scholarly journals 2-Allylphenyl glycosides as complementary building blocks for oligosaccharide and glycoconjugate synthesis

2012 ◽  
Vol 8 ◽  
pp. 597-605 ◽  
Author(s):  
Hemali D Premathilake ◽  
Alexei V Demchenko
Keyword(s):  
Building Blocks ◽  
Mechanistic Study ◽  
Leaving Group ◽  
Chemical Glycosylation ◽  
Activation Pathways

The O-allylphenyl (AP) anomeric moiety was investigated as a new leaving group that can be activated for chemical glycosylation under a variety of conditions, through both direct and remote pathways. Differentiation between the two activation pathways was achieved in a mechanistic study. The orthogonal-type activation of the AP moiety along with common thioglycosides allows for the execution of efficient oligosaccharide assembly.

scholarly journals Indolylthio Glycosides As Effective Building Blocks for Chemical Glycosylation

2020 ◽  
Vol 85 (24) ◽  
pp. 15885-15894
Author(s):  
Ganesh Shrestha ◽  
Matteo Panza ◽  
Yashapal Singh ◽  
Nigam P. Rath ◽  
Alexei V. Demchenko
Keyword(s):  
Building Blocks ◽  
Chemical Glycosylation

scholarly journals Glycosyl Alkoxythioimidates as Complementary Building Blocks for Chemical Glycosylation

2010 ◽  
Vol 12 (24) ◽  
pp. 5628-5631 ◽  
Author(s):  
Sneha C. Ranade ◽  
Sophon Kaeothip ◽  
Alexei V. Demchenko
Keyword(s):  
Building Blocks ◽  
Chemical Glycosylation

Influence of the Leaving Group on C–H Activation Pathways in Palladium Pincer Complexes

2018 ◽  
Vol 37 (13) ◽  
pp. 2086-2094 ◽  
Author(s):  
Melissa R. Hoffbauer ◽  
Cezar C. Comanescu ◽  
Brittany J. Dymm ◽  
Vlad M. Iluc
Keyword(s):  
Pincer Complexes ◽  
Leaving Group ◽  
Activation Pathways

scholarly journals Modeling the Alkaline Hydrolysis of Diaryl Sulfate Diesters: A Mechanistic Study

2020 ◽  
Author(s):  
Klaudia Szeler ◽  
Nicholas Williams ◽  
Alvan C. Hengge ◽  
Shina Caroline Lynn Kamerlin
Keyword(s):  
Alkaline Hydrolysis ◽  
Computational Study ◽  
Transition States ◽  
Building Blocks ◽  
Ester Hydrolysis ◽  
Mechanistic Study ◽  
Phosphate Ester ◽  
Sulfate Ester ◽  
The Impact ◽  
Hydrolysis Of

<div> <div> <div> <p>Phosphate and sulfate esters have important roles as biological building blocks and in regulating cellular processes. However, while there has been substantial experimental and computational investigation of the mechanisms and the transition states involved in phosphate ester hydrolysis, there is far less (in particular computational) work on sulfate ester hydrolysis. Here, we report a detailed computational study of the alkaline hydrolysis of diaryl sulfate diesters, using different DFT functionals and both pure implicit solvation as well as mixed implicit/explicit solvation with varying numbers of explicit water molecules. We consider both the impact of how the system is modeled on computed linear free energy relationships (LFER) and the nature of the transition states. Although our calculations consistently underestimate the absolute activation free energies, we obtain good agreement with experimental LFER data when using pure implicit solvent, and excellent agreement with experimental kinetic isotope effects for all models used. Our calculations suggest that the hydrolysis of sulfate diesters proceeds through loose transition states, with minimal bond formation to the nucleophile and with bond cleavage to the leaving group already initiated. Comparison to prior work indicates that these transition states are similar in nature to those of analogous reactions such as the alkaline hydrolysis of neutral arylsulfonate monoesters or charged phosphate diesters and fluorophosphates. Obtaining more detailed insight into the transition states involved assists in understanding the selectivity of enzymes that hydrolyze these reactions; however, this work also highlights the methodological challenges involved in reliably modeling sulfate ester hydrolysis. </p> </div> </div> </div>

scholarly journals Modeling the Alkaline Hydrolysis of Diaryl Sulfate Diesters: A Mechanistic Study

