Stereoselective epoxidations of vinylogous esters/carbonates directed by the 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl auxiliary: a route to near stereopure tertiary alcohols bearing functional arms

Bhatia, Gurpreet S.; Pritchard, Robin G.

doi:10.1039/a705498j

Cited by 12 publications

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References 13 publications

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“…To test our approach, we set out to prepare GlcNAc bis-acetals. Our synthesis was motivated by Stoodley et al, who used a glucose pendant group as a chiral auxiliary to explore stereoselective functionalization of vinylogous carbonates. − We first generated β-formyl glycoside 1 (Scheme ) using silver nitrate and formic acid. Wittig-type olefination of the formyl glycoside using 2-tributylphosphorane-methylpropionate delivered vinylogous carbonates 2-E and 2-Z .…”

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Carbohydrate Bis-acetal-Based Substrates as Tunable Fluorescence-Quenched Probes for Monitoring exo-Glycosidase Activity

Cecioni

Vocadlo

2017

J. Am. Chem. Soc.

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Tunable Förster resonance energy transfer (FRET)-quenched substrates are useful for monitoring the activity of various enzymes within their relevant physiological environments. Development of FRET-quenched substrates for exo-glycosidases, however, has been hindered by their constrained pocket-shaped active sites. Here we report the design of a new class of substrate that overcomes this problem. These Bis-Acetal-Based Substrates (BABS) bear a hemiacetal aglycon leaving group that tethers fluorochromes in close proximity, also positioning them distant from the active site pocket. Following cleavage of the glycosidic bond, the liberated hemiacetal spontaneously breaks down, leading to separation of the fluorophore and quencher. We detail the synthesis and characterization of GlcNAc-BABS, revealing a striking 99.9% quenching efficiency. These substrates are efficiently turned over by the human exo-glycosidase O-GlcNAcase (OGA). We find the hemiacetal leaving group rapidly breaks down, enabling quantitative monitoring of OGA activity. We expect this strategy to be broadly useful for the development of substrate probes for monitoring exo-glycosidases, as well as a range of other enzymes having constrained pocket-shaped active sites.

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confidence: 99%

Carbohydrate Bis-acetal-Based Substrates as Tunable Fluorescence-Quenched Probes for Monitoring exo-Glycosidase Activity

Cecioni

Vocadlo

2017

J. Am. Chem. Soc.

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Dioxirane Epoxidation of Alkenes

2002

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An ideal oxidant should be highly reactive, selective, and environmentally benign. It should transform a broad range of substrates with diverse functional groups, preferably under catalytic conditions, and be readily generated from commercially available and economical starting materials. Of course, such an ideal oxidant has not yet been invented; however, the dioxiranes, which have risen to prominence during the past few decades, appear to fulfill these requirements in many respects. These three membered ring cyclic peroxides are very efficient in oxygen transfer, yet very mild toward the substrate and product. They exhibit chemo‐, regio‐, diastereo‐, and enantioselectivities, act catalytically, and can be readily prepared from a suitable ketone (for example, acetone) and potassium monoperoxysulfate (2KHSO 5 · K 2 SO 4 · Caroate ® , Oxone ® , or Curox ® ), which are low‐cost commercial bulk chemicals. Throughout the text KHSO 5 is used to specify this oxygen source, rather than refer to one of the commercial trade names. Isolated dioxiranes (as solutions in the parent ketones) perform oxidation under strictly neutral conditions so that many elusive oxyfunctionalized products have been successfully prepared in this way for the first time. Epoxidations, heteroatom oxidations, and X‐H insertions constitute the most investigated oxidations by dioxiranes. An overview of these transformations is displayed in a rosette scheme. These preparatively useful oxidations have been extensively reviewed during the last decade in view of their importance in synthetic chemistry. This chapter deals mainly with the epoxidation of carbon‐carbon double bonds [π bonds in simple alkenes and with these electron donors (ED), electron acceptors (EA), and with both ED and EA] with either isolated or in situ generated dioxiranes. In view of the vast amount of material on alkene oxidation, the epoxidation of the double bonds in cumulenes (allenes, acetylenes) and arenes is covered in a separate chapter, together with the oxidation of heteroatom functionalities (nonbonding electron pairs), X‐H insertions (σ bonds) and transition‐metal complexes.

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Asymmetric Epoxidation of Electron‐Deficient Alkenes

Porter

Skidmore

2009

Organic Reactions

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Asymmetric epoxidation reactions have the distinction of being among the first enantioselective transformations to be widely sued in organic synthesis. The Sharpless asymmetric epoxidation is arguably one of the most important methods for the synthesis of enantiomerically enriched intermediates uses en route to a wide range of synthetic targets. To date most examples have employed electrophilic oxidizing agents and are thus applicable to electron‐neutral or electron‐rich double bonds. On the other hand alkenes substituted with electron‐withdrawing groups often react inefficiently with electrophilic oxidizing agents; such alkanes are more readily epoxidized using nucleophilic oxidants. The Weitz‐Scheffer epoxidation of alpha,beta‐unsaturated ketones to the corresponding epoxy ketones using basic hydrogen peroxide is the classical nucleophilic epoxidation reaction. This chapter considers the more general case of the conversion of an electron deficient alkene into the corresponding epoxide in an enantioselective fashion. Only methods based on chiral reagents or catalysts are covered. This review covers the literature to the end of 2005.

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Stereoselective epoxidations of vinylogous esters/carbonates directed by the 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl auxiliary: a route to near stereopure tertiary alcohols bearing functional arms

Cited by 12 publications

References 13 publications

Carbohydrate Bis-acetal-Based Substrates as Tunable Fluorescence-Quenched Probes for Monitoring exo-Glycosidase Activity

Carbohydrate Bis-acetal-Based Substrates as Tunable Fluorescence-Quenched Probes for Monitoring exo-Glycosidase Activity

Dioxirane Epoxidation of Alkenes

Asymmetric Epoxidation of Electron‐Deficient Alkenes

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