New Histamine-Related Five-Membered N-Heterocycle Derivatives as Carbonic Anhydrase I Activators.

A series of histamine (HST)-related compounds were synthesized and tested for their activating properties on five physiologically relevant human Carbonic Anhydrase (hCA) isoforms (I, II, Va, VII and XIII). The imidazole ring of HST was replaced with different 5-membered heterocycles and the length of the aliphatic chain was varied. For the most interesting compounds some modifications on the terminal amino group were also performed. The most sensitive isoform to activation was hCA I (KA values in the low micromolar range), but surprisingly none of the new compounds displayed activity on hCA II. Some derivatives (1, 3a and 22) displayed an interesting selectivity for activating hCA I over hCA II, Va, VII and XIII.

Synthesis and biological evaluation of histamine Schiff bases as carbonic anhydrase I, II, IV, VII, and IX activators.

A series of 20 histamine Schiff base was synthesised by reaction of histamine, a well known carbonic anhydrase (CA, E.C 4.2.2.1.) activator pharmacophore, with substituted aldehydes. The obtained histamine Schiff bases were assayed as activators of five selected human (h) CA isozymes, the cytosolic hCA I, hCA II, and hCA VII, the membrane-anchored hCA IV and transmembrane hCA IX. Some of these compounds showed efficient activity (in the nanomolar range) against the cytosolic isoform hCA VII, which is a key CA enzyme involved in brain metabolism. Moderate activity was observed against hCA I and hCA IV (in the nanomolar to low micromolar range). The structure-activity relationship for activation of these isoforms with the new histamine Schiff bases is discussed in detail based on the nature of the aliphatic, aromatic, or heterocyclic moiety present in the aldehyde fragment of the molecule, which may participate in diverse interactions with amino acid residues at the entrance of the active site, where activators bind, and which is the most variable part among the different CA isoforms.

Mono- and di-halogenated histamine, histidine and carnosine derivatives are potent carbonic anhydrase I, II, VII, XII and XIV activators.

Mono- and di-halogenated histamines, l-histidine methyl ester derivatives and carnosine derivatives incorporating chlorine, bromine and iodine were prepared and investigated as activators of five carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the cytosolic hCA I, II and VII, and the transmembrane hCA XII and XIV. All of them were activated in a diverse manner by the investigated compounds, with a distinct activation profile.

Synthesis and functional characterization of imbutamine analogs as histamine H3 and H4 receptor ligands.

Imbutamine (4-(1H-imidazol-4-yl)butanamine) is a potent histamine H3 (H3R) and H4 receptor (H4R) agonist (EC50 values: 3 and 66 nM, respectively). Aiming at improved selectivity for the H4R, the imidazole ring in imbutamine was methyl-substituted or replaced by various differently substituted heterocycles (1,2,3-triazoles, 1,2,4-triazoles, pyridines, pyrimidines) as potential bioisosteres. Investigations in [(35)S]GTPγS binding assays using membranes of Sf9 insect cells expressing the respective human histamine receptor subtype revealed only very weak activity of most of the synthesized hetarylalkylamines at both receptors. By contrast, the introduction of substituents at the 4-imidazolyl ring was most effective regarding H4R selectivity. This holds for methyl substitution in position 2 and, especially, in position 5. 5-Methylimbutamine (H4R: EC50 = 59 nM, α = 0.8) was equipotent with imbutamine at the hH4R, but revealed about 16-fold selectivity for the hH4R compared to the hH3R (EC50 980 nM, α = 0.36), whereas imbutamine preferred the hH3R. The functional activities were in agreement with radioligand binding data. The results support the hypothesis that, by analogy with histamine, methyl substitution in histamine homologs offers a way to shift the selectivity in favor of the H4R.

Deoxynucleoside triphosphates bearing histamine, carboxylic acid, and hydroxyl residues--synthesis and biochemical characterization.

