Evaluation of the antimicrobial property of Polyalthia longifolia var. pendula: isolation of a lactone as the active antibacterial agent from the ethanol extract of the stem.

Bioassay guided fractionation of the ethanolic extract of Polyalthia longifolia var. pendula stem, which showed promising antibacterial activity against thirteen Gram-positive and nine Gram-negative organisms, furnished (3S,4R)-3,4,5-trihydroxypentanoic acid-1,4-lactone (1) as the active principle. The structure of (1) was established by UV, IR, mass, 1H and 13C NMR as well as 2D NMR spectral studies and the formation of its acetate (1a).