Abstract
Modifications were attempted on the renin inhibitors, leucylleucylvalyltyrosine ethyl ester or leucylleucylvalylphenylalanine ethyl ester which were reported in the preceding paper. Borohydride reduction of the above peptide esters, prepared by the solid phase method using bromoacetyl polystyrene, afforded the respective C-terminal carbinol derivatives, which were moderately soluble in water and the renin inhibitory activity was found to be retained. Elongation of the aforementioned tetrapeptide esters or carbinols by a hydrophilic amino acid residue or introduction of the sodiumsulfomethyl group was rather fruitless with regards to solubility as well as to renin inhibitory activity. Octapeptide-carbinol derivative, prolylphenylalanylhistidylleucylleucylvalyltyrosyl-serinol was synthesized, whose dihydrochloride was moderately soluble in water and exhibited the highest renin inhibitory activity among the compounds tested throughout this series of work.
