Activity of the Extracts and Indole Alkaloids from Alstonia scholaris Against Mycobacterium tuberculosis H37Rv

Abstract

The crude methanolic extract of Alstonia scholaris (L.) R. Brown demonstrated in vitro antituberculosis activity (89% inhibition against Mycobacterium tuberculosis H37Rv at 50 I¼g mL-1) using Microplate Alamar Blue Assay (MABA). Gradient pH fractionation of the alkaloids gave three alkaloid extracts, AsA, AsB and AsC, which exhibited 69%, 99% and 99% inhibition, respectively. Group separation by silica gel vacuum liquid chromatography (VLC) of extracts AsA and AsB afforded fractions that showed 69–99% inhibition against the test mycobacterium. The previously reported indole alkaloids - 19,20Evallesamine ( Alstonia scholaris (L.) R. Brown demonstrated in vitro antituberculosis activity (89% inhibition against Mycobacterium tuberculosis H37Rv at 50 I¼g mL-1) using Microplate Alamar Blue Assay (MABA). Gradient pH fractionation of the alkaloids gave three alkaloid extracts, AsA, AsB and AsC, which exhibited 69%, 99% and 99% inhibition, respectively. Group separation by silica gel vacuum liquid chromatography (VLC) of extracts AsA and AsB afforded fractions that showed 69–99% inhibition against the test mycobacterium. The previously reported indole alkaloids - 19,20Evallesamine (1), a mixture of angustilobine B N4-oxide (2) and N4-methyl angustilobine B (3), 20Stubotaiwine (4), 6,7-seco-angustilobine B (5) and (+)-manilamine (6) from the most bioactive alkaloid fractions with 98–99% inhibition - showed weak activities. Among the six compounds, only alkaloid 4 demonstrated the highest activity with a minimum inhibitory concentration (MIC) of 100 I¼g mL-1. Compared with the standard rifampin (MIC 0.125 I¼g mL-1), all alkaloids were considered inactive. Key Words: Alstonia scholaris, antitubercular activity, dita, indole alkaloids, Mycobacterium tuberculosis H37Rv Abbreviations: FU - fluorescence unit, MABA – Microplate Alamar Blue Assay, MIC – minimum inhibitory concentration,VLC – vacuum liquid chromatography