Chloro-substituted 3-alkylamino-4H-1,2,4-benzothiadiazine 1,1-dioxides as ATP-sensitive potassium channel activators: impact of the position of the chlorine atom on the aromatic ring on activity and tissue selectivity

Cascade [4 + 1] Annulation through Activation of the C(sp2)-H Bond Enabling Benzothiadiazinoisoindolcarboxylate, Benzothiadiazinoisoindole, and Benzothiadiazinoisoindolepyrrolidinedione as Hybrid Spiro-Heterocyclic Frameworks†

Two structurally distinct and biologically privileged succinimide and isoindole heteroarenes bearing benzothiadiazinedioxide motif-centered hybrid conjugates are proficiently achieved through Rh(III)-catalyzed sequential C(sp2)-H bond activation, ortho-alkenylation and finally cascade intramolecular cyclization. The significant feature of this developed protocol is that the resulting diversely decorated heterocycles contain a quaternary carbon center and this has been coursed through atypical [4 + 1] annulation ignoring the prevalent [4 + 2]-cyclization pathway and interestingly the applied coupling partners (e.g., maleimide, maleate, and styrene) to materialize the protocol functioned only as C1 synthon. Furthermore, the selective reduction strategy enables to modify the hybrid conjugate of succinimide and benzothiazine dioxide to benzothiazine dioxide-based spirocyclic isoindolopyrrolidinedione skeleton following preferential reduction of one carbonyl group of imide functionality. Overall this methodology emerges to be easily handled, versatile, time-efficient, and manifests relatively unfamiliar spiro-cyclization and good functional group tolerance so easy to grab a library of the entirely new variant of decorated hybrid spiro-heterocyclic scaffolds.

Discovery of a Novel Benzothiadiazine-Based Selective Aldose Reductase Inhibitor as Potential Therapy for Diabetic Peripheral Neuropathy

Aldose reductase 2 (ALR2), an activated enzyme in the polyol pathway by hyperglycemia, has long been recognized as one of the most promising targets for complications of diabetes, especially in diabetic peripheral neuropathy (DPN). However, many of the ALR2 inhibitors have shown serious side effects due to poor selectivity over aldehyde reductase (ALR1). Herein, we describe the discovery of a series of benzothiadiazine acetic acid derivatives as potent and selective inhibitors against ALR2 and evaluation of their anti-DPN activities in vivo. Compound 15c, carrying a carbonyl group at the 3-position of the thiadiazine ring, showed high potent inhibition against ALR2 (IC50 = 33.19 nmol/L) and ∼16,109-fold selectivity for ALR2 over ALR1. Cytotoxicity assays ensured the primary biosafety of 15c. Further pharmacokinetic assay in rats indicated that 15c had a good pharmacokinetic feature (t1/2 = 5.60 h, area under the plasma concentration time curve [AUC(0-t)] = 598.57 ± 216.5 μg/mL * h), which was superior to epalrestat (t1/2 = 2.23 h, AUC[0-t] = 20.43 ± 3.7 μg/mL * h). Finally, in a streptozotocin-induced diabetic rat model, 15c significantly increased the nerve conduction velocities of impaired sensory and motor nerves, achieved potent inhibition of d-sorbitol production in the sciatic nerves, and significantly increased the paw withdrawal mechanical threshold. By combining the above investigations, we propose that 15c might represent a promising lead compound for the discovery of an antidiabetic peripheral neuropathy drug.

ARTICLE HIGHLIGHTS

Rhodium-Catalyzed Annulations and Heck Coupling/Aza-Michael Addition for the Synthesis of Benzothiadiazinoisoquinoline 6,6-Dioxides and Benzothiadiazinoisoindole 5,5-Dioxides, Respectively

A new and efficient protocol has been demonstrated for the synthesis of benzothiadiazinoisoquinoline 6,6-dioxides and benzothiadiazinoisoindole 5,5-dioxides in good to excellent yields. These compounds are formed through a sequential Rh(III)-catalyzed C-H cyclization of dihydrophenylbenzothiadiazine 1,1-dioxides with alkynes and oxidative Heck coupling/aza-Michael addition of dihydrophenylbenzothiadiazine 1,1-dioxides with acrylates, respectively.

