Gallic acid-cholesterol conjugate synthesis, spectroscopic characterization and quantum chemical calculations: Experimental and theoretical approach

Abstract

Gallic acid is the major constituent in fruits Phyllanthusemblica (amla), of the family phyllanthaceae. Gallic acid was first methylated to 3,4,5 trimethoxygallic acid, which upon esterification using steglich method with cholesterol resulted in the product (3S,8S,10R,13R,17R)-10,13-dimethyl-17-((R)-6-methylheptan-2-yl)-2,3,4,7,8,9,10,11,12,13,14,15,16,17- tetradecahydro-1H-cyclopenta[a]phenanthren-3-yl 3,4,5-trimethoxybenzoate. The synthesized compound has been characterized by 1H NMR, 13C NMR, UV, FT-IR and mass spectroscopy. Density functional theory (B3YLP) using a 6-31G (d,p) basis set has been used for quantum chemical calculations. The reactive site and reactivity within the molecule are rendered by global and local reactivity descriptors, whereas AIM (Atom in a molecule) approach illustrated weak molecular interactions within the molecule. The energies of HOMO and LUMO and frontier orbital energy gap are calculated by time dependent DFT approach using the IEFPCM model. A small value for the HOMO-LUMO energy gap indicates easier charge transfer within the synthesized compound. The nucleophilic and electrophilic reactivity is determined by MEP (molecular electrostatic potential) studies. The values calculated for polarizability, dipole moment, and first hyperpolarizability are used to depict the NLO (nonlinear optical) property of the synthesized compound.