Comparison crystal structure conformations of two structurally related biphenyl analogues: 4,4′-bis[3-(pyrrolidin-1-yl)prop-1-yn-1-yl]-1,1′-biphenyl and 4,4′-bis{3-[(S)-2-methylpyrrolidin-1-yl]prop-1-yn-1-yl}-1,1′-biphenyl

The title compounds, C₂₆H₂₈N₂, (I), and C₂₈H₃₂N₂, (II), were designed based on the structure of the potent α9α10 nicotinic acetylcholine receptor antagonist ZZ161C {1,1′-[[1,1′-biphenyl]-4,4′-diylbis(prop-2-yne-3,1-diyl)]bis(3,4-dimethylpyridin-1-ium) bromide}. In order to improve the druglikeness properties of ZZ161C for potential oral administration, the title compounds (I) and (II) were prepared by coupling 4,4′-bis(3-bromoprop-1-yn-1-yl)-1,1′-biphenyl with pyrrolidine, (I), and (S)-2-methylpyrrolidine, (II), respectively, in acetonitrile at room temperature. The asymmetric unit of (I) contains two half molecules that each sit on sites of crystallographic inversion. As a result, the biphenyl ring systems in compound (I) are coplanar. The biphenyl ring system in compound (II), however, has a dihedral angle of 28.76(11)°. In (I), the two independent molecules differ in the orientation of the pyrrolidine ring (the nitrogen lone pair points towards the biphenyl rings in one molecule, but away from the rings in the other). The torsion angles about the ethynyl groups between the planes of the phenyl rings and the pyrrolidine ring N atoms are 84.15(10) and -152.89(10)°. In compound (II), the corresponding torsion angles are 122.0(3) and 167.0(3)°, with the nitrogen lone pairs at both ends of the molecule directed away from the central biphenyl rings.