Optical resolution of 7-oxabicyclo[2.2.1]hept-21-ene derivatives. Diastereoselectivity in the formation of cyanohydrine-brucine complexes

A new, practical method for the optical resolution of bicyclic ketones if illusttrated by the preparation of (+)-(1R,4R)-7-oxabicyclo[2.2.1]bept-5-en-2-one ((+)- 1 ) and (+)-(1R, 2S,4R)-2-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yul acetate ((+)- 4 ). It involves the diastereoselective formation of a brucine complex with the corresponding cyanhydrine mixture.     

Analysis of mouse beta-haptoglobin chain by lectin affinoblotting detection

Two different human mammary carcinoma cell lines were xenotransplanted into nude mice. Serum samples were obtained prior to and after transplantation and investigated by two-dimensional electrophoresis (2-DE). By comparison of these silver-stained patterns additional protein spots were detected resulting either from proteins secreted or shed by the tumor itself or from mouse proteins induced by the tumor or the transplantation procedure. One group of spots detectable in post-transplantation serum as well as in control serum after mock-transplantation but not in pretransplantation serum was microsequenced and identified as mouse beta-haptoglobin. The carbohydrate structures of beta-haptoglobin were characterized by two different immunochemical glycoprotein staining procedures to detect differential terminal glycan modifications.     

Stereochemistry of planarchiral compounds,part X

2,7-Dibromo-1,6-methano[10]anulene (3) and 2,9-Dibromo-syn-1,6:8,13-diimino[14]anulene (9) were quantitatively separated into their enantiomers by chromatography on triacetylcellulose (TAC) in ethanol. X-ray structure analysis (Bijvoet technique) established the chiralities (+)(R)-3 and (+)(S)-9 for the dextrorotatory enantiomers.Comparison of the CD spectra allowed the configurational assignment to further optically active [10] and [14] anulenes which were also accessible by chromatography onTAC. Conversion of (+)(R)-2-bromo-1,6-methano[10]anulene (2) into the corresponding methylester (–)-4 confirmed its previously proposed chirality (–)(R).2,7-Dibromo-1,6-oxido[10]anulene (7) and 2,9-dibromo-syn-diimino[14]anulene (9) are in contrast to the 2,9-dibromo-syn-dioxido[14]anulene (10) optically stable until 250°C. Consequently their inversion barriers are higher than 42 kcal (176 kJ) mol^–1.The CD spectra of mono and disubstituted anulenes (with C₁ and C₂ symmetry, resp.) are compared: For the [10]anulenes theCotton effect around 330 nm seems to be specific for their configuration with a positive effect indicating (S)-chirality and vice versa. Some regularities concerning the chromatographic resolutions are discussed.

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Stereochemie planar chialer Verbindungen, 10. Mitt.: Röntgenkristallstruktur und absolute Chiralität überbrückter [10]- und [14] Anulene

Zusammenfassung 2,7-Dibrom-1,6-methano[10]anulen (3) und 2,9-Dibrom-syn-1,6:8,13-diimino[14]anulen (9) wurden durch Chromatographie an Triacetylcellulose (TAC) in Ethanol quantitativ in ihre Enantiomeren getrennt. Röntgenstruktur-analyse (Bijvoet-Technik) bewies für die rechtsdrehenden Enantiomeren die Chiralität (+)(R)-3 bzw. (+)(S)-9.Ein Vergleich der CD-Spektren ermöglichte die Konfigurationszuordnung weiterer optisch aktiver [10]- und [14]Anulene, die gleichfalls durch Chromato-graphie anTAC erhalten worden waren. Umwandlung von (+)(R)-2-Brom-1,6-methano[10]anulen (2) in den entsprechenden Methylester (–)-4 bestätigte dessen schon früher vorgeschlagene Chiralität (–)(R).Dibrom-1,6-oxido[10]anulen (7) und Dibrom-diimino[14]anulen (9) sind im Gegensatz zum Dioxido[14]anulen (10) bis 250°C optisch stabil. Ihre Inver-sionsbarrieren liegen somit über 42 kcal (176kJ) mol^–1.Die CD-Spektren von mono- und disubstituierten Anulenen (mit C₁ bzw. C₂-Symmetrie) werden verglichen: Für die [10]Anulene scheint derCottoneffekt um 330 nm konfigurationsspezifisch zu sein, wobei ein positiver Effekt (S)-Chiralität anzeigt — und vice versa. Einige Regelmäßigkeiten bezüglich der chromatographischen Enantiomerentrennung werden diskutiert.

     

Total Synthesis of L-Allose,L-Talose,and derivatives.

(1S, 4R, 5S, 6S)-5-exo, 6-exo-(Isopropylidenedioxy)-7-oxabicyclo[2.2.1]heptan-2-one ((?)- 1 ) was transformed with high stereoselectivity to L -allose. Similarly, enantiomer (+)- 1 was transformed into L -talose. The ketones (+)- 1 and (?)- 1 were derived from furan and 1-cyanovinyl (1S)-camphanate and 1-cyanovinyl (1R)-camphanate, respectively.     

Sulfur dioxide mediated one-pot, three- and four-component syntheses of polyfunctional sulfonamides and sulfonic esters: study of the stereoselectivity of the ene reaction of sulfur dioxide

The ene reaction of sulfur dioxide with enoxysilanes or with allylsilanes generates silyl sulfinates that can be brominated (Br(2) or NBS) or chlorinated (NCS or Cl(2)) to produce the corresponding sulfonyl halides. They react with primary and secondary amines or alcohols to give the corresponding sulfonamides and sulfonic esters, respectively. The hetero-Diels-Alder addition of sulfur dioxide to 1-oxy- or 1,3-dioxy-1,3-dienes generates zwitterions that add to enoxysilanes or allylsilanes giving silyl sulfinates that can be converted in situ into polyfunctional sulfonamides or sulfonic esters. This realizes quick access to libraries of complicated sulfonamides and sulfonic esters applying one-pot, three- and four-component methods.     

