Structure elucidation and absolute configuration determination of C26, C27 and C30 tirucallane triterpenoids from the leaves of Picrasma quassioides (D. Don) Benn

Abstract

Seven undescribed tirucallane-type triterpenoids, kumunorquassins A‒E and kumuquassins K and L, along with nine known analogues, have been isolated from the leaves of Picrasma quassioides (D. Don) Benn. Their structures and absolute configurations were elucidated based on comprehensive spectroscopic analyses, single-crystal X-ray diffraction analysis and electronic circular dichroism (ECD). The absolute configuration of cornusalterin J was unequivocally determined by X-ray diffraction based on its p-bromobenzoate derivative. A brief approach was presented in our study, which could rapidly and conveniently determine the relative and absolute configurations of OCH3-23 of kumuquassin L and cornusalterins J, H and G depending on the chemical shift differences (Δδ) of C-24 and C-25 and the chemical shifts of C-23, H-23 and H-24. In addition, the cytotoxicities of these compounds against two human tumour cell lines (HepG2 and Hep3B) were evaluated.