Polyhydroxylated carbocycles

In addition to terpenes (as described above), carbohydrates have also been used as substrates in domino metathesis reactions, the aim being to synthesize enan-tiopure polyhydroxylated carbocyclic rings. These structures are components of several biologically active compounds such as aminoglycoside antibiotics [254], inositol phosphates [255], and carbanucleosides [256]. An efficient entry to this skeleton was developed by Madsen s group using a domino RCM/CM of the carbohy-... 

Strictly speaking, the basic motif of a carbasugar possesses a carbohydrate counterpart, be it a real molecule or only hypothetically obtainable. To be precise, the carba counterpart of a monosaccharide arises from the replacement of the hemiacetal ring oxygen in carbohydrates by a carbon atom (usually a CH2), leaving the rest of the structure and chirality intact. In literature, however, this distinction does not appear to be so clear and often polyhydroxylated carbocyclic... 

Isolation and discovery of these biologically active compounds has encouraged researchers to carry out not only their total synthesis but also to accomphsh the synthesis of the aglycon [72-74] or modifications both in the cycHtol moiety and in the carbohydrate residue [75-82]. For instance, there are examples where the aminocyclopentitol motif has been replaced by either a six-membered polyhydroxylated carbocycle [83] or by a tetrahydropyrane moiety [84]. 

Synthesis of Polyhydroxylated Carbocyclic Derivatives with Large Rings... 

Bicyclic derivatives. Polyhydroxylated carbo-bicyclic derivatives may be regarded as carbasugars with the rigid structure resulting from the presence of the additional carbocyclic ring. The most convenient way for construction of the bicyclic skeleton consists of the Diels-Alder reaction of properly functionalized trienes (intramolecular version) or dienes and olefins (intermolecular). 

Ferrier carbocyclization can form only cyclohexanones. Nevertheless, chemical manipulations of the latter can provide us with seven-membered rings. This is illustrated by the synthesis of (—)-calystegine B2 by Boyer and Lallemand [305]. These natural polyhydroxylated nortropane compounds are growth stimulators of nitrogen fixing bacteria. 

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