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PubMed1996

Binding of alkaline cations to the double-helical form of gramicidin.

Gramicidin is a polypeptide antibiotic that forms monovalent cation-specific channels in membrane environments. In organic solvents and in lipids containing unsaturated fatty acid chains, it forms a double-helical "pore" structure, in which two monomers are intertwined. This form of gramicidin can bind two cations inside its lumen, and the crystal structures of both an ion complex and an ion-free form have been determined. In this study, we have used circular dichroism (CD) spectroscopy to examine the binding mechanism and the binding constants (K1 and K2) of cations to gramicidin in the double helical form in methanol solution. The dramatic change in optical rotation in the far-ultraviolet CD spectrum of gramicidin provides a useful tool for monitoring the binding. The binding mechanism appears to involve a large conformation change associated with the binding of ions to the first of the two sites. The calculated values for the K1 binding constants for alkaline cations are considerably smaller than the K2 binding constants. The order of binding affinity for alkaline cations is similar to that for the helical dimer "channel" form of gramicidin, i.e., Cs+ approximately Rb+ > > K+ > Li+, but in comparison to the helical dimer form, the binding to double-helical dimers is dominated by a cation size-dependent conformational change in the gramicidin structure.

Amino Acid Sequence↗
PubMed1997

Mapping fluorophore distributions in three dimensions by quantitative multiple angle-total internal reflection fluorescence microscopy.

The decay of evanescent field intensity beyond a dielectric interface depends upon beam incident angle, enabling the 3-d distribution of fluorophores to be deduced from total internal reflection fluorescence microscopy (TIRFM) images obtained at multiple incident angles. Instrumentation was constructed for computer-automated multiple angle-TIRFM (MA-TIRFM) using a right angle F2 glass prism (n(r) 1.632) to create the dielectric interface. A laser beam (488 nm) was attenuated by an acoustooptic modulator and directed onto a specified spot on the prism surface. Beam incident angle was set using three microstepper motors controlling two rotatable mirrors and a rotatable optical flat. TIRFM images were acquired by a cooled CCD camera in approximately 0.5 degree steps for >15 incident angles starting from the critical angle. For cell studies, cells were grown directly on the glass prisms (without refractive index-matching fluid) and positioned in the optical path. Images of the samples were acquired at multiple angles, and corrected for angle-dependent evanescent field intensity using "reference" images acquired with a fluorophore solution replacing the sample. A theory was developed to compute fluorophore z-distribution by inverse Laplace transform of angle-resolved intensity functions. The theory included analysis of multiple layers of different refractive index for cell studies, and the anisotropic emission from fluorophores near a dielectric interface. Instrument performance was validated by mapping the thickness of a film of dihexyloxacarbocyanine in DMSO/water (n(r) 1.463) between the F2 glass prism and a plano-convex silica lens (458 mm radius, n(r) 1.463); the MA-TIRFM map accurately reproduced the lens spherical surface. MA-TIRFM was used to compare with nanometer z-resolution the geometry of cell-substrate contact for BCECF-labeled 3T3 fibroblasts versus MDCK epithelial cells. These studies establish MA-TIRFM for measurement of submicroscopic distances between fluorescent probes and cell membranes.

3T3 Cells↗
PubMed1975

Biosynthesis of D- and L-glycero-L-galacto-octulose from pentoses and hexoses.

D-glycero-L-galacto-Octulose and L-glycero-L-galacto-octulose accumulated when leaves of Kenland red clover (Trifolium pratense) were allowed to imbibe solution of D-gulose or D-xylose and L-mannose or L-arabinose, respectively. The octuloses were isolated and identified by paper chromatography and by oxidative degradations to the corresponding lower sugars. Assignments of the D and L configuration were made on the basis of optical rotation. It is suggested that formation of the octuloses from the hexoses and pentoses is mediated through transketolase and aldolase or transaldolase catalysis, respectively.

Chromatography, Paper↗
PubMed1975

Structural studies of the capsular polysaccharide of Klebsiella type 81.

