Synthesis and dual histamine H₁ and H₂ receptor antagonist activity of cyanoguanidine derivatives

Premedication with a combination of histamine H₁ receptor (H₁R) and H₂ receptor (H₂R) antagonists has been suggested as a prophylactic principle, for instance, in anaesthesia and surgery. Aiming at pharmacological hybrids combining H₁R and H₂R antagonistic activity, a series of cyanoguanidines 14-35 was synthesized by linking mepyramine-type H₁R antagonist substructures with roxatidine-, tiotidine-, or ranitidine-type H₂R antagonist moieties. N-desmethylmepyramine was connected via a poly-methylene spacer to a cyanoguanidine group as the "urea equivalent" of the H₂R antagonist moiety. The title compounds were screened for histamine antagonistic activity at the isolated ileum (H₁R) and the isolated spontaneously beating right atrium (H₂R) of the guinea pig. The results indicate that, depending on the nature of the H₂R antagonist partial structure, the highest H₁R antagonist potency resided in roxatidine-type compounds with spacers of six methylene groups in length (compound 21), and tiotidine-type compounds irrespective of the alkyl chain length (compounds 28, 32, 33), N-cyano-N'-[2-[[(2-guanidino-4-thiazolyl)methyl]thio]ethyl]-N″-[2-[N-[2-[N-(4-methoxybenzyl)-N-(pyridyl)-amino] ethyl]-N-methylamino]ethyl] guanidine (25, pKB values: 8.05 (H₁R, ileum) and 7.73 (H₂R, atrium) and the homologue with the mepyramine moiety connected by a six-membered chain to the tiotidine-like partial structure (compound 32, pKB values: 8.61 (H₁R) and 6.61 (H₂R) were among the most potent hybrid compounds. With respect to the development of a potential pharmacotherapeutic agent, structural optimization seems possible through selection of other H₁R and H₂R pharmacophoric moieties with mutually affinity-enhancing properties.

Photoaffinity Labeling of the Anionic Sites in Caco-2 Cells Mediating Saturable Transport of Hydrophilic Cations Ranitidine and Famotidine

The H(2) antagonists, ranitidine and famotidine, exhibit saturable absorptive transport across Caco-2 cell monolayers and human intestine via a yet unidentified mechanism. A photoreactive derivative of famotidine has been synthesized and evaluated as a photoaffinity probe for the putative transporter protein(s). The probe irreversibly inhibited ranitidine transport across Caco-2 cell monolayers and irreversibly increased the transepithelial electrical resistance (TEER) after UV activation. Photoaffinity labeling was protected by a molar excess of famotidine.

Synthesis and pharmacological activity of fluorescent histamine H2 receptor antagonists related to potentidine

Fluorescently labeled histamine H(2) receptor antagonists were synthesized starting from N-cyano-N'-[3-(3-piperidin-1-ylmethylphenoxy)propyl]guanidines with an additional N"-omega-aminoalkyl substituent (chain lengths 2-8 methylene groups) or from 3-(3-piperidin-1-ylmethylphenoxy)propylamine. The primary amino group was derivatized with various fluorophores (fluorescein, acridine, dansyl, nitrobenzoxadiazole (NBD), indolo[2,3-a]quinolizine). On the isolated spontaneously beating guinea pig right atrium most of the fluorescent probes were only weakly active, however, the NBD-labeled substances proved to be potent histamine H(2) receptor antagonists achieving pA(2) values in the range of 7.5-8.0, comparable to the activity of famotidine.

Synthesis and antiulcer activity of N-substituted N'-[3-[3-(piperidinomethyl)phenoxy]propyl]ureas: histamine H2-receptor antagonists with potent mucosal protective activity

As an aim toward developing new antiulcer agents, new N-substituted N'-[3-[3-(piperidinomethyl)phenoxy]propyl]ureas were synthesized and evaluated for histamine H2-receptor antagonistic, gastric antisecretory, and gastric mucosal protective activities. A QSAR study showed that the most favorable N-substituents were electron-donating straight-chain alkyl groups of short length such as ethyl group from the viewpoint of dual action, i.e., gastric antisecretory and mucosal protective actions. Among the ureas studied, compounds 4, 5, and 8-10 were selected as candidates for further study.

Anti-Helicobacter pylori agents. 5. 2-(Substituted guanidino)-4-arylthiazoles and aryloxazole analogues

To extend the SAR study of guanidinothiazoles as a structurally novel class of anti-H. pylori agents, a series of 2-(substituted guanidino)-4-arylthiazoles and some 4-aryloxazole analogues were synthesized and evaluated for antimicrobial activity against H. pylori. Some of them were also subjected to H2 antagonist and gastric antisecretory assays. Several arylthiazoles were identified as potent anti-H. pylori agents, and of these, thienylthiazole derivative 44 exhibited the strongest activity (MIC = 0.0065 microg/mL) among the compounds obtained in our guanidinothiazole studies. Although 44 was void of H2 antagonist activity, pyridylthiazole derivative 39 had both potent anti-H. pylori and H2 antagonist activities. Thiazolylthiazole derivative 46 also showed potent anti-H. pylori activity, but the H2 antagonist activity was weak. On the other hand, no attractive activities were found in pyrimidyl, oxazolyl, isoxazolyl, imidazolyl, and oxadiazolylthiazole derivatives. The anti-H. pylori activity of the aryloxazole analogues was weaker than those of the corresponding arylthiazole derivatives, though they had potent H2 antagonist activity.

