Synthesis of Novel 3‐N‐substituted Carbazole Derivatives and Evaluation of their Abilities to Inhibit Platelet Aggregation

The carbazole moiety exhibits various biological activities, including anticancer, antiviral, anti‐inflammatory, and antimicrobial activities; some compounds containing the moiety also inhibit platelet aggregation. In the present study, we synthesized a series of 3‐N‐substituted carbazole derivatives and evaluated their abilities to inhibit in vitro platelet aggregation induced by collagen (5 μg/mL). Of the synthesized compounds, compound 5q (JSCa15), with a urea linkage within the carbazole framework, exhibited the strongest inhibitory activity (98.25% at 30 μM). Interestingly, reduction of the nitro group of compound 5q to an amine exhibited significantly decreased activity (compound 5r, 5.18% at 30 μM). Also, substitution of the urea moiety of compound 5q with a carbamate moiety resulted in a considerable loss of activity (compound 8a, 5.91% at 30 μM). These results suggest that the urea moieties and nitro groups of 3‐N‐substituted carbazole derivatives may play key roles in inhibiting in vitro platelet aggregation induced by collagen.