Diversity-oriented synthesis of enantiopure furofurans from carbohydrates: an expedient approach with built-in michael acceptor, masked aldehyde and leaving group in a single sugar derivative

A single sugar molecule containing three functional groups, namely a masked aldehyde, a Michael acceptor and a leaving group, reacts with a series of β-dicarbonyl compounds and related reagents to form up to three new bonds and up to three new stereocenters. The configuration of the sugar derivative controls the diastereoselectivity in the formation of all the new bonds without a requirement for any external reagent for asymmetric induction. This "Chiral pool" based diversity-oriented synthetic strategy has led to the formation of a series of furofurans based on different scaffolds and with appendage variations, and also to a hitherto unknown family of bicyclic 3,8-dioxabicyclo[4.2.1]nonanes

Furo[2,3-c]pyrans from a vinyl sulfone modified methyl 2,6-O-anhydro-α-D-hexopyranoside: an experimental and theoretical investigation

A vinyl sulfone modified bicyclic sugar molecule undergoes efficient Michael addition of hetero- and carbon nucleophiles to afford single diastereomers. The same molecule consisting of two other masked functional groups, namely an aldehyde and an oxocarbonium ion, turned out to be a unique synthetic intermediate. The adducts generated from this Michael acceptor and a series of β-dicarbonyl compounds and related reagents after acid treatment afforded a new class of furo[2,3-c]pyrans, forming up to three new bonds and three stereocenters. In-built chirality centers of the sugar derivative controlled the diastereoselectivity of formation of all new bonds without the requirement for any external reagent for asymmetric induction. DFT calculations revealed the formation of furopyrans as the only possible products, which corroborates the experimentally observed results

Synthesis of 1,8-dioxooctahydroxanthene C-nucleosides

Since reactions between carbohydrates and cyclic 1,3-dicarbonyl compounds do not produce 1,8-dioxooctahydroxanthenes in general, reaction strategies have been devised to generate new 1,8-dioxooctahydroxanthene C-nucleosides by reacting sugars masked with acid-labile protecting groups and with free hydroxyl groups with 1,3-cyclohexanedione or dimedone. Some of these compounds are more cytotoxic to the cancer cells than against normal fibroblasts

An experimental and theoretical study on the remarkable influence of protecting groups on the selectivity of addition of amines to vinyl sulfone-modified hex-2-enopyranosides

Although phenylmethylene-protected vinyl sulfone-modified carbohydrate 2α reacts with both primary and secondary amines in Michael fashion to afford aminated products, only primary amines react with the dibenzyl-protected 3α, 6-O-trityl-protected 4α, and unprotected 5α, highlighting for the first time the remarkable influence of protecting groups on the reaction patterns of vinyl sulfone-modified carbohydrates. The quantum chemical calculations suggest that the Michael addition of amines and proton transfer to vinyl sulfone-modified carbohydrates 2α and 5α are possible via relay process in a concerted mechanism. These calculations reveal that the addition of primary amines to vinyl sulfone-modified carbohydrate is preferential due to the low activation energy barriers, whereas the addition of secondary amines has relatively higher activation energy barriers. The theoretical conclusions are in line with the experimental observations

Synthesis of vinyl sulfoxide-modified pent-2-enofuranosides and hex-2-enopyranosides and preliminary studies of their reactivity

Vinyl sulfoxide-modified pent-2-enofuranosides and hex-2-enopyranosides have been synthesized by using a controlled oxidation of C-3-deoxy-C-3-thioaryl furanosides and pyranosides, respectively, followed by mesylation of the C-2-hydroxyl group and elimination. In the furanose system, both diastereomers were formed in almost equal ratio, whereas the pyranose ring imposed diastereoselectivity of oxidation of the sulfur atom to produce only Ss isomers in good overall yields. Vinyl sulfoxide-modified 2-enofuranosides were treated with NaCH2NO2 to obtain C-2 branched chain sugars. Furanosyl sulfoxides yielded products that were similar to the adducts obtained by treatment of the corresponding sulfones with nitromethane. The sulfinyl group in thepyranosides influenced the diastereoselectivity of addition to produce adducts that differed from the products obtained from the corresponding vinyl sulfones under similar reaction conditions

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Not AvailableSeverity of arsenic toxicity was reported to vary depending on its species. The present study reflects the status of different species of arsenic in goat following long-term exposure of arsenic leading to hepatic damage. The experiment was conducted with six black Bengal goats, which were administered with sodium arsenite orally at a dose rate of 2 mg kg 1 daily for 84 days. Faeces, urine, hair and blood samples were collected from those animals at 14 days interval. Excretion of total arsenic was reduced from 56 days onwards through both faeces and urine indicating higher accumulation of arsenic in body. The speciation study revealed that urinary arsenic was mainly of organic type, whereas hair accumulated almost equal proportion of arsenite, arsenate and organo arsenicals. Goats excreted high proportion of organo arsenicals through faeces possibly due to hepatobiliary secretion of organo arsenic into the gut. Significantly elevated serum alanine aminotransferase and aspartate aminotransferase activities (p < 0.05) alongwith histopathological changes in liver indicated hepatotoxicity. The arsenite fraction increased and organic proportion decreased in urine as the time progressed, which indicates that arsenite gets methylated in liver of goat. The study thus alluded that the toxicity of arsenic would aggravate if the animals were exposed for long time as the hepatotoxicity progressed resulting in decreased methylation and formation of organo arsenicals and decreased excretions through urine.ICAR-NAI