Intramolecular photocycloaddition of β-stilbazoles tethered by silyl chains

Intramolecular (2+2) photocycloaddition of β-stilbazoles tethered by silyl chains took place with high efficiency. Complexation with dicarboxylic acid or catechol further enhanced both the efficiency and stereoselectivity.     

Catalytic Hydrosilylation of Furan, Thiophene, and Pyridine Aldimines

The addition of hydrosilanes (HSiEt₃, HSiMe₂Ph, H₂SiPh₂) to the CH=N bond of heterocyclic azomethines has been studied in the presence of monovalent complexes of rhodium and palladium. The effect on the reaction of the CF₃ group of the aldimines, which were obtained from O-, S-, and N-heteroaromatic aldehydes and 2-trifluoromethylaniline, has been clarified, as were other regularities of the processes being studied. A series of corresponding furans, thiophenes, and pyridine amines has been synthesized.     

Synthesis of β-phenyl-δ,ε-unsaturated amino acids and stereoselective introduction of side chain groups into [4,3,0]-bicyclic β-turn dipeptides

(2S,3S)- and (2R,3R)-2-amino-3-phenyl-5-hexenoic acids have been synthesized in large scale by using Ni(II)-complexes as a template. The amino acids were used in the synthesis of [4,3,0]-bicyclic β-turn mimetics by a convergent methodology. The unique advantage of this strategy is the convenience of introducing side chain groups with predetermined chiralities on both the five- and six-membered heterocyclic rings.     

A new approach towards peptidosulfonamides: synthesis of potential inhibitors of bacterial peptidoglycan biosynthesis enzymes MurD and MurE

Peptidosulfonamides are an emerging group of peptidomimetics with a variety of applications in medicinal chemistry. We present a novel approach to the synthesis of peptidosulfonamides, and apply it to a series of new potential inhibitors of the bacterial peptidoglycan biosynthesis enzymes MurD and MurE. The synthesis was conducted via N-phthalimido β-aminoethanesulfonyl chlorides, which are new building blocks for the synthesis of peptidosulfonamides. In the most crucial step, sulfonic acids or their sodium salts were converted into the corresponding sulfonyl chlorides using an excess of either SOCl₂ or SOCl₂/DMF, and then coupled to the C-protected amino acid. None of the compounds significantly inhibited MurD, however, some inhibited MurE; one had an IC₅₀ below 200 μM, which constitutes a promising starting point for further development. Molecular modelling simulations were performed on two analogues to investigate the absence of inhibitory activity of the sulfonamide compounds on MurD.     

Synthesis of vinyl-substituted oxiranes and their transformation to dihydrofurans

The reaction of dimethylsulfonium methylide with the carbonyl function of 2-arylidene-cyclohexanones obtained from 2-methylcyclohexanone affords the corresponding spirooxiranes. The application of this reaction to 2,2-dimethyl-6-(5-methylfurfurylidene)cyclohexanone and 2,2-dimethyl-6-(5-chlorofurfurylidene)cyclohexanone leads to substituted 4,4-dimethyl-1-furyl-1,-3,4,5,6,7-hexahydroisobenzofurans.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1439–1443, August, 1994.     

Ethyl-4,4,4-trifluoroacetoacetate (ETFAA), a powerful building block for enantiopure chirons in trifluoromethyl-β-amino acid series

Herein are studied new transformations of ethyl-4,4,4-trifluoroacetoacetate (ETFAA), giving access to a series of enantiopure chirons bearing both a trifluoromethyl group and an amino moiety. The key intermediate is obtained optically pure by a resolution procedure.     

Cetyltrimethylammonium hydroxide (CTAOH) as a general, ecofriendly catalyst for the formation of carbon-carbon bond through nitroalkanes

Nitroalkanes have been found to give good yields in Michael and nitroaldol (Henry) reactions by the use of a catalytic amount (10 mol%) of CTAOH, at room temperature and under solvent free conditions and in very short reaction times. The methods do not need a large excess of the nitroalkanes and show good chemoselectivity toward further functionalities.     

Ionic liquid-regulated sulfamic acid: chemoselective catalyst for the transesterification of β-ketoesters

1-Propyl-3-methylimidazolium chloride ([C₃MIm]Cl) ionic liquid and sulfamic acid (NH₂SO₃H), as a synergetic catalytic medium, were used for the transesterification of acetoacetate with alcohols of different structures. It shows the good ability for the chemoselective transesterificatin of β-ketoesters and maintains its catalytic activity in the reuse.     

Free radical-mediated vinyl amination: a mild, general pyrrolidinyl enamine synthesis

The complete scope of free radical-mediated vinyl amination is described, using 5-exo-trig cyclizations of vinyl radicals to the nitrogen of azomethines. The focus is primarily on N,N-dialkyl enamines since their nucleophilicity renders them the most challenging enamines to synthesize using redox conditions. These studies establish several encouraging precedents for the broader application of this strategy.     

Synthesis and biological evaluation of 6-oxa-nor-tropane glycomimetics as glycosidase inhibitors

The preparation of polyhydroxylated 6-oxa-nor-tropane glycomimetics structurally related to the glycosidase inhibitor family of the calystegines is reported. The synthetic strategy involves the furanose→piperidine rearrangement of 5-deoxy-5-ureido-l-idose precursors, followed by intramolecular glycosylation involving the primary hydroxyl group. Inversion of the configuration at C-3 in the resulting 6-oxa-(+)-calystegine B₂ analogue allows accessing the elusive 3-epi-6-oxa-(+)-calystegine B₂ skeleton. Acid-catalyzed opening of the nor-tropane bicycle was observed, however, which could be avoided by careful neutralization of the reaction mixture. The inhibition results suggest that (+)-calystegine B₂ derivatives and the corresponding C-3 epimers can be seen as glucomimetics and galactomimetics, respectively, pointing to a 1-azasugar mode of action for this family of alkaloids.