Ab-Initio and DFT Study of the Muchimangin-B Molecule

Abstract

Muchimangin B is a xanthone derivative isolated from the root of Securidaca longepedunculata and exhibiting activity against pancreatic cancer. Detailed information about the molecular properties of a biologically active compound is important for the design of compounds with more potent activities. This work presents the results of an ab initio and DFT study of the muchimangin B molecule. HF/6-31G(d,p) and DFT/B3LYP/6-31+G(d,p) calculations were performed in vacuo with fully relaxed geometry, to identify conformational preferences. These preferences are dominantly determined by different intramolecular hydrogen bonding patterns, although the orientation of the rings with respect to the xanthone moiety also has significant influence. Frequency calculations were performed to verify that identified stationary points are true minima. Calculations in solution were performed on the in vacuo optimized geometries, as single point calculations at the DFT/B3LYP/6-31+G(d,p) level, considering three solvents with different polarity and H-bonding ability—chloroform, acetonitrile and water. Selected adducts with explicit water molecules were calculated, for their informative roles in view of the presence, in the muchimangin B molecule, of a high number of sites that can act as donors or acceptors of intermolecular hydrogen bonds with water molecules.