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.

scholarly journals Synthesis and Characterizations of Dipeptide Derivative of Gentamicin

2019 ◽  
Vol 28 (2) ◽  
pp. 73-82
Author(s):  
Oun D. Khudair ◽  
Diar A. Fatih
Keyword(s):  
Acid Chloride ◽  
Solution Method ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Free Hydroxyl ◽  
Ester Linkage ◽  
Amine Groups ◽  
Conventional Solution ◽  
Dipeptide Derivative

Abstract       The target derivative are gentamicin linked with L-Val- L-Ala by an ester linkage. These were synthesized by esterification method, which included the reaction of -OH hydroxyl group on (carbon No.5) of gentamicin with the acid chloride of the corresponding dipeptide, The preparation of new derivative of gentamicin involved protected the primary & secondary amine groups of Gentamicin, by Ethylchloroformate (ECF) to give N-carbomethoxy Gentamicin which was used for further chemical synthesis involving the free hydroxyl groups. Then prepared dipeptide (L-Val- L-Ala) by conventional solution method in present DCC & HoBt then reacted with thionyl chloride to prepared acid chloride of dipeptides, then after, linked by ester linkage to N-protection gentamicin in present pyridine as base, finally deportation the amino group of synthesized compound by using TFAA in present anisole. The characterization of the titled compounds were performed utilizing FTIR spectroscopy, CHNS elemental analysis, and by measurements of their physical properties.  

Hierarchial Structure and Physical Properties of Natural Cellulosic Fibers

1991 ◽  
Vol 255 ◽  
Author(s):  
Ludwig Rebenfeld
Keyword(s):  
Building Blocks ◽  
Decomposition Temperature ◽  
Fiber Axis ◽  
Hydroxyl Groups ◽  
Wood Fibers ◽  
Cellulosic Fibers ◽  
Naturally Occurring ◽  
Specific Source ◽  
Free Hydroxyl ◽  
Intramolecular Hydrogen

AbstractNatural cellulosic fibers have in common the fact that cellulose is the key polymeric component in the structure, although the chemical composition varies widely depending on the specific source of the fibers. Cellulose is a long-chain linear condensation polymer of β-D-glucose with three free hydroxyl groups on each monomeric unit, resulting in strong inter- and intramolecular hydrogen bonds. Because of the hydrogen bond network, and also due to restricted rotation around the polymeric 1,4- β-linkage, cellulose is a rigid and stiff chain with a Tg well above the chemical decomposition temperature.Despite the high Tg native cellulose is invariably highly crystalline as a result of the biosynthetic process. In naturally occurring cellulosic fibers, the cellulose crystallites are aggregated into fibrils which constitute the underlying building blocks of the fiber. In cotton, the fibrils are laid down during the development or growth of the fiber in the form of concentric layers. The fibrils are disposed at an angle of 23° with respect to the fiber axis and thus they describe a helical pattern. The sense of the helix reverses frequently along the length of the fiber. This morphology is unique to cotton; other cellulosic fibers such as ramie and jute have similar fibrillar structures, but fibrillar angles in the 5 to 10 degree range, with no reversals. Wood fibers, on the other hand, are structurally more heterogeneous and may be considered as composites.

scholarly journals Technological Aspects of Highly Selective Synthesis of Allyloxyalcohols—New, Greener, Productive Methods

Catalysts ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1559
Author(s):  
Magdalena Urbala
Keyword(s):  
Allyl Chloride ◽  
Industrial Applications ◽  
Solvent Free ◽  
Pt Catalyst ◽  
Hydroxyl Groups ◽  
Equimolar Ratio ◽  
Allyl Ethers ◽  
Solvent Free Conditions ◽  
Free Hydroxyl ◽  
By Products

Allyl ethers bearing free hydroxyl groups of CH2=CH-CH-O-A-OH type (hydroxyalkyl allyl ethers, allyloxyalcohols) are valuable chemicals in many environmentally friendly industrial applications. The development of technologically attractive methods for their production is necessary. The two pathways (L-L PTC and non-catalytic solvent-free conditions) were optimized for the highly selective and yield synthesis of 4-allyloxybutan-1-ol. Improvements in the PTC method (50% NaOH(aq), the equimolar ratio of NaOH to diol, cyclohexane as solvent) with a new highly selective and effective PT catalyst, i.e., Me(n-Oct)3N+Br− (0.3 mol%), resulted in 88% yield and 98% selectivity of 4-allyloxybutan-1-ol with minimal formation of allyl chloride hydrolysis by-products (<1%). In turn, application of non-catalytic solvent-free conditions and the change in the key substrate with an excess of diol and use of solid NaOH solely led to a mono-O-allylation product with an excellent yield of 99% in a relatively short reaction time (3.5 h), with trace amounts of by-products (<0.1%). This sustainable method is perfectly suitable for the synthesis on a larger scale (3 moles of the key substrate) and for the full O-allylation process.

