Hexofuranose analogs

The mass spectra of methyl 3-deoxy-p-v-tkreo-pentopyrano-side, methyl 4-deoxy-j3-T>-thieo-pentopyranoside, and 5-deoxy-fi-D-xylo-furanoside are discussed and compared fragmentation paths are sufficiently different to allow identification on the basis of their mass spectra. On the other hand, the mass spectra of methyl 2- and 3-deoxy-5-O-methyl-f3-i>-erythro-pentofuranosides do not exhibit fragmentation differences. The mass spectra of 3-deoxy-l,2 5,6-di-O-isopropylidene -d-xylo - hexofuranose, 5- deoxy -1,2-0-isopropylidene-D-xy o-hexofuranose, and 6-deoxy-l,2-0-iso-propylidene-D-glucofuranose show prominent differences, even between the 5- and 6-deoxy isomers. The interpretation of the spectra was aided by metastable-ion peaks, mass spectra of DzO-exchanged analogs, and the mass spectrum of an O-isopropylidene derivative prepared with acetone-d6. 

Several observations regarding this aspect have been published, and are briefly mentioned here. 5,6-Dideoxy-6-C-phosphono-D-arabino-hexofuranose (135), an isosteric phosphonate analog of D-arabinose 5-phosphate, is apparently converted, in the presence of enolpyruvate phosphate, into 3,8,9-trideoxy-9-C-phosphono-D-mcmno-2-nonulosonic acid (136) under catalysis by KDO 8-phosphate synthetase from Escherichia coli K 235. Compound 136, an isosteric phosphonate analog of KDO 8-phosphate, is a product inhibitor of the synthetase, and, by the nature of the phosphonate group, is not subject to dephosphorylation as catalyzed by KDO 8-phosphate phosphatase156 (see Scheme 40). Compound 119 (see Scheme 33) is a weak inhibitor of KDO 8-phosphate synthetase.81 KDO inhibits KDO 8-phosphate phosphatase,139 and D-ribose 5-phosphate has an inhibitory... 

An analogous methyl 2,3-dideoxy-3-C-methylene-a-L-en/thro-hexopyranoside (20) was obtained10 from methyl 4,6-O-benzylidene-2-deoxy-a-L-eri/t/iro-hexopyranosid-3-ulose (19) it was used in the synthesis of olivomycose (see p. 242). There was also reported32,34 the preparation of 3-deoxy-l,2 5,6-di-0-isopropylidene-3-C-methyl-ene-a-D-rifco-hexofuranose (22) from 1,2 5,6-di-0-isopropylidene-a-D-nfeo-hexofuranos-3-ulose (21) in about 60% yield, followed by transformations into branched-chain sugar derivatives, including... 

The formation of the pyridinol is prevented if, in the step 19 to 20, no anion can be eliminated from C-3 this is the case with 5-amino-3,5-dideoxy-l,2-0-isopropylidene-a-D-er /thro-pentofuranose, which, on acid hydrolysis, afFords only the Amadori rearrangement product and no pyridine derivative. The reaction then proceeds, according to the above mechanism, in only one direction from 19. The 3-deoxypentose is prepared, in a manner analogous to the formation of 15, from 3-deoxy-l,2-0-isopropylidene-a-D-riho-hexofuranose through catalytic reduction of the phenylhydrazone of its periodate-oxidation product. ... 

Deoxy-6-thio-D-a yfo-hexose forms a 1,6-anhydro compound analogous to 270. S-Acetyl-5-deoxy-l,2-0-isopropylidene-6-thio-a-D-xyZo-hexofuranose is obtained either by nucleophilic displacement on the corresponding 6-p-tolylsulfonyloxy compound with potassium thioacetate or by the photochemical addition of thioacetic acid to... 

Reduction of methyl 4,6-0-benzylidene-2,3-di-0-p-tolylsulfbnyl-a-D-glucopyranoside with lithium aluminum hydride in tetiahydrofuran affords methyl 4,6-0-benzylidene-3-deoxy-a-D-fifco-hexopyranoside (in 66% yield) by a mechanism analogous to that proposed by Overend and coworkers for the formation of 5-deoxy-l,2-0-isopropyli-dene-a-D-x /lo-hexofuranose. With the corresponding /3-d anomer, hydride reduction in tetrahydrofuran proceeds less readily, giving methyl 4,6-0-benzylidene-3-deoxy-/8-D-rtho-hexopyranoside in 38% yield. This compound was also obtained (in 22% yield) when hydride reduction was performed in p-dioxane, together with a second crystalline compound, identified as methyl 4,6-0-benzylidene-2,3-dideoxy-/3-D-er /thro-hexoside formed by direct displacement at C-2 and C-3 with hydride. 

As far as the nitrogen analogs are concerned, l,6-anhydro-(6-aceta-mido-2,3-di-0-acetyl-5,6-dideoxy-/3-D-xf/lo-hexofuranose) (260) was isolated after acetylation of the equilibrium mixture prepared from the corresponding 6-amino-5,6-dideoxyhexofuranose the original mixture also contained the parent sugar and traces of two additional azepine compounds.784... 

The 1,2-0-isopropylidenehexofuranose 5,6-trithiocarbonates undergo desulfurization with Raney nickel in the same manner as do the 5,6-episulfide analogs, with the formation of 5,6-dideoxy-l, 2-0-isopropylidene- t-D-a 2/Zo-hexofuranose (90). The 5,6-episulfides polymerize in aqueous alkali, presumably by a sequential, episulfide-cleavage reaction caused by thiolate anion and, for example, compound (84) gives a polymer, formu-... 

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