2020 ◽  
Author(s):  
Klaudia Szeler ◽  
Nicholas Williams ◽  
Alvan C. Hengge ◽  
Shina Caroline Lynn Kamerlin
Keyword(s):  
Alkaline Hydrolysis ◽  
Computational Study ◽  
Transition States ◽  
Building Blocks ◽  
Ester Hydrolysis ◽  
Mechanistic Study ◽  
Phosphate Ester ◽  
Sulfate Ester ◽  
The Impact ◽  
Hydrolysis Of

<div> <div> <div> <p>Phosphate and sulfate esters have important roles as biological building blocks and in regulating cellular processes. However, while there has been substantial experimental and computational investigation of the mechanisms and the transition states involved in phosphate ester hydrolysis, there is far less (in particular computational) work on sulfate ester hydrolysis. Here, we report a detailed computational study of the alkaline hydrolysis of diaryl sulfate diesters, using different DFT functionals and both pure implicit solvation as well as mixed implicit/explicit solvation with varying numbers of explicit water molecules. We consider both the impact of how the system is modeled on computed linear free energy relationships (LFER) and the nature of the transition states. Although our calculations consistently underestimate the absolute activation free energies, we obtain good agreement with experimental LFER data when using pure implicit solvent, and excellent agreement with experimental kinetic isotope effects for all models used. Our calculations suggest that the hydrolysis of sulfate diesters proceeds through loose transition states, with minimal bond formation to the nucleophile and with bond cleavage to the leaving group already initiated. Comparison to prior work indicates that these transition states are similar in nature to those of analogous reactions such as the alkaline hydrolysis of neutral arylsulfonate monoesters or charged phosphate diesters and fluorophosphates. Obtaining more detailed insight into the transition states involved assists in understanding the selectivity of enzymes that hydrolyze these reactions; however, this work also highlights the methodological challenges involved in reliably modeling sulfate ester hydrolysis. </p> </div> </div> </div>

scholarly journals Investigation of Glycosyl Nitrates as Building Blocks for Chemical Glycosylation

2018 ◽  
Vol 2018 (47) ◽  
pp. 6699-6705 ◽  
Author(s):  
Tinghua Wang ◽  
Yashapal Singh ◽  
Keith J. Stine ◽  
Alexei V. Demchenko
Keyword(s):  
Building Blocks ◽  
Chemical Glycosylation

scholarly journals Expedient synthesis of 1,6-anhydro-α-D-galactofuranose, a useful intermediate for glycobiological tools

2014 ◽  
Vol 10 ◽  
pp. 1651-1656 ◽  
Author(s):  
Luciana Baldoni ◽  
Carla Marino
Keyword(s):  
Hydroxy Group ◽  
Building Blocks ◽  
Nucleophilic Attack ◽  
Step Procedure ◽  
Leaving Group ◽  
Anomeric Carbon ◽  
Good Precursor

A new and efficient three-step procedure for the synthesis of 1,6-anhydro-α-D-galactofuranose is described. The key step involves the formation of the galactofuranosyl iodide by treatment of per-O-TBS-D-Galf with TMSI, the selective 6-O-desilylation by an excess of TMSI, and the simultaneous nucleophilic attack of the 6-hydroxy group on the anomeric carbon, with the iodide as a good leaving group. This compound is a good precursor for building blocks for the construction of 1→6 linkages.

scholarly journals Extending the S-benzimidazolyl (SBiz) platform: N-alkylated SBiz glycosyl donors with the universal activation profile

2017 ◽  
Vol 89 (9) ◽  
pp. 1321-1331
Author(s):  
Scott J. Hasty ◽  
Nigam P. Rath ◽  
Alexei V. Demchenko
Keyword(s):  
Lewis Acid ◽  
Building Blocks ◽  
Oligosaccharide Synthesis ◽  
Activation Profile ◽  
Chemical Glycosylation ◽  
High Yields ◽  
Activation Conditions ◽  
Glucose Pentaacetate ◽  
Glycosyl Donors

AbstractThis article describes the development of alkylated S-benzimidazolyl (SBiz) imidates as versatile building blocks for chemical glycosylation. The SBiz imidates have been originally developed as a new platform for active-latent glycosylations and its utility was further extended to other common strategies for oligosaccharide synthesis. This article expands upon the utility of these compounds. We developed a general protocol for the synthesis of a series of N-alkylated SBiz glycosides from N-protected SBiz aglycones by Lewis acid-mediated coupling with glucose pentaacetate. The N-alkylated SBiz moiety was found to be stable under strong basic conditions which allowed us to obtain both armed and disarmed N-alkylated SBiz donors. These donors showed good reactivity at a variety of activation conditions, and generally provided high yields in glycosylations.

