Chiral separation of omeprazole and several related benzimidazoles using supercritical fluid chromatography

A study of the enantiomeric separation of omeprazole and several related benzimidazoles, using supercritical fluid chromatography (SFC), on the amylose based column Chiralpak AD is presented in this work. The effect of the organic modifier as well as temperature on the retention and enantioresolution was investigated. Alcohol-type modifiers provided the best results, allowing the enantiomeric separation of all the compounds studied with resolutions that were in most cases higher than 2, and analysis times lower than 10 minutes. An investigation of the temperature effect revealed that the isoelution temperature was below the working temperature range in only two cases, and hence it was better to work at the highest temperature permitted.     

Fast atom bombardment mass spectrometry of neutral methanide and ionic carbene platinum(II) derivatives

The fast atom bombardment mass spectra of a series of neutral methanide and ionic carbene platinum(II) complexes of formula dPePtL₂ and [dPePt(LH)₂](BF₄)₂ (dPe = (C₆H₅)₂PCH₂CH₂P(C₆H₅)₂; L = ? C(OCH₃)-NCH₃, ? C(OCH₃) ? NC₆H₁₁, ? C(OCH₃) ? NC₆H₄p ? CH₃), respectively are reported. Glycerol, 3-mercapto-1,2-propanediol, bis (2-hydroxyethyl)sulphide, 3-nitrobenzyl alcohol, and 2,4-di-tert-pentylphenol have been used as matrices. Neutral and ionic derivatives containing the same ligand behave similarly and give the same quasi-molecular [dPePtL(L + H)]⁺ ion by different primary processes. Stepwise breakdown of the ligands L with retention or further loss of atoms or molecules of hydrogen is observed for all these complexes, followed by ejection of radicals from the dPe ligand. Elimination of CH₃OH from [dPePtL(L + H)]⁺ also occurs. The highest ionic yields of both neutral methanide and ionic carbene complexes are observed in 3-mercapto-1,2-propanediol, in bis(2-hydroxyethyl)sulphide, and in 3-nitrobenzyl alcohol with respect to glycerol. The [dPePt(LH)₂]²⁺ doubly charged ions are present in the spectra obtained with 3-nitrobenzyl alcohol and are rather strong when L is ? C(OCH₃) ? NCH₃ and ? C(OCH₃) ? NC₆H₄p ? CH₃. Substitution of ligands L with a molecule or with a fragment of a sulphur containing matrix takes place very seldom with this series of complexes.     

Mixed pseudohalide complexes of copper(II). Crystal and molecular structure of [Cu(N3)(NCS)(tmen)] n and of [Cu(N3)(NCO)(tmen)]2 (tmen = N,N,N′,N′-tetramethylethylenediamine)

The compounds [Cu(N₃)(NSC)(tmen)]_n (1), [Cu(N₃)(NCO)(tmen)]_n (2) and [Cu(N₃)(NCO)(tmen)]₂ (3) (tmen=N,N,N′,N′-tetramethylethylenediamine) were synthesized and studied by i.r. spectroscopy. Single crystals of compounds (1) and (3) were obtained and characterized by X-ray diffraction. The structure of compound (1) consists of neutral chains of copper(II) ions bridged by a single azido ligand showing the asymmetric end-to-end coordination fashion. Each copper ion is also surrounded by the other three nitrogen atoms; two from one N,N,N′,N′-tetramethylethylenediamine and one from a terminal bonded thiocyanate group. Compound (2) decomposes slowly in acetone and the product formed [Cu(N₃)(NCO)(tmen)]₂ (3) crystallizes in the monoclinic system (P2₁). The structure of (3) consists of dimeric units in which the Cu atoms are penta-coordinated and connected by μ(1,3) bridging azido and cyanate ligands. In both cases the five coordinated atoms give rise to a slightly distorted square-based pyramid coordination geometry at each copper ion. The thermal behavior of [Cu(N₃)(NSC)(tmen)]_n (1) and [Cu(N₃)(NCO)(tmen)]_n (2) were investigated and the final decomposition products were identified by X-ray powder diagrams.     

SmCP-networked films obtained by in situ photopolymerization of neat reactive banana-shaped liquid crystals

The synthesis and characterization of reactive banana-shaped compounds have been carried out, and their ability to be photopolymerized in their SmCP mesophase has been assessed. The presence of a SmCP liquid crystalline phase in these compounds has been confirmed by X-ray studies. The polymerization of these molecules has been demonstrated by calorimetric techniques as well as by the preparation and characterization of SmCP-ordered free films that are mechanically stable at room temperature. Furthermore, polymerized films exhibit second harmonic generation activity at room temperature in the absence of an electric field.     

bryA: an unusual modular polyketide synthase gene from the uncultivated bacterial symbiont of the marine bryozoan Bugula neritina

"Candidatus Endobugula sertula," the uncultivated bacterial symbiont of Bugula neritina, is the proposed source of the bryostatin family of anticancer compounds. We cloned a large modular polyketide synthase (PKS) gene complex from "Candidatus Endobugula sertula" and characterized one gene, bryA, which we propose is responsible for the initial steps of bryostatin biosynthesis. Typical PKS domains are present. However, acyltransferase domains are lacking in bryA, and beta-ketoacyl synthase domains of bryA cluster with those of PKSs with discrete, rather than integral, acyltransferases. We propose a model for biosynthesis of the bryostatin D-lactate starter unit by the bryA loading module, utilizing atypical domains homologous to FkbH, KR, and DH. The bryA gene product is proposed to synthesize a portion of the pharmacologically active part of bryostatin and may be useful in semisynthesis of clinically useful bryostatin analogs.     

