Evidence for a Hydride Shift in the Alkaline Rearrangements of D-Ribose

1971 ◽  
Vol 49 (9) ◽  
pp. 1433-1440 ◽  
Author(s):  
W. B. Gleason ◽  
R. Barker
Keyword(s):  
Small Proportion ◽  
Hydride Transfer ◽  
Aqueous Alkali ◽  
Hydride Shift ◽  
Presence And Absence

The synthesis of D-ribose-2-t from D-arabinose is described and its conversions in aqueous alkali in the presence and absence of oxygen reported. In both situations a significant amount of label is transferred from C-2 to -1 and a relatively small proportion is released to the solvent. It is concluded that hydride transfer is occurring and that enolization, which requires the loss of hydrogen from C-2, is not an obligatory first step in base-catalyzed rearrangements of D-ribose.

Catalyst-free construction of spiro [benzoquinolizidine-chromanones] via a tandem condensation/1,5-hydride transfer/cyclization process

2020 ◽  
Vol 18 (43) ◽  
pp. 8839-8843
Author(s):  
Siyuan Liu ◽  
Hang Wang ◽  
Baomin Wang
Keyword(s):  
Hydride Transfer ◽  
Catalyst Free ◽  
Highly Efficient ◽  
Hydride Shift ◽  
Cyclization Process ◽  
Free Construction

A highly efficient and quite mild protocol to achieve spiro [benzoquinoline-chromanones] through a catalyst-free condensation/[1,5]-hydride shift/6-endo cyclization sequence was developed.

A one-pot catalyst/external oxidant/solvent-free cascade approach to pyrimidines via a 1,5-hydride transfer

2019 ◽  
Vol 21 (1) ◽  
pp. 69-74 ◽  
Author(s):  
Mohit L. Deb ◽  
Paran J. Borpatra ◽  
Pranjal K. Baruah
Keyword(s):  
Hydride Transfer ◽  
Cascade Reaction ◽  
Solvent Free ◽  
One Pot ◽  
Hydride Shift

A cascade reaction for synthesizing pyrimidines by the functionalization of the C–H bond adjacent to nitrogen through a 1,5-hydride shift is reported.

Intramolecular hydride shift in some noncyclic isopropyl ketols

1981 ◽  
Vol 59 (4) ◽  
pp. 688-696 ◽  
Author(s):  
E. W. Warnhoff ◽  
Margaret Y. H. Wong ◽  
P. Sundara Raman
Keyword(s):  
Reaction Times ◽  
Hydride Transfer ◽  
Reformatsky Reaction ◽  
Tert Butyl ◽  
Hydride Shift ◽  
Aqueous Base ◽  
The Reformatsky Reaction

The acyclic ketols [Formula: see text] have been synthesized by a Reformatsky sequence. Each ketol undergoes intramolecular hydride transfer when refluxed in KOH–H2O–t-BuOH solution. When the procedure was applied to the synthesis of 34, hydride transfer occurred during the Reformatsky reaction to yield 33 instead. With longer reaction times, 33 underwent self-acylation and β-dicarbonyl cleavage to 37. Treatment of 33 with aqueous base gave a mixture of ketols 35 and 36 from hydride transfer and β-keto decarboethoxylation. The attempted conversion of the isobutyrate group of the Reformatsky intermediates 21 and 24 to tert-butyl was not practicable.

Deuterium labeling as a test of intramolecular hydride mechanisms in the fragmentation of 2-(1-hydroxybenzyl)-N1′-methylthiamin

2005 ◽  
Vol 83 (9) ◽  
pp. 1277-1280 ◽  
Author(s):  
Glenn Ikeda ◽  
Ronald Kluger
Keyword(s):  
Proton Transfer ◽  
Spectroscopic Analysis ◽  
Hydride Transfer ◽  
Fragmentation Reaction ◽  
Deuterium Labeling ◽  
Benzoylformate Decarboxylase ◽  
Hydride Shift ◽  
Benzoin Condensation ◽  
Normal Water ◽  
Amino Pyrimidine

