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Catalyst-free regioselective acetylation of primary hydroxy groups in partially protected and unprotected thioglycosides with acetic acid.

ABSTRACT: Highly regioselective acetylation of primary hydroxy groups in thioglycoside derivatives with gluco- and galacto-configurations was achieved by treatment with aqueous or anhydrous acetic acid (60-100% AcOH) at elevated temperatures (80-118 °C), avoiding complex, costly and time-consuming manipulations with protective groups. Acetylation of both 4,6-O-benzylidene acetals and the corresponding diols as well as the unprotected tetraol with AcOH was shown to lead selectively to formation of 6-O-acetyl derivatives. For example, the treatment of phenyl 1-thio-β-d-glucopyranoside with anhydrous AcOH at 80 °C for 24 h gave the corresponding 6-O-acetylated derivative in 47% yield (71% based on the reacted starting material) and unreacted starting tetraol in 34% yield, which can easily be recovered by silica gel chromatography and reused in further acetylation.

SUBMITTER: Abronina PI

PROVIDER: S-EPMC9057154 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Catalyst-free regioselective acetylation of primary hydroxy groups in partially protected and unprotected thioglycosides with acetic acid.

Abronina Polina I PI Malysheva Nelly N NN Zinin Alexander I AI Kolotyrkina Natalya G NG Stepanova Elena V EV Kononov Leonid O LO

RSC advances 20201006 60

Highly regioselective acetylation of primary hydroxy groups in thioglycoside derivatives with gluco- and galacto-configurations was achieved by treatment with aqueous or anhydrous acetic acid (60-100% AcOH) at elevated temperatures (80-118 °C), avoiding complex, costly and time-consuming manipulations with protective groups. Acetylation of both 4,6-O-benzylidene acetals and the corresponding diols as well as the unprotected tetraol with AcOH was shown to lead selectively to ...[more]

PMID: 35517942

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Project description:This article describes studies on the regioselective acetal protection of monosaccharide-based diols using chiral phosphoric acids (CPAs) and their immobilized polymeric variants, (R)-Ad-TRIP-PS and (S)-SPINOL-PS, as the catalysts. These catalyst-controlled regioselective acetalizations were found to proceed with high regioselectivities (up to >25:1 rr) on various d-glucose-, d-galactose-, d-mannose-, and l-fucose-derived 1,2-diols and could be carried out in a regiodivergent fashion depending on the choice of chiral catalyst. The polymeric catalysts were conveniently recycled and reused multiple times for gram-scale functionalizations with catalytic loadings as low as 0.1 mol %, and their performance was often found to be superior to the performance of their monomeric variants. These regioselective CPA-catalyzed acetalizations were successfully combined with common hydroxyl group functionalizations as single-pot telescoped procedures to produce 32 regioisomerically pure differentially protected mono- and disaccharide derivatives. To further demonstrate the utility of the polymeric catalysts, the same batch of (R)-Ad-TRIP-PS catalyst was recycled and reused to accomplish single-pot gram-scale syntheses of 6 differentially protected d-glucose derivatives. The subsequent exploration of the reaction mechanism using NMR studies of deuterated and nondeuterated substrates revealed that low-temperature acetalizations happen via a syn-addition mechanism and that the reaction regioselectivity exhibits strong dependence on the temperature. The computational studies indicate a complex temperature-dependent interplay of two reaction mechanisms, one involving an anomeric phosphate intermediate and another via concerted asynchronous formation of an acetal, that results in syn-addition products. The computational models also explain the steric factors responsible for the observed C2 selectivities and are consistent with experimentally observed selectivity trends.

Dataset Information

Catalyst-free regioselective acetylation of primary hydroxy groups in partially protected and unprotected thioglycosides with acetic acid.

Publications

Catalyst-free regioselective acetylation of primary hydroxy groups in partially protected and unprotected thioglycosides with acetic acid.

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