental composition was determined to be C 19 H 34 O 8 by negative-ion high-resolution (HR) FAB-MS. The IR spectrum of 4 showed a strong absorption band at 3401 cm Ϫ1 suggestive of a glycosidic structure. The 1 H-and 13 C-NMR spectra of 4 showed signals attributable to a b-glucopyranosyl unit, and two tertiary methyls at a geminal position, two secondary methyls, two methylenes, one methine without and two methines with hydroxyl groups, one disubstituted trans double bond, and two quarternary carbon atoms with and without a hydroxyl group, respectively. These functionalities were the same as those of megastigmane glucoside, dendranthemoside A (9) ([a] D 22 Ϫ44.2°), isolated from Dendranthema shiwogiku, 5) and the NMR spectroscopic data of 4 and 9 were essentially indistinguishable from each other. The absolute structure for 9 has been determined by Xcrystallographic analysis of its pentaacetate to have the 3S, 5R, 6S and 9R configurations.6) Since most glucose in Nature is of the D-series, the b-D-glucosylation-induced shift-trend in the 13 C-NMR spectroscopy was applied for the elucidation of absolute configuration. 7) On b-D-glucosylation o...