2-(1-Hydroxybenzyl)-N1′-methylthiamin (1b) is a model for the addition intermediate in the thiamin catalyzed benzoin condensation. However, N-alkylation alters the reactivity of the compound: instead of undergoing base-catalyzed formation of benzaldehyde and N1′-methylthiamin, it rapidly forms trimethyl amino pyrimidine (2b) and phenylthiazole ketone (3). The base-catalyzed fragmentation process is faster than the analogous enzymic reaction (in benzoylformate decarboxylase) under the same conditions. One possible mechanism for the rapid fragmentation is an internal hydride transfer from α-C2 to the methylene bridge between the heterocycles. To test the hydride mechanism we prepared α-C2-deuterated 1b and conducted the fragmentation reaction in normal water. Spectroscopic analysis revealed that the trimethyl aminopyrimidine product does not contain any deuterium, ruling out a hydride transfer mechanism. This supports a mechanism for fragmentation that proceeds instead via a proton transfer from α-C2. Since protonation (and hence, deprotonation) of that site is part of the normal catalytic cycle of benzoylformate decarboxylase, the enzyme must divert the reaction from the lowest energy pathway since it would share a common intermediate with the fragmentation process.Key words: thiamin, fragmentation, benzoylformate decarboxylase, proton transfer, hydride shift.

scholarly journals Regioselective biocatalytic self-sufficient Tishchenko-type reaction via formal intramolecular hydride transfer

2020 ◽  
Vol 56 (47) ◽  
pp. 6340-6343
Author(s):  
Erika Tassano ◽  
Kemal Merusic ◽  
Isa Buljubasic ◽  
Olivia Laggner ◽  
Tamara Reiter ◽  
...  
Keyword(s):  
Hydride Transfer ◽  
Alcohol Dehydrogenases ◽  
Type Reaction ◽  
Hydride Shift ◽  
Sufficient Reduction

Alcohol dehydrogenases catalyze the regioselective lactonization of dialdehydes via a bio-Tishchenko-like reaction. The nicotinamide-dependent self-sufficient reduction–oxidation sequence proceeds through a formal intramolecular hydride shift.

Cytoplasmic Tubules in Cells Infected with Laryngotracheitis Virus

1969 ◽  
Vol 27 ◽  
pp. 376-377
Author(s):  
A. M. Watrach
Keyword(s):  
Tissue Culture ◽  
Small Proportion ◽  
Chicken Embryo ◽  
Culture Cells ◽  
Tissue Culture Cells ◽  
Morphologic Characteristics ◽  
Infectious Laryngotracheitis ◽  
Laryngotracheitis Virus ◽  
In Cells

During a study of the development of infectious laryngotracheitis (LT) virus in tissue culture cells, unusual tubular formations were found in the cytoplasm of a small proportion of the affected cells. It is the purpose of this report to describe the morphologic characteristics of the tubules and to discuss their possible association with the development of virus.The source and maintenance of the strain of LT virus have been described. Prior to this study, the virus was passed several times in chicken embryo kidney (CEK) tissue culture cells.

Effects of Noise and Increased Vocal Intensity on Stuttering

1977 ◽  
Vol 20 (2) ◽  
pp. 233-240 ◽  
Author(s):  
Sharon F. Garber ◽  
Richard R. Martin
Keyword(s):  
Normal Level ◽  
Auditory Feedback ◽  
Concomitant Increase ◽  
Vocal Intensity ◽  
Presence And Absence

The present study was designed to assess the effects of increased vocal level on stuttering in the presence and absence of noise, and to assess the effects of noise on stuttering with and without a concomitant increase in vocal level. Accordingly, eight adult stutterers spoke in quiet with normal vocal level, in quiet with increased vocal level, in noise with normal level, and in noise with increased level. All subjects reduced stuttering in noise compared with quiet conditions. However, there was no difference in stuttering when subjects spoke with normal compared with increased vocal level. In the present study, reductions in stuttering under noise could not be explained by increases in vocal level. It appears, instead, that reductions in stuttering were related to a decrease in auditory feedback. The condition which resulted in the largest decrease in auditory feedback, speaking in noise with a normal level, also resulted in the largest decrease in stuttering.

