A mixture comprising of tert-Butyl 1-(2,5-dioxopyrrolidin-1-yl)-2-methyl-1-oxopropan-2-ylcarbamate (1 g, 3.52 mmol) (prepared according to the procedure described in EP1486498A1 page 20) and H-D-Homophe-OH (0.630 g, 3.52 mmol) in THF (16 ml)/water (4 ml) was treated with triethylamine (1.471 ml, 10.55 mmol). The reaction mixture was stirred at 50° C. for 9 hours. THF was removed in vacuo. The aqueous solution was further diluted with water and the pH adjusted to pH 2-3 using 1M HCl. The resulting aqueous phase was extracted with EtOAc. The organic portion was dried (MgSO4) and concentrated in vacuo to afford the title compound.