Synthetic approaches and pharmaceutical applications of chloro-containing molecules for drug discovery: A critical review

At present more than 250 FDA approved chlorine containing drugs were available in the market and many pharmaceutically important drug candidates in pre-clinical trials. Thus, it is quite obvious to expect that in coming decades there will be an even greater number of new chlorine-containing pharmaceuticals in market. Chlorinated compounds represent the family of compounds promising for use in medicinal chemistry. This review describes the recent advances in the synthesis of chlorine containing heterocyclic compounds as diverse biological agents and drugs in the pharmaceutical industries for the inspiration of the discovery and development of more potent and effective chlorinated drugs against numerous death-causing diseases.

Direct activation of β-cell KATP channels with a novel xanthine derivative

ATP-regulated potassium (KATP) channel complexes of inward rectifier potassium channel (Kir) 6.2 and sulfonylurea receptor (SUR) 1 critically regulate pancreatic islet β-cell membrane potential, calcium influx, and insulin secretion, and consequently, represent important drug targets for metabolic disorders of glucose homeostasis. The KATP channel opener diazoxide is used clinically to treat intractable hypoglycemia caused by excessive insulin secretion, but its use is limited by off-target effects due to lack of potency and selectivity. Some progress has been made in developing improved Kir6.2/SUR1 agonists from existing chemical scaffolds and compound screening, but there are surprisingly few distinct chemotypes that are specific for SUR1-containing KATP channels. Here we report the serendipitous discovery in a high-throughput screen of a novel activator of Kir6.2/SUR1: VU0071063 [7-(4-(tert-butyl)benzyl)-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione]. The xanthine derivative rapidly and dose-dependently activates Kir6.2/SUR1 with a half-effective concentration (EC50) of approximately 7 μM, is more efficacious than diazoxide at low micromolar concentrations, directly activates the channel in excised membrane patches, and is selective for SUR1- over SUR2A-containing Kir6.1 or Kir6.2 channels, as well as Kir2.1, Kir2.2, Kir2.3, Kir3.1/3.2, and voltage-gated potassium channel 2.1. Finally, we show that VU0071063 activates native Kir6.2/SUR1 channels, thereby inhibiting glucose-stimulated calcium entry in isolated mouse pancreatic β cells. VU0071063 represents a novel tool/compound for investigating β-cell physiology, KATP channel gating, and a new chemical scaffold for developing improved activators with medicinal chemistry.

An odorless, one-pot synthesis of nitroaryl thioethers via SNAr reactions through the in situ generation of S-alkylisothiouronium salts

The synthesis of nitroaryl thioethers using thiourea as the sulfur source in water by an odorless one-pot process was disclosed.

1,4,2-Benzo/pyridodithiazine 1,1-dioxides structurally related to the ATP-sensitive potassium channel openers 1,2,4-Benzo/pyridothiadiazine 1,1-dioxides exert a myorelaxant activity linked to a distinct mechanism of action

The synthesis of diversely substituted 3-alkyl/aralkyl/arylamino-1,4,2-benzodithiazine 1,1-dioxides and 3-alkylaminopyrido[4,3-e]-1,4,2-dithiazine 1,1-dioxides is described. Their biological activities on pancreatic β-cells and on smooth muscle cells were compared to those of the reference ATP-sensitive potassium channel (KATP channel) openers diazoxide and 7-chloro-3-isopropylamino-4H-1,2,4-benzothiadiazine 1,1-dioxide. The aim was to assess the impact on biological activities of the replacement of the 1,2,4-thiadiazine ring by an isosteric 1,4,2-dithiazine ring. Most of the dithiazine analogues were found to be inactive on the pancreatic tissue, although some compounds bearing a 1-phenylethylamino side chain at the 3-position exerted a marked myorelaxant activity. Such an effect did not appear to be related to the opening of KATP channels but rather reflected a mechanism of action similar to that of calcium channel blockers. Tightly related 3-(1-phenylethyl)sulfanyl-4H-1,2,4-benzothiadiazine 1,1-dioxides were also found to exert a pronounced myorelaxant activity, resulting from both a KATP channel activation and a calcium channel blocker mechanism. The present work highlights the critical importance of an intracyclic NH group at the 4-position, as well as an exocyclic NH group linked to the 3-position of the benzo- and pyridothiadiazine dioxides, for activity on KATP channels.

