Phytochemical Investigations of an Antitubercular Extract of Chilean Myrcianthes coquimbensis and Related Populations

Abstract

The CH2Cl2-MeOH (1:1) extract of a Chilean plant Myrcianthes coquimbensis (Barnéoud) Landrum et Grifo was found to inhibit the growth of Mycobacterium tuberculosis by 73% at a concentration of 50 μg/mL. The bioassay guided separation of this extract led to the isolation of a new monoterpene (1 S,3 S,4 R)-1-methyl-4-(1-methylethenyl)-1,3-cyclohexanediol (3β-hydroxy- cis-β-terpineol, 1), along with oleanolic acid, 3β-caffeoyl-olean-12-en-28-oic acid, trans-(+)-sobrerol, epi-catechin, and catechin. The structure of 1 was determined by GC/MS, and 1D and 2D NMR spectroscopic experiments, and its absolute configuration was established by Mosher's esterification. The antitubercular activities of all isolates were evaluated using the microplate alamar blue assay (MABA). Oleanolic acid was determined to be active with an MIC value of 65.04 μM in MABA and low cytotoxicity to African green monkey vero cells, with an IC50 value of >224.5 μM, whereas all other isolates were inactive. The CH2Cl2-MeOH (1:1) extracts of two additional populations of M. coquimbensis procured from different regions in Chile have also been analyzed by LC/MS and the compounds isolated have been identified in these extracts based on retention time, observed LC/MS parent ion, and MS/MS fragmentation pattern.