The present disclosure relates to a method for preparing 3-[(3S)-7-bromo-2-oxo-5-(pyridin-2-yl)-2,3-dihydro-1H-[1,4]-benzodiazepin-3-yl] propionic acid methyl ester from (2-amino-5-bromo-phenyl)-pyridin-2-yl-methanone. Also disclosed are compounds useful as intermediates in the method, methyl (4S)-4-amino-5-[4-bromo-2-(pyridin-2-carbonyl)anilino]-5-oxo-pentanoate hydrobromide salt and methyl (4S)-4-(benzyloxycarbonylamino)-5-[4-bromo-2-(pyridin-2-carbonyl)anilino]-5-oxo-pentanoate.