Biomimetic synthesis, manzamines

Further insights into the biosynthesis of manzamines came from the synthetic studies made on the conversion of 3-alkyl-dihydropyridinium salts to the unstable 3-alkyldihydropyridine reported in Fig.(24) [39]. Similar compounds were used in model studies towards a biomimetic synthesis of the alkaloids keramaphidin A and halicyclamine A [40]. 

A model reaction carried out by Baldwin and coworkers as part of a biomimetic synthesis of the manzamine alkaloids [71]. This reaction generates the tricyclic core of the ingenamine... 

As part of a biomimetic approach to the synthesis of the manzamine alkaloids, Baldwin et al. found that treatment of model compound 120 in pH buffer 8.3 for 18 h followed by reduction with excess sodium borohydride gave the adduct 121 in low yield (Figure 3.5) [71]. 

Two other methods toward the manzamines have been reported recently. A preliminary report by Baldwin s group at Oxford of a biomimetic approach described the preparation of a key tricycle, which bears a resemblance to likely natural product precursors to the manzamines (153). A multistep synthesis from Overman s group at the University of California at Irvine, featuring an intermolecular Mannich reaction, starts from D-(-)quinic acid, thus setting the absolute stereochemistry (154). 

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