Determination of unlabeled and 13C6-labeled moricizine in human plasma using thermospray liquid chromatography-mass spectrometry

Moricizine hydrochloride is an orally effective antiarrhythmic agent currently marketed in the Soviet Union and undergoing clinical testing in the United States. To facilitate the simultaneous analysis of unlabeled and 13C6-labeled moricizine in human plasma, a specific and sensitive method employing liquid-liquid extraction followed by thermospray liquid chromatography-mass spectrometry (LC-MS) was developed. Plasma samples, after addition of [2H11]moricizine as an internal standard, were extracted into methylene chloride under alkaline conditions. Extracts were evaporated, reconstituted with mobile phase, and chromatographed on an ODS column. The LC mobile phase consisted of methanol-0.1 M ammonium acetate containing 0.2% triethylamine (65:35) and it was used at a flow-rate of 1.5 ml/min. Under these conditions, moricizine and [13C6]moricizine coeluted at 1.2 min, while [2H11]moricizine eluted slightly earlier. The MS system consisted of a Finnigan 4600 TSQ and a Vestec thermospray interface. Selected ions at m/z 428, 434, and 439 were scanned at 0.2 s per ion. Over a plasma concentration range of 10-800 ng/ml, intra-day precision (n = 3) ranged from 1.8 to 13.3% and intra-day accuracy ranged from 1.9 to 15.8%. This method was successfully used to assay human plasma samples from a pilot moricizine bioavailability study in which tablets and solution containing moricizine hydrochloride and [13C6]moricizine, respectively, were simultaneously administered.     

Can inflation explain the second law of thermodynamics?

The inflationary model of the universe can explain several of the cosmological conundra that are mysteries in the standard hot big bang model. Paul Davies has suggested that inflation can also explain the second law of thermodynamics, which describes the time asymmetry of the universe. Here I note several difficulties with this suggestion, showing how the present inflationary models must assume the arrow of time rather than explaining it. If the second law is formulated as a consequence of the hypothesis that there were no long-range spatial correlations in the initial state of the universe, it is shown how some of the cosmological conundra might be explained even without inflation. But if the ultimate explanation is to include inflation, three, essential elements remain to be demonstrated which I list.     

Kinetics and mechanisms of hydrolysis and aminolysis of thioxocephalosporins

The effect of replacing the beta-lactam carbonyl oxygen in cephalosporins by sulfur on their reactivity has been investigated. The second-order rate constant for alkaline hydrolysis of the sulfur analogue is 2-fold less than that for the natural cephalosporin. The thioxo derivative of cephalexin, with an amino group in the C7 side chain, undergoes beta-lactam ring opening with intramolecular aminolysis by a reaction similar to that for cephalexin itself. However, the rate of intramolecular aminolysis for the S-analogue is 3 orders of magnitude greater than that for cephalexin. Furthermore, unlike cephalexin, intramolecular aminolysis in the S-analogue occurs up to pH 14 with no competitive hydrolysis. The rate of intermolecular aminolysis of natural cephalosporins is dominated by a second-order dependence on amine concentration, whereas that for thioxocephalosporins shows only a first-order term in amine. The Bronsted beta(nuc) for the aminolysis of thioxo-cephalosporin is +0.39, indicative of rate-limiting formation of the tetrahedral intermediate with an early transition state with relatively little C-N bond formation.     

