A GENERAL STRATEGY FOR THE SYNTHESIS OF LARGE PEPTIDES - THE COMBINED SOLID-PHASE AND SOLUTION APPROACH

In the synthesis of large peptides, the yield and purity of the end-products will be greatly improved when smaller segments are purified prior to their use for fragment coupling either on a solid-phase resin or in solution. The N(alpha)-Fmoc(9-fluorenylmethoxycarbonyl) method allows the selective acidolytic cleavage of fully protected peptides with a free alpha-carboxyl group from the solid-phase resin. For this cleavage, the highly acid-labile HMPB linker, 4-(4-hydroxymethyl-3-methoxyphenoxy)-butyric acid, has been developed. The lipophilic protecting groups, in particular Trt on asparagine, glutamine, and histidine, as well as Pmc (2,2,5,7,8-pentamethylchroman-6-sulfonyl) on arginine, confer a good solubility on most protected peptide segments in organic solution and enable their purification by silicagel chromatography. Whereas the addition of segments on solid-phase resins is often difficult, they can as a rule be coupled easily in solution to give products in high yield and purity. The combined solid-phase and solution strategy is illustrated by the syntheses of human calcitonin-(1-33), human neuropeptide Y, and the sequence 230-249 of mitogen-activated 70K S6 kinase.