Studies on the constituents of aceraceae plants. VI. Revised stereochemistry of (-)-centrolobol, and new glycosides from Acer nikoense.

Two diarylheptanoid glycosides, named aceroside VII (8), C25H34O8, mp 144-145°C, [α]15D -28.4°, and aceroside VIII (9), C30H42O12, [α]15D -64.8° were isolated from the stem bark of Acernikoense MAXIM. (Aceraceae). On acid hydrolysis 8 yielded (-)-centrolobol (10) and glucose, while 9, on partial hydrolysis, gave 8 and apiose. Acerosides VII (8) and VIII (9) were determined to be the 3-O-β-D-glucopyranoside and the 3-O-β-D-apiofuranosyl-(1→6)-β-D-glucopyranoside of (-)-centrolobol (10), respectively, on the basis of carbon-13 nuclear magnetic resonance (13C-NMR) spectral analyses and additional chemical data.The absolute configuration S for (-)-centrolobol (10) has been claimed, but the authors propose its revision to R(-) on the basis of Brewster's empirical rule on the correlation between absolute configuration and optical rotation. The stereochemistries of some compounds related to 10 such as acerogenin A (1) and (-)-centrolobin should also be revised. At the same time, partial revision of the 13C-NMR signal assignments for acerosides III (3) and VI (4) is also necessary.