[practical]

Hi guys,
I am trying out an EDC coupling to a long chain highly non-polar carboxylic acid. The amine is biotinhydrazide. The problem is that biotinhydrazide is highly soluble only in DMSO. However, when I attempted the coupling reaction in DMSO, I isolated unreacted starting material and the rearranged N-acylurea only. If any of you have any suggestions regarding an alternative solvent/ reaction conditions, it would be great!
Thanks in advance!

[opsomath]

It's much harder to pull off the coupling without an intermediate active-ester leaving group. I'd get some NHS or perfluorophenol or something. The reaction should work just fine in DMSO.

[practical]

Thanks! guess I will NHS a shot. Would you happen to know if the stable N-acyl by-product forms more easily in DMSO? I was reading somewhere about the di-electric constant being too high in DMSO for EDC coupling. Would a DMSO:water mixture be better?

[opsomath]

The dielectric is higher in water, actually. I know for sure I've seen examples of EDC/NHS amine coupling in DMSO.