| C-type lectin receptors (CLRs) are crucial for mediating a range of biological interactions including cell-cell contact, cell-matrix adhesion, and host-pathogen interactions. CLRs are important for homeostatic control, recognizing self-antigens and tolerizing the tissue environment. Alternatively, they can detect foreign pathogens. One CLR that is involved in many of these roles is DC-SIGN. DC-SIGN is found on the surface of dendritic cells and functions as an adhesion receptor for a variety of glycan-containing structures including glycoproteins found on the surface of pathogens. Pathogens such as HIV-1 and Mycobacterium tuberculosis can target DC-SIGN to infect cells or modulate immune responses to promote their survival. Thus, DC-SIGN has been implicated as an important therapeutic target. Herein, I describe the production of chemical tools for probing key functions of DC-SIGN activity.;We used high-throughput screening to identify small molecules that could target DC-SIGN. This approach yielded a class of compounds containing a quinoxalinone core. I developed a divergent synthetic route to the quinoxalinones highlighted by a tandem cross-metathesis-hydrogenation sequence as the penultimate transformation. This strategy allowed variation of the quinoxalinone scaffold to generate potent inhibitors of DC-SIGN.;With the appropriate synthetic tools, we demonstrated that small molecule inhibitors of DC-SIGN could be used as probes of DC-SIGN activity. In this regard, we designed a sensitive flow cytometry assay that revealed the utility of the quinoxalinones for preventing glycans from interacting with cells displaying DC-SIGN. Furthermore, the compounds were marginally active in blocking mycobacterial adhesion to DC-SIGN on dendritic cells.;The ability of the quinoxalinones to bind DC-SIGN and inhibit its interaction with a variety of glycan-containing structures prompted efforts to understand their mechanism of inhibition. We demonstrate that the compounds engage DC-SIGN at a site that is distal from the known carbohydrate-binding site. These findings suggest that the quinoxalinones inhibit DC-SIGN-glycan interactions through a mechanism that is distinct from known carbohydrate-based inhibitors of DC-SIGN. |
