Total synthesis of ingenol

A total synthesis of the biologically important diterpene ingenol has been completed. Ring-closing olefin metathesis was used to construct the strained "inside-outside" tetracyclic skeleton, and a series of diastereoselective reactions were employed to complete the synthesis. Another naturally occurring ingenane, 20-deoxyingenol, has also been prepared.     

Metallaborane reaction chemistry. A facile and reversible dioxygen capture by a B-frame-supported bimetallic: structure of [(PMe2Ph)4(O2)Pt2B10H10

[(PMe2Ph)4Pt2B10H10] reversibly takes up atmospheric dioxygen to give the fluxional dioxygen-dimetallaborane complex [(PMe2Ph)4(O2)Pt2B10H10], which has Pt-Pt 2.7143(3), Pt-O 2.141(4) and 2.151(4) and O-O 1.434(6)A.     

Formation of benzynes from 2,6-dihaloaryllithiums: mechanistic basis of the regioselectivity

The key elimination step for the formation of 3-chloro- and 3-fluorobenzyne from 2-chloro-6-fluorophenyllithium displays a pronounced solvent-dependent regioselectivity. 6Li and 13C NMR spectroscopic studies on 2-chloro-6-fluorophenyllithium reveal a single monomeric aryllithium, suggested by DFT computational studies to be a trisolvate. Rate studies indicate that the elimination of LiCl and LiF proceeds via trisolvated and disolvated monomers, respectively.     

Measurement of cell migration on surface-bound fibronectin gradients

A novel technique for the quantitative observation of cell migration along linear gradient substrates functionalized with adhesive proteins is presented. Gradients of the cell adhesion molecule fibronectin are generated by the cross diffusion of functionalizable alkanethiols on gold and characterized by X-ray photoelectron spectroscopy and surface plasmon resonance. Two distinct migration assays are described that characterize the movement of either sparsely populated noncontacting cells or a confluent monolayer of cells into free space. The drift speed of bovine aortic endothelial cells is measured and shown to increase along a fibronectin gradient when compared to a uniform control substrate using both assays. The results of these experiments establish reproducible conditions for studies of cell migration on gradients of surface-bound ligands.     

The propionyl cation heat of formation revisited

The 298 K heat of formation for the propionyl cation (C₂H₅CO⁺) has been measured previously by dissociative photoionization mass spectrometry. However, recent theoretical and experimental studies involving methylketene suggest that this may be significantly underestimated, resulting in a methylketene proton affinity that is too high by ∼30 kJ mol⁻¹. In this study, the previous m/z 57 appearance energies were carefully re-evaluated, with various possible sources of error being investigated. These include factors such as sample purity, carbon-13 contamination from lower energy m/z 56 processes, kinetic and/or competitive shifts, reverse activation energies, ionizing energy calibration errors and the availability of accurate supplementary thermochemical data. In addition, high-level ab initio calculations are used to model the relevant unimolecular fragmentation processes for each of the ionized precursor molecules. As a result, it is found that only the 2-butanone appearance energy can be used to provide a reliable value for the propionyl cation heat of formation. From the 298 K m/z 57 appearance energy of 10.199 ± 0.003 eV for 2-butanone measured here, a value of 617.8 ± 0.9 kJ mol⁻¹ is derived for , which corresponds to 845.4 ± 4.8 kJ mol⁻¹ for the proton affinity of methylketene. This is in good agreement with previous theoretical calculations and thermokinetic proton affinity measurements, indicating that a significant upward revision to the propionyl cation heat of formation is warranted. Copyright © 2004 John Wiley & Sons, Ltd.     

Selective ortho-cleavage of methoxymethyl- and 4-methoxybenzyl ethers

Iodine in methanol has been found to be an effective catalyst system for the cleavage of alkoxymethyl ethers. This catalyst system is particularly useful for the selective removal of ortho-methoxymethyl- and ortho-(4-methoxybenzyl) ethers in the presence of their para-counterparts. Further investigation of various metal salts in methanol for their ability to cleave alkoxymethyl ethers revealed high-valent salts as effective catalysts, presumably through the release of small quantities of HCl.     