New Set of Orthogonal Protecting Groups for the Modular Synthesis of Heparan Sulfate Fragments

2003 ◽  
Vol 5 (26) ◽  
pp. 4975-4978 ◽  
Author(s):  
Arati Prabhu ◽  
Andre Venot ◽  
Geert-Jan Boons
Keyword(s):  
Heparan Sulfate ◽  
Protecting Groups ◽  
Modular Synthesis

The Dielectic properties of Crystalline Alcohols containing sterically hindered Hydroxyl groups

1953 ◽  
Vol 6 (2) ◽  
pp. 104 ◽  
Author(s):  
RJ Meakins
Keyword(s):  
Hydrogen Bonding ◽  
Hydroxyl Group ◽  
Appreciable Amount ◽  
Hydroxyl Groups ◽  
Dipole Orientation ◽  
Hindered Rotation ◽  
Dielectric Absorption ◽  
Free Hydroxyl ◽  
Sterically Hindered ◽  
High Dielectric

It has been previously suggested that the high dielectric absorption of certain crystalline forms of long-chain alcohols is associated with hydrogen-bonding of the hydroxyl groups. This theory is supported by the results given in the present paper, which show that with other alcohols, in which the hydroxyl groups are sterically hindered, the loss is almost completely eliminated. The smallest losses are obtained with triphenylcarbinol and cholesterol which both possess hydroxyl groups embedded in a bulky molecular structure. For the former compound, infra-red data from the literature indicate the absence of any appreciable amount of hydrogen-bonding and are thus in agreement with the evidence from dielectric measurements. High frequency absorption observed in these compounds is considered to be associated with dipole orientation resulting from hindered rotation of the free hydroxyl groups. The effects of steric hindrance of the hydroxyl group are also observed in tert.-butanol.

Studies on the Lignin of Eucalyptus regnans. II. The Nature of the Hydroxyl Groups and the Presence of the Carbonyl Group in Thiolignin

1948 ◽  
Vol 1 (2) ◽  
pp. 241
Author(s):  
JWT Merewether
Keyword(s):  
Benzoyl Chloride ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Carbonyl Groups ◽  
Eucalyptus Regnans ◽  
Trimethyl Ether ◽  
Free Hydroxyl ◽  
Active Methylene ◽  
Methylene Group ◽  
Alcoholic Hydroxyl

E. regnans thiolignin reacts with p-toluenesulphonyl chloride in pyridine to form a hexatosyl derivative ; its trimethyl ether reacts likewise to form a tritosyl derivative. Both compounds still have a free hydroxyl group which can be acetylated. Similarly they yield a hexabenzoate and tribenzoate respectively by the Schotten-Baumann reaction, but in pyridine, thiolignin reacts with benzoyl chloride to give a heptabenzoate and trimethylthiolignin a tetrabenzoate. No reaction takes place when trimethyl thiolignin is treated with triphenylchloromethane in pyridine. The above data are interpreted as evidence that of the four alcoholic hydroxyl groups three are secondary and one tertiary. With phenylhydrazine, thiolignin yields a phenylosazone ; with p-nitrophenylhydrazine it yields a p-nitrophenylhydrazone. On the other hand, trimethylthiolignin does not react with phenylhydrazine, indicating the absence of non-enolizable carbonyl groups. Thiolignin condenses with benzaldehydes indicating the presence of an active methylene group. From this evidence it is deduced that the grouping CH2-CO-CHOH- is present.

scholarly journals Synthesis of carbohydrate building blocks via regioselective uniform protection/deprotection strategies

2019 ◽  
Vol 17 (20) ◽  
pp. 4934-4950 ◽  
Author(s):  
Tinghua Wang ◽  
Alexei V. Demchenko
Keyword(s):  
Building Blocks ◽  
Hydroxyl Group ◽  
Free Hydroxyl

Scope 1: sugar is uniformly protected leaving only one (or two) free hydroxyl group; scope 2: uniformly protected sugar is deprotected to liberate only one (or two) hydroxyl group.

