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Chelmical synthesis: Peptides were synthesized on a Rink amide resin, 0.45 mmol/g [Fmoc-Cys(Trityl)-Wang; Novabiochem, San Diego, Calif.] usinig N-(9-fluorenyl)methoxycarboxyl chemistry and standard side chain protection except on cysteine residues. Cysteine residues were protected in pairs with either S-trityl on the first and third cysteines or S-acetamidomethyl on the second and fourth cysteines. Amino acid derivatives were from Advanced Chemtech (Louisville, Ky.). The peptides were removed from the resin and precipitated, and a two-step oxidation protocol was used to selectively fold the peptides as described previously (Luo et al., 1999). Briefly, the first disulfide bridge was closed by dripping the peptide into an equal volume of 20 mM potassium feliicyanide and 0.1 M Tris, pH 7.5. The solution was allowed to react for 30 min, and the monocyclic peptide was purified by reverse-phase HPLC. Simultaneous removal of the S-acetamidomethyl groups and closure of the second disulfide bridge was carried out by iodine oxidation. The monocyclic peptide and HPLC eluent was dripped into an equal volume of iodine (10 mM) in H20/trifluoroacetic acid/acetonitrile (78:2:20 by volume) and allowed to react for 10 min. The reaction was terminated by the addition of ascorbic acid diluted 20-fold with 0.1percent trifluoroacetic acid and the bicyclic product purified by HPLC. Mass Spectrometry: Measurements were performed at the Salk Institute for Biological Studies (San Diego, Calif.) under the direction of Jean Rivier. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry and liquid secondary ionization mass spectrometry were used.
Peptide monomers of the present invention were synthesized using the Merrifield solid phase synthesis techniques on Protein Technology's Symphony multiple channel synthesizer. The peptides were assembled using HBTU (0-Benzotriazole-N,N,N',N'-tetramethyl-uronium- hexafluoro-phosphate), Diisopropylethylamine(DIEA) coupling conditions. For some amino acid couplings PyAOP(7-Azabenzotriazol- 1 -yloxy)tripyrrolidinophosponium hexafluorophosphate) and DIEA conditions were used. Rink Amide MB HA resin (100-200 mesh, 0.57 mmol/g) was used for peptide with C-terminal amides and pre-loaded Wang Resin with N-a-Fmoc protected amino acid was used for peptide with C-terminal acids. The coupling reagents (HBTU and DIEA premixed) were prepared at lOOmmol concentration. Similarly amino acids solutions were prepared at 100 mmol concentration. Peptide inhibitors of the present invention were identified based on medical chemistry optimization and/or phage display and screened to identify those having superior binding and/or inhibitory properties.[00611] The peptides were assembled using standard Symphony protocols. The peptide sequences were assembled as follows: Resin (250 mg, 0.14 mmol) in each reaction vial was washed twice with 4ml of DMF followed by treatment with 2.5ml of 20percent 4-methyl piped dine (Fmoc de- protection) for lOmin. The resin was then filtered and washed two times with DMF (4ml) and re -treated with N-methyl piperifine for additional 30 minute. The resin was again washed three times with DMF (4 ml) followed by addition 2.5ml of amino acid and 2.5ml of HBTU-DIEA mixture. After 45min of frequent agitations, the resin was filtered and washed three timed with DMF (4 ml each). For a typical peptide of the present invention, double couplings were performed. After completing the coupling reaction, the resin was washed three times with DMF (4 ml each) before proceeding to the next amino acid coupling.
General procedure: tGLP-1 and its analogues 2?13 were all synthesized using general solid-phase peptide synthesis of N-Fmoc/tBu chemistry. 63Fmoc Rink Amide-MBHA resin (0.1 mmol) was added to a 25 ml peptide synthetic vessel and swollen with DMF for 40 min. After deprotected by 25percent piperidine in DMF, a solution of Fmoc-AA-OH (0.4 mmol), HATU (0.4 mmol), HoAt (0.4 mmol) and DIPEA (0.8 mmol) in DMF was added to the vessel. After reacted for 1 h, the resin was washed three times with DMF and three times with CH2Cl2, then qualitative ninhydrin testing was performed to monitor whether some free amino groups still existed on the resin ornot. If not, the resin was washed three times with DMF again and repeated the procedures of deprotection and coupling. Forthe coupling of some unnatural amino acids, NMM instead of DIPEA and NMP instead of DMF were used. Besides, the reaction time was prolonged to 4 h. Following the final deprotection of N-terminus, the target peptide was cleaved from resin with Reagent K (TFA/thioanisole/water/phenol/EDT, 82.5:5:5:5:2.5) for 2 h atroom temperature. After filtration, the residue solution was concentrated, precipitated with cold diethyl ether and centrifuged for three times. The residue was dissolved in water and purified by Waters 2545 preparative RP-HPLC system. Sephadex G-25 was used for the further purification to remove some short peptide impurities. The molecular mass of the target peptide was confirmed by MALDI-TOF. The purity of peptide was tested with analytical RP-HPLC, and the conditions were as follows: a linear gradient of 20percent mobile phase A and 80percent mobile phase B to 80percent mobile phase A and 20percent mobile phase B (A: acetonitrile containing 0.1percent TFA; B: H2O containing 0.1percent TFA) in 30 min, at a flow rate of 1 mL/minute with UV detection at 214 nm.
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