Phenyllactic acid, biosynthetic

Fuller details on the incorporation of phenyllactic acid (25) into tropane alkaloids have been published." This acid is a better precursor than phenylalanine for the acid fragments of (20), (21), and (22). The significance of this difference is doubtful it may be the result of several causes, the simplest being more effective diversion of phenylalanine into other biosynthetic pathways. None the less phenyllactic acid (25) is clearly a precursor for tropic acid (19) and atropic acid [as (22)] since it is specifically incorporated and moreover labels the alkaloids in the same way as phenylalanine does. 

For our approach to be useful, we need a green source for the monomers. One such source is the biosynthetic pathway for the synthesis of a-amino acids. As an example, consider the biosynthetic pathway to L-phenylalanine shown in Figure 3. The last step in the synthesis is the amination of the a-ketoacid, but interception and reduction of the ketone would provide phenyllactic acid, a substituted lactic acid that could be converted to its cyclic dimer and polymerized. Frost has shown that the biosynthetic pathway can be altered to favor production of the desired a-hydroxyacid, and proper choice of the enzyme... 

Figure 3, Biosynthetic pathfway to phenylalanine and phenyllactic acid.

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