scholarly journals Gold-catalyzed glycosidation for the synthesis of trisaccharides by applying the armed–disarmed strategy

2013 ◽  
Vol 9 ◽  
pp. 2147-2155 ◽  
Author(s):  
Abhijeet K Kayastha ◽  
Srinivas Hotha
Keyword(s):  
Reaction Temperature ◽  
Acidic Medium ◽  
Gold Catalysis ◽  
Protecting Groups ◽  
Benzyl Ethers ◽  
Glycosyl Donor ◽  
Leaving Groups

The synthesis of oligosaccharides is still a challenging task as there is no universal glycosyl donor for the synthesis of all oligosaccharides. The gold catalysis for glycosidation reactions, in which alkynylated glycosides are used, has emerged as one of the versatile options in this regard. A cleavage of the interglycosidic bond that was thought to be due to the higher reaction temperature and the acidic medium was observed during the synthesis of trisaccharides. In addition, a very little percentage of deprotection of benzyl protecting groups at the C-6 position was observed and no deprotection of benzyl ethers in aliphatic molecules was noticed. In order to overcome this fact, a collection of leaving groups that contain an alkynyl moiety were screened. It was found that 1-ethynylcyclohexanyl (Ech) glycosides are suitable for carrying out the glycosidation at 25 °C in the presence of 5 mol % each of AuCl3 and AgSbF6. Subsequently, Ech-glycosides were observed to be suitable for the synthesis of trisaccharides under gold catalysis conditions.

Visible Light-Mediated Oxidative Debenzylation

2020 ◽  
Author(s):  
Cristian Cavedon ◽  
Eric T. Sletten ◽  
Amiera Madani ◽  
Olaf Niemeyer ◽  
Peter H. Seeberger ◽  
...  
Keyword(s):  
Reaction Time ◽  
Visible Light ◽  
Functional Groups ◽  
Continuous Flow ◽  
Protecting Groups ◽  
Benzyl Ether ◽  
Complex Molecules ◽  
Protective Groups ◽  
Benzyl Ethers ◽  
Harsh Conditions

Protecting groups are key in the synthesis of complex molecules such as carbohydrates to distinguish functional groups of similar reactivity. The harsh conditions required to cleave stable benzyl ether protective groups are not compatible with many other protective and functional groups. The mild, visible light-mediated debenzylation disclosed here renders benzyl ethers orthogonal protective groups. Key to success is the use of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as stoichiometric or catalytic photooxidant such that benzyl ethers can be cleaved in the presence of azides, alkenes, and alkynes. The reaction time for this transformation can be reduced from hours to minutes in continuous flow. <br>

A Facile, Efficient and Selective Deprotection of P - Methoxy Benzyl Ethers Using Zinc (II) Trifluoromethanesulfonate

2019 ◽  
Vol 16 (12) ◽  
pp. 955-958
Author(s):  
Reddymasu Sireesha ◽  
Reddymasu Sreenivasulu ◽  
Choragudi Chandrasekhar ◽  
Mannam Subba Rao
Keyword(s):  
Room Temperature ◽  
Protecting Groups ◽  
Side Reactions ◽  
Reaction Conditions ◽  
Acid Sensitivity ◽  
Time Period ◽  
Protective Groups ◽  
Benzyl Ethers ◽  
Last Stage ◽  
Zinc Triflate

: Deprotection is significant and conducted over mild reaction conditions, in order to restrict any more side reactions with sensitive functional groups as well as racemization or epimerization of stereo center because the protective groups are often cleaved at last stage in the synthesis. P - Methoxy benzyl (PMB) ether appears unique due to its easy introduction and removal than the other benzyl ether protecting groups. A facile, efficient and highly selective cleavage of P - methoxy benzyl ethers was reported by using 20 mole% Zinc (II) Trifluoromethanesulfonate at room temperature in acetonitrile solvent over 15-120 min. time period. To study the generality of this methodology, several PMB ethers were prepared from a variety of substrates having different protecting groups and subjected to deprotection of PMB ethers using Zn(OTf)2 in acetonitrile. In this methodology, zinc triflate cleaves only PMB ethers without affecting acid sensitivity, base sensitivity and also chiral epoxide groups.

scholarly journals A One-Pot Approach to Novel Pyridazine C-Nucleosides

Molecules ◽  
2021 ◽  
Vol 26 (8) ◽  
pp. 2341
Author(s):  
Flavio Cermola ◽  
Serena Vella ◽  
Marina DellaGreca ◽  
Angela Tuzi ◽  
Maria Rosaria Iesce
Keyword(s):  
Organic Chemistry ◽  
Research Field ◽  
Modified Nucleosides ◽  
Protecting Groups ◽  
Coupling Reactions ◽  
One Pot ◽  
Pharmacological Interest ◽  
Classical Methodology ◽  
Glycosyl Donor ◽  
Neutral Conditions

The synthesis of glycosides and modified nucleosides represents a wide research field in organic chemistry. The classical methodology is based on coupling reactions between a glycosyl donor and an acceptor. An alternative strategy for new C-nucleosides is used in this approach, which consists of modifying a pre-existent furyl aglycone. This approach is applied to obtain novel pyridazine C-nucleosides starting with 2- and 3-(ribofuranosyl)furans. It is based on singlet oxygen [4+2] cycloaddition followed by reduction and hydrazine cyclization under neutral conditions. The mild three-step one-pot procedure leads stereoselectively to novel pyridazine C-nucleosides of pharmacological interest. The use of acetyls as protecting groups provides an elegant direct route to a deprotected new pyridazine C-nucleoside.

