Polyhydroxylated cyclopentanes

C-Alkylation has also been observed in intramolecular reactions where the O-alkylation is not favoured.76 This property has been recently exploited in a stereocontrolled intramolecular cyclization of nitronate of nitro sugar 101 (Scheme 32), that provided the novel bicyclic nitrolactone 102, a synthetic precursor of tripeptide 103, that includes the first reported polyhydroxylated cyclopentane (3-amino acid.77... 

On the way to 7-oxa-PGE,123) starting with the same all-c -l,2-epoxycyclo-pentane-3,5-dio 27 as used for the synthesis of 7-oxa-PGF-derivatives, Fried and co-workers utilized some unusual selective reactivity of polyhydroxylated cyclopentanes. 

The general feature of these reactions is as follows When treated with Sml2, a reductive cyclization between the carbonyl compound and the 8-carbon of the olefin of [XHI] derived fi-om sugars [XII] gives the desired polyhydroxylated cyclopentane [XIV], in which a new C1/C5 bond (carbohydrate numbering) is formed between sjp- centers. In the overall sequence, the sp alcohol stereocenter at C5 is destroyed when oxidation occurs to form the carbonyl moieties and subsequently reinstated, upon treatment with Sml2, to form a new hydroxy-... 

A further example of the cyclization of a highly functionalized carbohydrate derivative is given by the preparation of polyhydroxylated cyclopentanes from halogenated carbohydrates19. Treatment of the olefinic halides with tributyltin hydride affords two isomeric products. 

Intramolecular nitroaldol reactions are a useful choice for the conversion of sugars into polyhydroxylated nitro cyclopentanes, nitro cyclohexanes and their derivatives.46 Baer et al. in the course of their studies on the cyclization of 6-deoxy-6-nitrohexoses under kinetic and thermodynamic control,47 established the reaction pathway involved in the formation of nitroinositols mediated by intramolecular Henry reactions. Firstly, a nitronate is formed and then, under thermodynamic control conditions, an epimerization occurs before cyclization. But, under kinetic controlled conditions, the cyclization occurs first.48... 

A sligth modification of this synthetic methodology allowed the development of a novel route to 4-amino-5-(hydroxymethyl)cyclopentane-l,2,3-triols, some of them display significant glycosidase inhibition properties. In addition, a similar approach starting from L-idose allowed the first polyhydroxylated dspentacine to be prepared.78... 

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