A mixture of the product from Step 13.g. (compound xxi, where R2, R3, R5, R6, and R7 are H, R4 is 2-methoxyphenyl, and n is 1) (1.30 g, 2.45 mmol), Boc-(L)-Cys(Trt)-OH (1.14 g, 2.45 mmol), NMM (270 uL, 2.45 mmol), and HOAt (333 mg, 2.45 mmol) in THF (20 ml) was treated with EDC (470 mg, 2.45 mmol) at room temperature under N2. The reaction was stirred overnight and then concentrated under reduced pressure. Saturated NaHCO3 solution (25 ml) was added and the product was extracted with a 3:2 mixture of hexanes:EtOAc. The extracts were applied to a silica gel column and the product was eluted with 3:2/hexanes:EtOAc. Product fractions were combined and concentrated under reduced pressure to obtain a white foam (2.31 g, 97%) which was used without further purification. Mass spec. 977.6 MH+.
