Crystal structures and absolute stereochemistry of tecomanine methoperchlorate and ‘alkaloid C’ methiodide: two monoterpene alkaloids from Tecoma stans

Abstract

Crystals of tecomanine methoperchlorate are monoclinic, a= 8.032(1), b= 10.019(1), c= 8.900(2)Å, β= 91.44(1)°, Z= 2, space group P2₁; crystals of ‘alkaloid C’ methiodide are orthorhombic, a= 8.874(1), b= 9.361(1), c= 16.861(2), Z= 4, space group P2₁2₁2₁. Both structures were determined from Patterson and Fourier synthesis, and refined by full-matrix and block-diagonal least-squares to R 0.047 (1305 observed reflexions, tecomanine methoperchlorate) and 0.049 (1412 observed reflexions, ‘alkaloid C’ methiodide). The two structures have identical absolute stereochemistry at their common asymmetric centres, and in each case the six-membered ring is in the chair, and the five-membered ring in the envelope confirmation.