I'm synthesizing short peptides and I'm using FMOC l-amino acids, DMF as a solvent and DIPEA, HATU and HOBT. I am already using the "magic mixture" for coupling and I still have positive kaiser test, any idea?
Thank you.
Try adding a detergent such as Triton in 1% loading or 0.4M chaotropic salts (LiCl or KSCN), it will help disrupt aggregates.
Protecting selected amide bonds every 5-8 residues can help too. Photolabile Hnb groups can assist with acyl transfer and can be removed orthogonally as needed.
If you have serine or threonine residues then using pseudoproline dipeptide building blocks helps.
Sometimes the simple means of using more concentrated solutions helps...
You can use a solution containing DCM and hexafluoroisopropanol (HFIP) (4:1) to improve the resin swelling... it works very well in Rink Amide resins. After that, you must wash the resin with DMF and DCM at least three times. Hope it works for you, even though I didn't know what type of resin you are using.
try fragment synthesis in solution or use pseudoproline dipeptides in the sequence ,, overcome the difficult sequences , both method work well .
if you have anymore question please feel free contact me : [email protected]
best regards.
Have you considered a different coupling strategy? I am aware that this may be financially unavailable (chemicals aren't cheap!) but it might pay off in the long-term?
I use PyBOP and NMM as my coupling reagents and haven't ran into much trouble, yet I work with some tricky sequences.
Maybe this could be something you could look into?
How long is your peptide? sometimes making shorter fragment and joining them by native chemical ligation helps.....also consider the pseudoproline chemistry.
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