Allenes: Versatile Building Blocks in cobalt-catalyzed C-H Activation

Synlett ◽  
2021 ◽  
Author(s):  
Chandra Volla ◽  
Rahul Shukla ◽  
Akshay Nair
Keyword(s):  
Transition Metal ◽  
Building Blocks ◽  
The Other ◽  
Lewis Acidity ◽  
Other Hand ◽  
Leaving Group ◽  
Widespread Interest

The unique reactivity of allenes have led to their emergence as resourceful coupling partners in transition metal mediated C-H activation reactions. On the other hand, cobalt due to its wide abundance and higher Lewis acidity is garnering widespread interest as useful catalyst for C-H activation. Summarised herein are the cobalt-catalyzed C-H activations engaging allenes as coupling partners followed by our studies on Co(III)-catalyzed C-8 dienylation of quinoline N-oxides with allenes bearing leaving group at α-position for realizing a dienylation protocol.

A mechanistic study of the [La2(OCH3)2]4+- and [(1,5,9-triazacyclodo-decane):Zn:(OCH3)]+-catalyzed methanolysis of carbonates: possible application for the recycling of bisphenol A polycarbonates

2013 ◽  
Vol 91 (11) ◽  
pp. 1139-1146 ◽  
Author(s):  
Alexei A. Neverov ◽  
Leanne D. Chen ◽  
Sean George ◽  
David Simon ◽  
Christopher I. Maxwell ◽  
...  
Keyword(s):  
Bisphenol A ◽  
Metal Ion ◽  
Catalytic Decomposition ◽  
Nucleophilic Attack ◽  
Alkyl Derivative ◽  
Mechanistic Study ◽  
Tetrahedral Intermediate ◽  
Rate Limiting Step ◽  
Leaving Group ◽  
Rate Limiting

The kinetics of the methanolysis of seven methyl aryl carbonates (3) and two methyl alkyl carbonates (4) promoted by [12[ane]N3:Zn:(OCH3)]+ and [La2(OCH3)2]4+ catalysts (1 and 2, respectively) have been studied at 25.0 °C. Brønsted plots of the [Formula: see text] values for methanolysis versus aryloxy and alkoxy leaving group (LG) [Formula: see text] or [Formula: see text] values (the pKa values of the parent ArOH or ROH in methanol) for substrates 3 and 4 show an apparent downward break at [Formula: see text] ∼16.6 and 15.2 with [12[ane]N3:Zn:(OCH3)]+ and [La2(OCH3)2]4+, respectively. The breakpoint is not due to a change in rate-limiting step in a two-step process involving metal ion delivery of a coordinated methoxide to a transiently associated substrate and the subsequent breakdown of a tetrahedral intermediate to form product. The more satisfactory explanation is that the break arises when one correlates the rate constants for two dissimilar sets of substrates, namely aryloxy- and alkoxy-substituted 3 and 4. DFT calculations for the 1-promoted reactions of methyl 4-nitrophenyl carbonate (3b), which has a good aryloxy leaving group, and methyl isopropyl carbonate (4b), which has a relatively poor alkyl one, indicate that the catalyzed processes involve two steps. Accordingly, the methanolysis of all 3 having [Formula: see text] values for the parent phenols ≤15.3 involves rate-limiting nucleophilic attack and fast breakdown. For the isopropyl alkyl derivative (4b) having a [Formula: see text] > 18.13, the rate-liming step is the metal ion promoted breakdown of a tetrahedral intermediate. The catalytic system employing 2 has utility for the catalytic decomposition of poly(bisphenol A carbonate). In a semi-optimized system where 1000 mg of poly(bisphenol A carbonate), treated at 100 °C for 30 min in 2 mL of 60:40 chloroform−methanol containing La(OTf)3:NaOMe (5:7.5 mmol L−1), the reaction gave an 84% yield of bisphenol A, corresponding to >300 turnovers per catalyst.

Sign in / Sign up

Export Citation Format

Share Document