A vinyl sulfone-modified carbohydrate mediated new route to aminosugars and branched-chain sugars

Vinyl sulfone-modified carbohydrates: Michael acceptors and 2π partners for the synthesis of functionalized sugars and enantiomerically pure carbocycles and heterocycles

Increasing demands for molecules with skeletal complexity, including those of stereochemical diversity, require new synthetic strategies. Carbohydrates have been used extensively as chiral building blocks for the synthesis of various complex molecules. On the other hand, the vinyl sulfone group has been identified as a unique functional group, which acts either as a Michael acceptor or a 2π partner in cycloaddition reactions. A combination of the high reactivity of the vinyl sulfone group and the in-built chiralities of carbohydrates has the potential to function as a powerful tool to generate a wide variety of enantiomerically pure reactive intermediates. Since CS bond formation in carbohydrates is easily achieved with regioselectivity, further synthetic manipulations of these thiosugars has led to the generation of a wide range of vinyl sulfone-modified furanosyl, pyranosyl, acyclic, and bicyclic carbohydrates. Several approaches have been studied to standardize the preparative methods for accessing vinyl sulfone-modified carbohydrates at least on a gram scale. Reactions of these modified carbohydrates with appropriate reagents afford a large number of new chemical entities primarily via (i) Michael addition reactions, (ii) desulfostannylation, (iii) Michael-initiated ring-closure reactions, and (iv) cycloaddition reactions. A wide range of desulfonylating reagents in the context of sensitive molecules such as carbohydrates have also been extensively studied. Applications of these strategies have led to the synthesis of (a) amino sugars and branched-chain sugars, (b) C-glycosides, (c) enantiomerically pure cyclopropanes, five- and six-membered carbocycles, (d) saturated oxa-, aza-, and thio-monocyclic heterocycles, (e) bi-and tricyclic saturated oxa and aza heterocycles, (f) enantiomerically pure and trisubstituted pyrroles, (g) 1,5-disubstituted 1,2,3-triazolylated carbohydrates and the corresponding triazole-linked di- and trisaccharides, (h) divinyl sulfone-modified carbohydrates and densely functionalized S,S-dioxothiomorpholines, and (i) modified nucleosides. Details of reaction conditions were incorporated as much as possible and mechanistic discussions were included wherever necessary.

Epoxides of d-fructose and l-sorbose: A convenient class of "click" functionality for the synthesis of a rare family of amino- and thio-sugars

The strained epoxide ring of oxirane-derived furanoside and pyranoside of d-fructose are regioselectively opened by various primary and secondary amines as well as azide to yield C4-alkylamino-C4-deoxy and the corresponding azido derivatives. The epoxide ring of a furanoside derived from l-sorbose, a C-5 epimer of d-fructose also afforded C4-amino and C4-azido analogues. All three epoxides generated piperazine linked disaccharides. These epoxides are also easily opened by p-tolylthiol to access thiosugars. One such thiosugar was converted to vinylsulfone-modified fructofuranoside and subjected to nucleophillic addition. A suitably designed vinyl sulfone-modified fructofuranoside having a leaving group at C-6, act as an efficient substrate for MIRC (Michael Initiated Ring Closure) reactions to construct cyclopropane skeleton in d-fructose. The strategy is general in nature and provides an easy access to cyclopropanated sugar derivatives. Thus, the easily accessible "spring loaded" epoxides of d-fructose and l-sorbose have been used as pivotal starting point for the synthesis of hitherto unknown modified carbohydrates.

Crystal structure of 6-(2-bromoacetamido)tetrahydro-2H-pyran-2,3,4,5-Tetrayl tetraacetate, C16H22BrNO10

[C16H22BrNO10], orthorhombic, P212121 (no. 19), a = 9.7453(13) Å, b = 9.9023(13) Å, c = 21.885(3) Å, V = 2111.9(5) Å3, Z = 4, R gt(F) = 0.0357, wR ref(F 2) = 0.0981, T = 296(2) K.