Modified nucleoside triphosphates (dA(Hs)TP, dU(POH)TP, and dC(Val)TP) bearing imidazole, hydroxyl, and carboxylic acid residues connected to the purine and pyrimidine bases through alkyne linkers were prepared. These modified dN*TPs were excellent substrates for various DNA polymerases in primer extension reactions. Moreover, the combined use of terminal deoxynucleotidyl transferase (TdT) and the modified dNTPs led to efficient tailing reactions that rival those of natural counterparts. Finally, the triphosphates were tolerated by polymerases under PCR conditions, and the ensuing modified oligonucleotides served as templates for the regeneration of unmodified DNA. Thus, these modified dN*TPs are fully compatible with in vitro selection methods and can be used to develop artificial peptidases based on DNA.

Carbonic anhydrase I and II activation with mono- and dihalogenated histamine derivatives.

Mono- and dihalogenated histamine derivatives incorporating fluorine, chlorine and bromine have been prepared together with the corresponding boc-protected compounds at the aminoethyl group. They have been investigated as activators of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). The cytosolic human (h) isoforms hCA I and II were moderately activated by the boc-protected halogenated histamines and very effectively activated by the deprotected ones. Low nanomolar and subnanomolar hCA I and II activators have been detected for the first time, starting from histamine as lead which has an affinity of 2 µM against isoform I and of 125 µM against hCA II.

A chemical switch for the modulation of the functional activity of higher homologues of histamine on the human histamine H3 receptor: effect of various substitutions at the primary amino function.

In an effort to establish the structural requirements for agonism, neutral antagonism, and inverse agonism at the human histamine H(3) receptor (H(3)R) we have prepared a series of higher homologues of histamine in which the terminal nitrogen of the side chain has been either mono- or disubstituted with several aliphatic, alicyclic, and aromatic moieties or incorporated in cyclic systems. The novel ligands have been pharmacologically investigated in vitro for their affinities on the human H(3)R and H(4)R subtypes by radioligand displacement experiments and for their intrinsic H(3)R activities via a CRE-mediated beta-galactosidase reporter gene assay. Subtle changes of the substitution pattern at the side chain nitrogen alter enormously the pharmacological activity of the ligands, resulting in a series of compounds with a wide spectrum of pharmacological activities. Among the several neutral H(3)R antagonists identified within this series, compounds 2b and 2h display an H(3)R affinity in the low nanomolar concentration range (pK(i) values of 8.1 and 8.4, respectively). A very potent and selective H(3)R agonist (1l, pEC(50) = 8.9, alpha = 0.94) and a very potent, though not highly selective, H(3)R inverse agonist (2k, pIC(50) = 8.9, alpha = -0.97) have been identified as well.

Potential histamine H2-receptor antagonists. 3. Methylhistamines.

Syntheses are described for all the mono- and some di- and trimethylhistamines. New methods are given for the known Npi, Ntau-, Nalpha-, 2-, and 4-methylhistamines and for the novel compounds, beta-methyl-, 4,Nalpha-dimethyl-, and 4,Nalpha,Nalpha-trimethylhistamines. Agonist activities are reported for stimulation of histamine H1 (guinea-pig ileum) and H2 (rat gastric acid secretion) receptors. H2-Receptor agonist activities indicate that a methyl group is more readily accommodated at the 4 and Nalpha positions than elsewhere in the histamine molecule and that receptor binding is substantially retained with a methyl substituent in these positions. Thus, for the design of potential antagonists, two sites are identified as being worthwhile exploring for the introduction of lipophilic substituents.

Synthesis and pharmacological identification of neutral histamine H1-receptor antagonists.

