Gastric antisecretory and pharmacologic properties of N,N-dimethyl-N'-(2-diisopropylaminoethyl)-N-(4,6-dimethyl-2-pyridyl)ur ea (L-634,366).

N,N-Dimethyl-N'-(2-diisopropylaminoethyl)-N-(4,6-dimethyl-2-pyridyl)urea (L-634,366) was selected from a series of pyridylurea compounds with antisecretory activity as a potential therapeutic agent for the treatment of ulcer disease. L-634,366 was an effective inhibitor of gastric secretion evoked by gastrin, histamine and 2-desoxy-D-glucose (2-DG) in conscious dogs. Orally, L-634,366 was slightly less potent than the reference H2 receptor blocker, cimetidine as an inhibitor of secretion evoked by histamine, but was equipotent as an inhibitor of secretion evoked by gastrin and 2-DG. In vitro L-634,366 was a weak antagonist of histamine (H2) receptor responses in the guinea-pig atria and rat uterus; in the atria the antagonism appeared to be noncompetitive. In the anesthetized dog, L-634,366 possessed weak anticholinergic activity as compared to atropine in reducing vagally mediated cardiovascular, antral motor responses and with regard to antagonizing the pressor response to the muscarinic stimulant, McN 343-A. The anticholinergic activity of L-634,366 was lower and more selective than that of pirenzepine or atropine in producing mydriasis in mice, in antagonizing acetylcholine induced bradycardia in guinea-pig atria, methacholine and acetylcholine elicited contractions in the guinea-pig ileum and QNB binding to muscarinic receptors. L-634,366, like carbenoxolone, increased incorporation of 3H-glucosamine in gastric mucous indicating an increase in synthesis or turnover of mucous. L-634,366 is a novel compound possessing a broad spectrum of antisecretory activity; in vitro studies suggested a weak noncompetitive inhibition of the histamine-H2 receptor in atria.

Structure-activity, theoretical, and X-ray studies on the intramolecular interactions in a series of novel histamine H2 receptor antagonists.

The furan ring of the histamine H2 receptor antagonist 3-amino-4-[[2-[[[5-[(dimethylamino)methyl]-2-furanyl]-methyl] thio]ethyl]amino]-1,2,5-thiadiazole 1-oxide (1a) was replaced by thiophene, pyridine, benzene, and pyrrole. The relative receptor affinities of these analogues were estimated by in vitro and in vivo techniques. A theoretical model for the stacking interaction, observed by single crystal X-ray analysis of 1a, was developed, and the ability to enter into this type of interaction was estimated. The X-ray analysis of the pyridine analogue of 1a revealed no intramolecular stacking interaction. The theoretical studies were evaluated in light of the observed receptor affinities, and the relevance of the solid-state geometry of 1a to the receptor-bound geometry was assessed. It is suggested that the stacked geometry found in the X-ray structure of 1a does not represent a conformation that is relevant to that bound at the histamine H2 receptor.

A deuterium isotope effect on the inhibition of gastric secretion by N,N-dimethyl-N'-[2-(diisopropylamino)ethyl]-N'-(4,6-dimethyl-2-pyridyl)urea. Synthesis of metabolites.

The use of isotopic substitution to retard the oxidative metabolism of the gastric antisecretory agent N,N-dimethyl-N'-[2-(diisopropylamino)ethyl]-N'-(4,6-dimethyl-2-pyridyl)urea (1) and improve its antisecretory potency was examined. The pyridine ring methyl hydrogens of 1 were replaced with either deuterium or fluorine. The hexadeuterated analogue (12) was found to be approximately 2.1 times more potent than the protio form (1) as an inhibitor of gastric acid secretion stimulated by gastrin tetrapeptide. The hexafluoro analogue (11) was 0.4 times as potent as 1. A useful pyridine ring synthesis was developed to prepare the metabolites of 1, 10a (4-hydroxymethyl) and 10b (6-hydroxymethyl), and the hexafluoro analogue 11. These syntheses involved the condensation of 1,3-diketones with an appropriately N-substituted amidinoacetate.

Studies on MK-208 (YM-11170) a new, slowly dissociable H2-receptor antagonist.

