A new pH-metric methodology for the determination of thermodynamic inclusion constants of guest/cyclodextrin complexes.

A new methodology of pH-metric data treatment was developed to extract the stoichiometry and the thermodynamic association constants of guest-cyclodextrin inclusion complexes in dilute aqueous solution when the guest is a participant in an acid-base equilibrium. pH-metric titration curves in the presence of cyclodextrin (CD) were treated by a curve-fitting technique according to a nonlinear least-squares regression. Equations corresponding to the different kinds of acid-base pairs (AH/A-, BH+/B) and stoichiometries (1:1 and 1:2) were established. The methodology was validated by studying the 5-phenylbarbituric acid complexation with beta-CD and the 4-cyanobenzoic acid complexation with alpha-CD. Then it was applied to chlorpromazine. Both the acid form (constant K1 = 3260) and the base form (constant G1 = 13,100) gave complexes with beta-CD according to 1:1 stoichiometry.

Synthesis of N-beta-D-glucopyranosyluronate derivatives of barbital, phenobarbital, metharbital, and mephobarbital.

The synthesis and characterization of barbital, phenobarbital, metharbital, and mephobarbital glucuronides is reported. The condensation of per(trimethylsilyl)-barbital and -phenobarbital with methyl 1,2,3,4-tetra-O-acetyl-beta-D-glucopyranuronate in the presence of trimethylsilyl trifluoromethanesulfonate gave moderate yields of the N1-(beta-D-glucopyranosyluronate) barbiturate derivatives. The diastereomers of the phenobarbital derivatives were resolved by use of C18 reversed-phase HPLC. The homologous N3-methyl barbiturate N1-glucuronates were prepared by reaction of the barbital and phenobarbital N1-glucuronate derivatives with diazomethane. The absolute configuration of the phenobarbital N1-beta-D-glucopyranuronate epimers was determined by oxidative removal of the glycon from the mephobarbital N1-beta-D-glucopyranuronate epimers to give the optical isomers of mephobarbital. The spectroscopic data for this series of compounds will facilitate the characterization of N-glycosylated imide xenobiotics that may be detected as mammalian metabolites in biodisposition studies.

Barbital N-glucoside is not detected as a urinary excretion product of barbital in humans.

A study was undertaken to determine if humans excreted barbital N-glucoside as a urinary metabolite following oral administration of barbital. A liquid chromatography method using gradient elution was developed for detecting and quantifying barbital N-glucoside and barbital in urine. Following a single oral dose of barbital to male caucasian and oriental subjects that had previously been shown to excrete amobarbital and phenobarbital N-glucosides, no barbital N-glucoside conjugate was observed in the urine. This result indicates that N-glucosylation of barbiturates is not a general pathway for the biodisposition of barbiturates in man.

Synthesis of N-beta-D-glucopyranosyl derivatives of barbital, phenobarbital, metharbital, and mephobarbital.

The condensation of per(trimethyl)silylbarbital and -phenobarbital with 1,2,3,4,6-penta-O-acetyl-beta-D-glucopyranose in the presence of stannic chloride in dichloroethane gave moderate yields of the beta-coupled barbiturate N-D-glucopyranosyl derivatives. Reaction of metharbital and mephobarbital under the same conditions was unsuccessful. The homologous N-methylglucosides were prepared by reaction of the barbital and phenobarbital N-glucosyl derivatives with diazomethane. The diastereomers of the phenobarbital and mephobarbital derivatives were resolved by use of C-18 reverse-phase h.p.l.c. 1H- and 13C-n.m.r. spectroscopy, and thermospray 1.c.-m.s. proved to be the most useful methods for characterizing the barbiturate glucosides.

Tumor promoting activities of ethylphenylacetylurea and diethylacetylurea, the ring hydrolysis products of barbiturate tumor promoters phenobarbital and barbital, in rat liver and kidney initiated by N-nitrosodiethylamine.

The ring hydrolysis products of the multi-tissue tumor promoting barbiturates, phenobarbital (PB) and barbital (BB), were fed to F344/NCr male rats previously given a single initiating injection of N-nitrosodiethylamine. Ethylphenylacetylurea (EPAU) and diethylacetylurea (EEAU), derived, respectively, from PB and BB, both promoted development of hepatocellular adenomas, but were much weaker in this respect than PB. Both acetylureas were also selective inducers of P-450IIB1-mediated benzyloxyresorufin O-dealkylase activity, but both were much less potent inducers than PB. Neither EPAU nor EEAU had an effect on tumor development in the thyroid, unlike both PB and, as shown previously, BB. EEAU, but not EPAU, strongly promoted development of renal cortical epithelial tumors. The opening of the barbiturate heterocyclic ring and the subsequent decarboxylation to yield the dialkylacetylurea analogs thus resulted in compounds displaying a marked reduction in liver tumor promoting activity. EEAU appears to possess an ability to promote renal neoplasms similar to that of its parent compound, BB. Ring opening appears to be accompanied by loss of promoting activity for thyroid follicular epithelium.

The reaction mechanism of the novel vanadium-bromoperoxidase. A steady-state kinetic analysis.

