Phytochemical analysis and in vitro antimicrobial screenings of the methanolic stem bark extract and constituents of Parkia bicolor A. Chev. (Leguminosae)

The phytochemical study of the methanolic extract of the stem bark of Parkia bicolor A. Chev. (Leguminosae) led to the isolation and characterization of ellagic acid (1), 3,3’-dimethoxyel­lagic acid (2), 3,3’,4,4’-tetramethoxyellagic acid (3), 3-glucopyranoside-3’-methoxyellagic acid (4), gallic acid (5), methylgallate (6), oleanolic acid (7), erythrodiol (8), β-amyrin (9), β-sitosterol (10), stigmasterol (11) and stigmasterol-3-O-β-D-glucopyranoside (12). The structures of these compounds were determined by spectroscopic analyses of 1D and 2D NMR and EI- and ESI-MS and comparison with the reported data. Compounds 1-4 are reported here from this species for the first time. The crude methanolic extract and isolated compounds 1-6 were submitted to micro dilution assay against the Gram negative bacteria Escherichia coli ATCC 8739 and Salmonella typhi clinical strain as well as the Gram positive bacterium Staphylococcus aureus clinical strain. While the methanolic extract showed moderate to significant antibacterial activ­ity against above tests strain with MICs in the range of 64-128 μg/mL, compound 4 displayed the best activity against Salmonella typhi and Staphylococcus aureus clinical strains with an MIC of 33.4 μM against both, compared to gentamycin with 0.1-2.0 μM. Compounds 1-3 and 5, 6 showed moderate to weak antibacterial activity with MICs in the range of 44.6 ± 0.9 to 376.4 ± 1.5 μM. MBCs were above the MICs in the range of 128-512 μg/mL for the methanolic extract resulting in MBCs/MICs in the range of 2 to 8. In antifungal assays, the methanolic extract when tested at 50 mg/mL gave growth inhibition of 34.3, 31.3, 28.3, 33.1, 30.6 and 22.4 % against Aspergillus flavus strain 1, Aspergillus flavus strain 2, Aspergillus niger, Aspergillus gandidus, Ab­sidia sp < /em>. and Penicillium sp < em>., respectively. When tested at 2 mg/mL, 4-glucopyranoside-4’-me­thoxyellagic acid (4) showed a moderate inhibition potency against all the fungal strains with growth inhibition of 24.50 to 40.40% compared to fluconazole with 100% at 2 mg/mL.