Studies on the constituents of aceraceae plants. IV. Carbon-13 nuclear magnetic resonance spectra of acerogenin A, rhododendrol and related compounds, and structure of aceroside IV from Acer nikoense.

Abstract

The assignment of chemical shifts in the carbon-13 nuclear magnetic resonance (13C NMR) spectra of acerogenin A (1), acerogenin B (2), rhododendrol (5) and related compounds was carried out on the basis of signal multiplicity in the off-resonance spectra, the results of proton selective decoupling, the effect of O-methylation of ortho-monosubstituted phenols on the aryl carbon shielding, and comparison with NMR data for some known compounds, including the effect of oxidation of sec-alcohols to the corresponding ketones on the neighboring carbon shielding. The results offer a useful means for structure elucidation of diarylheptanoids and arylbutanols analogous to 1 and 5. The 13C NMR spectrum of aceroside IV (6), C25H30O8, mp 153°C, [α]D-39.5°, isolated from the stem bark of Acer nikoense (Aceraceae) suggested that 6 is a β-D-glucopyranoside of a new diarylheptanoid, acerogenin C (17), C19H20O3, mp 116°C [the ketonic derivative of acerogenin A (1)]. The structure of 6 was finally confirmed by chemical means.