A Qualitative Test for Monitoring Coupling Completeness in Solid Phase Peptide Synthesis Using Chloranil.

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Abstract
A qualitative test is described which can be carried out in the presence of the reaction mixture. At intervals, a resin sample is removed from the reactor, and the chloranil test is carried out directly. If free amino groups are present, a green to blue color develops on the resin beads in less than 5 min. The test can also be used when the N-terminal amino acid residue is proline. By applying the chloranil test, it is demonstrated that the coupling rates depend on the respective amino acid and the position in the peptide. The test was applied to dicyclohexylcarbodiimide couplings and an active ester coupling.