Optimized conditions for 2‐aminobenzamide labeling and high‐performance liquid chromatography analysis of N‐acylated monosaccharides

The monosaccharides GlcNAc (N‐acetylglucosamine) and the home‐made GlcNC₁₆ (N‐palmitoyl‐D‐glucosamine) were labeled with 2‐AB (2‐aminobenzamide) by reductive amination of the sugar. The aldehyde group of the monosaccharide reacts with the amino group of 2‐AB, forming a Schiff base. In the second step, the Schiff base is reduced with sodium cyanoborohydride to yield a stable secondary amine. We describe here a simple and fast procedure. Previous studies reported the same labeling at high concentration (10^?1 M) during 30 h with further purification steps. In the present paper all operations were carried out in an Eppendorf tube and the reaction medium was directly analyzed without purification. Using the described protocol, the whole procedure can be accomplished in less than 6 h at 65°C at very low concentration (10^?4 M). For both GlcNC₁₆ and GlcNAc, the 2‐AB labeling conditions were optimized and, in addition, new conditions of high‐performance liquid chromatography analysis were developed. These N‐alkylated sugars were analyzed on reversed‐phase HPLC with fluorimetric detection at excitation and emission wavelengths of 340 and 400 nm, respectively. The separation was achieved on a C₁₈ column with a gradient mobile phase composed of water (0.1% formic acid)–methanol (volume varying) in less than 19 min with 12.5 and 18.3 min retention times for GlcNAc and GlcNC16, respectively. Positive‐ion electrospray ionization mass spectrometry (ESI‐MS) analysis enabled their structural determination. Copyright © 2009 John Wiley & Sons, Ltd.     

A Joint Theoretical and Experimental Insight into the Electronic Structure of Chromophores Derived from 6H,12H‐5,11‐Methanodibenzo[b,f][1,5]diazocine

We report on the synthesis and electronic spectra of the chiral, donor‐acceptor (push‐pull) chromophores (±)‐ 4 and (±)‐ 5 with a 6H,12H‐5,11‐methanodibenzo[b,f][1,5]diazocine scaffold (Scheme 1 and Fig. 2). The electronic structures of these compounds were investigated at a quantum‐chemical level (Figs. 2 and 3). The chemical reactivity of 6H,12H‐5,11‐methanodibenzo[b,f][1,5]diazocine ((±)‐ 11 ) towards aromatic electrophilic substitution (Scheme 2 and Table) provided additional information about its electronic structure and confirmed nonnegligible delocalization of the lone pair of the bridge‐head N‐atoms in this heterocyclic system.     

New trends in the chemistry of iron(III) citrate complexes: correlations between X-ray structures and solution species probed by electrospray mass spectrometry and kinetics of iron uptake from citrate by iron chelators

Despite the crucial role of "iron(III) citrate systems" in the iron metabolism of living organisms (bacteria as well as plants or mammals), the coordination chemistry of ferric citrate remains poorly defined. Variations in the experimental conditions used for the preparation of so-called ferric citrates (iron salt, Fe:cit molar ratio, base, pH, temperature, solvent) lead to several different species, which are in equilibrium in solution. To date, six different anionic complexes have been structurally characterized in the solid state, by ourselves or others. In the work described herein, we have established the experimental conditions leading to each of them. Five were obtained from aqueous solution. With the exception of a nonanuclear species (of which fragments have been detected), all were identified in aqueous solution on the basis of electrospray ionization mass spectrometry. In addition, the spectra revealed a new trinuclear species, which could not be crystallized. Kinetic studies of iron uptake from citrate species by iron chelators confirmed the results indicated by the ESI-MS studies. These studies also allowed the relative molar fraction of mononuclear versus polynuclear complexes to be determined, which depends on the Fe:cit molar ratio.     

Capillary electrophoresis combined with microdialysis in the human spinal cord: a new tool for monitoring rapid peroperative changes in amino acid neurotransmitters within the dorsal horn

