3 (R)-amino-2-oxopyrrolidineacetamide and the d-lactam residue 3 (S)-amino-2- oxopiperidineacetamide. The corresponding y-lactam analogues of< Glu-Leu-Gly-NHz were also synthesized. In a second series of analogues, the glycinamide residue of PLG was replaced with the 2-ketopiperazine, 3 (S)-amino-2-pyrrolidone, and 3 (S)-amino-2- piperidone residues. The above analogues were tested for their ability to enhance the ...