Stereoselective Glycosidation Research Articles

A stereoselective glycosidation using thioglycosides, activation by combination of N-bromosuccinimide and strong acid salts

A stereoselective glycosidation with thioglycosides was effected under mild and neutral conditions by combined use of N-bromosuccinimide (NBS) and a catalytic amount of various strong acid salts. A combination of NBS with Ph 2IOTf, Bu 4NOTf, or Bu 4NClO 4 was advantageous for β-selective glucosidation with 2- O-acylated or 2- O-benzylated donors by virtue of either the neighboring group participation or the known solvent effect of nitrile, respectively. α-Selective glucosidation was effected by the use of a 2- O-benzylated donor in the presence of LiClO 4 or LiNO 3 as a catalyst in ether. Addition of silica gel to the reaction mixture increased both the α-selectivity and reaction rate.

Convenient synthesis of O-(2-acitamido-2-deoxy-β-D-glucopyranosyl)-serine and -threonine building blocks for solid-phase glycopeptide assembly

The suitably protected building blocks for solid-phase glycopeptide synthesis, Nα-Fmoc-Ser(Ac3-β-D-GlcNAc)-OPfp, 11, and Nα-Fmoc-Ther(Ac3-β-D-GlcNAc)-OPfp, 12, have been synthesized by stereo-selective glycosidation of the 2-allyloxycarbonylamino glycosyl donor 7 with Nα-Fmoc-Ser -OPfp, 3, and Nα-Fmoc-Thr -OPfp, 4, followed by Pdo-catalysed allyl transfer from the N-allyloxycarbonyl group in the presence of acetic anhydride.

Preparation of ether-linked 2-acetamido-2-deoxy β-glycolipids via zinc chloride promoted coupling of Ac 4GlcNAcCl with lipid hydroxy groups

Stereoselective glycosidation of lipid hydroxy groups has been achieved using 2-acetamido-3,4,6-tri- O-acetyl-2-deoxy-α-D-glycosyl chloride as the glycosyl donor in CH 2Cl 2. In the presence of ZnCl 2 (1 equiv.) and various “promoters” (1 equiv.) such as Ph 3CCl, 18-crown-6/KCl, n-Bu 4NBr, or Me 3SiCl, β-glycolipid conjugates are formed as the initial products, but they undergo anomerization on prolonged reaction times. The promoters may enhance the solubility of ZnCl 2 in CH 2Cl 2.

Total synthesis of calicheamicin .gamma.1I. 3. The final stages

The first total synthesis of calicheamicin γ 1 I (1) has been achieved. The stereoselective glycosidation, joining the appropriately functionalized aglycon 3 with the oligosaccharide fragment 2, was realized uding Schmidt's trichloroacetimidate methodology. Segment 4, equipped with the photolabile 2-nitrobenzyl group at the reducing end, was synthesized using similar chemistry to that applied to the synthesis of its methyl glycoside counterpart (see accompanying paper). Stereoselective reduction of oxime 31, obtained from the coupling product, with NaCNBH 3 in the presence of BF 3 -OEt 2 , late in the synthetic scheme, generated the desired alkoxylamine 32 and its A-4 isome 32-epi

A new approach to the synthesis of glycosides

Abstract

Stereoselective synthesis of α-linked 2-deoxysaccharides and furanosaccharides by use of 2-deoxy 2-pyridyl-1-thio pyrano- and furanosides as donors and methyl iodide as an activator

A practical and highly stereoselective glycosidation methodology is described, where anomeric mixture of 2-deoxy 2-pyridyl-1-thiopyranoside donors ( 1–3, 27) have been coupled with several sugar alcohols ( 4–8,29,31) on activation by methyl iodide to obtain axially linked 2-deoxysaccharides ( 9–17,30,32,33). Application of this method for the synthesis of disaccharide fragment 28 of avermectin is also described. Utility of this method is also shown by use of 2-pyridyl-1-thiofuranosides ( 34–36) as donors to prepare α-linked furnaosides ( 42–51).

