Understanding alpha-amino acid chemistry from X-ray diffraction structures

The geometry and conformation for a variety of reactive alpha-amino acid and peptide derivatives, as obtained from X-ray diffraction analyses, are reviewed in detail. The derivatives are (a) carboxylic acid halides, (b) anhydrides, (c) esters, (d) azides, and (e) amides. The contribution of this information to our understanding of amino acid reactivity, regiospecificity, and tendency to racemization is discussed.