Alanine synthetic equivalents

This procedure is typical of a general method for the preparation of enantiomerically pure a-amino acid derivatives using the zinc reagent 2 as the synthetic equivalent of an alanine P-anion 5.37 The method is based on the work of Yoshida et ah, who were instrumental in... 

The same procedure is used for the formation of resins 2 and 8 by reaction of the nitroarenes with the resin-bound [3-alanine or mercaptan/ amine linker, respectively. The o-fluoronitroarenes (Fig. 3) are dissolved in DMSO or NMP (at a concentration between 1.5 and 2 M) and added to the resin, followed by diisopropylethylamine (10 equivalents) and additional DMSO or NMP (if required) to ensure resin solvation. Although many nitroarenes react rapidly at room temperature, in a library format the resin/nitroarene mixture is heated overnight at 50° to help achieve equivalent reaction kinetics between different monomers. Under the same conditions, some o-chloronitroarenes are synthetically useful. The extent of the reaction can be assessed qualitatively (or quantitatively, if desired) by carrying out a ninhydrin test to check for the presence of free amine. In any case, the resins are acetylated with five equivalents of acetic anhydride/pyridine/DMF (1 1 10) for 20 min to cap any unreacted amine. 

Chemistry, Uptake, and Metabolic Role. This vitamin, which can be considered a derivative of j3-alanine, is asymmetric (Fig. 8.38). The natural form has the T>(+) configuration. TheL(-) stereoisomer is inactive. The reduced alcohol form, pantothenol, is considered as equally active as the parent acid. Many of the multiple vitamin products use a synthetic, racemic mixture. This means that double the amount of synthetic vitamin must be used to obtain equivalent active vitamin. 

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