Determination of the chiral purity of dipeptide isosteres containing a reduced peptide bond by gas chromatographic analysis.

The stereochemical purity of psi (CH2-NH) dipeptides has been determined using gas chromatography-mass spectrometry. Different structures were found due to the derivatization procedures. A selective preparation of the linear bistrifluoroacetylated derivative and the monotrifluoroacetylated lactam makes it possible to monitor the chiral purity of the pseudodipeptides synthesized. Racemization occurring during peptide hydrolysis can be differentiated from racemization during the synthesis by using deuterium labelling. The method allows the optimization of the synthesis protocols and will be useful for further monitoring of the chiral purity of the pseudopeptides synthesized.

Synthesis and conformational study of two L-prolyl-L-leucyl-glycinamide analogues with a reduced peptide bond.

The peptide bond between Pro-Leu or Leu-Gly in Pro-Leu-Gly-NH2 was replaced by a CH2-NH function. The 1H and 13C n.m.r. studies demonstrated that HCl X Pro-Leu psi (CH2-NH)Gly-NH2 10 adopted a conformation in DMSO that is similar to the previously postulated beta-turn for the natural hormone. This was not the case for the other analogue. In vivo tests on 10 revealed an activity approximately equal to the natural compound and an increased toxicity.