Effect of a novel histamine H2 receptor antagonist, IT-066, on acute gastric injury induced by ischemia-reperfusion in rats, and its antioxidative properties

Oxocarbon Acids and their Derivatives in Biological and Medicinal Chemistry

The biological and medicinal chemistry of the oxocarbon acids 2,3- dihydroxycycloprop-2-en-1-one (deltic acid), 3,4-dihydroxycyclobut-3-ene-1,2-dione (squaric acid), 4,5-dihydroxy-4-cyclopentene-1,2,3-trione (croconic acid), 5,6-dihydroxycyclohex- 5-ene-1,2,3,4-tetrone (rhodizonic acid) and their derivatives is reviewed and their key chemical properties and reactions are discussed. Applications of these compounds as potential bioisosteres in biological and medicinal chemistry are examined. Reviewed areas include cell imaging, bioconjugation reactions, antiviral, antibacterial, anticancer, enzyme inhibition, and receptor pharmacology.

Palladium-Catalyzed Domino Reaction for the Assembly of Norbornane-Containing Chromones with Dimethyl Squarate as the Solid C1 Source

Reported herein is a novel palladium-catalyzed [2 + 2 + 1] domino annulation of 3-iodochromones, bridged olefins, and dimethyl squarate allowing the construction of chromone-containing polycyclic compounds in good to high yields. Importantly, dimethyl squarate is first employed as the solid C1 source in organic synthesis. Gram-scale experiments, late-stage modification of natural products, as well as transformations of products show potential for further synthetic elaborations.

Squaric acid analogues in medicinal chemistry

In this review, we summarize the published data on squaric acid analogues with a special focus on their use in medicinal chemistry and as potential drugs. Squaric acid is an interesting small molecule with an almost perfectly square shape, and its analogues have a variety of biological activities that are enabled by the presence of significant H-bond donors and acceptors. Unfortunately, most of these compounds also exhibit reactive functionalities, and this deters the majority of medicinal chemists and pharmacologists from trying to use them in drug development. However, this group of compounds is experiencing a renaissance, and large numbers of them are being tested for antiprotozoal, antibacterial, antifungal, and antiviral activities. The most useful of these compounds exhibited IC₅₀ values in the nanomolar range, which makes them promising drug candidates. In addition to these activities, their interactions with living systems were intensively explored, revealing that squaric acid analogues inhibit various enzymes and often serve as receptor antagonists and that the squaric acid moiety may be used as a non-classical isosteric replacement for other functional groups such as carboxylate. In summary, this review is focused on squaric acid and its analogues and their use in medicinal chemistry and should serve as a guide for other researchers in the field to demonstrate the potential of these compounds based on previous research.

Experimental (13C NMR, 1H NMR, FT-IR, single-crystal X-ray diffraction) and DFT studies on 3,4-bis(isoproylamino)cyclobut-3-ene-1,2-dione

In this work, 3,4-bis(isoproylamino)cyclobut-3-ene-1,2-dione C(10)H(16)N(2)O(2) (I), was synthesized and characterized by (13)C NMR, (1)H NMR, FT-IR, UV-vis spectroscopy and single-crystal X-ray diffraction. DFT method with 6-31G(d,p) basis set has been used to calculate the optimized geometrical parameters, atomic charges, vibrational frequencies and chemical shift values. The calculated vibrational frequencies and chemical shift values are compared with experimental FT-IR and NMR spectra. The results of the calculation shows good agreement between experimental and calculated values of the compound I. The existence of N-H⋯O type intermolecular ve C-H⋯O type intramolecular hydrogen bonds can be deduced from differences between experimental and calculated results of FT-IR and NMR. In addition, the molecular electrostatic potential map and frontier molecular orbitals and electronic absorption spectra were performed at B3LYP/6-31G(d,p) level of theory. HOMO-LUMO electronic transition of 4.90 eV are derived from the contribution of the bands π→π* and n→π* The spectral results obtained from FT-IR, NMR and X-ray of I revealed that the compound I is in predominantly enamine tautomeric form, which was supported by DFT calculations.

Oxidative stress and ischemia-reperfusion injury in gastrointestinal tract and antioxidant, protective agents

Exacerbation of hypoxic injury after reoxygenation is a crucial mechanism mediating organ injury in transplantation, and in myocardial, hepatic, gastrointestinal, cerebral, renal, and other ischemic syndromes. The occlusion and reperfusion of the splanchnic artery is a useful animal model to elucidate the mechanism of gastrointestinal injury induced by ischemia-reperfusion (I/R). Although xanthine oxidase is a major source of reactive oxygen species (ROS), which plays an important role in the I/R-induced intestinal injury, there are many other sources of intracellular ROS. Various treatment modalities have been successfully applied to attenuate the I/R injury in animal models. This review focuses on the role of oxidant stress in the mechanism of I/R injury and the use of antioxidant agents for its treatment.

Molecular Structure, Infrared Spectrum, and Photochemistry of Squaric Acid Dimethyl Ester in Solid Argon

Squaric acid dimethyl ester (C(6)O(4)H(6); 3,4-dimethoxycyclobut-3-ene-1,2-dione; DCD) was studied by matrix isolation infrared spectroscopy and by density functional theory (B3LYP) and ab initio (MP2) calculations with the 6-31++G(d,p) and 6-311++G(d,p) basis sets. Three conformers of the compound were theoretically predicted. The two most stable conformers were identified in low-temperature argon matrixes and the energy gap between them was determined. The trans-trans conformer (C(2)(v)) was found to be more stable than the cis-trans form (C(s)) by 4.2 kJ mol(-1), in consonance with the theoretical predictions (MP2 calcd = 3.9 kJ mol(-1)). In situ broadband UV irradiation (lambda > 337 nm) of the matrix-isolated compound was found to induce the ring-opening reaction leading to production of the bisketene, 2,3-dimethoxybuta-1,3-diene-1,4-dione as well as the trans-trans --> cis-trans conformational isomerization. The latter phototransformation allowed separation of the infrared spectra of the two conformers initially trapped into a low-temperature matrix. Upon higher energy irradiation (lambda > 235 nm), the main observed photoproducts were CO and deltic acid dimethyl ester (C(5)O(3)H(6); 2,3-dimethoxycycloprop-2-en-1-one), the latter being obtained in two different conformations (trans-trans and cis-trans). According to the experimental data, deltic acid dimethyl ester is produced by decarbonylation of the initially formed bisketene and not by direct CO extrusion from DCD.

