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PubMed2005

Reducing-difference infrared spectral analysis of cis- and trans-configurated lactams.

The conventional (non-polarized) and linear-polarized IR-spectra of 2-pyrrolidone and laurolactam as typical representatives of lactams with cis- and trans-amide configuration, respectively, were studied by means of difference IR-spectroscopy. The application of this method to treatment of the non-polarized IR-spectra permits additional conclusions about the likely self-associates of these compounds dissolved in aprotic solvents. By means of the difference linear-dichroic IR-spectroscopy, a more precise assignment of the characteristic bands of the lactam cis- and trans-peptide forms as well as their stereo structures were accomplished. A comparative analysis with the linear-dichroic IR-spectra of epsilon-caprolactam and caprylolactam, as similar compounds, with cis- and trans-conformation, respectively, was also carried out.

Isomerism↗

PubMed2005

Development of a reliable alkaline wastewater treatment process: optimization of the pre-treatment step.

Alkaline waters produced by caprolactam plants polymerizing the fibres of nylon-6 are characterized by a very high alkalinity, salinity and COD values, in addition to the presence of recalcitrant organic molecules. These characteristics make alkaline wastewaters very difficult to treat; so the development of the suitable sequence to carry out in a depuration process appears of great interest. The proposed general process consists of three main steps: first, pre-treatment for the acidification of the polluted stream, second, a successive extraction of the bio-recalcitrant compound (noted as cycloexanecarboxysulphonic acid (CECS)) and a final biological treatment. In particular, this paper deals with the pre-treatment step: it consists of an acidification process by means of sulphuric acid with the concomitant precipitation of black slurries in the presence of different substances, such as solvents, CaCl2, bentonite, several flocculants and coagulants. The aim of this study is to set an experimental procedure, which could minimize fouling problems during sludge filtration. The use of additives like bentonite seems to give the best results, because it allows good COD reductions and a filterable precipitate, which avoids excessive fouling problems of the experimental apparatus.

Acetates↗

PubMed1996

Bicontinuous cubic phase: a model for investigating the effects on a lipid bilayer due to a foreign substance.

Biological effects of foreign substances are usually caused by their interaction within lipid bilayers with the membrane lipids. It is therefore desirable in many situations to determine the effects and the partition of xenobiotic substances, as well as drugs, added to amphiphile-water systems. Bicontinuous cubic liquid crystals provide three-dimensional isotropic matrices with symmetries easily obtained by X-ray diffraction, and were shown to be a useful tool for an initial investigation of the molecular properties possessed by a foreign substance. The concept is illustrated by adding the transdermal penetration enhancer Azone (n-dodecyl-caprolactam) to V2-phases in the glycerol monooleate (GMO)-water system. The weakly polar, water immiscible, Azone is known to favour reversed types of phases in liquid crystals. In the present investigation, Azone was shown to prefer the lipid bilayer interior, with about 19% anchored in the lipid-water interfacial region. Some dependence of its location on water concentration was indicated. The unexpected swelling behaviour of monoacylglycerols in water (L2-->L alpha-->V2) were postulated to result from the lipids changing their polar headgroup conformation, thus allowing for an increase in packing parameter upon increasing the water content.

Chemical Phenomena↗

PubMed2003

Chiral liquid chromatography-mass spectrometry for high-throughput screening of enzymatic racemase activity.

In finding suitable biocatalysts for processes in chemical industry, expression libraries are constructed containing typically >10,000 clones. Search for a desired activity is done by examination of all the clones in one or more libraries using a high-throughput screening assay. Here we describe a method for the screening of the enzymatic racemase activity of clones from an expression library on alpha-amino-epsilon-caprolactam (ACL) using a fast chiral LC separation and ionspray-MS as the detection technique. After substrate incubation with S-ACL, the 96-well microplates were centrifuged to remove cell material. The conversion of S-ACL to R-ACL was monitored by quantitation of the R-ACL enantiomer. Separation of the two ACL enantiomers was performed on a Crownpak CR+ column within 1 min. A Gilson 215 autosampler with a 889 multiple injection probe was used for injecting the samples into the LC system. The total analysis time for a 96-well microplate was 56 min. The MS was operated in the positive-ion mode using selected ion monitoring at m/z 129 [M+H]+ of ACL. Using this method over 12,000 samples were analyzed without loss in performance of the system. The LC column remained stable without loss of resolution and the MS system did not show loss in sensitivity throughout the screening. Inter-day reproducibility was within 15%.

Amino Acid Isomerases↗

PubMed2000

Separation of enantiomers by capillary electrophoresis-mass spectrometry employing a partial filling technique with a chiral crown ether.

