The isolation, structure elucidation and biological testing of compounds from Plectranthus hadiensis.

Abstract

Three diterpenes of the abietane class, 7b-acetoxy-6b-hydroxyroyleanone (I), 6b,7b- dihydroxyroyleanone (II) and ent-pimara-8(14),15-diene-3b,11a-diol (III) and three triterpenes, 2a,3a,19 -trihydroxyurs-12-en-28-oic acid (IV), stigmasterol (V) and lupeol (VI) were isolated from the stem and leaf material of Plectranthus hadiensis. The structures of the compounds were elucidated using 2D NMR spectroscopy and Mass spectrometry. All six compounds have been isolated previously, but this is the first occurrence of compounds III-VI in Plectranthus hadiensis. This is also the first report of the isolation of a pimarene from Plectranthus, which provides a biochemical link to other genera in the family Lamiaceae where this class of compounds exist. Compounds I to IV were tested for their antibacterial activity against Enterococcus faecalis and Pseudomonas aeruginosa as well as their anticancer activity against breast (MCF-7), renal (TK- 10) and melanoma (UACC-62) cell lines. Compounds I and II exhibited good antibacterial activity against Enterococcus faecalis and Pseudomonas aeruginosa and although the entpimara- 8(14),15-diene-3 ,11 -diol (III), was inactive against E. faecalis, it was very active against P. aeruginosa. Compound IV, the triterpenoid, was structurally different to I-III and did not show any anti-bacterial activity. Compounds I-III were weakly active toward the cancerous renal (TK-10), melanoma (UACC-62) and breast (MCF-7) cell lines, while IV was inactive in all of the cell lines.