Ab initio vibrational calculations on ara-T molecule: Application to analysis of IR and Raman spectra

The FTIR and FT-Raman spectra are reported for the arabinonucleoside ara-T (1-beta -D-arabinofuranosylthymine), which shows antiviral activity. The ac curate knowledge of the vibrational modes is a prerequisite for the elucida tion of drug-nucleotide and drug-enzyme interactions. The FTIR and FT-Raman spectra of ara-T were recorded from 4000 to 30 cm(-1). A tetradeuterated d erivative (deuteration at N-3, and hydroxyl groups O'(2), O'(3), and O'(5)) was synthesized and the observed isotopic shifts in its spectra were used for the vibrational analysis of ara-T. The theoretical frequencies and the potential energy distribution (PED) of the vibrational modes of ara-T were calculated using the ab initio Hartree-Fock/3-21G method. An assignment of the vibrational spectra of ara-T is proposed considering the scaled FED and the observed band shifts under deuteration. The scaled ab initio frequenci es were in reasonable agreement with the experimental data. (C) 2001 John W iley & Sons, Inc.