Orthoesters formation leading to mismatched Helferich glycosylations at O-3 of N-trichloroacetylated glucosamine residues.
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| Title: | Orthoesters formation leading to mismatched Helferich glycosylations at O-3 of N-trichloroacetylated glucosamine residues. |
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| Authors: | Forman, Adam1, Auzanneau, France-Isabelle1 fauzanne@uoguelph.ca |
| Source: | Carbohydrate Research. Apr2016, Vol. 425, p10-21. 12p. |
| Subjects: | Alkoxy group, Glycosylation, Glucosamine, Trisaccharides, Acetylation |
| Abstract: | Using trisaccharide diol acceptors displaying two glucosamine residues free at O-3, we observed that α- l -fucosylation with α armed donor proceeded smoothly at the most accessible N -trichloroacetyl nonreducing end glucosamine residue. In contrast, glycosylations with peracetylated glycosyl bromide donors activated under Helferich conditions seemed to proceed preferentially or exclusively at the more sterically hindered N -acetylated reducing end unit. Thus, we concluded that disarmed donors were mismatched at O-3 of the N -trichloroacetylated glucosamine residue regardless of α or β configuration of the glycosidic bond formed and d or l configuration of the donor. Interestingly orthoester formation occurred in some cases at this position while they were not observed at the reducing end unit. Conversion of the nonreducing end trichloroacetamido to an acetamido allowed the Helferich catalyzed galactosylation to occur at both positions and revealed the impact of the N -trichloroacetamido on the mismatched glycosylations. Changing the activation conditions from the mild Lewis acid Hg(CN) 2 to the stronger acid AgOTf revealed that in fact β- d -galactosylation at the less hindered N -trichloroacetylated residue was kinetically favored over that at the reducing end residue. Isolation of equal amounts of orthoester at this position suggested that it was formed first but that the strong AgOTf Lewis acid was able to promote rearrangement to the β- d -galactosidic bond. These results shed additional light on the apparent mismatch of disarmed glycosyl donors with hydroxyl groups deemed more accessible. Depending on electronic factors imposed by the acceptor and activation conditions, transient unstable orthoester formation may explain in some cases why these donors appear mismatched with the most accessible hydroxyl groups which are otherwise glycosylated by armed donors. [ABSTRACT FROM AUTHOR] |
| Copyright of Carbohydrate Research is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | Engineering Source |
| FullText | Text: Availability: 0 |
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| Header | DbId: egs DbLabel: Engineering Source An: 114393361 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Orthoesters formation leading to mismatched Helferich glycosylations at O-3 of N-trichloroacetylated glucosamine residues. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Forman%2C+Adam%22">Forman, Adam</searchLink><relatesTo>1</relatesTo><br /><searchLink fieldCode="AR" term="%22Auzanneau%2C+France-Isabelle%22">Auzanneau, France-Isabelle</searchLink><relatesTo>1</relatesTo><i> fauzanne@uoguelph.ca</i> – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Carbohydrate+Research%22">Carbohydrate Research</searchLink>. Apr2016, Vol. 425, p10-21. 12p. – Name: Subject Label: Subjects Group: Su Data: <searchLink fieldCode="DE" term="%22Alkoxy+group%22">Alkoxy group</searchLink><br /><searchLink fieldCode="DE" term="%22Glycosylation%22">Glycosylation</searchLink><br /><searchLink fieldCode="DE" term="%22Glucosamine%22">Glucosamine</searchLink><br /><searchLink fieldCode="DE" term="%22Trisaccharides%22">Trisaccharides</searchLink><br /><searchLink fieldCode="DE" term="%22Acetylation%22">Acetylation</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: Using trisaccharide diol acceptors displaying two glucosamine residues free at O-3, we observed that α- l -fucosylation with α armed donor proceeded smoothly at the most accessible N -trichloroacetyl nonreducing end glucosamine residue. In contrast, glycosylations with peracetylated glycosyl bromide donors activated under Helferich conditions seemed to proceed preferentially or exclusively at the more sterically hindered N -acetylated reducing end unit. Thus, we concluded that disarmed donors were mismatched at O-3 of the N -trichloroacetylated glucosamine residue regardless of α or β configuration of the glycosidic bond formed and d or l configuration of the donor. Interestingly orthoester formation occurred in some cases at this position while they were not observed at the reducing end unit. Conversion of the nonreducing end trichloroacetamido to an acetamido allowed the Helferich catalyzed galactosylation to occur at both positions and revealed the impact of the N -trichloroacetamido on the mismatched glycosylations. Changing the activation conditions from the mild Lewis acid Hg(CN) 2 to the stronger acid AgOTf revealed that in fact β- d -galactosylation at the less hindered N -trichloroacetylated residue was kinetically favored over that at the reducing end residue. Isolation of equal amounts of orthoester at this position suggested that it was formed first but that the strong AgOTf Lewis acid was able to promote rearrangement to the β- d -galactosidic bond. These results shed additional light on the apparent mismatch of disarmed glycosyl donors with hydroxyl groups deemed more accessible. Depending on electronic factors imposed by the acceptor and activation conditions, transient unstable orthoester formation may explain in some cases why these donors appear mismatched with the most accessible hydroxyl groups which are otherwise glycosylated by armed donors. [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Carbohydrate Research is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1016/j.carres.2016.02.012 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 12 StartPage: 10 Subjects: – SubjectFull: Alkoxy group Type: general – SubjectFull: Glycosylation Type: general – SubjectFull: Glucosamine Type: general – SubjectFull: Trisaccharides Type: general – SubjectFull: Acetylation Type: general Titles: – TitleFull: Orthoesters formation leading to mismatched Helferich glycosylations at O-3 of N-trichloroacetylated glucosamine residues. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Forman, Adam – PersonEntity: Name: NameFull: Auzanneau, France-Isabelle IsPartOfRelationships: – BibEntity: Dates: – D: 29 M: 04 Text: Apr2016 Type: published Y: 2016 Identifiers: – Type: issn-print Value: 00086215 Numbering: – Type: volume Value: 425 Titles: – TitleFull: Carbohydrate Research Type: main |
| ResultId | 1 |