scholarly journals New glucuronic acid donors for the modular synthesis of heparan sulfate oligosaccharides

2014 ◽  
Vol 12 (13) ◽  
pp. 2087-2098 ◽  
Author(s):  
Omkar P. Dhamale ◽  
Chengli Zong ◽  
Kanar Al-Mafraji ◽  
Geert-Jan Boons
Keyword(s):  
Heparan Sulfate ◽  
Glucuronic Acid ◽  
Building Blocks ◽  
Modular Synthesis ◽  
Heparan Sulfate Oligosaccharides

A streamlined approach has been developed for the preparation of modular disaccharide building blocks for the assembly of libraries of HS oligosaccharides that avoids postglycosylation oxidation.

scholarly journals Preparation of diversely protected 2-azido-2-deoxyglycopyranoses from glycals

1995 ◽  
Vol 73 (3) ◽  
pp. 343-350 ◽  
Author(s):  
Stanislas Czernecki ◽  
Ebtissam Ayadi
Keyword(s):  
Sodium Azide ◽  
Protecting Groups ◽  
Hydroxyl Group ◽  
High Yield ◽  
Second Step ◽  
Trimethylsilyl Azide ◽  
Free Hydroxyl ◽  
Second Procedure ◽  
Hydrolysis Of ◽  
Mercury Trifluoroacetate

A new and efficient preparation of diversely protected 2-azido-2-deoxyglycopyranosides from the corresponding glycals is described. The glycals are first transformed into protected phenyl 2-azido-2-deoxy-selenoglycopyranosides by azido-phenylselenylation. Two procedures were employed according to the protecting groups present: sodium azide and diphenyldiselenide in the presence of (diacetoxyiodo)benzene for peracetylated glycals (Procedure A) or trimethylsilyl azide and tetra-n-butylammonium fluoride in the presence of N-phenylselenophthalimide for perbenzylated glycals (Procedure B). A gluco–manno mixture (90%) is obtained from protected d-glucal whereas only the galacto isomer is formed from protected d-galactal (75%). The compatibility of the second procedure with one free hydroxyl group and a variety of protecting groups was verified with 1,5-anhydro-2-deoxy-3,4-O-isopropylidene-d-lyxo-hex-1-enitol and its 6-O-acetyl, 6-O-allyl, 6-O-benzyl, and 6-O-tert-butyldimethylsilyl derivatives as well as with 1,5-anhydro-4,6-O-benzylidene-2-deoxy-d-lyxo-hex-1-enitol and its 3-O-acetyl and 3-O-benzyl derivatives, which were transformed into phenyl 2-azido-2-deoxy-α-d-selenogalactopyranoside derivatives in good yield. In the second step, hydrolysis of these selenoglycosides afforded diversely protected glycopyranoses in high yield. Peracetylated derivatives were hydrolyzed in the presence of N-iodosuccinimide, whereas mercury trifluoroacetate was employed for 3,4-O-isopropylidene, 4,6-O-benzylidene, and perbenzylated derivatives. In some cases the two steps can be carried out without isolation of the intermediate selenoglycoside. Keywords: glycals, 2-azido-2-deoxygalactopyranose, 2-azido-2-deoxyglucopyranose, selenoglycosides.

The hydroxyl stretching frequencies and conformations of Flavan-4-ols and Thiaflavan-4-ols

1969 ◽  
Vol 22 (11) ◽  
pp. 2337 ◽  
Author(s):  
GF Katekar ◽  
AG Moritz
Keyword(s):  
Carbon Tetrachloride ◽  
Benzene Ring ◽  
Hydroxyl Group ◽  
Hydroxyl Groups ◽  
Frequency Shifts ◽  
Characteristic Frequencies ◽  
Carbon Tetrachloride Solution ◽  
Free Hydroxyl ◽  
Related Compounds

The hydroxyl stretching frequencies of some 2,4-cis and 2,4-trans flavan-4-ols, thiaflavan-4-ols, and related compounds have been measured in dilute carbon tetrachloride solution. Characteristic frequencies are observed at 3626�2 cm-1 (free hydroxyl), 3616�1, and 3597�2 cm-1. The 3616 and 3597 cm-1 bands are assigned to pseudo-axial and pseudo-equatorial hydroxyl groups respectively. Evidence is presented to show that the frequency shifts arise from differences in the interaction of the hydroxyl group with the π-electrons of the fused benzene ring, and that these flavans and thiaflavans exist in half- chair, rather than sofa conformations.

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