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.