Gas Chromatography-Mass Spectrometry and Fourier Transform Infrared Spectroscopy Analysis of Potential α-Glucosidase Inhibitors from Terminalia catappa Leaf Extracts

Aims: Postprandial hyperglyceamia is often caused by insulin insufficiency or cellular glucose uptake complications, and conventional treatments often yield undesirable side effects. The aim of the current work was to assess the α-glucosidase inhibitory activities of T. catappa leaf extracts and use spectroscopic techniques to partially characterize possible inhibitors.

Study Design: Phytochemical screening, enzyme inhibition assay and spectrometric and spectroscopic characterization of bioactive compounds from leaf extract and fractions of T. catappa.

Place and Duration of Study: The entire work was carried out at the Department of Applied Chemistry and Biochemistry, University for Development Studies, Ghana within nine months.

Methodology: T. catappa leaf extract and fractions were qualitatively screened for phytochemicals and their biological activity assessed in α-glucosidase inhibition assay. The potential enzyme inhibitors were characterized by Gas Chromatography-Mass Spectrometry (GC-MS) and Fourier Transform Infrared (FT-IR) Spectroscopy.

Results: Phytochemical screening of the extract and the various solvent fractions revealed the presence of alkaloids, flavonoids, saponins, flavanol glycosides, phenolics, and terpenoids. The α-glucosidase inhibition potential of the crude leaf extract was concentration-dependent with a half-maximal inhibitory concentration (IC50) of 337.5 µg/ml. Solvent fractions from the crude extract demonstrated α-glucosidase inhibitory activity with IC50 values ranging from 170.40 µg/ml for ethyl acetate (EtOAc) fraction to 71.90 µg/ml for n-hexane (n-Hex) fraction. Acarbose, the control drug, demonstrated significant α-glucosidase inhibition activity in a similar pattern with IC50 of 6.16 µg/ml. The enzyme inhibition kinetics parameters, specifically the Michaelis constant (KM) and Maximum reaction velocity (Vmax) values, suggested that the inhibition of α-glucosidase by T. catappa extract followed a competitive mode. GC-MS and FT-IR analysis of the n-Hexane fraction identified the compounds Eugenol, Urs-12-en-24-oic acid, 3-oxo-, methyl ester (+)-, phytol, trans-isoeugenol, α-amyrin, and squalene as the potential antidiabetic agents that might be responsible for reducing postprandial blood glucose levels.

Conclusion: These findings show that T. catappa leaf extract contains α-glucosidase inhibitors and therefore serves as a valuable resource in the discovery of natural anti-diabetic agents.