I am trying out a Steglich esterification of a PEG with a Boc protected amino acid and stuck on working out how to deprotect the amino group without breaking the acid sensitive ester bond. Thanks in advance for the suggestions.
using dry HCl. the reaction should be carried out strictly under anhydrous conditions. just bubble HCl gas through your compound dissolved in a suitable dry solvent. you may look into methods of generating HCl elsewhere. sulphuric acid + NaCl is a common method to generate HCl. you may find better methods though.
did you try Tfa/DCM 1:1?or HCl gas /EtoAc?
also consider to use fmoc protected amino acids...
Thank you everyone. I will try the TFA/DCM and the HCl gas method and keep you updated
Why don't you use a different protecting group instead of Boc? Something you can remove with a base, for instance
Iris Bermejo we have the boc amino acids in the lab and they are quite expensive so I want to try it first using this method before ordering other kinds of protected amino acids
If your material is thermally stable, you can deprotect without acid, simply by heating under vacuum to about 190ºC.
V.H. Rawal, M.P. Cava, Tetrahedron Lett. (1985) 26:6141
H.H. Wasserman, G.D. Berger,Tetrahedron (1983) 39:2459
Just an update. For me both TFA in DCM and HCl in EtOAc worked. HCl gave deprotection without breaking any ester bonds but takes 6 h. TFA gave 100% deprotection in 30 min but I lost 10-20% of my ester bonds. Thank you for the great recommendations
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