Vibrational spectra and ab initio molecular orbital calculations of the novel anti-cancer drug combretastatin A-4 prodrug

The NIR-FT Raman and FT-IR spectral studies of the novel antineoplastic and antiangiogenesis substance comprestatin A-4 prodrug (CA4P) were carried out. The equilibrium geometry, various bonding features and harmonic vibrational frequencies of CA4P have been investigated with the help of B3LYP density functional theory (DFT) method. The most preferred cis-configuration for its bioactivity has been demonstrated on the basis of torsional potential energy surface (PES) scan studies. Stability of the molecule arising from hyperconjugative interactions leading to its bioactivity, charge delocalization and mesomeric effects have been analyzed using natural bond orbital (NBO) analysis. Detailed assignments of the vibrational spectra have been made with the aid of theoretically predicted vibrational frequencies. The optimized geometry shows near-planarity of phenyl rings and perpendicular conformation of meta substituted methoxy group. The vibrational analysis confirms the differently acting ring modes, steric repulsion, π conjugation and back-donation.