Geissoschizine-type alkaloids

Elegant chemical synthesis of geissoschizine (46) and geissoschizine-type derivatives which are important for early steps in Rauvolfia alkaloid biosynthesis, have been reported decades ago by Winterfeldt and coworkers. 

Cryptopine-type indole alkaloid bumamicine (572) has been synthesized from geissoschizine methyl ether (31) (287). In the first step, geissoschizol (34) was prepared, and then cleavage of the C/D ring fusion was carried out by means of ethyl chloroformate. Finally, C-3 carbonyl and 7V-methyl groups were developed by simple oxidation, reduction, and repeated oxidation steps. 

The findings from experiments with H-labelled loganin are collected later but it must be noted here that [2- H, 2- C]loganin (10), in which the label corresponds to position 20 of geissoschizine (41), is incorporated into all three types of alkaloids, e.g. (1), (4), and (6), with complete loss of H. Retention of H in any one of these cases would have cast doubt on geissoschizine as a precursor as it is, additional strength is gained. 

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