Arabinose ester

Psidium guajava L. Fan Shi Lui (Guava) (fruit) Avicularin, guaijaverin, arabinose ester, amritoside, crataegolic acid, luteioic acid, argamolic acid.33 Treat dysentery and acute gastrointestinal inflammation. 

Fischer s original method for conversion of the nitrile into an aldehyde involved hydrolysis to a carboxylic acid, ring closure to a cyclic ester (lactone), and subsequent reduction. A modern improvement is to reduce the nitrile over a palladium catalyst, yielding an imine intermediate that is hydrolyzed to an aldehyde. Note that the cyanohydrin is formed as a mixture of stereoisomers at the new chirality center, so two new aldoses, differing only in their stereochemistry at C2, Tesult from Kiliani-Fischer synthesis. Chain extension of D-arabinose, for example, yields a mixture of D-glucose and o-mannose. 

The hydrolysis of zeaxanthin esters by a carboxyl ester lipase indeed enhanced both the incorporation of zeaxanthin in the micellar phase and uptake of zeaxanthin by Caco-2 cells. As mentioned earher, carotenoids can also be linked to proteins by specific bindings in nature and these carotenoid-protein complexes may slow the digestion process and thus make their assimilation by the human body more difficult than the assimilation of free carotenoids. Anthocyanins are usually found in a glycosylated form that can be acetylated and the linked sugars are mostly glucose, galactose, rhamnose, and arabinose. 

An Arbuzov reaction between gem-dibromocyclopropanes yields phosphonate esters (55) accompanied by debrominated compounds successful reaction requires the presence of traces of water (and is thus not the normal Arbuzov reaction) which, by studies with D2O, has been shown to supply the a-proton of (56), Normal Arbuzov reactions, using ethyl diphenyl phosphite, have been used to prepare a phosphonate isostere of B-D-arabinose-1,5-diphosphate. ... 

D-Lyxose yielded a D-lyxosyl chloride 2,3,4-tri(chlorosulfate) which, on treatment with chloride ion, led to a dichlorodideoxy compound, most probably 2,4-dichloro-2,4-dideoxy-L-arabinose.353 D-Glucose gave a compound presumed to be 4,6-dichloro-4,6-dideoxy-a,/3-D-galactosyl chloride 2,3-di(chlorosulfate),360 and D-xylose afforded a monochloromonodeoxy derivative formulated, on indirect evidence, as 4-chloro-4-deoxy-L-arabinopyranosyl chloride 2,3-di(chlorosulfate).360 3,4-Dichloro-3,4-dideoxy-/3-D-ribopyranosyl chloride 2-(chlorosulfate) was the major, and 4-chloro-4-deoxy-a-D-xylopyranosyl chloride 2,3-di(chlorosulfate) the minor, product from the reaction of L-arabinose with sulfuryl chloride at room temperature for 24 hours.357,361 It has been established that, on reaction with sulfuryl chloride at low temperature, crystalline a-D-xylopyranose and /3-D-lyxopyranose afford, respectively, the 2,4,6-tri(chlorosul-fate)s of /3-D-xylopyranosyl chloride and a-D-lyxopyranosyl chloride,362 363 confirming that substitution at C-l occurs by an Sn2 process on a l-(chlorosulfuric) ester intermediate. 

The procedure that Kuhn and Baschang99 had reported for the synthesis of NeuAc was extended by Hershberger and Binkley100 to a synthesis of KDO, as follows. Condensation of di-ter -butyl oxalacetate (85 see Scheme 25) with D-arabinose gave the epimeric mixture of lactone esters, 86 and 87, which was separated by fractional recrystallization. When 86 was heated in aqueous solution, the enol lactone, 88, was produced from 87, an enol lactone diastereomeric with 88 was obtained under these conditions. Compound 88 was converted into ammonium KDO by treatment with aqueous ammonia. 

Aldono-1,5-lactones and free aldonic acids react with alcohols in the presence of hydrogen chloride to give the corresponding alkyl aldonates (84). The reaction is slower with 1,4-lactones. Because esterification takes place very slowly in the absence of an acidic catalyst, aldonic acids and their lactones may be recrystallized from boiling alcohols without appreciable esterification (85). However, in some instances, alkyl esters are formed under these conditions. For example, essentially pure ethyl L-mannonate was isolated (6.4% yield) from the mother liquors of crystallization L-man-nono-1,4-lactone, obtained by Kiliani synthesis from L-arabinose (86). Similarly, repeated recrystallization from ethanol of crude 2,3,4,6-tetra-O-acetyl-D-glucono- 1,5-lactone afforded the corresponding ethyl gluconate derivative (87). 

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