Abstract: The invention relates to a process and compounds useful therein for producing a compound having an amino acid sequence defining a biologically active peptide or protein from a compound of the formulaH--X--Pro--Peptidein which X is the residue of a naturally occurring amino acid and Peptide is a sequence of amino acids defining a biologically active peptide or protein, which comprises subjecting H--X--Pro--Peptide to conditions under which a diketopiperazine of the H--X--Pro-- moiety is formed with accompanying cleavage and release of Peptide.

Abstract: A class of compounds having activity in treating and/or preventing foot and mouth disease is disclosed. The compounds contain a sequence of the formulaX-A-Y-B-Zin which A and B are amino acid residue sequences comprising sequences of the foot-and-mouth disease virus VP.sub.1 capsid protein serotypes, one of which contains from 18 to 24 amino acid residues and includes the amino acid residue sequence in positions 141 to 158 of the O serotype or the equivalent sequence of other serotypes and the other of which contains from 14 to 20 amino acid residues and includes the amino acid residue sequence in positions 200 to 213 of the O serotype or the equivalent sequence of other serotypes;X is H, H-Cys, or H-Cys-Cys, the sulfhydryls of which may be blocked or free;Z is OH, Cys-OH, or Pro-Cys-Gly-OH, the sulfhydryls of which may be blocked or free; andY is a sequence of from about 2 to about 6 amino acid residues.