Proline
= Proline
{wiki}
<Proline> is a cyclic <alpha-amino acid> whose <amine> <nitrogen> is joined to two <carbon> positions within a five-membered ring. This explains the exception to $\mathrm{H_2N{-}CH}(R)\mathrm{{-}COOH}$ in <amino acid>. <Organic Chemistry by John McMurry>[§26.1, primary alpha-amino-acid and secondary proline structures]{ref}