The reaction of vanadium-bromoperoxidase from the brown alga Ascophyllum nodosum with hydrogen peroxide, bromide, and 2-chlorodimedone has been subjected to an extensive steady-state kinetic analysis. Systematic variation of pH and the concentrations of these three components demonstrate that the reaction model includes four enzyme species: native bromoperoxidase, a bromoperoxidase-bromide inhibitory complex, a bromoperoxidase-hydrogen peroxide intermediate, and a bromoperoxidase-HOBr species. This latter intermediate did not display any direct interaction with the nucleophilic reagent as oxidized bromine species (Br-3, Br2, and/or HOBr) were the primary reaction products. The generation of oxidized bromine species was as fast as the bromination of 2-chlorodimedone. The enzyme did not show any specificity with regard to bromination of various organic compounds. Formation of the bromoperoxidase-bromide inhibitory complex was competitive with the reaction between hydrogen peroxide and enzyme. From the steady-state kinetic data lower limits for the second-order rate constants at various pH values were calculated for individual steps in the catalytic cycle. This pH study showed that native enzyme must be unprotonated prior to binding of hydrogen peroxide (second-order association rate constant of 2.5.10(6) M-1.s-1 at pH greater than 6). The pKa for the functional group controlling the binding of hydrogen peroxide was 5.7 and is ascribed to a histidine residue. The reaction rate between bromide and enzyme-hydrogen peroxide intermediate also depended on pH (second-order association rate constant of 1.7.10(5) M-1.s-1 at pH 4.0).

A barbital derivative as an atypical antidepressant drug in mice.

An isopropyl derivative of barbital (5,5-diethyl-2-(isopropyloxy)pyrimidine-4,6-dione, O2IB) was administered intraperitoneally 30 min before tests in mice. Former experimental investigations have shown that O2IB has an antidepressant psychopharmacological spectrum. It increases toxicity of yohimbine in mice at 175 mg/kg, antagonises from 50 mg/kg on hypothermia induced by a high dose of apomorphine and is active on the behavioural despair test at 125 mg/kg. These effects are those observed with classical antidepressants. Since phenytoin has an antidepressant profile in mice, carbamazepine is active on manic-depressive illness and beta-mimetic drugs are antidepressants, the question presents itself whether isopropylation or anticonvulsive activity is more important for the antidepressant psychopharmacological spectrum, or whether both are of equal importance.

The effect of a putative antidepressant, an O2-substituted derivative of barbitone on apomorphine induced hypomotility.

The effects of the chronic administration of barbitone and its O2-substituted isopropyl derivative (O2IB) was studied on the hypomotility induced in rats by the acute administration of a low dose of apomorphine. Neither drug was found to selectively antagonize the hypomotility caused by acute apomorphine administration. No correlation could be found between the behavioural effects of the barbiturates and changes in the concentrations of biogenic amines and GABA in four discrete brain regions. The results of this study do not support the conclusions of previous acute studies in which O2IB has been shown to have an antidepressant profile.

Isopropyl substitution on barbiturate ring: effects on 'open field' and 'hole board' behaviour and on biogenic amines concentrations in discrete regions of the rat brain after acute and chronic administration.

Previous studies have shown that slight modification of the barbitone molecule can lead to enhanced sedative activity, convulsant activity or putative antidepressant activity according to the position of the isopropyl substituent on the N- or O-moiety. When the acute effects of the N-, O2- and O4-isopropyl derivatives of barbital (NIB, O2IB), O4IB on the concentrations of brain biogenic amines were determined, it was found that NIB and O4IB increased the serotonin concentrations in several brain regions examined without markedly changing the 5-hydroxy-indole acetic acid (5-HIAA) concentrations; in contrast, O2IB increased the 5-HIAA concentration. Barbitone and NIB raised the concentration of noradrenaline in two of the regions examined whereas the O2-substituted derivative had a smaller effect; the dopamine concentration was slightly raised by NIB and O2IB. Following their chronic (14 days) administration, only barbitone and O2IB raised the serotonin concentration; O2IB raised the concentration of 5-HIAA in some regions as did NIB, which suggests that these compounds may increase serotonin turnover. Barbitone and O2IB slightly increased the noradrenaline content of the brain stem while only O2IB decreased the dopamine content. These results suggest that the effects of acute and chronic administration of barbitone and its isopropyl derivatives are qualitatively different; their effects are less marked after chronic administration. The GABA concentration was only affected after chronic administration, when NIB was shown to increase and O2IB to decrease the concentration. Following their chronic administration, O2IB decreased while NIB increased the locomotor activity of rats in the 'open field' and 'hole board' apparatus.(ABSTRACT TRUNCATED AT 250 WORDS)

Heteroassociation of O- and N-isopropyl derivatives of barbital and phenobarbital with 9-ethyladenine.

Heteroassociation of O- and N-isopropyl derivatives of barbital and phenobarbital with 9-ethyladenine (9-EA) in CCl4 solutions were studied by infrared spectroscopy. Cyclic heterodimers of high stability (725 less than KH less than 1960 1 X mol-1) compared to the corresponding homodimers (20 less than KD less than 60 1 X mol-1) were formed. The heteroassociation constants are interpreted in terms of both the hydrogen bonding tendency of the donor and acceptor centres and the number of sites available for the formation of hydrogen bonds. Such measurements may contribute to the understanding of the interactions between barbiturates, adenosine and their receptors in the brain.