The structure of the capsular polysaccharide from Klebsiella Type 81 has beeninvestigated. Methlylation analysis, uronic acid degradation, Smith degradation, andgraded acid hydrolysis were the principle methods used. Theanomeric nature of theglycosidic linkages was determined by characterization of fragments obtained from thevarious methods of degradation used. One of the L-rhamnosidic linkages was notpresent in any of these fragments, but is assumed to be an alpha-linkage from consideerationsof optical-rotation data. These studies show that they polysaccharide consits of thefollowing hexasaccharide repeating-unit: yield2)-alpha-L-Rhap-(1yields3)-alpha-L-Rhap-(1-yields4)-beta-D-GlcAP-(1-yields2)-alpha-L-Rhap-(1-yields3)-alpha-L-Rhap-(1-yields3)-beta-D-Galp-(1-yields.

Chemical Phenomena↗
PubMed1981

Structural investigation of Klebsiella K-type 4 capsular polysaccharide.

The capsular polysaccharide from Klebsiella K4 contains the tetrasaccharide repeating-sequence leads to 3)-alpha-D-Glcp-(1 leads to 2)-alpha-D-Glcp A-(1 leads to 3)-alpha-D-Manp-(1 leads to 3)-beta-D-Glcp-(1 leads to. P.m.r. spectroscopy and the measurement of optical rotation were used to establish the anomeric linkages in the polysaccharide and in the oligosaccharides derived by partial hydrolysis. The repeating unit also contains one 0-acetyl group.

Carbohydrate Conformation↗
PubMed1980

The molecular structure of the capsular polysaccharide from Klebsiella type 27.

The capsular polysaccharide of Klebsiella serotype K27 had been investigated by techniques involving methylation analysis, autohydrolysis, and graded hydrolysis with acid. The anomeric configurations of the sugar constituents were determined, where possible, on the basis of p.m.r. spectroscopy and optical rotation data. The results of these studies are consistent with a primary structure in which the repeating-unit is the doubly branched hexasaccharide.

Carbohydrate Sequence↗
PubMed1975

Four isomeric ethyl 1-thioglycosides from 2-amino-2-deoxy-D-arabinose.

Ethyl 2-amino-2-deoxy-1-thio-alpha- and -beta-D-arabinopyranoside (2 and 4) were obtained by direct ethanethiolation of 2-amino-2-deoxy-D-arabinose (1), and their structures were determined by mass and p.m.r. spectrometry. Ethyl 2-amino-2-deoxy-1-thio-alpha- and -beta-D-arabinofuranoside (11 and 13) were prepared by partial demercaptalation of 2-amino-2-deoxy-D-arabinose diethyl dithioacetal (6) with mercuric chloride (or, preferably, with bromine), with or without protection of the 5-hydroxyl group. Demercaptalation with mercuric chloride gave the beta-D anomers almost exclusively, and treatment with bromine gave a mixture of the alpha and beta anomer in the ratio of similar to 1:1. Alternatively, direct ethanethiolation of 1 in trifluoracetic acid yielded the alpha-D anomer. The structures of 11 and 13 were determined by mass spectrometry, by direct comparison of their N-acetyl derivatives with an authentic enantiomorph (15b), and by p.m.r. spectroscopy. The physicochemical properties of the four 1-thioglycosides (2,4,11, and 13) were compared with those of the O-GLYCOSIDES of D-arabinose.

Amino Sugars↗
PubMed1985

Steric control in the polymerization of 1,2-anhydro-3,4,6-tri-O-benzyl-beta-D-mannopyranose.

Polymerization of 1,2-anhydro-3,4,6-tri-O-benzyl-beta-D-mannopyranose under acid catalysis has led to a series of polymers varying in anomeric configuration from approximately 90% alpha to 70% beta. Optical rotations follow 13C-n.m.r. estimates of anomeric composition linearly over this range. Low-temperature polymerization with trifluoromethanesulfonic anhydride as initiator favors mainly cis-opening of the anhydro ring, presumably through the intermediary of a macroester. These results are compared with related glycosylation and polymerization reactions on 1,2-anhydro sugar derivatives, and some mechanistic conclusions are proposed.

