D-Ribopyranose derivatives

T. Yoshida, Y. Katayama, S. Inoue, and T. Uryu, Synthesis of branched ribofuranans and their sulfates with strong anti-AIDS virus activity by selective ring-opening copolymerization of l,4-anhydro-o -D-ribopyranose derivatives, Macromolecules, 25 (1992) 4051 1057. 

Conformalioda] EqiuHliria [Pg.62]

Also in D-ribopyranose derivatives there appears to be a conformational dependence of the geminal coupling. The numerical... 

To facilitate the n.m.r. studies of the series of D-ribopyranose derivatives, use was made of a facility for the electronic subtraction of spectra. The spectrum of a-D-ribopyranose tetrabenzoate, which is not known in the pure form, was obtained at 100 Me./sec. by electronic subtraction of the spectrum of /3-D-ribopyranose tetrabenzoate from the mixture of anomers using the Varian C-1024 computer. 

Thio-D-ribopyranose derivatives have been prepared by similar procedures. " " Thiolacetate replacement of the 5-substituent in methyl 2,3-0-isopropyhdene-5-0-p-tolylsulfonyl-/3-D-ribofuranoside (127), followed by saponification and acid hydrolysis in an inert atmosphere, gave a sirup formulated as 5-thio-D-ribopyranose (128) on the basis of its slow reaction with iodine acetylation converted it into a crystalline. 

In addition to the above mentioned 4J couplings, we have now observed several examples of couplings across five bonds—i.e. 5J. For example, the ribopyranose derivative (13) shows a coupling of ca. 0.1 Hz between Hx and H4. Further examples occur in the spectrum of 2,3,4-tri-0-acetyl-l,6-anhydro-/ -D-glucopyranose (12), where Ji,4 = ca. 0.1 Hz and J2,5 = 0.5 Hz. Whether it is significant that these couplings all occur between equatorially oriented protons must await further studies. 

The Michaelis-Arbuzov reaction of methyl 5-deoxy-5-iodo-2,3-0-isopropylidene-/ -D-ribofuranoside38 (43) with diethyl ethylphosphonite gave,35 in 80% yield, the 5-C-[(ethoxy)ethylphosphinyl] derivative which, on treatment with SDMA and then mineral acid, yielded (30%) 5-deoxy-5-C-[(RS)-ethylphosphinyl]-D-ribopyranose (44) as a mixture of diastereoisomers. These compounds showed no mutarotation in methanol during 24 h. Upon treatment with acetic anhydride-pyridine, the product, 44, was converted (90% yield) into a syrup, presumably consisting of four diastereoisomers of the peracetate 45, separation of which was not attempted. Treatment of 45 with sodium methoxide in methanol regenerated 44 quantitatively. 

D-Ribopyranose tetraacetate56 has been used as a derivative for the identification of D-ribose14 and, more recently, Hardegger, Schreier and El Heweihi57 have prepared dimethyl, ethylene and dibenzyl thioacetals (mercaptals) of D-ribose for this purpose. According to Zinner58 the di-n-propyl and diisobutyl thioacetals are particularly suitable derivatives for the identification of ribose. 

As mentioned above, the triacyl-/3-D-ribopyranosyl halides may react with alcohols in the presence of an acid acceptor to give orthoester derivatives. Thus Levene and Tipson56 showed that triacetyl-/3-D-ribopyranosyl bromide reacts with methanol in the presence of silver carbonate to give 3,4-diacetyl-D-ribopyranose methyl 1,2-orthoacetate (LXIV) while Klingensmith and Evans135 obtained an analogous compound (LXV) upon condensing dihydroxyacetone monoacetate with the same halide. The structures of these two orthoesters, LXIV and LXV, have recently been discussed by Pacsu.186... 

An example of a sugar derivative held rigidly in a skew conformation is 3-0-benzoyl-l,2,4-0-benzylidene-a-D-ribopyranose (10). 

The nature of the solvent and its polarity do not appear to affect in any regular way the position of the conformational equilibria for example, /3-D-xylopyranose tetrabenzoate, which exists in ace-tone-de (dielectric constant, e, = 20.7) as a 1 1 mixture of the CJ(d) and 1C(d) conformations, shows practically the same conformational population in a range of solvents, including benzene-rie = 2.3), toluene-dg ( = 2.4), chloroform-d (e = 4.8), pyridine-dg (e = 12.3), hexachloroacetone, and methyl sulfoxide-dg ( = 48.9). Similar results, showing negligible dependence of conformational populations on the polarity of the solvent, were obtained with jS-D-ribopyranose tetraacetate, tri-0-acetyl-/3-D-xylopyranosyl chloride, and some simpler derivatives of tetrahydropyran. In contrast, as the polarity of the solvent was increased, there was observed with methyl 2,3,4-tri-0-benzoyl-/3-D-xylopyranoside a broad trend in favor of that conformation having the C-1 substituent equatorially attached. 

This conformational change has also been detected in a pento-pyranoid system. Thus, although l-0-acetyl-3-benzamido-2,4-di-0-benzoyl-3-deoxy-3-C-(ethoxycarbonyl)-/3-D-ribopyranose (22) adopts the 1C(d) conformation in chloroform solution, the corresponding nucleoside derivative 23 exists preponderantly in the CJ(d) conformation. 

The confonnational mobility of a-cyclodextrin derivative 24 and some related compounds in solvents such as benzene, dichloromethane, and chloroform has been thoroughly investigated by dynamic n.m.r. spectroscopy, and the H-n.m.r. chemical shifts and coupling constants for a- and P-cyclodextiin and their permethyl ethers in neutral aqueous media have been assigned to obtain accurate data, the experimental spectra were analysed with the Raccoon spin simulation program. The structure of the copolymer obtained by treatment of l,4-anhydro-2,3-0-benzylidene-a-D-ribopyranose and l,4-anhydro-2,3-di-0-benzyl-a-D-ribopyranose with SbCls (see Chapter 5) has been determined from its C-n.m.r. spectrum and its optical rotation. ... 

Acetonation of D-ribose and D-arabinose using ethyl (or methyl) isopropenyl ether in DMF containing a trace of toluene-p-sulphonic acid has been reported. D-Ribose yielded principally 3,4-O-isopropylidene-jS-D-ribopyranose, together with other minor products such as 2,3-O-isopropylidene-D-ribofuranose, and D-arabinose gave mostly 3,4-0-isopropylidene-)3-D-arabinopyranose and some l,2 3,4-diacetal. D-Fucose and 6-0-methyl-D-galactose afforded 3,4-0-isopro-pylidene derivatives, in 40—60% yield, on treatment with acetone and anhydrous cupric sulphate. D-Ribose also yielded a 3,4-0-isopropylidene derivative (15—20%) on similar treatment, whereas 4,6-0-isopropylidene-D-glucose was obtained in low yield when D-glucose reacted in the presence of DMF. 

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