Role of nitric oxide and prostaglandin in the protective effect of pibutidine hydrochloride, a novel histamine H2-receptor antagonist, on the gastric mucosal lesions in rats

1. The role of endogenous nitric oxide (NO) and prostaglandins (PGs) in the gastric mucosal protective action of pibutidine hydrochloride (IT-066), a novel histamine H2-receptor antagonist, was investigated in a 0.15 N hydrochloride (HCl) + 60% ethanol (EtOH)-induced gastric lesion model. 2. The 0.15 N HCl + 60% EtOH-induced lesion formation was reduced significantly by IT-066 (3 mg/kg, PO), NOR3 (spontaneous NO releaser; 0.03-0.1 mg/kg, SC) or PGE2 (0.01 mg/kg, PO) but was not reduced by famotidine (1-10 mg/kg, PO). 3. Pretreatment with NG-nitro-L-arginine methyl ester (L-NAME) (3 mg/kg, IV), an inhibitor of NO synthase, inhibited the protective action of IT-066 (3 mg/kg, PO), and the inhibitory effect of L-NAME was reversed by L-arginine (300 mg/kg, IV). The protective effect of PGE2 (0.01 mg/kg, PO) was not affected by the pretreatment with L-NAME (3 mg/kg, IV). 4. Infusion of carboxy-PTIO (1 mg/kg/min), a direct NO scavenger, inhibited the protective effect of IT-066 (3 mg/kg, SC) or NOR3 (0.1 mg/kg, SC). Pretreatment with indomethacin (5 mg/kg, SC) markedly reduced the protective effect of IT-066 (3 mg/kg, PO) or NOR3 (0.1 mg/kg, SC). 5. These results suggest that endogenous NO and PGs may be implicated in the gastric mucosal protection induced by IT-066 and that the endogenous PGs may contribute to the protective effect of NO.

Neutrophils, lipid peroxidation, and nitric oxide in gastric reperfusion injury in rats

Nitric oxide (NO) modulation of ischemia-reperfusion injury was investigated by measuring lipid peroxide and neutrophil accumulation in rat stomachs treated with NG-nitro-L-arginine (L-NNA), a specific NO synthase inhibitor. Ischemia-reperfusion injury was induced in the rat stomach. Treatment with L-NNA for 3 days at a dose of 3 mg/kg/day significantly enhanced this injury. This enhancement was reversed by the simultaneous administration of L-arginine at a dose of 30 mg/kg/day. Both thiobarbituric acid (TBA)-reactive substances, an index of lipid peroxidation, and myeloperoxidase (MPO) activity, an index of tissue-associated neutrophil accumulation, were increased in the gastric mucosa after ischemia-reperfusion. L-NNA treatment enhanced these increases in TBA-reactive substances and MPO activity. The increase in the area of gastric erosions correlated closely with accumulation of TBA-reactive substances as well as the increase in MPO activity. Enhancement of ischemia-reperfusion injury by L-NNA treatment was inhibited by injection with anti-neutrophil antibody, anti-platelet activating factor (PAF) antagonist, and anti-leukotriene B4 (LTB4) receptor antagonist. In addition, the increase in TBA-reactive substances and MPO activity was decreased by these antibodies or antagonists. Enhancement of reperfusion-induced gastric mucosal injury associated with inhibition of NO synthesis may involve neutrophil infiltration and lipid peroxide accumulation in the gastric mucosa, mediated by PAF and LTB4.

Effect of plaunotol on gastric injury induced by ischaemia-reperfusion in rats

Plaunatol, an anti-ulcer drug, increases prostaglandin content in gastric tissue but its effect on radical-mediated gastric damage or activity against reactive oxygen species is unknown. We examined the effects of oral administration of plaunotol (Kelnac) on the acute gastric mucosal lesion and its progression to ulcer lesion induced by ischaemia-reperfusion in rats. Plaunotol (30 and 100 mg kg-1, 15 min before ischaemia) significantly reduced the total erosion area observed immediately after ischaemia-reperfusion. When plaunotol (30 and 100 mg kg-1, once a day) was administrated orally 60 min after reperfusion, it prevented the progression from erosion to ulcer. At 72 h after ischaemia-reperfusion, the total area of ulcers lesions was significantly reduced compared with that without plaunotol administration. Furthermore, treatment with plaunotol (100 mg kg-1) significantly increased prostaglandin E2 content in gastric tissues of both acute gastric mucosal lesion and gastric ulcer lesion. In in-vitro experiments, plaunotol (1-3 mg mL-1) reduced the superoxide radicals generated by leucocytes, but not by xanthine oxidase. These results indicate that plaunotol has protective effects on both the onset of acute gastric mucosal injury and its progression to ulcer lesion induced by ischaemia-reperfusion. Both effects of plaunotol on increase in prostaglandin content in gastric tissues and inhibition of superoxide radical from leucocytes may play important roles on the protection against gastric mucosal injury.