Facile synthesis of benzothiadiazine 1,1-dioxides, a precursor of RSV inhibitors, by tandem amidation/intramolecular aza-Wittig reaction

Reaction of o-azidobenzenesulfonamides with ethyl carbonochloridate afforded the corresponding amide derivatives, which gave 3-ethoxy-1,2,4-benzothiadiazine 1,1-dioxides through an intramolecular aza-Wittig reaction. The reaction was found to be general through the synthesis of a number of benzothiadiazine 1,1-dioxides. Acid-catalyzed hydrolysis of 3-ethoxy-1,2,4-benzothiadiazine 1,1-dioxides furnished the 2-substituted benzothiadiazine-3-one 1,1-dioxides in good yields and high purity, which is the core moiety of RSV inhibitors.

Structural nucleotide analogs are potent activators/inhibitors of pancreatic β cell KATP channels: an emerging mechanism supporting their use as antidiabetic drugs

The 2H-1,4-benzoxazine derivatives are novel drugs structurally similar to nucleotides; however, their actions on the pancreatic β cell ATP-sensitive K+ (KATP) channel and on glucose disposal are unknown. Therefore, the effects of the linear/branched alkyl substituents and the aliphatic/aromatic rings at position 2 of the 2H-1,4-benzoxazine nucleus on the activity of these molecules against the pancreatic β cell KATP channel and the Kir6.2ΔC36 subunit were investigated using a patch-clamp technique. The effects of these compounds on glucose disposal that followed glucose loading by intraperitoneal glucose tolerance test and on fasting glycemia were investigated in normal mice. The 2-n-hexyl analog blocked the KATP (IC₅₀ = 10.1 × 10⁻⁹ M) and Kir6.2ΔC36 (IC₅₀ = 9.6 × 10⁻⁹ M) channels, which induced depolarization. In contrast, the 2-phenyl analog was a potent opener (drug concentration needed to enhance the current by 50% = 0.04 × 10⁻⁹ M), which induced hyperpolarization. The ranked order of the potency/efficacy of the analog openers was 2-phenyl > 2-benzyl > 2-cyclohexylmethyl. The 2-phenylethyl and 2-isopropyl analogs were not effective as blockers/openers. The 2-n-hexyl (2-10 mg/kg) and 2-phenyl analogs (2-30 mg/kg) reduced and enhanced the glucose areas under the curves, respectively, after glucose loading in mice. These compounds did not affect the fasting glycemia as is observed with glibenclamide. The linear alkyl chain and the aromatic ring at position 2 of the 1,4-benzoxazine nucleus are the determinants, which confer the KATP channel blocking action with glucose-lowering effects and the opening action with increased glucose levels, respectively. The opening/blocking actions of these compounds mimic those that were observed with ATP and ADP. The results support the use of these compounds as novel antidiabetic drugs.

Recent advances in drug discovery of benzothiadiazine and related analogs as HCV NS5B polymerase inhibitors

Hepatitis C virus (HCV) is a major health burden, with an estimated 170 million chronically infected individuals worldwide, and a leading cause of liver transplantation. Patients are at increased risk of developing liver cirrhosis, hepatocellular carcinoma and even liver failure. In the past two decades, several approaches have been adopted to inhibit non-structural viral proteins. The RNA-dependent RNA polymerase (NS5B) of HCV is one of the attractive validated targets for development of new drugs to block HCV infection. In this review, we report the recent progress made towards identifying and developing benzothiadiazines as HCV NS5B polymerase inhibitors. The substituted benzothiadiazine class was identified by HTS in 2002 as an NS5B inhibitor. Further optimization and modification of the core has improved the potency and pharmacokinetic properties of substituted benzothiadiazines. Research on palm site-binding benzothiadiazine analogs and related derivatives and analogs is discussed in this article.

