Experimental procedure
1): A solution of
Cbz-Asn-OH (79.8 mg, 0.3 mmol) and triethylamine (41.8 µL, 0.3 mmol) in methanol (2.6 mL) is cooled to -20 °C, and treated with a solution of Dimethylthiophosphinoyl Chloride (Mpt-Cl, 38 mg, 0.3 mmol) in methanol (0.9 mL), and the mixture stirred for 20 min. The solution is added to a solution of the tetrapeptide (
1, 133.3 mg, 0.3 mmol) and triethylamine (41.8 µL, 0.3 mmol) in methanol (7.0 mL) and water (3.0 mL) at -20 °C. After the mixture has been stirred for 40 minutes the Cbz-Asn-OMpt solution and triethylamine (0.3 mmol each) are added and the stirring continued at -20 °C for 2 h and at 0 °C for 48 h. The precipitate is filtered and washed with chloroform, ethanol, water, and ether, and dried to give the pentapeptide (
2, 173.7 mg, 84 %).