X-Ray determination of the molecular structure and absolute configuration of vincamine and of its hydrobromide methanolate

Abstract

The structure and absolute configuration of the indole alkaloid vincamine (I) have been determined by X-ray analysis of the natural product and of its hydrobromide methanolate (II). A comparison of both molecular structures shows that protonation and different crystal packing have no measurable effect on bond lengths and bond angles, but noticeable differences in torsion angles and consequently in the finer details of the conformation are observed. Crystal data: (I), space group P2₁2₁2₁, Z= 4, a= 7·708(4), b= 14·527(7), c= 16·776(6)Å; (II), space group P2₁, Z= 2, a= 7·390(2), b= 17·843(3), c= 9·437(4)Å, β= 115·69(2)°. The structures were solved from diffractometer data by the multi-solution (I) and heavy-atom methods (II), and refined by least-squares techniques to R 0·042 [(I), 1341 reflections] and 0·045 [(II), 2033 reflections].