Synthesis and biological evaluation of peptidyl organotrifluoroborates and their corresponding boron analogs

Six peptidyl organotrifluoroborates and their corresponding boronate esters and/or boronic acid analogs were designed and synthesized. Their anti-proliferative activity against hepatocellular carcinoma cells (HepG2) and human metastatic breast cancer cells (MDA-MB231) were evaluated by use of an MTT assay. Potassium {4-[(3S,6S,9S)-3,6-dibenzyl-9-isopropyl-4,7,10-trioxo-11-oxa-2,5,8-triazadodecyl]phenyl}trifluoroborate (B6) was potent (IC₅₀ = 29.9 μM) against MDA-MB231, and {4-[(3S,6S,9S)-6-benzyl-3-((benzyloxy)methyl)-9-isopropyl-4,7,10-trioxo-11-oxa-2,5,8-triazadodecyl]phenyl}boronic acid (B9) and Potassium {4-[(3S,6S,9S)-6-benzyl-3-((benzyloxy)methyl)-9-isopropyl-4,7,10-trioxo-11-oxa-2,5,8-triazadodecyl]phenyl}trifluoroborate (B10) had broad anti-proliferative activity against HepG2 (IC₅₀ = 24.7 and 21.8 μM, respectively) and MDA-MB231 (IC₅₀ = 24.5 and 18.9 μM, respectively).     

Phase transfer catalysts anchored to polystyrene

Quarternary phosphonium and ammonium salts attached to polystyrene resins by short (2 - 3 atom) carbon chains are highly active phase transfer catalysts for a variety of nucleophilic substitution reactions.     

BH3-catalyzed oligomerization of ethyl diazoacetate: the role of C-boron enolates

In contrast to trialkyl boranes, the reaction of borane (BH3) and ethyl diazoacetate (EDA) generates dimer, trimer, and oligomers of EDA. The products arise from double, triple, and multiple insertions of CHCO2Et groups in B-C bonds. On the basis of NMR spectroscopic data, trapping experiments, and computational studies, a novel C-boron enolate has been identified as a key intermediate in this reaction. This C-boron enolate species is calculated to be 7.1 kcal/mol (gas phase) more stable than its isomeric O-boron enolate form. Both spectroscopic data and trapping results also reveal the formation of a doubly borylated enolate generated as a side product by a proton transfer between the C- and O-boron monoenolates.     

Novel flavonoids of Thelypteris torresiana

In our continuing research on cytotoxic components from the Formosan pteridophyte Thelypteris torresiana (GAUD.) ALSTONONE, two new compounds, a novel flavonoid, flavotorresin (1), and a flavonoid diglycoside, multiflorin C (2), along with five known compounds, were isolated. The structural elucidation was established on the basis of spectroscopic data analysis. The possible biosynthetic pathway of the flavonoids from this fern is summarized.     

An approach to the synthesis of stenine

A type 2 N-acylnitroso intramolecular Diels-Alder reaction followed by reductive N-O bond cleavage formed the B and C rings of the Stemona alkaloid stenine. Further elaboration provided the functionalized tricyclic core.     

Organo-silica hybrid functional nanomaterials: how do organic bridging groups and silsesquioxane moieties work hand-in-hand?

Bridged polysilsesquioxanes (BPS) are a class of versatile functional hybrid materials with tunable chemical, physical and mechanical properties. This tutorial review describes recent advances of these functional hybrid nanomaterials. The review includes control of factors affecting nanometre scale morphology, the preparation of spherical hybrid nanoparticles, along with applications in fields including energy, optics and electronics. Special emphasis will be made regarding the synergy between the organic component of the hybrid material and the polysilsesquioxane moieties.     

Tenuipyrone, a novel skeletal polyketide from the entomopathogenic fungus, Isaria tenuipes, cultivated in the presence of epigenetic modifiers

The concomitant addition of the histone deacetylase inhibitor and the DNA methyltransferase inhibitor to the culture medium of an entomopathogenic fungus, Isaria tenuipes, greatly enhanced its secondary metabolite production and led to the isolation of tenuipyrone (1), a novel polyketide with an unprecedented tetracyclic ring system bearing a spiroketal structural component, along with two known C(10)-polyketides, cephalosporolide B (2), which is a plausible biosynthetic precursor of 1, and cephalosporolide F (3).     

Adsorption of PTCDI on Au(1 1 1): Photoemission and scanning tunnelling microscopy

The adsorption of perylene-3,4,9,10-tetracarboxylic-3,4,9,10-diimide (PTCDI) on Au(1 1 1) has been studied using synchrotron-based X-ray photoelectron spectroscopy and in situ scanning tunnelling microscopy. Direct topographic and surface coverage information provided by the scanning probe measurements have enabled us to correlate peaks in the relatively complex carbon core-level photoemission to interactions of the surface with different parts of the PTCDI molecule. A strong interaction between the imide ends of the molecule with the underlying gold substrate is evidenced by a large chemical shift in the imide carbon peaks, which is observed only for the first adsorbed layer.     

Regioselective SNAr reactions of substituted difluorobenzene derivatives: practical synthesis of fluoroaryl ethers and substituted resorcinols

In this Letter, we describe a practical and highly selective method for the preparation of fluoroaryl ethers and differentially substituted resorcinol derivatives. This synthetic strategy relies on a selective S_NAr of substituted difluorobenzene derivatives with various alcohols.