Mild Reductive Cleavage of the 9-Anthracenesulfonamido Function. The 9-Anthracenesulfonyl (Ans) Group: A New Approach to the Protection of the Guanidino Function of Arginine Residues in Peptide Synthesis

Convenient syntheses of L-arginine derivatives bearing the 9-anthracenesulfonyl (Ans) protective group at the ω-guanidino site are described. Simple arginine-containing peptides bearing the Ans group are shown to be stable to the normal conditions of peptide synthesis. The Ans group is removed either by acidolysis with trifluoroacetic acid over a period of hours or by a variety of novel, mild reducing conditions including reaction with aluminum amalgam and photo-induced ruthenium-catalyzed reduction with 1-benzyl-1, 4-dihydronicotinamide. Application of the Ans group to a synthesis of bradykinin is reported, and detailed preparative procedures for the useful derivatives N^α-Boc L-Arg(N^ω-Ans)-OH and N^α-Bpoc-L-Arg(N^ω-Ans)-OH are described.