Influence of Configuration at the 4- and 6-Positions on the Conformation and Anomeric Reactivity and Selectivity of 7-Deoxyheptopyranosyl Donors : Discovery of a Highly Equatorially Selective l-glycero-d-gluco-Heptopyranosyl Donor
The preparation of four per-O-benzyl-d- or l-glycero-d-galacto and d- or l-glycero-d-gluco heptopyranosyl sulfoxides and the influence of their side-chain conformations on reactivity and stereoselectivity in glycosylation reactions are described. The side-chain conformation in these donors is determined by the relative configuration of its point of attachment to the pyranoside ring and the two flanking centers in agreement with a recent model. In the d- and l-glycero-d-galacto glycosyl donors, the d-glycero-d-galacto isomer with the more electron-withdrawing trans,gauche conformation of its side chain was the more equatorially selective isomer. In the d- and l-glycero-d-gluco glycosyl donors, the l-glycero-d-gluco isomer with the least disarming gauche,gauche side-chain conformation was the most equatorially selective donor. Variable temperature NMR studies, while supporting the formation of intermediate glycosyl triflates at -80 °C in all cases, were inconclusive owing to a change in the decomposition mechanism with the change in configuration. It is suggested that the equatorial selectivity of the l-glycero-d-gluco isomer arises from H-bonding between the glycosyl acceptor and O6 of the donor, which is poised to deliver the acceptor antiperiplanar to the glycosyl triflate, resulting in a high degree of SN2 character in the displacement reaction.
| Medienart: |
E-Artikel |
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| Erscheinungsjahr: |
2021 |
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| Erschienen: |
2021 |
| Enthalten in: |
Zur Gesamtaufnahme - volume:86 |
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| Enthalten in: |
The Journal of organic chemistry - 86(2021), 17 vom: 03. Sept., Seite 12199-12225 |
| Sprache: |
Englisch |
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| Beteiligte Personen: |
Upadhyaya, Kapil [VerfasserIn] |
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| Links: |
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| Anmerkungen: |
Date Completed 22.10.2021 Date Revised 04.09.2022 published: Print-Electronic Citation Status MEDLINE |
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| doi: |
10.1021/acs.joc.1c01535 |
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| funding: |
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| Förderinstitution / Projekttitel: |
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| PPN (Katalog-ID): |
NLM328874809 |
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| 245 | 1 | 0 | |a Influence of Configuration at the 4- and 6-Positions on the Conformation and Anomeric Reactivity and Selectivity of 7-Deoxyheptopyranosyl Donors |b Discovery of a Highly Equatorially Selective l-glycero-d-gluco-Heptopyranosyl Donor |
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| 500 | |a Date Revised 04.09.2022 | ||
| 500 | |a published: Print-Electronic | ||
| 500 | |a Citation Status MEDLINE | ||
| 520 | |a The preparation of four per-O-benzyl-d- or l-glycero-d-galacto and d- or l-glycero-d-gluco heptopyranosyl sulfoxides and the influence of their side-chain conformations on reactivity and stereoselectivity in glycosylation reactions are described. The side-chain conformation in these donors is determined by the relative configuration of its point of attachment to the pyranoside ring and the two flanking centers in agreement with a recent model. In the d- and l-glycero-d-galacto glycosyl donors, the d-glycero-d-galacto isomer with the more electron-withdrawing trans,gauche conformation of its side chain was the more equatorially selective isomer. In the d- and l-glycero-d-gluco glycosyl donors, the l-glycero-d-gluco isomer with the least disarming gauche,gauche side-chain conformation was the most equatorially selective donor. Variable temperature NMR studies, while supporting the formation of intermediate glycosyl triflates at -80 °C in all cases, were inconclusive owing to a change in the decomposition mechanism with the change in configuration. It is suggested that the equatorial selectivity of the l-glycero-d-gluco isomer arises from H-bonding between the glycosyl acceptor and O6 of the donor, which is poised to deliver the acceptor antiperiplanar to the glycosyl triflate, resulting in a high degree of SN2 character in the displacement reaction | ||
| 650 | 4 | |a Journal Article | |
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| 700 | 1 | |a Crich, David |e verfasserin |4 aut | |
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