Alkylating Angiotensin II Analogues: Synthesis, Analysis, and Biological Activity of Angiotensin II Analogues Containing the Nitrogen Mustard Melphalan in Position 8

Melphalan derivatives suitable for peptide synthesis, i.e., Boc-Mel and Mel-OBzl.HCl, have been prepared, and the integrity of their nitrogen mustard alkylating groups was examined by NMR, Volhard chlorine analysis, and colorimetric assay with 4-(p-nitrobenzyl)pyridine. By using the sensitive colorimetric assay, the stability of melphalan toward conditions commonly used for peptide synthesis, purification, and bioassay was evaluated. Further qualitative and quantitative assessment of the integrity of nitrogen mustard groups in angiotensin II was attempted in order to evaluate the significance of the observed biological results. [Ac-Asn1,Mel8]angiotensin II was a potent competitive antagonist of angiotensin II in vitro (rat uterus) but a transient and reversible inhibitor in vivo.