Conformation of Roxatidine Acetate Hydrochloride by 1H, 13C and 15N NMR and AM1 Calculations and Its Interaction with Model Membranes Studied by 31P NMR

Roxatidine acetate hydrochloride is a widely prescribed H2-receptor antagonist for peptic ulcers. Its conformation has been studied using 1H, 13C, and 15N NMR spectroscopy in DMSO-d6 and H2O:D2O (90:10) solvents coupled with AM1 calculations. The results show a folded conformation in DMSO-d6 as opposed to an extended structure in water. Its conformation in DMSO has been constructed with AM1 calculations and closely resembles the structures seen for cimetidine, ranitidine and famotidine in the solid state and in solution. Its structure in water is comparable to its crystallographic state. The interaction of roxatidine with model membranes prepared from DPPC has also been investigated by 31P NMR. Roxatidine is seen to induce the formation of lipid structures (cubic or rhombic or tetragonal) not normally seen for pure DPPC. The formation of such structures is seen to occur in a narrow dose regimen.