Design of the Synthetic Route for Peptides and Proteins Based on the Solubility Prediction Method. I. Synthesis and Solubility Properties of Human Proinsulin C-Peptide Fragments

The usefulness of the solubility prediction method is demonstrated using relatively small peptide fragments of human proinsulin C-peptide. The propriety of the solubility prediction method for peptides having polar side chains is also examined in the following respects: (1) Peptide intermediates smaller than a heptapeptide have high solubility regardless of their values; (2) the values of peptide intermediates are useful for judging solubility of peptide intermediates equal to or larger than an octapeptide level; (3) the Pro residue in a central position of a peptide chain is effective for increasing peptide solubility; and (4) there is critical chain length for peptide insolubility caused by a β-sheet aggregation. A strategy suitable for the design of the synthetic route for human proinsulin C-peptide is subsequently discussed on the basis of the solubility prediction of peptide intermediates.