Glycosides↗
PubMed2001

Synthesis and characterisation of N-glycosyl amines from the reaction between 4,6-O-benzylidene-D-glucopyranose and substituted aromatic amines and also between 2-(o-aminophenyl)benzimidazole and pentoses or hexoses.

Twelve N-glycosyl amines were synthesised using 4,6-O-benzylidene-D-glucopyranose and different substituted aromatic amines, including some diamines that resulted in bis-glycosyl amines. Another set of six N-glycosyl amines was synthesised using different hexoses and pentoses and 2-(o-aminophenyl)benzimidazole. All compounds were isolated as solid products and purified, their elemental compositions were established, and these were characterised by NMR (1H and 13C), UV-Vis, and FTIR spectroscopy, by FAB mass spectrometry (molecular-ion peaks gave molecular weights), and by their optical rotations. While the protected saccharide, 4,6-O-benzylidene-D-glucopyranose, exists as a mixture of beta and alpha anomers in solution, the corresponding N-glycosyl amines were of only the beta anomeric form as determined by NMR and FTIR spectroscopy. On the other hand, N-glycosyl amines synthesised from 2-(o-aminophenyl)benzimidazole prefer the alpha anomeric form, and in two cases a mixture of both the beta and the alpha anomers were observed. The trends observed in the chemical shifts were compared among different products.

Amines↗
PubMed2001

Interaction of metal ions with N-glycosylamines: isolation and characterization of the products of 4,6-O-benzylidene-N-(o-carboxyphenyl)-beta-D-glucopyranosylamine with different metal ions.

Metal-ion complexes of Li(+), Na(+), K(+), Mg(2+), Ca(2+), Ba(2+), Pb(2+), Cd(2+), Hg(2+) with 4,6-O-benzylidene-N-(o-carboxyphenyl)-beta-D-glucopyranosylamine were synthesized and isolated as solid products and characterized by analytical means as well as by spectral techniques, such as, 1H and 13C NMR, FTIR, absorption, FAB mass spectrometry, optical rotation and CD. While the alkali metal ions formed ML type of complexes, the other metal ions formed ML(2) type complexes. Molecular weights of the complexes of Li(+), Na(+) and K(+) were established based on the molecular-ion peaks in the FAB mass spectra. The saccharide portion remains in the beta-anomeric form even after the complexation. The spectral data, as well as the trends observed in the chemical shifts, indicate the interaction preferences between this glycosyl amine and different metal ions, and further reveal certain structural features of the complexes.

Cadmium↗
PubMed2003

Structure of the O-specific polysaccharide of Providencia rustigianii O14 containing N(epsilon)-[(S)-1-carboxyethyl]-N(alpha)-(D-galacturonoyl)-L-lysine.

The O-specific polysaccharide of Providencia rustigianii O14 was obtained by mild acid degradation of the LPS and studied by chemical methods and NMR spectroscopy, including 2D 1H,(1)H COSY, TOCSY, NOESY, and 1H,(13)C HSQC experiments. The polysaccharide was found to contain N (epsilon)-[(S)-1-carboxyethyl]-N(alpha)-(D-galacturonoyl)-L-lysine ('alaninolysine', 2S,8S-AlaLys). The amino acid component was isolated by acid hydrolysis and identified by 13C NMR spectroscopy and specific optical rotation, using synthetic diastereomers for comparison. The following structure of the trisaccharide repeating unit of the polysaccharide was established:Anti-P. rustigianii O14 serum was found to cross-react with O-specific polysaccharides of Providencia and Proteus strains that contains amides of uronic acid with N(epsilon)-[(R)-1-carboxyethyl]-L-lysine and L-lysine.

Carbohydrate Conformation↗
PubMed2002

Chiral liquid chromatography separation and chiroptical properties of the enantiomers of dimethyl alpha-hydroxyfarnesylphosphonate, a precursor of a farnesyl protein transferase inhibitor.

