Lythraceous alkaloids

Over 40 alkaloids have been isolated from Lythraceous plants since Ferris isolated 7 alkaloids from Decodon verticillatus in 1962 (/). Before the last review in this treatise (2), the structures and stereochemistries of all Lythraceous alkaloids had been established. No reports on the isolation of new alkaloids from this family have been published since 1981. On the other hand, development of new synthetic technologies has opened new avenues to the total synthesis of Lythraceous alkaloids. The earlier classification (types A-E) of Lythraceous alkaloids introduced by Fuji et al. (J) and adopted in the last review (2) is not used in this chapter because it does not indicate the structural features. This chapter covers the literature from 1979 to 1987, except for two papers (4, 5) already included in the last review (2) in Volume 18 of this treatise. 

Lythraceous alkaloids include several 4-arylquinolizidin-2-ols and their esters, as well as a variety of piperidine- and quinolizidine-based maciocyclic variants (macrolides, cyclophanes) possessing biaryl linkages. Only the former groiq> is relevant to this review. No new simple quinolizidine metabolites have been reported for over two decades, and recent publications have dealt almost exclusively with the synthesis of fom alkaloids, lasubine I (909), lasubine II (910), and their 3,4-dimethoxyciimamate esters subcosine I (911) and subcosine II (912) (Fig. 17). The naturally occurring enantiomers are represented in the diagrams. 

Corey s general method of electrostatically-driven cyclization of hydroxy-acids to medium and large rings has been applied to a new synthesis of vertaline (32). The hydroxy-acid (35), obtained by hydrolysis of natural vertaline, was converted into vertaline by reaction with 2-pyridyl disulphide and triphenylphosphine. Even on a small scale the yield was 67%, and clearly this will be an invaluable cyclization procedure in the synthesis of lythraceous alkaloids. 

Fuji K, Yamada T, Fujita E, Murata H 1978 Lythraceous alkaloids. X. Alkaloids of Lagerstroemia subcostata and L. fauriei A contribution to the chemotaxonomy. Chem Pharm Bull 26 2515-2521... 

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