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