The
finding by scientists at Hoffmann-La Roche that cis-imidazolines could disrupt the protein–protein interaction
between p53 and MDM2, thereby inducing apoptosis in cancer cells,
raised considerable interest in this scaffold over the past decade.
Initial routes to these small molecules (i.e., Nutlin-3) provided
only the racemic form, with enantiomers being enriched by chromatographic
separation using high-pressure liquid chromatography (HPLC) and a
chiral stationary phase. Reported here is the first application of
an enantioselective aza-Henry approach to nonsymmetric cis-stilbene diamines and cis-imidazolines. Two novel
mono(amidine) organocatalysts (MAM) were discovered to provide high
levels of enantioselection (>95% ee) across a broad range of substrate
combinations. Furthermore, the versatility of the aza-Henry strategy
for preparing nonsymmetric cis-imidazolines is illustrated
by a comparison of the roles of aryl nitromethane and aryl aldimine
in the key step, which revealed unique substrate electronic effects
providing direction for aza-Henry substrate–catalyst matching.
This method was used to prepare highly substituted cis-4,5-diaryl imidazolines that project unique aromatic rings, and
these were evaluated for MDM2-p53 inhibition in a fluorescence polarization
assay. The diversification of access to cis-stilbene
diamine-derived imidazolines provided by this platform should streamline
their further development as chemical tools for disrupting protein–protein
interactions.
Migratory insertion of benzylidene carbene ligands into arylpalladium(II) species generates η(3)-benzylpalladium intermediates that can cyclize to generate five- and six-membered rings with new sp(3) centers. The reaction tolerates a range of arene functional groups and stabilized enolates. The products generated through this reaction are 1-arylindanes and 1-aryltetralins that are common to a range of natural products.
Palladium-catalyzed carbene insertion was utilized in a formal synthesis of (±)-picropodophyllone and a total synthesis of (±)-brazilin. All prior syntheses of brazilin have involved a Friedel−Crafts alkylation in the key carbon− carbon bond forming events. The palladium-catalyzed [4 + 1] reaction generates a 1-arylindane with all of the functionalities needed for formation of the indano[2,1-c]chroman ring system of brazilin. The synthesis of (±)-brazilin was achieved in 11 steps (longest linear sequence) with an overall 11% yield.
Phenolic resin is the material of choice used for composite liners in solid rocket motor nozzles. We investigate the effect of the cure conditions (94, 116, and 155 C) on vacuum only (VO) processed composite mechanical, thermal, and microstructural changes. Although the T g 's correlated with the processing conditions, mechanical properties showed unexpected non-linear degradation after 94 C processing. This difference is primarily due to the lower cure state of the
A concise
total synthesis of (±)-pestalachloride C and (±)-pestalachloride
D was achieved through a Knoevenagel/hetero-Diels–Alder cascade
reaction to test the nonenzymatic biosynthetic hypothesis of Shao,
Wang, and co-workers. The cascade reaction generates a mixture of
racemic indano[2,1-c]chromans like those found in
the natural products.
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