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Antileishmanial and Antimicrobial Clerodane Diterpenes from Polyalthia longifolia
Polyalthia longifolia is an evergreen tree used in Indian System of Medicine as traditional febrifuge and tonic. Various biological activities, including antibacterial, antifungal and cytotoxic activities, were reported for this plant. In this study, three clerodane diterpenes were isolated by bioassay-guided fractionation and identified as (-) kolavenic acid (1), 16α-hydroxycleroda-3,13(14)Z-diene-15,16-olide (2) and 16-oxocleroda-3,13(14)E-diene-15-oic acid (3). Compound 4 – 6 and 7 were prepared from compounds 2 and 3, respectively. The antileishmanial, antimicrobial and cytotoxic activity of these compounds was evaluated. Compound 2 and its acetylation product (4) displayed potent antileishmanial activity with IC50 values of 1.77 and 2.36 µg/mL, respectively, against Leishmania donovani promastigote. Both the compounds, 2 and 4, were also evaluated against L. donovani axenic amastigote and amastigote in THP1 macrophage cultures, where they displayed strong activities with IC50 values of < 1.60 and 2.34 µg/mL, and 2.34 and 3.72 µg/mL, respectively.