D-Tryptophan → Dicyclohexylcarbodiimide
Reaction equation
N[C@@H](C(O)=O)CC1[C:12]2[C:7](=[CH:8][CH:9]=[CH:10][CH:11]=2)[NH:6][CH:5]=1.O[C:17]1[C:25]2N=N[NH:22][C:21]=2[CH:20]=[CH:19][CH:18]=1>>[CH:21]1([N:22]=[C:5]=[N:6][CH:7]2[CH2:8][CH2:9][CH2:10][CH2:11][CH2:12]2)[CH2:25][CH2:17][CH2:18][CH2:19][CH2:20]1Participants
Procedure
This is followed by coupling of the first D-tryptophan by the active ester technique with hydroxybenzotriazole (HOBt) obtained "in situ" by means of dicyclohexylcarbodiimide (DCC). 1.5 milliequivalents (3-fold excess with respect to the amine groups of the resin) of Fmoc-D-tryptophan (0.639 g) and 2 milliequivalents of HOBt (0.310 g) are dissolved in 12 ml of 2:1 DCM/DMF, transferred into the reactor of the apparatus and, after pre-equilibration for 2 minutes with stirring, 1.5 ml of 1 M DCC in 2:1 DCM/DMF (equal to 1.5 milliequivalents) are added, thus initiating the automatic coupling cycle (line 9 in Table 2). At the end of the cycle described in the table, the Kaiser test is carried out on an aliquot of resin; if the degree of incorporation of the amino acid is greater than 99%, the automatic protective group removal from the amine group is carried out; otherwise, the coupling is repeated. For the successive couplings, always according to the plan in Table 2, the following amino acids were used in the quantities indicated: Fmoc-DTrp (0.639 g for each of the 3 further couplings), Fmoc-valine (0.509 g), Fmoc-tyro-sine t-butyl ether (0.689 g) and Fmoc-t-butyl aspartate (0.617 g). After the last coupling, the protective group removal cycle is repeated, the resin is taken out of the reactor and dried in vacuo over potash, giving 1.650 g of product. This is then followed by the detachment of the peptide from the resin and simultaneous protective group removal from the side chains by trifluoroacetic acid (TFA). 1.5 g of peptide-resin are placed into a small flask containing 30 ml of a solution consisting of 27:1.5:1.5 (volume/volume) TFA/ethanedithiol/p-cresol and the mixture is maintained for 2 hours in a water bath at 35° C. with magnetic stirring. To precipitate the crude product, 10 volumes of ethyl ether and 5 volumes of petroleum ether, both cooled to 0° C., are added. The mixture is kept overnight at -78° C. and filtered over a porous funnel-shaped filter , giving 350 mg of crude crystalline product. For the purification by high-pres-sure liquid chromatography, the procedure of Example 1 is followed, giving 12 mg of product; characterization by HPLC analysis (conditions as described in Example 1): Rt=12.6 minutes, HPLC purity=98%.
Sources & evidence
- ORD record
- ord-560fc52a93f3434cae21be11ab69ce71
- Source dataset
- uspto-grants-1992_07
- Patent number
- US05128447
Reaction notes
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