Genistein complexes with amines. Part II: ab initio study of the complexeswith piperazine and triethylamine

The piperazine and triethylamine complexes of genistein, exhibiting high im munosuppressant activity, were ab initio modeled at RHF/6-31G** level and r esults were compared with those obtained for genistein-morpholine complexes by Xray, NMR and theoretical methods. The most stable genistein-piperazine complex is formed due to hydrogen bonding of genistein's OH group at posit ion C7 to piperazine's nitrogen atom. In the most stable genistein-triethyl amine complex genistein's OH group at position C4' (position para to phenyl substituent) and trimethylamine nitrogen atom an engaged in hydrogen bond formation. The calculations confirmed our previous NMR conclusion that pipe razine is more strongly complexed by genistein than is morpholine or trieth ylamine. The theoretical C-13 NMR spectra correlate fairly well with the ex perimental spectra. (C) 2000 Elsevier Science B.V. All rights reserved.