Nontraditional Synthesis of Disaccharides via Acyclic Vinylic Ether Intermediates: Catalytic C-O Cross-Coupling as the Enabling Link.

We describe complementary methods for synthesizing acyclic vinylic ethers from two carbohydrate-derived synthons. We compare a nonstereoselective olefination approach with a stereoselective catalytic C-O cross-coupling method, preparing 1,2-disubstituted vinylic ethers with complexity on both sides of the ether linkage. Upon epoxidation/ oxacyclization of acyclic vinylic ethers, we synthesized disaccharides with α-d-galacto-, α-d-talo-, β-d-allo-, and α-d-altropyranoside stereochemistry, from d-lyxose and d-ribose precursors.

Stereospecific Cu(I)-Catalyzed C-O Cross-Coupling Synthesis of Acyclic 1,2-Di- and Trisubstituted Vinylic Ethers from Alcohols and Vinylic Halides.

CuI and -,-dimethylcyclohexyldiamine catalyze the single-step C-O bond cross-coupling between 1,2-di- and trisubstituted vinylic halides with functionalized alcohols, producing acyclic vinylic ethers. This stereospecific transformation selectively gives each of the ()- and ()vinylic ether products from the corresponding vinyl halide precursors. This method is compatible with carbohydrate-derived primary and secondary alcohols and several other functional groups.

A Tropomycin-Related Kinase B Receptor Activator for the Management of Ocular Blast-Induced Vision Loss.

Pressure waves from explosions or other traumatic events can damage the neurons of the eye and visual centers of the brain, leading to functional loss of vision. There are currently few treatments for such injuries that can be deployed rapidly to mitigate damage. Brain-derived neurotrophic factor (BDNF) and activation of its receptor tropomycin-related kinase B (TrkB) have neuroprotective effects in a number of degeneration models.

Alkynylation of Pentose Derivatives with Stereochemical Fidelity: Implications for the Regioselectivity of Alkynyl Diol Cycloisomerizations to Cyclic Enol Ethers.

This work characterizes a previously undetected epimerization in the preparation of alkynyl diols from pentose precursors utilizing the Ohira-Bestmann reagent. Lithium trimethylsilyldiazomethane (Colvin reagent) additions to the d-ribose and d-lyxose-derived benzylidene acetals provide the respective alkynyl diol stereoisomers, without epimerization. Regioselective tungsten-catalyzed cycloisomerizations of the d-ribose- and d-lyxose-derived alkynyl diols yield rigid bicyclic pyranose glycals, confirming the stereochemical fidelity of the Colvin alkynylation process.

Sequential exo-mode oxacyclizations for the synthesis of the CD substructure of brevenal.

We describe a novel strategy for synthesizing the CD bicyclic ether substructure of the fused polycyclic ether natural product brevenal. This product arises from a three-step sequence beginning with (1) regio- and diastereoselective iodoetherification of an acyclic diene-diol, followed by (2) alkene metathesis with an epoxyalkene synthon, concluding with (3) palladium-catalyzed cycloisomerization. Despite the modest yield and long reaction period for the cycloisomerization step, these studies provide valuable insights into the nature of byproducts generated and the mechanisms by which they form.

Stereoselective Synthesis of Pyrans from Epoxyalkenes: Dual Catalysis with Palladium and Brønsted Acid.

We describe regio- and stereoselective cycloisomerizations of alcohols tethered to epoxyalkenes, to construct alkene-substituted pyrans. These transformations are best catalyzed by Pd(PPh) in the presence of phosphite ligands, and with diphenylphosphinic acid as an essential Brønsted acid cocatalyst for activation of the epoxyalkene.

Synthesis of the ABC Substructure of Brevenal by Sequential exo-Mode Oxacyclizations of Acyclic Polyene Precursors.