MK-208 [3-(((2-(aminoiminomethyl)amino)-4-thiazolyl)-methyl)thio)-N'-(a minosulfonyl) propanimidamide], also known as YM-11170, is a highly potent histamine H2-receptor antagonist in guinea-pig atria, acting via a unique binding mechanism. Unlike ranitidine, the onset of action of this compound was slow and its inhibitory action was difficult to remove from the tissues by repeated washing. Preincubation of atria with ranitidine, however, protected the H2-receptor from these prolonged inhibitory effects of MK-208. The H2-receptor antagonism produced by MK-208 was not surmountable by increasing concentrations of dimaprit. The compound did not alter the response of this tissue to isoproterenol or affect basal atrial rate under conditions where maximal H2-receptor blockade was achieved. In dogs, MK-208 was effective in inhibiting gastric acid secretion evoked by histamine, gastrin and 2-deoxy-D-glucose. Orally, it was approximately 7 times as potent as ranitidine against histamine-induced secretion, and its duration of action was substantially longer. The compound was also highly effective in inhibiting basal acid secretion in chronic gastric fistula rats.

Inhibitors of gastric acid secretion: antisecretory 2-pyridylurea derivatives.

A series of aminoalkyl-substituted pyridylureas has been prepared and evaluated as inhibitors of gastric acid secretion. N,N-Dimethyl-N'-[2-(diisopropylamino)ethyl]-N'-(4,6-dimethyl-2-pyridyl)urea (8g) was the most potent example of the class. Comparison of this compound with cimetidine showed it to be equipotent in dogs stimulated with gastrin tetrapeptide but approximately half as potent in dogs stimulated with histamine. Inhibition of secretion does not appear to result from antagonism of the histamine H2 receptor, since the compounds show only weak inhibition of the H2 receptor in vitro.

Apparent irreversible H2-receptor blocking and prolonged gastric antisecretory activities of 3-N-(3-[3-(1-piperidinomethyl)phenoxy]propyl) amino-4-amino-1,2,5-thiadiazole-1-oxide (L-643, 441).

L-643,441 is a highly potent histamine H2-receptor antagonist in guinea-pig atria, acting via a unique mechanism. Unlike ranitidine, the onset of action of this compound was slow and its inhibitory action persisted after repeated washing of the tissues. Preincubation of atria with ranitidine, however, protected the H2-receptor from the apparently irreversible antagonism of L-643,441. H2-receptor antagonism produced by L-643,441 was not surmountable by increasing the concentration of dimaprit. The compound did not alter the response of this tissue to isoproterenol or affect basal atrial rate under conditions in which maximal H2-receptor blockade was achieved. In dogs, L-643,441 was effective both orally and i.v. in inhibiting gastric acid secretion evoked by histamine, gastrin, 2-deoxy-D-glucose and food. Orally, it was equipotent with ranitidine against histamine-induced secretion, but the duration of action of L-643,441 was substantially longer.

Conformational requirements for histamine H2-receptor inhibitors: a structure-activity study of phenylene analogues related to cimetidine and tiotidine.

Two series of compounds related to cimetidine and tiotidine were synthesized as part of a study to evaluate the importance of conformational parameters in binding at histamine H2 receptors. The flexible methylthioethyl connecting chain was replaced by a conformationally restricting phenylene unit. These compounds were evaluated for antagonism of the dimaprit-stimulated chronotropic response in the guinea pig atrium and inhibition of histamine stimulated secretion of gastric acid in the dog. In both series, biological activity is markedly dependent on the m-phenylene regioisomers. Histamine H2-receptor activity is retained in both series; however, in the tiotidine series, gastric antisecretory activity is significantly improved. Regardless of the end group, N-cyanoguanidine 1,1-diamino-2-nitroethene or 3,4-diamino-1,2,5-thiadiazole 1-oxide, each 3 3-(2-guanidino-4-thiazolyl)phenyl analogue was ca. 8 and 90 times more potent intravenously than tiotidine and cimetidine, respectively. The electronic influences of the phenylene unit on biological activity were also evaluated. It was concluded that the geometric constraints imposed by the m-phenylene connecting element were more important than electronic factors in binding events at the histamine H2 receptor.

2-Mercaptoacetamidines as gastric antisecretory agents.

