To a suspension of homobiotin 83 (10 mg, 0.039 mmol) and compound 13 (11 mg, 0.043 mmol) in anhydrous DMF (0.5 ml) was added EDCl (7 mg, 0.047 mmol) and DIPEA (6 mg, 0.045 mmol) and stirred under a nitrogen atmosphere at ambient temperature for 12 h. The reaction mixture was diluted with dichloromethane (25 ml) and washed with water (25 ml) and brine (25 ml). The organic layer was dried over sodium sulphate, filtered and concentrated in vacuo. The residue was purified by silica gel chromatography eluting with 19:1 dichloromethane/methanol to give a yellow oil (18 mg, 46%).
