Process for the preparation of pentapeptides having an action on the immune system and intermediate products for this process

A process for the preparation of a peptide of the formula

• Arg--Lys--S--Val--Y
• wherein
• S denotes glutamic acid or .alpha.-aminoadipic acid, in each case in the L- or D-configuration, and
• Y denotes tyrosine or tryptophan, in each case in the L- or D-configuration, or their esters, amides, alkylamides, cycloalkylamides or aralkylamides, which comprises subjecting a tetrapeptide of the formula
• Z--Arg(Z')--Lys(Z')--S--(Bzl)--Val--OH
• in which S is as defined above and Z' represents an amino-protective group of the benzyl type, to a condensation reaction with the corresponding tyrosine ester or amide or tryptophan ester or amide and splitting off the protective groups of the benzyl type by catalytic transfer hydrogenation with formic acid/dimethylformamide or dimethylacetamide mixtures.