Constitution and absolute stereochemistry of the biphenyl alkaloid lythranine: X-ray analysis of the crystal structure of bromolythranine hydrobromide ethanol solvate

Abstract

The constitution and stereochemistry of lythranine, a biphenyl alkaloid from Lythrum anceps, has been defined by X-ray analysis of the crystal structure of bromolythranine hydrobromide ethanol solvate. In the biphenyl system of the alkaloid, the dihedral angle between the benzene planes is 75°. The piperidinium ring has a chair conformation with torsion angles in the range 52–60°, mean 56°. The crystals are orthorhombic, space group P2₁2₁2₁, with Z= 4 in a cell of dimensions a= 21·768(17), b= 15·223(12), c= 9·873(7)Å. The atomic co-ordinates were determined by Fourier and least-squares calculations, and the analysis terminated at R 7·7% over 1443 reflections. The absolute configuration was established by the anomalous dispersion effect.