Synthesis of beta-lactams by Ag+-induced ring expansion of 1-hydroxycyclopropylamines: a theoretical analysis

A theoretical analysis of the silver-induced ring expansion of N-chloro-N-methyl-1-hydroxycyclopropylamine to form N-methyl-2-azetidinone, and of the Cl(-) elimination from this substrate without Ag(+) assistance, was performed using the B3LYP method and the 6-31+G(d) basis set for C, N, O, H, and Cl atoms and the relativistic effective core pseudopotential LANL2DZ complemented with one set of f polarization functions (zeta(f) = 0.473) for the Ag atom. The partial Ag(+)-assisted extrusion of Cl(-) at the rate-determining transition state provokes an important change in the nodal properties of the frontier molecular orbitals of the H(3)CClNCOHAg(+) fragment, thus making very stabilizing HOMO-LUMO interactions between this fragment and the C(2)H(4) moiety possible. This interaction leads to the ring opening and release of most of the strain energy, giving rise to a low energy barrier for the process. Also, by assisting the Cl(-) extrusion, Ag(+) avoids the elimination of the hydroxyl hydrogen atom, which would provoke the fragmentation of the system instead of the formation of the beta-lactam.     

Topographical properties of polymer films deposited in capillaries for electrophoretic separations of large organic molecules

Topography and thickness of hydrophilic polymer coatings of fused-silica capillaries for capillary electrophoresis (CE) were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), and profilometry. Three hydrogels, poly(2-hydroxyethyl methacrylate) [poly(HEMA)], poly(diethylene glycol monomethacrylate) [poly(DEGMA)], and poly(triethylene glycol monomethacrylate) [poly(TEGMA)], were deposited using two procedures, either by simple physical sorption of the polymers, or by derivatization of the capillary wall surface with glycidyl methacrylate (EPMA) followed by polymerization of the appropriate monomers. The performance of the modified capillaries was tested under CE conditions (decrease in the electroosmotic flow, EOF dependence on pH, separation of milk and standard proteins). It has been found that the most important property of the polymer coating is its thickness, whereas its topography and the degree of its hydrophobicity are less significant. Film deposition by physical adsorption is preferable to polymerization on the derivatized surface.     

Quassinoids from Picrasma crenata

From woods of Picrasma crenata, a new stereoisomer dihydronorneoquassin was obtained together with others well knowns dihydronorneoquassin, parain, alpha-neoquassin, beta-neoquassin and quassin. The structures were determined by spectroscopic data and chemical evidence.     

An alternative method for pucker determination in carbohydrates from residual dipolar couplings: a solution NMR study of the fructofuranosyl ring of sucrose

A simple solution NMR method is presented for pucker determination of five-membered rings using only residual dipolar couplings obtained in a single liquid crystalline medium, DMPC/DHPC bicelles (DMPC = dimyristoylphosphatidylcholine; DHPC = dihexanoylphosphatidylcholine). The method was applied to determine the pucker of the fructofuranosyl ring of sucrose. The results indicate a fructofuranosyl pucker phase in the 20 degrees - 70 degrees range. The pucker phases are in agreement with those from previous NMR and optical spectroscopic studies and, importantly, do not rely on empirically parametrized Karplus curves. Furthermore, the analysis implies more than one stable pucker phase and rapid ring interconversion in this range. The present results suggest that using residual dipolar couplings alone can reveal multiple conformations present in solution. Hence, when a sufficient number of residual dipolar coupling constants is measured, the outcome is a robust, reliable, and independent route for determining carbohydrate and nucleic acid structure by NMR spectroscopy.     

Isolation of a new member of the ecdysteroid glycoside family: 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside

A new ecdysteroid glycoside, 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside, is isolated from the herb Silene italica ssp. nemoralis (Waldst. and Kit.) Nyman. The compound is purified with multistep chromatography, such as classical column chromatography on alumina and droplet countercurrent distribution. Also, it is expanded using twice low-pressure reversed-phase liquid column chromatography. Chromatography in four steps results in the purified 2-deoxy-20-hydroxyecdysone 22-O-beta-D-glucopyranoside. Two other ecdysteroids have also been separated, including the formerly identified integristerone A and 24(28)-dehydromakisterone A.     

