Resin cleavage (revision 7)
Old revision·13:17, 27 Oct 2024·ExternalLinksEli
| Resin cleavage | |
|---|---|
| Reagent, Fmoc chemistry | Trifluoroacetic acid with scavengers |
| Simultaneous | Side-chain deprotection |
| Isolation | Precipitation into cold ether |
| Analytical method infobox · conventions | |
Resin cleavage is the step that releases an assembled peptide from the solid support. In Fmoc chemistry it also removes the acid-labile side-chain protecting groups, so a single treatment with concentrated trifluoroacetic acid accomplishes both.[1]
The removed protecting groups generate reactive carbocations, which will alkylate electron-rich side chains — tryptophan, methionine, cysteine and tyrosine — unless captured. Scavengers are included in the cleavage cocktail for that purpose, and their selection depends on which residues the sequence contains.[1]
Cleavage is therefore not a neutral release step. It is a chemical operation with its own characteristic impurities, and a substantial part of the difference between a clean and a dirty crude is decided here.[2]
Cocktails and scavengers
[edit]A typical cocktail is trifluoroacetic acid with a few per cent each of water, triisopropylsilane and, where cysteine or methionine is present, a thiol scavenger. Water and silane trap the tert-butyl and trityl cations; thiols address the more persistent species.[1]
Time and temperature are the other variables. Arginine's sulfonyl protecting groups are the slowest to remove, so a peptide rich in arginine requires longer treatment — during which more sensitive residues are exposed to acid for longer.
The trade-off is direct: insufficient time leaves protected species in the crude, excessive time generates degradation. This is one of the process choices that a certificate does not report but whose consequences it may show.[2]