Ca2+ -Langerin-IN-1 (Compound 3) is an allosteric inhibitor of the protein Langerin, a C-type lectin expressed on Langerhans cells, which plays a crucial role in pathogen recognition and innate immune activation. Under Ca²⁺ and Ca²⁺-free competitive conditions, the KD values of Ca2+ -Langerin-IN-1 for the murine Langerin CRD domain are 17 μM and 53 μM, respectively. It induces conformational changes and competitively displaces Ca²⁺, thereby inhibiting the carbohydrate recognition function of the protein. Ca2+ -Langerin-IN-1 can be utilized in studies of immunoregulatory therapies.