Enantiomer separations were performed by capillary electrophoresis-mass spectrometry (CE-MS) with (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H4) as a chiral selector. In order to prevent the introduction of the nonvolatile chiral, selector, 18C6H4, into the nozzle of the CE-MS interface and/or the orifice plate, a partial filling technique was employed in this study. By the partial filling technique, the contamination caused by the nonvolatile chiral selector was avoided not only during the analysis but also during the washing of capillary with the separation solution prior to the run. Several racemic compounds having a primary amino group were successfully separated. Racemic 3-aminopyrrolidine and racemic alpha-amino-epsilon-caprolactam have no strong UV absorption, but such compounds were detected with a high sensitivity by MS detection. In this paper, the effects of the length of separation zone and those of the 18C6H4 concentration were described. As the length of the separation zone was longer or as the concentration of 18C6H4 was higher, the enantiomer resolution was enhanced more and more. However, the optimization of 18C6H4 concentration was practically enough to obtain the baseline separation.

Electrophoresis, Capillary↗

PubMed2001

Evaluation of derivatives of 3-(2-oxo-1-pyrrolidine)hexahydro-1H-azepine-2-one as dermal penetration enhancers: side chain length variation and molecular modeling.

The present study examined the enhancement effect of two series of compounds derived from 3-(2-oxo-1-pyrrolidine)hexahydro-1H-azepine-2-one. One series possessed alkyl side chains (series I) and the other alkyl ester side chains (series II). An in vitro diffusion study was performed to investigate the effect of variation in alkyl/alkyl ester side chain length of two series of compounds on the permeation of hydrocortisone (HC) across hairless mouse skin. The permeability coefficient (P), 24 h receptor concentration (Q(24)) and skin content (SC), as well as the enhancement ratios (ER) for each parameter were recorded. A parabolic relationship was observed between the ER(P), and the alkyl side chain length of the enhancers. The relationship between the length of ester side chains and ER(P) appeared to be relatively linear with R(2) of 0.9676. The relationship between the calculated lipophilicity (CL) and enhancement activity of the enhancers showed that for CL 5-9, series I showed higher P values compared with Azone, but this was not observed with series II. For CL values 4.57-7.75, a significant correlation existed between P of HC and CL of series II compounds (R(2)=0.9967). 1-Tetradecyl-3-(2-oxo-1-pyrrolidine)-epsilon-caprolactam showed the highest P and Q(24), with 40.5- and 18.6-fold increases over the control. In conclusion, the alkyl side chain series of compounds showed more enhancing activity than the alkyl ester side chain series.

Animals↗

PubMed2000

EPC syntheses and structure-activity relationships of hypoglycaemic semicyclic amidines.

A series of homochiral sterically hindered mono- and bicyclic amidines was prepared as hypoglycaemic agents by lethargic reaction of O-methylcaprolactim and 3-ethoxy-2-azabicyclo[2.2.2]oct-2-ene, respectively, with homochiral cis-2-substituted cyclopentane amines provided by asymmetrical reductive amination of racemic 2-substituted cyclopentanones. All compounds, except the cyclohexylmethyl-isoquinuclidone derivative which inhibited secretion at 100 microM, significantly stimulated insulin secretion 2-8-fold at 10 microM and 100 microM in INS-1 cells. The most potent activator was the 2-cyclopentyl-substituted caprolactam derivative 5e. The stimulatory effects on secretion increased with rising steric hindrance of both the amidine alpha-carbon and the bicyclic amidine moiety itself. Enantiomeric discrimination was observed for the 2-¿(cis-2-bulkysubstituted cyclopentyl)iminohexahydroazepine halides 5e and 5f and for the 3-¿(cis-2-substituted cyclopentyl)imino-2-azabicyclo¿2.2.2ŏctane halides 6a and 6c. The amidines depolarized INS-1 cells and generated action potentials, accompanied by a decrease of membrane conductance. Simultaneously [Ca(2+)](i) increased, probably due to Ca(2+)-entry through voltage-dependent Ca(2+)-channels. At high concentrations, where inhibition of secretion was observed, ¿Ca(2+)(i) still rose upon application of the amidines, indicating an additional inhibitory pathway downstream to the elevation of ¿Ca(2+)(i). Even at high concentrations (100 microM), the amidines had no toxic effects on insulin secreting INS-1 cells.

Amidines↗

PubMed2003

Vibrational and electronic couplings in ultraviolet resonance Raman spectra of cyclic peptides.