Anti-Helicobacter pylori agents endowed with H2-antagonist properties

New anti-Helicobacter pylori (H. pylori) agents endowed with H2-antagonists properties were obtained by combining the lamtidine derived pharmacophoric group with the antibiotic calvatic acid. All the compounds were tested for their irreversible H2-antagonist properties and for their ability to inhibit 20 H. pylori strains, two of them metronidazole resistant. The most active derivative (compound 4) displayed antimicrobial activity similar to metronidazole.

Anti-Helicobacter pylori agents. 4. 2-(Substituted guanidino)-4-phenylthiazoles and some structurally rigid derivatives

In order to find a new class of anti-Helicobacter pylori (H. pylori) agents, a series of 4-[(3-acetamido)phenyl]-2-(substituted guanidino)thiazoles and some structurally rigid analoges were synthesized and evaluated for antimicrobial activity against H. pylori. Among the compounds obtained, high anti-H. pyrori activities were observed in benzyl derivative 34 (MIC = 0.025 microg/mL) and phenethyl derivatives 35 and 36 (MIC = 0.037 microg/mL and 0.017 microg/mL). Though alkyl derivatives generally showed lower activity, the 2-methoxyethyl derivative 28 preserved significant activity (MIC = 0.32 microg/mL) and also exhibited more potent gastric antisecretory activity than ranitidine. Structural restriction by bridging between the thiazole and the phenyl rings with an alkyl chain did not improve the activity in this series.

Anti-Helicobacter pylori agents. 3. 2-[(Arylalkyl)guanidino]-4-furylthiazoles

A series of 2-[(arylalkyl)guanidino]-4-[(5-acetamidomethyl)furan-2-yl]thiazole s and some 4-acetamidomethyl positional isomers were synthesized and evaluated for antimicrobial activity against Helicobacter pylori. Among the compounds that had potent antimicrobial activity (MIC < 0. 1 microgram/mL), compounds 31 and 36 additionally possessed H2 antagonist and gastric antisecretory activities. Though compound 51, an analogue incorporating a methyl group onto the furan nucleus of 36, and compound 54, a positional isomer of 51, also showed potent anti-H. pylori activity, the H2 antagonism profile was eliminated from these compounds. Thus, two types of potent anti-H. pylori agents could be derived from the same scaffold.

Combined histamine H1/H2 receptor antagonists: part II. Pharmacological hybrids with pheniramine- and tiotidine-like substructures

Hybrid molecules combining the crucial structural features of both pheniramine-type histamine H1 receptor antagonists and guanidinothiazole-type H2 receptor antagonists have been synthesized and tested for in vitro pharmacological activity at the isolated ileum and the spontaneously beating right atrium of the guinea-pig. In the title compounds the basic side chain nitrogen of the H1 antagonist and the so-called 'polar group' (cyanoguanidine, urea, or nitroethenediamine) of the H2 antagonist moiety have been linked by a polymethylene spacer. The new substances displayed high affinities to both histamine receptor subtypes and a dual type of antagonism (surmountable/insurmountable) characterized by a shift of the concentration response curves to the right accompanied by a depression of the maximal response to the agonist if the antagonist concentration was >/=100 nM. Highest combined histamine antagonist activities were found in the nitroethenediamine series with pKB values ranging from 8.16 to 9.04 in the ileum (H1) and 7.0-8.08 in the atrium (H2)

Combined histamine H1/H2 receptor antagonists: part I. Pharmacological hybrids with pheniramine- and roxatidine-like substructures

A series of hybrid compounds combining the pharmacophores of both pheniramine-type histamine H1 receptor antagonists and roxatidine-type H2 receptor antagonists have been synthesized and tested for histamine antagonism at the isolated ileum (H1) and the spontaneously beating right atrium (H2) of the guinea pig. The 'polar group' of the H2 antagonist moiety (cyanoguanidine, nitroethenediamine or urea) and the side chain amino group of the H1 antagonist portion have been linked by a polymethylene spacer or by a piperazine system. The incorporation of a flexible spacer (2-7 methylene groups) resulted in H1 antagonists achieving up to 2.4 times the activity of pheniramine. Depending on the nature of the polar group the highest H2 antagonist potency resides in compounds with spacers ?2 methylene groups. Nitroethenediamine 24c with a seven-membered chain and a chlorpheniramine substructure proved to be approximately equipotent with pheniramine at the H1 and with ranitidine at the H2 receptor (pKB values 7.82 and 7.1, respectively).

Anti-Helicobacter pylori agents. 2. Structure activity relationships in a new series of 2-alkylguanidino-4-furylthiazoles

SAR for antimicrobial activity against H. pylori was investigated in a new series of 2-alkylguanidino-4-furylthiazoles. Of the compounds obtained, cyclohexylmethyl and ethoxyethyl derivatives were identified as a novel class of anti-H. pylori agents which possessed potent and selective antimicrobial activity against H. pylori. These compounds also showed gastric antisecretory activity.

A novel histamine 2(H2) receptor antagonist with gastroprotective activity. II. Synthesis and pharmacological evaluation of 2-furfuryl-thio and 2-furfurylsulfinyl acetamide derivatives with heteroaromatic rings

We recently found that N-[3-[3-(piperidinomethyl)phenoxyl]propyl]acetamide derivatives with a thioether function showed gastric anti-secretory and gastroprotective activities and that the thioether function (particularly furfurylthio or furfurylsulfinyl) was essential for gastroprotection. In the present study, a series of 2-furfurylthio and 2-furfurylsulfinyl acetamide derivatives were synthesized and evaluated for histamine H2 receptor antagonistic activity, gastric anti-secretory activity and gastroprotective action. Based on the structure of N-[3-[3-(piperidinomethyl)phenoxyl]propyl]acetamide, we designed compounds, in which the 3-(piperidinomethyl)phenoxy part is substituted with many types of heteroaromatic ring attached to the tertiary amine and the propyl group is replaced with other carbon linkages. Structure-activity relationships are discussed. 2-Furfurylsulfinyl-N-[4-[4-(piperidinomethyl)-2-pyridylox y]- (Z)-2-butenyl]acetamide was the most potent among the tested compounds and was given the code designation FRG-8813.

