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.

scholarly journals Preparation of a set of selectively protected disaccharides for modular synthesis of heparan sulfate fragments: toward the synthesis of several O-sulfonated [β-D-GlcUA-(1→4)-β-D-GlcNAc]OPr types

2005 ◽  
Vol 3 (4) ◽  
pp. 803-829 ◽  
Author(s):  
Hammed Hassan
Keyword(s):  
Heparan Sulfate ◽  
Building Blocks ◽  
Protecting Groups ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Allyl Ethers ◽  
Modular Synthesis ◽  
Stereocontrolled Synthesis ◽  
Benzyl Ethers ◽  
Free Hydroxyl

AbstractA concise method for a stereocontrolled synthesis of a set of selectively protected disaccharides is reported. Coupling of the donor 11 onto acceptors 23 and 24, promoted by trimethylsilyl triflate-N-iodosuccinimide (TMSOTf-NIS), generated the disaccharides 25 and 26. Under typical conditions, condensation of the fully protected donor 12 onto acceptors 23 and 24 produced the disaccharides 27 and 28. The building blocks 25–28 were prepared in moderate yields having exclusive β-stereoselectivity. A unique pattern of protecting groups distinguished clearly between positions to be sulfated and functional groups remaining as free hydroxyl groups. Acetyl and/or levulinoyl esters temporarily protected the positions to be sulfated, while benzyl ethers were used for permanent protection. The anomeric positions were protected as allyl ethers, whereas the 4′-positions were masked as p-methoxybenzyl (PMB) ethers. The orthogonality of the PMB and allyl groups can then be used for further elongation of the chain by recurrent deprotection and activation steps. The hydroxyl group, OH-6, of glucosamine moieties was protected as a TBDPS ether to avoid oxidation. A five-step deprotection/sulfonation sequence was applied to the disaccharide 27 to generate the corresponding sulfated [β-D-GlcUA-2-OSO3Na-(1→4)-β-D-Glc pNAc]-(1→O-Pro) 34.

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 Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952*

1954 ◽  
Vol 44 (3) ◽  
pp. 471-479
Author(s):  
Maurice Ewing ◽  
Frank Press
Keyword(s):  
Internal Friction ◽  
Rayleigh Waves ◽  
Shear Velocity ◽  
Velocity Curve ◽  
The Core ◽  
Long Period ◽  
A Value ◽  
The Earth ◽  
Dispersion Data ◽  
Kamchatka Earthquake

Abstract Mantle Rayleigh waves from the Kamchatka earthquake of November 4, 1952, are analyzed. The new Palisades long-period vertical seismograph recorded orders R6–R15, the corresponding paths involving up to seven complete passages around the earth. The dispersion data for periods below 400 sec. are in excellent agreement with earlier results and can be explained in terms of the known increase of shear velocity with depth in the mantle. Data for periods 400-480 sec. indicate a tendency for the group velocity curve to level off, suggesting that these long waves are influenced by a low or vanishing shear velocity in the core. Deduction of internal friction in the mantle from wave absorption gives a value 1/Q = 370 × 10−5 for periods 250-350 sec. This is a little over half the value reported earlier for periods 140-215 sec.

I Think, I Am Mad. Derrida, Gaslight and the Irony of the Cogito

2014 ◽  
Vol 36 (1) ◽  
pp. 81-93
Author(s):  
Dirk Setton
Keyword(s):  
Active Form ◽  
Transcendental Philosophy ◽  
Central Point ◽  
Transcendental Function ◽  
Stanley Cavell ◽  
The Core ◽  
A Value ◽  
Female Protagonist ◽  
History Of ◽  
Supreme Principle

At the climax of George Cukor's Gaslight, a film melodrama from 1944, the female protagonist utters the phrase ‘I am mad’ which Stanley Cavell takes to reveal her Cogito. As such, the formula seems to be a perfect exemplification of Derrida's central point in Cogito and the History of Madness, namely that there is ‘a value and a meaning of the Cogito’, detectable in Descartes's Mediations, which welcomes madness as its genuine and necessary possibility. But how can we conceive of the ‘I think’—the supreme principle of transcendental philosophy constituting the objectivity of cognition and experience—as embracing unreason as its own condition? This article attempts to highlight a quasi-transcendental interpretation of Derrida's answer to this question: deconstruction reveals a certain irony at the core of the primary text of transcendental philosophy. I argue that the formula ‘I am mad’ contains the decisive key to the argument: the irony of the Cogito consists in the fact of its double transcendental functioning—a transcendental function in the ‘middle’ form and a transcendental function in the active form.

