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BEAD LOADING Rink Amide MBHA resin (87 mg, 0.06 mmol, 0.69 mmol/g loading) was pre-swelled in a 5 mL disposable syringe equipped with a frit by rotating with DCM (3 mL) for 1 h. The resin was then washed with DMF (5 X 4 mL). The Fmoc protecting group on the bead was removed by treatment with 5 bed volumes (ca. 4 mL) of a 20% piperidine solution in DMF for 20 min. Meanwhile, Fmoc-Phe-OH (116 mg, 0.3 mmol, 5 equiv) was dissolved in DMF (3 mL) along with HOBt (41 mg, 0.3 mmol, 5 equiv). Diisopropyl carbodiimide (DIC) (50 muL, 0.3 mmol, 5 equiv) was then added and the resulting mixture was stirred at room temperature for 20 min. After 20 minutes, the resin was washed with DMF (5 X 4 mL). To the thoroughly washed resin bed, was added the coupling solution (Fmoc-Phe-OH,HOBt, and DIC), and the resulting mixture was rotated for 12 h. The loaded resin was then washed with DMF (5 X 4 mL) and used in subsequent Fmoc solid phase peptide synthesis as described below. FMOC REMOVAL The Fmoc group of the terminal amino acid of the growing peptide chain was deprotected by treating the resin beads (0.69 mmol/g loading) with a 20% solution of piperidine in DMF (ca. 4 mL) with rotation for three minutes. The deprotection cocktail was then discharged from the syringe and the resin beads were treated with a fresh portion of 20% piperidine in DMF for three minutes.This protocol is repeated until the resin beads have been treated with four aliquots of 20% piperidine in DMF. The final portion is then discharged from the syringe and the deprotected beads are washed with DMF (5 X 4 mL). The washed, deprotected resin beads were then immediately coupled with the next amino acid in the sequence. HOBT-MEDIATED COUPLING The next amino acid in a desired sequence was activated as the HOBt ester by dissolving the desired amino acid (0.3 mmol, 5 equivalents relative to the 0.69 mmol/g resin loading) along with HOBt (41 mg, 0.3 mmol, 5 equiv) in DMF/DCM (1:1) (3 mL). To the resulting solution was added DIC (50 muL, 0.3mmol, 5 equiv) and the resulting solution was stirred at room temperature for twenty minutes (usually while the terminal amino acid of the resin bound sequence is deprotected).The resulting solution of HOBt ester was added to the N-terminal deprotected, resin-bound, peptide sequence and the mixture was rotated for one hour. The resin beads were then thoroughly washed with DMF (5 X 4 mL). The resulting N-terminal, Fmoc-protected, resin-bound peptide sequence was then resubjected to the Fmoc removal protocol and subsequent HOBt couplings until the desired sequence had been assembled. N-TERMINAL O-IODOBENZOATE CAPPING The N-terminus of the peptide was capped with the o-iodoarylamido active site by the HOBt active ester methodology. The o-iodobenzoic acid (0.3 mmol, 5 equivalents relative to the 0.69 mmol/g resin loading) was dissolved along with HOBt (41 mg, 0.3 mmol, 5 equiv) in DMF/DCM (1:1) (3 mL). To the resulting solution was added DIC (50 muL, 0.3 mmol, 5 equiv) and the resulting solution was stirred at room temperature for twenty minutes (usually while the terminal aminoacid of the resin bound sequence is deprotected).The resulting solution of HOBt ester was added to the N-terminal deprotected, resin-bound, peptide sequence and the mixture was rotated for one hour. The resin beads were then thoroughly washed with DMF (5 X 4 mL). TFA CLEAVAGE/GLOBAL SIDE-CHAIN DEPROTECTION OF PEPTIDES Peptides were cleaved from the resin beads by employing the following protocol: The fully assembled, resin-bound peptides were prepared for cleavage by washing the beads with DMF (5 X 4 mL), DCM (5 X 4 mL), and methanol (5 X 4mL). The syringe plunger was removed from the barrel and the resin beads were dried overnight in the vacuum oven at 25 C. The following day, the resin was treated with a cleavage cocktail comprised of a mixture of TFA/H2O/TIS(95:2.5:2.5) (3 mL) for 2.5 h with minimal, intermittent agitation. The cleavage cocktail, containing the solvated, resin-free peptide was then ejected into a 5 mL pear-shaped flask and the solvent was removed under a stream of nitrogen to give a thick oil. The crude peptide was then precipitated by the addition of ice-cold diethyl ether. The solid peptide was then isolated by vacuum filtration and washed with copious amounts (ca. 15-20 mL) of cold ethyl ether. The solid peptide was then dried in vacuo. The identity of the desired sequence was verified by MALDI-TOF mass spectrometry. |
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