Carbohydrates fused

Girniene et al.21 have applied classic benzylation conditions to naked carbohydrate-fused OZTs to produce per-Cfb -benzylated derivatives (Scheme 55). 

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. 

The most well known and most widely used compounds mentioned in the chapter are the doubly protected monosaccharide derivatives (cf. Schemes 16-18 and 27-29), which serve as building blocks for the regio- and stereospecific synthesis of a host of more complex carbohydrates. A number of newly discovered alkaloids contain fused 5 6 6-triheterocyclic systems these compounds may come from not only traditional (plant) sources, for example, compounds 96, 292-294, 446, and 447, but also insects (compounds 531-533), marine animals of various kinds, for example, sponges (compounds 58 R = H or OH) and ascidians (compound 289), and amphibians (compound 535). Although the majority of these alkaloids are known to be toxic in sufficient quantity, any possible therapeutic applications have apparently not yet been disclosed. 

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. 

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... 

Thionocarbamates and carbohydrate scaffolds may be connected to give either fused, anchored or spiro compounds (Fig. 1). 

Some features were put into light (a) condensation of thiocyanic acid on carbohydrate-based a-hydroxyketones favors the formation of a fused OZT over an OXT, whereas the opposite is observed on acyclic systems 48 taking the different geometries into account, this is indicative of a thermodynamic... 

Uzan et al. have reported an alternative route to 1,2-fused thionocarbamates from 1,2-carbohydrate sulfites.49 The reaction proceeded via formation of a -configured thiocyanate, which further epimerizes to the ot-anomer, ready to undergo cyclisation into the fused OZT (Scheme 36). 

The condensation of DMDP with carbon disulfide/dicyclohexylcarbodiimide (DCC) afforded the indolizine derivative—potentially biological active thionocarbamate on carbohydrate scaffold, fused from the nitrogen side. 

We report here some literature examples 13, 55 of A-vinylsulfonylation and reduction to A-vinyl derivatives. Reactions were applied to different types-fused, anchored, spiro-OZTs on carbohydrate scaffolds and the examples shown indicate that the location of the OZT moiety with respect to the anomeric carbon can sometimes influence the results obtained. 

In summary, it was shown that a thionocarbamate function can be connected on carbohydrate scaffolds according to three different possibilities fused, anchored and spiro. Each linkage can be selectively obtained depending on the synthetic pathway and/or the carbohydrate backbone. 

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. 

Five-membered lactones (y-butyrolactones) fused to carbohydrates have proven to be convenient synthons towards branched-chain sugars through opening of the lactone unit. Velaskes et al. [208] described the synthesis of y-butyrolactones... 

With respect to five-membered lactones fused to hexopyranose units, some approaches have been reported so far and the exploitation of their synthetic potential has led to the access of new carbohydrate derivatives. Bicyclic derivatives of this type are key intermediates in the synthesis of the epimer at C-3 of the sugar moiety contained in miharamycins [212, 213]. The latter are antibiotics known to inhibit strongly Pyricularia oryzae, which produces the rice blast disease. These compounds are also considered to be a potential bioterrorism agent (Scheme 42). Hence, the 3,3-spiroepoxide 176 was converted into the 3-C-cyanomethyl derivative 177, the hydrolysis of which led to spontaneous cyclization in the presence of... 

---