I want to use DIC/HOAt for forming a peptide bond with carboxylic acid group on a surface and primary amine on an oligonucleotide, using DCM as a solvent to remove the excess urea formed.
may I ask, why DCM ? we do fmoc spps in DMF, works perfectly.
I guess the choice of solvent is rezin depented, we work with TGA, DMF is best then.(dry DMF ofcourse)
you would like to remove fmoc with 20% piperidene, notice it will cristalize in DCM.
usually you would avoid DMF because it's high boiling point, not a problem in spps because u can just wash it out. otherwise it's the best solvent, as I found, for coupling.
If you want to couple in solution phase with DCM simply take your acid dissolve in DCM if possible then add DIC and HOBt stir 5-10 minutes then add your amine stir 1-2 hour at r.t. Then filter with a plug of slica gel using EtOAc or acetone as solvent. your by product urea will stay on silica. Then concentrate your crude and purify on SGC if needed.
For PS chemistry if your acid is not attached on poylmer support then I would use PS-DCC or DIC for the coupling and this time you may use DMF as solvent. Hope that helps.
You want to use EDC chemistry in buffer for the H2N-Oligo to dissolve, or use dry exchanged Bu4N salts of H2N-Oligo in DMF for attached H2N-oligo to an COOH surface. H2N-Oligo in any form will never disslove in DCM.
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