Proline derivatives, alkaloid synthesis from

Stereoselective addition of hydrogen to a C=C double bond of an (S)-proline derivation was applied in the total synthesis of gephyrotoxin, a biologically active alkaloid 87). Optically active pyrrolizidine bases have been synthesized by Robins and Sakdarat88) from chiral hydroxyproline derivatives by hydrogenation (ds > 60 %). 

When the amino alcohol (244) derived from proline reacted with A,A -carbonyldiimidazole, the bicyclic carbamate (245) was obtained. This reaction was applied to the synthesis of some pum-iliotoxin A alkaloids <83JCS(Pl)395>. A similar cyclization described by Overman, is based on the... 

Here, these alkaloids will be described in this chapter as alkaloids based on a porphine skeleton. Their biosynthesis is completely different from that of prodigiosin described in the chapter on alkaloids derived from proline (Chapter 5). Total synthesis of chlorophyll a was achieved [2,3], and the assignment of all resonances in the nuclear magnetic resonance (NMR) spectrum of chlorophyll b has been accomplished [4]. Also the biosynthesis and chemistry of the chlorophylls have been reviewed [5—8]. 

An important contribution elucidating the potential of primary amines derived from Cinchona alkaloids has been the aldol cyclodehydration of achiral 4-substituted-2,6-heptanediones to enantiomerically enriched 5-substituted-3-methyl-2-cyclohexene-l-ones, presented by List and coworkers in 2008 (Scheme 14.26). Both 9-deo>y-9-amino-epr-quinine (QNA) and its pseudoenantiomeric, quinidine-derived amine QDA, in combination with acetic acid as cocatalyst, proved to be efficient and highly enantio-selective catalysts for this transformation, giving both enantiomers of 5-substituted-3-methyl-2-cyclohexene-l-ones with very good results. The authors observed that proline and the catalytic antibody 38C2 delivered poor enantioselectivity in this reaction. Furthermore, the synthetic utility of the reaction was exemplified by the first asymmetric synthesis of both... 

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