Bioassay-Guided Isolation and Structural Modification of the Anti-TB Resorcinols from Ardisia gigantifolia

Tuberculosis (TB) is a highly contagious disease mainly caused by Mycobacterium tuberculosis H37RV. Antitubercular (anti-TB) bioassay-guided isolation of the CHCl3 extract of the leaves and stems of the medicinal plant Ardisia gigantifolia led to the isolation of two anti-TB 5-alkylresorcinols, 5-(8Z-heptadecenyl) resorcinol (1) and 5-(8Z-pentadecenyl) resorcinol (2). We further synthesized 15 derivatives based on these two natural products. These compounds (natural and synthetic) were evaluated for their anti-TB activity against Mycobacterium tuberculosis H37RV. Resorcinols 1 and 2 exhibited anti-TB activity with MIC values at 34.4 and 79.2 mu M in MABA assay, respectively, and 91.7 and 168.3 mu M in LORA assay, respectively. Among these derivatives, compound 8 was found to show improved anti-TB activity than its synthetic precursor (2) with MIC values at 42.0 mu M in MABA assay and 100.2 mu M in LORA assay. The active compounds should be regarded as new hits for further study as a novel class of anti-TB agents. The distinct structure-activity correlations of the parent compound were elucidated based on these derivatives.