Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Optical Rotation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed2000

Synthesis of (-)-7-epiaustraline and (-)-1-epicastanospermine.

Highly efficient and selective syntheses of the title compounds are described. The cornerstone of the synthetic plan is the tandem inter [4 + 2]/inter [3 + 2] cycloaddition process. These syntheses differ from previous applications of this strategy in that they incorporate an alkylation in the hydrogenolysis step to close the second ring of the azabicyclic systems. Notable features of the sequence are (1) the highly regio- and stereoselective [3 + 2] cycloaddition of nitronate 15 with siloxymethyl (Z)-beta-silylvinyl ketone (Z)-22b and (2) the highly selective reduction of the resulting ketone 24a with L-Selectride. A single-crystal X-ray structure analysis of synthetic (-)-7-epiaustraline confirmed that the targeted structure was successfully synthesized. This stimulated a reexamination of the structural assignment of the natural product. (-)-1-Epicastanospermine was synthesized in four steps from the common intermediate 27a. The absolute configuration of (-)-1-epicastanospermine was assured by single-crystal X-ray structure analysis of intermediate (-)-27a. Thus, the sign of the optical rotation had to be revised. The overall efficiency of these syntheses were 9 steps and 23% yield for (-)-7-epiaustraline and 10 steps and 20% yield for (-)-1-epicastanospermine

Alkylation↗
PubMed1975

Complex formation between mycobacterial polysaccharides or cyclodextrins and palmitoyl coenzyme A.

The mycobacterial polysaccharides MMP (3-O-methyl-mannose-containing polysaccharide), MGLP (lipolysaccharide containing 6-O-methylglucose and glucose), and the cyclodextrins (cyclohexaamylose and cycloheptaamylose) form stoichiometric complexes with palmitoyl-CoA (Machida, Y., Bergeron, R., Flick, P., and Bloch, K. (1973) J. Biol. Chem. 248, 6246-6247). Complex formation is presumed to result from hydrophobic interactions. In order to enhance the hydrophobic character of the cyclodextrins the following derivatives have been synthesized: heptakis (2,di-O-propyl)-, heptakis (2,6-di-O-methyl)-, pentakis (6-O-methyl)-, heptakis (3-O-methyl)-, and permethylated beta-cyclo-dextrin. These compounds stimulate fatty acid synthesis catalyzed by the Mycobacterium smegmatis fatty acid synthetase, the magnitude of the effect decreasing in the order in which the alkylated cyclodextrins are listed above. MMP or MGLP are qualitatively indistinguishable from alkylated cyclodextrins both with respect to palmitoyl-CoA binding and with respect to effects on enzyme systems, suggesting that they form inclusion complexes of the same type. On the basis of model building it is postulated that MMP in solution assumes a helical conformation with a hydrophobic channel about 6 A in diameter and approximately 29 A long, dimensions appropriate for accommodating the paraffinic chain of palmitoyl-CoA in the form of an inclusion complex. Since palmitoyl-CoA binds to polysaccharide much more tightly than free palmitate it is further postulated that ionized groups of the CoA moiety of acyl CoA participate in the binding and do so by hydrogen bonding to the hydrophilic exterior of helical MMP. Palmitoyl-CoA, and to a lesser extent palmitate, affect the optical rotation of MMP and also of the alkylated cyclodextrins indicating that complex formation induces conformational changes in the polysaccharides.

Binding Sites↗
PubMed1984

The absolute structures of rubeomycins A and A1 (carminomycins II and III) and rubeomycins B and B1 (4-hydroxybaumycinols A1 and A2).

The absolute configurations of rubeomycins A and A1 (corresponding to carminomycins II and III) and rubeomycins B and B1 (corresponding to 4-hydroxybaumycinols A1 and A2), except at the C-1" position, were determined by comparison of the optical rotations and other spectral data of rubeomycin derivatives with those of daunomycin and L-(+)-lactic acid.

Anthracyclines↗
PubMed2006

Kettapeptin: isolation, structure elucidation and activity of a new hexadepsipeptide antibiotic from a terrestrial Streptomyces sp.

The ethyl acetate extract of the Streptomyces sp. isolate GW99/1572 exhibited significant biological activity against Gram-positive bacteria and delivered kettapeptin (1), a new hexadepsipeptide antibiotic of the azinothricin type. The structure was elucidated by various 1D and 2D NMR techniques, mass spectrometry and by comparison of the NMR data with those of closely related antibiotics. The absolute configuration of the compound was derived by crystal structure analysis and by comparison with the optical rotation data of related compounds.

