Three new abietane-type diterpenoids from the leaves of Indonesian Plectranthus scutellarioides

Three new diterpenoids, spiroscutelones A-C (1-3), along with known diterpene 4, were isolated from the leaves of Plectranthus scutellarioides. Their structures were established based on extensive spectroscopic analyses, including MS and NMR spectroscopy. Spiroscutelone A (1) represents the first example of an abietane-type terpenoid skeleton with a cyclobutane moiety linking the B and C rings. Of compounds 1-4, spiroscutelone B (2) exhibited the most potent cytotoxicities against the three tested human cancer lines [breast (MCF-7), pancreatic (PSN-1), and cervical (HeLa)) with IC50 values ranging from 17.9 mu M to 29.8 mu M and low cytotoxicity against a lung fibroblast (WI-38) normal cell line.