Phytochemical investigation of Mezoneuron benthamianum Baill, isolation, in vitro antioxidant, alpha-amylase inhibition, and in silico modelling studies

Abstract

Mezoneuron benthamianum (Leguminosae-caesalpinioideae family), is widely used across West Africa for the treatment of bacterial, fungal, and inflammatory diseases. This study is aimed at investigating the antioxidant and antidiabetic activities of extracts and isolated compounds from Mezoneuron benthamianum leaf and root. The pulverized leaf (1 kg) was extracted by maceration with dichloromethane and methanol to give the dichloromethane (MBLD) and methanol (MBLM) extracts, while the root (2 kg) samples were extracted using dichloromethane and methanol (1:1) to give the dichloromethane-methanol extract (MBRDM) which was further partitioned to give the hexane (MBRH), ethyl acetate (MBRE) and methanol (MBRM) extracts respectively. The leaf methanol extract (MBLM) was fractionated using column chromatography (70–230 mesh size) which led to the isolation of compound 1. The extracts and isolated compounds were subjected to in-vitro antioxidant assay with 1,1-diphenyl-2-picrylhydrazyl (DPPH) and α-amylase inhibitory assay using porcine pancreatic α-amylase respectively. FT-IR spectroscopic analysis compound 1 showed strong peaks at 1678 and 1612 cm−1 suggesting the presence of a carbonyl and an aromatic group respectively. 1H NMR spectroscopic analysis of compound 1 showed two peaks at 3.80 (3H, s) and 7.04 ppm (2H, s) indicating methoxy and aromatic protons respectively. 13C NMR also confirmed the presence of the methoxy peak at 50.8 ppm, four aromatic peaks at 108.76, 120.19, 131.25, 145.14 ppm indicating a para-disubstituted benzene ring, and a carbonyl peak at 167.80 ppm, this led to the elucidation of compound 1 known as methyl gallate. The antioxidant activities of the extracts and compounds showed that MBLM (IC50 = 112.0 μg/ml) and MBRE (IC50 = 91.84 μg/ml) had the highest activity of the leaf and root extracts respectively while methyl gallate (IC50 = 91.84 μg/ml) had lower activity than gallic acid (IC50 = 27.4 μg/ml), ascorbic acid (IC50 = 43.94 μg/ml) and BHT (68.94 μg/ml). The α-amylase inhibitory activities showed that MBLD (IC50 = 27.4 μg/ml), MBRE (IC50 = 72.2 μg/ml), gallic acid (IC50 = 27.4 μg/ml) and methyl gallate (IC50 = 43.9 μg/ml) had higher activity than the standard drug acarbose (IC50 = 378.2 μg/ml). For the In silico study, methyl gallate was docked into the active site of the targeted diabetic proteins; human pancreatic alpha-amylase, pig pancreatic alpha-amylase, and tetrameric IIB-HSDI. The results showed that methyl gallate had good interactions with the proteins, with binding affinities of −4.8, −4.8 and −6.5 kcal/mol respectively. Furthermore, in silico pharmacokinetics and toxicology properties of methyl gallate using the AdmetSAR and SwissADME software showed that the compound has good pharmacokinetic properties and it is generally non-toixc. This research has revealed detailed chemical and biological studies on Mezoneuron benthamianum and its isolated compound as an antioxidant and antidiabetic.