Synthesis of Pseudellone Analogs and Characterization as Novel T-type Calcium Channel Blockers

T-type calcium channel (Ca_V3.x) blockers are receiving increasing attention as potential therapeutics for the treatment of pathophysiological disorders and diseases, including absence epilepsy, Parkinson's disease (PD), hypertension, cardiovascular diseases, cancers, and pain. However, few clinically approved Ca_V3.x blockers are available, and selective pharmacological tools are needed to further unravel the roles of individual Ca_V3.x subtypes. In this work, through an efficient synthetic route to the marine fungal product pseudellone C, we obtained bisindole alkaloid analogs of pseudellone C with a modified tryptophan moiety and identified two Ca_V3.2 (2, IC₅₀ = 18.24 µM; 3, IC₅₀ = 6.59 µM) and Ca_V3.3 (2, IC₅₀ = 7.71 µM; 3, IC₅₀ = 3.81 µM) selective blockers using a FLIPR cell-based assay measuring Ca_V3.x window currents. Further characterization by whole-cell patch-clamp revealed a preferential block of Ca_V3.1 activated current (2, IC₅₀ = 5.60 µM; 3, IC₅₀ = 9.91 µM), suggesting their state-dependent block is subtype specific.