Structures of Representative Alkaloids

A series of lycoposerramines isolated by Takayama et al. were fawcettimane-type and fawcettidane-type alkaloids from the same species Lycopodium serratum in Japan which contains huperzines in China. The structure of lycoposerramine-A (21), which has a l,2,4-oxadiazolidin-5-one residue in the molecule, was elucidated through spectroscopic data and X-ray analysis (31,32). Seven new alkaloids, lycoposerramines B (22), C (23), D (24), E (25), P (26), Q (27), S (28), and U (29), with novel, fawcettimine-related structures were isolated from the club moss Lycopodium serratum in Japan (33). Their relative and absolute stereochemistries were analyzed by spectroscopic data. X-ray analysis, and chemical correlations. The skeleton of lycoposerramine A (21) may be constructed by the incorporation of NH3, NH2OH, and a Ci unit into a fawcettimine-type skeleton. 

Furthermore, ten new alkaloids, lycoposerramines F (30), G (31), H (32), I (33), J (34), K (35), L (36), M (37), N (38), and -O (39), having lycopodine-related structures, were isolated from the club moss Lycopodium serratum and their structures were elucidated on the basis of spectroscopic analysis and/or chemical transformation (34). Lycoposerramines F (30) and J (34) were the same structures as miyoshianines A and B, respectively, isolated from Huperzia miyoshiana (50). 

Lycopodium alkaloids are a class of natural products with unique ring systems, which have attracted great interest from a biogenetic point of view. These unique skeletons have prompted extensive phytochemical work and a project was initiated on the alkaloids of the club moss Lycopodium serratum var. serratum. Three new alkaloids, serratezomines A (40), B (41), and C (42), with a seco-serratinine-type, a serratinine-t)q)e, and a lycodoline-t5rpe skeleton, respectively, were isolated from the club moss L. serratum var. serratum (35). All of the structures are listed in Table I. 

Furthermore, the relative configuration at C-12 was estimated by the floating chirality method (57), which allows the distance constraints to guide the molecule into configurations consistent with its NOE data (Fig. 2). For molecules possessing complex ring systems, high-temperature dynamics alone may fail to invert certain chiral centers 

Serratezomine A (40) is a novel structural type of alkaloid consisting of a 2-oxabicyclo[3.3.1]nonan-3-one and an indolizidine ring coimected through a spiro carbon. 

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Numerous UCNMR investigations on alkaloids have been reported in the literature [598, 599]. In Table 5.13 the 13C chemical shifts and structures of representative alkaloids of different types are collected Pyrrolidine, piperidine and pyridine [600-602], tropane [600, 603-605], izidine [606-612], indole [600, 603, 613-633], isoquinoline [599, 630, 634-647], quinolinic [648-656], imidazole [657], yuzurimine alkaloids [658], alkaloids with exocyclic nitrogen [659, 660], diterpenoid [661-663], steroid [664-666] and peptide alkaloids [667-671], The complete signal assignment for the alkaloids given in Table 5.13 was achieved using the correlations between 13C NMR spectral parameters and structural properties and the 13C chemical shift values of model compounds described in Chapters 3 and 4 of this monograph. 

Fig. 1. Structures of representative alkaloids. The carbon atoms in the rings and the hydrogen atoms attached to them are not designated by letter symbols. However, there is understood to be a carbon atom at each comer (except for the cross-over in the structure of morphine) and each carbon atom has four bonds, so that any bonds not shown or represented by attached groups are joined to hydrogen atoms...

Structures of Representative Alkaloids Biosynthesis and Biogenesis Total Synthesis... 

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