scholarly journals Prebiotic Access to Enantioenriched Glyceraldehyde Mediated by Peptides

2021 ◽  
Author(s):  
Jinhan Yu ◽  
Alexander X. Jones ◽  
Luca Legnani ◽  
Donna G Blackmond
Keyword(s):  
Kinetic Resolution ◽  
Selective Reaction ◽  
Reaction Proceeds

A prebiotically plausible route to enantioenriched glyceraldehyde is reported via a kinetic resolution mediated by peptides. The reaction proceeds via a selective reaction between the L-peptide and the L-sugar producing...

Attempted enantiotopic group selective cyanohydrin formation from α-alkoxy aldehydes by double stereodifferentiation

2001 ◽  
Vol 79 (11) ◽  
pp. 1775-1785 ◽  
Author(s):  
Dale E Ward ◽  
Marcelo Sales ◽  
Matthew J Hrapchak
Keyword(s):  
Kinetic Resolution ◽  
Reaction Kinetic ◽  
Selective Reaction ◽  
The Poor

Enantiotopic group selectivity can result from the competition between substrate and reagent double stereodifferentiation. We have examined this approach for enantioselective hydrocyanation of racemic α-alkoxy aldehydes (e.g., 2-(phenylmethoxy)heptanal (1)). Reaction of 1 with TMSCN mediated by chiral nonracemic alkoxy Ti(IV) reagents under conditions known to be reasonably enantioface selective in reactions with achiral aldehydes, proceeded with very low enantiotopic group selectivity (<2:1). It was established that TMSCN can react with Ti(IV) reagents to produce "TiCN" adducts that are capable of hydrocyanation but with low substrate-controlled diastereoselectivity in reactions with 1. The poor enantiotopic group selectivity observed can be rationalized to result from this low diastereoselectivity despite the respectable levels of enantioface selectivity associated with these reagents in hydrocyanation of achiral aldehydes. Highly diastereoselective hydrocyanation of α-alkoxy aldehydes can be achieved with TMSCN in the presence of excess MgBr2·OEt2. High diastereoselectivity was also observed using achiral and chiral TiCN adducts in place of TMSCN. Although the putative TiCN adducts obtained from nonracemic alkoxy Ti(IV) reagents are implicated in enantioface selective hydrocyanation, these reagents were not enantiotopic group selective under these conditions and showed no evidence of double stereodifferentiation. The use of nonracemic bisoxazoline ligands for Mg(II) was also ineffective.Key words: cyanohydrin, 2-alkoxyalkanal, double stereodifferentiation, enantiotopic group selective reaction, kinetic resolution.

scholarly journals Biocatalytic asymmetric construction of secondary and tertiary fluorides from β-fluoro-α-ketoacids

2021 ◽  
Author(s):  
Jason Fang ◽  
Laura Turner ◽  
Michelle Chang
Keyword(s):  
Asymmetric Synthesis ◽  
Kinetic Resolution ◽  
Bond Formation ◽  
Aldol Reaction ◽  
Building Blocks ◽  
Critical Element ◽  
Type Ii ◽  
Fluorinated Building Blocks ◽  
Reaction Proceeds ◽  
New Donors

Fluorine is a critical element for the design of bioactive compounds, but its incorporation with high regio- and stereoselectivity using environmentally friendly reagents and catalysts remains an area of development. Stereogenic tertiary fluorides pose a particular synthetic challenge and are thus present in only a few approved pharmaceuticals such as fluticasone, solithromycin, and sofosbuvir. The aldol reaction of fluorinated donors provides an atom-economical approach to asymmetric C-F motifs via C-C bond formation. Here we report that the type II pyruvate aldolase HpcH and engineered mutants thereof are biocatalysts for carboligation of ß-fluoro-α-ketoacids (including fluoropyruvate, ß-fluoro-α-ketobutyrate, and ß-fluoro-α-ketovalerate) with many diverse aldehydes. The reaction proceeds with kinetic resolution in the case of racemic donors. The reactivity of HpcH towards these new donors, which are non-native in both steric and electronic properties, grants access to enantiopure fragments with secondary or tertiary fluoride stereocenters. In addition to representing the first asymmetric synthesis of tertiary fluorides via biocatalytic carboligation, the afforded products could improve the diversity of fluorinated building blocks and enable the synthesis of fluorinated drug analogs.

Cytochemical Localization of Polysaccharides in Diplodia Maydis With Thiosemicarbazide : Evaluation of Three Fixatives For Pa:Tsc:Os Reaction

1976 ◽  
Vol 34 ◽  
pp. 48-49 ◽  
Author(s):  
Judith A. Murphy ◽  
Mary R. Thompson ◽  
A.J. Pappelis
Keyword(s):  
Reaction Center ◽  
Osmium Tetroxide ◽  
Periodic Acid ◽  
Cytochemical Localization ◽  
Thin Sections ◽  
Selective Reaction ◽  
Amorphous Character

In an attempt to identify polysaccharide components in thin sections of D. maydis, procedures were employed such that a PAS localization could be carried out. Three different fixatives were evaluated ie. glutaraldehyde, formaldehyde and paraformaldehyde. These were used in conjunction with periodic acid (PA), thiosemicarbazide(TSC), and osmium tetroxide(Os) to localize polysaccharides in V. maydis using a pre-embedded reaction procedure. Polysaccharide localization is based on the oxidation of vic-glycol groups by PA, and the binding of TSC as a selective reaction center for the formation of osmium black. The reaction product is sufficiently electron opaque, insoluble in lipids, not altered when tissue is embedded, and has a fine amorphous character.

