Quaternary phosphonium reversible inhibitors of cholinesterases of different animals

The quaternary phosphonium compounds were found to be reversible inhibitors of cholinesterases of different animals and showed species-specificity of action depending on their inhibitor structure. We have revealed difference in the inhibitory specificity of various acetylcholinesterase preparations. A difference has been shown in inhibitory parameters of optic ganglia of individuals of the squid Berryteuthis magister from different habitat areas. For the first time in comparing phosphonium and ammonium isologues-tetrabutyl- and tributylhexyl derivatives, it has been shown that they are agents practically similar by the character of the anticholinesterase action.     

Organosilicon reversible inhibitors of cholinesterases of different animals

The review presents data on cholinesterase effects of 28 specially synthesized organosilicon compounds (monoonium, organoelement, and bisonium derivatives) studied as reversible inhibitors of acetylcholinesterase (acetyl-ChE) of human erythrocytes, butyryl-ChE of horse blood serum, ChE of brain of common frog Rana temporaria, ChE of the optical ganglia tissue of Pacific squid Todarodes pacificus and of individuals of Commandor squid Berryteuthis magister from various habitats in the Northwestern aquatoria of the Pacific ocean. Among the tested compounds, there are revealed highly specific inhibitors of mammalian ChE as well as of ChE of the B. magister individuals from various habitats.     

Anabasine derivatives as reversible and irreversible inhibitors of cholinesterases from different animals

A comparative study was carried out of action of 18 specifically synthesized anabasine derivatives and their analogs, including diiodomethylates of anabasine acylates and bis-anabasine derivatives of dicarboxylic glutaric, adipic, azelaic, and sebacic acids, on activity of cholinesterase of brain of frog Rana temporaria and visual ganglia of the Pacific squid Todarodes pacificus and Commander squid Berryteuthis magister from different zones of habitations in the northwest part of the Pacific Ocean as well as of erythrocyte acetylcholinesterase and serum butyrylcholinesterase. These compounds were not submitted to cholinesterase hydrolysis and turned out to be efficient reversible inhibitors that have to certain degree specificity toward the studied enzymes both by their potency and by the type of their inhibitory action. Specificity of effects of the key structural fragments of the anabasine grouping on anticholinesterase efficacy was checked. Also performed was analysis of action of 24 reversible and irreversible organophosphorus inhibitors, anabasine derivatives, toward erythrocyte acetylcholinesterase and serum butyrylcholinesterase. The anticholinesterase effects of anabasine-containing inhibitors differing in structure and action mechanism was compared.     

Siliconorganic reversible inhibitors of cholinesterases of various animals

The review present data on cholinesterase effects of 28 specially synthesized siliconorganic compounds (monoonium, clementorganic, and bisonium derivatives) studied as reversible inhibitors of acetylcholinesterase (acetyl-ChE) of human erythrocytes, butyryl-ChE of horse blood serum, ChE of brain of common frog Rana temporaria, ChE of the optical ganglia tissue of Pacific squid Todarodes pacificus and of individuals of Commandor squid Berryteuthis magister from various habitats in the Northwestern aquatoria of the Pacific ocean. Among the tested compounds, there are revealed highly specific inhibitors of mammalian ChE as well as of ChE of the B. magister individuals from various habitats.     

Alkylammonium chlorobenzoates are a new group of ester-containing reversible inhibitors of cholinesterases of different animals

Interaction with cholinesterases (ChEs) of nine specially synthesized derivatives of dimethylaminoalkyl esters of 2-chloro-and 2,4-dichlorobenzoic acids and their iodoalkylates is studied. Used as enzyme sources were partially purified preparations of acetylcholinesterase (AChE) from human erythrocytes and butyrylcholinesterase (BChE) from horse blood serum, as well as water homogenates of the frog Rana temporaria brain and of the Pacific squid Todarodes pacificus optical ganglia. The studied benzoates failed to be hydrolyzed by the studied ChEs at the enzyme concentrations exceeding 10 times those used for determination of the acetylthiocholine hydrolysis rate. These compounds have turned out to be reversible inhibitors of ChEs of the mixed-noncompetitive type of action. Effects on the anticholinesterase activity of such structural elements of the inhibitors as the acidic part of the benzoate molecule, length of polymethylene chain in the molecule alcoholic part, and the structure of ammonium group are studied. This study has allowed revealing some peculiarities of the reaction capability of vertebrate and invertebrate ChEs.     

