Mode of action of (1→4)-β-d-arabinoxylan arabinofuranohydrolase (AXH) and |ga=l-arabinofuranosidases on alkali-extractable wheat-flour arabinoxylan
摘要:
Arabinoxylan-derived oligosaccharides were treated with (1-->4)-beta-D-arabinoxylan arabinofuranohydrolase (AXH) and two types of alpha-L-arabinofuranosidase, A and B. Analysis of reaction products by high performance anion-exchange chromatography indicated the removal of arabinofuranosyl groups from singly substituted xylopyranosyl residues. In addition, differences in the specificity of these enzymes towards the various differently substituted oligosaccharides were observed. 1H NMR spectroscopy and methylation analysis of alkali-extractable wheat-flour arabinoxylan treated with AXH confirmed the specificity of AXH towards (1-->3)-linked arabinofuranosyl groups on singly substituted xylopyranosyl residues. With these techniques, alpha-L-arabinofuranosidase B was found to cause minor changes in (1-->2)- and (1-->3)-linked arabinofuranosyl groups on doubly substituted xylopyranosyl residues.
RNA nucleosides as chiral sensing agents in NMR spectroscopy
作者:N. Lokesh、S. L. Sachin、L. V. Narendra、K. Arun、N. Suryaprakash
DOI:10.1039/c5ob00513b
日期:——
The study reports chiral sensing properties of RNA nucleosides. Adenosine, guanosine, uridine and cytidine are used as chiral derivatizing agents to differentiate chiral 1°-amines. A three component protocol has been adopted for complexation of nucleosides and amines. The chiral differentiating ability of nucleosides is examined for different amines based on the 1H NMR chemical shift differences of
该研究报告了RNA核苷的手性传感特性。腺苷,鸟嘌呤,尿苷和胞苷用作手性衍生剂,以区分手性1°-胺。已经采用了三组分方案来使核苷和胺络合。核苷的手性分化能力进行检查用于基于所述不同的胺1度非对映体的1 H NMR化学位移差(Δ δ [R ,小号)。在多个化学上不同的质子位点观察到对映异构分化。腺苷和鸟苷表现出大的手性分化(Δ δ [R ,小号)由于存在嘌呤环。使用腺苷测得的非对映异构体过量度(de)与重量值高度吻合。
Dipyrrolidinomethylaminophosphoric acid triamide (DPMPA) as an activator for the samarium diiodide-mediated reduction of alkyl and aryl halides
作者:Chriss E. McDonald、Jeremy R. Ramsey、David G. Sampsell、Laura A. Anderson、Jordan E. Krebs、Samantha N. Smith
DOI:10.1016/j.tet.2013.02.025
日期:2013.4
The use of the conjugate base of dipyrrolidinomethylaminophosphoric triamide (DPMPA−) as an activator of samariumdiiodide is reported. This phosphoramidate has been shown to be a very potent ligand, allowing for the efficient, low-temperature reduction of alkyl and aryl chlorides. Reductive cyclizations of haloalkenylnaphthalenes are also reported.
The first totalsynthesis of the potent antibiotic disciformycin B (2) is described, which is exceptionally isomerization‐prone and transforms into disciformycin A (1) even under notably mild conditions. To outweigh this bias, the approach to 2 hinged on the use of a silyl residue at C4 to lock the critical double bond in place and hence insure the integrity of the synthetic intermediates en route
Determination of the absolute configuration of monosaccharides by 1H NMR spectroscopy of their per-O-(S)-2-methylbutyrate derivatives
作者:William S. York、Stephen Hantus、Peter Albersheim、Alan G. Darvill
DOI:10.1016/s0008-6215(97)00050-5
日期:1997.5
Abstract An empirical method was developed to determine the absoluteconfiguration of monosaccharides, based on high-field 1H NMR spectroscopy of their per- O-(S)-2-methylbutyrate (SMB) derivatives. The SMB derivatives of the D and L forms of a given monosaccharide are diastereomers, allowing them to be distinguished on the basis of differences in their 1H NMR chemical shifts. The reproducibility of
Silver-assisted gold-catalyzed solid phase synthesis of linear and branched oligosaccharides
作者:Yogesh Sutar、Madhuri Vangala、Srinivas Hotha
DOI:10.1039/d1cc06270k
日期:——
Unlike solidphasesynthesis of peptides, synthesis of oligosaccharides by solidphase methods is lagging behind owing to inherent challenges faced while executing glycosidations. In this communication, silver-assisted gold-catalyzed glycosidations are found to be excellent for solidphase oligosaccharide synthesis. Glycosidations under catalytic conditions, one time coupling with four equivalents