A series of N-substituted 2-mercaptoacetamidines was synthesized and evaluated for gastric antisecretory activity in dogs stimulated with gastrin tetrapeptide. The most potent analogues showed 80--95% inhibition of acid secretion after an oral dose of 8 mg/kg. Thus, these compounds represent a new structural type having significant antisecretory activity. Disulfides had essentially the same antisecretory potency as the corresponding mercaptoacetamidines, indicating a metabolic interconversion. Alkylation of the mercapto group decreased potency. Higher carboxamidine homologues such as 2- and 3-mercaptopropionamidines had very low activity. Hydroxyacetamidines and mercaptoacetamides also had low potency. Side effects observed with this series of compounds included emesis, tachycardia, and gastric bleeding.

Subcutaneous administration of somatostatin analogs as a major factor in the enhancement of the duration of action.

Somatostatin and Des(Ala1Gly2)desaminol[Cys3]descarboxy-]Cys14[-]D-Trp8[dicarba3,14-somatostatin (Ia) are more potent inhibitors of glucagon, insulin and growth hormone release than the L-Trp8 analog (Ib). However when infused intravenously, these three compounds are equipotent but short-acting inhibitors of pentagastrin evoked gastric secretion in the dog. The duration of inhibition of equieffective antisecretory doses is significantly increased following subcutaneous administration 30 min prior to a food stimulus. The longest duration of antisecretory action is seen with the D-Trp8 analog (Ia) after subcutaneous administration.

Piperazinylpyrazines with central serotoninmimetic activity.

A series of 2-(1-piperazinyl)pyrazines was synthesized and evaluated for central serotonin-like activity. The most interesting member of the series, 6-chloro-2(1-piperazinyl)pyrazine (3a), had pharmacological properties characteristic of potent central serotoninmimetic activity and only weak peripheral serotoninmimetic action. Structural similarities between 3a and serotonin are discussed.

The anticonvulsant action of methazolamide in mice: antagonism by various inhibitors of dopamine beta-hydroxylase.

The dopamine beta-hydroxylase inhibitors, FLA-63 and picolinic acid, antagonized the anticonvulsant action of methazolamine in mice; disulfiram and pyrimidinethiol were inactive. FLA-63 and picolinic acid, but not disulfiram or pyrimidinethiol prevented pheniprazine restoration of the anticonvulsant action of methazolamide in reserpinized mice. The present findings clearly demonstrate that differences exist among inhibitors of dopamine beta-hydroxylase regarding their ability to antagonize the anticonvulsant action of methazolamide under various test conditions.

The antiarrhythmic and hemodynamic actions of alpha, alpha-dimethyl-4-(alpha, alpha, beta, beta-tetrafluorophenethyl) benzylamine (MK-251).

Alpha,alpha-Dimethyl-4-(alpha,alpha,beta,beta-tetrafluorophenethyl)benzylamine (MK-251) has been found to prevent certain types of experimentally induced ventricular arrhythmias and at maximally effective doses possesses substantial hemodynamic safety in contrast to standard antiarrhythmic agents. MK-251 prevented or modified ventricular arrhythmias produced by injection of tetrafluorohexachlorobutane into the coronary artery of dogs and baboons. In dogs, the dose estimated to prevent 80% of the arrhythmic impulses (ED80) was 0.5 mg/kg i.v. and 5.0 mg/kg p.o. The duration of action after oral administration of 5.0 mg/kg to the dog or baboon exceeded 5 to 6 hours. MK-251 delayed the onset of arrhythmias resulting from coronary artery ligation, reduced their severity and permitted a conversion back to normal sinus rhythm earlier than in control dogs. In cats, the doses of digoxin required to induce ventricular ectopic activity, ventricular tachycardia and ventricular fibrillation were elevated by MK-251. In anesthetized dogs, 4 times the i.v. ED80 produced no change in blood pressure, cardiac contractility or output, or in ventricular conduction. The only effect after 8 times the ED80 was a slight decrease in contractility. In contrast. lidocaine at its ED80 (0.21 mg/kg/min), decreased blood pressure and contractility; there was no change in ventricular conduction. Quinidine at the ED80 (8.8 mg/kg i.v.) and above produced hypotension, decreased contractility and prolonged conduction in a dose-related manner.