Nuclear magnetic resonance spectroscopy has been applied to the study of carbamate formation in solutions of amino acids and peptides in a carbonate-bicarbonate system. The possible conformations of these carbamates are discussed in terms of the n.m.r. data obtained. The n.m.r. parameters are reported for the diastereomers L-alanyl-L or D-phenylalanine and L-phenylalanyl-L or D-alanine and for the dipeptide glycyl-L-phenylalanine and their carbamates. The results are interpreted in terms of preferred rotamers about the C.-CD bond of the phenylalanine residue and a p-type conformation of the peptide chain, wherein the two a-protons lie in the plane of the amide bond. All observations are in agreement with a shorter end to end distance in L,D-compared with L,L-dipeptides.

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Esters of 2-alkyl-A3-thiazoline-4-carboxylic acids are smoothly dehydrogenated by phenanthraquinone to the corresponding thiazole derivatives. Methyl 2-benzamidomethyl-A2-thiazoline-4-carboxylate is dehydrogenated only slowly by phenenthraquinone but rapidly by manganese dioxide. The possible application of these reactions to the detection of thiazoline rings in peptides is discussed.* Although not a peptide, firefly luciferin contains a thiazoline ring possibly derived from cysteine.'

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