Facile preparation of disulfide‐bridged peptides using the polymer‐supported oxidant CLEAR‐OX^TM*

Abstract

Formation of disulfide bonds in synthetic peptides is one of the more challenging transformations to achieve in peptide chemistry, in view of the possible formation of oligomeric by-products and other side reactions, as well as occasional solubility problems in aqueous oxidizing media. It was shown previously that 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB identical with Ellman's reagent), when attached to polyethylene glycol-polystyrene (PEG-PS), controlled-pore glass (CPG), or modified Sephadex supports, was an effective oxidizing agent that promoted disulfide formation under mild conditions. More recently, this work was extended to Cross-Linked Ethoxylate Acrylate Resin (CLEAR) supports, because of their compatibility with both organic and aqueous solvent mixtures. The resultant new tool, termed CLEAR-OX, was used to conveniently produce several model cyclic disulfides with improved purities and yields, when compared with solution oxidations. A particularly striking example was the gram-scale oxidation of a urotensin II antagonist peptide containing a hindered penicillamine unit.

Oxidative folding of hepcidin at acidic pH

“…21 This polymer-supported oxidant had been previously applied to the oxidative folding of one-, two-, and three-disulfide peptides, 21,22 but to our knowledge is yet to be attempted for a tightly folded four-disulfide peptide such as hepcidin. Although it was unclear how the polymer-supported folding of a complicated four-disulfide peptide would proceed, we investigated the CLEAR-OX 2 -assisted folding of purified linear hepcidin at pH 3.3, 4.0, 5.5, and 7.5.…”

Oxidative Folding of Conotoxins in Immobilized Systems

“…Other modifications of the oxidative folding methodology include immobilization of the protein disulfide isomerase or small-molecule dithiols [5,6]. Polymerattached oxidants, such as immobilized Ellman's reagent (CLEAR-OX TM ) have been successfully used to oxidize disulfide-containing peptides [7,8]. Optimization of oxidative folding, however, still remains an empirical challenge for protein and peptide chemists [9,10].…”

PEG-related polymer resins as synthetic supports

“…Meldal further investigated the use of SPOCC resins, such as the SPOCC-1500 and SPOCC-400 resins [53] (These figures, such as 1500 and 400, represent the molecular weight of PEG chain). In addition, more hydrophilic PEG-based resins were developed, including those containing a small amount of polystyrene or polyamide, made by Meldal and coworkers [57,58], or acrylate with polymerizable vinyl groups in the work of Barany [59][60][61] . Furthermore, PEG-based resins were independently developed by Meldal et al [52] and Côté [62].…”