A novel histamine 2(H2) receptor antagonist with gastroprotective activity. I. Synthesis and pharmacological evaluation of N-phenoxypropylacetamide derivatives with thioether function

In an attempt to develop new types of anti-ulcer agents, a series of N-(phenoxypropyl)acetamide derivatives with a thioether moiety and their sulfur-oxidized analogues were synthesized and evaluated for histamine H2-receptor antagonistic activity, Ca antagonistic activity and gastric anti-secretory activity in the lumen-perfuseed rat. Selected compounds were also tested for gastroprotective activity, which was expected to be based on Ca antagonistic activity. Structure-activity relationships are discussed. As a thioether moiety, -CH2-S(O)p-CH2-Ar (Ar; phenyl or furyl) was found to be optimal for the above activities. Especially, N-[3-[(3-(piperidinomethyl) phenoxy]propyl]acetamide with a benzyl sulfinyl, benzylsulfonyl, furfurylsulfinyl or furfurylsulfonyl group showed potent gastroprotective activity upon oral administration in a rat model. These compounds are candidates for novel anti-ulcer drugs with gastric anti-secretory and gastroprotective activities. 2-Furfurylsulfinyl-N-[3-[(piperidinomethyl)phenoxy]propyl]ac etamide was the most potent among the compounds tested and was given the code designation FRG-8701.

[Synthesis and antiulcer activity of N-2-(2-hydroxy-2-phenyl)ethyl-N"-(methanesulfonyl)guanidine analogue of ranitidine. Development of a new antiulcer agent T-593]

A series of the aryl-substituted N'-2-(2-hydroxy-2-phenyl)ethyl derivatives of N"-methanesulfonyl-N-2-((5-dimethylaminomethyl or 5-methylaminomethyl) furfurylthio)ethylguanidine have been synthesized as potential antisecretory and mucosal protective antiulcer agents. The synthetic routes involves, at the last stage, the reaction of 2-hydroxy-2-phenylethylamines with N-2-(furfurylthio)-ethyl-N'-methanesulfonyl-S-methylisothiourea or its O-phenylisourea counterpart. The primary screening test to assess the inhibitory activity of the synthetic compounds on histamine-induced gastric acid secretion was carried out in anesthetized rats by the lumen-perfusion technique of Ghosh and Schild and also by the pylorus-ligated preparation method. The best profile of histamine H2-antagonist activity was much better than that of the prototype ranitidine, and obtained with N'-(2-(2-hydroxy-2-(4-hydroxyphenyl)) ethyl-N"-methanesulfonyl-N-2-(5-(methylaminomethyl)furfurylthio)et hylguanidine (12f), which was also characterized by enhancing the gastric mucosal blood flow in rabbits as observed by the thermoelectric method. This compound 12f, designated as T-593, significantly inhibited the formation of the indomethacin-induced gastric lesions in rats; 3.5-fold more potent than ranitidine, but 4-fold less active than famotidine. On the other hand, T-593 and famotidine displayed comparable activities in healing the acetic acid-induced gastric ulcer with and without the dosing of indomethacin. Additional notable features of T-593, as determined in rats, are that its protective effect on the hemorrhagic shock-induced lesion under the prior dosing of histamine is ca. 10- and 2-fold greater than ranitidine and famotidine, respectively, and that a decrease in the gastric mucosal blood flow caused by a partial blood-withdrawal is more strongly recovered with T-593 than with famotidine. These experimental results suggest that the antiulcer efficacy of T-593 can be explained by its dual activities: antisecretion of gastric acid and, more importantly, protection of gastric mucous membrane.

Indenopyridazinone derivatives as potential antisecretory and antiulcer agents

A series of substituted indenopyridazinones (4b-h) has been synthesized and tested for their antisecretory and antiulcer activity, in comparison with ranitidine, as reference drug. While the monomethoxy (4b-d), as well as the benzyloxy (4f) and the 6,9-dimethoxy (4g) derivatives were found to be devoid of overt antisecretory properties, the 9-methoxy (4e) was weakly active. The most interesting compound of this class was the 7,8-dimethoxy substituted (4h), which at an oral dose of 30 mg/kg still retains a significant activity. The dihydroderivatives of 4g,h (compounds 1g,h) were more active (1g) or comparable (1h) to the parent compounds, thus proving that the 4, 4a-double bond, which was an essential requirement in the analogues 2 and 3, is not necessary in this new series. The disubstituted derivatives (1g,h; 4g,h) were also tested as antiulcer agents, in two different models. All compounds were able to prevent haemorragic lesions induced in rats by 90% ethanol in a dose dependent manner. In the indomethacin model they still showed a significant activity, though lower than in the previous test. Attempts have been made to elucidate their mechanism of action.

Anti-Helicobacter pylori agents. 1. 2-(Alkylguanidino)-4-furylthiazoles and related compounds

A series of 2-(alkylguanidino)-4-[5-(acetamidomethyl)furan-2-yl]thiazoles and related compounds were synthesized and evaluated for antimicrobial activity against Helicobacter pylori, inhibitory effect on gastric acid secretion, and histamine H2-receptor antagonist activity. Introduction of alkyl substituents on the guanidino moiety resulted in a significant increase in antimicrobial activity, which was associated with the alkyl chain length. Of the compounds obtained, the n-hexylguanidino derivative 13 demonstrated a 250-fold improvement in activity (MIC = 0.11 micrograms/mL) over the unsubstituted guanidino derivative 7. Alkyl-substituted guanidino derivatives also displayed gastric antisecretion and H2-antagonist activities. However, a simple correlation between the alkyl chain length and the activities was not found in these assays. Replacement of the guanidine with other bioisosteric groups (thiourea, urea, or (dimethylamino)methyl) resulted in loss of all activities tested. Thus the guanidino moiety was found to be essential for activity in this series of compounds.

