Hi,
I want to attach biotin-lysine at the C terminal of peptide sequence [DPVLWRHFILSGPGYK(Biotin)CONH2]. I read that 20% piperidine can be used for deprotection (Solid-phase peptide synthesizer) followed by overnight coupling using 0.2M biotin lysine/0.2M PyBOP/0.2M HoBT (manual). I tried this but did not get the correct mass. Please suggest if I can try anything else or modifications.
Thanks.
It sounds like you're trying to add Lys(biotin) to the Nter of a peptide that already has Lys(biotin) on the Cter. I'm not sure why you would want to do this. Would you care to share your plan?
It also sounds like you're trying to do this starting with a (dissolved) peptide that has already been deprotected, cleaved from the solid support, deblocked, and possibly purified. That strategy is highly unlikely to work. This is because your peptide bears reactive side chains on many amino acids. Even though you have no free amino groups other than the Nter, side chains on Arg, His, Ser, and Tyr will be acylated. Also, PyBOP will activate the free carboxyl side chain on your Nter Asp, so that it can acylate intramolecularly. You'll observe many reaction products.
Peptide synthesis is normally performed using amino acid derivatives with the side chains temporarily blocked to prevent side chain reactions. After assembly, when the peptide is cleaved from the solid phase, the cleavage reagent also typically removes the side chain blockers. If you already have a free soluble peptide bearing plenty of reactive side chains, there's no good way to achieve a single peptide bond.
Hi John,
I am trying to attach lysine biotin to C- terminal of my peptide, not to the N-terminal. Y residue will be used for radiolabelling & GGG is the linker. I am using rink amide resin. Thanks for your enquiry on my question & feel free to ask any details about it.
ok. The peptide is still on the resin, with side chain blockers suitable for Fmoc chemistry. Good. But I’m still confused. Of course you can’t add amino acids to the Cter. Do you want to put biotin on the side chain of a Lys that’s already on the peptide chain? That is tricky. Please clarify. Is the Lys already in the chain? Cter or Nter? What is blocking the Lys side chain? I don’t see GGG in your sequence. Are you also adding it now? Where?
What is currently on the resin, and and do you want to make?
Hi John,
I am mentioning steps:
1. Deprotection of resin
2. Coupling of resin to Fmoc-lys(biotin)
3. Peptide synthesis: DPVLWRHFILSGPGY (N---Cterm)
Yes, I want to attach biotin to the side chain of lysine which is on the C terminal of the peptide.
Also, the strategy I tried worked well.
OK. You need to tell me what you really coupled to the resin. Not Lys(biotin), because you want to add the biotin now. So what is currently on the Lys side chain amino group, where you hope to couple biotin? Is it MTT? tBoc? We may be able to get the side chin free without deblocking the rest of the peptide.
The other problem is that the C-ter is sterically hindered, because of the peptide chain. Your chances are better, if the resin has a low substitution level,
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