Synthesis of Branched-Chain Sugars with a DHAP-Dependent Aldolase: Ketones are Electrophile Substrates of Rhamnulose-1-phosphate Aldolases

Dihydroxyacetone phosphate (DHAP)-dependent rhamnulose aldolases display an unprecedented versatility for ketones as electrophile substrates. We selected and characterized a rhamnulose aldolase from Bacteroides thetaiotaomicron (RhuABthet) to provide a proof of concept. DHAP was added as a nucleophile to several α-hydroxylated ketones used as electrophiles. This aldol addition was stereoselective and produced branched-chain monosaccharide adducts with a tertiary alcohol moiety. Several aldols were readily obtained in good to excellent yields (from 76 to 95 %). These results contradict the general view that aldehydes are the only electrophile substrates for DHAP-dependent aldolases and provide a new C-C bond-forming enzyme for stereoselective synthesis of tertiary alcohols.

Enantiopure Trisubstituted Tetrahydrofurans with Appendage Diversity: Vinyl Sulfone- and Vinyl Sulfoxide-Modified Furans Derived from Carbohydrates as Synthons for Diversity Oriented Synthesis

Enantiomerically pure 2-substituted-2,5-dihydro-3-(aryl) sulfonyl/sulfinyl furans have been prepared from the easily accessible carbohydrate derivatives. The orientation of the substituents attached at the C-2 position of furans is sufficient to control the diastereoselectivity of the addition of various nucleophiles to the vinyl sulfone/sulfoxide-modified tetrahydrofurans, irrespective of the size of the group. The orientation of the substituents at the C-2 center also suppresses the influence of sulfoxides on the diastereoselectivity of the addition of various nucleophiles. The strategy leads to the creation of appendage diversity, affording a plethora of enantiomerically pure trisubstituted furanics for the first time.

1,1-Dioxothiomorpholines with asymmetric environments: protecting group directed diastereoselectivity of glyco divinyl sulfone cyclization

Formation of 1,1-dioxothiomorpholines from divinyl sulfone-modified pyranosides dramatically varied when benzylidene protection is replaced by benzyl protecting groups.

A versatile method for functionalizing surfaces with bioactive glycans

Microarrays and biosensors owe their functionality to our ability to display surface-bound biomolecules with retained biological function. Versatile, stable, and facile methods for the immobilization of bioactive compounds on surfaces have expanded the application of high-throughput "omics"-scale screening of molecular interactions by nonexpert laboratories. Herein, we demonstrate the potential of simplified chemistries to fabricate a glycan microarray, utilizing divinyl sulfone (DVS)-modified surfaces for the covalent immobilization of natural and chemically derived carbohydrates, as well as glycoproteins. The bioactivity of the captured glycans was quantitatively examined by surface plasmon resonance imaging (SPRi). Composition and spectroscopic evidence of carbohydrate species on the DVS-modified surface were obtained by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. The site-selective immobilization of glycans based on relative nucleophilicity (reducing sugar vs amine- and sulfhydryl-derived saccharides) and anomeric configuration was also examined. Our results demonstrate straightforward and reproducible conjugation of a variety of functional biomolecules onto a vinyl sulfone-modified biosensor surface. The simplicity of this method will have a significant impact on glycomics research, as it expands the ability of nonsynthetic laboratories to rapidly construct functional glycan microarrays and quantitative biosensors.

A surprising C-4 epimerization of 5-deoxy-5-sulfonylated pentofuranosides under Ramberg-Bäcklund reaction conditions

Treatment of methyl 5-deoxy-2,3-O-isopropylidene-5-(benzylsulfonyl)-β-D-ribofuranoside with CBr(2)F(2)-KOH/Al(2)O(3) afforded the corresponding olefinic sugar. The methyl- and the isopropyl-analogues in contrast underwent epimerization at C-4 to generate the α-L-lyxo derivatives.