Pistaciaphenols A–E: novel chalcone-based biflavonoids from the branches of Pistacia chinensis

Abstract

Pistacia chinensis (Anacardiaceae) is a deciduous tree widely distributed in East Asia. Despite its long-standing use for ornamental, timber, and medicinal purposes, its secondary-metabolite profile remains only partially characterized. In this study, branches of P. chinensis were extracted with methanol, and the ethyl acetate-soluble fraction was subjected to repeated chromatographic separation, yielding five previously undescribed chalcone-containing biflavonoids, pistaciaphenols A–E (1–5), along with the known biflavonoid pauferrol B (6) and two flavanones, (2S,3S)-aromadendrin (7) and (2S,3S)-taxifolin (8). Comprehensive spectroscopic analyses, including 1D and 2D NMR (HMQC, HMBC, and double quantum filtered COSY) and high-resolution electrospray ionization mass spectrometry, established the structures of 1–5 as dimers composed of either isoliquiritigenin- or dihydroisoliquiritigenin-derived units linked to flavanone or flavone counterparts. Pistaciaphenols A (1) and C (3) possessed a liquiritigenin-derived flavanone moiety, whereas pistaciaphenol B (2) contained a flavone unit. Pistaciaphenols D (4) and E (5) featured a rare spiro-structure, a structural motif previously reported only from several Daphne species. The absolute configurations of 1 and 3 (2′′R,3′′S) were determined via analysis of electronic circular dichroism (ECD) spectra in conjunction with empirical correlations reported for C-3-substituted flavanones. For 4 and 5, GIAO-based ¹³C NMR chemical-shift calculations with DP4 + and CP3 analysis, together with experimental and time-dependent DFT-calculated ECD data, established 4 as 2′′R,3′′R and supported assignment of 5 as most plausibly 2′′R,3′′S. These findings expand the structural diversity of chalcone-based biflavonoids in Anacardiaceae and provide new scaffolds for future biological evaluation.

Graphical abstract

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