A Tetrazine-Based Synthesis for Accessing Underutilized Aza-Indole Analogues.

Area of Science:

• Medicinal Chemistry
• Synthetic Organic Chemistry
• Drug Discovery

Background:

• Aza-indoles are crucial in drug discovery, offering improved pharmacological properties and on-target activities compared to privileged indole scaffolds.
• Synthetic access to many aza-indole cores, particularly pyrazolopyridazines, remains limited, hindering their exploration in medicinal chemistry.

Purpose of the Study:

• To develop an efficient synthetic strategy for accessing the underutilized pyrazolopyridazine aza-indole scaffold.
• To enable late-stage functionalization of this scaffold for diverse analogue synthesis.

Main Methods:

• A novel reaction cascade was employed, reacting a protected propargylhydrazine with dichlorotetrazine.
• Development of regioselective methods for functionalizing various positions on the pyrazolopyridazine core.

Main Results:

• An expedited synthetic route to the pyrazolopyridazine aza-indole core was successfully established.
• The synthesized scaffold demonstrated superior physiochemical properties compared to indole analogues.
• Methods for late-stage functionalization were validated, allowing for diverse chemical modifications.

Conclusions:

• The developed synthetic approach provides valuable access to a rare and promising aza-indole scaffold.
• This work facilitates the exploration of pyrazolopyridazines in drug discovery programs, potentially leading to novel therapeutics.