(Published Online: Jul 10 2009) SPECTROSCOPY PROPERTIES OF THE AMIDE GROUP IN VALPROMIDE AND SOME DERIVATIVES WITH ANTIEPILEPTIC ACTIVITY

NIEVES C. COMELLI,; NESTOR E. MASSA; EDUARDO A. CASTRO; ALICIA H. JUBERT

JOURNAL OF RAMAN SPECTROSCOPY

Wiley-Blackwell

Lugar: New York; Año: 2009

0377-0486

ABSTRACT: Infrared at 300K and 77K and Raman spectra at 300K of the Valpromide (Vpd), Nsubstituted derivatives: N-ethylvalpromide (Etvpd), N-isopropylvalpromide (Ipvdp) and the N,N-disubstituted derivative: N,N-dimethylvalpromide (Dmvpd) with antiepileptic activity have been measured and analyzed with results derived from computational chemistry calculation. In agreement with theoretical predictions, experimental data indicate that while in the Etvpd, Dmvp and Ipvpd there are four different conformational co-existing: components Etvpd: TTCG+, TCCG-, TTTC, G+G+C G+; Dmvpd: TTCC, G-TTA+, G+A-TC, +A-C A+; Ipvpd: TTCT, TCCT, TCCC, G-TTT, in the Vpd there are only three distinct stable conformations of C1 symmetry group; TTC, TCT, G+G+T. Based in the accuracy of the B3LYP calculation, with the 6-31+G** basis set estimated by comparison between the predicted values of the vibrational modes and the available experimental data, we performed a structural and vibrational study of the amide group in the Vpd and their derivative. We find that small nonplanarity deviations of C(=O)N backbone induce significant changes on the structural and spectroscopic properties. These are not compatible with the decreasing of the resonance effect as it is produced when the twisting around the C(=O)-N increases. From the Natural Bond Orbital (NBO) analysis it becomes evident the existence in those structures of stabilizing electrostatic interactions of type C-H…O/N and C–…HN/ C which induce significant structural changes and a complex electronic redistribution of charge on the ð-system. We view this as a consequence of the filled electron densityNsubstituted derivatives: N-ethylvalpromide (Etvpd), N-isopropylvalpromide (Ipvdp) and the N,N-disubstituted derivative: N,N-dimethylvalpromide (Dmvpd) with antiepileptic activity have been measured and analyzed with results derived from computational chemistry calculation. In agreement with theoretical predictions, experimental data indicate that while in the Etvpd, Dmvp and Ipvpd there are four different conformational co-existing: components Etvpd: TTCG+, TCCG-, TTTC, G+G+C G+; Dmvpd: TTCC, G-TTA+, G+A-TC, +A-C A+; Ipvpd: TTCT, TCCT, TCCC, G-TTT, in the Vpd there are only three distinct stable conformations of C1 symmetry group; TTC, TCT, G+G+T. Based in the accuracy of the B3LYP calculation, with the 6-31+G** basis set estimated by comparison between the predicted values of the vibrational modes and the available experimental data, we performed a structural and vibrational study of the amide group in the Vpd and their derivative. We find that small nonplanarity deviations of C(=O)N backbone induce significant changes on the structural and spectroscopic properties. These are not compatible with the decreasing of the resonance effect as it is produced when the twisting around the C(=O)-N increases. From the Natural Bond Orbital (NBO) analysis it becomes evident the existence in those structures of stabilizing electrostatic interactions of type C-H…O/N and C–…HN/ C which induce significant structural changes and a complex electronic redistribution of charge on the ð-system. We view this as a consequence of the filled electron density