C-H Functionalization of Peptides via Cyclic Aminal Intermediates

Area of Science:

• Organic Chemistry
• Catalysis
• Peptide Chemistry

Background:

• Palladium-catalyzed C-H functionalization is a powerful tool in organic synthesis.
• Directing groups are crucial for achieving regioselectivity in C-H activation reactions.
• Cyclic ketoaminals derived from dipeptides offer a unique scaffold for chemical modification.

Purpose of the Study:

• To develop a novel method for regioselective C-H functionalization of protected dipeptides.
• To evaluate the efficacy of different directing groups, specifically 2-(methylthio)aniline (MTA) and 8-aminoquinoline (AQ).
• To demonstrate the compatibility of the functionalization process with peptide synthesis workflows.

Main Methods:

• Protected dipeptides were converted into cyclic ketoaminals.
• Palladium-catalyzed regioselective C-H functionalization was performed using MTA and AQ directing groups.
• Analysis of reaction products included assessment of regioselectivity and stereochemical integrity (epimerization).
• Cleavage of directing and protecting groups was performed to yield modified dipeptides.

Main Results:

• Cyclic ketoaminals underwent successful palladium-catalyzed regioselective C-H functionalization.
• The 2-(methylthio)aniline (MTA) directing group provided superior regioselectivity compared to the 8-aminoquinoline (AQ) group.
• No epimerization of stereogenic centers within the dipeptide was observed during the functionalization process.
• The functionalized dipeptides could be readily deprotected and incorporated into larger peptide structures.

Conclusions:

• The developed method enables efficient and regioselective C-H functionalization of protected dipeptides via cyclic ketoaminals.
• The MTA directing group is a highly effective alternative to AQ for this transformation.
• The methodology preserves the stereochemical integrity of the dipeptide, making it suitable for complex peptide synthesis.