Inhibition of cholinesterases by quaternary phosphonium compounds

Alkyl tributylphosphonium and triphenylphosphonium derivatives as well as tetraphenylphosphonium were first studied as inhibitors of acetylcholinesterase of human blood erythrocytes and butyrylcholinesterase of horse blood serum. The inhibition is reversible, of mixed type, with a different contribution of competitive and uncompetitive components. The value of the inhibitory effect is essentially dependent on the structure of phosphonium compounds, especially in experiments with butyrylcholinesterase: allyltriphenylphosphonium is 290 times as strong enzyme inhibitor as methyltributylphosphonium. Hexyltributylphosphonium is identical to hexyltributylammonium in both the pattern and efficiency of the inhibitory action on cholinesterases.     

Compounds with the dioxopyrimidine cycle inhibit cholinesterases from different groups of animals

We firstly synthesized derivatives of 6-methyluracil, alloxazine, and xanthine, containing omega-tetraalkylammonium (TAA) groups at the N(1) and N(3) atoms in a pyrimidine cycle and assayed their anticholinesterase activities. Compounds with triethylpentylammoniumalkyl groups behaved as typical reversible inhibitors of acetylcholinesterase (AChE) (pI(50) 3.20-6.22) and butyrylcholinesterase (BuChE) (pI(50) 3.05-5.71). Compounds, containing two ethyl residues and a substituted benzyl fragment in the tetraalkylammonium group at N(3) atoms or two similar TAA groups at N(1) and N(3) atoms, possessed very high anticholinesterase activity. Although these compounds displayed the activity of typical irreversible AChE inhibitors (a progressive AChE inactivation; k(i) 7.6x10(8) to 3.5x10(9)M(-1)min(-1)), they were reversible inhibitors of BuChE (pI(50) 3.9-6.9). The efficiency of AChE inhibition by some of these compounds was more than 10(4) times higher than the efficiency of BuChE inhibition. Several synthesized TAA derivates of 6-methyluracil reversibly inhibited electric eel and cobra venom AChEs and horse serum BuChE. However, depending on their structure, the tested compounds possessed the time-progressing inhibition of mammalian erythrocyte AChE, typically of irreversible inhibitors. As shown upon dialysis and gel-filtration, the formed mammalian AChE-inhibitor complex was stable. Thus, a new class of highly active, selective, and irreversible inhibitors of mammalian AChE was described. In contrast to classical phosphorylating or carbamoylating AChE inhibitors, these compounds are devoid of acylating functions. Probably, these inhibitors interact with certain amino acid residues at the entrance to the active-site gorge.     

Thiosubstrates of different cholinesterases

Review of the own and literature data on substrate specificity with use of thiosubstrates for cholinesterases of various species. Dependence of cholinesteratic hydrolysis parameters on various elements of their structure is considered: the acyl part, alkyl "bridge" between ester atom and onion group, and ammonium grouping of molecule of 44 thioesters. A comparative enzymological analysis of the substrate specificity is performed with use of thiocholine esters of acetic, propionic, and butyric acids for 40 cholinesterase preparations of mammals, insects, molluscs, and plants.     

Comparative analysis of sensitivity of cholinesterases of different origin to monoonium reversible inhibitors

The analytic review of the literature data on constants of interaction of cholinesterases of different animal (vertebrates and squids) with 89 onium (ammonium, phosphonium, sulfonium) reversible inhibitors constituting homologous series with regularly varied structure is carried out. Values of the competitive, uncompetitive and generalized inhibitor constants are compared. On the basis of that, conclusions about the mechanism of action of the studied compounds and primary place of their sorption—in “anionic” or peripheral “anionic” sites of enzymes—are made. The presented data are considered from the point of view of comparative biochemistry and in light of current concepts of cholinesterase active center structure.     

