Naturally Occurring Anti-TB Agents: Isolation, Chemical Transformations and In Vitro Antitubercular Activities of Secondary Metabolites of Rhizomes of Alpinia galanga

A bioactivity-guided chemical examination of the acetone extract of the rhizomes of Alpinia galanga led to the isolation of six secondary metabolites, eucalyptol derivative (1) and phenylpropanoids (2–6). The structures of all of the isolated compounds (1– 6) were elucidated on the basis of their spectral data. The isolated compounds (1–6) were in vitro assayed against active and dormant phenotypes of Mycobacterium tuberculosis H37Ra, respectively. Interestingly, 1′S-1′-acetoxychavicol acetate (2) showed good antitubercular activities against both active and dormant phenotypes of M. tuberculosis with IC50 values of 1.04 μM and 2.69 μM, respectively. Tsuji-Trost and homodimerization reactions of the active compound (2) respectively resulted in the formation of two analogues, 7 and 8. Both of these synthesized analogueswere also found to be active in vitro against active [IC50 s of 3.24 and 3.87 μM, respectively, for compounds 7 and 8] and dormant [IC50 s of 8.33 and 2.41 μM, respectively, for compounds 7 and 8] phenotypes of M. tuberculosis H37Ra, respectively.