Furanosides

Our present evidence suggests that (193) is a single diastereomer although the precise structure is at this time unknown. However, de- 

These cyclohexano pyranosides, cyclopentano furanosides, and their transformation products promise to be valuable synthons judging from recent efforts directed towards biomimetic synthesis of camptothecin (196) and its analogues from the congener (195) by Hutchinson and co-workers 61). 

It will be of interest to see how successfully the chiral information can be transmitted from the original sugar to the complex polycyclic systems and studies directed with this objective in mind are in progress in the authors laboratory. 

Anderson, R. C., and B. Fraser-Reid A Synthesis of Optically Pure Avenaciolide from D-Glucose. The Correct Stereochemistry of the Natural Product. J. Amer. Chem. Soc. 97, 3870 (1975). 

----A Synthesis of Naturally Occurring (—)-Isoavenaciolide. Tetrahedron Letters 

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Galactose methyl furanoside H NMR, 4, 579 <64CC369> of-Glucose methyl furanoside H NMR, 4, 579 (64CC369)... 

LiBF4, CH3CN, 70°, 3-8 h, 81-90% yield. This system of reagents also cleaves benzylidene acetals. Conventional reagents failed to cleave these glycosides. It is interesting to note that the /3-anomers are cleaved more rapidly than the a-anomers and that the furanoside derivatives are not cleaved. 

The dithioacetal can be converted to an 0,5-acetal."" The mixed acetals were then used to prepare furanosides. 

Mosher and coworkers have adopted this strategy for the enandoselecdve synthesis of 2,3-thdeoxy-3-nitro-furanosides and pyranosides using chirM nitronate dianions, as shown in Eq. 5.5."... 

Treatment of l,4 3,6-dianhydro-D-glucitol with boron trichloride gives l,6-dichloro-l,6-dideoxy-D-glucitol (20). Although methyl 6-chloro-6-deoxy-a-D-glucopyranoside (isolated as the tribenzoate) could be isolated from the reaction of methyl 3,6-anhydro-a-D-glucopyranoside with boron trichloride (21), the application to the isomeric furanoside derivative led to complex results. 

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. 

The 5-deoxy isomer, methyl 5-deoxy-/ -D-xt/Zo-furanoside (6), gives a mass spectrum (Figure 3) which contains no molecular-ion peak, but does contain peaks at m/e 117 [119] and m/e 116 [117] for the losses of the C-l methoxyl group and a molecule of methanol, respectively. 

Methyl 5-deoxy-D-xt/Zo-furanoside. . 207 Methyl 6-deoxy-a-D-glucopyranoside 126 Methyl 4-deoxy-a-D-xylo-... 

Intermolecular reaction of the mannose-derived 2,3-0-isopropylideiie-a-D-/y.vc>-pentodialdo-l,4-furanoside 13 affords a diastereomeric mixture of nitroalcohols 14. Upon fluoride-catalyzed desilylation, a stereoisomerically pure nitrocyclitol 15 was obtained from a successive intramolecular nitroaldol reaction as a consequence of the reversibility of the nitroaldol reaction which, in this case, allows the equilibration of isomers through open-chain intermediates33. 

Chiral tricyclic compounds have been prepared by thermal and Eu(fod)j-catalyzed cycloadditions of furanosidic a,-unsaturated aldehydes 26-29 (Figure 3.4) with cyclopentadiene (18) [31]. The diastereofacial selectivity depends markedly on the stereochemistry of the anomeric benzyloxy and methoxy groups. 

The preparation of glycosyl fluorides is described next. Aiming to have a convenient glycosyl donor convertible into 1,2-CM-furanosides, Mukaiyama and coworkers prepared 2,3,5-tri-O-benzyl-yS-D-ribofuranosyl fluoride (36y3) by treatment of a protected D-ribofuranose (35) with 2-fluoro-1 -meth-ylpyridinium tosylate (FMPTs) the total yield was raised by anomerizing the simultaneously produced a-1-fluoride (36a, 7, p 66, 72.f 24 Hz) to 36 (7, F 63.5 Hz, 72,F very small ) by treatment with BF3-OEt2. 

C-(Trifluoromethyl)-gulo- (570) and -talo-furanosides 571 were pre-pared from 3-trifluoromethyl-A -butenolide (569) through a sequence of reactions. 

D-Arabinose occurs in arabinogalactans and arabinomannans elaborated by Mycobacterium species. When this had been determined, for example, for some arabinomannans, it was found to be furanosidic and a-linked. The arabinogalactan from Mycobacterium tuberculosis,however, contains both a- and y -linked D-arabinofuranosyl residues. It also occurs in the a-form in the LPS from Pseudomonas maltophila strain NCIB 9204. l-Arabinose is a component of the LPS from the purple, sulfur bacterium Chromatium vinosum. °... 

Deoxy-L-galactose (L-fucose) is common, and has only been found as the a- or )3-pyranoside. The rare D-fucose has, however, been found both as a-pyranoside, in the LPS frorn Pseudomonas cepacia serotypes B and E, and as a-furanoside, in the cell-wall antigen from Eubacterium saburreum L 452 and the O-antigens from different strains of Psuedomonas syrin-gae The a-furanoside, as in 3, has a cis relationship between the aglycon and OH-2. The corresponding P form has not yet been found. 6-Deoxy-o-and -L-talose are components of the extracellular polysaccharides from some strains of Butyrivibrio fibrisolvens and of the LPS from some strains of E. coli respectively. 

Y. pseudotuberculosis VB, however, the same sugar is a-furanosidic. The LPS from other species of Yersinia contain 6-deoxy-o-gulose, which is a-pyranosidic in the LPS from Y. enterocolitica serovar 0 6,31. 

In addition to the sugars discussed in this Section, a number of glyculo-sonic acids will be discussed in Section V. D-t/ireo-Pentulose ( o-ribulose ) is a component of some LPS from Pseudomonas and Yersinia species for example, that from Y. enterocolitica 0 5,27, and occurs as -D-furanosidic terminal groups (16). 

The effect of lactone ring-size on the inhibition was studied, for N-acetyl-)3-D-glucosaminidase from bovine epididymis, with lactones and lactone derivatives unable to undeigo ring-isomerization, by Pokomy and co-workers. From a comparison of Kj values for 2-acetamido-2-deoxy-D-glu-cono-1,5-lactone (0.45 nM) with the 1,4-lactone (4.5 fiM) and of Kj for the methyl ) -furanoside with that for the pyranose (4 mM), it was concluded that the 1,4-lactone has an 10-fold lower inhibitory potency than the 1,5-lactone. The weak inhibition by the 5,6-O-isopropylidene derivative of the... 

Since carbohydrates constitute an inexpensive and highly modular chiral source for preparing chiral ligands," Claver et al. have reported the use of a series of thioether-phosphite" and thioether-phosphinite furanoside ligands" in the test palladium-catalysed allylic substitution reaction. In the first type of ligand, a systematic variation of the donor group attached to the carbon atom C5 indicated that the presence of a bulky phosphite functionality had a positive effect on the enantioselectivity. Indeed, the enantioselectivity was controlled mainly by the phosphite moiety. This was confirmed by the use of a ligand... 

Test reaction with furanoside thioether-phosphite or -phosphinite ligands. 

Furanoside thioether-phosphinite ligand for Pd-catalysed allylic substitutions of acyclic and cyclic allylic substrates. 

Scheme 8.4 Hydrogenations of olefins with furanoside thioether-phosphinite ligands.

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