Home About us Contact
|
Home About us Contact | ||
|
|
||
Mild Acid Hydrolysis (mild + acid_hydrolysis)
Selected AbstractsSeparation of Escherichia coli 055:B5 lipopolysaccharide and detoxified lipopolysaccharide by high-performance capillary electrophoresisELECTROPHORESIS, Issue 17 2003Nicola Volpi Abstract A rapid, highly sensitive and reproducible high-performance capillary electrophoresis (HPCE) method (electrokinetic chromatography with sodium dodecyl sulfate) is described for the determination of the lipopolysaccharide (LPS) and detoxified LPS (D-LPS), produced by both alkaline treatment in anhydrous conditions and mild acid hydrolysis, from Escherichia coli 055:B5 bacteria. LPS and D-LPS are separated and readily determined within 25 min on an uncoated fused-silica capillary using normal polarity at 20 kV and detection at 200 nm. A linear relationship (correlation coefficient greater than about 0.97) was found for the LPS and the two D-LPS species over a wide range of concentrations, from approximately 120 to 360 ng, with a detection sensitivity less than about 100 ng. Furthermore, HPCE was able to separate several molecular species mainly due to the presence of populations with O -specific polysaccharides of distinct and increasing mean chain lengths. This approach could be of great importance for the quantitative determination of LPS and D-LPS during the purification and preparation processes, also considering the importance of D-LPS in the preparation of human vaccines, and for the qualitative evaluation of the heterogeneity of LPS and the O -polysaccharide components. [source] The structure of the core region of the lipopolysaccharide from Klebsiella pneumoniae O3FEBS JOURNAL, Issue 6 2001-D-manno-octulosonic acid (, -Kdo) residue in the outer part of the core, 3-Deoxy-, O12 lipopolysaccharides, a common structural element of Klebsiella pneumoniae O The structure of lipid A,core region of the lipopolysaccharide (LPS) from Klebsiella pneumoniae serotype O3 was determined using NMR, MS and chemical analysis of the oligosaccharides, obtained by mild acid hydrolysis, alkaline deacylation, and deamination of the LPS:where P is H or ,-Hep; J is H or ,-GalA; R is H or P (in the deacylated oligosaccharides).Screening of the LPS from K. pneumoniae O1, O2, O4, O5, O8, and O12 using deamination showed that they also contain ,-Hep-(1,4)-,-Kdo-(2,6)-GlcN and ,-Kdo-(2,6)-GlcN fragments. [source] Structural analysis of the core region of lipopolysaccharides from Proteus mirabilis serotypes O6, O48 and O57FEBS JOURNAL, Issue 8 2000Evgeny Vinogradov The structure of lipid A core region of the lipopolysaccharides (LPS) from Proteus mirabilis serotypes O6, O57 and O48 was determined using NMR, MS and chemical analysis of the oligosaccharides, obtained by mild acid hydrolysis, alkaline deacylation, and deamination of LPS: Incomplete substitutions are indicated by bold italic type. All sugars are present in pyranose form, ,-Hep is the residue of lglycero -,- dmanno -Hep, ,- dd -Hep is the residue of dglycero -,- dmanno -Hep, l -Ara4N is 4-amino-4-deoxy- l -arabinose, Qui4NAlaAla is the residue of 4- N -(l -alanyl- l -alanyl)-4-amino-4,6-dideoxyglucose. All sugars except l -Ara4N have d -configuration. ,-GalA* is partially present in the form of amide with 1,4-diaminobutane (putrescine)-HN(CH2)4NH2 or spermidine-HN(CH2)3NH(CH2)4NH2. [source] The Nonchiral Bislactim Diethoxy Ether as a Highly Stereo-Inducing Synthon for Sterically Hindered, , -Branched , -Amino Acids: A Practical, Large-Scale Route to an Intermediate of the Novel Renin Inhibitor AliskirenHELVETICA CHIMICA ACTA, Issue 8 2003Richard Göschke The diastereoselective synthesis of the sterically hindered, , -branched , -amino acid derivative (2S,4S)- 24a and its N -[(tert -butoxy)carbonyl](Boc)-protected alcohol (2S,4S)- 19, both key intermediates of a novel class of nonpeptide renin inhibitors such as aliskiren (1), is described. Initially, the analogous methyl ester (2S,4S)- 17 was obtained by alkylation of the chiral Schöllkopf dihydropyrazine (R)- 12a with the dialkoxy-substituted alkyl bromide (R)- 11a, which proceeded with explicitly high diastereofacial selectivity (ds ,98%) to give (2S,5R,2,S)- 13a (Scheme,4), followed by mild acid hydrolysis and N -Boc protection (Scheme,5). Conversely, the complete lack of stereocontrol and poor yields for the reaction of (R)- 11a with the enantiomeric (S)- 12b suggested, in addition to the anticipated shielding effect by the iPr group at C(2) of the auxiliary, steric repulsion between the MeOC(6) and the bulky residues of (R)- 11a in the proposed transition state, which would strongly disfavor both the Si and Re attack of the electrophile (see Fig.). Based on this rationale, alkylation of the readily accessible achiral diethoxy-dihydropyrazine 21 with (R)- 11a was found to provide a 95,:,5 mixture of diastereoisomers (2S,2,S)- 22a and (2R,2,S)- 23a in high yield (Scheme,6), which afforded in two steps and after recrystallization enantiomerically pure (2S,4S)- 24a. Similarly, the stereochemical course for the alkylation reactions of the related alkyl bromides (S)- 28a and (R)- 28b with both (R)- 12a and (S)- 12b as well as with the achiral 21 was investigated (Schemes,7,9). The precursor bromides (R)- 11a, (S)- 11b, (R)- 28a, and (S)- 28b were efficiently synthesized via the diastereoselective alkylation of the Evans 3-isovaleroyloxazolidin-2-ones (R)- 7a and (S)- 7b either with bromide 6 or with benzyl chloromethyl ether, and subsequent standard transformations (Schemes,3 and 7). A practical and economical protocol of the preparation of (2S,4S)- 24a on a multi-100-g scale is given. This is the first report of the application of an achiral dihydropyrazine, i.e., in form of 21, as a highly stereo-inducing synthon providing rapid access to a N -protected , -branched , -amino acid with (2S) absolute configuration. [source] Simultaneous wet ball milling and mild acid hydrolysis of rice hullJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 1 2010Jinxiang Zhou Abstract BACKGROUND: Rice hull, an abundant residue but a big issue for the rice processing industry, has the potential to serve as a feedstock for production of ethanol because of its lignocellulosic composition. Simultaneous wet ball milling and mild acid hydrolysis of rice hull was studied in this work. RESULTS: Ball milling with 150 small stainless steel beads and rotation speed of 600 rpm in citrate solvent of pH 4 was the optimal condition for hydrolysis, and the yield of sugar increased with increased milling time. Corresponding structure transformations before and after milling analyzed by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM) and transmission fourier transform infrared spectroscopy (FT-IR) clearly indicate that this hydrolysis could be attributed to the crystalline and chemical structure changes of cellulose in rice hull during ball milling in mild acid solvent. CONCLUSION: This combined treatment of ball milling and citrate solvent greatly changed the crystalline and chemical structure and continuously generated sites accessible to citrate solvent, thus enabling hydrolysis of the rice hull. Copyright © 2009 Society of Chemical Industry [source] Elucidation of the molecular structure of lipid A isolated from both a rough mutant and a wild strain of Aeromonas salmonicida lipopolysaccharides using electrospray ionization quadrupole time-of-flight tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2005Anas El-Aneed The chemical structure of lipid A, isolated by mild acid hydrolysis from a rough mutant and a wild strain of Aeromonas salmonicida lipopolysaccharide, was investigated using electrospray ionization quadrupole time-of-flight (QqToF) hybrid tandem mass spectrometry and showed a great degree of microheterogeneity. The chemical structure of the main constituent of this heterogeneous mixture was identified as a , -D-(1,,,6) linked D-glucosamine disaccharide substituted by two phosphate groups, one being bound to the non-reducing end at position O-4, and the other to the position O-1 of the reducing end of the D-glucosamine disaccharide. The location of the fatty acids linked to the disaccharide backbone was established by identifying diagnostic ions in the conventional QqToF-MS scan. Low-energy collision tandem mass spectrometry analysis of the selected precursor diagnostic ions confirmed, unambiguously, their proposed molecular structures. We have established that myristyloxylauric (C14:0(3- O(12:0))) acid residues were both N-2, and O-3, linked to the non-reducing end of the D-GlcN residue, and that two 3-hydroxymyristic (C14:0(3-OH)) acid chains acylated the remaining positions of the reducing end. The MS and MS/MS data obtained allowed us to determine the complex molecular structure of lipid A. The QqToF-MS/MS instrument has shown excellent superiority over a conventional quadrupole-hexapole-quadrupole tandem instrument which failed to fragment the selected precursor ion. Copyright © 2005 John Wiley & Sons, Ltd. [source] Full Structure of the Carbohydrate Chain of the Lipopolysaccharide of Providencia rustigianii,O34CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2008Abstract A lipopolysaccharide isolated from an opportunistic pathogen of the Enterobacteriaceae family Providencia rustigianii,O34 was found to be a mixture of R-, SR-, and S - forms consisting of a lipid moiety (lipid,A) that bears a core oligosaccharide, a core with one O-polysaccharide repeating unit attached, and a long-chain O-polysaccharide, respectively. The corresponding carbohydrate moieties were released from the lipopolysaccharide by mild acid hydrolysis and studied by sugar and methylation analyses along with one- and two-dimensional NMR spectroscopy and high-resolution electrospray ionization mass spectrometry. As a result, the structures of the core and the O-polysaccharide were established, including the structure of the biological repeating unit (an oligosaccharide that is preassembled and polymerized in biosynthesis of the O-polysaccharide), as well as the mode of the linkage between the O-polysaccharide and the core. Combining the structure of the carbohydrate moiety thus determined and the known structure of lipid,A enabled determination of the full lipopolysaccharide structure of P. rustigianii,O34. [source] | ||||||||||