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Lys(Boc)-Pra-Asn(Trt)-Thr(tBu)-Ala-Thr(tBu)-Ala(N3)-Ala-Pal-PEG resin (16) (0.498 g, 0.09 mmol) was cleaved with TFA/iPr3SiH/H2O (v/v/v; 95/2.5/2.5, 5.0 mL) for 2 h, peptide was isolated as described in the general section to afford 47.3 mg of crude peptide 17. The crude peptide 17 (16.3 mg) was purified by RP-HPLC on a preparative Phenomenex Gemini C18, column at a flow rate of 5 mL min-1, using a linear gradient of 1percentB to 61percentB over 60 min (ca. 1percentB per minute) and lyophilised to give the title compound 17 as a white amorphous solid (4.9 mg, 18percent).
Lys(Boc)-Pra-Asn(Trt)-Thr(tBu)-Ala-Thr(tBu)-Ala(N3)-Ala-Pal-PEG resin (16) (0.498 g, 0.09 mmol) was cleaved with TFA/iPr3SiH/H2O (v/v/v; 95/2.5/2.5, 5.0 mL) for 2 h, peptide was isolated as described in the general section to afford 47.3 mg of crude peptide 17. The crude peptide 17 (16.3 mg) was purified by RP-HPLC on a preparative Phenomenex Gemini C18, column at a flow rate of 5 mL min-1, using a linear gradient of 1percentB to 61percentB over 60 min (ca. 1percentB per minute) and lyophilised to give the title compound 17 as a white amorphous solid (4.9 mg, 18percent). Purified Lys-Pra-Asn-Thr-Ala-Thr-Ala(N3)-Ala-NH2 (17) (4.4 mg, 5.42 x 10-3 mmol) was dissolved in a mixture of water and tert-butyl alcohol (1 : 2.5, 3.5 mL in total). A stock solution of CuSO4 (0.87 mg, 5.42 x 10-3 mmol) and sodium ascorbate (2.68 mg, 13.6 x 10-3 mmol) in water (1.5 mL) was added and the mixture was microwaved for 20 min at 80 °C in a sealed reaction vessel (120 W max) to afford crude peptide (8), containing inseparable dehydroalanine by-product. The crude peptide (8) was purified by RP-HPLC on a preparative Waters XTerra.(R). Prep. C18 column at a flow rate of 10 mL/min, using a linear gradient of 1percentB to 51percentB over 50 min (ca. 1percentB per minute). Fractions were lyophilised to give the title compound 8 as a white amorphous solid (0.7 mg, 18percent), containing inseparable dehydroalanine by-product.
General procedure: Fmoc SPPS was performed on a Liberty Microwave Peptide Synthesiser (CEM Corporation, Mathews, NC) using the Fmoc/tBu strategy as previously described35 or manually starting from PAL-PEG polystyrene resin (0.21 mmol/g). For manual synthesis the following steps were undertaken: (a) Fmoc deprotection with 20percent piperidine for 5 min, then 15 min, washing with DMF 5.x.; (b) coupling of the Fmoc amino acid (5 equiv) in the presence of HBTU in DMF (4.9 equiv) and iPr2NEt (10 equiv) for 1 h and washing with DMF 5.x.. For coupling of Fmoc-Pra (1.5 equiv) and Fmoc-N3Ala (1.5 equiv), 1.45 equiv of HBTU and 4.5 equiv of iPr2NEt were used. The progress of the acylation step was monitored by the Kaiser test. A minimum amount of DMF was used for dissolution of the Fmoc amino acid. The resulting peptides were cleaved from the resin with simultaneous side chain protecting group removal by treatment with either TFA/iPr3SiH/DODT/H2O (v/v/v/v; 94/1/2.5/2.5), or with TFA/iPr3SiH/H2O (v/v/v; 95/2.5/2.5) for 2 h at room temperature. Crude peptides were precipitated and triturated with cold diethyl ether, isolated (centrifugation), dissolved in 20percent acetonitrile (aq) containing 0.1percent TFA and lyophilized. Analytical RP-HPLC was performed using a Dionex P680 (flow rate of 1 mL/min), or Dionex Ultimate U3000 system (flow rate of 0.5 mL/min or 0.2 mL/min) using Waters XTerra.