A backbone amide protecting group for overcoming difficult sequences and suppressing aspartimide formation

Area of Science:

• Organic Chemistry
• Peptide Chemistry
• Synthetic Chemistry

Background:

• Peptide synthesis is crucial for drug discovery and development.
• Aggregation and aspartimide formation are common challenges in synthesizing peptides.
• Existing methods for overcoming these challenges are often inefficient.

Purpose of the Study:

• To introduce and evaluate a novel backbone amide protecting group, 2-hydroxy-4-methoxy-5-nitrobenzyl (Hmnb), for improved peptide synthesis.
• To demonstrate the utility of Hmnb in preventing aspartimide formation and facilitating the synthesis of difficult peptide sequences.

Main Methods:

• Automated introduction of the Hmnb protecting group during peptide assembly on a resin.
• On-resin reduction to form a secondary amine, followed by intramolecular acyl transfer for efficient coupling.
• Acidolysis for deprotection after nitro group reduction to aniline.

Main Results:

• The Hmnb protecting group significantly improved the synthesis of aggregation- and aspartimide-prone peptides.
• Automated introduction and efficient coupling via an activated ester were demonstrated.
• Successful synthesis of challenging sequences, including an aspartimide-prone peptide, ACP (65-74), and a polyalanine homopolymer, was achieved.

Conclusions:

• The Hmnb protecting group is a valuable tool for overcoming common challenges in peptide synthesis.
• Its ease of introduction, efficient coupling, and facile removal make it suitable for automated solid-phase peptide synthesis.
• Hmnb offers a promising strategy for the synthesis of complex and difficult peptide targets.