Tetramethyl uronium tetrafluoroborate

Beck-Sickinger AG, Dtirr H, Jung G (1991) Semiautomated T-bag peptide synthesis using 9-fluorcn-yl-methoxycarbonyl-strategy and benzotriazol-l-yl-tetramethyl uronium tetrafluoroborate activation, Peptide Res 4 88-94. 

This is the reason why peptide chemists, to decrease the problems of purification prefer for long peptides to use protecting groups (tert-butyloxycarbonyl (t-Boc), benzyloxycarbonyl (Z), fluorenylmethyloxycarbonyl (FMOC).) and classical reagents such as T.B.T.U. (0-lH-benzotriazol-l-yl)-l,l,3,3-tetramethyl uronium tetrafluoroborate), B.O.P.(benzotriazol-l-yl-oxy-tris (dimethylamino) phosphonium hexafluorophosphate and so on in polar solvents such as N,N-dimethylformamide or N-methylpyrrolidone. But this solvents are not compatible with the acidic deprotection reagents such as trifluoroacetic acid and... 

Unprotected glycosylamines could be directly coupled to carbojg l groups of protected aminoacids. The most commonly used reagents include benzotriazo-l-yl-oxytris (dimethylamino) phosphonium hexa-fluorophosphate (BOP), 0-[lH- benzotriazo-l-yl)- N, N, M // -tetramethyl-uronium tetrafluoroborate (TBTU), hexafluorophosphate (HBTU), l-hydrojybenzotriazole (HOBt) and 3,4-dihydro-3-hydro g -4-one-l,2,3-triazine. Unprotected glycosylamines could also be coupled to the pentafluoro activated ester of FmocAspO Bu. 

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