Anti-Infective Agents↗
PubMed1997

[Stereochemical structure of d-borneol in "the Japanese Standards of Food Additives"].

d-Borneol is shown at "The Japanese Standards of Food Additives" the sixth edition. Though the absolute stereochemistry of this compound is described as 1S, 2R-form, the opposite optical rotation for the same structure is described in other literatures. The application of improved Mosher's method to d-borneol resulted in 1R, 2S-form for its absolute stereochemistry.

Camphanes↗
PubMed1996

Stereoconfiguration of anteiso-fatty biosynthesized from DL-isoleucine in rat skin.

Isoleucine (Ile) is a precursor for the biosynthesis of anteiso-fatty acids in rat skin, and among the four possible stereoisomers of Ile, L-Ile, and L-allo-Ile were selectively used for biosynthesis of anteiso-fatty acids. This study examined the optical rotation of anteiso-fatty acid derived from DL-Ile to ascertain its stereoconfiguration. Specific rotation of anteiso-fatty acid derived from DL-Ile favorably compared with that derived from L-Ile, suggesting the selective biosynthesis of the (S)-enantiomer of anteiso-fatty acid in rat skin.

Animals↗
PubMed1978

The complexing of guanine nucleosides by poly(inosinic acid).

Under conditions where it is single-stranded (pH 7.0, 0.05 M Na+), poly(inosinic acid) complexes guanosine and 2'-deoxyguanosine in a strongly cooperative process that ultimately results in gel formation. The binding isotherm for formation of the poly(I).deoxyguanosine complex at 3.5 degrees C shows that it contains approximately one molecule of deoxyguanosine bound per IMP residue of the poly(I). This is compatible with the complex having a structure similar to that of the four-stranded secondary structure of poly(I) in which two of the poly(I) strands are replaced by helical arrays of deoxyguanosine molecules. The complex is laevorotatory at wavelengths longer than 300 nm. Optical rotation and ultraviolet absorbance versus temperature profiles show that on thermal dissociation the complex undergoes a co-operative helix-coil transition with Tm in the range 10--20 degrees C.

Deoxyguanosine↗
PubMed1983

Synthesis of conformationally restricted acidic lipids. I. Cyclopentanoid analogs of phosphatidylserine.

A series of six analogs of phosphatidylserine (PS) was synthesized in which the conformational mobility of the backbone was limited. Each analog was a derivative of one of the three diastereoisomeric cyclopentane-1,2,3-triols, so that the glycerol moiety of the PS was, in effect, replaced by each cyclopentane-1,2,3-triol. Four of the members of the series were vicinal dipalmitates [1,2/3-(1P); 1,2/3-(3P); 1,2,3/0-(1P); 1,3/2-(1P)] while the other two members were "unnatural" in that they contained a 2-phosphate group. The two 2-phosphate derivatives were meso-forms and each of the other four derivatives was a DL-pair. Each PS analog was obtained as a stable microcrystalline precipitate analyzing for the monohydrate of a mixture of mono- and di-sodium salts. The infrared spectra, melting behavior, and chromatographic mobility of each sodium salt mixture resembled those obtained for bovine (glycero-)-phosphatidyl-L-serine; the stereochemical differences in the ring caused only marginal variation in these properties. The optical rotation values of the compounds varied with the stereochemistry of the ring. The all-trans-2-phosphate isomer 8d exhibited a negative rotation value, in contrast to each of the other isomers. The all-trans isomer [1,3/2-(1P)] was shown to undergo diazometholysis with diazomethane to give the dimethyl ester of cyclopentano-phosphatidic acid.

Chromatography, Thin Layer↗
PubMed2005

Preparative separation and identification of derivatized beta-methylphenylalanine enantiomers by chiral SFC, HPLC and NMR for development of new peptide ligand mimetics in drug discovery.

A direct preparative purification of all four isomers of the unnatural amino acid beta-methylphenylalanine was achieved using supercritical fluid chromatography (SFC) with stacked-injection. Final purification of the Cbz-methyl ester derived isomers was performed on a Daicel Chiralpak AD-H column (20 mm x 250 mm), using 50:50 methanol/ethanol as the organic modifier and resulted in purification of over 3.4 g of material in 6.25 h with >90% total recovery. The absolute stereochemical assignment of the purified amino acids was determined through a combination of chiral HPLC, NMR and optical rotation studies. To our knowledge, this is the first reported preparative approach that has yielded all four compounds in a single chromatographic run.