Thiourea isosteres as anion receptors and transmembrane transporters

Compounds containing cyanoguanidine and 3-amino-1,2,4-benzothiadiazine-1,1-dioxide have been studied as anion receptors and transporters. Significant affinity for oxo-anions was observed in organic solution and the receptors were found to function as transmembrane chloride/nitrate antiporters with transport rates enhanced in the presence of valinomycin-K(+) complex.

Impact of the nature of the substituent at the 3-position of 4H-1,2,4-benzothiadiazine 1,1-dioxides on their opening activity toward ATP-sensitive potassium channels

The synthesis of diversely substituted 3-isopropoxy-, 3-isopropylsulfanyl-, 3-isopropylsulfinyl-, and 3-isobutyl-4H-1,2,4-benzothiadiazine 1,1-dioxides is described. Their activity on pancreatic β-cells (inhibitory effect on the insulin releasing process) and on vascular and uterine smooth muscle tissues (myorelaxant effects) was compared to that of previously reported K(ATP) channel openers belonging to 3-isopropylamino-4H-1,2,4-benzothiadiazine 1,1-dioxides. The present study aimed at evaluating the impact on biological activity of the isosteric replacement of the NH group of 3-alkylamino-4H-1,2,4-benzothiadiazine 1,1-dioxides by a O, S, S(═O), or CH(2) group. By comparing compounds bearing identical substituents, the following rank order of potency on pancreatic β-cells was observed: 3-isopropylamino > 3-isobutyl > 3-isopropoxy > 3-isopropylsulfanyl > 3-isopropylsulfinyl-substituted 4H-1,2,4-benzothiadiazine 1,1-dioxides (NH > CH(2) > O > S > S(═O)). A molecular modeling study revealed that 3-isopropoxy-, 3-isopropylsulfanyl-, and 3-isopropylamino-substituted compounds adopted a similar low-energy conformation (preferred orientation of the isopropyl chain). Moreover, no direct relationship was detected between the conformational freedom of the different classes of benzothiadiazines (from the most to the lowest conformationally constrained compounds: NH > O > S > CH(2)) and their biological activity on insulin-secreting cells. Therefore, the present study confirmed the critical role of the NH group at the 3-position for the establishment of a strong hydrogen bond responsible for optimal activity expressed by 3-alkylamino-4H-1,2,4-benzothiadiazine 1,1-dioxides on insulin-secreting cells. Radioisotopic and fluorimetric experiments conducted with 7-chloro-3-isopropoxy-4H-1,2,4-benzothiadiazine 1,1-dioxide 10c demonstrated that such a compound, bearing a short branched O-alkyl group instead of the NH-alkyl group at the 3-position, also behaved as a specific K(ATP) channel opener. Lastly, the present work further identified 3-(alkyl/aralkyl)sulfanyl-substituted 7-chloro-4H-1,2,4-benzothiadiazine 1,1-dioxides as a class of promising myorelaxant drugs acting on uterine smooth muscles, at least in part, through the activation of K(ATP) channels.

Discovery of orally available spirodiketopiperazine-based CCR5 antagonists

Using the previously reported novel spirodiketopiperazine scaffold, the design and synthesis of orally available CCR5 antagonists was undertaken. Compounds possessing a carboxylic acid function in the appropriate position showed improved oral exposure (AUC) relative to the initial chemical leads without reduction in the antagonist activity. The optimized compound 40 was found to show potent anti-HIV activity. Full details of structure-activity relationship (SAR) study are presented.