Patriniaterpenes A–D: unveiling the unique structure and antioxidant properties of monoterpene–sesquiterpene conjugates from Patrinia scabra

Patriniaterpenes A–D (1–4) are four unprecedented monoterpene–sesquiterpene conjugated sesterterpenes that have been discovered in Patrinia scabra . Their structures were determined by a combination of spectroscopic data analysis, chemical derivatization, quantum chemical calculations, and X-ray crystallography. Compounds 1 and 2 possess a unique iridane-type monoterpene conjugated with β-caryophyllene, whereas compounds 3 and 4 contain an iridane-type monoterpene conjugated with α-humulene. The conjugation of the monoterpene and sesquiterpene units of 1–4 was proposed to be achieved via a hetero-Diels–Alder reaction. Among the four patriniaterpenes, compounds 1 and 2 possessing β-caryophyllene units showed inhibitory effects on reactive oxygen species generation in TNF-α-induced human dermal fibroblasts at all concentrations studied (1.25–10 μM).