In situ 1,3-dipolar azide cycloaddition reaction: synthesis of functionalized d-glucose based chiral piperidine and oxazepine analogues

Total Synthesis of (-)-Piericone D

The total synthesis of (-)-piericone D, a potential antithrombotic dihydrochalcone featuring an [3.3.0] octane core, is reported. Salient features of our synthesis include a stereoselective β-O-glycosylation to install the asebogenin aglycone and a late-stage global deprotection followed by simultaneous lactonization. The convergent synthesis paved the way for further structure-activity relationship (SAR) studies of (-)-piericone D.

A rapid entry to amino acid derived diverse 3,4-dihydropyrazines and dihydro[1,2,3]triazolo[1,5-a]pyrazines through 1,3-dipolar cycloaddition

Practical synthesis of diverse 3,4-dihydropyrazines, 6,7-dihydro-[1,2,3]triazolopyrazines and 7,8-dihydro-[1,2,3]triazolodiazepines through intramolecular 1,3-dipolar cycloaddition from amino acid derived intermediates is described.

Synthesis of 1,2,3-triazole and 1,2,3,4-tetrazole-fused glycosides and nucleosides by an intramolecular 1,3-dipolar cycloaddition reaction

Various 1,2,3-triazole and 1,2,3,4-tetrazole fused multi-cyclic compounds were synthesized from carbohydrate derived azido-alkyne and azido-cyanide substrates. The acid sensitive 1,2-O-isopropylidene group of the furanosyl sugar was utilized for diversification to glycosides and nucleosides under Fischer glycosidation and Vorbruggen's conditions, respectively.

Synthesis of highly condensed polycyclic carbohydrates by reaction of a spirocyclic enamino sulfonate derived from d-xylofuranose with bifunctional reagents

The appropriately substituted 5-O-tosyl derivative (1), easily prepared from 1,2-O-isopropylidene-alpha-d-xylofuranose, serves as a useful precursor for the preparation of highly condensed cyclic carbohydrates. The synthesis involves a first cyclization of the 5-O-tosyl sugar derivative 1 to a highly reactive cyclic enamine, which subsequently undergoes the nucleophilic attack of a bifunctional reagent X(CH2)nZ in a regio- and stereospecific way. Finally, a spontaneous cyclization step allows the formation of a stereochemically defined extra ring, fused to the sugar backbone. The functionalization and size of this ring can be varied by the proper choice of the bifunctional reagent. X-ray diffraction analysis and intensive NMR studies with one of these carbohydrates were performed to highlight the strained nature of these compounds.

Bis- and Trisuracil Nucleosides with Nucleobases Anchored to 11-, 12-, and 16-Membered Macrocyclic Scaffolds: Synthesis and Aggregation Study

Bis- and trisuracil nucleosides, in which the nucleobases are anchored to isoxazoline ring-fused 11-, 12-, and 16-membered macrooxacycles, were synthesized by nucleosidation of 1,2-isopropylidenefuranose ring-fused macrocycles. The nucleosides exhibited spherical and fiber-like morphologies in water. In one case, the morphology was significantly altered by complexation with an adenine nucleoside via complementary base pairing.

A Cyclic Enamine Derived from 1,2-O-Isopropylidene-α-d-xylofuranose As a Novel Carbohydrate Intermediate To Achieve Skeletal Diversity

The commercially available carbohydrate 1,2-O-isopropylidene-alpha-D-xylofuranose was efficiently transformed into the high-added-value synthetic scaffold 8. The transformation requires the synthesis of the 5-O-tosyl derivative 7 and its subsequent intramolecular cyclization under basic conditions to give the cyclic enamine 8. Reaction of 8 with O-, N-, S-, and C-nucleophiles and amino acids allowed its efficient transformation (one-step, high yields, and easy purifications) into fused cyclic sugar derivatives with rather unusual molecular skeletons in a completely regio- and stereoselective manner. The characteristics of the sugar derivative 8 established here, high reactivity, synthetic accessibility, and the potential for conversion into a vast collection of products by the action of different nucleophiles, indicate that it will prove to be a useful chiral intermediate for achieving skeletal diversity. The constrained structures and dense functionalization of the polycyclic sugar derivatives generated from 8 make these compounds promising candidates for use as starting agents for the production of new analogues and as drugs.

Nucleoside synthesis from 3-alkylated sugars: role of 3beta-oxy substituents in directing nucleoside formation

Using Vorbrüggen's protocol, reaction of persilylated uracil with xylofuranose derivatives having 3beta-oxy-3alpha-alkyl substitution produced both alpha- and beta-nucleosides. Only the beta-nucleosides were formed from substrates having the reverse stereochemistry at C-3 or lacking the 3-alkyl substituent. Participation of the 3beta-oxy substituent in stabilizing the incipient C-1 carbonium ion (or oxonium ion) intermediate has been suggested from analysis of energy-minimized conformations.

Synthesis and Intramolecular Nitrile Oxide Cycloaddition of 3,5‘-Ether-Linked Pseudooligosaccharide Derivatives: An Approach to Chiral Macrooxacycles

3,5'-ether-linked pseudooligopentose derivatives were synthesized for the first time from readily available carbohydrate precursors. The 1,2-isopropylidene-protected ether-linked oligopentoses are potentially important as precursors of novel RNA analogues. Intramolecular cycloaddition of the nitrile oxides prepared from these derivatives led to the diastereoselective formation of chiral isoxazolines fused to 10-16-membered oxacycles. The stereochemistry of some of these isoxazolines was established by X-ray diffraction and NOESY analysis.

Bicyclic nucleoside analogues from d-glucose: synthesis of chiral as well as racemic 1,4-dioxepane ring-fused derivatives

The dioxepanofuranose derivatives 4 and 12, obtained through the cyclization of the 3-(2-hydroxyethyl) ether of a D-xylo-pentodialdose derivative, were appropriately functionalized and elaborated to the first examples of the new class of 3'-O and 5'-O-bicyclic nucleoside analogues 9, 10, and 14 with a fused seven-membered ring. Reactions carried out through the intermediacy of the D-xylo-pentodialdose derivative 5 yielded racemic products, while prior protection of the 4-formyl group (as in 7) before deprotection of the 1,2-hydroxyl groups led to optically active analogues.

Expeditious synthesis of enantiopure symmetrical macroheterocycles by ring-closing metathesis of ether and tether-linked 1,2-O-isopropylidenefuranosides

Bis-olefinic symmetrical carbohydrate derivatives were prepared by joining two 1,2-O-isopropylidenefuranose units either through an ether linkage or by a tether of variable size. The ring-closing metathesis (RCM) of these substrates using Grubbs' first-generation catalyst led to the synthesis of enantiopure symmetrical macroheterocycles containing nine- to twenty-five-membered rings fused to the 1,2-O-isopropylidenefuranose ring.