Aluminum- and boron-mediated c-glycoside synthesis from 1,2-anhydroglycosides

Antiproliferation and apoptosis induced by C-glycosides in human leukemia cancer cells

A large series of alkyl C-glycosides was synthesized from D-glucal or D-galactal. These compounds were screened against the human promyelocytic leukemia cell line (HL60), showing significant activity and apoptosis. Up to 13 C-glucopyranosides, but no C-galacto- or C-mannopyranosides, exhibited inhibitory concentrations (IC(50) values) below 20 microM, five of them in the range 4-8 microM. Preliminary structure-activity relationships were established.

Anti versus syn opening of epoxides derived from 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine with Me3Al: factors controlling the stereoselectivity

Upon epoxidation with dimethyldioxirane, the 2',5'-bis-O-silyl derivatives of 9-(3-deoxy-beta-D-glycero-pent-3-enofuranosyl)adenine gave the respective "3',4'-up" epoxides exclusively. Reaction between these epoxides and Me3Al was investigated in detail. It was found that the stereoselectivity of epoxide ring opening (anti versus syn) varied significantly upon changing the amount of Me3Al, the solvent, the O-silyl protecting group, and the reaction temperature. A possible reaction mechanism is proposed.

Synthesis of the C1-phosphonate analog of UDP-GlcNAc

We describe the first synthesis of the C1-phosphonate analog of UDP-GlcNAc, based on a new preparation of the corresponding glycosyl phosphonate. This C-glycosyl analog is shown to be a very weak inhibitor (Ki>10 mM) of fungal chitin synthase, indicating that at least in this case the replacement of the anomeric oxygen with a methylene group is not an innocent substitution.

Novel and Efficient Method for the Allylation of Carbonyl Compounds and Imines Using Triallylaluminum

This is the first report of the use of triallylaluminum as a reagent for the allylation of carbonyl compounds and imines. The allylation of ketimines without additional metal catalyst is known so far only in the case of the Grignard reagent. Triallylaluminum is a useful alternative to provide the homoallylic amines in excellent yield upon addition to aldimines and ketimines. The significant reactivity of this reagent was confirmed by its reaction with a sterically rigid ketone such as adamantanone to provide 1-adamantyl-3-buten-1-ol in 98% yield. The chemoselectivity of triallylaluminum was demonstrated by using different ketoesters. It is noteworthy that triallylaluminum is prepared from allyl bromide and aluminum metal, and not from a Grignard reagent, and that the procedure is operationally simple, leading to good to excellent product yields.

Total Synthesis of Gambierol: The Generation of the A–C and F–H Subunits by Using a C-Glycoside Centered Strategy

Gambierol, a representative of the marine ladder toxin family, consists of eight ether rings, 18 stereocenters, and two challenging pyranyl rings having methyl groups that are in a 1,3-diaxial orientation to one another. Herein we describe the generation of gambierol's A-C and F-H ring systems and demonstrate the versatility of the glycosyl anhydride, enol ether-olefin RCM strategy to fused polycyclic ethers. This work has both enabled us to generate sufficient quantities of the gambierol precursors and has enabled us to better understand the chemical transformations that were key to these efforts. Fundamental work included efforts to C-glycosides and C-ketosides, Claisen rearrangements, and enol ether-olefin RCM reactions.

Mirror-image carbohydrates: synthesis of the unnatural enantiomer of a blood group trisaccharide

Methyl D-glucoside and d-glucose pentaacetate are transformed, respectively, into methyl alpha-O-glucuronide 3 and hydroxymethyl beta-C-glucuronide 9, which undergo decarboxylative elimination efficiently to produce 4-deoxypentenoside 4 and L-glucal 10. These unsaturated pyranosides provide an expeditious entry into mirror-image oligosaccharides, as demonstrated in the synthesis of the unnatural enantiomer of the H-type II blood group determinant trisaccharide (D-Fuc-(alpha1-->2)-L-Gal-(beta1-->4)-L-GlcNAc-beta-OMe). This work illustrates that D-glucose, a common starting material in the synthesis of naturally occurring carbohydrates, can also be used to prepare their mirror-image analogues.

An oxidative entry into the amido trioxadecalin ring system

The amido trioxadecalin ring system is a key structural component of the architecturally interesting anticancer and immunosuppressive agents of the mycalamide, theopederin, and onnamide families of natural products. We report a new entry into this structure in which a mixed acetal serves as a surrogate for a formaldehyde hemiacetal in an addition to an oxidatively generated acyliminium ion. The stereochemical outcome of this process can be explained by the conformational preferences of the product ring system. [reaction: see text]

Synthesis of an F-H gambierol subunit using a C-glycoside-centered strategy

[structure: see text] This manuscript describes our synthesis of the F-H subunit of gambierol. In addition to the synthesis of the tricycle, of note is an interesting protecting group influence on the generation of a C(23) C-glycoside as well as the use of ring-closing metathesis to generate a tetrasubstituted enol ether.

Addition of organozinc species to cyclic 1,3-diene monoepoxide

[reaction: see text] The reaction of organozinc reagents (ZnEt(2), ZnPh(2)) with cyclic 1,3-diene monoepoxides in the presence of CF(3)COOH gave the cis-addition products. Lewis acids such as (CF(3)CO(2))(2)Zn and ZnCl(2) mediated the nucleophilic addition of ZnEt(2) to cyclooctadiene monoepoxide with high stereoselectivity.

C-glycosides to fused polycyclic ethers. A formal synthesis of (+/-)-hemibrevetoxin B

This paper describes a formal total synthesis of the marine ladder toxin hemibrevetoxin B from Danishefsky's dienes. This approach couples the generation of C-glycosides from cyclic enol ethers with metathesis or acid-mediated annulation reactions. The result is a highly efficient synthesis of the tetracyclic ring system of hemibrevetoxin B.