Hexos-5-ulose preparation

In the Lobry de Bruyn-Alberda van Ekenstein transformation (reviewed by Speck ) of a ketose to the epimeric aldoses, formation of the 3-deoxy-uloses is normally considered to be a side reaction, and both reactions are considered to proceed through a common intermediate, the 1,2-enediol of the sugar. Under the conditions used for preparation of the 3-deoxy-hexos-uloses from the diketose-(amino acids), the former were, however, the main products and the epimeric aldoses only minor products. Furthermore, under these conditions, both reactions were irreversible and the products so stable that the amounts of the two t3rpes of compound were a measure of their rates of formation. The rapid rate of decomposition of the diketose-(amino acids) was probably due to their ready enolization, even in the absence of strong alkali or acid, to give the 1,2-enolammonium compound... 

Treatment with base of the hexos-5-ulose 23, prepared from the acetal 22, gives mainly the inosose 24 with all the hydroxyl groups equatorial (Scheme 5) [13], and similarly the... 

Baker and Buss425 used the Pfitzner-Moffatt procedure (phosphoric acid-A /V -dicyclohexylcarbodiimide dimethyl sulfoxide) for the preparation of methyl 3-benzamido-4,6-0-benzylidene-3-deoxy-Q -D-uraZ) o-hexopyranosid-2-ulose and methyl 2-benzamido-4,6-(3-benzylidene-2-deoxy-a-i>n/ >o-hexo-pyranosid-3-ulose in yields of 90%. 

A quinone-dependent sugar oxidoreductase, purified from Agaricus bisporus, catalyzes C-2 and C-3 oxidation of D-glucose to o-arabino-hexos-2-ulose and preferentially to D-n fto-hexos-3-ulosc. The two aldoketoses accumulate transiently in the reaction mixture, being converted into the same end-product, D-eryt/zro-hexos-2,3-diulose. D-Galactose is oxidized exclusively at C-2 to produce D - /y.w - h c x o s - 2 - u 1 o s c.447 Fukui and Hochster448 prepared n-/vAo-hexos-3-ulose (219) by enzymic oxidation and hydrolysis of sucrose. 

D-n/)o-Hexos-3-ulose (219), treated with methanolic hydrogen chloride, afforded 238 and 239 as the main products.457 They were converted into the glycoside 240 by mild treatment with acid this product was further converted into D-n Zw-3-hexulose (241). The preparation of 241 by partial reduction of 219 was not practicable. 

H. P. Humphries and O. Theander, Reaction of D-ribo-hexos-3-ulose and 1,2 5,6-di-0-isopropylidene-a-D-ribo-hexo-l,4-furanos-3-ulose 3-hydrate with methanol in hydrogen chloride. A preparation of D-ribo-3-hexulose, Carbohydr. Res., 16 (1971) 317-325. 

Interruption of such a reaction at the intermediate stage should provide more-positive evidence for the mechanism proposed. Treatment of inositol cyclase with charcoal removed the NAD, and, when the enzyme was reconstituted, its properties were found to have been modified. By using this preparation, hydrogen from NADH-t was transferred to C-5 of both xyZo-hexos-5-ulose 6-phosphate (59) and L-sorbose 1-phosphate, giving a mixture of D-glucose-5-f 6-phosphate (58) with lL-mi/o-inositol 1-phosphate (61) or D-glucitol-5-f 6-phosphate, respectively.166 This shows that the enzyme can catalyze the partial reaction corresponding to reduction of the oxidized intermediate proposed. 

Incubation of dTDP-6-deoxy-D-xyZo-[U-l4C]hexos-4-ulose with the cell-free extract led to the same products II-IV as with dTDP-D-[U-,4C]glucose as substrate. Product III was isolated as the methyl glycoside from an incubation performed on a preparative scale. 

The preparation of some aldos-5-uloses, starting from hexose-5-enes was introduced by Helferich and Himmen in their synthesis of 6-deoxy-n-xylo-hexos-5-ulose. 

Deoxy-D-x2/Zo-hexos-5-ulose reduced cold Fehling solution and readily formed a bis[(p-nitrophenyl)hydrazone] at room temperature and was rather alkali-labile. It showed mutarotation. The structure was deduced from elemental analysis of the compound and its derivative, and from the mode of preparation. 

Recently, the 4-methyl ethers of (90A) and (91A), methyl 4-0-methyl-d-D-ara ino-hexopyranosidulose and methyl 4-0-methyl- 8-D-ri6o-hexo-pyranosid-3-ulose, respectively, have also been prepared by using chromium trioxide/acetone oxidation. The latter, which was preponderant, was obtained crystalline. 

Tetradentate Cu, Pt and Pd complexes of the l,2-bis(thiosemicarbazone) derived from 3-deoxy-D-eryrhro-hexos-2-ulose have been prepared, and some sugar analogues of cisplatin which incorporate a mono-N-sugar-substituted ethylene diamine unit have been synthesized. ... 

Other examples have been given of the preparation of branched-chain and extended-chain alkenes by application of Wittig reagents to sugar aldehydes and ketones,and the mass spectra of alkenes derived from 1,2 5,6-di-O-iso-propylidene-D-r/Z o-hexos-3-ulose have been described.Compound (25) was... 

Deoxy-4-0-jS-D-galactopyranosyl-D-erj rAro-hexos-2-ulose has been obtained by hydrazinolysis of its bis(benzoylhydrazone) derivative which was prepared from lactose. l,5-Anhydro-4-deoxy-D- /ycero-hex-l-en-3-ulose (7)... 

An Interesting paper on selective monobenzoylation of pento- and hexo-pyranosldes before and after.treatment with di- or tri-butyltln oxide is referred to in Chapter 7> as is the use of 3,4- -stannylene derivatives of a-L-arabinopyranosldes in the preparation of 3-coumaroyl esters. The brominolysls of such a derivative gave a glycosld-4 ulose from which a 4-amino- -deoxyarabinoside was produced (Chapter 9) The X-ray crystal structure of methyl 4,6- -benzylidene-2,3-0-dlbutylstannylene-a-D-mannoslde has been reported (see Chapter 22). 

Optimum conditions for the electro-oxidation of l,2 5,6-di-Q-isopropylidene-a-D-glucofuranose to the corresponding 3-uIose have been developed In a study of the hydration of methyl 4,6-0-benzylidene-2-bromo- and 2-chloro-2-deo) -a- and -D-xvlo-hexopvranosid-3-ulose in acetone solution, only the fl-D-xylo-derivatives were observed to hydrate and in another investigation the isomeric composition of freshly prepared D-ribo-hexos-3-ulose in DjO has been examined by H-n.m.r. spectroscopy. Full details have been published on the regioselective monooxidation of unprotected glycosides by reaction of Q-stannyl derivatives with bromine. ... 

A doubly linked 4,6-dideoxy-D-j/ rgo-hexos-2-ulose residue was identified in the cardenolide glycoside (1) isolated from Asclepias curassavica stems, and a branched hexos-4-ulose derivative isolated from Pittosporum tobira flowers is covered in Chapter 14. Oxidation (MCPBAAleOH) of unsaturated derivative (2) (obtained by base treatment of methyl 3,4-0-isopropylidene-2,6-di-0-methyl-P-D-galactopyranoside) afforded L-arabino-hexos-S-ulose derivative (3) and then (4) after acid hydrolysis. The hexopyranosid-3-uloses (5) have been prepared by oxidation (Cr03/Ac20/pyridine) of the corresponding 3-alcohols. ... 

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