The TFA-labile Wang resin is a standard support for batch synthesis of peptide acids following the Fmoc-/tBu-protection scheme.(1,2) It is easily cleaved by treatment with 95% TFA. Special attention should be given to the attachment of the first amino acid residue to this benzyl alcohol type support, because the activation step can lead to a substantial degree of racemization. For the incorporation of the C-terminal amino acids, the following coupling methods are recommended: carbodiimide/dimethyl aminopyridine (DMAP) in dichloromethane,(3) 2,6-dichlorobenzoyl chloride/pyridine in dimethyl formamide (DMF),(4) 1- hydroxybenzotriazole (HOBt)/N,N´-dicyclohexylcarbodiimide (DCC) in DMF (catalytic amounts of DMAP optional),(5) 1-(2- mesitylenesulfonyl)-3-nitro-1H-1,2,4-triazole (MSNT) in the presence of N-methylimidazole,(6) or the Mitsunobu coupling reaction.(7,8)
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