Guettarda eximia

Kan-Fan and Husson reported the isolation and structure elucidation of 4,21-dehydrogeissoschizine chloride (32) from the leaves of Guettarda eximia (39). It has been suggested that this alkaloid is a biosynthetic intermediate of several... 

Cathenamine (100) has been identified as an early intermediate in terpenoid indole alkaloid biosynthesis (cf. Vol. 8, p. 27). It has also been isolated from Guettarda eximia. Another alkaloid, 4,21-dehydrogeissoschizine (99), has now been isolated from this plant it is readily converted into (100) in alkaline solution.29 On incubation with an enzyme preparation from Catharanthus roseus cell cultures in the presence of NADPH at pH 7, (99) was converted into ajmalicine (102), 19-ep/-ajmalicine (103), and tetrahydroalstonine (104), which are the normal products with this enzyme preparation. In the absence of NADPH, cathenamine (100) accumulated.30 The reaction to give (100) proceeded linearly with time, and was dependent on the concentration of protein and substrate. No conversion occurred in the absence of enzyme. 

However, only the E-alkene (78) has been isolated from Guettarda eximia, and the related alkaloids geissoschizine and the isosit-... 

A new alkaloid (100), related to cathenamine (82), has been isolated from Guettarda eximia. It is readily converted chemically into cathenamine (82), presumably via (81). It seems likely that (100) has a biosynthetic role, and it may be that access to alkaloids with different stereochemistries at C-19 and C-20 occurs via (81) (100). ° ... 

Cathenamine (20, 21-dihydroajmalicine) and 4,21-dehydrogeissoschizine have been isolated from the leaves of Guettarda eximia (71, 86). 

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