Novel Glycosylation of Aromatic Amines Through 1, 2-Anhydrosugars (original) (raw)
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ChemPlusChem, 2020
C-glycosides represent an important group of naturally occurring glycosylation derivatives but are also efficient mimetics of native O-glycosides. Here, a one-pot four-component methodology is described toward a library of N-alkylated C-glycosyl amino acid derivatives comprising seven different isopropylidene-protected carbohydrate units. The applied methodology tolerates different amines and isocyanides and provides access to Ugi products in yields up to 85 %. X-ray analysis of selected products bearing three different carbohydrate motifs and comparison of their crystal structures with similar ones deposited in Cambridge Crystallographic Database revealed that four structures adopt different conformations, mostly not typical for peptide structures. This property opens the possibility to exploit here described N-alkylated C-glycosyl amino acid derivatives as templates to access different biotic and abiotic secondary structures.
Tetrahedron, 1998
A general method for the stereoselective coupling of unprotected oligosaccharides with any substrate containing a N,O-disubstituted hydroxylamine group is described. The cyclic nature of the oligusaccharide reducing unit is preserved and the substrate glycosylated with high diastereoselectivity to sugar through an amino (N[OR2]-) or an aminoxy (N[RI]-O-) linkage. Due to the uniquely high chemical reactivity and specificity of disubstituted hydroxylamine toward the sugar reducing end, neither protecting groups nor activation methods are required to perform the reaction in aqueous solution. The characteristic features and the scope of this new type of glycosylation reaction are exemplified for the chemoselective synthesis of model glycopeptides.
A diversity oriented one-pot synthesis of novel iminosugar C-glycosides
A mild and highly efficient one-pot method has been developed for the stereoselective synthesis of structurally diverse novel iminosugar C-aryl glycosides. The generality of this methodology is demonstrated with a wide variety of aryl nucleophiles and amines. The synthetic potential of this methodology is further shown in the domino synthesis of iminosugar based hybrid molecules.
European Journal of Organic Chemistry
A comprehensive study of the preparation and reactivity of N‐tert‐butanesulfinyl glycosylamines with simple Grignard and organo lithium reagents in batch vs. continuous flow chemistry is reported. As they readily react as latent imine equivalents with a variety of carbon nucleophiles, these carbohydrate derivatives constitute very useful precursors for the diastereoselective synthesis of bioactive compounds such as iminosugar‐C‐glycosides. A hybrid protocol, involving the addition of benzylmagnesium chloride to a (SR)‐arabinofuranosylamine substrate in flow, at room temperature, combined with a cyclization protocol in batch is also described for the first time. Of note, this semi‐continuous flow process shortens the synthesis of imino‐C‐glycoside scaffolds to a single workday.
InBr3-Catalyzed Cyclization of Glycals with Aryl Amines
Angewandte Chemie International Edition, 2003
Dedicated to Professor Goverdhan Mehta on the occasion of his 60th birthday Glycals are ambident electrophiles capable of reacting with various nucleophiles such as alcohols, malonates, and silyl nucleophiles under the influence of acid catalysts or oxidants to produce 2,3-unsaturated glycosides. [1, 2] In recent times, indium halides have emerged as versatile Lewis acid catalysts imparting high regio-, chemo-, and diastereoselectivity to a variety of organic transformations. [3] Compared to conventional Lewis acids, indium tribromide, in particular, has advantages of low catalyst loading, moisture stability, and
Organic Letters, 2009
In the Rh 2 (OAc) 4-catalyzed amidoglycosylation of glucal 3-carbamates, anomeric stereoselectivity and the extent of competing C3-H oxidation depend on the 4O and 6O protecting groups. Acyclic protection permits high α-anomer selectivity with further improvement in less polar solvents, while electron-withdrawing protecting groups limit C3-oxidized byproducts. Stereocontrol and bifurcation between alkene insertion and C3-H oxidation reflect an interplay of conformational, stereoelectronic, and inductive factors. 2-Amino sugars having a 2,3-cis stereo array include N-acetylmannosamine (ManNAc, 1), which is the biosynthetic precursor of the sialic acids, 1 and 2-allosamine, a constituent of the potent chitinase inhibitor allosamidin (2) 2 and a useful ligand scaffold (3) 3 for asymmetric catalysis. The challenge of stereoselective C2-N bond construction is acute in these systems, and control of anomeric configuration in the preparation of glycoside derivatives is desirable. Synthetic methods based on intermolecular additions to glycals typically place the C2-N group trans to the C3-oxygen substituent. 4 Gin's activated-sulfoxide-mediated acetamidoglycosylation 5 of glucals is an exception, producing ManNAc structures, though with N-acetylglucosamine (GlcNAc) byproducts. 5c As an alternative, 6 we have used intramolecular nitrogen atom delivery from allal 3azidoformates, 7 allal 3-carbamates, 8 and glucal 3-carbamates 9 to establish the 2,3-cis relationship. With the 3O-carbamoyl glycals, we extended Du Bois's C-H amidation method 10 to alkene insertion, 11,12 a new reaction of allylic carbamates. 13 Mechanistic studies 14 imply that these conditions produce rhodium nitrenoids having reactivity strikingly analogous to metal carbenoids. 15 With iodosobenzene (PhIO) 16 instead of PhI(OAc) 2 as the oxidant, we achieved in situ glycosylation of alcohols without nucleophilic competition from acetate, an overall amidoglycosylation process.
Enzymatic Glycosylation of Small Molecules: Challenging Substrates Require Tailored Catalysts
2012
Abstract Glycosylation can significantly improve the physicochemical and biological properties of small molecules like vitamins, antibiotics, flavors, and fragrances. The chemical synthesis of glycosides is, however, far from trivial and involves multistep routes that generate lots of waste. In this review, biocatalytic alternatives are presented that offer both stricter specificities and higher yields. The advantages and disadvantages of different enzyme classes are discussed and illustrated with a number of recent examples.
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Organic & biomolecular chemistry, 2014
A 1,2-cis-alkyl glycosidation protocol that makes use of unprotected phenyl 1-thioglycosyl donors is reported. Glycosylation of various functionalized alcohols was accomplished in moderate to high yield and selectivity to give the 1,2-cis-glycosides. In order to quickly develop optimum glycosylation conditions, an FIA (flow injection analysis)-ESI-TOF-MS method was developed that enabled rapid and quantitative evaluation of yield on small scale. This methodology, coupled with NMR spectroscopy, allowed for rapid evaluation of the overall reactions.