Identification of minor C18 triene and conjugated diene isomers in hydrogenated soybean oil and margarine by GC-MI-FT-IR spectroscopy

Vegetable oils are partially hydrogenated in order to produce palatable products of suitable plasticity. The constituents of these new dietary products are complex mixtures of fatty acid isomers with different nutritional properties. A rapid method is described for separating and identifying fatty acid methyl ester (FAME) isomers of linolenic (octadecatrienoic, 18:3) acid and of conjugated octadecadienoic (18:2) acid, minor species found in hydrogenated soybean oil and margarine, by capillary gas chromatography-matrix isolation-Fourier transform-infrared (GC-MI-FT-IR) spectroscopy. FAMEs of 18:3 acid isomers in margarine, soybean oil hydrogenated in our laboratory, and isomerized linolenic acid were identified by this method, and MI-FT-IR spectra of FAME geometric isomers of octadecatrienoic and conjugated octadecadienoic acids are reported for the first time. Five major C18 triene GC peaks are found in chromatograms of isomerized methyl linolenate, representing species with tri-cis and tri-trans configurations and three species with cis-trans mixed configurations. FAME isomers with these configurations are also found for a hydrogenated soybean oil having an iodine value of 111. Methyl linolenate (tri-cis) is no longer found when soybean oil is further hydrogenated to an iodine value of 96. IR spectra characteristic of a tri-trans isomer are obtained for two test samples with iodine values of 111 and 96. Besides methyl linolenate, only isomers with a mono-trans di-cis configuration are found for the margarine analyzed. Conjugated cis-trans and trans-trans 18:2 FAME isomers are also found in all the hydrogenated soybean oil and margarine analyzed.     

Molecular structure of 6-methyleneoxytetracycline hydrobromide

The structure of 4(dimethylamino)-1, 4, 4a, 5, 5a, 6, 11, 12a-octahydro-3, 5, 10, 12, 12a-pentahydroxy-6-methylene-1, 11-dioxo-2-naphthacenecarboxamide hydrobromide salt was determined by an X-ray analysis. One methacycline cation and one bromide anion were found in the asymmetric unit of an orthorhombic cell, space group P2₁2₁2₁,a 9.580(1),b 12.147(2),c 18.735(3) å,V2180.0(5) å³, Z4,D _c 1.59 g cm^–3, (MoK) 19.15 cm^–1. The structure was solved and refined toR(F) 0.062 andR _w(F) 0.064 by a full matrix least-squares procedure. The conformation of the methacycline cation is found to be similar to that reported for 6-demethyl-7-chlorotetracycline hydrochloride trihydrate.     

Different transition-state structures for the reactions of beta-lactams and analogous beta-sultams with serine beta-lactamases

Beta-sultams are the sulfonyl analogues of beta-lactams, and N-acyl beta-sultams are novel inactivators of the class C beta-lactamase of Enterobacter cloacae P99. They sulfonylate the active site serine residue to form a sulfonate ester which subsequently undergoes C-O bond fission and formation of a dehydroalanine residue by elimination of the sulfonate anion as shown by electrospray ionization mass spectroscopy. The analogous N-acyl beta-lactams are substrates for beta-lactamase and undergo enzyme-catalyzed hydrolysis presumably by the normal acylation-deacylation process. The rates of acylation of the enzyme by the beta-lactams, measured by the second-order rate constant for hydrolysis, kcat/K(m), and those of sulfonylation by the beta-sultams, measured by the second-order rate constant for inactivation, k(i), both show a similar pH dependence to that exhibited by the beta-lactamase-catalyzed hydrolysis of beta-lactam antibiotics. Electron-withdrawing groups in the aryl residue of the leaving group of N-aroyl beta-lactams increase the rate of alkaline hydrolysis and give a Bronsted beta(lg) of -0.55, indicative of a late transition state for rate-limiting formation of the tetrahedral intermediate. Interestingly, the corresponding Bronsted beta(lg) for the beta-lactamase-catalyzed hydrolysis of the same substrates is -0.06, indicative of an earlier transition state for the enzyme-catalyzed reaction. By contrast, although the Bronsted beta(lg) for the alkaline hydrolysis of N-aroyl beta-sultams is -0.73, similar to that for the beta-lactams, that for the sulfonylation of beta-lactamase by these compounds is -1.46, compatible with significant amide anion expulsion/S-N fission in the transition state. In this case, the enzyme reaction displays a later transition state compared with hydroxide-ion-catalyzed hydrolysis of the beta-sultam.