Synthesis of sulphur-containing heterocycles by ring closing diene metathesis

We have shown that, surprisingly, the Schrock molybdenum alkylidene catalyst 1 can perform ring closing metathesis reactions on substrates containing a sulphide group, converting diallyl sulphide 5 to 2,5-dihydrothiophene 6 with >99 % conversion. By contrast, the ruthenium alkylidene catalyst 2, which is generally more tolerant of functional groups in the substrate, is unreactive towards diallylsulphide. However even the molybdenum catalyst 1 proved unable to catalyse ring closure of tetrathiafulvalene derivative 7.     

Synthesis and Evaluation of a Synthetic Polymeric Chiral Stationary Phase for LC Based on the N, N′-[(1R,2R)-1,2-Diphenyl-1,2-Ethanediyl]bis-2-Propenamide Monomer

A synthetic polymeric chiral stationary phase for liquid chromatography based on N, N′-[(1R,2R)-1,2-diphenyl-1,2-ethanediyl]bis-2-propenamide monomer was prepared via a simple solution initiated radical polymerization. This stable chiral stationary phase showed enantioselectivities for a large number of racemates in polar organic and normal phase modes and high sample loading ability. However, none of the generated data has been optimized in terms of column performance. Different enantioselectivities were observed on this new chiral stationary phase compared with the commercial polymeric chiral stationary phase based on N-(2-acryloylamino-(1R,2R)-cyclohexyl)-acrylamine monomer. Consequently, these two chiral stationary phases are considered complementary to one another. Furthermore they utilize the same mobile phase and optimization procedures. This polymeric chiral stationary phase appears to be useful for preparative separations since high amounts of analyte can be injected without loosing enantioselectivity.     

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.     

Regioselective Acylation of Ginsenosides by Novozyme 435 to Generate Molecular Diversity

Ginsenosides are major bioactive constituents of ginseng (Panax spp.; Araliaceae), a traditional Chinese medicinal herb. In order to increase the molecular diversity and broaden the potential usage of ginsenosides, ginsenosides Rd ( 1 ), Rg3 ( 2 ), (20R)‐Rg3 ( 3 ), Rh2 ( 4 ), Re ( 5 ), Rh1 ( 8 ), Rg2 ( 9 ), gypenoside XVII ( 6 ), and pseudoginsenoside F11 ( 7 ) were regioselectively acylated with vinyl acetate, catalyzed by Novozyme 435 (lipase B from Candida antarctica), in organic solvents to afford different mono‐acetyl ginsenosides. Ginsenoside Rd ( 1 ) was also acylated with vinyl decanoate or vinyl cinnamate to generate 1b and 1c , respectively. Acylation of glucosylated ginsenosides ( 1 – 4, 6, 8 ) occurred at the primary 6‐OH function of the terminal glucose (Glc) moiety of the sugar at C(3) or C(20) of the dammarane‐type aglycone. In contrast, ginsenosides 5, 7 , and 9 , containing mixed sugar moieties, resulted in acylation of both the rhamnose (Rha) and the glucose (Glc) moieties. In the case of ginsenoside Re ( 5 ) and pseudoginsenoside F11 ( 7 ), acylation at the secondary 4‐OH function of the terminal Rha moiety, attached at C(3) of the aglycone, is preferred. The structures of all acylated products were determined by extensive MALDI‐TOF‐MS and NMR analyses.     

Solid-state NMR study of ureidopyrimidinone model compounds

High-resolution (1)H and (15)N{(1)H} solid-state NMR experiments were conducted on two ureidopyrimidinone model compounds: dimeric 2-butylureido-6-methyl-4-pyrimidinone (1) and its bifunctional analogue N,N-1,6-hexanediyl(2-ureido-6-methyl-4-pyrimidinone) (4). High magic angle spinning rates and (1)H decoupling schemes were used to increase the proton spectral resolution. Upon heating 1 to 440 K, an increase in mobility was observed for non-hydrogen-bonded protons; the dimer remained in keto tautomeric form, which is capable of much stronger intermolecular hydrogen bonding than the enol tautomer. From these findings, it was concluded that this ureidopyrimidinone moiety should allow the design of strongly bonded molecular assemblies whose thermal stability compares favourably with that of conventional engineering polymers.     

X-ray Crystallographic Study of the Ruthenium Blue Complexes [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2): Steric Interactions and the Ru-Ru "Bond Length"

X-ray crystal structures are reported for the following complexes: [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O (tacn = 1,4,7-triazacyclononane), monoclinic P2(1)/n, Z = 4, a = 14.418(8) ?, b = 11.577(3) ?, c = 18.471(1) ?, beta = 91.08(5) degrees, V = 3082 ?(3), R(R(w)) = 0.039 (0.043) using 4067 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, monoclinic P2(1)/a, Z = 4, a = 13.638(4) ?, b = 12.283(4) ?, c = 18.679(6) ?, beta = 109.19(2) degrees, V = 3069.5 ?(3), R(R(w)) = 0.052 (0.054) using 3668 unique data with I > 2.5sigma(I) at 293 K; [Ru(2)I(3)(tacn)(2)](PF(6))(2), cubic P2(1)/3, Z = 3, a = 14.03(4) ?, beta = 90.0 degrees, V = 2763.1(1) ?(3), R (R(w)) = 0.022 (0.025) using 896 unique data with I > 2.5sigma(I) at 293 K. All of the cations have cofacial bioctahedral geometries, although [Ru(2)Cl(3)(tacn)(2)](PF(6))(2).4H(2)O, [Ru(2)Br(3)(tacn)(2)](PF(6))(2).2H(2)O, and [Ru(2)I(3)(tacn)(2)](PF(6))(2) are not isomorphous. Average bond lengths and angles for the cofacial bioctahedral cores, [N(3)Ru(&mgr;-X)(3)RuN(3)](2+), are compared to those for the analogous ammine complexes [Ru(2)Cl(3)(NH(3))(6)](BPh(4))(2) and [Ru(2)Br(3)(NH(3))(6)](ZnBr(4)). The Ru-Ru distances in the tacn complexes are longer than those in the equivalent ammine complexes, probably as a result of steric interactions.     