In the present study we searched for neutral antagonists for the human histamine H(1)-receptor (H(1)R) by screening newly synthesized ligands that are structurally related to H(1)R agonists for their affinity using radioligand displacement studies and by assessing their functional activity via performing a NF-kappaB driven reporter-gene assay that allows for the detection of both agonistic and inverse agonistic responses. Starting from the endogenous agonist for the H(1)R, histamine, we synthesized and tested various analogues and ultimately identified several compounds with partial inverse agonistic properties and two neutral H(1)-receptor antagonists, namely 2-[2-(4,4-diphenylbutyl)-1H-imidazol-4-yl]ethylamine (histabudifen, 18d) (pK(i) = 5.8, alpha = 0.02) and 2-[2-(5,5-diphenylpentyl)-1H-imidazol-4-yl]ethylamine (histapendifen, 18e) (pK(i) = 5.9, alpha = -0.09).

Congener derivatives and conjugates of histamine: synthesis and tissue and receptor selectivity of the derivatives.

A series of 19 congener derivatives and conjugates of histamine was synthesized and tested to determine whether the ligands would alter the conventional histamine activity in various tissues. The derivatives, which contained either branched or unbranched aliphatic groups, aromatic amide groups, or dipeptides, exhibited affinities for histamine type 1 and/or type 2 receptors that were widely different from the progenitor. The p-trifluoromethyl derivative of histamine with an intermediate chain length of four methylenes (compound 13) was the most potent lymphocytes H2 receptor agonist but was inactive on guinea pig myocardium H2 receptors. The deletion of a single methylene chain (compound 12) from this compound resulted in total loss of its H2 activity on lymphocytes and its H1 activity on aorta. Compound 12 became an exclusive H1 agonist on lymphocytes H1 receptors. The dipeptide conjugate (compound 17) and the aliphatic congener derivative (compound 18), both with four methylenes, retained some of the activity on guinea pig myocardium H2 receptors, but lost their activity on lymphocytes H2 receptors. Therefore, histamine can be modified at sites that are at a distance from the imidazole moiety, resulting in tissue selective histamine receptor agonists.

Potential histamine H2-receptor antagonists. 4. Benzylhistamines.

As part of our studies aimed at designing histamine H2-receptor antagonists, the effect on histaminergic activity of introducing benzyl substituents at various positions in the histamine molecule is described. New synthetic methods are reported for the novel 4-benzyl-, beta-benzyl- and 4,N tau-dibenylhistamines and the reported 2-benzylhistamine. The novel N tau-benzylhistamine was synthesized by the versatile route reported by us for the synthesis of N tau-methylhistamine. These benzylhistamines, together with the reported N alpha- and N pi-benzylhistamines, were tested for agonist and antagonist activity at both H1 and H2 receptors. The results obtained indicate that introduction of a benzyl group into the histamine molecule causes a marked reduction in H1- or H2-agonist activity, and none of the compounds showed consistent antagonist activity. Evidently, the sterically demanding benzyl substituent is not easily accommodated in the agonist binding mode and is unable to locate a lipophilic receptor region for potential hydrophobic binding.

N(alpha)-imidazolylalkyl and pyridylalkyl derivatives of histaprodifen: synthesis and in vitro evaluation of highly potent histamine H(1)-receptor agonists.