value-rich exposures in medical education; synthesizing the concept

2021 ◽  
Author(s):  
Leila Afshar ◽  
Shahram Yazdani ◽  
Seyed Abbas Foroutan ◽  
hakimeh sabeghi
Keyword(s):  
Medical Education ◽  
Lived Experience ◽  
Life Experiences ◽  
Synthesis Method ◽  
Real Life ◽  
Educational Process ◽  
Phenomenological Method ◽  
Professional Identities ◽  
Hermeneutic Phenomenological ◽  
A Value

Abstract Background: Proper transfer of professional values is an essential part of medical education. Real-life experiences in the educational process are one of the most effective methods for achieving values and assisting the student in developing his/her value framework. This study aimed to develop and characterize the concept of value-rich exposures in medical education to bring this concept closer to the practice.Methods: We used Walker and Avant concept synthesis method. In order to perform the synthesis, a combination of hermeneutic phenomenological method and literature review was used.Results: We defined the concept of value-rich exposure in medical education under five themes while implementing the steps of Walker and Avant's concept synthesis: probing self-inner values, value-rich program, value mentor, value-rich interactions, and value-rich environment. The elements and relationships of the themes were depicted in the form of a conceptual matrix.Conclusions:A value-rich exposure is a type of lived experience that occurs during a student’s professional life, a necessity that, with proper planning, can play an important role in shaping medical students' professional identities.

The Dimensional Synthesis of Spatial Cable-Driven Parallel Mechanisms

2013 ◽  
Vol 5 (4) ◽  
Author(s):  
K. Azizian ◽  
P. Cardou
Keyword(s):  
Synthesis Method ◽  
Sufficient Condition ◽  
Nonlinear Program ◽  
Parallel Mechanisms ◽  
Dimensional Synthesis ◽  
End Effector ◽  
A Value ◽  
Null Value ◽  
Objective Value

This paper presents a method for the dimensional synthesis of fully constrained spatial cable-driven parallel mechanisms (CDPMs), namely, the problem of finding a geometry whose wrench-closure workspace (WCW) contains a prescribed workspace. The proposed method is an extension to spatial CDPMs of a synthesis method previously published by the authors for planar CDPMs. The WCW of CDPMs is the set of poses for which any wrench can be produced at the end-effector by non-negative cable tensions. A sufficient condition is introduced in order to verify whether a given six-dimensional box, i.e., a box covering point-positions and orientations, is fully inside the WCW of a given spatial CDPM. Then, a nonlinear program is formulated, whose optima represent CDPMs that can reach any point in a set of boxes prescribed by the designer. The objective value of this nonlinear program indicates how well the WCW of the resulting CDPM covers the prescribed box, a null value indicating that none of the WCW is covered and a value greater or equal to one indicating that the full prescribed workspace is covered.

Gliders Measure Western Boundary Current Transport from the South Pacific to the Equator*

2012 ◽  
Vol 42 (11) ◽  
pp. 2001-2013 ◽  
Author(s):  
Russ E. Davis ◽  
William S. Kessler ◽  
Jeffrey T. Sherman
Keyword(s):  
El Niño ◽  
El Nino ◽  
Layer Structure ◽  
Western Boundary Current ◽  
Western Boundary ◽  
Boundary Current ◽  
The Core ◽  
A Value ◽  
Coral Sea ◽  
Near Shore

Abstract “Spray” gliders, most launched from small boats near shore, have established a sustainable time series of equatorward transport through the Solomon Sea. The first 3.5 years (mid-2007 through 2010) are analyzed. Coast-to-coast equatorward transport through the Solomon Sea fluctuates around a value of 15 Sv (1 Sv ≡ 106 m3 s−1) with variations approaching ±15 Sv. Transport variability is well correlated with El Niño indices like Niño-3.4, with strong equatorward flow during one El Niño and weak flow during two La Niñas. Mean transport is centered in an undercurrent focused in the western boundary current; variability has a two-layer structure with layers separated near 250 m (near the core of the undercurrent) that fluctuate independently. The largest variations are in midbasin, confined to the upper layer, and are well correlated with ENSO. Analysis of velocity and salinity on isopycnals shows that the western boundary current within the Solomon Sea consists of a deep core coming from the Coral Sea and a shallow core that enters the Solomon Sea in mid basin. Analysis of the structure of transport and its fluctuations is presented.

Sign in / Sign up

Export Citation Format

Share Document