Dear everyone,
I synthesize peptides with a common Fmoc-strategy starting from a
Cysteamine 2-chlorotrityl resin. That works fine and usually I cleave the peptide from the resin with a mixture of TFA/TIS/H2O, and that works fine as well. What I would like to do now is immediately oxidize the thiols located on the Cysteamine to disulfides while I cleave the peptide from the resin, that I will be left with the (symmetric) dimer.
What would be a proper strategy to do that? I know I can, in principle, still oxidize the monomer later on, but for very specific reasons I do not want to do that.
Every suggestion is appreciated!
I don't have a complete answer, but first, you need to raise the pH enough to deprotonate the thiols. Then, a mild oxidizing agent is needed in a stoichiometric amount (to remove two electrons). Iodine, for example, is too strong and over-oxidizes the sulfur to some extent, even during a titration; see Article Identification of the oxidation products of cysteamine and c...
Thanks for the answer! Actually I already fixed the problem. What I do is, I isolate the monomer with the free thiol on the Cysteamine. I subsequently dimerize the monomer in a borate buffer solution (made from B2O3) at pH = 8.16, add 1.1 eq. of sodium perborate and stir for a few hours. Then I isolate the dimer on a C18 column with water/acetonitrile gradient + 0.1 % TFA and freeze-dry. That works well!
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