Synthetic Exploration of Cystargolide-Based Fatty Acid Conjugates and Prodrug Precursors

The ubiquitin-proteasome system (UPS) is a critical pathway in cellular homeostasis, with its dysregulation implicated in various cancers. While proteasome inhibitors (PIs) are clinically validated anticancer agents, current therapies like bortezomib face limitations including adverse effects and issues with cellular infiltration and stability. To address these challenges, we report the design and synthesis of novel cystargolide-based analogues, strategically modified to enhance therapeutic properties. Our synthetic campaign involved the efficient preparation of key building blocks, including N-Boc-L-Valine, and a dipeptide intermediate. We demonstrated the versatility of our approach by synthesizing an N-hexanoyl-dipeptide, aimed at improving cellular permeability. The final coupling of the peptidic fragment with a 𝛽-lactone core proceeded effectively. All synthesized compounds were rigorously characterized by NMR and HRMS, confirming their precise chemical structures and high purity. These compounds embody strategic modifications, such as fatty acid conjugation for improved cellular infiltration and precursors for 𝛽-lactone prodrugs for enhanced stability and targeted activation within the cancer microenvironment. This work establishes a robust synthetic foundation for next-generation cystargolide PIs. Comprehensive biological evaluation, including assessments of proteasome inhibition, cellular uptake, and cytotoxicity, is currently underway to validate these designed properties.