Fused ring carbohydrates

L. D. S. Yadav, V. P. Srivastava, V. K. Rai, and R. Patel, Diversity oriented synthesis of fused-ring 1, 3-oxazines from carbohydrates as biorenewable feedstocks, Tetrahedron, 64 (2008) 4246-4253. 

In this section, we shall examine the various approaches by which crown compounds that have their chiral elements associated in some way with fused ring systems can be constructed. A selection of the wide and growing range of saturated chiral diols—many of them derived finom readily available carbohydrates—which have been incorporated, as relatively inexpensive sources of chirality, into crown ether derivatives are displayed in Figure IS. It may be noted that the saturated chiral diols rely for their chirality on centers of the classical type (C abcd)—not so the chiral dihydroxy compounds associated with the unsaturated systems listed in Figure 16. These examples reveal that axes and planes of chirality join with less conventional chiral centers (C aaaa) in being sources of chirality in optically active crown ethers. 

There is no settled convention for the representation of polyacetals and other complex cyclic derivatives of carbohydrates. To facilitate the comparison of polycyclic derivatives of carbohydrates with alicyclic compounds, the carbohydrate derivatives will be drawn in perspective, with single rings and fused rings placed in the plane of the paper, and with darkened or broken lines used to show the orientation of substituents and bridges above or below the plane of the rings, respectively, as is customary for terpenes and steroids. 

Of the theoretically possible bicyclic systems arising via combinations of five- and six-membered rings, we discuss only three of the most common in carbohydrate chemistry here. These are the 5 + 5, 5 + 6 and 6 + 6 variations, in which the two fused rings have only two adjacent common atoms, representing the [3,3,0]octane, the [4,3,0]nonane and the [4,4,0]decane systems. Theoretically, all three can form cis or trans fused systems, but because of the high steric strain of a trans fused 5 + 5 bicyclic system, this combination can be disregarded (Figure 2.30). 

The absolute configuration of the benzylic centre in some benzyli-dene derivatives of acyclic polyhydric alcohols and of some carbohydrate benzylidene acetals containing fused-ring systems have been established. The method utilizes the observation that 2-phenyI-... 

Hydroxyl-containing materials comprise the vast majority of natural materials. These include the carbohydrates (or saccharides), lignin, many steroids and fused ring systems (such as cholesterol, luciferin, anhal-amine, folic acid. Vitamin E, riboflavin, and tetracycline). With the possible exception of the saccharides, these materials are either vastly underused (such as lignin) or unused as commercial polymers or as feedstock within the chemical industry. 

Vancomycin, ristocetin A and teicoplanin are produced as fermentation products of Streptomyces orientalis, Nocardia lurida and Actinoplanes teichomyceticus, respectively. All three of these related compounds consist of an aglycone basket made up of fused macrocyclic rings and pendant carbohydrate moieties (Fig. 2-1). The macrocycles contain both ether and peptide linkages. The aglycones of vancomycin and teicoplanin contain two chloro-substituted aromatic rings, while the analogous portion of ristocetin A contains no chloro substituents. 

Chiral 10 to 12-membered nitrogen and oxygen heterocycles, fused to isoxazo-line rings have been prepared with high regio- and stereoselectivity by INOCs of tethered N- and O-allyl carbohydrate derivatives. The use of a -Y-Ar-CH2 tether, containing a 1,2-disubstituted aromatic ring between the heteroatom attached to... 

The synthesis of vicinal doubly substituted carbohydrates can be achieved, as mentioned earlier, by successive formation of simple branched-chain carbohydrates. Other methods have emerged that are mostly based on the formation of 3-, 4-, 5-, or 6-membered ring fused to a pyranose-furanose ring. This process allows high stereocontrol on the two newly... 

C. Audin, J. M. Lancelin, and J. M. Beau, Radical cyclization on carbohydrate pyranosides A controlled formation of functionalized ring-fused bicyclic acetals. Tetrahedron Lett. 29 3691 (1988). 

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