A Chemo-Enzymatic Approach to Some Indole and Quinolizidine Alkaloids From Cs -Symmetric Precursors

In this review we describe the asymmetrization of readily available Cs-symmetric compounds by enzyme-catalyzed reactions to provide chiral building blocks for the effective enantioselective synthesis of certain indole and quinolizidine alkaloids. By the asymmetrization of 1,2-disubstituted cyclo cyclohex-4-enes a series of class I alkaloids, such as (-)-antirhine, (-)-akagerine, and (posative)-meroquinene, have been synthesized from the relevant chiral precursors. By employing the same chemo-enzymatic approach, asymmetrization of Cs-symmetric 3,5-disubstituted piperidines provides access to 15,20-dihydrocleavamine and its analogues, as well as to (posative)-tacamonine. The synthetic design and details of the various syntheses are presented. In addition, the scope and prospects of the symmetrization-asymmetrization strategy are discussed with special reference to the quinolizidine alkaloids. Keywords: Quinolizidine alkaloids, Symmetric precursors, Class I Alkaloids, Antirhine, Antirhea putaminosa, Akagerine, Meroquinene, Intramolecular michael reactions, Indole alkaloids, Cs symmetric, 3,5 disubstituted, Tacamonine, Piperidines, Wittig or Wittig type, Swern oxidation, Parikh oxidation