Simple Quinolizidine Alkaloids Lasubines

Simple quinolizidine alkaloids of the Lythraceae, "which include the well-known natural products (2S,4S,9aR)-(—)-lasubine I (1341) and (2S,4S,9aS)-(—)-lasubine II (1342) and substituted cinnamate esters thereof such as subcosines I and II, (1343) and (1344), are less common than those in which the quinolizidine forms part of a macroHde or cyclophane system containing a biaryl component (Figure 32). Since the macrocychc alkaloids are not pertinent to this review, they will not—with one exception—be discussed further vide infra). 

Figure 32 Simple quinolizidine alkaloids of the Lythraceae (-)-lasubine I (1341) —)-lasubine II (1342) (+)-subcosine I (1343) (+)-subcosine II (1344) (+)-sarusubine A (1347).

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. 

---