Triisobutylaluminium mediated carbocyclisation of sugar derived spiroketals and ketosides

From D-glucose to enantiomerically pure cycloctanoses. The glycosidase inhibitory capacity of medium-ring carbasugars

Exhaustive dihydroxylation of the pair of cyclooctadienols consisting of 4 and 5, which are available in enantiomerically pure form from d-glucose, resulted in the formation of two diastereomeric tetraols in each case. The difference in polarity of the 6/7 and 8/9 pairs facilitated their chromatographic separation. Ensuing acetylation and PMB deprotection allowed for the assignment of relative (and ultimately absolute) stereochemistry to the resulting monohydric alcohols on the basis of J(HH) analysis of their (1)H NMR spectra. The highly functionalized exomethylenecyclooctanes 14-17, which were derived by periodinane oxidation and Wittig olefination, were further elaborated by hydroboration and global deprotection. The eight members of the cyclooctanose family of carbasugars and their precursor intermediates consistently showed patterns of J(HH) values in line with the contiguous stereochemical relationships. Also assayed was their specific inhibitory behavior toward glycosidases.

Methyl 4-O-Acetyl-3-azido- and 3-Azido-4-O-methylsulfonyl-2,3,6,-trideoxyhex-5- enopyranosides in DFT-Level Conformational Studies

Geometry optimizations at the B3LYP level of density functional theory (DFT) are reported for methyl 4-O-acetyl-3-azido- and 3-azido-4-O-methylsulfonyl-2,3,6-trideoxy-alpha,beta-d-threo- and -beta-d-erythro-hex-5-enopyranosides. The most stable conformers for each compound are presented, along with the corresponding enthalpies and Gibbs free energies. The influence of the exocyclic double bond on the chair conformation is discussed. Conformations of the 1-OMe, 3-N3, and 4-OAc groups were examined, and delocalization in the OAc and N3 groups was demonstrated. The contributions of particular conformers to the total number of structures found for each hex-5-enopyranoside were calculated. The theoretical results are compared with assignments based on 1H NMR studies.

The Oxygen-Bridge Templating Approach to Eight- and Nine-Membered Carbocycles: Recent Developments Based on Catalytic Reactions

Recent developments concerning metal-catalyzed reactions have led to the implementation of new, rapid, and practical routes to eight- and nine-membered carbocycles based on an oxygen-bridge templated cyclization.

From Common Carbohydrates to Enantiopure Cyclooctane Polyols and Glycomimetics via Deoxygenative Zirconocene Ring Contraction

D-Arabinose and D-glucose are transformed into the identical vinyl furanoside, whose role is to serve as the precursor to enantiopure cyclooctadienone 6. The key steps of this relay involve a zirconocene-promoted ring contraction and [3,3] sigmatropic rearrangement of an enynol. Subsequently defined are convenient synthetic routes to several cyclooctane-1,2,3-triols, 1,2,3,4,5-pentaols, and structurally related glycomimetics.

Synthesis and glycosidase inhibitory activity of new hexa-substituted C8-glycomimetics

Background

Glycosidases are involved in several metabolic pathways and the development of inhibitors is an important challenge towards the treatment of diseases, such as diabetes, cancer and viral infections including AIDS. Thus, inhibition of intestinal α-glucosidases can be used to treat diabetes through the lowering of blood glucose levels, and α-glucosidase inhibitors are being marketed against type 2 (non-insulinodependent mellitus) diabetes (i.e.: Glyset^® or Diastabol^®, Basen^® and Glucor^® or Precose^®).

Results

In that context, new C8-carbasugars and related aminocyclitols have been targeted in order to study the effect of the enhanced flexibility and of the new spatial distribution displayed by these structures on their adaptability in the active site of the enzymes. The synthesis of these new C8-glycomimetics is described from enantiomerically pure C₂-symmetrical polyhydroxylated cyclooctenes. Their obtention notably involved a syn-dihydroxylation, and more extended functionalization through formation of a cis-cyclic sulfate followed by amination and subsequent reductive amination. This strategy involving the nucleophilic opening of a cis-cyclic sulfate by sodium azide is to our knowledge the first example in C8-series. It revealead to be an efficient alternative to the nucleoplilic opening of an epoxide moiety which proved unsuccessful in this particular case, due to the hindered conformation of such epoxides as demonstrated by X-ray cristallographic analysis.

Conclusion

The biological activity of the synthesized glycomimetics has been evaluated towards 24 commercially available glycosidases. The weak observed activities can probably be related to the spatial disposition of the hydroxy and amino groups which depart too much from that realized in glycomimetics such as valiolamine, voglibose and valienamine. Nevertheless, the synthetic strategy described here is efficient and general, and could be extended to increase the diversity of the glycosidase inhibitors obtained since this diversity is introduced in an ultimate step of the synthesis.

Synthesis and conformational studies on methyl 4-O-acetyl-3-azido-2,3,6-trideoxy-hex-5-enopyranosides of the l series

Methyl 3-azido-2,3-dideoxy-alpha-D-xylo-, -alpha-D-lyxo-, and -beta-D-xylo-hexopyranosides were converted into 4-O-acetyl-3-azido-6-iodo-2,3,6-trideoxy analogues via 6-O-p-tolylsulfonyl compounds. The elimination of hydrogen iodide from 6-iodo glycosides yielded methyl 4-O-acetyl-3-azido-2,3,6-trideoxy-beta-L-erythro-, -alpha-L-threo-, and -beta-L-threo-hex-5-enopyranosides. The configuration and conformation of all products are evaluated in depth on the basis of (1)H and (13)C NMR data. Factors determining conformational energy in 4-O-protected-3-azido-2,3,6,-trideoxy-hex-5-enopyranosides are discussed.

Enantioselective Route from Carbohydrates to Cyclooctane Polyols

[reaction: see text] A synthetic route to select cyclooctane-1,2,3-triols and 1,2,3,4,5-pentaols has been defined. The starting materials are d-glucose or d-arabinose, and the key steps consist of a zirconocene-promoted ring contraction, a [3,3] sigmatropic rearrangement, and more extended functionalization of the resulting cyclooctadienone.

Zirconocene-mediated route to enantiopure 9-oxabicyclononanes functionalized on both carbon bridges

[reaction: see text] A zirconocene-mediated ring contraction of 4-vinylfuranosides generated either from d-arabinose or d-glucose is followed by sequential oxidation to the ketone and alkynyl Grignard addition. The resulting cis-cyclobutanediols are subjected in turn to thermal rearrangement and intramolecular oxymercuration-demercuration. The regiochemistry of the final ring closure is controlled by the nature of R.