Observations of the Thermal Decomposition of Brucite

1968 ◽  
Vol 26 ◽  
pp. 446-447
Author(s):  
P. L. Burnett ◽  
W. R. Mitchell ◽  
C. L. Houck
Keyword(s):  
Thermal Decomposition ◽  
Magnesium Oxide ◽  
Basal Plane ◽  
Magnesium Ions ◽  
A Value ◽  
Reaction Proceeds

Natural Brucite (Mg(OH)2) decomposes on heating to form magnesium oxide (MgO) having its cubic ﹛110﹜ and ﹛111﹜ planes respectively parallel to the prism and basal planes of the hexagonal brucite lattice. Although the crystal-lographic relation between the parent brucite crystal and the resulting mag-nesium oxide crystallites is well known, the exact mechanism by which the reaction proceeds is still a matter of controversy. Goodman described the decomposition as an initial shrinkage in the brucite basal plane allowing magnesium ions to shift their original sites to the required magnesium oxide positions followed by a collapse of the planes along the original <0001> direction of the brucite crystal. He noted that the (110) diffraction spots of brucite immediately shifted to the positions required for the (220) reflections of magnesium oxide. Gordon observed separate diffraction spots for the (110) brucite and (220) magnesium oxide planes. The positions of the (110) and (100) brucite never changed but only diminished in intensity while the (220) planes of magnesium shifted from a value larger than the listed ASTM d spacing to the predicted value as the decomposition progressed.

Synthesis of B-ring-fluorinated (−)-epicatechin gallate derivatives

2020 ◽  
Vol 18 (21) ◽  
pp. 4024-4028
Author(s):  
David D. S. Thieltges ◽  
Kai D. Baumgarten ◽  
Carina S. Michaelis ◽  
Constantin Czekelius
Keyword(s):  
Kinetic Resolution ◽  
Convergent Sequence ◽  
Epicatechin Gallate

Electronically modified, fluorinated catechins and epicatechins are enantioselectively synthesized in a short, convergent sequence via kinetic resolution.

Probing the Parallel Kinetic Resolution of Racemic Oxazolidinones using Quasi-enantiomeric Profens

2006 ◽  
Author(s):  
Jason Eames ◽  
Gregory Coumbarides ◽  
Marco Dingjan ◽  
Tony Flinn ◽  
Northern Northen ◽  
...  
Keyword(s):  
Kinetic Resolution ◽  
Parallel Kinetic Resolution

Solar photocatalysis mediated by ZnO for the removal of last traces of Indigo carmine dye pollutant from water

2018 ◽  
Vol 4 (02) ◽  
Author(s):  
Veena Vijayan ◽  
Suguna Yesodharan ◽  
E. P. Yesodharan
Keyword(s):  
Indigo Carmine ◽  
Parent Compound ◽  
Oxygen Demand ◽  
Green Technology ◽  
Solar Photocatalysis ◽  
Reaction Proceeds ◽  
Transient Intermediates ◽  
Significant Chemical ◽  
Hydroxyl Free Radicals ◽  
Purification Of Water

Solar photocatalysis as a potential green technology for the removal of traces of the dye pollutant Indigo carmine (IC) from water is investigated using ZnO as the catalyst. Degradation/decolorization alone does not result in complete decontamination as seen from the significant Chemical Oxygen Demand (COD) of water even after the parent compound has disappeared completely. The degradation proceeds through many intermediates which also get mineralized eventually but slowly. Oxalic acid is identified as a stable slow mineralizing degradation product which itself is formed from other transient intermediates. Effect of various parameters such as catalyst dosage, concentration of the dye, pH, temperature, presence of contaminant salts etc. on the degradation is investigated and quantified. Oxidants such as S2O82- and H2O2 have only moderate influence on the degradation. The degradation follows variable kinetics depending on the concentration of the substrate. The reaction proceeds very slowly in the absence of O2 indicating the importance of reactive oxygen species and hydroxyl free radicals in photocatalysis. H2O2 formed insitu in the system undergoes concurrent decomposition resulting in stabilization in its concentration. The study demonstrates that solar photocatalysis can be used as a viable tool for the purification of water contaminated with traces of IC.

Visible Light-Promoted Catalytic Ring-Opening Isomerization of 1,2-Disubstituted Cyclopropanols to Linear Ketones

2019 ◽  
Author(s):  
Marharyta V. Laktsevich-Iskryk ◽  
Nastassia A. Varabyeva ◽  
Volha V. Kazlova ◽  
Vladimir N. Zhabinskii ◽  
Vladimir A. Khripach ◽  
...  
Keyword(s):  
Visible Light ◽  
Functional Groups ◽  
Ring Opening ◽  
Radical Intermediates ◽  
Reaction Proceeds

In this article, we report a photocatalytic protocol for the isomerization of 1,2-disubstituted cyclopropanols to linear ketones. The reaction proceeds <i>via</i> radical intermediates and tolerates various functional groups.

Visible Light-Promoted Catalytic Ring-Opening Isomerization of 1,2-Disubstituted Cyclopropanols to Linear Ketones

2019 ◽  
Author(s):  
Marharyta V. Laktsevich-Iskryk ◽  
Nastassia A. Varabyeva ◽  
Volha V. Kazlova ◽  
Vladimir N. Zhabinskii ◽  
Vladimir A. Khripach ◽  
...  
Keyword(s):  
Visible Light ◽  
Functional Groups ◽  
Ring Opening ◽  
Radical Intermediates ◽  
Reaction Proceeds

In this article, we report a photocatalytic protocol for the isomerization of 1,2-disubstituted cyclopropanols to linear ketones. The reaction proceeds <i>via</i> radical intermediates and tolerates various functional groups.

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