The principal members of this group (Chart 6.1) are derived mainly from the Wieland-Gumlich aldehyde (or its equivalent). An alternate ring closure gives the closely related aspidospermatine class of which condylocarpine is a member. None of the biosynthetic steps are known but might proceed according to the experimentally realized 6/5-Mannich condensation (Chapter III, p. 25) equivalent to the hypothetical scheme in Chart 2.2 or by the routes sketched in Charts 2.3 or 12.2. The alkaloids of this group were first discovered in the genus, Strychnos (family, Loganiaceae) but strangely the dimeric curare alkaloids (tertiary and quaternary) occur only in the South American species. In the Apocynaceae, e.g. picralima and vinca species, products of the further oxidation of the Wieland-Gumlich aldehyde are found. The Wieland-Gumlich aldehyde shows a great tendency to dimerize which may in the absence of other enzymatic pathways in a particular plant make it almost mandatory for it to be isolated as a dimeric derivative. Such a doubling up can be prevented by acetylation (diaboline), oxidation (akuammicine) or reduction (spermostrychnine). The chemistry of strychnine has not played as direct a role in the development of heterocyclic chemistry as morphine because its structure for so long defied exact description. It did, however, generate some important theoretical questions and was there, for half the twentieth century as one of the great chemical challenges and upon it almost every useful reaction in degradative chemistry has been applied usually with some success. Although its structure is now known with certainty by degradation, synthesis and X-ray crystallography, many of its reactions deserve renewed study for their mechanistic implications. Practically all the compounds of this group are interconvertible and since strychnine is commercially available and cheap it is the conventional starting point for model studies or partial syntheses.