Fluorescein labeling of peptides on solid phase

  1. To label fluorescein on a side chain of an amino acid, I often choose Fmoc-Lysine(DDE)-OH as the coupling amino acid.
  2. Remove the DDE protection group with 2% hydrazine in DMF. Use the same volume of DMF wash and deprotect 4X with 5min each.
  3. Wash the resin with DMF 5X.
  4. Fluorescein can also be labeled at the N-termini.
  5. labeling with 1.5eq of fluorescein and 1.5eq DCC in a same volume of the coupling step.
  6. Check the labeling efficiency with a small-scale cleavage and ESI test. If necessary, a second time labeling can be performed.
  7. Cleave the peptide with cocktail K.

Cleavage cocktail K: TFA/thioanisole/water/phenol/EDT (90 : 2.5 : 2.5 : 2.5 : 2.5 v/v)