Two pyrrolo[1,2-a]azepine type alkaloids from Stemona collinsae Craib: structure elucidations, relationship to asparagamine A, and a new biogenetic concept of their formation.
The alkaloids 1',2'-didehydrostemofoline (2) and 2'-hydroxystemofoline (3) from Stemona collinsae Craib (Stemonaceae) were studied by X-ray crystallography and NMR spectroscopy, and they are compared with the parent compound stemofoline (1). The X-ray analysis of the CH2Cl2 solvate of 2'-hydroxystemofoline (3) allowed the determination of the absolute configuration of this compound unequivocally, whereas optical rotation was used to infer the absolute configuration of 1',2'-didehydrostemofoline (2). Based on these results, it is shown that asparagamine A isolated from Asparagus racemosus Willd. (Asparagaceae) is identical to 1',2'-didehydrostemofoline obtained from S. collinsae Craib, and that the reported plant source of asparagamine A was most likely a Stemona species. In the context of the current investigations, a novel concept on the biosynthesis of Stemona alkaloids has been worked out and is presented here.
Seger
Christoph
C
Institute of Organic Chemistry, University of Vienna, Währingerstrasse 38, A-1090 Vienna. christoph.seger@uibk.ac.at
Mereiter
Kurt
K
Kaltenegger
Elisabeth
E
Pacher
Thomas
T
Greger
Harald
H
Hofer
Otmar
O
D000470:Alkaloids / Q000096:biosynthesis / Q000737:chemistry* / Q000302:isolation & purification; D001381:Azepines / Q000737:chemistry* / Q000302:isolation & purification; D006576:Heterocyclic Compounds, 4 or More Rings / Q000737:chemistry* / Q000302:isolation & purification; D010936:Plant Extracts / Q000096:biosynthesis / Q000737:chemistry / Q000302:isolation & purification; D018514:Plant Structures; D041901:Stemonaceae
D000470:Alkaloids; D001381:Azepines; D006576:Heterocyclic Compounds, 4 or More Rings; D010936:Plant Extracts; C481859:didehydrostemofoline