A method of producing of methyl ether of 3‒[(S)‒7‒bromo‒2‒(2‒oxo‒propylamino)‒5‒pyridine‒2‒yl‒3H‒1,4‒benzodiazepine‒3‒yl] propionic acid and reactive composition exept compounds for transformation, containing oxidizing agent, solvent and catalyst of formula (I-1),(I-2) or (I-3), which values of X, R1, R2, R3, R4 and R5 substitudes are provided in the claims； at that, reactive composition does not contain ammonium ion or contains therein amount of 170 mn or in less mass correlation relative to compound. Table: 3
