Sugars cyclic carbonates

Easily prepared from the appropriate monosaccharide, a glycal is an unsatu-rated sugar with a C1-C2 double bond. To ready it for use in potysaccharide synthesis, the primary -OH group of the glycal is first protected at its primary -OH group by formation of a silvl ether (Section 17.8) and at its two adjacent secondary - OH groups by formation of a cyclic carbonate ester. Then, the protected glycal is epoxidized. 

Just as certain pyranose sugars can give rise to bis-acetal or bis-ketal derivatives which constitute linearly fused 5 6 6 systems (cf. Section 12.17.2.1.7), another set of bis-acetals and bis-ketals - in many cases derived from the same sugars - correspond to angularly fused 5 6 6 systems. These, like their linearly fused analogues, serve to protect, selectively, four hydroxyl groups of the parent sugars, and cyclic carbonates (l,3-dioxolan-2-ones) may fulfill similar functions. 

H. Komura, T. Yoshino, and Y. Ishido, Preparation of cyclic carbonates of sugar derivatives with some carbonylating agents, Carbohydr. Res, 40 (1975) 391-395. 

An l-hydroxy-l,2-benziodoxol-3(17/)-one 1-oxide (IBX)-mediated process provides another efficient and stereoselective preparative route for the s)uithesis of amino sugars. For example, reaction of the D-glucal derivative 113 with p-methoxybenzene isocyanate in the presence of a catalytic amount of l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) followed by treatment with IBX furnishes the cyclic carbonate 115, through urethane 114. Subsequent removal of the p-methoxybenzyl (PMB) protecting group by CAN affords the protected amino sugar 116 (O Scheme 56) [94]. 

The reaction of phosgene with vic-diols (including sugars) leads to cyclic carbonates (Kawabata et al., 1986). 

The carbonate and thiocaibonate derivatives used in the carbohydrate field have been reviewed 112]. The cyclic carbonates are sensitive to alkali and stable to add hydrolysis, and in these respects are complementary to the cydic isopropylidene acetals. Cydic carborrates may be made from sugars by the action of chloroformate esters. The original phosgerre method is also applicable, either directly or in a solvent. The solvent usually used is toluene, or a reaction-promoting solvent such as pyridine or quinoline may be used. 

Shen Y., Chen X., Gross R.A., Polycarbonates from sugars Ring opening polymerization of 1,2-0-isopropylidene-D-xylofuranose-3,5-cyclic carbonate (IPXTC), Macromolecules, 32, 1999, 2799-2802. 

The sugars react with methyl (or ethyl) chloroformate at 0°C. in the presence of alkali to give a mixture of cyclic carbonate and acyclic 0-meth-oxycarbonyl (or 0-ethoxycarbonyl) derivatives 91), The cyclic carbonate structures resemble those of the isopropylidene cyclic acetals as shown in the formulas. 

Several carbonylating reagents used in the preparation of cyclic carbonates of sugar derivatives have been compared the results are summarized in Scheme 41. ... 

This may be overcome by forming the imidazolidate of the pyrophosphate and reacting this with the nucleoside monophosphate. Alternatively, the cyclic carbonate may be hydrolyzed by treatment with aqueous triethylamine. The imidazolidate method is presently the method of choice for the synthesis of ATP and GTP analogues modified at the base and/or sugar portion. One... 

Paulsen s group has reported the synthesis of derivatives (256) and (257) of the hydroxyethyl-branched octose that is found as a component of the quinocycline complexes isolated from Streptomyces aureofaciens. The route from the epoxyketone (255) is outlined in Scheme 59. An identical route was used to prepare branched-chain analogues in the o-series, in which it was shown that acid-catalysed methanolysis of the hydroxyethyl-branched derivative (258) yielded the more stable isomer (259) via the anhydro-sugar d-(257). Paulsen s group has also described a synthesis of a derivative (260) of pillarose (see Vol. 9, p. 99), a component of the antibiotic pillaromycin, using the dianion (261) prepared from 2-hydroxymethyl-l,3-dithiane to introduce the branch at C-4 (Scheme 60). A similar approach, using the anion derived from 2-methyl-l,3-dithiane, and subsequent desulphurization and reduction, etc., was adopted in a synthesis of a derivative (262) of aldgarose (4,6-dideoxy-3-C-[(i )-l-hydroxyethyl]-D-W6o-hexopyranose 3,3 -cyclic carbonate) (cf. Vol. 8, p. 100). 

Oxirans. - Treatment of methyl 4,6-0-benzylidene-a-D-glucopyranoside with a mixture of diethyl carbonate and potassium carbonate in DMF has afforded directly a new simple synthesis of methyl 2,3-anhydro-4,6-0-benzylidene-a-D-allopyranoside. The corresponding 2,3-cyclic carbonate is postulated as an intomediate. Some carbohydrate examples have been published of the use of sodium hydride and p-toluenesulfonyl chloride for the conversion of 1,2-diols to epoxides. Simple routes to the Cemy epoxides 6 and 7 finom D-glucal have been develc red (Scheme 1). In this scheme the flrst step involves a dehydration elimination with allylic rearrangement Syntheses of methyl 2,3-anhydro-a- and L-OTthiofuranoside have been reported. Some nitro-sugar epoxides are mentioned in Chapter 10. 

Alkylation of enamines with epoxides or acetoxybromoalkanes provided intermediates for cyclic enol ethers (668) and branched chain sugars were obtained by enamine alkylation (669). Sodium enolates of vinylogous amides underwent carbon and nitrogen methylation (570), while vicinal endiamines formed bis-quaternary amonium salts (647). Reactions of enamines with a cyclopropenyl cation gave alkylated imonium products (57/), and 2-benzylidene-3-methylbenzothiazoline was shown to undergo enamine alkylation and acylation (572). A cyclic enamine was alkylated with methylbromoacetate and the product reduced with sodium borohydride to the key intermediate in a synthesis of the quebrachamine skeleton (57i). 

Nucleosides are compounds formed when a base is linked to a sugar via a gly-cosidic bond (Figure 11.10). Glycosidic bonds by definition involve the carbonyl carbon atom of the sugar, which in cyclic structures is joined to the ring... 

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