Search for novel leads for histamine H3-receptor antagonists: oxygen-containing derivatives

This study was performed in order to develop new leads for antagonists of the histamine H3-receptor subtype. omega-(1 H-Imidazol-4-yl)alkyl derivatives with ester, ketone or alcohol functionality in the side chain were synthesized and tested concerning their H3-receptor antagonist activity on synaptosomes of rat cerebral cortex. The novel compounds, which possess no nitrogen-containing polar group in the side chain of the imidazole moiety, presented moderate to high antagonist potency in vitro. In this series 3-(1 H-imidazol-4-yl)propyl-3-cyclopentylpropanoate (4) was the most potent compound in vitro with -log Ki = 8.5. Unfortunately, no central antagonist H3-receptor activity was detectable for ester derivatives in the in vitro H3-receptor assay based upon measurement of brain N tau-methylhistamine levels after p.o. administration to mice. Some of these novel antagonists are useful tools for investigations on ligand-receptor interaction because of their distinct receptor activities. On the other hand, the ketone derivative 1-(1 H-imidazol-4-yl)-7-phenyl-4-heptanone (9) in vitro presented an ED50-value of 3.5 +/- 1.5 mg/kg p.o. thus proving to be a new lead for further drug investigations. The most potent compounds in vitro and in vivo also showed high H3-receptor selectivity when tested at other histamine receptor subtypes.

Synthesis and structure-activity relationships of dual histamine H2 and gastrin receptor antagonists with modified benzodiazepine skeletons

Three different types of dual histamine H2 and gastrin receptor antagonists, e.g. those bearing a benzazepine, benzoxazepine, or benzothiazepine skeleton instead of the benzodiazepine one as a gastrin receptor antagonistic moiety were synthesized to reduce high hydrophobicity of parent compounds and evaluated for the dual activities. These skeletal modifications significantly potentiated the binding affinity of dual antagonists with histamine H2 receptor but markedly diminished their binding affinity with the gastrin receptor and the gastrin versus CCK-A receptor selectivity. We evaluated in vivo gastric acid antisecretory activities for some representative compounds by the rat pylorus ligation method for 10 mg kg(-1) dose by oral route. However, they exerted only low inhibitory activities for oral dose with % inhibition values ranging between 32 and 53%.

Synthesis and structure-activity relationships of dual histamine H2 and gastrin receptor antagonists with noncyclic gastrin receptor antagonistic moieties

In order to study structure-activity relationships of dual histamine H2 and gastrin receptor antagonists as well as to improve their low oral absorbability, their prototype benzodiazepine gastrin receptor antagonistic moieties were altered to a conformationally flexible noncyclic dipeptide equivalent. This skeletal modification significantly potentiated the binding affinity of hybrid compounds for the histamine H2 receptor, whereas their affinity for the gastrin receptor and receptor selectivity over the CCK-A receptor varied widely with the substituents on the gastrin moiety. Among them, [3-[3-(3-piperidin-1-ylmethylphenoxy)propylcarbamoyl]p ropyl carbamic acid 3-[3-([(3-methoxyphenyl)[(methylphenylcarbamyl)methyl]carbamoyl]me thyl)ureido]benzyl ester (7a) showed the highest dual histamine H2 and gastrin receptor antagonistic activities. It also displayed distinct gastric acid antisecretory activity in vivo for two assays, namely, Schild's rat method by i.d. administration and the rat pylorus ligation method by oral administration. With the latter case, dose-response relationships were observed for the first time, suggesting its substantially improved oral absorbability. However, 7a did not display distinct in vivo gastric acid antisecretory activity for the assay with Heidenhain pouch dogs.

Synthesis and structure-activity relationships of dual histamine H2 and gastrin receptor antagonists with decreased hydrophobicity

In order to study structure-activity relationships of the previously reported dual histamine H2 and gastrin receptor antagonists and also to improve their low oral absorbability, we tried two chemical modifications. One tried to decrease the high hydrophobicity of the parent hybrid compounds to an appropriate level by incorporating a hydrophilic group into the molecule and the other by replacing the more hydrophobic groups with less hydrophobic ones. The former compounds (type I) involved hybrid compounds with a hydroxyl group at a position of a spacer, a piperidine moiety of H2A, or a phenyl ring at the C5 of the benzodiazepine skeleton as well as those with a free carboxyl group in the piperidine moiety of H2A. The latter (type II) involved hybrid compounds with the C5-phenyl group replaced with either a methyl group or hydrogen atom. Among them, only a type I compound, ([2-[3-(3-piperidin-1-ylmethylphenoxy)propylcarbamoyl] ethylcarbamoyl]methyl)carbamic acid 3-[3-[5-(3-hydroxyphenyl)-1-methyl-2-oxo-2,3-dihydro-1H-1,4-benzodiaz epin-3-yl]ureido]benzyl ester (18), showed potent dual histamine H2 and gastrin receptor antagonistic activity, whereas others resulted in a significant decrease of histamine H2 receptor antagonistic activity. The in vivo gastric acid antisecretory activity of 18 evaluated by Schild's rat method, however, did not suggest any notable improvement in oral absorbability.

