Peptides were synthesized using a CS-Bio 136 automated peptide synthesizer (CS Bio Co., Menlo Park, CA) with a standard solid phase Fmoc chemistry protocol. All protected amino acids used were purchased from GL Biochem Ltd. (Shanghai, China). Rink amide resin (0.38 ~ 0.45 mmol/g, Nankai Hecheng S&T Co. Ltd., Tianjin, China) was used. Coupling of the amino acids was achieved using O-benzotriazol-1-yl-N,N,N',N'-tetramethyl-uronium hexafluorophosphate (HBTU, GL Biochem, Shanghai, China) and

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... opylethylamine (DIEA, Acrose) as an activator and an active base, respectively, in N,N-dimethylformamide (DMF) solution. The Fmoc protective group was removed using 20% piperidine/DMF. Between every coupling or Fmoc removal, the resin was washed five times with DMF, and three times with dichloromethane (DCM). The carboxyl termini were amidated upon cleavage from the resin, and the amino termini were capped with acetic acid