Reversal of stereoselectivity in [5 + 2] pyrone--alkene cycloadditons using a sulfoxide-to-sulfoximine switch. Enantiodivergent synthesis of 8-oxabicyclo[3.2.1]octane systems

[reaction: see text] Switching from a sulfinyl to a sulfonimidoyl group allows the reversal of the sense of asymmetric induction in thermal [5C + 2C] intramolecular pyrone-alkene cycloadditions. Removal of the sulfoximine unit from the resulting cycloadducts yields optically active oxabicyclic systems that are enantiomeric to those obtained using the sulfinyl chiral auxiliary.     

The kinetics of radical polymerization—XXVII. Investigation of the radical reactivity of 3,3′- and 4,4′-disubstituted azobenzenes in the polymerization of vinylacetate

A study was made on the inhibition by some 3,3′- and 4,4′-disubstituted azobenzenes of the polymerization of vinylacetate initiated by azoisobutyronitrile at 50°. The inhibitory effects of these substances can be attributed to their ability to engage in radical addition giving a less reactive hydrazyl type radical. The mechanism of the inhibition has been established by ESR and kinetic (stoichiometric) measurements. The value of k₅/k₂ (characteristic of the reactivity of an inhibitor) was determined for 9 substituents. The radical reactivity of the aromatic azo group was decreased by electron donor substituents and increased by electron acceptors. The substituent effect can be well interpreted by the Hammett equation; the value of the reaction constant was ? = +0.53.     

Mikronachweis der Salicylsäure als Silbersalicylat

Zusammenfassung Es wird eine Methode beschrieben, nach der die Salicylsäure über ihr Ammonsalz als Silbersalicylat in kleinsten Mengen nachgewiesen werden kann. Es bilden sich dabei monokline Prismen in Form von Rhomboiden, die durch die Kristallwinkel, die schiefe Auslöschung und deren Beziehung zum Kristallumriß als Silbersalicylat identifiziert werden können. Erfassungsgrenze: 0,4 Salicylsäure. Ferner wird das unter Umständen ebenfalls bei der Reaktion auftretende Silbersalz der Benzoesäure und seine Unterscheidung von Silbersalicylat auf optischem Wege besprochen. Die Reaktion gelingt auch mit Mikrosublimaten.

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Summary A method is described whereby minimal amounts of salicylic acid can be detected as silver salicylate, viâ the ammonium salt. Monoclinic prisms of the form of rhomboids are produced, which may be identified as silver salicylate from the crystal angles, the oblique extinction, and the relationship of these to the crystal outline. The limit of the method is 0,4 salicylic acid. The optical method for distinguishing between silver salicylate and silver benzoate, which is also formed in certain circumstances in the course of the reaction, is discussed. The reaction may be successfully applied to micro-sublimates.

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Résumé On décrit une méthode, qui permet de déceler des plus petites quantités de l'acide salicylique comme salicylate d'argent en préparant d'abord le salicylate d'ammonium. Des prismes monoclines, en forme rhombique, se forment d'abord, qui peuvent être identifiés comme salicylate d'argent par l'angle du cristal (Kristallwinkel), l'extinction oblique (schiefe Auslöschung) et les relations de ceux aux contoures du cristal (Kristallumriß). Limite d'identification: 0,4 d'acide salicylique. Ensuite on discute aussi la différence entre le salicylate d'argent et le benzoate d'argent, qui se forme parfois au cours de la réaction, d'un mode optique. — La réaction peut être appliquée aussi à des micro-sublimés.

     

Simple and rapid micellar electrokinetic capillary chromatographic method for simultaneous determination of four antiepileptics in human serum

A very rapid and simple MEKC method was developed for the simultaneous determination of four antiepileptic drugs, ethosuximide (Etho), primidone (Pri), phenytoin (Pht) and carbamazepine (Cbz) in human serum. Sample analysis required only 100 microL of human serum which only needed to be centrifuged, decanted and combined with the running buffer [5.3 mM Na(2)HPO(4)/3.2 mM borax buffer (pH 9.5) containing 55 mM SDS and 3.5% (v/v) acetone]. The analysis was performed in only 10 min into fused-silica capillaries (57 cm total length with 50 microm i.d. and 50 cm to the detector) using the MEKC methodology with diode-array detection at 220 nm. The calibration graphs were established for ethoximide, primidone, phenytoin and carbamazepine between 0 and 20 mg/L. Recoveries were between 85 and 87%. The simplicity of the proposed methodology makes it suitable for routine clinical use, especially for epileptic patients on polytherapy.