Accelerated screening of phage-display output with alkaline phosphatase fusions

When using multiple targets and libraries, selection of affinity reagents from phage-displayed libraries is a relatively time-consuming process. Herein, we describe an automation-amenable approach to accelerate the process by using alkaline phosphatase (AP) fusion proteins in place of the phage ELISA screening and subsequent confirmation steps with purified protein. After two or three rounds of affinity selection, the open reading frames that encode the affinity selected molecules (i.e., antibody fragments, engineered scaffold proteins, combinatorial peptides) are amplified from the phage or phagemid DNA molecules by PCR and cloned en masse by a Ligation Independent Cloning (LIC) method into a plasmid encoding a highly active variant of E. coli AP. This time-saving process identifies affinity reagents that work out of context of the phage and that can be used in various downstream enzyme linked binding assays. The utility of this approach was demonstrated by analyzing single-chain antibodies (scFvs), engineered fibronectin type III domains (FN3), and combinatorial peptides that were selected for binding to the Epsin N-terminal Homology (ENTH) domain of epsin 1, the c-Src SH3 domain, and the appendage domain of the gamma subunit of the clathrin adaptor complex, AP-1, respectively.     

Electrochemical and spectroelectrochemical characterization of Ru(2)(4+) and Ru(2)(3+) complexes under a CO atmosphere

Eleven different Ru(2)(4+) and Ru(2)(3+) derivatives are characterized by thin-layer FTIR and UV-visible spectroelectrochemistry under a CO atmosphere. These compounds, which were in-situ electrogenerated from substituted anilinopyridine complexes with a Ru(2)(5+) core, are represented as Ru(2)(L)(4)Cl where L = 2-CH(3)ap, ap, 2-Fap, 2,3-F(2)ap, 2,4-F(2)ap, 2,5-F(2)ap, 3,4-F(2)ap, 3,5-F(2)ap, 2,4,6-F(3)ap, or F(5)ap. The Ru(2)(5+) complexes do not axially bind CO while mono- and bis-CO axial adducts are formed for the Ru(2)(4+) and Ru(2)(3+) derivatives, respectively. Six of the eleven investigated compounds exist in a (4,0) isomeric form while five adopt a (3,1) geometric conformation. These two series of compounds thus provide a large enough number of derivatives to examine trends and differences in the spectroscopic data of the two types of isomers in their lower Ru(2)(4+) and Ru(2)(3+) oxidation states. UV-visible spectra of the Ru(2)(4+) derivatives and IR spectra of the Ru(2)(3+) complexes under CO are both isomer dependent, thus suggesting that these data can be used to reliably predict the isomeric form, i.e., (3,1) or (4,0), of diruthenium complexes containing four unsymmetrical substituted anilinopyridinate bridging ligands; this was confirmed by X-ray crystallographic data for seven compounds whose structures were available.     

tert‐Butyl 5‐methoxy‐3‐pentyl­indole‐1‐carboxyl­ate

The molecule of the title compound, C₁₉H₂₇NO₃, is essentially planar, with all non‐H atoms within 0.2 Å of the nine‐membered indole plane, except for the three tert‐butyl C atoms. The C₅ pentyl chain is in an extended conformation, with three torsion angles of 179.95 (13), 179.65 (13) and −178.95 (15)° (the latter two angles include the C atoms of the C₅ chain only). Three intramolecular C—H⋯Ozdbnd;C contacts are present (C⋯O < 3.05 Å and C—H⋯O > 115°), and an intermolecular C—H⋯Ozdbnd;C contact and π–π stacking complete the intermolecular interactions.     

Extended Peptide Nucleic Acid Nucleobases Based on Isoorotic Acid for the Recognition of A–U Base Pairs in Double-Stranded RNA

Peptide nucleic acids (PNA) with extended isoorotamide containing nucleobases ( I _o ) were designed for binding A–U base pairs in double-stranded RNA. Isothermal titration calorimetry and UV thermal melting experiments revealed improved affinity for A–U using the Io scaffold in PNA. PNAs having four sequential Io extended nucleobases maintained high binding affinity.