13C, 15N CP-MAS, FT-IR and PM5 studies of some Schiff bases of gossypol in solid

The Schiff bases of racemic gossypol with l-arginine methyl ester (GSB1), 2-(aminomethyl)-18-crown-6 (GSB2) and 5-hydroxy-3-oxapentylamine (GSB3) were studied by FT-IR, 13C and 15N CP-MAS spectroscopy as well as by PM5 semiempirical calculations. The spectroscopic methods give clear evidence that all Schiff bases exist in the solid state as enamine-enamine tautomers. The structures of GSB1-GSB3 and the hydrogen bonds within these structures are discussed.