Neighboring group effects were investigated in gluco- and manno-configured thioglycosides under NIS/TfOH activation. Donors possessing a 2-O-benzoyl group that are capable (1,2-trans) and incapable (1,2-cis) of exerting nucleophilic push were compared with donors possessing a participatory neutral 2-O-benzyl group. By using competition experiments between sets of glycosyl donors the direct effect of neighboring group participation and the electron withdrawing effect of the 2-O-benzoyl group could be separated. The study brings insight into how the stereochemistry of the 1 and 2 position and how the nature of the aglycon (Ph or Et) have a pronounced effect on glycosyl donor reactivity.
α-d-Gal-cyclophellitol cyclosulfamidate is a new class of neutral, conformationally-constrained competitive glycosidase inhibitor that stabilizes α-gal A and prevents its degradation both in vitro and in cellulo by mimicry of the Michaelis complex conformation.
Gas-phase action and fluorescence spectroscopy of fluorescein anions and two derivatives reveal important information on what determines the Stokes shift.
A high-yielding palladium-catalyzed
C–S cross-coupling is
presented for utilization in carbohydrate chemistry as a key transformation
for attachment of a second chelating sulfur atom that allows the exploitation
of a latent–active glycosylation strategy with Cu(OTf)2 as the promoter. The novel approach employs o-Br-benzyl thioglycosides as latent glycosyl donors and o-SMe-benzyl thioglycosides as the active counterparts.
A novel Ferrier-type carbocyclization is reported. It involves a carbohydrate-derived lactone acetal synthesized from methyl α-d-glucopyranoside, which upon treatment with excess vinylmagnesium bromide provides a highly substituted carbocyclic product as a single stereoisomer. The yield is greatly increased when N,N,N',N'-tetramethylethylenediamine is added to the reaction mixture. Optimized reaction conditions have been applied to lactone acetals derived from other carbohydrates. Based on the obtained results, a possible reaction mechanism has been proposed. Furthermore, scalability of the reaction up to 15 g scale and derivatization of the carbocyclic product has been demonstrated, including the formation of a rare trans-bicyclo[4.3.0]nonene scaffold via a ring-closing metathesis. The structure of this and all carbocyclic products were confirmed by X-ray crystallographic analysis.
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