Abstract
Synthetic cannabinoids (SCs), a class of widely abused new psychoactive substances, are characterized by their structural diversity and rapid evolution. Structure-affinity relationships are crucial for predicting pharmacological effects and potential toxicity. Traditional methods for affinity testing are often complex and less applicable to newly modified compounds. In contrast, Surface Plasmon Resonance (SPR) is a sensitive and label-free technology that detects molecular interactions by measuring refractive index changes on a metallic surface with the advantages of high sensitivity, low sample consumption, and high-throughput capability. In this study, we used SPR to determine the receptor affinity constants of 10 SCs, including some first-reported substances, and analyzed their structure-affinity relationships to validate the method's reliability. The results showed that (1) indazole-based SCs exhibited stronger CB1 receptor affinity compared to their indole counterparts, (2) the head structure of p-fluorophenyl enhanced affinity relative to 5-fluoropentyl, (3) and the affinity rankings obtained from SPR experiments were consistent with those derived from traditional methods. These results collectively demonstrate the reliability and effectiveness of SPR in assessing CB1 receptor affinity and differentiating affinity differences among structurally similar analogs, with promising application prospects in drug research, particularly in the development and screening of therapeutic agents targeting cannabinoid receptors.