Inhibitory Effect of Sterols from Ruprechtia triflora and Diterpenes from Calceolaria pinnifolia on the Growth of Mycobacterium tuberculosis

Abstract

Bioactivity-guided fractionation of the CH₂Cl₂/MeOH extract of the aerial part of Ruprechtia triflora Griseb. led to the identification of several sterols and a triterpene as the active components against Mycobacterium tuberculosis. This is the first report of a chemical investigation of a member of the genus Ruprechtia. The novel acylated sterol, 5α,8α-epidioxyergosta-6,22-dien-3β-yl stearate, was isolated and its structure determined on the basis of spectral evidence including NMR (especially selective 1D NOE, selective 1D TOCSY, HSQC, HMBC) and MS (HR-FAB). In addition, several terpenes obtained from Calceolaria pinnifolia Cav. were also evaluated for their antimycobacterial activity. In a microplate alamar blue assay, sterols from R. triflora were found to be active with MIC values ranging from 2 - 128 μg/mL, with 5α,8α-epidioxyergost-6,22-dien-3β-ol, 5α,8α-epidioxystigmasta-6,22-dien-3β-ol and stigmast-4-en-6β-ol-3-one being the most active, each with an MIC value of 2 μg/mL. Among the diterpenes from C. pinnifolia, 19-malonyloxydehydroabietinol and 19-methylmalonyloxy-ent-isopimara-8(9),15-diene were most active each with an MIC value of 4 μg/mL. MIC values for the triterpenes 3-epi-ursolic acid and 3-epi-oleanolic acid from C. pinnifolia were determined to be 8 and 16 μg/mL, respectively.

Key words

Ruprechtia triflora - Polygonaceae - Calceolaria pinnifolia - Scrophulariaceae - sterols - diterpenes - triterpenes - structure elucidation - antimycobacterial activity

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