Exploratory studies on the sequential exo-mode oxacyclizations of acyclic polyene precursors have provided a substantial substructure of brevenal, including the fused tricyclic polyether with stereochemical patterns consistent with the AB and BC ring fusions. The synthesis of acyclic substrates featured two variations of Cr(II)/Ni(II) couplings for preparing 1,1-disubstituted allylic alcohols. A sequence of iodine-promoted cycloetherification, base-promoted intramolecular conjugate addition, and mercury-promoted cycloetherification produced the tricyclic substructure.

Gram-scale, chemoselective synthesis of -[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide (HIOC).

-[2-(5-hydroxy-1H-indol-3-yl)ethyl]-2-oxopiperidine-3-carboxamide (HIOC) is a potent activator of the TrkB receptor in mammalian neurons and of interest because of its potential therapeutic uses. In the absence of a commercial supply of HIOC, we sought to produce several grams of material. However, a synthesis of HIOC has never been published.

Blockade of glioma proliferation through allosteric inhibition of JAK2.

The gene that encodes the epidermal growth factor receptor (EGFR) is frequently overexpressed or mutated in human cancers, including glioblastoma. However, the efficacy of EGFR-targeted small-molecule inhibitors or monoclonal antibodies in glioblastomas that also have mutation or deletion of the gene encoding phosphatase and tensin homolog (PTEN) has been modest. We found that EGFR signaling was blocked by a small molecule (G5-7) that selectively inhibited Janus kinase 2 (JAK2)-mediated phosphorylation and activation of EGFR and STAT3 (signal transducer and activator of transcription 3) by binding to JAK2, thereby decreasing the activity of downstream signaling by mTOR (mammalian target of rapamycin) and inducing cell cycle arrest.

Biomimetic syntheses from squalene-like precursors: synthesis of ent-abudinol B and reassessment of the structure of muzitone.

We achieved the stereoselective syntheses of two different structural patterns corresponding to the enantiomers of the marine natural products abudinol B and muzitone, by developing two-directional tandem biomimetic cyclizations of polyepoxides of squalene analogues in which one alkene was functionalized as an enolsilane. In the course of this work, we demonstrated that the structure of muzitone was misassigned.

Convergent synthesis of fostriecin via selective alkene couplings and regioselective asymmetric dihydroxylation.

A highly convergent synthesis of fostriecin is described, featuring sequential palladium-catalyzed Negishi cross couplings to form the C7-C8 bond and C8-methyl bond, followed by late-stage regio- and stereoselective dihydroxylation of C8-C9.

Stereo- and regioselective synthesis of squalene tetraepoxide.

Squalene tetraepoxide, a putative biosynthetic precursor to a variety of oxacyclic triterpenoid natural products, has been efficiently synthesized by anionic coupling of two farnesol-derived diepoxides, which have arisen from electronic control of the regioselectivity in organocatalytic enantioselective epoxidations.

Brønsted acid-promoted glycosylations of disaccharide glycal substructures of the saccharomicins.

An acid-promoted glycosylation and alkynol cycloisomerization sequence provided direct access to the 2-deoxytrisaccharide corresponding to the fucose-saccharosamine-digitoxose substructure of saccharomicin B. In the course of this work, the absolute stereochemistry of the repeating fucose-saccharosamine disaccharide of saccharomicins was also confirmed.

Total synthesis of the sphingolipid biosynthesis inhibitor fumonisin B(1).

The first total synthesis of the sphingolipid biosynthesis inhibitor fumonisin B(1) has been achieved. This convergent synthesis utilizes oxonia Cope rearrangements to prepare two key homoallylic alcohols, which are then functionalized to the primary components A and B for cross-coupling. Other highlights of our approach include a new and efficient synthesis of the diprotected tricarballylic acid C and a global deprotection strategy as the final step.

1,5-Alpha-D-mannoseptanosides, ring-size isomers that are impervious to alpha-mannosidase-catalyzed hydrolysis.

