Investigation of the reactivity difference between thioglycoside donors with variant aglycon parts

Lahmann, Martina; Oscarson, Stefan

doi:10.1139/v02-101

Cited by 54 publications

(51 citation statements)

References 24 publications

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“…With this in mind we again turned to the use of the tertiary thioglycosides, which are more readily activated by the N -iodosuccinimide triflic acid combination than aryl thioglycosides or primary and secondary alkyl thioglycosides. 37,66 Accordingly, reaction of thioglycoside 25 37 with imidazole sulfonyl azide in the presence of copper sulfate and potassium carbonate gave 92% of the azide 26 , which was converted to the donor 27 on standard acetylation (Scheme 4). Alternatively, and following reports by Zbiral and Schmidt, 22,51 conversion of acetamide 6 to the N -nitrosoacetamide 7 followed by treatment with sodium isopropoxide and trifluoroethanol and then hydrazoic acid gave 27 in 51% yield (Scheme 4).…”

Section: Resultsmentioning

confidence: 99%

Stereoselective Synthesis of 5-epi-α-Sialosides Related to the Pseudaminic Acid Glycosides. Reassessment of the Stereoselectivity of the 5-Azido-5-deacetamidosialyl Thioglycosides and Use of Triflate as Nucleophile in the Zbiral Deamination of Sialic Acids

2016

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With a view to the eventual synthesis of glycosyl donors for the stereocontrolled synthesis of pseudaminic acid glycosides, the stereocontrolled synthesis of a d-glycero-d-gulo sialic acid adamantanylthioglycoside carrying an axial azide at the 5-position is described. The synthesis employs levulinic acid as nucleophile in the oxidative deamination of an N-acetyl neuraminic acid thioglycoside leading to the formation of a 3-deoxy-d-glycero-d-galacto-2-nonulosonic acid (KDN) derivative selectively protected as 5-O-levulinate. Replacement of the levulinate by triflate enables introduction of the axial azide and hence formation of the glycosyl donor. A shorter synthesis uses trifluoromethanesulfonate as nucleophile in the oxidative deamination step when the 5-O-triflyl KDN derivative is obtained directly. Glycosylation reactions conducted with the 5-azido-d-glycero-d-gulo configured sialyl adamantanylthioglycoside at −78 °C are selective for the formation of the equatorial glycosides suggesting that the synthesis of equatorial pseudaminic acid glycosides will be possible as suitable donors become available. A comparable N-acetylneuraminic acid adamantanylthioglycoside carrying an equatorial azide at the 5-position was also found to be selective for equatorial glycoside formation under the same conditions, suggesting that reinvestigation of other azide-protected NeuAc donors is merited. Glycosylation stereoselectivity in the d-glycero-d-gulo series is discussed in terms of the side chain conformation of the donor.

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Section: Resultsmentioning

confidence: 99%

Stereoselective Synthesis of 5-epi-α-Sialosides Related to the Pseudaminic Acid Glycosides. Reassessment of the Stereoselectivity of the 5-Azido-5-deacetamidosialyl Thioglycosides and Use of Triflate as Nucleophile in the Zbiral Deamination of Sialic Acids

2016

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“…However, no reaction was observed. Noting the work of Oscarson and Lahmann on the reactivity order of various thioglycosides (glucose and galactose), 6,7,8 we turned our attention to the use of more reactive thiosialoside donors, which could possibly be activated in nitrile solvents at low temperature when improved α-selectivities could be anticipated. Here we describe an investigation into the sialylations of 1-adamantanyl thiosialoside donors 2 and 3.…”

Section: Introductionmentioning

confidence: 99%

α-Selective Sialylations at −78 °C in Nitrile Solvents with a 1-Adamantanyl Thiosialoside

