[RESEARCH NOTE] Activity of the Extracts and Indole Alkaloids from Alstonia scholaris Against Mycobacterium tuberculosis H37Rv

Allan Patrick  Macabeo; Karsten  Krohn; Dietmar  Gehle; Roger Read; Joseph  Brophy; Scott  Franzblau; Ma. Alicia  Aguinaldo

Allan Patrick Macabeo Phytochemistry Laboratory, Research Center for the Natural Sciences, Thomas Aquinas Research Complex, University of Santo Tomas, Espana, Manila, Philippines
Karsten Krohn University of Paderborn, Department of Chemistry, Warburger Str. 100, 33098 Paderborn, Germany
Dietmar Gehle University of Paderborn, Department of Chemistry, Warburger Str. 100, 33098 Paderborn, Germany
Roger Read School of Chemistry, University of New South Wales, Sydney 2052, Australia
Joseph Brophy School of Chemistry, University of New South Wales, Sydney 2052, Australia
Scott Franzblau Institute for Tuberculosis Research, College of Pharmacy, University of Illinois at Chicago, 833 S. Wood St., Chicago, Illinois USA 60612-7231
Ma. Alicia Aguinaldo Phytochemistry Laboratory, Research Center for the Natural Sciences, Thomas Aquinas Research Complex, University of Santo Tomas, Espana, Manila, Philippines

Keywords: Alstonia scholaris, antitubercular activity, dita, indole alkaloids, 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 μg 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 μg mL-1. Compared with the standard rifampin (MIC 0.125 μg mL-1), all alkaloids were considered inactive.