Lactam sulfonamides as potent inhibitors of the Kv1.5 potassium ion channel

Challenges Faced with Small Molecular Modulators of Potassium Current Channel Isoform Kv1.5

The voltage-gated potassium channel Kv1.5, which mediates the cardiac ultra-rapid delayed-rectifier (IKur) current in human cells, has a crucial role in atrial fibrillation. Therefore, the design of selective Kv1.5 modulators is essential for the treatment of pathophysiological conditions involving Kv1.5 activity. This review summarizes the progress of molecular structures and the functionality of different types of Kv1.5 modulators, with a focus on clinical cardiovascular drugs and a number of active natural products, through a summarization of 96 compounds currently widely used. Furthermore, we also discuss the contributions of Kv1.5 and the regulation of the structure-activity relationship (SAR) of synthetic Kv1.5 inhibitors in human pathophysiology. SAR analysis is regarded as a useful strategy in structural elucidation, as it relates to the characteristics that improve compounds targeting Kv1.5. Herein, we present previous studies regarding the structural, pharmacological, and SAR information of the Kv1.5 modulator, through which we can assist in identifying and designing potent and specific Kv1.5 inhibitors in the treatment of diseases involving Kv1.5 activity.

Benzenesulfonamides act as open-channel blockers on KV3.1 potassium channel

KV3.1 blockers can serve as modulators of the rate of action potential firing in neurons with high rates of firing such as those of the auditory system. We studied the effects of several bioisosteres of N-alkylbenzenesulfonamides, and molecules derived from sulfanilic acid on KV3.1 channels, heterologously expressed in L-929 cells, using the whole-cell patch-clamp technique. Only the N-alkyl-benzenesulfonamides acted as open-channel blockers on KV3.1, while molecules analogous to PABA (p-aminobenzoic acid) and derived from sulfanilic acids did not block the channel. The IC50 of six N-alkyl-benzenesulfonamides ranged from 9 to 55 µM; and the Hill coefficient suggests the binding of two molecules to block KV3.1. Also, the effects of all molecules on KV3.1 were fully reversible. We look for similar features amongst the molecules that effectively blocked the channel and used them to model a blocker prototype. We found that bulkier groups and amino-lactams decreased the effectiveness of the blockage, while the presence of NO2 increased the effectiveness of the blockage. Thus, we propose N-alkylbenzenesulfonamides as a new class of KV3.1 channel blockers.

4-Chloro-3-nitro-N-butylbenzenesulfonamide acts on KV3.1 channels by an open-channel blocker mechanism

The effects of 4-chloro-3-nitro-N-butylbenzenesulfonamide (SMD2) on K_V3.1 channels, heterologous expressed in L-929 cells, were studied with the whole cell patch-clamp technique. SMD2 blocks K_V3.1 in a reversible and use-dependent manner, with IC₅₀ around 10 µM, and a Hill coefficient around 2. Although the conductance vs. voltage relationship in control condition can be described by a single Boltzmann function, two terms are necessary to describe the data in the presence of SMD2. The activation and deactivation time constants are weakly voltage dependent both for control and in the presence of SMD2. SMD2 does not change the channel selectivity and tail currents show a typical crossover phenomenon. The time course of inactivation has a fast and a slow component, and SMD2 significantly decreased their values. Steady-state inactivation is best described by a Boltzmann equation with V _1/2 (the voltage where the probability to find the channels in the inactivated state is 50%) and K (slope factor) equals to -22.9 ± 1.5 mV and 5.3 ± 0.9 mV for control, and -30.3 ± 1.3 mV and 6 ± 0.8 mV for SMD2, respectively. The action of SMD2 is enhanced by high frequency stimulation, and by the time the channel stays open. Taken together, our results suggest that SMD2 blocks the open conformation of K_V3.1. From a pharmacological and therapeutic point of view, N-alkylsulfonamides may constitute a new class of pharmacological modulators of K_V3.1.

Mass spectrometry study of N-alkylbenzenesulfonamides with potential antagonist activity to potassium channels

Herein, we report the synthesis and mass spectrometry studies of several N-alkylbenzenesulfonamides structurally related to sulfanilic acid. The compounds were synthesized using a modified Schotten-Baumann reaction coupled with Meisenheimer arylation. Sequential mass spectrometry by negative mode electrospray ionization (ESI(-)-MS/MS) showed the formation of sulfoxylate anion (m/z 65) observed in the mass spectrum of p-chloro-N-alkylbenzenesulfonamides. Investigation of the unexpected loss of two water molecules, as observed by electron ionization mass spectrometry (EI-MS) analysis of p-(N-alkyl)lactam sulfonamides, led to the proposal of corresponding fragmentation pathways. These compounds showed loss of neutral iminosulfane dioxide molecule (M-79) with formation of ions observed at m/z 344 and 377. These ions were formed by rearrangement on ESI(+)-MS/MS analysis. Some of the molecules showed antagonistic activity against Kv3.1 voltage-gated potassium channels.

Adamantane derivatives of sulfonamide molecular crystals: structure, sublimation thermodynamic characteristics, molecular packing, and hydrogen bond networks

The crystal structures of six adamantane derivatives of sulfonamides have been determined by X-ray diffraction and their sublimation and fusion processes have been studied.