ChemInform Abstract: Highly Stereoselective Glycosidation of Ribose Solubilized in Apolar Organic Media via Host‐Guest Complexation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthese von 2‐Desoxy‐α‐O‐glycopeptiden mit dem N‐Iodsuccinimid‐(NIS‐) Verfahren

Synthesis of 2‐Deoxy‐α‐O‐glycopeptides by the N‐Iodosuccinimide (NIS) ProcedureGlycosidation of amino acid/peptide derivatives of serine, threonine, or hydroxyproline with glycals like tris‐O‐acetyl‐D‐glucal 1 or tris‐O‐acetyl‐D‐galactal 2 and N‐iodosuccinimide (NIS) gives 2‐deoxy‐2‐iodo‐α‐O‐glycopeptides with high yields and excellent anomeric purity. Disaccharide glycals like per‐O‐acetyl‐D‐cellobial 15, per‐O‐acetyl‐D‐lactal 16, and 2′,3′,4′,6′‐tetra‐O‐acetyl‐β‐D‐galactopyranosyl‐(1 – 3)‐4,6‐di‐O‐benzyl‐D‐galactal 17 can also be used as glycosyl donors in this process. They give moderate to good yields of α‐O‐glycoside with formation of small amounts of β‐O‐glycopeptide. The NIS procedure is especially favored for the direct and stereoselective glycosidation of larger peptide fragments, which is very difficult with classical techniques. The so‐formed 2‐deoxy‐2‐iodo‐α‐O‐glycopeptides were deiodinated by using different methods and then deacetylated in the sugar moiety.

Stereoselective synthesis of α-linked saccharides by use of per O-benzylated 2-pyridyl 1-thio hexopyranosides as glycosyl donors and methyl iodide as an activator

A new, practical, stereoselective glycosidation methodology is described where per O-benzylated 2-pyridyl 1-thio-α/β-hexopyranosyl donors of D-gluco-(1), D-galacto-(2),D-manno-(3) and L-rhamno-(4) configurations have been efficiently coupled with diverse sugar alcohols (6,8–11) on activation by methyl iodide to obtain the α-linked disaccharides (7,12–19). Coupling of donor 1 with the disaccharide acceptor 20 and the disaccharide donor 5 with 8 to obtain α-linked trisaccharides 21 and 22 is also described. A possible mechanism for the α-selectivity is also discussed.

Tumor‐associated antigen synthesis synthesis of the gal‐α‐(1→3)‐gal‐β‐(1→4)‐GlcNAc epitope a specific determinant for metastatic progression?

AbstractA versatile synthesis of the Gal‐α‐(1→3)‐Gal‐β‐(1→4)‐GlcNAc epitope coupled to an alkyl spacer molecule could be developed. The important building block 3′‐allyl‐D‐lactal 6 was prepared in high yield by the action of dibutyltin oxide and allyl bromide on D‐lactal and converted in several steps into the lactosamine derivative 13 with free 3′‐OH group. Stereoselective glycosidation with the β‐trichloroacetimidate of benzylated D‐galactose 18 led to the trisaccharide in high yield. Activation of the protected Gal‐α‐(1→3)‐Gal‐β‐(1→4)‐GlcNAc derivative 21 by desilylation and trichloroacetimidate formation followed by glycosidation with ethyl 9‐hydroxynonanoate furnished the spacer‐bound trisaccharide hapten 24 in excellent yield after simple two‐step deprotection. The trisaccharide hapten 24 can easily be used as immunogen after coupling to an immunogenic carrier.

Glycosyltransferase-catalysed stereoselective glycosidation of monosaccharide-based glycosidase inhibitors: a new approach to the synthesis of sequence-specific glycosidase inhibitors

β-1,4-Galactosyltransferase was used as catalyst for galactosidation of 5-thioglucose, glucal and 1-deoxynojiriycin to form the corresponding β-1,4-galactosides as potential sequence-specific glycosidase inhibitors.

Novel stereoselective glycosidation by the combined use of trityl halide and Lewis acid.

A Novel stereoselective glycosidation was achieved by the combined use of trityl halide and Lewis acid under mild reaction conditions. The stereoselectivity was found to be drastically changed by the presence of trityl halide.