1,5-D-mannoseptanosyl di- and trisaccharide ring-size isomers of the corresponding mannopyranosyl oligosaccharides have been prepared. Remarkably, these compounds show no inhibition of the alpha-mannosidase-catalyzed hydrolysis of p-nitrophenyl-alpha-D-mannopyranoside.

Modular synthesis of the C9-C27 degradation product of aflastatin A via alkyne-epoxide cross-couplings.

A modular approach to the synthesis of complex polyketide natural products is demonstrated for the synthesis of the C9-C27 degradation product from aflastatin A. The product of the cross-coupling of C23-C27 terminal alkyne with C17-C22 epoxide underwent functionalization of the resulting internal alkyne, which was then coupled similarly with C9-C16 epoxide. This synthesis concluded with regio- and stereoselective addition of methyl onto the internal alkyne followed by stereoselective hydroboration-oxidation.

Stereo- and regioselective glycosylations to the bis-C-arylglycoside of kidamycin.

In explorations toward the total synthesis of the antitumor anthrapyran natural product kidamycin, the regioselective introduction of aminosugars angolosamine and vancosamine as C-arylglycosides has been accomplished onto hydroxylated anthrapyran aglycones. Specifically, the 9,11-dihydroxylated anthrapyran A undergoes sequential glycosylations with angolosamine synthon B and vancosamine synthon C to regio- and stereoselectively afford bis-C-glycoside D corresponding to the C-glycoside pattern of kidamycin.

Fischer carbene catalysis of alkynol cycloisomerization: application to the synthesis of the altromycin B disaccharide.

[reaction: see text] The tungsten-catalyzed cycloisomerization of alkynyl alcohols can be conducted without using photochemistry, using a stable tungsten Fischer carbene as the precatalyst for this transformation. A variety of alkynyl alcohols undergo cycloisomerization under these conditions to provide endocyclic enol ethers of five-, six-, and seven-membered ring sizes. The utility of this method is further demonstrated in the stereoselective synthesis of the disaccharide substructure of altromycin B.

Density Functional Study of Mo-Carbonyl-Catalyzed Alkynol Cycloisomerization: Comparison with W-Catalyzed Reaction.

Mo-catalyzed endo-cycloisomerizations of alkynes tethered to alcohols have been studied using density functional theory, and comparisons were made with the W-catalyzed reaction. The cycloisomerization is initiated with the formation of metal alkyne pi complex and is followed by the rate-determining step, which transforms the pi complex to a vinylidene carbene complex, considered to be critical for endo-mode cyclization. Several different alkynols have been selected to investigate five- and six-membered ring endo-cycloisomerizations in the presence of Mo(CO)(5) catalyst.

New chiral synthons for efficient introduction of bispropionates via stereospecific oxonia-cope rearrangements.

Compounds 1 and 2 are novel synthons for bispropionate synthesis, undergoing stereospecific Lewis acid-catalyzed transfer of the bispropionate unit with a variety of aldehydes, including alpha-chiral aldehydes. Thus 1 leads to the E-alkene bispropionate 3 with anti-stereochemistry, whereas diastereomer 2 gives the Z-alkene product 4, under mild conditions and with complete stereospecificity. The efficacy of this methodology is demonstrated in a short synthesis of invictolide beginning with 2 and (R)-2-methylpentanal.

Synthesis of 1-deoxysphingosine derivatives with conformationally restricted pyrrolidinediol head groups.

[structure: see text] A family of cyclic 1-deoxysphingolipid derivatives of structure 4 has been designed and synthesized, which may serve as tumorigenesis suppressors for various cancers. Compound 4 is a second-generation analogue developed from sphingosine (1), in which a hydroxyl substituent is moved from C1 to C5 and a methylene is added for conformational rigidity between the C2-nitrogen substituent and C4. The synthetic chemistry for pyrrolidine ring closure at C3-C4 features ring-closing metathesis followed by hydroboration-oxidation.