Abstract: The present invention is directed to a composition and method relating to the preparation of aspartyl peptides having the general formula: ##STR1## where the radical-NHR represents an amino acid or peptide group. In the method, a .beta.-monoester of aspartic acid having the general formula: ##STR2## where R.sub.1 represents a hydrocarbon-containing radical, is reacted with a .beta.-dicarbonyl compound, preferably ethylacetoacetate to protect the aspartyl amino group and form an enamine. The enamine is then coupld to an amino acid or peptide, following which any protecting groups are removed to yield .alpha.-aspartyl peptides without any .beta.-isomer. In its composition aspects, the present invention is directed to novel enamines resulting from reaction of the .beta.-monoester of aspartic acid with a .beta.-dicarbonyl compound.