From tubocurare (Chondodendron tomentosum R. & P., Menispermaceae): Boehm, Arch. Pharm. 235, 660 (1897); Sp"ath et al., Ber. 61, 1698 (1928). Structure: Sp"ath, Kuffner, Ber. 67, 55 (1934); Faltis et al., Ber. 69, 1269 (1936); King, J. Chem. Soc. 1939, 1157. Configuration: Bick, Clezy, ibid. 1953, 3893; Hultin, Acta Chem. Scand. 17, 753 (1963). Biosynthetic study: D. S. Bhakuni et al., Tetrahedron 43, 3975 (1987). Ca2+ channel interactions: J. P. Felix et al., Biochemistry 31, 11793 (1992).