direction; mixed anhydride, bis(2)-oxooxazolidin-3-yl)phosphinoyl chloride (Bop-Cl), or dicyclohexylcarbodiimide (DCC), 2-amino-2-methyl-3-(methylamino)-propionicacid and 2-amino-2-ethyl-3-(methylamino)propionic acid ( = 2-amino-2-[(methylamino)methyl]butanoic acid) are incorporated in the central position of tri-, penta-, and heptapeptides (see 3–7, 21, and 22). The fragment coupling of the β -amino group