The geometry of the alkaloid molecules were optimized in gas phase using B3LYP functional as implemented in Gaussian 09 software (26) using the 6-311+G(d,p) basis set. The geometry optimization of the molecules was also done using another hybrid density functional with empirical dispersion correction (ωB97XD) (27) with same basis set for verification. The energies of the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) and the electron density distributions of these frontier orbitals were captured by using GAUSS-VIEW software. The HOMO-LUMO energy gap has been linked to reactivity of a molecule and extrapolated to the activity of the bound inhibitor inside the enzyme catalytic cavity .