A mixture of 900 mg of 2-(3-(benzyloxycarbonylamino)-2-oxopyridin-1(2H)-yl)acetic acid (˜2.32 mmol), 744 mg of TBTU (2.32 mmol), 313 mg of HOBt (2.32 mmol) is dissolved in 25 mL of DMF. By addition of 985 μL of DIPEA (5.79 mmol, 2.5 eq) a pH value is adjusted to ˜9. 539 μL of isopentylamine (4.63 mmol) is added and the mixture is stirred at RT for 2.5 h. The solvent is removed in vacuo and the obtained residue is taken up in 100 mL of DCM and subsequently washed with 10% citric acid (3×75 ml), saturated NaHCO3 solution (3×75 ml) and brine (75 mL). The organic phase is dried over Na2SO4, filtered and concentrated in vacuo in dryness. Brown solid is obtained and it is suitable for further processing without purification.
