Bismuth trichloride catalyzed synthesis of α-aminonitriles

A simple and efficient one-pot method has been developed for the synthesis of α-aminonitriles from aldehydes, amines, and trimethylsilyl cyanide in the presence of a catalytic amount of bismuth trichloride.     

Polymer-DNA hybrids as electrochemical probes for the detection of DNA

The syntheses of several norbornene block copolymers containing oligonucleotide and ferrocenyl side chains and their use in the electrochemical detection of DNA are described. Two kinds of DNA-containing block copolymers with either ferrocenyl or dibromoferrocenyl groups were prepared via ring-opening metathesis polymerization (ROMP). Based on these two distinct ferrocene derivatives, a triblock copolymer labeling strategy was developed. With this strategy, the identity of DNA target can be determined by the E1/2s of the ferrocenyl moieties and the ratio of peak currents. These polymers exhibit predictable and tailorable electrochemical properties, high DNA duplex stability, and unusually sharp melting transitions, which are highly desirable characteristics for DNA detection applications. Significantly, single-base mismatches could be easily detected using two distinct block copolymers as dual-channel detection probes in an electrochemical DNA detection format.     

Synthesis and characterization of platinum diimine bis(acetylide) complexes containing easily derivatizable aryl acetylide ligands

New Pt(II) diimine bis(acetylide) complexes where the diimine is a substituted bipyridine or phenanthroline and the arylacetylide is 4-ethynylbenzaldehyde have been prepared in good to excellent yields. Spectroscopic characterization supports a square planar coordination geometry with cis-alkynyl ligands, and the crystal structure of one of the complexes, Pt(phen)(Ctbd1;CC(6)H(4)CHO)(2) (1), confirms the assignment. The new diimine bis(acetylide) complexes exhibit an absorption band ca. 400 nm that corresponds to a Pt(d) --> pi diimine charge transfer transition and are brightly emissive in fluid solution, with excited state lifetimes in the range 100-800 ns. Correlation of diimine substituent with lambda(max) for the 400 nm absorption band gives strong support to the MLCT assignment. Complex 1 undergoes electron transfer quenching, showing good Stern-Volmer behavior with a variety of oxidative and reductive quenchers. Quenching studies conducted with DNA nucleosides (A, T, C, G) were also investigated. Silyl-protected adenosine and guanosine were found to quench the luminescence of 1 better than similarly protected cytidine or thymidine. Since the former are the more easily oxidized bases, the results suggest that the Pt(II) diimine bis(acetylide) complexes are more powerful photooxidants than photoreductants with regard to electron transfer to DNA bases.     

Scandium triflate as an efficient and useful catalyst for the synthesis of β-amino alcohols by regioselective ring opening of epoxides with amines under solvent-free conditions

A simple and efficient method has been developed for the synthesis of β-amino alcohols by ring opening of epoxides in the presence of a catalytic amount of Sc(OTf)₃ at room temperature under solvent-free conditions. The reaction works well with both aromatic and aliphatic amines. High regio-, and diastereoselectivity can be considered as a noteworthy advantage of this method.     

Synthesis, structure, characterization, and photophysical studies of a new platinum terpyridyl-based triad with covalently linked donor and acceptor groups