Search for novel leads for histamine H3-receptor antagonists: amine derivatives

In search for novel leads for histamine H3-receptor antagonists a number of amine derivatives of different (1 H-imidazol-4-yl)anilines and omega-(1 H-imidazol-4-yl)alkanamines were prepared. Pharmacological in vitro H3-receptor investigations of the prepared urea, amide, inverse amide, thioamide, and thiourea derivatives on synaptosomes of rat cerebral cortex proved that the aniline derivatives are inactive at H3-receptors, whereas derivatives of the omega-(1 H-imidazol-4-yl)-alkanamines showed moderate to good activity. Some compounds are active in the nanomolar concentration range. The most potent compounds in this series are the thioamide derivative 7 and the urea derivatives 11, 12 of 3-(1 H-imidazol-4-yl) propanamine. Therefore, the urea derivatives were tested in vitro on isolated organs of the guinea pig for their activity on the other two histamine receptor subtypes proving their high selectivity. In vivo studies of the effects of the urea derivatives 11 and 12 on brain Nt-methylhistamine levels, a test of central H3-receptor activity after peroral application to mice, showed no detectable activity. Thus, the urea type antagonists are useful potent and selective H3-receptor tools for in vitro studies and for investigations of ligand-receptor interactions.

Synthesis and assessment of formamidines as new histamine H2-receptor antagonists

Four series of compounds whose substructure contains a formamidine functionalized as a novel group in the chemistry of histamine H2-receptors have been synthesized. Series design, synthesis and pharmacological data including inhibition of histamine-stimulated acid secretion, inhibition of acid secretion p.o. and pA2 are reported. N-[(E)-[[2-[[[2](Diaminomethylene)amino]-4-thiazolyl] methyl]thio]ethyl]amino]methylene]-4-bromo-benzenesulfonamide (ebrotidine, CAS 100981-43-9, FI-3542) was selected for further research.

Computer design and syntheses of antiulcer compounds. 2nd Communication: N-substituted N'-[3-[3-(1-piperidinomethyl)phenoxy]propyl]ureas

The in vitro and in vivo antiulcer effect of a series of N-substituted N'3-[3-(1-piperidinomethyl)phenoxy]propyl]ureas was modeled by making use of the OASIS computer system for QSAR analysis. Various research schemes were employed depending on structural representation of chemicals under investigation, such as non-protonated (neutral), protonated at the piperidine and urea fragmental nitrogens, and with intramolecular hydrogen binding. According to the modeling results, it is likely a variety of structural forms of antagonist molecules to take part in the receptor interaction. The QSAR study showed that the larger the electron acceptor properties of the nitrogen and oxygen atoms of the urea fragment, the higher is in vitro and in vivo activity of the antagonists.

Computer design and syntheses of antiulcer compounds. 1st communication: N-[3-[3-(1-piperidinomethyl)phenoxy]propyl]amines and benzamides

Aiming to develop new antiulcer agents, a quantitative structure-activity relationship (QSAR) study on in vitro (pA2) and in vivo histamine H2-receptor antagonistic activity of a series of N-[3-[3-(1-piperidinomethyl)phenoxy]propyl]amines was carried out using the OASIS computer system. The results showed that pA2 increases with the decrease (increase) of electron donor (acceptor) properties of molecules, particularly at the NH-reaction site. The finding is consistent with the assumption for an increase of histamine H2-receptor activity of the antagonists with their ability to form H-bonds with the receptor through NH groups. The correlations with hydrophobicity and related topological indices are consistent with the hypothesis that logP should indirectly reflect receptor interactions. In addition a series of N-[3-[3-(1-piperidinomethyl)phenoxy]propyl]benzamides are synthesized. The theoretically predicted in vitro activities of these compounds were found to be in accordance with in vivo tests (percent of inhibition of gastric juice and acid output [mEq/H+/3 h]).

Synthesis and pharmacology of combined histamine H1-/H2-receptor antagonists containing diphenhydramine and cyproheptadine derivatives

The classical histamine H1-receptor antagonists diphenhydramine (3a) and cyproheptadine (9) and their derivatives (3b-d, 10) were connected with a 2-guanidinothiazole containing structure (28) derived from the H2-receptor antagonist tiotidine in order to obtain combined H1-/H2-receptor antagonists. The two moieties were not directly linked together, but were separated by a polymethylene spacer and a polar group (nitroethenediamine or urea). Thus 12 compounds were obtained that proved in vitro to possess high H1- and H2-receptor antagonist activity at the isolated guinea-pig ileum (H1) and the isolated guinea-pig right atrium (H2), respectively. The incorporation of the diphenhydramine as well as the cyproheptadine component provides high affinity to H1-receptors. The tricyclic cyproheptadine and its 10,11-dihydro derivative (30-32, 34), however, cause a decrease of H2-receptor antagonist potency compared to the diphenhydramines (29a-d, 33a-d). Using nitroethenediamine as the polar group is apparently more favourable to H1- and H2-receptor affinity as the urea function. All compounds elicit a dual mode of competitive and noncompetitive antagonism. Among the novel compounds the nitroethenediamines with 4-fluoro- or 4-methyl-substituted diphenhydramine as H1-receptor antagonist moiety (29c, d) display the most potent H1- and H2-receptor antagonist effects. The presented concept is a very promising way to combine H1- and H2-receptor antagonist properties in one molecule.

Syntheses and pharmacological properties of new 2-aminobenzimidazole derivatives

The paper reports the structures, syntheses and pharmacological properties of new compounds having a 2-aminobenzimidazole group. They exhibit various activities: histamine H1- and H2-receptors blocking activities, antilipidemic and platelet antiaggregatory, anti-inflammatory and analgesic properties, antimicrobial, fungicidal, parasiticide, antiarrythmic activity and muscle relaxant, comparable to those of drugs used in therapy.

