The crystal and molecular structures of rac-threo-ifenprodil and two other 4-benzylpiperidinyl derivatives

Abstract

The crystal structures of threo-ifenprodil [threo-2-(4-benzyl-piperidin-1-yl)-1-(4-hydroxyphenyl)-propan-1-ol] (1), potent NMDA receptor antagonist, and two related, biologically active compounds: threo-2-(4-benzyl-piperidin-1-yl)-1-(4-fluorophenyl)-propan-1-ol (2) and 4-benzyl-1-phenethyl-piperidinium chloride (3) have been determined by X-ray structure analysis of single crystals. Compound 1 crystallizes in an orthorhombic system, with a space group Pna2₁ (a = 34.843(3) Å, b = 6.0261(13) Å, c = 8.9343(9) Å), compound 2 – in a monoclinic space group P2₁/c (a = 14.194(1) Å, b = 6.2831(6) Å, c = 20.948(1) Å, β = 101.762(6)^○), and compound 3 – in an orthorhombic space group Pbca (a = 10.4627(8) Å, b = 11.2166(6) Å, c = 31.669(2) Å). The piperidine rings are close to ideal chair conformations, the substituents are in equatorial positions. Overall shapes of the molecules, defined by the dihedral angles between the terminal aromatic rings, are very similar in all three cases. In 1 and 3 the crystal packing is mainly determined by the hydrogen bonds, while in case of 2 – by weak van der Waals interactions. The molecules of 1 and 3 are disordered, and the disorder is caused by a rotation around the N–C bond.