Ultraviolet spectroscopy of anticonvulsant enaminones

The ultraviolet (UV) spectra of selected enaminones were determined in acidic, alkaline and neutral media and compared to their anticonvulsant activities. The wavelength of maximum absorption and molar absorptivity were compared with the anticonvulsant activity of the selected secondary and tertiary enaminones, and general inferences were made. The UV spectra of the enaminones had hypsochromic shifts in acidic media in comparison with neutral media. Generally, a small hypsochromic shift occurred in alkaline media when compared to the neutral solutions of the enaminones. The tertiary enaminones absorbed UV light at longer wavelength than the secondary enaminones in acidic, neutral and alkaline media. In particular, the tertiary enaminones displayed absorption at the higher end and secondary enaminones towards the lower end of the UV wavelength range 292-315nm in aqueous media. Tertiary enaminones (30-33) which were devoid of the NH proton were found to be uniformly inactive in a mouse model of electroshock seizures, while some secondary enaminones (1, 5-8, 12, 16, 18, 20, 23-25, 28 and 29) had anticonvulsant activity. Thus the NH group of secondary enaminones is very important for anticonvulsant activity, and this agrees with an already established trend in proton NMR spectroscopy. In addition, the para-substitution on the phenyl group in some enaminones result in higher molar absorptivity (epsilon) values that enhance anticonvulsant activity. These results indicate that the anticonvulsant activity of enaminones is not due to electronic effect alone, but is probably due to a combination of factors including electronic and steric effects, lipophilicity, and hydrogen bonding.