Ferusamarbiclins A−C and Ferusamarelemanolide A, Sesquiterpenes from the Roots of Ferula samarkandica

Four sesquiterpenes with previously undescribed backbones, named ferusamarbiclins A−C (1−3) and ferusamarelemanolide A (4), were isolated from the roots of Ferula samarkandica. Structurally, ferusamarbiclins A−C shared a 4-methyl-7-isopropyl-bicyclo[5.3.1]undecane-type sesquiterpene scaffold termed ferusamarbiclane, closely related to germacrane-type sesquiterpenoids in terms of origin. Ferusamarelemanolide A represented a 6,7-seco-elemane-type sesquiterpene lactone with the architecture designated ferusamarelemane. Their structures were established on the basis of comprehensive spectroscopic analysis, including HRESIMS, NMR, UV, and IR. The absolute configurations were determined by ECD calculations combined with single-crystal X-ray diffraction crystallography. Furthermore, plausible biosynthetic pathways were proposed. Compounds 1−4 displayed a weak antimicrobial activity against Candida albicans and Staphylococcus aureus.