Tetrahydropyranyl Backbone Protection for Enhanced Fmoc Solid-Phase Peptide Synthesis

Fmoc solid-phase peptide synthesis has been indispensable for the efficient manufacture of research grade peptides and proteins, and peptide APIs. However, the solid-phase approach is still hampered by solubility issues and aggregation of the resin-bound peptide chain, which limits routine access to peptides > 40 amino acids in length. The use of backbone amide protecting groups, such as through the introduction of N-benzyl-based moieties and pseudoproline dipeptides, ameliorates this synthetic inefficiency somewhat. But benzyl groups can be difficult to remove postassembly, and pseudoprolines are limited to serine, threonine, and cysteine-rich peptide segments. To enhance the utility of backbone protection, we have evaluated the tetrahydropyranyl (Thp) group as a more acid labile alternative to benzyl protection. The Thp group can be efficiently introduced to the resin-bound peptide as a protected dipeptide and is readily cleaved and scavenged postsynthesis. A drastic improvement in the solid-phase assembly of aggregation-prone amyloid-β and prion-derived peptide fragments is observed using Thp as a backbone protecting group. We envisage that Thp-protected dipeptides will become useful building blocks for peptide manufacturing, complementing existing backbone protecting group strategies.