Aminobutyrates↗
PubMed2001

Acid-catalyzed dehydrative cyclization of 4-(D-galacto -pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole. synthesis and anomeric configuration of D-lyxo-C-nucleoside analogs.

Dehydration of 4-(D-galacto-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole with 20% methanolic sulfuric acid afforded the anomeric pairs of nucleosides, 4-(alpha-D-lyxopyranosyl)-2-phenyl-2H-1,2,3-triazole (major component) and its beta-anomer, as well as 4-(alpha-D-lyxofuranosyl)-2H-1,2,3-triazole and its beta-anomer. The four anomeric C-nucleosides were separated by chromatography, and their structure and anomeric configuration were determined by periodate oxidation, acylation, and NMR spectroscopy as well as mass spectrometry. The anomeric assignment from optical rotation was not in agreement with final structure assignment and represented a violation of the Hudson isorotation rules. NOE studies and X-ray diffraction measurements confirmed the anomeric configuration.

Catalysis↗
PubMed1999

Lactonamycin, a new antimicrobial antibiotic produced by Streptomyces rishiriensis MJ773-88K4. II. Structure determination.

The absolute structure of a new antibiotic lactonamycin is described. The NMR studies deduced one of four possible structures for the aglycon attached by a rhodinose through glycosidic bond. The stereochemistry of the sugar obtained by an acid hydrolysis was determined to be L-form by measuring optical rotation. The stereochemistry of the aglycon was determined by X-ray crystallographic analysis.

Anti-Bacterial Agents↗
PubMed1996

Degradation of double-stranded xanthan by hydrogen peroxide in the presence of ferrous ions: comparison to acid hydrolysis.

Conformationally ordered, double-stranded xanthan, degraded in the presence of H2O2 and Fe2+ (at 20 degrees C) or in dilute acid (0.1 M HCl at 80 degrees C), produced xanthan variants with weight-average molecular weights (Mw) ranging from 2 x 10(6) to 5.4 x 10(4). In both cases the fraction of cleaved linkages in the glucan backbone (alpha), measured as reducing ends, increased to very high values (0.05 for Mw = 2-3 x 10(4)), demonstrating that a large number of linkages in the backbone could be cleaved without a correspondingly large reduction in Mw, in accordance with the double-stranded nature of xanthan. Extensive degradation (more than 10-fold reduction in Mw) in both cases released single-stranded, conformationally disordered oligomers; this release was accompanied by an increase in the rate of acid hydrolysis of the glucan backbone and a pronounced increase in the rate of release of glucose monomer. In contrast, there was no significant change in the rate of reducing end-group formation associated with the release of oligomers upon degradation with H2O2/Fe2+. Both types of degradation were accompanied by changes in the composition of the side chains. However, in contrast to acid hydrolysis, where the terminal beta-D-mannose is preferentially hydrolyzed, the reaction with H2O2/Fe2+ resulted in removal of both mannose and glucuronic acid at approximately equal rates. This observation can be explained by a preferential attack on the inner alpha-D-mannose, with concomitant removal of the entire side chain. Removal of side chains and the release of single-stranded oligomers by H2O2/Fe2+ strongly influenced the optical rotation and also broadened the chiroptically detected conformational transition, whereas no change in the transition temperature was observed.

Carbohydrate Conformation↗
PubMed2002

Structure of the O-specific polysaccharide of Providencia alcalifaciens O16 containing N-acetylmuramic acid.

The O-specific polysaccharide of Providencia alcalifaciens O16 was obtained by mild-acid degradation of the lipopolysaccharide and studied by chemical methods and NMR spectroscopy, including 2D 1H,(1)H COSY, TOCSY, NOESY, and 1H,(13)C HSQC experiments. It was found that the polysaccharide contains N-acetylmuramic acid, which was isolated by solvolysis with trifluoromethanesulfonic acid and identified by the specific optical rotation and NMR spectroscopy. The following structure of the trisaccharide repeating-unit of the polysaccharide was established:

Carbohydrate Conformation↗
PubMed1996

Experimental chiroptical verification of linkage flexibility in methyl 3-O-(alpha-d-mannopyranosyl)-alpha-d-mannopyranoside.