(R). column (MS C18, 150 mm .x. 4.6 mm; 5 mum) or, Phenomenex Aqua column (C18, 250 mm .x. 4.6 mm; 5mu), or Phenomenex, Gemini column (C18, 50 mm .x. 2.0 mm, 5mu), using gradient systems as indicated in the Supplementary data. The solvent system used was A (0.1percent TFA in H2O) and B (0.1percent TFA in acetonitrile) with detection at 210 nm, 254 nm, and 280 nm****. The ratio of products was determined by integration of spectra recorded at 210 nm. Peptide masses were confirmed by an inline Thermo Finnegan MSQ mass spectrometer using ESI in the positive mode. When appropriate, a Bruker micrOTOF-Q II mass spectrometer was used for ESI-MS analysis (positive mode). Infrared spectra were obtained using a Perkin Elmer Spectrum One Fourier Transform infrared spectrometer with a universal ATR sampling accessory. Peptide purification was performed using a Waters 600E or Dionex Ultimate U3000 system using a Waters XTerra.(R). column (C18, 300 mm .x. 19 mm; 10 mum), or Phenomenex Gemini C18, 250 mm .x. 10 mm; 5 mum column. Gradient systems were adjusted according to the elution profiles and peak profiles obtained from the analytical RP-HPLC chromatograms. Fractions were collected, analysed by either RP-HPLC or ESI-MS, pooled and lyophilised three times from 10 mM aq HCl.
General procedure: Fmoc SPPS was performed on a Liberty Microwave Peptide Synthesiser (CEM Corporation, Mathews, NC) using the Fmoc/tBu strategy as previously described35 or manually starting from PAL-PEG polystyrene resin (0.21 mmol/g). For manual synthesis the following steps were undertaken: (a) Fmoc deprotection with 20percent piperidine for 5 min, then 15 min, washing with DMF 5.x.; (b) coupling of the Fmoc amino acid (5 equiv) in the presence of HBTU in DMF (4.9 equiv) and iPr2NEt (10 equiv) for 1 h and washing with DMF 5.x.. For coupling of Fmoc-Pra (1.5 equiv) and Fmoc-N3Ala (1.5 equiv), 1.45 equiv of HBTU and 4.5 equiv of iPr2NEt were used. The progress of the acylation step was monitored by the Kaiser test. A minimum amount of DMF was used for dissolution of the Fmoc amino acid. The resulting peptides were cleaved from the resin with simultaneous side chain protecting group removal by treatment with either TFA/iPr3SiH/DODT/H2O (v/v/v/v; 94/1/2.5/2.5), or with TFA/iPr3SiH/H2O (v/v/v; 95/2.5/2.5) for 2 h at room temperature. Crude peptides were precipitated and triturated with cold diethyl ether, isolated (centrifugation), dissolved in 20percent acetonitrile (aq) containing 0.1percent TFA and lyophilized. Analytical RP-HPLC was performed using a Dionex P680 (flow rate of 1 mL/min), or Dionex Ultimate U3000 system (flow rate of 0.5 mL/min or 0.2 mL/min) using Waters XTerra.(R). column (MS C18, 150 mm .x. 4.6 mm; 5 mum) or, Phenomenex Aqua column (C18, 250 mm .x. 4.6 mm; 5mu), or Phenomenex, Gemini column (C18, 50 mm .x. 2.0 mm, 5mu), using gradient systems as indicated in the Supplementary data. The solvent system used was A (0.1percent TFA in H2O) and B (0.1percent TFA in acetonitrile) with detection at 210 nm, 254 nm, and 280 nm****. The ratio of products was determined by integration of spectra recorded at 210 nm. Peptide masses were confirmed by an inline Thermo Finnegan MSQ mass spectrometer using ESI in the positive mode. When appropriate, a Bruker micrOTOF-Q II mass spectrometer was used for ESI-MS analysis (positive mode). Infrared spectra were obtained using a Perkin Elmer Spectrum One Fourier Transform infrared spectrometer with a universal ATR sampling accessory. Peptide purification was performed using a Waters 600E or Dionex Ultimate U3000 system using a Waters XTerra.(R). column (C18, 300 mm .x. 19 mm; 10 mum), or Phenomenex Gemini C18, 250 mm .x. 10 mm; 5 mum column. Gradient systems were adjusted according to the elution profiles and peak profiles obtained from the analytical RP-HPLC chromatograms. Fractions were collected, analysed by either RP-HPLC or ESI-MS, pooled and lyophilised three times from 10 mM aq HCl.
