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Background: Lamiaceae is one of the large families that occur worldwide and has species that are adaptable to almost all habitats and altitudes. Plectranthus is an important genus of Lamiaceae, recognized globally as an ornamental as well as a medicinal herb with good economic interest. The Plectranthus species possess antiseptic, vermicidal and purgative activities. Objective: The isolated compounds (1-3) from Plectranthus bishopianus were tested for their preliminary pharmacological evaluation for antibacterial, antioxidant and cytotoxic activities. Materials and Methods: The Plectranthus bishopianus leaves were collected from the Western Ghats of India. Extractions followed by isolation of the three compounds and structures were identified by NMR, HRMS. Results: The isolated compounds, 6,7-dehydroroyleanone (1), 6β-hydroxy-7α-methoxyroyleanone (2) and 6β, 7α-dihyroxyroyleanone (3) showed good antioxidant activity by DPPH method. The results of the cytotoxicity evaluation of the compounds (1-3) displayed excellent activity against MCF-7 cell line with IC50 values at 3.8 µg/mL, 3.85 µg/mL and 3.7 µg/mL respectively, which is more potent than the reference standard cisplatin. Conclusion: The structures of isolated compounds were confirmed by NMR, LC-HRMS and further pharmacological evaluation was accomplished. In addition, the isolates (1-3) were subjected to insilico molecular properties prediction by employing Molinspiration software for calculating their oral bioavailability and predicted to possess excellent oral bioavailability.

Chemical examination of the MeOH extract of Plectranthus bishopianusBenth., a rare and endangered plant, resulted in isolation of a new abietane diterpene, 6β-hydroxy-7α-methoxyroyleanone (1), along with two more diterpenoids, 6,7-dehydroroyleanone, and 6β,7α-dihydroxyroyleanone, a triterpene oleanolic acid, and two sterols, β-sistosterol and stigmasterol. The structures of the isolated compounds were elucidated on the basis of spectroscopic data and also by comparison with authentic samples.