Comparative analysis of sensitivity of cholinesterases of different origin to reversible bis-onium inhibitors

Analytical review of literature data has been carried out about kinetic parameters of cholinesterases (ChE) of various animals (vertebrates and squids) with 45 reversible bis-onium inhibitors forming homologous series with regularly changing structure. Values of competitive, non-competitive, and generalized inhibitory constants are compared. Interspecies and intraspecies differences are revealed in sensitivity of ChE to bis-onium inhibitors. Results of conformational analysis of molecules of the studied ligands are presented. Data on population of individual conformations are compared with values of anticholinesterase efficiency. Conclusions are made about mechanisms of action of the studied compounds and the predominant site of their sorption. The presented data are discussed from the point of view of comparative enzymology and in the light of the current information about structure of active center of cholinesterases.     

Comparative analysis of sensitivity of cholinesterases of different origin to bis-onium reversible inhibitors

Analytical review of the literature data on interaction constant of cholinesterases from different animal (vertebrates and squids) with 45 bis-onium reversible inhibitors forming homologous series with regularly varied structure has been carried out. Values of the competitive, uncompetitive and generalized inhibitor constants are compared. Interspecies and intraspecies differences in sensitivity of ChE are revealed. Results of conformational analysis of the investigated ligand molecules are presented. The data on population of individual conformations are compared with the data on anticholinesterase potency. Conclusions are made on the action mechanism of the investigated compounds and predominant place of their sorption. The presented data are considered from the point of view of comparative biochemistry and in the light of current information about the active center structure of cholinesterases.     

Salicylanilide diethyl phosphates as cholinesterases inhibitors

Based on the presence of dialkyl phosphate moiety, we evaluated twenty-seven salicylanilide diethyl phosphates (diethyl [2-(phenylcarbamoyl)phenyl] phosphates) for the inhibition of acetylcholinesterase (AChE) from electric eel (Electrophorus electricus L.) and butyrylcholinesterase (BChE) from equine serum. Ellman’s spectrophotometric method was used. The inhibitory activity (expressed as IC₅₀ values) was compared with that of the established drugs galantamine and rivastigmine. Salicylanilide diethyl phosphates showed significant activity against both cholinesterases with IC₅₀ values from 0.903 to 86.3 μM. IC₅₀s for BChE were comparatively lower than those obtained for AChE. All of the investigated compounds showed higher inhibition of AChE than rivastigmine, and six of them inhibited BChE more effectively than both rivastigmine and galantamine. In general, derivatives of 4-chlorosalicylic acid showed enhanced activity when compared to derivatives of 5-halogenated salicylic acids, especially against BChE. The most effective inhibitor of AChE was O-{5-chloro-2-[(3-bromophenyl)carbamoyl]phenyl} O,O-diethyl phosphate with IC₅₀ of 35.4 μM, which is also one of the most potent inhibitors of BChE. O-{5-Chloro-2-[(3,4-dichlorophenyl)carbamoyl]phenyl} O,O-diethyl phosphate exhibited in vitro the strongest inhibition of BChE (0.90 μM). Salicylanilide diethyl phosphates act as pseudo-irreversible cholinesterases inhibitors.     

Thiosubstrates of cholinesterases of different origin

Review of the own and literature data on investigation of substrate specificity of different cholinesterases using thiosubstrates is presented. Dependence of cholinesteratic hydrolysis parameters on various elements of their structure—the acyl part, alkyl “bridge” between ester atom and onium group, and the molecule ammonium grouping—is considered using 44 thioesters in total. A comparative enzymological analysis of the substrate specificity is performed with use of thiocholine esters of acetic, propionic, and butyric acids for 40 cholinesterase preparations of mammals, insects, mollusks, and plants.     

Cage amines as the stopper inhibitors of cholinesterases

Cage amines 1-4 are potent peripheral anionic site-bound reversible inhibitors of both acetylcholinesterase and butyrylcholinesterase. Cage amines 1-3 are selective butyrylcholinesterase inhibitor versus acetylcholinesterase. For both enzymes, the -log K(i) values linearly correlate with the difference of substituted phenyl radius of cage amines (-log K(i)=5.4+3.4Deltagamma for acetylcholinesterase, -log K(i)=5.9+3.2Deltagamma for butyrylcholinesterase). Moreover, the relationship between the enzymes and cage amines mimics that between bottles and stoppers.