All peptides were synthesized on a 0.2 mmol scale using manual Fmoc-SPPS chemistry under flow using a 3 minute cycle for each amino acid. Specifically, all reagents and solvents are delivered to a stainless steel reactor containing resins at a constant flow rate using HPLC pump; temperature of the reactor was maintained at 60 °C during the synthesis using water bath. Procedure for each amino acid coupling cycle included a 30 second coupling with 1 mmol Fmoc-protected amino acid, 1 mmol HBTU, and 500 of diisopropyl ethyl amine (DIEA) in 2.5 mL of DMF at a flow rate of 6 mL/min (note that for coupling of cysteine and tryptophan, 190 of DIEA was used to prevent racemization); 1 minute wash with DMF at a flow rate of 20 mL/min; 20 second deprotection with 50percent (v/v) piperidine in DMF at a flow rate of 20 mL/min; and 1 minute wash with DMF at a flow rate was 20 mL/min. After completion of the stepwise SPPS, the resin was washed thoroughly with DCM and dried under vacuum. The peptide is simultaneously cleaved from the resin and side-chain deprotected by treatment with 2.5percent (v/v) water, 2.5percent (v/v) 1 ,2- ethanedithiol (EDT), and 1percent (v/v) triisoproprylsilane in neat trifluoroacetic acid (TFA) for 2 hours at room temperature. The resulting solution containing peptide was evaporated by blowing a stream of nitrogen gas over its surface for 15 minutes, then triturated and washed with cold diethyl ether three times. The obtained gummy-like solid was dissolved in 50percent H20: 50percent acetonitrile containing 0.1percent TFA and lyophilized. These same solvent compositions were used in majority of experiments and will be referred to as A: 0.1percent TFA in H20 and B: 0.1percent TFA in acetonitrile. c. Peptide Purification The crude peptide was dissolved in 95percent A: 5percent B with 6 M guanidinium hydrochloride and purified by semi-preparative RP-HPLC (Agilent Zorbax SB C18 column: 21.2 x 250 mm, 7 mutaueta, linear gradient: 5-50percent B over 90 min, flow rate: 5 mL/min). 1 of each HPLC fraction was mixed with 1 mu^ of alpha-cyano-4-hydroxycinnamic acid (CHCA) matrix in 75percent A: 25percent B, spotted with MALDI, and checked for fractions with desired molecular mass. The purity of fractions was confirmed by analytical RP-HPLC (Agilent Zorbax SB C3 column: 2.1 x 150 mm, 5 muiotaeta, gradient: 0-2 minutes 5percent B, 2-11 minutes 5- 65percent B, 11-12 minutes 65percent B, flow rate: 0.8 mL/min). HPLC fractions containing only product materials were confirmed by LC-MS analysis, combined, and then lyophilized. Peptides synthesized using fast flow-based SPPS and purified by RP-HPLC are listed in Table SI .
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