Glycosynthases: Mutant Glycosidases for Glycoside Synthesis

2002 ◽  
Vol 55 (2) ◽  
pp. 3 ◽  
Author(s):  
S. J. Williams ◽  
S. G. Withers
Keyword(s):  
Substrate Specificity ◽  
Product Formation ◽  
Protecting Groups ◽  
Rapid Screening ◽  
Widespread Application ◽  
Glycoside Synthesis ◽  
General Methodology ◽  
Glycosyl Donor ◽  
Substrate Variation ◽  
Catalytic Power

Glycosynthases are engineered mutant glycosidases that catalyse the formation of a glycosidic bond from a glycosyl donor and an acceptor alcohol. They are constructed by mutation of the enzymic nucleophile of a retaining glycosidase to a small non-nucleophilic residue. To date, five glycosynthases have been reported capable of synthesizing a range of β-glycosidic linkages. Methods to integrate protecting groups into glycosynthase-mediated glycosylations have been developed that broaden their applicability and enable finer control over product formation. Mutagenesis studies have improved the catalytic power of the original Abg glycosynthase, and a general methodology has been developed that allows the rapid screening of libraries of mutant glycosynthases for catalysts with improved activity. A method for determining aglycon substrate specificity has been developed to define the limits of substrate variation tolerated by a parent glycosidase and thence the derived glycosynthase. Together, these developments portend a bright future for the discovery of new glycosynthases and their widespread application as catalysts to assist in the rapid and efficient assembly of complex glycoconjugates.

Use of polymers as protecting groups in organic synthesis. III. Selective functionalization of polyhydroxy alcohols

1976 ◽  
Vol 54 (6) ◽  
pp. 926-934 ◽  
Author(s):  
Jean M. J. Fréchet ◽  
Lucy J. Nuyens
Keyword(s):  
Acidic Medium ◽  
Functional Group ◽  
Primary Alcohol ◽  
Protecting Groups ◽  
Hydroxyl Groups ◽  
Ether Linkage ◽  
Reaction Conditions ◽  
Selective Functionalization ◽  
One Step ◽  
Insoluble Polymers

Insoluble polymers containing trityl chloride residues were used to block one primary alcohol functional group of several polyhydroxy alcohols. After protecting the remaining hydroxyl groups by benzoylation, the ether linkage between the polymer and the protected alcohol was cleaved in acidic medium. Depending on the reaction conditions and the nature of the starting alcohol, several alcohols or bromides in which only one of the two primary hydroxyls had been esterified, were obtained. In some cases benzoyl migrations were observed. The trityl chloride polymers could be regenerated in one step without degradation or appreciable loss of activity.

Unique and Convenient Use of Raney Nickel for the Reduction of Aryl Bromides, Benzyl Alcohols, Benzyl Ethers, and Benzylamines in an Acidic Medium.

ChemInform ◽  
2004 ◽  
Vol 35 (44) ◽  
Author(s):  
Mitsuhiro Okimoto ◽  
Yukio Takahashi ◽  
Yuji Nagata ◽  
Masanori Satoh ◽  
Satoru Sueda ◽  
...  
Keyword(s):  
Raney Nickel ◽  
Acidic Medium ◽  
Benzyl Alcohols ◽  
Aryl Bromides ◽  
Benzyl Ethers

scholarly journals Total Synthesis of Tiacumicin B: Study of the Challenging β-Selective Glycosylations

2020 ◽  
Author(s):  
cedric Tresse ◽  
Marc François-Eude ◽  
Vincent Servajean ◽  
Rubal Ravinder ◽  
Clemence Lesieur ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Cross Coupling ◽  
Protecting Groups ◽  
Ring Size ◽  
Efficient Removal ◽  
Full Account ◽  
Leaving Groups ◽  
Total Beta

