2-Alkynyl-8-aryladenines possessing an amide moiety: their synthesis and structure-activity relationships of effects on hepatic glucose production induced via agonism of the A(2B) adenosine receptor

A series of 2-alkynyl-8-aryladenine derivatives bearing an amide moiety at the 9-position of adenine was synthesized. These analogues were evaluated for inhibitory activity on N-ethylcarboxamidoadenosine (NECA)-induced glucose production in primary cultured rat hepatocytes. The m-primary benzamide derivative 15f was the most potent compound (IC(50)=0.017 microM), being 15-fold more active than the corresponding 9-methyl derivative (1). Compound 15f showed 72- and 5.2-fold selectivity for human A(2B) receptor versus human A(1) and A(2A) receptors, respectively. Structure-activity relationship (SAR) studies of the synthesized compounds indicated that a three-carbon linker, fixed in the form of a benzene ring, between the adenine core and the amide moiety is important for both A(2B) antagonistic activity and selectivity. The IC(50) values in rat hepatocyte glucose assay correlated well with the IC(50) values in cAMP assay using Chinese hamster ovary cells stably transfected with human A(2B) receptors (r(2)=0.94). The A(1) and A(2A) affinities showed no correlation with the potency to inhibit NECA-induced glucose production. These results strongly support our previous conclusion that adenosine agonist-induced hepatic glucose production in rat hepatocytes is mediated through the A(2B) receptor.

2-Alkynyl-8-aryl-9-methyladenines as novel adenosine receptor antagonists: their synthesis and structure-activity relationships toward hepatic glucose production induced via agonism of the A(2B) receptor

Novel adenosine antagonists, 2-alkynyl-8-aryl-9-methyladenine derivatives, were synthesized as candidate hypoglycemic agents. These analogues were evaluated for inhibitory activity on N-ethylcarboxamidoadenosine (NECA)-induced glucose production in primary cultured rat hepatocytes. In general, aromatic moieties at the 8-position and alkynyl groups at the 2-position had significantly increased activity compared to unsubstituted compounds. The preferred substituents at the 8-position of adenine were the 2-furyl and 3-fluorophenyl groups. In modifying the alkynyl side chain, change of the ring size, cleavage of the ring, and removal of the hydroxyl group were well tolerated. The order of the stimulatory effects of adenosine agonists on rat hepatocytes was NECA > CPA > CGS21680, which is consistent with involvement of the A(2B) receptor. In Chinese hamster ovary cells stably transfected with human A(2B) receptor cDNA, one of the compounds potent in hepatocytes, 15o (IC(50) = 0.42 microM), antagonized NECA-induced stimulation of cyclic AMP production (IC(50) = 0.063 microM). This inhibitory effect was much more potent than those of FK453, KF17837, and L249313 which have been reported to be respectively A(1), A(2A), and A(3) selective antagonists. These findings agree very well with the result that, compared to 15o, these selective antagonists for each receptor subtype showed only marginal effects in rat hepatocytes. These results suggest that adenosine agonist-induced glucose production in rat hepatocytes is mediated through the A(2B) receptor. Furthermore, 15o showed hypoglycemic activity in an animal model of noninsulin-dependent diabetes mellitus, the KK-A(y) mice. It is possible that inhibition of hepatic glucose production via the A(2B) receptor could be at least one of the mechanisms by which 15o exerts its in vivo effects. Further elaboration of this group of compounds may afford novel antidiabetic agents.

[Effects of E3123 on pancreatic injury in the isolated, perfused rat pancreas and in a pancreatic slice]

We studied the effect of E3123 on pancreatic injury induced in the isolated, perfused pancreas or in a pancreatic slice. Exposure of the isolated, perfused rat pancreas to trypsin-taurocholate or phospholipase A2 caused the leakage of pancreatic enzyme (lipase) into the perfusate. In trypsin-taurocholate-induced pancreatic injury, E3123 and nafamostat mesilate suppressed the leakage of lipase at concentrations of 0.1-1 microM and 1-10 microM, respectively. In phospholipase A2 induced pancreatic injury, E3123 at 10 microM significantly suppressed the enzyme leakage, and nafamostat mesilate had a weak suppressive effect. Exposure of a rat pancreatic slice to phospholipase A2 also caused the leakage of pancreatic enzyme, while the inhibition of enzyme leakage by E3123 was similar to that observed in the isolated, perfused pancreas; nafamostat mesilate was not effective. This finding suggests the possible involvement of a unique mechanism of action in the protection against pancreatic injury by E3123. Therefore, we studied the effect of E3123 on hemolysis by osmotic shock using rat red blood cells. E3123 demonstrated a potent protective effect against the hemolysis, suggesting that a membrane-stabilizing action may contribute to the protection E3123 affords against pancreatic injury.

