Lead discovery and optimization of T-type calcium channel blockers

doi:10.1016/j.bmc.2006.11.004

Bioorganic & Medicinal Chemistry

Volume 15, Issue 3, 1 February 2007, Pages 1409-1419

https://doi.org/10.1016/j.bmc.2006.11.004 Get rights and content

Abstract

A series of compounds were designed as T-type calcium channel blocker containing 6 or 5 pharmacophore features from structure-based virtual screening. To optimize the suggested structure, over 130 derivatives were synthesized and their inhibitory activities on T-type calcium channel were assayed using in vitro screening system with α1_G and α1_H clones. For the compounds with higher activities in FDSS assay system, the efficacy was measured by patch–clamp method. Among the library with 5 features, alkaneamide derivatives (7b, 9j, 11b, 11g, 11h) with 4-arylsubstituted piperazine showed better IC₅₀ values than Mibefradil.

Graphical abstract

Novel series of piperazine derivatives with hypothetical pharmacophoric features were prepared and evaluated for T-type calcium channel (α1_G) by FDSS assay and patch clamp method. Among them, alkanamide derivatives with 4-arylsubstituted piperazine (7b, 9j, 11b, 11g, 11h) showed better efficacy than Mibefradil.

Introduction

Voltage-gated calcium channels are transmembrane proteins involved in the regulation of calcium influx in a number of cell types.1, 2 A number of different types of calcium channels have been identified in native tissues and divided into various categories based on functional and pharmacological criteria.3, 4 High-voltage-activated (HVA) channels which can be subdivided further into L-, N-, P/Q-, and R-types5, 6 require strong depolarization for activation, whereas low-voltage-activated or T-type (transient) channels first activate at relatively more negative voltage range and rapidly inactivate.7, 8, 9 The main structural component of the voltage-gated calcium channel is the α₁ subunit, which forms the pore and the channel gate. So far, 10 α₁ subunits have been identified by molecular cloning. α_1A–α_1E and α_1S encode HVA channels Ca²⁺, whereas α_1G–α_1I encode T-type channels. Pharmacological agents that have selective activity on α₁ subtypes have been key in studying calcium channel function in physiological systems, but a selective antagonist of T-type calcium channel is not yet available. Mibefradil, which blocks T-type Ca²⁺ channels at concentration lower than that needed to block L-type Ca²⁺ channels,10, 11 appeared to be a promising drug for the treatment of hypertension, and angina pectoris.12, 13, 14 Unfortunately, the drug had to be withdrawn by the manufacturer due to its interaction with the cytochrome P-450 3A4 enzyme, an effect unrelated to T-type Ca²⁺ channel blockade. T-type Ca²⁺ channels participate in cardiac pacemaking,¹⁵ regulation of vascular tone and hormone secretion.16, 17 Involvement of T-type Ca²⁺ channels in cell growth and proliferation has been proposed.¹⁸ The distribution and properties of T-type Ca²⁺ channels have been reported to be altered in pathophysiological conditions such as ventricular hypertrophy19, 20 and cardiomyopathy.²¹ Thus, T-type Ca²⁺ channels are now considered to be novel therapeutic targets for the treatment of various cardiovascular disorders such as heart failure, arrhythmia, and hypertension and neuronal disorders such as epilepsy and pain. Even with these properties as promising drug target, the speed of development is surprisingly slow compared to other areas. It is because of non-availability of X-ray structure and existence of several subtypes of the channel. To obtain a lead compound as a T-type calcium channel blocker, the strategy we used involved the pharmacophore model generated from structure-based virtual screening and hypothetical mapping with the designed structure.

The first set of compounds with 6 pharmacophore features (5) was prepared and their activities were assayed with calcium imaging screening system. Disappointingly, they showed weaker activity than mibefradil. Then we need to understand the relative importance of the pharmacophores by comparing the activities of the compounds with 5 features without one hydrogen bond acceptor or the linker carbon length is varied. The 2nd set of libraries (7, 13, 15) in which the number and position of the proposed features were varied have been designed and synthesized. The synthetic procedure of the compounds with 5 features without one carbonyl group was simplified and the library was easily prepared. The FDSS results of this library showed relatively better activity than that of the compounds with initial 6 features. The 3rd set of libraries (9, 11, 17, 19, 21) in which the number of rotatable carbon and halogen of aniline moiety are varied were prepared. The in vitro screening assays to figure out the selectivity and hERG channel blocking activity are still going on.

Section snippets

Chemistry

The synthesis of suggested compound which generated from statistically best 6-pharmacophore features hypothesis was not successful. Then it was modified to fit the 6-features (Fig. 1) and increase conformational rigidity.

A series of compounds with 6 features were prepared by routine procedures shown in Scheme 1. To obtain the derivatives easily, the common intermediates from aniline moiety were used as starting material and the piperazine derivatives were introduced at final step. All the steps

Materials and methods

All commercially available chemicals were of reagent grade and used as purchased unless stated otherwise. All reactions were performed under an inert atmosphere of dry argon or nitrogen using distilled dry solvents. Reactions were monitored by TLC analysis using Merck silica gel 60 F-254 thin layer plates. Flash column chromatography was carried out on Merck silica gel 60 (230–400 mesh) by preparative LC system. ¹H and ¹³C NMR spectra were recorded on a spectrometer operating at Bruker 400 and

Acknowledgments

We thank to Prof. Sang-gi Lee and Dr. Bang Sook Lee in Ewha Women’s University and Min Jung Park for their contribution in this work. We also acknowledge Prof. Jung-Ha Lee’s group in Sogang University for biological assay of compounds (5a–f). This study was supported by Vision 21 Program (2E 18970) and National Research Laboratory Program (2E 19310) from Korea Institute of Science and Technology.

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Lead discovery and optimization of T-type calcium channel blockers

Abstract

Graphical abstract

Introduction

Section snippets

Chemistry

Materials and methods

Acknowledgments

Trends Pharmacol. Sci.

Trends Neurosci.

Cell Calcium

Clin. Ther.

Bioorg. Med. Chem.

Biochem. Biophys. Res. Commun.

Bioorg. Med. Chem. Lett.

Science

Nature

Voltage-gated calcium channels

Drug Dev. Res

Science