Synthesis and histamine H2-receptor antagonist activity of 4-(1-pyrazolyl)butanamides, guanidinopyrazoles, and related compounds

A series of 4-(1-pyrazolyl)butanamides, pyrazolylalkyl cyanoguanidines, and related compounds with diverse functional groups (e.g. nitro, amino, guanidino groups) in the 3-position of the pyrazole ring was prepared via 4-(3-nitro-1-pyrazolyl)butanenitrile (5) and the corresponding carboxylic acid 7 as central intermediates. The amides 9a-d were prepared from the primary amines 8a-d which represent partial structures of the H2-receptor antagonists roxatidine, cimetidine, ranitidine, and famotidine. The roxatidine-derived 4-(3-nitro-1-pyrazolyl)butanamide (9a) proved to be the compound with the highest H2-receptor antagonist activity of 23 compounds tested at the isolated guinea pig right atrium preparation, achieving about 6 times famotidine's or 160 times cimetidine's potency. By contrast, in Ghosh-Schild rats 9a did not inhibit histamine-stimulated gastric acid secretion at a dosage of 0.1 mumol/kg i.v. Compounds 20a (the 3-(trifluoroethyl-guanidino)pyrazole analogue of 9a, 12a (the cyanoguanidine analogue) and N-(4-[3-(trifluoroethylguanidino)-1-pyrazolyl]butyl)cyanogua nidine (29), which are about as active as famotidine in the atrium, turned out to be very potent inhibitors of gastric acid secretion as well (e.g., 29: 74% inhibition at 0.025 mumol/kg). These compounds are comparable to famotidine in the rat stomach and by far superior to cimetidine and ranitidine in this test system.

Synthesis of 2-imidazolidinylidene propanedinitrile derivatives as stimulators of gastrointestinal motility--III

Recently, we reported that a ranitidine derivative 2 (fumarate: KW-5092), which had a 2-imidazolidinylidene propanedinitrile moiety (A), showed potent gastrointestinal motility enhancing activity. We have also found that introduction of substituents such as benzyl or 4-fluorobenzyl (i.e., giving 3 or 4) at the N-3 position of the moiety (A) significantly increased this activity. In this study, novel 2-imidazolidinylidene propanedinitrile derivatives possessing a thioether 5-15 were prepared and evaluated for in vitro assays; acetylcholinesterase (AChE) inhibitory activity and potentiating action on electrically induced contractions of guinea pig ileum. Compound 5, in which a nitrogen atom of compound 2 was replaced by a sulfur atom, was more potent than 2 in these tests. Also, in a series of thioether derivatives, introduction of substituents at the N-3 position of the 2-imidazolidinylidene propanedinitrile moiety markedly influenced both activities. In particular, compounds 12 and 13, which showed an excellent potency during in vitro study (AChE IC50 = 3.6 and 2.7 nM; ES. EC30 = 2.1 and 2.5 nM, respectively), were found to be more active in the enhancement of gastrointestinal motility in anesthetized rabbits than their corresponding parent compounds 3 and 4, respectively. In addition, compounds 12 and 13 showed lower affinity for the histamine H2-receptor than ranitidine. Therefore, these compounds may be potent and selective stimulators of gastrointestinal motility.

Synthesis and pharmacology of two new histamine receptor antagonists related to ranitidine

Pyridyl and 1,6-dihydropyridyl ranitidine analogues 1 and 2 were obtained by applying an improved modification of ranitidine synthesis. Compound 1 shows a selective H2 antagonistic activity while compound 2 is a non-selective histamine antagonist.

[Synthesis and combined H1-/H2 antagonist activity of mepyramine, pheniramine and cyclizine derivatives with cyanoguanidine, urea and nitroethenediamine partial structures]

Compounds with combined histamine H1- and H2-receptor antagonist activity were synthesized by connecting H1- and H2-receptor substructures via cyanoguanidine, urea, or nitroethenediamine moieties. Loss of the strongly basic side-chain nitrogen results in a decrease of H1-receptor activity compared to single reference compounds. At the guinea-pig right atrium (H2-receptor model) compounds with mepyramine or cyclizine structure are also less active than the single references tiotidine, ranitidine, or lamtidine. Nevertheless substances with a pheniramine like partial structure proved to be potent histamine H2-receptor antagonists at the atrium model (about 27 times more active than cimetidine).

Studies on antiulcer drugs. 7. 2-Guanidino-4-pyridylthiazoles as histamine H2-receptor antagonists with potent gastroprotective effects against nonsteroidal antiinflammatory drug-induced injury

A series of 2-guanidino-4-pyridylthiazole derivatives were synthesized and evaluated for anti-aspirin-ulcer, gastric antisecretory, and histamine-H2-receptor-antagonist activities. Several compounds showed superior anti-aspirin-ulcer activity to that of clinically used H2-antagonists in the rat. Among them, 4-[6-(acetamidomethyl)pyridin-2-yl]-2-guanidinothiazole (8) demonstrated potent inhibitory activities against gastric lesions caused by two kinds of nonsteroidal antiinflammatory drugs, aspirin and indomethacin, respectively, in addition to strong antisecretory activity. Compound 8 possessed a preventable ability for the aspirin-induced reduction of the gastric mucosal blood flow at an intragastric administration of 32 mg/kg in the rat. On the other hand, famotidine (32 mg/kg) exhibited no significant effect and ranitidine (100 mg/kg) aggravated the blood flow in this system.

