Two new compounds and the anti-mycobacterial activity of the constituents from Zanthoxylum leprieurii root bark

Abstract

The emergence of resistance to the existing TB drugs necessitated a search for new anti-mycobacterial compounds from Z. leprieurii root bark, which is used locally for the treatment of tuberculosis (TB) in Uganda. Two new compounds: (E)-N-isobutyl-3-(4-((3-methylbut-2-en-1-yl)oxy)phenyl)acrylamide (1) and 4-(5,5a,6,8,8a,9-hexahydrofuro[3′,4′:6,7]-naphtha[2,3-d][1,3]dioxol-5-yl)-2-methoxyphenol (2), were isolated from the dichloromethane (DCM) extract. In addition, sixteen known compounds were isolated from the DCM and methanol extracts, with two of them, N-isobutylcinnamamide (9) and (E)-3-(4-hydroxy-3-methoxyphenyl)-N-isobutylacrylamide (14), being reported from a natural source for the first time. The structures of the isolates were elucidated by a combination of spectroscopic techniques. The isolated compounds were subjected to anti-mycobacterial activity testing using the microplate Alamar blue assay (MABA). Five compounds, 10 (MIC, 0.98 μg/mL), 11 (MIC, 7.82 μg/mL), 12 (MIC, 1.95 μg/mL), 13 (MIC, 3.91 μg/mL), and 14 (MIC, 3.91 μg/mL) exhibited significant anti-mycobacterial activities against the susceptible (H37Rv) strain and could provide vital templates for developing new and highly effective TB drugs. Also, compounds 4 (MIC, 62.50 μg/mL), 7 (MIC, 62.50 μg/mL) and 16 (MIC, 62.50 μg/mL) exhibited moderate activity against H37Rv.