<div>We report here a full account of the total synthesis of tiacumicin B (Tcn-B), a natural glycosylated macrolide with remarkable antibiotic properties. Our strategy is based on our experience with the synthesis of the tiacumicin B aglycone and on unique 1,2-<i>cis</i>-glycosylation steps. It features the conclusive use of sulfoxide anomeric leaving-groups in combination with a remote 3-<i>O</i>-picoloyl group on the donors allowing highly beta-selective rhamnosylation and noviosylation that rely on H-bond-mediated Aglycone Delivery (HAD). The rhamnosylated C1-C3 fragment was anchored to the C4-C19 aglycone fragment by a Suzuki-Miyaura cross-coupling. Ring-size selective Shiina macrolactonization provided a semi-glycosylated aglycone that was engaged directly in the noviosylation step with a virtually total beta-selectivity. Finally, a novel deprotection method was devised for the removal of a 2-naphthylmethylidene (Nap) ether on a phenol and efficient removal of all the protecting groups provided synthetic tiacumicin B.<br></div><div> </div>

scholarly journals Total Synthesis of Tiacumicin B: Study of the Challenging β-Selective Glycosylations

2020 ◽  
Author(s):  
cedric Tresse ◽  
Marc François-Heude ◽  
Vincent Servajean ◽  
Rubal Ravinder ◽  
Clemence Lesieur ◽  
...  
Keyword(s):  
Total Synthesis ◽  
Cross Coupling ◽  
Protecting Groups ◽  
Ring Size ◽  
Efficient Removal ◽  
Full Account ◽  
Leaving Groups ◽  
Total Beta

<div>We report here a full account of the total synthesis of tiacumicin B (Tcn-B), a natural glycosylated macrolide with remarkable antibiotic properties. Our strategy is based on our experience with the synthesis of the tiacumicin B aglycone and on unique 1,2-<i>cis</i>-glycosylation steps. It features the conclusive use of sulfoxide anomeric leaving-groups in combination with a remote 3-<i>O</i>-picoloyl group on the donors allowing highly beta-selective rhamnosylation and noviosylation that rely on H-bond-mediated Aglycone Delivery (HAD). The rhamnosylated C1-C3 fragment was anchored to the C4-C19 aglycone fragment by a Suzuki-Miyaura cross-coupling. Ring-size selective Shiina macrolactonization provided a semi-glycosylated aglycone that was engaged directly in the noviosylation step with a virtually total beta-selectivity. Finally, a novel deprotection method was devised for the removal of a 2-naphthylmethylidene (Nap) ether on a phenol and efficient removal of all the protecting groups provided synthetic tiacumicin B.<br></div><div> </div>

scholarly journals Visible-Light-Mediated Oxidative Debenzylation Enables the Use of Benzyl Ethers as Temporary Protecting Groups

2021 ◽  
Author(s):  
Cristian Cavedon ◽  
Eric T. Sletten ◽  
Amiera Madani ◽  
Olaf Niemeyer ◽  
Peter H. Seeberger ◽  
...  
Keyword(s):  
Visible Light ◽  
Protecting Groups ◽  
Benzyl Ethers

scholarly journals Synthesis and Evaluation of Fluorinated Benzyl Ethers as Alternate Protecting Groups for Enhanced NMR Resolution in Oligosaccharide Synthesis

2022 ◽  
pp. 39-46
Author(s):  
Ntai M Khoabane ◽  
Elizabeth J Grayson ◽  
Alan M Kenwright ◽  
Manoharan K Pillai
Keyword(s):  
High Field ◽  
Synthesis Method ◽  
Protecting Groups ◽  
Hydroxyl Groups ◽  
Oligosaccharide Synthesis ◽  
Suitable Alternative ◽  
The Core ◽  
A Value ◽  
Benzyl Ethers ◽  
Ether Synthesis

Oligosaccharides have been playing an important role in biological systems. Synthesis of oligosaccharides requires the protection from hydroxyl groups present in the corresponding monosaccharide units. The existing methods of protection have drawbacks, including formation of anomeric mixtures, change in hydrophilicity or lipophilicity and solubility of the products, participation of the protecting groups in the reactions of the core of monosaccharide units, problems associated with chemoselectivity, regioselectivity and overall stereochemical outcomes of reactions. Additionally, there has been a spectral overlap of these protecting groups with carbohydrate core, which yielded more complex spectra. Therefore, the identification and synthesis of suitable alternative protecting groups have received attention in the oligosaccharide synthesis. The objective of the present study was to synthesize various fluorinated benzyl ethers of methyl-α-D-mannopyronoside and to evaluate these ethers as the alternative protecting groups for enhancing NMR resolution in the oligosaccharide synthesis. Various fluorinated benzyl ethers of methyl-α-D-mannopyronoside were prepared through the reaction of methyl-α-D-mannopyronoside with various fluorinated benzyl bromides by using Williamson ether synthesis method. Spectral analysis of these fluorinated benzyl ethers showed that the peaks of methylene carbons shifted to a value of 10-20 parts per million (ppm) to a high field region in the 13C NMR, compared to the non-fluorinated benzyl ether. As a result, the spectral complexity decreased and enhanced the spectral resolution. In this study, we concluded that fluorinated benzyl ethers could be a suitable alternative to the non-fluorinated benzyl ethers to protect the hydroxyl groups of monosaccharides in the synthesis of oligosaccharides.

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