Antibacterial and antioxidant activities of 3-O-methyl ellagic acid from stem bark of Polyalthia longifolia Thw.

Polyalthia longifolia (Annonaceae) is an ornamental plant that is used in Indian traditional medicine and mistakenly known in Hindi as Ashoka. It is often used as an adulterant or substitute of the genuine Asoka (Saraca indica) bark. P. longifolia is used traditionally for treatment of a number of complications. The present investigation was carried out with an objective to separate and isolate active phytomolecules from stem bark of P. longifolia and to screen their antibacterial and antioxidant potential. Column chromatography of the butanol fraction of the hydroalcoholic extract (methanol:water, 1:1) has led to the isolation of a phenolic compound. Structural elucidation was done by IR,¹H NMR,¹³C NMR, DEPT, COSY, HSQC, HMBC and mass spectroscopy techniques, and purity was checked by HPTLC and HPLC. Butanol fraction and the isolated compound were screened for antibacterial activity (against facultative aerobic and fastidious aerobic bacterial strains) and antioxidant potential (determined by DPPH and ABTS methods). The compound was identified as 3-O-methyl ellagic acid (compound 1) and the purity of compound 1 was 99.6%. The isolated compound comprised of promising antibacterial and antioxidant activities. MIC of compound 1 and butanol fraction against tested bacterial strains were in the range of 80-160 and 160-320 μg/ml. The IC₅₀ value in DPPH method was 24.28 μg/ml for compound 1 and 266.59 μg/ml for butanol fraction. Further, the total antioxidant capacity (ABTS method) of compound 1 and butanol fraction was 2486.94±10.20 and 207.93±9.91 μmol TE/ g dry weight of sample. In the present study, we have reported a phenolic compound, 3-O-methyl ellagic acid from stem bark of P. longifolia with antibacterial and antioxidant activities.