Pharmacological activities of a novel thienodiazepine derivative as a platelet-activating factor antagonist. Effects on microvascular permeability, hypotension and nephrosis

The effects of a newly synthesized platelet-activating factor (PAF) antagonist, (S)-(+)-6-(2-chlorophenyl)-3-cyclopropanecarbonyl-8,11- dimethyl-2,3,4,5-tetrahydro-8H-pyrido[4',3':4,5]thieno[3,2-f] [1,2,4]triazolo[4,3-a][1,4]diazepine (E-6123, CAS 131614-02-3) on microvascular permeability, systemic hypotension and nephrosis were investigated. E-6123 inhibited PAF injection-induced microvascular permeability (edema) in guinea pigs after oral administration at 3 micrograms/kg. The inhibitory effects of E-6123 were very potent compared to those of other PAF antagonists. E-6123 reversed PAF and/or endotoxin injection-induced hypotension in rats after intravenous administration at 3 micrograms/kg. The increase in urinary protein excretion of rats in which nephrosis had been induced by intraperitoneal injection of aminonucleoside was not inhibited by oral administration of E-6123 at 10 mg/kg/d.

Inhibitory effects of the novel platelet activating factor receptor antagonist, 1-ethyl-2-[N-(2-methoxy)benzoyl-N-[(2R)-2-methoxy-3-(4- octadecylcarbamoyloxy) piperidinocarbonyloxypropyloxy]carbonyl] aminomethyl-pyridinium chloride, in several experimentally induced shock models

E5880 (1-ethyl-2-[N-(2-methoxy)benzoyl-N-[(2R)-2-methoxy-3-(4- octadecylcarbamoyloxy) piperidinocarbonyloxypropyloxy] carbonyl]aminomethylpyridinium chloride, CAS 128420-61-1) is a novel analog-type antagonist of platelet activating factor (PAF). This paper describes the in vitro PAF antagonistic activity of E5880 and its in vivo effect in various experimentally induced shock models. Inhibition by E5880 of [3H]platelet activating factor (PAF) binding to human platelet PAF receptor was extremely potent; its IC50 value was 0.27 nmol/l, so that it was about 5 times more potent than PAF itself. Its IC50 value in inhibition of washed human platelet aggregation induced by PAF was 0.66 nmol/l. Intravenous treatment with E5880 dose-dependently reversed PAF-induced hypotension in rats and protected mice from lethality caused by PAF. Lipopolysaccharide (LPS)-induced hypotension in rats was inhibited by both pre- and post-treatment with E5880. It was also confirmed that blood PAF level, measured by the GC-NICI-MS method, was increased after LPS challenge in this model. Furthermore, E5880 was extremely effective in preventing passive anaphylactic lethality in mice. Blood PAF level in this model was also increased immediately after antigen challenge, and this was coincident with the time at which signs of shock became apparent. These findings support the concept that PAF is an important mediator in the development of LPS-induced shock and anaphylactic shock, and suggest that E5880, a novel and potent PAF antagonist, may be effective in clinical treatment for shock states.

Further studies on the determinant role of brain level of pentobarbital for the development of acute hypnotic tolerance

Controlling the brain level of pentobarbital and the duration of hypnosis at the initial treatment in relation to development of acute hypnotic tolerance was studied. Simultaneous treatment of bemegride or TRH with pentobarbital attenuated the hypnotic effect of pentobarbital in a dose dependent manner, but neither the brain level of pentobarbital nor the development of tolerance was modified by this treatment. The effect of TRH was further demonstrated in rats by concomitant intracarotidal infusion with pentobarbital maintaining the brain concentration of pentobarbital and also the duration of exposure of the brain to pentobarbital under a constant condition. On the other hand, THC significantly prolonged the hypnosis induced by pentobarbital but did not potentiate the effect of pentobarbital to develop acute tolerance. Thus, the brain level of pentobarbital at the initial treatment is the primary determinant for the development of acute tolerance and the duration of hypnosis is not the essential factor in this mechanism.