Methods for preparing novel dipeptide compounds or pharmacuetically acceptable salts thereof

A method for preparing a dipeptide compound represented by the following formula (IA):

• ##STR18## wherein R.sub.1 represents a 5-membered or 6-membered monocyclic hydrocarbon group or heterocyclic group wherein 3 or fewer substituents other than hydrogen are present on the cyclic group;
• R.sub.21 and R.sub.22 each represents a hydrogen atom or a linear or branched aliphatic hydrocarbon group having 1-6 carbon atoms;
• and
• R.sub.3 represents a linear or branched aliphatic hydrocarbon group having 1-6 carbon atoms or a monovalent group comprising an aromatic monocyclic hydrocarbon group having 12 or fewer carbon atoms in total, wherein a halogen atom can be substituted on the aromatic ring of the aromatic monocyclic hydrocarbon group;
• comprising the steps of:
• (i) coupling a compound of the following formula (XA):
• ##STR19## wherein R.sub.21, R.sub.22 and R.sub.3 have the same definition as above, with a compound of the following formula (XI):
• ##STR20## wherein B is an amino protecting group, to produce a compound of the following formula (XIIA):
• ##STR21## wherein R.sub.21, R.sub.22, R.sub.3 and B have the same definition as above;
• (ii) deprotecting the compound having the formula (XIIA) by removing the amino protecting group, and
• (iii) acylating the product of step (ii) with a compound having the following formula (XIII):
• ##STR22## wherein R.sub.1 has the same definition as above, to produce the dipeptide compound of the formula (IA).