Recent progress in the chemistry of indole alkaloids and mould metabolites

Recent progress in the chemistry of indole alkaloids and mould metabolites

“…The product, from (197) and (196b), was (+) 192-methyl geissoschizoate (200), which was converted as before into the 2-isositsirikine epimers (1 89) and (190) (Scheme 27). Alternatively, (197) and (196a) led by the same route to (+-)-methyl geissoschizoate (201) and thence to (+)-geissoschizine (202). A refinement of this synthesis, by way of an ingenious synthesis of optically pure S-(l97), afforded a new synthesis of ( + )-geissoschizine (202).…”

“…The Z-isositsirikine epimers (189) and (190) have also been synthesized by an ingenious new approach to this group of tetracyclic alkaloids. "* This involved, as critical steps, the stereoselective 1,4-addition of a vinylcuprate (196) to the tetracyclic lactam (197), methanolysis of the lactam (198) via the corresponding imidate salt, and cyclization of the formaldiminium ion derived from reaction of the vinyl silane ( I 99) with paraformaldehyde. The product, from (197) and (196b), was (+) 192-methyl geissoschizoate (200), which was converted as before into the 2-isositsirikine epimers (1 89) and (190) (Scheme 27).…”

“…"* This involved, as critical steps, the stereoselective 1,4-addition of a vinylcuprate (196) to the tetracyclic lactam (197), methanolysis of the lactam (198) via the corresponding imidate salt, and cyclization of the formaldiminium ion derived from reaction of the vinyl silane ( I 99) with paraformaldehyde. The product, from (197) and (196b), was (+) 192-methyl geissoschizoate (200), which was converted as before into the 2-isositsirikine epimers (1 89) and (190) (Scheme 27). Alternatively, (197) and (196a) led by the same route to (+-)-methyl geissoschizoate (201) and thence to (+)-geissoschizine (202).…”

Alkaloids: Chemical and Biological Perspectives

“…X-ray crystal analysis of calebassinine 1 (436) has shown it to possess the quinoline structure 46a. The suggestion has been made that it could arise through a number of oxidative transformations from 2,16-dihydroakuammicine (47); a variant on the route originally proposed has been outlined (437). Isolation of the alkaloid from S. solimoesana (325) would thus imply the occurrence of an akuammicine derivative in the plant, which has not yet been demonstrated.…”