Sugars heterocyclic derivatives

Carbon-linked sugar-heterocycles were also obtained by reaction of the lithiated derivatives obtained from 2-bromopyridine, a-picoline, and ben-zothiazole with 4-0-benzyl-2,3 6,7-di-0-cydohexylidene-D-g(ycero-D-gulo-htplono-1,5-lactone (55). The corresponding o-glycero-D-gulo-hepto-pyranose-substituted compounds 56a-c were isolated in 35-43.5% yields. With other heterocycles (for example furan), 1-disubstituted guloheptitols were obtained (59). 

Furthermore, spiro-heterocycles derived from sugars are attractive targets, and some representative molecules of this class, such as hydantocidin3 (Figure 2), are interesting bioactive molecules. (7)... 

To constmct the anhydro skeleton in the sugar molecule standard synthetic methods, used for the formation of normal heterocyclic derivatives, are applicable [4,5]. Generally, one of the hydroxyl groups of the diol (from which the anhydro ring is formed) is activated (by... 

An interesting methodology to highly oxygenated p)razolidines and indolizidines from 2,3-unsaturated sugar lactones was presented by Chmielewski [84]. The synthesis was initiated by a 1,4-addition of nitrogen nucleophiles to unsaturated lactones 93, which resulted in formation of appropriate heterocyclic derivative 94 (O Scheme 38). 

Glycosyl isothiocyanates have also been allowed to react with unprotected 2-amino-2-deoxyaldoses and 1-amino-1-deoxy-2-ketoses.68 This reaction leads to the formation of heterocyclic derivatives resulting from cy-clization involving the carbonyl group of the amino sugar moiety following the mechanistic pathway already discussed for similar condensation reactions with alkyl and aryl isothiocaynates. 

The elongation of sugar chains via heterocyclic derivatives is mentioned in Chapter 8. Thiazoline derivatives are referred to in Chapter 10. 

Other heterocyclic ligands have also been used for such alkylations. The use of imine-based ligands and sugar-related derivatives have also led to high enantiomeric excesses (Table 2). 

Khan MTH (2007) Recent Advances on the Sugar-Derived Heterocycles and Their Precursors as Inhibitors Against Glycogen Phosphorylases (GP). 9 33-52 Khan MTH (2007) Heterocyclic Compounds Against the Enzyme Tyrosinase Essential for Melanin Production Biochemical Features of Inhibition. 9 119-138 Khan MTH (2007) Molecular Modeling of the Biologically Active Alkaloids. 10 75-98 Khan MTH, Ather A (2007) Microbial Transformation of Nitrogenous Compoimds. 10 99-122... 

Sugar-derived Heterocycles and Their Precursors as Inhibitors Against Glycogen Phosphorylases (GP)... 

In the last twenty years, nitro sugars became powerful chemical tools on account of their usefulness for the construction of carbon-carbon bonds prior to the transformation of the nitro group into a variety of other chemical functionalities. As a result, a diverse range of funcionalized carbohydrates and other derivatives as carbasugars, cyclitols and heterocycles have been prepared. 

Intermediate 331 was used in the reaction with ketone-derived sugars 133 (from D-glucose) or 270 (from D-fructose) and with the protected estrone 280 so that, after hydrolysis, diols 337-339"° " were obtained in 25-80% yield. Further cyclization of these diols under Mitsunobu-type reaction conditions (PPh3, DIAD, benzene reflux) gave the mixed heterocyclic sugars 340 and 341"°, and the steroid derivative 342", respectively, in 45-50% yield. 

More complex examples exist where the 2-substituent on the furan is a polyhydroxyalkyl or glycosyl moiety <89CAR(l9l)209>. In these cases, the rearrangement products provide useful intermediates for the preparation of heterocycle-substituted sugar derivatives. Sometimes Baeyer-Vil-liger-type products are observed, such as 3-keto enoic esters instead of 3-keto enol esters <81TL1443>. 

It is conceivable that, starting from a pre-formed, five-membered heterocycle of the tetrahydrofuranol type, or even a furanosyl derivative, a contraction or extension of a side chain, according to the situation, would permit synthesis of a 2,5-anhydride of a sugar. This method has been used effectively on several occasions. 

This Chapter will discuss the formation of heterocycles that contain nitrogen and that involve atoms of the original sugar, and not the combination of existing heterocycles with saccharide derivatives. Thus, for example, the synthesis of nucleosides will not be included, but the formation of anhydronucleosides, in which a new heterocyclic ring has been introduced into the molecule, will be treated. 

An alternate approach comprises replacing the pendant sugar by either a carbo-cyclic or a heterocyclic ring. The enantioselective synthesis starts by formation of the imide (45-3) by reaction of the aion from the chiral auxiliary (45-2), derived from S-phenylalaninol and the pentene ester (45-1). Treatment of the product with triethyl amine and the trifalate from dibutylboronic acid leads to the transient enol borate (45-4). Aldol addition of that enol to acrolein proceeds stereospecifically to the alcohol (45-5) due to the transfer of chirality from the chiral auxiliary. 

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