2007

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Novel 1-adamantanylthio sialosides were synthesized and coupled to acceptors under NIS/TfOH promotion conditions. These donors showed higher reactivity than the phenylthio sialosides and could be activated by NIS/TfOH in nitrile solvents at −78 °C to afford improved α-sialylations. With the N-acetyl-5-N,4-O-oxazolidinone protected 1-adamantanylthio sialyl donor, high α-selectivities could be achieved in the sialylations of both primary and sterically hindered secondary acceptors, including the important galactose 3-OH acceptors.Oligosaccharides and glycoconjugates incorporating sialic acid residues are ubiquitous in high animals and human beings, and play important roles in a wide variety of biological processes. 1 Over the years considerable efforts have been spent on the development of sialoside donors bearing various leaving groups for efficient installation of α-sialyl linkages, among which 2-sulfide donors of Neu5Ac, ethyl) and S-aryl (phenyl and substituted phenyl) sialosides, have been widely applied. 2 In a previous report, we noted that an N-acetyl-5-N,4-O-oxazolidinone protected 2-phenylthio sialoside donor 1 gave excellent yields and α-selectivities in linking to various primary alkyl and carbohydrate acceptors under the NIS/TfOH in situ activation conditions at −40 °C in dichloromethane (Scheme 1). 3 Importantly, following glycosylation, the oxazolidinone group was readily cleaved under mild conditions leaving the acetamide intact. 3 Similar investigations were also reported by the Takahashi and De Meo groups with N-desacetyl analogs of 1, but harsher conditions were required for cleavage of the oxazolidinone moiety. 4 In an attempt to increase the α-selectivities of the sialylations of 1 with secondary sugar acceptors by means of the nitrile effect, 5 glycosylations promoted by NIS/TfOH were attempted in nitrile solvents at −40 °C. However, no reaction was observed. Noting the work of Oscarson and Lahmann on the reactivity order of various thioglycosides (glucose and galactose), 6,7,8 we turned our attention to the use of more reactive thiosialoside donors, which could possibly be activated in nitrile solvents at low temperature when improved α-selectivities could be anticipated. Here we describe an investigation into the sialylations of 1-adamantanyl thiosialoside donors 2 and 3. The 1-adamantanyl group was chosen because of its greater electron donating properties compared to Oscarson's preferred cyclohexyl group, and the solid (m.p. 99-106°C ) non-volatile nature of 1-adamantanethiol, the precursor for the installation of 1-adamantanylthio leaving group, which reduces the odor problem common to most thiols. 9The penta-acetate derivative 4 10 of neuraminic acid was reacted with 1-adamantanethiol in the presence of BF 3 ·Et 2 O in CH 2 Cl 2 at room temperature to afford 81% of the 1-adamantanyl thiosialoside 5 (Scheme 2). 11 Donor 2 then was derived from 5 in quantitative yield by treatment with i-propenyl acetate catalyzed by CSA at 65 °C (Scheme 2).The preparation of donor 3 started...

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“…Although glycosylations with hybrid donor 1 were swift, high yielding and β-stereoselective, 10 we feared that the reduced reactivity could translate into decreased efficacy of these building blocks in sequential chemoselective glycosylations in one-pot. This led us to a hypothesis that the use of a more reactive S -ethyl leaving group 11 would help us to develop a complementary superarmed glycosyl donor with a superior reactivity profile whilst still maintaining β-stereoselectivity.…”

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confidence: 99%

Conformationally superarmed S-ethyl glycosyl donors as effective building blocks for chemoselective oligosaccharide synthesis in one pot

et al. 2017

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A new series of superarmed glycosyl donors has been investigated. It was demonstrated that the S-ethyl leaving group allows for high reactivity, which is much higher than that of equally equipped S-phenyl glycosyl donors that were previously investigated by our groups. The superarmed S-ethyl glycosyl donors equipped with a 2-O-benzoyl group gave complete β-stereoselectivity. Utility of the new glycosyl donors has been demonstrated in a one-pot one-addition oligosaccharide synthesis with all of the reaction components present from the beginning.

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Investigation of the reactivity difference between thioglycoside donors with variant aglycon parts

Cited by 54 publications

References 24 publications

Stereoselective Synthesis of 5-epi-α-Sialosides Related to the Pseudaminic Acid Glycosides. Reassessment of the Stereoselectivity of the 5-Azido-5-deacetamidosialyl Thioglycosides and Use of Triflate as Nucleophile in the Zbiral Deamination of Sialic Acids

Stereoselective Synthesis of 5-epi-α-Sialosides Related to the Pseudaminic Acid Glycosides. Reassessment of the Stereoselectivity of the 5-Azido-5-deacetamidosialyl Thioglycosides and Use of Triflate as Nucleophile in the Zbiral Deamination of Sialic Acids

α-Selective Sialylations at −78 °C in Nitrile Solvents with a 1-Adamantanyl Thiosialoside

Conformationally superarmed S-ethyl glycosyl donors as effective building blocks for chemoselective oligosaccharide synthesis in one pot

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