Vacuum UV CD spectra of methyl 3-O-(alpha-D-mannopyranosyl)-alpha-D- mannopyranoside in D2O and as a cast film were obtained in the 145-200 nM region. The disaccharide solution CD per residue is nearly identical to that of the monosaccharide solution CD, and to the monosaccharide film CD. Conversely, the disaccharide film spectrum exhibits a strong positive CD linkage contribution in the 160-170 nm range, which is consistent with the known crystal conformation under the aegis of previously determined sector rules. The close similarity between the monosaccharide and disaccharide solution spectra, therefore, reflects conformational averaging in which the net linkage contribution is approximately zero. The present observation of significant solution linkage flexibility confirms previous conclusions based on optical rotation, as well as conclusions of others based on nmr data. Moreover, when combined with those earlier results, the present work demonstrates the population of at least three distinct potential energy wells on the disaccharide phi,psi potential energy surface.

Carbohydrate Conformation↗
PubMed1976

An extracellular fungal polysaccharide composed of 2-acetamido-2-deoxy-D-glucuronic acid residues.

The black yeast-like fungus NRRL YB-4163, now tentatively identified as Rhinocladiella elatior Mangenot, has been found to produce an extracellular microbial polysaccharide composed mainly of 2-acetamido-2-deoxy-D-glucuronic acid residues. Polysaccharide (PS) YB-4163, when isolated in good yield as the neutral potassium salt, dissolves readily in water to produce extremely viscous solutions, which form stable foams and emulsions. By depolymerizing PS YB-4163 with [14C]methanol-HCl, the polysaccharide can be both identified and quantitated radiochemically by determining the individual [14C]methyl glycosides after their separation by paper chromatography. When the methyl glycosides of PS YB-4163 were reduced with NaB3H4, only the methyl glycosides of 2-acetamido-2-deoxy-D-[6-3H]glucose were found. Analysis of the monosaccharide released from carboxyl-reduced PS YB-4163 by acid hydrolysis or methanolysis also showed 2-acetamido-2-deoxy-D-glucuronic acid to be the main constituent. Previously, the only polysaccharides known to be composed entirely or hexosaminuronic acid have been cellular products from pathogens. Of these, the antigenic polysaccharide (SPSA) from Staphylococcus aureus is composed entirely of 2-amino-2-deoxy-D-glucuronic acid, but its amino groups are substituted equally with acetyl and N-acetylalanyl groups. The specific optical rotation of PS YB-4163, [alpha]20D -75 degrees (c 0.5, water), is similar to that of SPSA (-91 degrees), and suggests beta-D-linkages that must be either (1 leads to 3) or (1 leads to 4).

Glucuronates↗
PubMed1981

Analysis of pilocarpine and isopilocarpine in ophthalmic solutions by UV spectrophotometry-polarimetry.

An improved analytical method was developed that simultaneously quantitates pilocarpine and isopilocarpine in the presence of each other and pilocarpic acid. Pilocarpine and isopilocarpine are first separated from any pilocarpic acid present in the sample by eluting with water-washed chloroform through a column packed with acid-washed diatomaceous earth. The concentrations of pilocarpine and isopilocarpine then are determined by a combination of UV spectrophotometric and polarimetric measurements. UV absorbance is measured at the absorption maximum (215 nm), and optical rotation is measured at the 254-nm line of mercury. Standard curve and standard recovery data are presented. The method is applicable to several commercially available ophthalmic solutions of pilocarpine and is compared to both the USP colorimetric method and a high-performance liquid chromatographic method.

Magnetic Resonance Spectroscopy↗
PubMed1989

Molecular origins of acetan solution properties.

Acetan is a branched acidic heteropolysaccharide secreted by Acetobacter xylinum. X-ray diffraction studies of oriented fibres suggest non-crystalline helices with fivefold symmetry and a pitch of 4.8 nm. Optical rotation and circular dichroism studies are consistent with the retention of the helical structure in solution and a helix-coil transition upon heating and cooling. Aqueous solutions yield high 'low shear rate' viscosity and shear-thin upon shearing.

Acetobacter↗
PubMed1987

Polarimetric assay for the determination of the native collagen content of soluble collagen.

Two standardized assays for determining the amount of native collagen in a collagen solution are described which are based on polarimetric measurements. Native collagen content is calculated from the loss of optical rotation during transition from the original to the denatured conformation using constants which were obtained from standard collagen of highest available native collagen content. While Method I gives information on the content of helical collagen, Method II estimates collagen which is resistant to peptic degradation. Both methods are simple to perform and suitable for routine quality control.

Animals↗