The HPLC enantiomeric separation of racemic and non-racemic samples of dimethyl alpha-hydroxyfarnesylphosphonate (1) was accomplished using Chiralcel OD as chiral stationary phase. Single enantiomers were isolated by semipreparative HPLC and their CD spectra and optical rotations were measured. The method ascertains enantiomeric excess of 1, obtained by oxidation of dimethylfarnesylphosphonate with enantiopure oxaziridines, avoiding converting the enantiomers to diastereomers by the use of a chiral auxiliary. Stability of the solutions of 1 is strongly dependent on the nature of the solvent.

Chromatography, High Pressure Liquid↗
PubMed2003

Quantitation and test of enantiomeric purity of the L-ketohexoses by liquid chromatography with dual refractive index and laser-based chiroptical detection.

Experimental data for the synthetic methods of preparation of the L-ketohexoses have been lacking an analytical method for monitoring the chemical or enzymatic reactions described. Dual refractive index and laser-based chiroptical detection provides an ideal method for following the reactions, since the refractive index detector quantifies the amount of analyte, while the ratio of optical rotation to refractive index response allows the enantiomer mole fraction to be determined. Sulfonated polystyrenedivinylbenzene resin in the Ca form as the stationary phase with H2O at 80 degrees C as the eluent gives base-line separation of sorbose, fructose, tagatose, and psicose. Dependent on the complexity of the reaction mixture, analysis times range from 20 to 60 min.

Calibration↗
PubMed2001

ent-Pimarane derivatives from Dysoxylum hainanense.

Four ent-pimarene diterpenoids. ent-18-acetoxy-8(14)-pimarene-15S, 16-diol, ent-18-acetoxy-16-hydroxy-8(14)-pimaren-15-one, ent-16,18-dihydroxy-8(14)-pimaren-15-one and ent-19-nor-4,16,18-trihydroxy-8(14)-pimaren-15-one, together with three known damarane triterpenoids, richenoic acid, eichleriainic acid and shoreic acid were isolated from the bark of Dysoxyhum hainanense Merr. Their structures were elucidated on the basis of spectroscopic techniques. The absolute configurations of four diterpenoids were assigned as ent-pimarene type by chemical transformation and by co-occurrence in the plant as well as by negative optical rotations for four compounds.

Abietanes↗
PubMed1993

L-galactose containing galactans from the carrageenophyte Gigartina skottsbergii.

Alkaline treatment of a partially cyclized mu/v-carrageenan and further fractionation with potassium chloride yielded a fraction soluble in 2 M KCl with negative optical rotation. We report the analysis and some structural features of this product, such as the presence of L-galactose and 3,6-anhydro-L-galactose.

Carbohydrate Sequence↗
PubMed2001

Part III. Direct enzymatic esterification of lactic acid with fatty acids.

Lipase catalyzed esterification reactions between lactic acid and several fatty acids have been studied. Difficulties arise in esterifying lactic acid because of the potential for this substance to act both as an acyl donor and as a nucleophile. These difficulties were minimized via strategies which greatly increased the yield of the desired ester. Use of the companion fatty acid in excess with respect to lactic acid in an apolar solvent (n-hexane) in which the lactic is not completely dissolved has been employed to minimize the potential for lactic acid to act as an acyl donor in a self-polymerization reaction.Beneficial and sinergistic effects of both silica gel and molecular sieves on conversion to the desired product are described. However, careful control of the amount of molecular sieves used is required. This fact is a consequence of two opposing effects of this material: i.e. adsorption of both lactic acid and water from the reaction mixture. For reaction between caprylic and lactic acids, use of an excessive amount of enzyme reduces the extent of conversion to 2-O-caproyl-lactic acid.A very pure ester of the L-enantiomer (optical rotation of [alpha]D(25) = -23.5) can be prepared in n-hexane using a four fold excess of caprylic acid and Candida antarctica lipase. Optimum reaction conditions lead to 35% yield of 2-O-caproyl-lactic acid, a result which is close to the maximum yield that can be enantioselectively obtained from commercial grade lactic acid (68 mole per cent monomer).

Journal Article↗