Laser flash photolysis in a O3/Cl2 mixture at 266 nm in a very low-pressure flow system

The laser flash photolysis in a very low-pressure flow system with mass spectrometry detection technique was developed for the study of oxidation reactions of chlorofluorocarbons. In this work, we have studied the UV photolysis of O3 in the presence of Cl2 at room temperature, which presents two catalytic cycles of O3 depletion with efficiencies dependent on the partial pressures in the photoreactor. The ozone dissociation was initiated with fourth harmonic pulses of a Nd:YAG laser. The detection of the reactants and the final and intermediate reaction products was performed with real-time mass spectrometry. The variations of the O3, Cl2 and ClO concentration were measured. The equations system associated to a proposed kinetic scheme was solved numerically and excellent agreement with the experimental results was obtained. The results from this work allowed the determination of the wall loss rates of the O(1D), Cl and ClO radicals.     

Dynamic and structural NMR studies of cavitand-based coordination cages

The interionic structure, kinetic stability, and degree of anion encapsulation of coordination cages 1 were studied by PGSE, NOE, and EXSY NMR techniques. The rate constants for the formation/dissociation processes at 296 K were obtained independently via (1)H-NOESY and (19)F-NOESY experiments giving, respectively, k(obs) = 0.30 +/- 0.04 s(-1) in CDCl(3) and k(obs) = 5.2 +/- 0.8 s(-1) in CD(3)NO(2)/CDC(13) (7.1) mixture with the proton probe, and k(obs) = 0.33 +/- 0.06 s(-1) in CDCl(3) and k(obs) = 5.0 +/- 0.8 s(-1) in CD(3)NO(2)/CDC(13) (7/1 mixture) with the (19)F probe. PGSE experiments showed that in CDCl(3) not only the encapsuled anion but also the external anions translate with the same rate as the cage. (19)F,(1)H-HOESY experiments indicated that an average of five external triflate anions are located in the equatorial sites close to the palladium moieties, while two of them approach the polar pockets formed by the alkyl chains. In a CD(3)NO(2)/CDCl(3) (7/1) mixture only one or two anions are in close proximity with the cage, while the others are solvated. In all the considered solvents (benzene, chloroform, methylene chloride, and nitromethane) the inclusion of a single unsolvated triflate anion in the cage is quantitative. (19)F,(1)H-HOESY experiments indicated that the charged guest head points toward one metal center. Therefore, while the ionic aggregation level and kinetic stability of coordination cages 1 are solvent dependent, anion encapsulation is not.     

Deoxygenation of alcohols employing water as the hydrogen atom source

Trialkylboranes (BMe3, BEt3, and BBu3) have been shown to mediate reductive deoxygenation reactions of O-alkyl-S-methyl dithiocarbonates (methyl xanthates) in which water or deuterium oxide functions as the source of hydrogen or deuterium. This method has proven versatile with regard to substrate scope and is capable of providing protio- or deuterioalkane products in high yields with excellent levels of D-incorporation. Ab initio calculations suggest that the trialkylborane-water complex possesses an unusually low O-H bond dissociation energy (73 kcal/mol) and support a radical chain mechanism for this process. Taken together, this report provides evidence for fundamentally novel and previously overlooked modes of reactivity for water and trialkylboranes of wide ranging importance in both theoretical and applied investigations.     

A thin chip microsprayer system coupled to Fourier transform ion cyclotron resonance mass spectrometry for glycopeptide screening

A thin polymer microchip was coupled with a Fourier transform ion cyclotron resonance (FTICR) 9.4 T mass spectrometer and the method was optimized in negative ion mode for glycopeptide screening. The interface between the polymer microchip and FTICR mass spectrometer consists of an in-laboratory conceived and designed mounting system that exhibits robust and controllable alignment of the chip toward the inlet of the mass spectrometer. The particular attribute of the polymer chip coupled to the FTICR mass spectrometer, to achieve an increase in ionization efficiency and sensitivity under the premise of high mass accuracy of detection, is highlighted by the large number of major and minor glycopeptide structures detected and identified in highly heterogeneous mixtures obtained from urine matrices. Glycoforms expressing various saccharide chain lengths ranging from tri- to dodecasaccharide, bearing up to three sialic acid moieties, could be detected and assigned based on the accuracy of the mass measurement (average mass deviation below 6 ppm) of their molecular ions. -Thin chipESI-FTICRMS is a potent novel system for glycomic screening of complex mixtures, as demonstrated for identification of singly sialylated O-glycosylated amino acids and peptides from urine matrices, and could be considered for general applicability in the glycoanalytical field.     

Complexation of Vinpocetine with Cyclodextrins in the Presence or Absence of Polymers. Binary and Ternary Complexes Preparation and Characterization

Inclusion complexation between -cyclodextrin (-CD),hydroxypropyl--cyclodextrin (HP--CD), water-solublepolymers (PVP and HPMC) and vinpocetine was studied in aqueous solution and in the solid state.Phase solubility studies were used to evaluate the complexation in aqueous solution at roomtemperature. Stability constants (K_c) of binary and ternary complexes were determined spectrophotometrically. Differential scanning calorimetry (DSC)was used to characterize kneaded, co-evaporated and lyophilised binary and ternary systems.The K_c values obtained were 70.14 M^-1 and 35.01 M^-1 for vinpocetine--CD and vinpocetine-HP--CD and increased in a range of 17% to 94%by addition of water-soluble polymers. Some preliminary evidences ofinclusion complexation were obtained from DSC suggesting that co-evaporated and lyophilised binary andternary systems were truly inclusion complexes.