Application of preparative high-speed countercurrent chromatography for isolation of a bicyclo-[3.2.1]-octanoid neolignan from Piper multinodum C. DC. and determination of its absolute stereochemistry.

This study aimed to propose a straightforward approach for isolating a novel neolignan compound using high-speed countercurrent chromatography (HSCCC) in combination with spectrometric techniques. The bicycleneolignan compound was detected in the dichloromethane partition obtained from methanolic leaf extract of Piper multinodum. After evaluating several two-phase solvent systems, the n-hexane/ethyl acetate/methanol/water in ratio 3:1:1:1 (v/v/v/v) demonstrated the highest efficiency for HSCCC separation of the target compound, as evidenced by the optimal distribution coefficient KD value of 1.55, using the tail-to-head elution mode, yielding 87.0 mg in 96.7 %. Its relative structure and absolute stereochemistry were unequivocally determined through 1D and 2D-NMR spectroscopy and HRMS data, complemented by NMR quantum-mechanical calculations, and application of the DP4+ method, as well as electronic circular dichroism data. Our findings confirmed the identification of the new compound multinodine -(7R,8S,1'R,3'R) (E)7-(benzo[3,4]-dioxol-1-yl)-3',6'-dimethoxy-8-methyl-1'-(prop-7'-en-7'-yl) bicyclo-[3.2.1]-oct-5'-en-4'-one).