Pseudosugar

An approach that affords cyclohexyl rings, with single carboxylate substituents, and is suitable for the preparation of some carbahexopyranoses (pseudosugars) depends on the initial condensation of O-substituted pentoses in the aldehydo forms with dimethyl malo-nate to give atkenes [17]. Thus, 2,3,4-tri-0-benzyl-5-0-f-butyldiphenylsilyl-D-ribose 29 (Scheme 8) can be converted to the alkene 30 in 85% yield by application of the... 

Then, pseudo-p-DL-gulopyranose (14) was synthesized by hydroxylation of 2,5-di-hydroxy-3-cyclohexene-l-methanol triacetate (12), which was prepared by Diels-Alder cycloaddition of 1,4-diacetoxy- 1,3-butadiene (10) and allyl acetate (11), with osmium tetroxide and hydrogen peroxide and successive acetylation as the pentaacetate (13). Analogous hydrolysis of 13 in ethanolic hydrochloric acid afforded the free pseudosugar 14 in 33% yield from 12 [2] (Scheme 7). 

Now, all the predicted sixteen stereoisomers of racemic pseudo-sugars have been synthesized and their physical constants are listed in Table 1. The first three pseudosugars 9,14 and 17 have been synthesized by McCasland and his coworkers. The two pseudo-sugar pentaacetates 28 and 29 were prepared from myo-inositol. All the remaining eleven pseudo-sugars have been synthesized from the Diels-Alder adduct... 

All the theoretically predictable sixteen racemic pseudo-sugars have been synthesized, as well as the ten enantiomers. The most accessible starting material for the synthesis was the Diels-Alder adduct 33 of furan and acrylic acid. Furthermore, the adduct 33 was readily resolved by means of optically active a-methylbenzylamines into the two antipodes 86 and 87, which were also used for the preparation of enatiomeric pseudosugars. A chiral synthesis from true sugars was another prominent method for the preparation of the enantiomers. The remaining twenty two unknown enantiomeric pseudo-sugars will be prepared by either one of the two methods in the near future. 

Sugar enol-ethers, which inherently carry both the masked nucleophilic and electrophilic functions, were converted to carbocycles in different reactions. Among the carbocyclization methods the Ferrier (II) cyclization of hex-5-enopyranosides affording six membered carbocycles in the presence of Hg(II) salts is perhaps the most popular one (Scheme 3) [32], This remarkable reaction has provided a practical route to a large variety of bioactive substances such as aminocyclitols [33], pseudosugars [34], inositols [35], and other complex hexitols [36]. 

Pseudosugars are carbohydrate derivatives in which the ring oxygen has been replaced by a methylene group. 

The term carbasugars (alias pseudosugars) is used to identify an ample and varied family of polyhydroxylated cyclic organic compounds that share a homomorphic relationship with structures that fall into the class of the carbohydrates [1]. 

Entwistle, D.A. et al. Synthesis of Pseudosugars from Microbial Metabolites. 3.1 1995 [118]... 

Ogawa, S, Matsunaga, N, Li, FI, Palcic, M M, Pseudosugars, 40 — synthesis of ether- and imino-linked octyl A-acetyl-5a -carba-beta-lactosaminides and -isolactosaminides acceptor substrates for alpha-(l— 3/4)-fucosyltransferase, and enzymatic synthesis of 5a -carbatrisaccharides, Eur. J. Org. Chem., 631-642, 1999. 

Paulsen, H, Vonde3m, W, Cyclitol reactions 13. S3mthesis of pseudosugars from D-glucose by intramolecular Homer-Emmons olefination, Liebigs Ann. Chem., 2, 125-131, 1987. 

Sudha, A V R L, Nagarajan, M, Carbohydrates to carbocycles an expedient synthesis of pseudosugars, Chem. Commun., 925-926, 1998. 

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