Hygrine and Hygroline

Electrochemistry offers a new and promising alternative for the generation of masked iminium ions. This approach is illustrated by the elegant syntheses of hygrine and hygroline (Scheme 22) (168). 

Scheme 22. Electrochemical syntheses of hygrine and hygroline. (a) HOCH2CH2OH, H (b) LiAIR, (c) H 96% overall.

Two reviews on pyrrolidine alkaloids have appeared in volumes I (7) and VI (2) of this series. At that time, the only alkaloids mentioned were hygrine (1), hygroline (2), cuscohygrine (3), stachydrine (4), and betonicine (5). Carpaine,... 

Hygrine (1) and hygroline (2) were known compounds when the first reviews on pyrrolidine alkaloids in this series were written. Since 1950, the configurations of 1 and 2 have been determined and new sources of the alkaloids have been found. 

Oxopropyl)hygrine 5-(2-Hydroxypropyl)hygrine 5-(2-Hydroxypropyl)hygroline Fig. 3.3 Simple pyrrolidine alkalaids of the hygrine and hygroUne type... 

New sources of hygrine are the roots of Nicandra physaloides (L.) Gaertn. (Solanaceae) (9, JO), Dendrobium chrysanthum Wall. (Orchidaceae) (11), and Cochlearia arctica Slecht (Cruciferae) (12). Hygroline was also isolated from this latter source as well as from Carallia brachiata (Lour.) Merr. (Rhi-zophoraceae), a plant from eastern Asia, New Guinea, and Queensland (13), and... 

In the few years since the chapter on the pyrrolidine alkaloids was written they have not been the subject of much additional work. The recent investigations to be described relate to hygrine, hygroline, cuscohygrine, stachydrine, betonicine, and turicine. The structure of carpaine has also been fully elucidated, and this alkaloid has been shown to be a piperidine and not a pyrrolidine alkaloid and hence will be described under the heading The P3addine Alkaloids. ... 

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