L-Pyroglutamic Acid → Z-Glu(OtBu)-Lys(Boc)-Lys(Boc)-Glu(OtBu)-Val-Val-Glu(OtBu)-Glu(OtBu)-Ala-Glu(OtBu)-Asn-OtBu

Participants

Reaction Steps

The DMF:DMSO-containing solution of H-Glu(OtBu)-Val-Val-Glu(OtBu)-Glu(OtBu)-Ala-Glu(OtBu)-Asn-OtBu (~32 mmol) from (b) was combined with Z-Glu(OtBu)-Lys(Boc)-Lys(Boc)-OH (III, 36.8 g, 46 mmol, 1.44 eq.) and HOBt (14.7 g, 96 mmol, 3 eq.) added and the solution cooled to 0°. DCC (10.9 g, 52 mmol, 1.65 eq.) was added to the cold stirring (mechanical) reaction mixture and the pH was maintained at 7.5-8.0 by addition of N-methylmorpholine (21 mL). Stirring proceeded for 2 h at 0° and 21 h at 25°. The resultant gelatenous reaction mixture was poured into H2O (9.0 L) and stirred for 4 h. The product was collected by filtration, washed with H2O (8×500 mL), dried and washed with MeOH using the centrifuge to separate the 2 phases. When all the dicyclohexylurea was removed the product was combined and dried in vacuo to give 45.22 g (71.5%); mp 312° dec; [ α]D25 -18.20° (c 1, DMSO); [α]D25 -13.27° (c 1, TFE); Rf 0.81 (n-BuOH:AcOH:Pyr:H2O; 15-3-10-12); Rf 0.52 (CHCl3 :MeOH:AcOH; 85-10-5).

Provenance & Evidence