A new terpyridyl-containing Pt triad [Pt(pytpy)(p-CC-C6H4-NH-CO-C6H2(OMe)3)](PF6)2 (4), where pytpy = 4'-(4-pyridin-1-ylmethylphenyl)-[2,2';6',2' ']terpyridine and p-CC-C6H4-NH-CO-C6H2(OMe)3 = N-(4-ethynylphenyl)-3,4,5-trimethoxybenzamide, has been synthesized and structurally characterized. The related donor-chromophore dyad [Pt(ttpy)(p-CC-C6H4-NH-CO-C6H2(OMe)3)]PF6 2, where ttpy = 4'-p-tolyl-[2,2';6',2' ']terpyridine, and the chromophore-acceptor dyad [Pt(pytpy)(CCC6H5)](PF6)2 (3), where CCC6H5 = ethynylbenzene, have also been studied. The multistep syntheses culminate with a CuI-catalyzed coupling reaction of the respective acetylene with either [Pt(ttpy)Cl]PF6 or [Pt(pytpy)Cl](PF6)2. X-ray and spectroscopic studies support assignment of a distorted square planar environment around the Pt(II) ion with three of its coordination sites occupied by the terpyridyl N-donors and the fourth coordination site occupied by the acetylenic carbon. Although the parent compound [Pt(ttpy)(CCC6H5)]PF6 (1) is brightly luminescent in fluid solution at 298 K, dyad 2 as well as triad 4 exhibit complete quenching of the emission. The chromophore-acceptor (C-A) dyad 3 displays weak solution luminescence at room temperature with a phi(rel)(em) of 0.011 (using Ru(bpy)3(2+) as a standard with phi(rel)(em) = 0.062). Electrochemically, the donor-chromophore (D-C) dyad and the donor-chromophore-acceptor (D-C-A) triad exhibit both metal-based and donor ligand-based oxidations, whereas the triad and the C-A dyad show the expected pyridinium- and terpyridine-based reductions. Transient absorption studies of the dyad and triad systems indicate that although the trimethoxybenzene group acts as a reductive donor, in the present system, the pyridinium group fails to act as an acceptor.     

Computational and conformational evaluation of FTase alternative substrates: insight into a novel enzyme binding pocket

Protein farnesyltransferase (FTase) is an important anticancer drug target. In an effort to develop isoprenoid diphosphate-based FTase inhibitors, striking variations have been observed in the ability of conservatively modified analogues to bind to the enzyme. For example, 2Z-GGPP is an alternative substrate with high binding affinity, while GGPP is not an alternative substrate. Using the availability of high-resolution FTase crystal structures, we have used pharmacophore and docking studies to elucidate a new binding pocket for isoprenoid analogues. The unique conformations between the first two isoprene units of 2Z-GGPP, but not GGPP, allows 2Z-GGPP to exploit this new binding pocket. The discovered conformation allows the molecule to adopt a reactive conformation while placing hydrophobic groups within the predominately hydrophobic binding pocket. This computational finding is supported by NMR studies on (13)C-labeled 2Z-farnesol, which confirm that the computationally predicted conformation is also favored in solution. These discoveries suggest that ligand conformational flexibility may be an important design consideration for the development of both inhibitors and alternative substrates of FTase.     

Vibrational excitation and relaxation of five polyatomic molecules in an electrical discharge

Vibrational excitation and relaxation of five linear polyatomic molecules, OCS, OC3S, HC3N, HC5N, and SiC2S, have been studied by Fourier transform microwave spectroscopy in a supersonic expansion after the application of a low-current dc electric discharge. For each chain, the populations in bending and stretching modes have been characterized as a function of the applied discharge current; for stable OCS and HC3N, vibrational populations were studied as well in the absence of a discharge. With no discharge present the derived vibrational temperatures are slightly below T, the temperature of the gas before the supersonic expansion (i.e., 300 K). In the presence of the discharge, vibrational excitation occurs via inelastic collisions with the electrons and the vibrational temperatures rise as the applied current increases. Global vibrational relaxation is governed by rapid vibration-vibration (VV) energy transfer and slow vibration-translation (VT) energy transfer. The latter process is rate-determining and depends primarily on the wave number of the vibration. Vibrational modes with wave numbers near and below kT/hc (where T = 300 K and kT/hc-210 cm(-1)) are efficiently cooled by VT transfer because a sufficient number of collisions occur in the initial stages of the supersonic expansion. Vibrational modes with wave numbers around 450 cm(-l) appear to be inefficiently cooled in the molecular beam; at these energies VV and VT rates are probably comparable. For high-frequency vibrations, VV energy transfer dominates. For the longer chains OC3S and HC5N, higher-lying modes are generally not detectable and vibrational temperatures of most lower-lying modes were found to be lower than those of OCS and HC3N, suggesting that as the size of the molecules increases, intermode VV transfer becomes more efficient, plausibly due to the higher density of vibrational levels. New high resolution spectroscopic data have been obtained for several vibrationally excited states of OC3S, HC3N, and HC5N. Rotational lines of the 13C and 15N isotopic species of HC5N have been measured, yielding improved rotational and centrifugal distortion constants; 14N nitrogen quadrupole coupling constants for the isotopic species of HC5N with 13C have been determined for the first time.