Histamine analogues, XXXV: 2-substituted histamine derivatives containing classical moieties of H2-antagonists--a novel class of H1-agonists

A new type of H1-agonists resulted from the combination of the essential histamine structure with parts of H2-antagonists. 2,4-Disubstituted imidazole derivatives were synthesized by reaction of imidic acid methyl esters with 1,3-dihydroxypropanone, 1,4-dihydroxybutanone or 2-oxo-4-phthalimido-1-butylacetate in liquid NH3. The imidazole intermediates were converted into histamine analogues by simple deprotection, Gabriel synthesis followed by deprotection, or by side-chain elongation via the nitriles and final hydrogenation. The new compounds were screened for H1-activity on the isolated guinea-pig ileum and for H2-antagonistic activity on the isolated guinea-pig right atrium. The substances are comparably weak H1-agonists and moderate H2-blockers.

Synthesis and H2-antagonist properties of some 1,2,5-thiadiazole-1-oxide derivatives

A series of 1,2,5-thiadiazole-1-oxide derivatives has been synthesized and studied for its H2-antagonist properties. These derivatives can be considered derived from classical H2-antagonists in which the structure was deeply modified in order to evidence the minimal structural requirements for the activity. It was found that it is sufficient to have the 1,2,5-thiadiazole-1-oxide ring substituted with an alkylamino moiety and with an aliphatic chain linked to the hydroxy or ether group to achieve compounds as active as cimetidine. A few considerations on the binding on guinea-pig cerebral cortex of a series of H2-antagonists with more and more simplified structures are also reported.

The effect of lipophilic substituents on the H2-histaminergic activity of some close analogues of impromidine

The cimetidine-like moiety of the potent H2-agonist impromidine (9a) and three closely related guanidines (10a, 11a, and 12a) which are modified in the imidazolylpropyl portion, has been replaced by 2-[(2-pyridyl)methylthio]ethyl, 2-(benzylthio)ethyl and 3,3-diphenylpropyl substituents. Guanidines 10-12 were obtained from acidic hydrolysis of corresponding N-benzoyl guanidines 7, 8, and 15, accessible by successive aminolysis of diphenyl N-benzoyl carbonimidate (2) according to known methods. Compared with leads 10a and 11a lipophilic substitution affords almost equipotent H2-agonists 10b-d and 11b-d, while substituents with increasing lipophilicity enhance both intrinsic activity and potency of the weak partial agonist 12a at guinea-pig atrial H2-receptors. Guanidines 10-12 are weak H1-antagonists on the isolated guinea-pig ileum.

Studies on Antiulcer Drugs. VI. 4-Furyl-2-guanidinothiazoles and Related Compounds as Potent Histamine H2-Receptor Antagonists

A series of 4-furyl-2-guanidinothiazole derivatives and related compounds were synthesized and evaluated for histamine H2-receptor antagonist and gastric acid antisecretory activities. Among them, compounds I-17, I-48 and I-49 showed high activities in these tests. In addition, compound I-17 possessed potent inhibitory activities on each of the gastric ulcers induced by stress, ethanol and HCl-aspirin. On the other hand, compound I-48 demonstrated antimicrobial activity against Helicobacter Pylori and the potency was far stronger than that of clinically used H2-antagonists. Some structure-activity relationships are discussed.

Studies on Antiulcer Drugs. V. Synthesis and Antiulcer Activity of Aralkylbenzazoles

A series of 2-alkylamino-5- or 6-aralkyl-substituted benzazoles were synthesized and tested for histamine H2-receptor antagonist and anti-stress ulcer activities. These new compounds showed little or no histamine H2-receptor antagonist activity in contrast to imidazo[1,2-a]pyridine analogues (I). On antiulcer assay, however, some pyridine derivatives (II) exerted higher activity than the reference compounds, sofalcone, sucralfate and cimetidine. The structure-activity relationships of these compounds are discussed.

Potential Histamine H2-Receptor Antagonists: Synthesis and Pharmacological Activity of Derivatives Containing Acylamino-furazan Moieties

Analogues of 3-amino-4-[2-[(5-dimethylaminomethyl-2-furyl)methylthio]ethylamino] furazan (1) containing carbonyl groups joined to the amino functions linked to the furazan system have been synthetized and investigated for their H2-antagonist properties on the isolated guinea pig right atrium. The presence of the carbonyl group lowers the activity in respect to the corresponding leads. The decrease in activity is only by 1-2 orders of magnitude in the 3-acylamino-furazan series versus inactivity in the 4-acylamino isomers and in the diacylated series.

Studies on Antiulcer Drugs. IV. Synthesis and Antiulcer Activities of Imidazo(1,2-a)pyridinylethylbenzothiazoles and -benzimidazoles

A series of 6-[2-(imidazo[1,2-a]pyridin-2-yl)ethyl]benzothiazoles (II) and benzimidazole analogues (III) was synthesized and tested for histamine H2-receptor antagonist, gastric antisecretory and anti-stress ulcer activity. A benzimidazole derivative (IIIa) exhibited strong antisecretory activity, whereas the corresponding benzothiazole derivative (IIb) lacked this potency in in vivo test. In contrast to compound IIIa, however, compound IIb demonstrated good inhibition against stress induced ulcer. The structure-activity relationships of these compounds are discussed.

[Quinazolinones. 18. Synthesis and H1/H2-antihistaminic action of omega-[2-aryl-2,3-dihydro-4(1H)-quinazolinone-1-yl]alkyl substituted ureas and cyanoguanidines]

A series of (2-aryl-2,3-dihydro-4(1H)-quinazolinon-1-yl)alkyl-substituted cyanoguanidines and ureas with histamine, cimetidine or roxatidine partial structure was prepared and tested for H1- and H2-antagonism at the isolated ileum and the isolated right atrium of the guinea-pig. All compounds investigated were only very weak H1-antagonists, whereas the 3-[3-(1-piperidinyl-methyl)phenoxy]propyl-cyanoguanidines and -ureas were more potent H2-antagonists than cimetidine, maximally achieving about ranitidine's potency.

