The HCl salt of (E)-methyl 4-(2-aminoethylamino)-4-oxobut-2-enoate (0.515 mmol) was taken up in 10 mL of CH3CN along with R-lipoic acid (TCI, 106 mg, 0.515 mmol), HATU (215 mg, 0.567 mmol) and DIEA (270 μL, 1.55 mmol). The resulting reaction mixture was stirred at room temperature for 18 h and diluted with EtOAc. The organic layer was washed with brine, dried (Na2SO4) and concentrated under reduced pressure. Purification by silica gel chromatography (95% CH2Cl2, 5% MeOH) afforded 120 mg of (R,E)-methyl 4-(2-(5-(1,2-dithiolan-3-yl)pentanamido)ethylamino)-4-oxobut-2-enoate. MS (EI) calcd for C15H24N2O4S: 360.12. found 361 (M+1).
