This study investigated bioactive extracts of Polyalthia debilis (Annonaceae) with antimicrobial, antimalarial and cytotoxic activities. Extensive chromatographic isolations provided azafluorenone alkaloids; onychine (1) and 7-methoxyonychine (2) together with a mixture of β–sitosterol and stigmasterol. The two alkaloids were isolated from the P. debilis for the first time. Isolated fractions containing a mixture of triterpenoids (C7, C8 and C9) exhibited the most potent antimicrobial activity against many bacterial strains with minimum inhibitory concentration of 64 μg/mL. Fractions with antimalarial and cytotoxic activities were also observed. The findings suggest the potential use of P. debilis in medicinal applications.

The objective of the study was to isolate bioactive acetogenin compound and to investigate antimicrobial, antioxidant as well as cytotoxic activities of the isolate, fractions and extracts of Polyalthia debilis. The P. debilis (roots) extracts and isolated compound were tested for their antimicrobial (agar dilution method) against twentyseven strains of microorganisms (gram positive and gram negative bacteria, and diploid fungus), antioxidant (DPPH assay) and cytotoxic activities. The plant extracts were isolated by column chromatography and structure of compound was confirmed by spectral data. The plant extracts and isolated fractions exhibited antioxidant and cytotoxic activities. The isolated acetogenin 1 (debilisone E) displayed antimicrobial activity against Morexella catarrhalis with the MIC of 64 g/mL, Corynebacterium diphtheriae NCTC 10356 and Streptococcus pyogenes with partial inhibition (50-75%) at 128 g/mL. The compound 1 exerted cytotoxic activity against 5 cancer cells (HepG2, A549, HCC-S102,HL-60 and P388) with IC50 values 18.4 -40.3g/mL. The results demonstrate novel bioactivities of P. debilis as antimicrobials and anticancer agents.