Ultraviolet resonance Raman (UVRR) spectra are reported for a series of cyclic amides. 2-Azacyclotridecone, which has a 13-membered ring, shows a classic trans-amide UVRR spectral pattern, with comparable enhancement of the amide modes II, III and S. When the ring is diminished to eight (epsilon -caprolactam) or seven (2-azacyclooctanone) members, this pattern is replaced by a single strong band near 1497 cm(-1), characteristic of the Cz-N stretch of a cis-amide vibration (amide IIc). Further shrinkage of the ring decreases the amide IIc frequency. It is lowered over 100 cm(-1) to 1389 cm(-1) in the case of a 4-membered ring (2-azaidine), reflecting diminution of the Cz-N bond order due to ring strain and pyramidalization of the C and N atoms. At the same time the amide Ic (Cz=O stretching) frequency increases, reflecting the localization of the Cz=O double bond. Also the sensitivity to hydrogen-deuterium exchange reverses for amide Ic and IIc modes as ring size decreases. The UV absorption maximum, which is red-shifted for cis-relative to trans-amides, shifts increasingly to the blue as the ring size decreases, again reflecting localization of the pi bonding. In the case of amides with 5- and 6-membered rings (2-pyrrolidinone and delta-eloctam) multiple UVRR bands are seen in the amide IIc region, whose relative intensities are temperature-dependent. These are assigned to conformers in which different members of the ring are out of the mean plane, resulting in variable perturbations of the amide bond. The cyclic dipeptides cyclo(Gly-Gly) and cyclo(Gly-Pro) have perturbed amide IIc frequencies, reflecting the kinematic mixing of the amide coordinates into in- and out-of-phase modes. Excitation profiles reveal electronic mixing as well, with the transition dipoles adding for the in-phase and cancelling for the out-of-phase modes.

Molecular Structure↗

PubMed2006

Chemical characteristics and origins of nitrogen-containing organic compounds in PM2.5 aerosols in the Lower Fraser Valley.

Some nitrogen-containing organic compounds (NOCs) in PM2.5 aerosols in forest, tunnel, urban, rural, and mixed forest/ urban areas in the Lower Fraser Valley (LFV), British Columbia, Canada, were measured to assess their chemical characteristics, temporal and spatial distributions, and origins. The levels of E-caprolactam, isoindole-1,3-dione, benzothiazolone, and N-butyl-benzensulfonamide showed significant differences among the sites, with the highest level at the mixed forest/urban site, indicating that aerosols at this site were impacted by chemical manufacturing activities. N,N-diethyl-m-toluamide (deet) was detected at all locations but was highest in the forest area, demonstrating a widespread usage as an insect repellent in the LFV and at camps at the forest site. Alkyl amides, tracers from wood burning and cooking, ranging from C6 to C20 including two unsaturated amides, hexadecenamide, and 9-octa-decenamide, were detected at all sites. Three patterns of carbon number distributions of alkyl amides varied with location and time, and were mainly impacted by biomass burning or cooking compared to levoglucosan and cholesterol in the LFV. Ratio of oleamide to stearamide (C18:1/C18:0) was discussed as a potential indicator for determining "age" or transport range of biomass combustion plumes.

Air Pollutants↗

PubMed2002

Characterization of a soluble molecular magnet: unusual magnetic behavior of cyano-bridged Gd(III)-Cr(III) complexes with one-dimensional and nanoscaled square structures.

Two cyano-bridged Gd(III)-Cr(III) complexes [Gd(urea)(4)(H(2)O)(2)](2)[Cr(CN)(6)](2) (1) and ([Gd(capro)(2)(H(2)O)(4)Cr(CN)(6)].H(2)O)(n)(2) (capro represents caprolactam) have been synthesized and characterized structurally and magnetically. Complex 1 has a tetranuclear Gd(2)Cr(2) square structure, in which two cis-CN(-) ligands of each [Cr(CN)(6)] link two [Gd(urea)(4)(H(2)O)(2)] groups and in turn, two [Gd(urea)(4)(H(2)O)(2)] link two [Cr(CN)(6)] in a cis fashion. Complex 2 is composed of 1D chains with alternating [Gd(capro)(2)(H(2)O)(4)] and [Cr(CN)(6)] moieties connected by the trans-CN(-) ligands of [Cr(CN)(6)]. The dehydration of 2 at 120 degrees C generates a new complex, [Gd(capro)(2)(H(2)O)(2)Cr(CN)(6)] (2'). Magnetic studies show the existence of antiferromagnetic Gd(III)-Cr(III) interaction in these complexes. On the basis of the tetranuclear model, the magnetic susceptibilities of 1 have been analyzed giving the intermetallic magnetic coupling constant of -0.36 cm(-1). Complex 2' exhibits a ferrimagnetic order below 2.1 K. Interestingly, 2' is quite soluble in water, and slow evaporation of the solution gives the hydrated complex 2. Therefore, 2' is a soluble molecular magnet, and this significant behavior implies potential applications. Isothermal magnetization measurements of 2' and other cyano-bridged Gd(III)-Cr(III) molecular magnets show unusual field-induced metamagnetic behavior from the ferrimagnetic ground state to the ferromagnetic state. Field dependence of magnetization of the cyano-bridged Gd(III)-Cr(III) complexes shows unusual field-induced metamagnetic behavior from the ferrimagnetic ground state to the ferromagnetic state.

