VIBRATIONAL FORCE-FIELD CALCULATIONS OF ARA-A - APPLICATION TO THE ANALYSIS OF ITS INFRARED AND RAMAN-SPECTRA

The vibrational spectra of the arabinonucleoside 9-beta-D-arabinofuran osyladenine, ara-A, are reported. Ara-A is of interest because of its antiviral activity. An accurate knowledge of the vibrational modes is a valuable help for the elucidation of drug-nucleotide and drug-enzyme interactions. The FTIR and FT-Raman spectra of ara-A were recorded fr om 4000 to 30 cm(-1). A hexadeuterated derivative (deuteration at C8, the amino and hydroxyl groups) was synthesized, and its spectra were a lso used for the vibrational analysis of ara-A, Theoretical frequencie s as well as the potential energy distribution of the vibrational mode s of ara-A were calculated using the ab initio HF/3-21G method, the se miempirical PM3 method, and two valence force fields. The results obta ined are compared in order to show the accuracy and reliability of eac h method. The observed spectra and the vibrational frequencies of ara- A are assigned considering the potential energy distributions and the observed band shifts by deuteration. Scaled ab initio and PM3 frequenc ies are in a good agreement with the experimental data. The valence fo rce field was found to reproduce them with enough accuracy when a larg e set of harmonic force constants is used. Previous normal coordinate analyses of the adenine and related molecules are compared with these results.