Pentofuranosides

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. 

Figure 4. Mass spectrum of methyl 2-deoxy-5-0-methyl-f3-n-erythro-pentofuranoside (7).

Figure 5. Mass spectrum of methyl 3-deoxy-5-0-methyl-B-D-erythro-pentofuranoside (8).

A satisfactory result was obtained in AgOTf- or NIS/TfOH-activated condensation of S-benzothiazolyl pentofuranosides 93, 94 and 95 with l,2 3,4-di-isopropylidene-a-D-galactopyranose 96 and l,6-anhydro-3,4-isopropylidene-P-D-galactopyranose 97 as the acceptor to afford the corresponding disaccharides in moderate to good yields and stereoselectivity [445],... 

From their kinetic results Bishop and collaborators >8) calculated the velocity constants of the furanoside anomerisations of their seven aldoses (Table 1), and rationalised them in terms of ring conformations and group interactions. Thus, for example, in the extreme cases methyl a-D-arabinofuranoside (4), having the fewest non-bonded steric interactions, is the most stable pentofuranoside, while methyl p-o-lyxofurano-side (5), having the least stable ring, reacts most rapidly. 

Addition of a catalyst containing sulfuric acid and acetic anhydride to 3, 5 -di-0-acetylthymidine in acetonitrile results in an equilibrium mixture of a- and ]3-anomers that, after time, gave a substantial quantity of a diastereoisomeric mixture of fully acetylated open-chain nucleosides. These were of type 1.5 with 2 -deoxy and 4 -acetoxy substituents (93TL6779). Open-chain nucleoside was also obtained as well as the expected nucleoside when 5-nitrouracil was condensed with methyl-2,3-dideoxy-3-fluoro-5-0-(4-phenylbenzoyl)-]3-D-cryr/zro-pentofuranoside (94S516). 

In 2008, the research group of Singh reported the synthesis of imidazohum-based ionic liquids in which the chiral moiety was constituted of a pentofuranoside unit [79]. The 2,3,5-tri-O-benzyl-D-arabinofuranose 45, easily prepared from commercial D-arabinose in 75% yield following known procedures, was transformed... 

The dihydrofuran derivative 35 was also employed for the synthesis of ethyl 3-amino-3-deoxy-/3-DL-arafiino-pentofuranoside (40b). The synthesis was accomplished27 in three stages. By the action of calcium hypochlorite on 35, a chlorohydrin intennediate was formed which, on treatment with a base, afforded a mixture of the epoxides 37, 38,... 

Such compounds have been identified amongst the products of deamination, followed by reduction, of methyl 2-amino-2-deoxy-a-and -/3-D-glucopyranoside.89a Two methyl 2-deoxy-2-(hydroxy-methyl)pentofuranosides, epimeric at C-2, were detected in each case, and the results of deuterium-incorporation experiments suggested that the primary product was epimerized, probably during reduction with sodium borohydride. However, in the writer s opinion, the configurations assigned to the primary and epimerized products are incorrect and should be reversed. 

E. Reaction of Methyl Pentofuranosides with Sulfuryl Chloride ... 

To a cooled (dry ice-acetone) solution of the methyl pentofuranoside (1.7 g, 10 mmol) in dry pyridine (8 mL) and chloroform (20 mL) was added sulfuryl chloride (4 mL, 30 mmol) dropwise, with stirring. Cooling was continued for an additional 2 h, and then the... 

A detailed study of the methyl glycosidation of the four aldopentoses has been made by Bishop and Cooper,16 42 with the aid of gas chromatography of the esters of the resulting pentofuranosides and pentopyranosides. Three competing reactions were established for the formation of the furanosides (1) an irreversible formation of furanosides from the free sugars (2) an anomerization of the furanosides and (3) conversion of the furanosides into the pyranosides. (A fourth reaction, anomerization of the pyranosides, will not be considered here.)... 

The phenyl L-thioglycoside of the axenose donor 186 was synthesized from the methyl 2-deoxy-D-eryt/zro-pentofuranoside 185 (Scheme 54). 

S. Watanabe, J. Kavai, and M. Bobek, Cyano sugars synthesis by opening of an epoxide ring in pentofuranosides with diethylaluminium cyanide, J. Carbohydr. Chem., 14 (1995) 685-701. 

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