Journal Article↗

PubMed2003

Asymmetric Schmidt reaction of hydroxyalkyl azides with ketones.

An asymmetric equivalent of the Schmidt reaction permits stereocontrol in ring expansions of symmetrical cyclohexanones. The procedure involves the reaction of chiral 1,2- and 1,3-hydroxyalkyl azides with ketones under acid catalysis; the initial reaction affords an iminium ether that can be subsequently opened with base. A systematic study of this reaction is reported, in which ketone substrates, chiral hydroxyalkyl azides, and reaction conditions are varied. Selectivities as high as ca. 98:2 are possible for the synthesis of substituted caprolactams, with up to 1,7-stereoselection involved in the overall process. The fact that either possible migrating carbon is electronically identical provides an unusual opportunity to study a ring-expansion reaction controlled entirely by stereoelectronic factors. The mechanism of the reaction and the source of its stereoselectivity are also discussed.

Azides↗

PubMed2003

Unusual tethering effects in the Schmidt reaction of hydroxyalkyl azides with ketones: cation-pi and steric stabilization of a pseudoaxial phenyl group.

The Lewis acid-promoted reactions of chiral 2-aryl-3-azido-1-propanols with 4-substituted cyclohexanones lead to iminium ethers and ultimately caprolactams (following a hydrolysis step). In this study, it is shown that these reactions afford variable ratios of products, depending on the electronic nature of the phenyl group. These results are interpreted in the context of a cation-pi stabilizing effect in the product-determining reaction intermediate. Remarkably, the best selectivity was obtained when an azidopropanol reagent containing a quaternary center was used; a control experiment showed that the high selectivity observed in this result depended upon the free rotation of the pseudoaxial aromatic group in the intermediate that affords the major product.

Azides↗

PubMed2006

Chemical engineering of the single-walled carbon nanotube-nylon 6 interface.

We report an approach to the chemical engineering of the single-walled carbon nanotube (SWNT)-polymer interfacial interaction in a nylon 6 graft copolymer composite which is based on the degree of SWNT functionality. Continuous fibers are drawn from composites fabricated from the in situ polymerization of caprolactam with SWNTs possessing a range of carboxylic acid (SWNT-COOH) and amide (SWNT-CONH(2)) functionalities. Mechanical performance evaluation of the composite fibers shows that a high concentration of the carboxylic acid functional groups leads to a stronger SWNT-nylon interfacial interaction, as reflected in greater values of the Young's modulus and mechanical strength. Replacement of the COOH group by CONH(2) in the SWNT starting material changes the grafting polymerization chemistry, thereby leading to the covalent attachment of longer graft copolymer chains to the SWNTs, and alters the composite morphology while increasing the composite flexibility and toughness.

Journal Article↗

PubMed2006

Beckmann rearrangement of 15N-cyclohexanone oxime on zeolites silicalite-1, H-ZSM-5, and H-[B]ZSM-5 studied by solid-state NMR spectroscopy.

By means of solid-state 15N NMR spectroscopy, evidence for the formation of nitrilium ions as intermediates of the Beckmann rearrangement of 15N-cyclohexanone oxime to epsilon-caprolactam on silicalite-1, H-ZSM-5, and H-[B]ZSM-5 is reported. The zeolites under study are characterized by different acid strengths (silicalite-1 < H-[B]ZSM-5 < H-ZSM-5). Depending on the nature of catalytically active surface OH groups, reactant and product molecules exist in the nonprotonated or protonated state. In addition, formation of byproducts such as 5-cyano-1-pentene and epsilon-aminocapric acid as a result of dehydration and hydrolysis of the reactant and product molecules, respectively, were observed.

Journal Article↗

PubMed1993

Synthesis and amnesia-reversal activity of a series of 7- and 5-membered 3-acylamino lactams.

