Crystal structure and absolute configuration of yohimbine hydrochloride, C₂₁H₂₇ClN₂O₃

Abstract

Yohimbine (C₂₁H₂₆N₂O₃) is an important indole alkaloid found in the Indian snake rootrauwolfia serpentina, and is very closely related to reserpine. Yohimbine hydrochloride (C₂₁H₂₇ClN₂O₃) is orthorhombic:P2₁2₁2₁, a = 11.54, b = 24.88, c = 7.00 Å, Z = 4. X-ray diffraction data to a Bragg angle of 80° were collected on a G.E. diffractometer using CuK α radiation. The structure was solved by direct methods, and refined to a reliability index of 9.9 % by the block-diagonal least-squares method. Yohimbine has a ring system very similar to that of reserpine, though the conformations of the rings C and D about the C-N bond are different in the two molecules. The absolute configuration of the molecule, determined by X-ray anomalous scattering, confirms the 3α, 15α, 20β configuration assigned earlier by conformational analysis.