Inhibitory effect of sterols from Ruprechtia triflora and diterpenes from Calceolaria pinnifolia on the growth of Mycobacterium tuberculosis.

Bioactivity-guided fractionation of the CH 2 Cl 2 /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, 5alpha,8alpha-epidioxyergosta-6,22-dien-3beta-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 microg/mL, with 5alpha,8alpha-epidioxyergost-6,22-dien-3beta-ol, 5alpha,8alpha-epidioxystigmasta-6,22-dien-3beta-ol and stigmast-4-en-6beta-ol-3-one being the most active, each with an MIC value of 2 microg/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 microg/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 microg/mL, respectively.