Barbaterpene and Barbatusterol, New Constituents from Plectranthus barbatus Growing in Saudi Arabia

Background: Plectrantus barbatus Andr. (Lamiaceae) has been used in Hindu and Ayurvedic Indian traditional as well as Brazilian folk medicine for the treatment of several diseases. Chemical investigation of different parts of this plant has led to isolation of essential oil, diterpenes (abietane and labdane), flavonoids, phenolic compounds with interesting biological properties. The objective of study was to isolate pure new chemical entities from aerial parts of P. barbatus. Methods: Different chromatographic methods were used to isolate pure compounds from the ethyl acetate soluble fraction of ethanol extract of P. barbatus. Their chemical structures were verified utilizing various spectroscopic experiments such as NMR (1H, 13C, COSY, HMBC, HSQC), Mass spectrometry (EI-MS experiments) as well as by chemical degradation. Results: The chemical investigation of ethyl acetate soluble fraction of the ethanol extract of P. barbatus resulted in six compounds, barbaterpene (2) (2`R-hydroxydocosanoylursa-12-en-3 beta-ol) and barbatusterol (3) new to the literature along with four known compounds, stigmasterol (1), sugiol (4), 11,14-dihydroxy-8,11,13-abietatrien-7-one (5), and caffeic acid (6). Conclusion: Two new metabolites: barbaterpene (2) (2` R-hydroxydocosanoylursa-12-en-3 beta-ol) and barbatusterol (3) (3 beta, 5 alpha-dihydroxy-stigma-7(8), 22-diene), in addition to stigmasterol (1), sugiol (4), 11,14-dihydroxy-8,11,13-abietatrien-7-one (5), and caffeic acid (6) were separated from the aerial parts of P. barbatus.