The Development of a Highly Potent and Selective Human Toll-like Receptor 2 Agonist: Synthesis and Biological Evaluation of CaLGL-1 and Its Derivatives

Toll-like receptor 2 (TLR2) plays a crucial role in detecting microbial pathogen-associated molecular patterns, offering potential applications as an adjuvant for vaccines and antitumor therapies. Here, we present the gram-scale synthesis of CaLGL-1 and its derivatives, natural products known for activating mouse TLR2 (EC₅₀ = 3.2 μM). This synthesis involves a streamlined six-step reaction sequence utilizing oxidant-promoted acetalization, effectively preserving the acid-sensitive glycosidic bond for maintaining the compounds' functional integrity. Our structure-activity relationship studies identified R-7d as a potent human TLR2 activator. It demonstrated subnanomolar activity (EC₅₀ = 116 pM) in human THP-1 cells, comparable to that of diprovocim (EC₅₀ = 110 pM). Experiments revealed that R-7d enhances NF-kB promoter activation through TLR2/TLR1 heterodimers rather than TLR2/TLR6. The discovery of R-7d as a robust human TLR2 agonist opens up new possibilities for combination therapies.