A series of 3-(acylamino)-epsilon-caprolactams and 3-(acylamino)-2-pyrrolidinones was synthesized. Some of these compounds reversed at different degrees electroconvulsive shock- and Scopolamine-induced amnesia, using a step-through passive avoidance in mice. Classical nootropic drugs, i.e., Aniracetam, Oxiracetam, and Piracetam, were used as reference compounds. Within the analyses of data performed, we introduced a new parameter, the confrontation index (CI), which is a function of Mann-Whitney's U statistic. The CI permits a common scale of activity of substances to be generated, independently of probabilistic hypotheses, with higher scores representing higher activities. The most active compounds were characterized by the formylamino and [3-(trifluoromethyl)benzoyl]amino groups in the 3-position of the ring. None of the substances assayed showed any effect on spontaneous behavior and neurovegetative system.

Amnesia↗

PubMed2002

SAR and X-ray. A new approach combining fragment-based screening and rational drug design: application to the discovery of nanomolar inhibitors of Src SH2.

(pp60)Src is a protein involved in signal transduction and is mainly expressed in neurones, platelets, and osteoclasts. Its precise biological role was recently discovered with the KO experiments by Soriano that gave rise to no other apparent phenotype than osteopetrosis, a disease resulting in excedent bone formation. The SH2 domain of the Src family specifically recognizes a sequence of tetrapeptide featuring a phosphotyrosine and a lipophilic aminoacid at the +1 and +3 positions. Recently we engaged in the search for SH2 ligands via modular peptidomimicry of this tetrapetide. This gave rise to several families of nanomolar inhibitors; the best one incorporated a caprolactam scaffold, a biphenyl moiety, and a phosphotyrosine. However, these inhibitors still incorporated the phosphate group that confers good binding affinity to the protein. Phosphates have undesirable features for drug candidates, namely, high rate of hydrolysis of the phosphate group by phosphatases and high charge content precluding cell penetration. Therefore, while searching for optimal non-peptide ligands for Src SH2, we looked for phosphate replacements. For this, we have designed an SAR by fragment crystallography approach. The start of this work resulted from two experimental observations. First, the fact that phenyl phosphate itself displayed detectable binding affinity for Src SH2 permitted us to perform a screening of small aromatic compounds as phenyl phosphate surrogates. Second, the obtention of large Src SH2 crystals displaying a channel large enough for soaking purposes allowed structure determination of over 40 of these small aromatic compounds bound in the phosphotyrosine binding pocket. This search and the way it gave rise to low nanomolar range Src SH2 inhibitors devoid of phosphate groups will be the subject of the present paper.

Crystallography, X-Ray↗

PubMed2005

Is the Beckmann rearrangement a concerted or stepwise reaction? A computational study.

[reaction: see text] RB3LYP calculations were performed on the Beckman rearrangement by the use of three substrates, acetone oxime (1), acetophenone oxime (2), and cyclohexanone oxime (3). Acidic solvents were modeled by H+ (CH3COOH)3 and H3O+ (H2O)6, and reaction paths were determined precisely. For 1, a two-step process involving a sigma-type cationic complex was obtained. For 2, a three-step process with pi- and sigma-type complexes was found in H+ (CH3COOH)3 and a two-step process involving a sigma-type cationic complex was obtained in H3O+ (H2O)6. However, for 3, a concerted process without pi and sigma complexes was calculated, which leads to the product, epsilon-caprolactam. Three different mechanisms were explained in terms of FMO theory.

Journal Article↗

PubMed2005

Preparation and Suzuki-Miyaura coupling reactions of tetrahydropyridine-2-boronic acid pinacol esters.

[reaction: see text] A study on the conversion of lactam-derived vinyl triflates and phosphates into the corresponding vinyl boronates was carried out. While delta-valerolactam-derived vinyl triflates were successfully converted into 1,4,5,6-tetrahydropyridine-2-boronic acid pinacol ester derivatives by Pd-catalyzed coupling reaction with both bis(pinacolato)diboron and pinacolborane, pyrrolidinone and epsilon-caprolactam derivatives either did not react or were readily reduced. The delta-valerolactam-derived vinyl boronates are thermally stable compounds that efficiently coupled, under Pd catalysis, with structurally diverse aryl and heteroaryl bromides and triflates, vinyl iodides and bromides, and aromatic acid chlorides, to give the corresponding 2-substituted piperidines in good to excellent yields. The number of electrophiles that can virtually be coupled with these new boronic esters makes them very useful reagents for the synthesis of N-heterocyclic compounds.

Journal Article↗