Structure-activity studies of pyridinylalkyl-isocytosine H1-receptor antihistamines and identification of an active conformation

For a series of 2-(pyridin-2-ylbutylamino)-5-(3-picolinylmethyl)pyrimidin- 4(1H)-ones (isocytosines) substituted in the pyridine 3-position, activity as H1- and H2-receptor histamine antagonists appears to correlate with the size of the 3-substituent. Steric interaction between the substituent and the butyl chain is explored by conformational analysis using Molecular Mechanics and Molecular Orbital calculations on 2-propyl- and 2-propyl-3-methyl-pyridines; it appears that the substituent may alter activity by changing the preferred conformation of the drug. This observation is extended by synthesis of a semirigid bicyclic analogue wherein 3-methylpyridinylbutyl is replaced by tetrahydroquinolinylpropyl. This compound is 2-3 times more potent as an H1-receptor antagonist confirming that a trans/trans conformation favours activity. Although derived from an H2-antagonist structure, the compound is not an antagonist at histamine H2 receptors thus proving that the conformational requirements are different at H1 and H2 receptors.

H2-antagonists: synthesis and activity of 2-amino-5-thiazolyl derivatives

2-Amino- and 2-guanidinothiazole derivatives having in position 5 a methylthioalkyl side-chain with urea-equivalent moieties were prepared for comparison with H2-antagonists of cimetidine and tiotidine series. Examination of the pharmacological results obtained from experiments on guinea pig atria and in cat gastric fistula, suggests some general observations about the structure-activity relationship of the compounds synthesized. The activity trend of these products is different from that of H2-imidazole antagonists while it is similar to that of the tiotidine series. Unlike the tiotidine similar compounds, the 2-guanidino-5-thiazolyl derivatives are less potent than the corresponding 2-amino-5-thiazolyl products. The activity of the latter ones is reduced in comparison to that of tiotidine or cimetidine.

Potential histamine H2-receptor antagonists. Synthesis, structure and activity of a few open models related to classical H2-antagonists

A few ethers and oximes structurally related to classical H2-antagonists have been synthetized and tested for their in vitro H2-antagonist activity. The compounds in which cyclic "urea equivalent" groups are joined to a cyclohexylmethyl moiety showed a high increase of activity in comparison with the unsubstituted analogues. This finding supports the hypothesis of the existence of an accessorial binding area on H2-receptor near the site fitted by cyclic "urea equivalent" groups.

[Quinazolinones. 16. Synthesis and in vitro pharmacology of 2-aryl-1- ([3-(imidazol-4-yl)propyl]-guanidinylalkyl)-2,3-dihydro-4(1H)- quinazolinones]

A series of 2-aryl-1- ([3-(imidazol-4-yl)propyl]guanidinylalkyl)-2,3-dihydro-4(1H)- quinazolinones were prepared starting with appropriate aminoalkyl-quinazolinones. The substances proved to be moderate H1-antagonists at the isolated guinea-pig ileum as well as H2-agonists, maximally achieving 1.6 times the activity of histamine at the isolated guinea-pig right atrium. Compounds with a three-membered carbon chain connecting the bicyclus and the guanidine system are up to 100 times more active at the atrium (chronotropic effect) than the corresponding lower homologues.

Synthesis of 3-[2-(2,3-dihydro-5-phenyl-4-substituted-3H-1,2,4- triazole-3-thione-2-yl)-acetylamino]-2-methyl-4(3H)-quinazolinones and their pharmacological activities

Some 2-methyl-3-triazole-substituted-4(3H)-quinazolinones 3a-f were prepared and tested for their H1- and H2-antihistaminic activities. In addition these compounds are central nervous system depressants and anticonvulsants. 3e shows highly significant decrease of locomotor activity.

Synthesis and activity of pyridine analogues of histamine H2-receptor antagonists

Derivatives of 2-amino-3-nitropyridine (4; see Table I for structures) and 2-amino-3-nitro-1H-pyrid-6-one (5), conceived as cyclic 'urea equivalents' of histamine H2-receptor antagonists, were prepared. Pharmacological testing, using the histamine-induced guinea pig atrial chronotropic response, indicated that the R1-pyridyl substituent was a determinant of activity, since the relative activities within an isomeric series were 4-pyridyl greater than 3- and 2-pyridyl. In comparison with analogous 2-amino-3-nitropyridines. (4), 2-amino-3-nitro-1H-pyrid-6-ones (5) had a substantially less histamine H2-receptor antagonist activity. This reduction in activity is attributed to altered orientation of the dipole due to the presence of the C-6 oxo substituent, and/or to the overall effect of oxo in decreasing lipophilicity. The most potent antagonist, 2-[( 2-[(4-pyridyl)methylthio]ethylamino])-3-nitro-6-methoxypyridine, was four times less active than cimetidine.

[Alkyl- and alkoxy-substituted lamtidine analogs: synthesis and H2-antagonistic activity. 38. H2-antihistaminics]

In studies on the structure-activity relationships of histamine H2-receptor antagonists, lamtidine analogous derivatives of ortho-, meta- und para-substituted piperidinomethylphenoxypropylamines bearing an additional substituent on the aromatic ring were prepared and tested for their H2-antagonistic activity on the isolated guinea-pig atrium. An additional substituent decreases the H2-antagonistic activity of the 3-(3-piperidinomethyl-phenoxy)-propylamine derivatives, while 2-membered substituents neighboring the connecting chain increase the activity of the ortho- and para-piperidinomethyl-substituted phenoxypropylamine derivatives.