Stereoselective syntheses of 1,4-dideoxy-1,4-imino-octitols and novel tetrahydroxyindolizidines

A new route for the preparation of four new indolizidines, (1R,2S,6S,7S,8aS)- and (1R,2S,6R,7R,8aS)-1,2,6,7-tetrahydroxyindolizidine (30 and 32) and (1S,2R,7S,8S,8aR)- and (1S,2R,7R,8R,8aR)-1,2,7,8-tetrahydroxyindolizidine (44 and 46), is reported. The synthesis is based on Knoevenagel homologation of the readily available enantiomerically pure pyrrolidin-carbaldehydes 13 and 37followed by asymmetric dihydroxylation of the subsequent alkenyl pyrrolidines and cyclization of the corresponding imino-octitols. The new indolizidines and their precursors (imino-octitols 20, 25, 26) and indolizidinones 28a and 28b have been tested for inhibitory activities toward 26 glycosidases. The enzymatic inhibition of trans-7-hydroxy-d-(-)-swainsonine (44) toward alpha-mannosidases is similar to that described for trans-7-hydroxy-l-(+)-swainsonine (11b) toward naringinase (alpha-l-rhamnosidase from Penicillium decumbens).     

Acid-Catalyzed Rearrangements of 5,6-exo-Epoxy-7-oxabicyclo[2.2.1]hept-2-yl Derivatives. Migratory Aptitudes of Acyl vs. Alkyl Groups in Wagner-Meerwein Transpositions

In the presence of HSO₃F/Ac₂O in CH₂CL₂, 2-exo- and 2-endo-cyano-5,6-exo-epoxy-7-oxabicyclo[2.2.1]hept-2-yl acetates ( 6a , b ) gave products derived from the epoxide-ring opening and a 1,2-shift of the unsubstituted alkyl group (σ bond C(3)–C(4)). In contrast, under similar conditions, the 5,6-exo-epoxy-7-oxabicyclo[2.2.1]heptan-2-one ( 6c ) gave 5-oxo-2-oxabicyclo[2.2.1]heptane-3,7-diyl diacetates 20 and 21 arising from the 1,2-shift of the acyl group. Acid treatment of 5,6-exo-epoxy-2,2-dimethoxy-7-oxabicyclo[2.2.1]heptane ( 6d ) and of 5,6-exo-epoxy-2,2-bis(benzyloxy)-7-oxabicyclo[2.2.1]heptane ( 6e ) gave minor products arising from epoxide-ring opening and the 1,2-shift of σ bond C(3)–C(4) and major products ( 25 , 29 ) arising from the 1,3-shift of a methoxy and benzyloxy group, respectively. Under similar conditions, 5,6-exo-epoxy-2,2-ethylenedioxy-7-oxabicyclo[2.2.1]heptane ( 6f ) gave 1,1-(ethylenedioxy)-2-(2-furyl)ethyl acetate ( 32 , major) and a minor product 33 , arising from the 1,2-shift of σ bond C(3)–C(4). The following order of migratory aptitudes for 1,2-shifts toward electron-deficient centers has been established: acyl > alkyl > alkyl α-substituted with inductive electron-withdrawing groups. This order is valid for competitive Wagner-Meerwein rearrangements involving equilibria between carbocation intermediates with similar exothermicities.     

Organosulfur compounds: electrophilic reagents in transition-metal-catalyzed carbon-carbon bond-forming reactions

Transition-metal-catalyzed carbon-carbon bond-forming reactions are among the most powerful methods in organic synthesis and play a crucial role in modern materials science and medicinal chemistry. Recent developments in the area of ligands and additives permit the cross-coupling of a large variety of reactants, including inexpensive and readily available sulfonyl chlorides. Their desulfitative carbon-carbon cross-coupling reactions (Negishi, Stille, carbonylative Stille, Suzuki-Miyaura, and Sonogashira-Hagihara-type cross-couplings and Mizoroki-Heck-type arylations) are reviewed together with carbon-carbon cross-coupling reactions with other organosulfur compounds as electrophilic reagents.     

A New Total Synthesis of D-threo-L-talo-Octose

A new approach to the total, asymmetric synthesis of D -threo-L -talo-octose ((?)- 1 ) and its derivatives is presented. It is based on the chemoselective Wittig-Horner monoolefination of a 5-deoxy-D -ribo-hexodialdose derivative 4 obtained by selective reduction of (?)-5-deoxy-2.3-O-isopropylidene-/β-D -ribo-hexofuranurono-6,1-lactone ((?)- 3 ). Allylic bromination of the resulting methyl (E)-oct-6-enofuranuronate (+)- 5 followed by intramolecular nucleophilic displacement of the so-obtained bromides gave a 13.3:1 mixture of (?)-methyl (E)-l,4-anhydro-6,7-dideoxy-2,3-O-isopropylidene-β-L -talo-oct-6-enopyranuronate ((?)- 8 ) and methyl (E)-l,4-anhydro-6,7-dideoxy-2,3-O-isopropylidene-α-D -allo-oct-6-enopyranuronate ( 9 ). The double hydroxylation of the enoate (?)- 8 followed Kishi's rule and gave the corresponding D -threo-β-L -talo-octopyranuronate derivative (?)- 11 with a good diastereoselectivity. Reduction of ester (?)- 11 and deprotection led to pure (?)- 1 .