Studies on the Secondary Structure of Bradykinin in Aqueous Solution. Syntheses, Circular Dichroism Spectra, and Biological Activities of Bradykinin Analogs Containing 5-Aminovaleric Acid Residue

Eight bradykinin analogs containing 5-aminovaleric acid residue were synthesized by a solution method. Based on the consideration concerning their CD spectra, the presence of an intramolecular 3→1 hydrogen bond between the carbonyl oxygen of Ser6 and the amide proton of Phe8, an intramolecular 4→1 hydrogen bond between the carbonyl oxygen of Pro2 and the amide proton of Phe5, and a salt bridge between the guanidino group of Arg1 and the carboxyl group of Arg9, was proposed for the secondary structure of bradykinin in aqueous solution. The biological activities of these analogs depend on the presence of both Phe residues at positions 5 and 8, and Arg residues at positions 1 and 9. No correlation between the biological activities and the secondary structure could be found.