A novel series of N(alpha)()-imidazolylalkyl and pyridylalkyl derivatives of histaprodifen (6, 2-[2-(3,3-diphenylpropyl)imidazol-4-yl]ethanamine) was synthesized and evaluated as histamine H(1)-receptor agonists. The title compounds displayed partial agonism at contractile H(1)-receptors of guinea pig ileum and were at least equipotent with histamine. Agonist effects of the new derivatives were susceptible to blockade by the H(1)-receptor antagonist mepyramine (2-100 nM). In the imidazole series, suprahistaprodifen (51, [2-[2-(3,3-diphenylpropyl)-1H-imidazol-4-yl]ethyl]-[2-(1H-imidazol-4-yl)ethyl]amine, N(alpha)-2-[(1H-imidazol-4-yl)ethyl]histaprodifen) showed the highest H(1)-receptor agonist potency ever reported in the literature (pEC(50) 8.26, efficacy E(max) 96%). Elongation of the alkyl spacer from ethyl to butyl decreased activity from 3630% (ethyl, 51) to 163% (butyl, 53) of histamine potency. The exchange of the terminal imidazole nucleus for a pyridine ring resulted in compounds with comparably high potency. A decrease in agonist potency and efficacy was observed when the attachment of the alkyl spacer was consecutively changed from the ortho to the meta and the para position, respectively, of the pyridine ring. The pyridine series that contained a butyl chain possessed the highest potency and affinity. N(alpha)-[4-(2-pyridyl)butyl]histaprodifen (56) emerged as a strong partial agonist, being almost equipotent with 51 (pEC(50) 8.16, E(max) 89%). Compounds 51 and 56 also showed potent partial agonism at contractile H(1) receptors in guinea pig aorta and potently activated H(1)-receptor-mediated endothelium-dependent relaxation in the rat aorta. Compounds 51-65 displayed low to moderate affinity at H(2), H(3), and M(3) receptors in functional models of guinea pig. Collectively, N(alpha)-imidazolylalkyl- and N(alpha)-pyridylalkyl-substituted histaprodifens represent a novel class of potent H(1)-receptor agonists. These compounds may be useful to define the (patho)physiological role of the H(1)-receptor and refine molecular models of H(1)-receptor activation.

Characterization of the binding site of the histamine H3 receptor. 1. Various approaches to the synthesis of 2-(1H-imidazol-4-yl)cyclopropylamine and histaminergic activity of (1R,2R)- and (1S,2S)-2-(1H-imidazol-4-yl)-cyclopropylamine.

Various approaches to the synthesis of all four stereoisomers of 2-(1H-imidazol-4-yl)cyclopropylamine (cyclopropylhistamine) are described. The rapid and convenient synthesis and resolution of trans-cyclopropylhistamine is reported. The absolute configuration of its enantiomers was determined by single-crystal X-ray crystallographic analysis. The distinct trans-cyclopropylhistamine enantiomers were tested for their activity and affinity on the histamine H3 receptor. (1S,2S)-Cyclopropylhistamine (VUF 5297) acts as an agonist both on the rat cortex (pD2 = 7.1; alpha = 0.75) and on guinea pig jejunum (pD2 = 6.6; alpha = 0.75). Its enantiomer, (1R, 2R)-cyclopropylhistamine (VUF 5296), is about 1 order of magnitude less active. Both enantiomers show weak activity on H1 and H2 receptors. All synthetic attempts to cis-cyclopropylhistamine were unsuccessful. Nevertheless, the results of this study provide an ideal template for molecular modeling studies of histamine H3 receptor ligands.

Preparation of radioactive iodinated cholylhistamine for use in the radioimmunoassay of cholic acid.

A major handicap in the development of simple and accurate radioimmunoassay procedures for bile acids has been the lack of a radioactive standard of high specific activity. To provide such a compound, we first synthesized cholylhistamine using the carbodiimide reaction. The hypothesized structure was confirmed by elemental analysis, thin-layer chromatography, infrared and mass spectral analysis. The cholylhistamine was then iodinated with 125I, using the choloramine-T method. The 125I-cholylhistamine was bound by antisera raised against a cholic acid-bovine serum albumin conjugate. This procedure should prove useful in preparing radioactive conjugates for all of the bile acids.

Synthesis of histamine analogs.

Nineteen histamine analogs were synthesized, and their biological actions were compared to those of histamine in blood pressure, gastric secretion, and nasal decongestant screens. The analogs include N-substituted 4-aminoethylimidazoles, N-substituted 2-pyridylethylamines, 2-pyridylcyclohexylamines, and 2-pyridylcyclopropylcarbamates. None of the compounds showed appreciable histamine agonist or antagonist properties.

Carbonic anhydrase activators. Part 24. High affinity isozymes I, II and IV activators, derivatives of 4-(4-chlorophenylsulfonylureido-amino acyl)ethyl-1H-imidazole.

