Abstract: Addition compounds having the formula ##STR1## wherein R.sub.1 represents an aliphatic oxycarbonyl group, benzyloxycarbonyl group which can have nuclear substituents, or benzoyl, aromatic sulfonyl or aromatic sulfinyl group; R.sub.2 represents methyl, isopropyl, isobutyl, isoamyl or benzyl group; R.sub.3 represents a lower alkoxyl, benzyloxy or benzhydryloxy group and n represents 1 or 2 are produced by reacting an N-substituted monoaminodicarboxylic acid having the formula ##STR2## with an amino carboxylic acid ester having the formula ##STR3## in the presence of a protease.

Abstract: Addition compounds having the formula ##STR1## wherein R.sub.1 represents an aliphatic oxycarbonyl group, benzyloxycarbonyl group which can have nuclear substituents, or benzoyl, aromatic sulfonyl or aromatic sulfinyl group; R.sub.2 represents methyl, isopropyl, isobutyl, isoamyl or benzyl group; R.sub.3 represents a lower alkoxyl, benzyloxy or benzhydryloxy group and n represents 1 or 2 together with methods for preparing (I) and for decomposing (I) into the constituent dipeptide esters and amino acid esters.

Abstract: A peptide having the formulaX--A--B--Ywherein A and B are the same or different and represent an amino acid residue or a peptide residue; X represents an amino protective group and Y represents a carboxyl protective group, is prepared by reacting an amino acid or peptide having an N-terminal protective group or a salt thereof of the formula:X--A--OHwith an amino acid or peptide having a C-terminal protective group or a salt thereof of the formula:H--B--Yin the presence of metalloproteinase in an aqueous solution having a pH which maintains the enzyme activity of said metalloproteinase.

Abstract: A peptide having the formulaX--A--B--Ywherein A and B are the same or different and represent an amino acid residue or a peptide residue; X represents an amino protective group and Y represents a carboxyl protective group, is prepared by reacting an amino acid or peptide having an N-terminal protective group or a salt thereof of the formula:X--A--OHwith an amino acid or peptide having a C-terminal protective group or a salt thereof of the formula:H--B--Yin the presence of metalloproteinase in an aqueous solution having a pH which maintains the enzyme activity of said metalloproteinase.

Abstract: A peptide having the formulaX--A--B--Y--wherein A and B are the same or different and each represents an amino acid residue or a peptide residue, X represents an amino protective group, Y represents a carboxyl protective group selected from the group consisting of tertiary alkoxy, and benzyloxy, benzylamino and benzhydrylamino which can be substituted with an inert substituent, is prepared by a process which comprises reacting an amino acid or peptide having an N-terminal protective group, or a salt thereof of the formula:X--A--OHwith an amino acid or peptide having a C-terminal protective group or a salt thereof of the formula:H--B--Yin the presence of a thiol proteinase or serine proteinase enzyme in an aqueous solution having a pH sufficient to maintain the enzyme activity of said thiol proteinase or serine proteinase.