Powerful and Easy Peptide Coupling Reagent

Fluoro-N,N,N',N'-tetramethylformamidinium hexafluorophosphate (TFFH, 1) is a useful peptide coupling reagent for solution and solid phase peptide synthesis.^1,2) Moreover, 1 is an efficient reagent for the acylation of alcohols, thiols and dithiocarbamates.^1-4) 1 is not hygroscopic and can be stored in a refrigerator, hence it is easy to handle under standard laboratory conditions.

Typical Procedure: Solution phase synthesis of protected leucine enkephalin²⁾
To a solution of Fmoc-Phe-OH (0.189 g) and H-Leu-O^tBu•HCl (0.112 g) in CH₂Cl₂ (10 mL), 5% aqueous solution of Na₂CO₃ (5 mL) is added and stirred at room temperature. To the mixture, 1 (0.198 g) in CH₂Cl₂ (5 mL) is added. The reaction is stirred for 1 h. The organic layer is separated and washed with H₂O and saturated NaCl solution, and then dried over MgSO₄. The solvent is removed in vacuo to give a white solid which is dissolved in CH₂Cl₂ (10 mL). The solution is used directly for deblocking by adding tris(2-aminoethyl)amine (TAEA) (7 mL) to give H-Phe-Leu-O^tBu. Additional amino acids are added similarly until the protected leucine enkephalin [Fmoc-Tyr(^tBu)-Gly-Gly-Phe-Leu-O^tBu] is obtained as a white solid (0.265 g, Y. 60.7%).