Factor XII Determinations in the Presence and Absence of Phospholipid Antibodies

1998 ◽  
Vol 79 (01) ◽  
pp. 87-90 ◽  
Author(s):  
D. W. Jones ◽  
M. Winter ◽  
M. J. Gallimore
Keyword(s):  
Lower Limit ◽  
Lupus Anticoagulant ◽  
Factor Xii ◽  
Chromogenic Substrate ◽  
Plasma Samples ◽  
Presence And Absence ◽  
Lower Limit Of Normal

SummaryFactor XII (FXII) levels were determined in plasma samples from 29 normal donors, 10 patients with inherited FXII deficiency (all lupus anticoagulant [LA] negative) and 67 LA positive patients, using clotting (FXIIct), chromogenic substrate (FXIIcs) and immunochemical (FXIIag) assays. Excellent correlations were obtained in the three FXII assays with the LA negative samples and between the FXIIcs and FXIIag assays in the LA positive samples. Correlations between both the FXIIcs and FXIIag with FXIIct in the LA positive patients were poor. Of 67 LA positive samples studied, 25 (37.3%) showed lower values in the FXIIct assay; 13 (19.4%) of these patients were pseudo FXII deficient with values of FXII below the lower limit of normal.These results indicate that a diagnosis of FXII deficiency can be made inappropriately in the presence of phospholipid antibodies and that such a diagnosis should not be made by FXIIct assay alone.

Effect of Fibrin-Like Stimulators on the Activation of Plasminogen by Tissue-Type Plasminogen Activator (t-PA) - Studies with Active Site Mutagenized Plasminogen and Plasmin Resistant t-PA

1990 ◽  
Vol 64 (01) ◽  
pp. 061-068 ◽  
Author(s):  
H R Lijnen ◽  
B Van Hoet ◽  
F De Cock ◽  
D Collen
Keyword(s):  
Active Site ◽  
Peptide Bond ◽  
Tissue Type ◽  
Wild Type ◽  
Single Chain ◽  
Plasmin Activity ◽  
Soluble Fibrin ◽  
Type Plasminogen Activator ◽  
Presence And Absence ◽  
Chain Form

SummaryThe activation of plasminogen by t-PA was measured in the presence and absence of fibrin stimulation, using natural human plasminogen (nPlg) and rPlg-Ala740, a recombinant plasminogen with the active site Ser740 mutagenaed to Ala. Recombinant wild type t-PA (rt-PA) was used as well as rt-PA -Glul275, a recombinant single chain t-PA in which the Arg of the plasmin sensitiv e Arg275- Ile276 peptide bond was substituted with Glu. Conversion of 125I-labeled single chain plasminogen to two-chain plasmin by wild-type or mutant t-PA, was quantitated by SDS gel electrophoresis and radioisotope counting of gel slices, and expressed as initial activation rates (v0 in pM s−1) per 1 μM enzyme. In the absence of fibrin stimulation, the vs for the activation of nPlg and rPlg-Ala740 with the single chain forms of both t-PAs were comparable (0.6 to 2.7 pM s−1) but were lower than with the corresponding two-chain forms (5.3 to 23 pM s−1). In the presence of 1 μM soluble fibrin monomer (desAAfibrin), the v0 for nPlg and rPlg-Ala740 by single chain rt-PA was also comparable (24 and, 33 pM s-1 respectively), whereas with 1 pM CNBr-digested fibrinogen, the vs for nPlg with single chain rt-PA was about 20-fold higher than that of rPlg-Ala740 (135 and 7.5 pM s−1 respectively). In contrast, the vs for nPlg and rPlg-Ala740 by single chain rt-PA- G1u275, two-chain rt-PA-G1u275 or two-chain rt-PA were comparable in the presence of either desAAfibrin or CNBr-digested fibrinogen.These findings confirm and establish: 1) that single chain t-PA is an active enzyme both in the presence and absence of fibrin stimulator; 2) that, in a system devoid of plasmin activity (rPlg- Ala740), the two-chain form of t-PA is about L5 times more active than the single chain form in the absence of fibrin but equipotent in the presence of desAAfibrin; and 3) that the mechanism of stimulation of plasminogen activation with single chain t-PA by CNBr-digested fibrinogen is different from that by soluble fibrin.

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