Mercapto-4-dibenzofuranol

Guy Solladie Frangoise Colobert University Louis Pasteur, Strasbourg, France 

Introduction. 6-Mercapto-4-dibenzofuranol is a reagent developed specifically as an optimal spacing element to facilitate the intramolecular 0,Wacyl transfer during the second stage of the amide-bond-forming protocol known as the thiol capture strategy. As a result, it plays a special role in a relatively new solid phase polypeptide synthesis strategy. 

Step A (eq 1)—the disulfide bond formation between a peptide fragment derivatized at the C-terminus as 6-mercapto-dibenzofuranyl ester and a peptide fragment bearing an 5 sulfenylthiocarbonate (Scm) activated cysteine residue at its N-terminus, occurs cleanly and very rapidly at submillimolar concentrations in protic solvents or solvent mixtures. The intramolecular acyl transfer (step B, eq 1) is highly efficient (effective molarity 1 M), to the effect that, for most cases, a very weakly activated phenolic ester can be employed and many quite reactive side-chain functions in R and R can be left unprotected. These high reactivity criteria are met best in the protein-solubUizing solvent hexafluoro-2-propanol (HFIP) and its mixtures with water and acetonitrile.  

A list of General Abbreviations appears on the bont Endpapers 

The use of a phenolic ester as anchoring group limits the choice of the protective groups. An appropriate choice is tert-butyloxy-carbonyl (Boc, trifluoroacetic acid cleavable) for N -blocking of the amino acid esterified with the phenol and functionalized benzyl groups for side-chain functions. An alternative (preferred in many applications) is tert-butyl derived side-chain blocking groups and 2-p-biphenylyl-2-propyloxycarbonyl (Bpoc) for N -protection.  

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