N-1-Tritylsulfenyl histamine was synthesized by reaction of histamine (Hst) with tetrabromophthalic anhydride followed by protection of its imidazole moiety with tritylsulfenyl chloride. After hydrazinolysis, it afforded a key intermediate which was derivatized at the aminoethyl group in order to obtain new types of activators of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). Reaction of the key intermediate with 4-chlorophenylsulfonylureido amino acids (cpu-AA) in the presence of carbodiimides afforded, after deprotection of the imidazolic nitrogen atom, a series of compounds with the general formula cpu-AA-Hst (cpu, 4-ClC(6)H(4)SO(2)NHCO). Some structurally related dipeptide derivatives with the general formula cpu-AA1-AA2-Hst (AA, AA1 and AA2 represent amino acyl moieties) were also prepared by a strategy similar to that applied for the amino acyl compounds mentioned above. The new derivatives proved to be efficient activators of three CA isozymes. Best activity was detected against hCA I and bCA IV, for which some of the new compounds showed affinities in the 1-10 nM range (h, human; b, bovine isozymes). hCA II, on the other hand, was less prone to activation by the new derivatives, which possessed affinities around 20-50 nM for this isozyme. This new class of CA activators might lead to the development of drugs/diagnostic agents for CA deficiency syndrome, a genetic disease of bone, brain and kidneys.

Luminescent ruthenium complexes for theranostic applications.

The water-soluble and visible luminescent complexes cis-[Ru(L-L)2(L)2](2+) where L-L = 2,2-bipyridine and 1,10-phenanthroline and L= imidazole, 1-methylimidazole, and histamine have been synthesized and characterized by spectroscopic techniques. Spectroscopic (circular dichroism, saturation transfer difference NMR, and diffusion ordered spectroscopy NMR) and isothermal titration calorimetry studies indicate binding of cis-[Ru(phen)2(ImH)2](2+) and human serum albumin occurs via noncovalent interactions with K(b) = 9.8 × 10(4) mol(-1) L, ΔH = -11.5 ± 0.1 kcal mol(-1), and TΔS = -4.46 ± 0.3 kcal mol(-1). High uptake of the complex into HCT116 cells was detected by luminescent confocal microscopy. Cytotoxicity of cis-[Ru(phen)2(ImH)2](2+) against proliferation of HCT116p53(+/+) and HCT116p53(-/-) shows IC50 values of 0.1 and 0.7 µmol L(-1). Flow cytometry and western blot indicate RuphenImH mediates cell cycle arrest in the G1 phase in both cells and is more prominent in p53(+/+). The complex activates proapoptotic PARP in p53(-/-), but not in p53(+/+). A cytostatic mechanism based on quantification of the number of cells during the time period of incubation is suggested.

Optical modulation of supramolecular assembly of amphiphilic photochromic diarylethene: from nanofiber to nanosphere.

A diarylethene derivative with histamines as side chains was synthesized and the morphology of self-assembled supramolecular architecture can be tuned from nanofiber to nanosphere by photo irradiation. The theoretical calculation and model of the self-assembled nanostructure are presented to illuminate the possible self-assembly mechanism.

Histaminol: identification and HPLC analysis of a novel compound in wine.

Histaminol, a minor histamine metabolite originating from imidazole acetaldehyde, has been detected in a food matrix as complex as wine. The standard molecule was synthesized, and subsequently the chemical structure was confirmed by ESI-MS and NMR measurements. The development, optimization, and in-house validation of a HPLC-DAD chromatographic method for the quantitative determination of histaminol in wine are described and discussed. The expanded uncertainty (U(k=2)) of the procedure was estimated as 11.06%. Twenty commercial Italian wine samples were selected. All samples (16 red and 4 white wines) were analyzed after a C-18 SPE cartridge fractionation procedure. The content of this alcohol was in the range of 0.289-1.094 mg/L (minimum and maximum values were obtained for Nero d'Avola vintage 2007 and Barolo vintage 1969, respectively).