Base-Mediated Transformation of Glycals to Their Corresponding Vinyl Iodides and Their Application in the Synthesis of C-3 Enofuranose and Bicyclic 3,4-Pyran-Fused Furanose

A simple method for the iodination of unsaturated sugars to form sugar vinyl iodides was developed under oxidant-free conditions using NaH/DMF/iodine as a reagent system at ambient temperature. 2-Iodoglycals bearing ester, ether, silicon, and acetonide protection were synthesized in good to excellent yield. 3-Vinyl iodides derived from 1,2:5,6-diacetonide glucofuranose were transformed to C-3 enofuranose and bicyclic 3,4-pyran-fused furanose via Pd-catalyzed C-3 carbonylation and intramolecular Heck reaction, respectively, as the key step.

P(v) intermediate-mediated E1cB elimination for the synthesis of glycals

Glycals are highly versatile and useful building blocks in the chemistry of carbohydrate and natural products. However, the practical synthesis of glycals remains a long-standing and mostly unsolved problem in synthetic chemistry. Herein, we present an unprecedented approach to make a variety of glycals using phosphonium hydrolysis-induced, P(v) intermediate-mediated E1cB elimination. The method provides a highly efficient, practical and scalable strategy for the synthesis of glycals with good generality and excellent yields. Furthermore, the strategy was successfully applied to late-stage modification of complex drug-like molecules. Additionally, the corresponding 1-deuterium-glycals were produced easily by simple ^tBuONa/D₂O-hydrolysis–elimination. Mechanistic investigations indicated that the oxaphosphorane intermediate-mediated E1cB mechanism is responsible for the elimination reaction.

A novel glucosylphosphonium-hydrolysis induced E1cB-elimination provides a highly efficient, practical and scalable method for the synthesis of glycals with good compatibility and excellent yields.

Organocatalytic Conversion of Nucleosides to Furanoid Glycals

A class of organocatalysts that are highly active for the conversion of 2'-deoxynucleosides to furanoid glycals have been discovered. These phosphorimides, (Ph₂PS)₂NH and (Ph₂PSe)₂NH, were shown to effectively mediate persilylation of 2'-deoxynucleosides allowing the elimination of the nucleobase giving the corresponding glycal. These mild conditions were demonstrated in the syntheses of glycals with various substitution patterns while minimizing the formation of undesired byproducts and expanding the scope of this methodology.

Bioactive secondary metabolites from new endophytic fungus Curvularia. sp isolated from Rauwolfia macrophylla

Over the last decades, endophytic fungi represent a new source of pharmacologically active secondary metabolites based on the underlying assumption that they live symbiotically within their plant host. In the present study, a new endophytic fungus was isolated from Rauwolfia macrophylla, a medicinal plant from Cameroon. The fungus showed a highest homology to Curvularia sp. based on complete nucleotide sequence data generated from the internal transcribed spacer (ITS) of ribosomal DNA region. Large scale fermentation, working-up and separation of the strain extract using different chromatographic techniques afforded three bioactive compounds: 2'-deoxyribolactone (1), hexylitaconic acid (2) and ergosterol (3). The chemical structures of compounds 1–3 were confirmed by 1 and 2D NMR spectroscopy and mass spectrometry, and comparison with corresponding literature data. Biologically, the antimicrobial, antioxidant activities and the acetylcholinesterase inhibitory of the isolated compounds were studied.