A method originally developed for the separation of the three neurotransmitters gamma-aminobutyric acid (GABA), glutamate (Glu) and L-aspartate (L-Asp) in microdialysis samples from rat brain (Sauvinet et al., Electrophoresis 2003, 24, 3187-3196) was applied to human spinal dialysates obtained during peroperative microdialysis from patients undergoing surgery against chronic pain. Molecules were tagged on their primary amine function with the fluorogene agent, naphthalene-2,3-dicarboxaldehyde (NDA), and, after separation by capillary electrophoresis (CE, 75 mmol/L borate buffer, pH 9.2, containing 70 mmol/L sodium dodecyl sulfate and 10 mmol/L hydroxypropyl-beta-cyclodextrin, + 25 kV voltage), were detected by laser-induced fluorescence detection (LIFD) using a 442 nm helium-cadmium laser. The complete method, including microdialysis sampling and analysis by CE-LIFD, has been validated for the analysis of human spinal microdialysates. The analytical detection limits were 1, 3.7 and 17 nmol/L for GABA, Glu and L-Asp respectively. This method allows an accurate measurement of the three amino acid neurotransmitters during an in vivo monitoring performed as rapidly as every minute in the human spinal dorsal horn. In addition, the effect of a brief peroperative electrical stimulation of the dorsal rootlets was investigated. The results obtained illustrate the advantages of combining microdialysis with CE-LIFD for studying neurotransmitters with such a high sampling rate.     

Rearrangement reactions of aziridinylbenzaldoximes

Reactions of 2,2-dimethylaziridine with benzohydroximoyl chlorides [ArC(Cl)?NOH] give aziridinylbenzaldoximes 1 . It has been found that the aziridine ring in these compounds undergoes ring opening in hydrogen chloride-dioxane solution to give (Z)-N-hydroxy-N′-(2-chloro-2-methylpropyl)benzenecarboximidamides [ArC(NHCH₂CR¹R²Cl)?NOH, 4 ]. Treatment of 1 with hydrochloric acid followed by neutralization with aqueous sodium hydroxide gave 6,6-dimethyl-3-aryl-1,2,4-oxadiazines 2. Reaction of 4 with sodium hydride in dioxane gave 5-isopropyl-3-aryl-4,5-dihydro-1,2,4-oxadiazoles 5. Reaction of the 4,5-dihydro-1,2,4-oxadiazoles 5 with N-chlorosuccinimide gave the heteroaromatic 1,2,4-oxadiazoles 6 . It is suggested that reactions of 4 with sodium hydride in dioxane solution involve the conjugate base of 4 which undergoes a 1,2-hydride shift that is concerted with loss of chloride ion. In aqueous sodium hydroxide solution it is suggested that the conjugate base of 4 undergoes ionization of the chlorine atom followed by nucleophilic attack by the oximate anion.     

Total Synthesis of (−)‐Lithospermoside

The total synthesis of the naturally occurring noncyanogenic cyanoglucoside (?)‐lithospermoside ( 1 ) was achieved starting from optically pure oxatrinorbornenone (+)‐ 2 in 12 steps and 10% overall yield. The key step of the synthesis, the glycosidation, turned out to be very sensitive to steric hindrance, and we had, therefore, to optimize the choice of the protection used for the two other OH functions of the aglycone. Finally, the desired β‐D ‐glucoside 15 was obtained in a very good yield (72%) under Koenigs–Knorr‐glycosidation conditions, closely related to those used for the total synthesis of (?)‐bauhinin.     

Internal coordinate modeling of DNA: Force field comparisons

The Jumna internal coordinate program for modeling nucleic acids was extended to include the force field developed for the Amber program. This forms a bridge between internal and Cartesian coordinate modeling approaches. Using the extensive conformational mapping and substate search facilities available within Jumna, we rigorously compared the behavior of the different force fields and also of different continuum solvent models. The results, which help to explain trends seen in earlier minimization and molecular dynamics simulations, point to the superiority of the latest Amber parameterization (Parm94) and to a surprising degree of agreement with the Flex force field originally developed for Jumna. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 :1043–1055, 1997     

Enantioselective alkylidenecyclopropanation of norbornenes with terminal alkynes catalyzed by palladium–phosphinous acid complexes

Pd(II)-coordinated phosphinous acids catalyzed the formal enantioselective [2+1] cycloaddition of norbornene derivatives with terminal alkynes. The absolute configuration of (+)-3aa was assigned using VCD.     

Dispersion and Strichartz estimates for the Liouville equation

We consider the Liouville equation associated to a metric g and we prove dispersion and Strichartz estimates for the solution of this equation in terms of the geometry of the trajectories associated to g. In particular, we obtain global Strichartz estimates in time for metrics where dispersion estimate is false even locally in time. We also study the analogy between Strichartz estimates obtained for the Liouville equation and the Schrödinger equation with variable coefficients. To cite this article: D. Salort, C. R. Acad. Sci. Paris, Ser. I 342 (2006).