Make the protected peptide on SASRIN resin and cleave with 1 % TFA/DCM. Neutralize with 3-fold excess DIEA and rotovap to a syrup. Re-suspend in THF or acetonitrile (easy to remove at the end of cyclization) and check the pH with wet PH paper (make it 8-9 with DIEA). Make the peptide concentration approximately 25 micromolar. I perform the cyclization using a syringe pump to add HBTU (100 mM in DMF) to the reaction at 100 microliters per minute. I monitor the reaction by HPLC.
Workup is simple: rotovap followed by Dowex ion exchange resin to remove unreacted linear peptide and the RP-HPLC for final separation.
have fun
Hank Wolfe
Nycomed AMersham
Wayne Pa