Production of constrained L-cyclo-tetrapeptides by epimerization-resistant direct aminolysis

Area of Science:

• Medicinal Chemistry
• Organic Synthesis
• Peptide Chemistry

Background:

• Constrained 12-membered ring synthesis is difficult due to cyclization constraints.
• Excessive activation causes epimerization; insufficient activation leads to oligomerization.

Purpose of the Study:

• To develop a novel framework for efficient synthesis of constrained cyclic tetrapeptides.
• To overcome challenges in peptide cyclization, including epimerization and oligomerization.

Main Methods:

• Utilized a beta-thiolactone framework for direct aminolysis.
• Employed a mechanism restricting C-terminal carbonyl rotation while maintaining reactivity.

Main Results:

• Successfully synthesized over 20 challenging cyclic tetrapeptides with high efficiency.
• Achieved non-epimerizable head-to-tail amidation, minimizing oligomerization.
• Synthesized previously unattainable macrocycles, including a potent micro-opioid receptor agonist (EC50 = 2.5 nM).

Conclusions:

• The beta-thiolactone framework provides a practical solution for constrained peptide cyclization.
• This method enables the synthesis of novel cyclic peptides with potential therapeutic applications, such as MOR agonists.