A chemo-enzymatic approach to some indole and quinolizidine alkaloids fromC-s-symmetric precursors

In this review we describe the asymmetrization of readily available C-S-sym metric compounds by enzyme-catalyzed reactions to provide chiral building b locks for the effective enantioselective synthesis of certain indole and qu inolizidine alkaloids. By the asymmetrization of 1,2-disubstituted cycle cy clohex-4-enes a series of class I alkaloids, such as (-)-antirhine, (-)-aka gerine, and (+)-meroquinene, have been synthesized from the relevant chiral precursors. By employing the same chemo-enzymatic approach, asymmetrizatio n of C-S-symmetric 3,5-disubstituted piperidines provides access to 15,20-d ihydrocleavamine and its analogues, as well as to (+)-tacamonine. The synth etic design and details of the various syntheses are presented. In addition , the scope and prospects of the symmetrization-asymmetrization strategy ar e discussed with special reference to the quinolizidine alkaloids.