On the capillary gas chromatographic separation of enantiomers of N-trifluoroacetyl-O-alkyl esters of selected amino acids on 2,3-di-O-pentyl-6-O-acyl cyclodextrins

In this work, the separation of enantiomers of N-TFA-O-alkyl amino acids on the 2,3-di-O-pentyl-6-O-acyl alpha-, beta- and gamma-cyclodextrin stationary phases has been studied. The influence of structure differences in the alkyl substituents bonded to the stereogenic carbon atom (R1), as well as in the ester group (R2) of the selected amino acid derivatives, and the selectivity of modified alpha-, beta- and gamma-cyclodextrin phases in gas chromatographic separation of derivatized amino acid enantiomers was studied in detail. A model set of N-TFA-alkyl esters of four amino acids was separated on five columns. The separation of enantiomers was evaluated in terms of the interactions of the alkyl substituents bonded to the stereogenic carbon (R1) and/or the ester group (R2) of the N-TFA-O-alkyl amino acid derivatives as well as the nature of the 3-O-acyl group in the 2,6-di-O-pentyl-3-O-acyl alpha-, beta- and gamma-cyclodextrins. It was shown that the variation in the enantiomeric separation with temperature and the retention order of enantiomers on a given cyclodextrin capillary column depends both on the nature of the bonded R1 and R2 alkyl groups. It was found that the temperature dependencies of selectivity factors, ln alpha on 1/T, were mostly non-linear. The thermodynamic data [delta(deltaS) and [delta(deltaH)] which characterize the chiral recognition were used to gain more insight into the mechanistic aspects of enantio separation of the N-TFA-O-alkyl amino acid derivatives on 2,6-di-O-pentyl-3-O-acyl-alpha-, beta- and gamma-cyclodextrins.     

Separation of chiral furan derivatives by liquid chromatography using cyclodextrin-based chiral stationary phases

The enantiomeric separation of a set of 30 new chiral furan derivatives has been achieved on native and derivatized beta-cyclodextrin stationary phases using high performance liquid chromatography (HPLC). The hydroxypropyl-beta-cyclodextrin (Cyclobond RSP), the 2,3-dimethyl-beta-cyclodextrin (Cyclobond DM), and the acetyl-beta-cyclodextrin (Cyclobond AC) stationary phases are the most effective chiral stationary phases (CSPs) for the separation of these racemates in the reverse phase mode. No enantioseparations have been observed on the native beta-cyclodextrin chiral stationary phase (Cyclobond I 2000) and only a few separations have been attained on the S-naphthylethyl carbamate beta-cyclodextrin (Cyclobond SN) and 3,5-dimethylphenyl carbamate beta-cyclodextrin (Cyclobond DMP) chiral stationary phases in the reverse phase mode. The polar organic and the normal phase mode on these CSPs are not effective for separation of these compounds. The characteristics of the analytes, including steric bulk, hydrogen bonding ability, and geometry, play an important role in the chiral recognition process. The pH affects the enantioseparation of compounds with ionizable groups and the addition of 0.5% methyl tert-butyl ether to the mobile phase significantly enhances the separation efficiency for some highly retained compounds.     

Some factors responsible for high ionic conductivity in simple solid compounds

The ionic conductivities, activation energies for mobility, and crystal structures of solid electrolytes are reviewed. The high conductivity of a group of compounds containing simple anions is examined in some detail.For a solid to possess high ionic conductivity there must be: (a) an excess of acceptable lattice sites for the mobile ion, (b) only a small energy difference between the ordered and disordered distribution of the mobile ions over these sites, and (c) a low heat of activation for movement of the mobile ion. These conditions are most readily realized when the cations are monovalent and stable in both 4-coordinated (tetrahedral) and 3-coordinated configurations. Since only Ag^I and Cu^I satisfy these requirements, their nearly unique conduction properties become understandable. Moreover, these requirements appear to be satisfied only with highly polarizable anions; a characteristic of the anions present in the good conductors.     

Calculation of the π-electronic structures of vinyl boron compounds by the free-electron Method

The free-electron model has been used to investigate the -electronic structures and spectra of two vinylboranes. It is concluded that none of the simple F. E. methods is satisfactory alone and agreement between calculated and observed spectral quantities is only obtained when electron interaction is explicitly included in the calculations.

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Zusammenfassung Das Elektronengasmodell wurde zur Untersuchung der -Elektronenstrukturen und Spektren von zwei Vinylboranen angewendet. Es wurde gefunden, daß keine der einfachen Elektronengasmethoden allein befriedigend ist und daß ein Übereinstimmen zwischen berechneten und beobachteten Spektralwerten nur dann erreicht werden kann, wenn die Elektronenwechselwirkung explizit berücksichtigt wird.

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Résumé Le modèle de l'électron libre a été utilisé pour étudier les niveaux d'énergie électronique et les bandes d'absorption de deux boranes vinyliques. C'est trouvé que les méthodes simples ne sont pas satisfaisantes et l'accord entre les spectres calculés et observés est obtenu seulement quand l'interaction électronique est comprise dans les calculs.

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The authors thank Dr. B. J. Duke (University Computing Laboratory) for invaluable help and the D. S. I. R. for a maintenance grant (to D. R. A.). We are also indebted to Prof. D. M. Ritter for supplying copies of spectra.