Selective reagent for the introduction of the benzyloxycarbonyl (Cbz or Z) protecting group, avoiding the formation of amino acid dimers: Tetrahedron Lett., 4765 (1966); J. Antibiot., 25, 695 (1972); 34, 513 (1981); Can. J. Chem., 60, 976 (1982). Especially convenient for the selective protection of the -amino group of lysine and ornithine: Can. J. Chem., 54, 733 (1976); Rec. Trav. Chim., 99, 400 (1980).