Removal of iodine by solid phase adsorption to charcoal following iodine oxidation of acetamidomethyl-protected peptide precursors to their disulfide bonded products: oxytocin and a Pre-S1 peptide of hepatitis B virus illustrate the method.

Chemical quenching, gel filtration or liquid phase extraction procedures are currently in vogue for taking iodine off from the reaction mixtures in which it is used to cause the formation of disulfide bonds in acetamidomethyl or trityl protected peptides. It has been found that charcoal effectively, selectively and rapidly removes iodine by solid phase extraction from reaction mixtures in which it is used to convert the acetamidomethyl protected precursors of oxytocin or a peptide from the Pre-S1 region of hepatitis B virus into their intramolecularly disulfide-bonded products. The advantages of this new method, namely simplicity, rapidity, quantitative yields, freedom from side reactions, linear scalability, cost effectiveness and adsorption of iodine on to solid charcoal are discussed.