Carbonic anhydrase and cholinesterase inhibitory activities of isolated flavonoids from Oxalis corniculata L. and their first-principles investigations

Abstract

Phytochemical investigations of Oxalis corniculata L. shown the existence of biologically active secondary metabolites like phenols, flavanoids, alkaloids, tannins, triterpenes, sterols, and volatile oils. In this work, ethanolic extract of Oxalis corniculata L. was prepared to explore the carbonic anhydrase and cholinesterase inhibitory activities against epilepsy and anti-Alzheimer's disease (AD) potential. Upon fractionation, chloroform and ethyl acetate fractions showed high phenolic (168.56 and 171.11 μg ascorbic acid/g extract) and flavonoid contents (115.72 and 99.35 μg (+)-catechin/g extract), respectively and were the most active ones against acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and carbonic anhydrase inhibition. The bioactivity-guided isolation from chloroform and ethyl acetate extract of Oxalis corniculata afforded nine flavonoids. The newly isolated flavonoid (1) and eight source compounds 2–9 screened by cholinesterase (AChE and BChE) and carbonic anhydrase-II (CA-II) inhibitory assays. Carbonic anhydrase inhibition rate for compounds 1–9 ranged 65.21–90.82 with the IC50 17.11–25.18, compared with reference acetazolamide. Cholinesterase (AChE and BChE) inhibitory potential (49.52 and 29.12 μg/mL) of newly isolated compound 1 whereas compounds 3, 5, 8 and 9 showed considerable significant inhibition potential using standard inhibitor serine. Moreover, the ground state geometries of all the nine compounds along with positive drugs were optimized by Density functional theory (DFT) at B3LYP/TZ2P level to explore the electronic properties and active sites. The effect of substituents on the molecular descriptors, frontier molecular orbitals, molecular electrostatic potential and Hirshfeld charges was explored.