Iodonium ion promoted reactions at the anomeric centre. II An efficient thioglycoside mediated approach toward the formation of 1,2- trans linked glycosides and glycosidic esters

N-iodosuccinimide (NIS) in the presence of an organic acid was found to be effective for the activation of fully acylated thioglycosides leading to 1,2-trans linked esters. On the other hand, NIS together with a catalytic amount of trifluoromethanesulfonic acid proved to be very convenient for the rapid, high-yielding and stereoselective (1,2-trans) glycosidation of esterified thioglycosides with glycosyl acceptors.

Glycosidation of sialic acid

Sialic acid is located at the non-reducing ends of carbohydrate chains of glycoproteins and glycolipids and plays an important role in biological processes. The synthesis of sialylated oligosaccharides has been encouraged in order to clarify their vital functions. In the synthesis of sialylated oligosaccharides, the most difficult problem remaining is the stereoselective glycosidation of sialic acid by the creation of the α-glycosidic linkage. This Report discusses enzymic and synthetic approaches to the glycosidation of sialic acid by new methodologies.

Highly stereoselective glycosidation of ribose solubilized in apolar organic media via host-guest complexation 1

Ribose complexed with resorcinol-dodecanal cyclotetramer via hydrogen bonding in CCl 4 undergoes highly stereoselective glycosidation with methanol to give methyl β-ribofuranoside under mild and neutral conditions.

ChemInform Abstract: Glycosidation of Sialic Acid

Abstract Sialic acid is located at the non-reducing ends of carbohydrate chains of glycoproteins and glycolipids and plays an important role in biological processes. The synthesis of sialylated oligosaccharides has been encouraged in order to clarify their vital functions. In the synthesis of sialylated oligosaccharides, the most difficult problem remaining is the stereoselective glycosidation of sialic acid by the creation of the α-glycosidic linkage. This Report discusses enzymic and synthetic approaches to the glycosidation of sialic acid by new methodologies.

ChemInform Abstract: Stereoselective Glycosidation Reactions of Activated Glycals with a C1‐Oxygenated Allylsilane: Synthesis of a cis‐Pyrano(2,3‐b)pyran.

AbstractThe dihydropyrans (II) and (IV) react with the 1‐silylallyl alcohol (I) in the presence of boron trifluoride etherate to give the dihydropyranyl ethers (III) or (V).

Stereoselective glycosidation reactions of activated glycals with a c1-oxygenated allylsilane: Synthesis of a cis-pyrano[2,3-b]pyran

A highly stereoselective synthesis of a cis-pyrano[2, 3-b]pyran has been developed utilizing a BF 3·OEt 2 catalyzed glycosidation reaction of activated glycals with 1-hydroxy-2-propenyltrimethylsilane (1). The reaction resulted in incorporation of a 1-trimethylsilyl-2-propenyloxy-1-yl function. A subsequent fluoride ion promoted internal conjugate addition reaction was used for the construction of the cis-pyranopyran.

Selective deacetylation of anomeric sugar acetates with tin alkoxides

There are three main categories of methods for synthesising glucosides and glucuronides (1 + 2 + 3), namely, (a) the Koenigs-Knorr reaction (1, where Y = halogen) and its modifications2, (6) reactions catalysed by Lewis acids3 (1, Y = OAc), and (c) reactions where HO-1 of the starting derivative is unsubstituted (1, Y = OH). Category (c) includes methods in which HO-1 is initially converted into a more reactive species 4a-g, and those which involve a Lewis acid catalyst’S4h. Direct coupling is attractive since it avoids the preparation of reactive, unstable, and readily hydrolysable derivatives of 1 with Y = Br, OCNHCC&, OCNHNHR, etc. The need for simple methods for the preparation of sugar derivatives with HO-1 unsubstituted is further exemplified by conversions into glycosyl fluorides which are useful in stereoselective glycosidations’. + R3-OH __L1

Distribution of tautomers in acylated ketoses an important factor in ketoside synthesis

Formation of tautomers upon acylation of D-fructose and several 1-0-substituted derivatives thereof is studied and appropriate intermediates are used in stereo-selective glycoside synthesis.