A detailed NMR (1H , COSY, ROESY) spectroscopic study of complexation of enalapril maleate with b-cyclodextrin was carried out. The 1H NMR spectrum of enalapril maleate confirmed the existence of cis-trans equilibrium in solution, possibly due to hindered rotation along the amide bond. The cis-trans ratio remained almost the same in the presence of b-cyclodextrin but in one case it was found significantly different which suggests a catalytic role of b-cyclodextrin in the isomerization. 1H NMR titration studies confirmed the formation of an enalapril-b-cyclodextrin inclusion complex as evidenced by chemical shift variations in the proton resonances of both the host and the guest. The stoichiometry of the complex was determined to be 2:1 (guest: host). The mode of penetration of the guest into the b-cyclodextrin cavity as well as the structure of the complex were established using ROESY spectroscopy.
Print version ISSN 0100-4042
Quím. Nova vol.29 no.4 São Paulo July/Aug. 2006
Syed Mashhood Ali*, I; Arti MaheshwariI; Fahmeena AsmatI; Mamoru KoketsuII
IDepartment of Chemistry, Aligarh Muslim University, Aligarh 202002 (UP), India
IIDivision of Instrumental Analysis, Life Science Research Center, Gifu University, Gifu, 501-1193, Japan
Enalapril maleate, which exists in two geometrical forms in solution, forms a 1: 2 host-guest inclusion complex with b-CD in the concentration range studied. The aromatic ring of one guest molecule enters the b-CD cavity from narrower rim side while 5-membered ring penetrates through wider rim side as evidenced by ROESY spectrum. The structure for the complex has been proposed.