Furanoid rings

Of particular value, was the reagent s ability to oxidize a hydroxyl group attached directly to a furanoid ring (6, 7, 46), as is illustrated by the conversion of l,2 5,6-di-0-isopropylidene-a-D-glucofuranose into l,2 5,6-di-0-isopropylidene-a-D-n o-hexofuranos-3-ulose (1). The follow-... 

The features common to 2-deoxy ribose 5-phosphate and the two 3-deoxy hexulosonic acid 6-phosphates are that they all have a deoxy group next to the carbonyl group and that they can form only the furanoid ring (35, 78a, 80a) as long as the phosphate group is attached to the terminal, primary alcohol. However, they can all assume the pyranoid ring... 

Ring expansion of a furanoid ring. . 146 Ring expansion of a pyranoid ring. 148... 

In general, the major consequences of food thermal processing, either at laboratory or commercial scales, on carotenoids are the transformation of the 5,6-epoxy to the 5,8-furanoid rings, trans- to cis- isomerization and oxidation. In addition, independently of the food matrix or thermal... 

Electron density map of morphine showing the aromatic and part of the furanoid ring. Courtesy ofC. Matta. 

The furanoid ring is nonplanar. All of the oxygen atoms, except 0-1 and 0-4 of the lactone group, participate in hydrogen bonding (see formula 6). 

X-ray work was hampered by radiation damage to the crystal, which also hindered the study of a caldariomycin derivative in which there are also two chlorine atoms on one carbon atom.52] All of the five-membered rings are nonplanar, although the furanoid ring is almost planar. The initial formulation of structure was based on the concept that dichloromethylene would react with the double bond on the accessible, exo side of the trioxabicyclo[3.3.0]octene ring-system, and the structure found confirmed this hypothesis. Thus, the two rings attached to the furanoid ring are trans (or anti) to each other. 

Compound 55 is one of the rare examples of a 2,5-anhydro sugar that also possesses a furanoid ring it has various interesting properties as a result of ring strain in the bicyclo[2,2.1] system, and these are discussed later (see p. 212). 

Inspection of molecular models reveals that 2,5-anhydro-arabinose and -lyxose are the only 2,5-anhydroaldopentoses wherein the simultaneous presence of a 1,4-furanoid ring is sterically possible. 

Studies on the rates of hydrolysis of di-O-isopropylidene derivatives of ketoses indicated that the relative order of stability of 2,2-di-methyl-l,3-dioxolane rings is in the order cis-fused to a furanoid ring > sptro-fused to a pyranoid ring > cts-fused to a pyranoid ring > sptro-fused to a furanoid ring.8 Thus, partial hydrolysis of l,2 3,4-di-0-isopropylidene-/3-D-en/fhro-2-pentulofuranose (1) to the 3,4-acetal (2)... 

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