The solid-phase synthesis and use of N-monosubstituted piperazines in chemical library synthesis

An efficient solid-phase synthesis of mono-N-substituted piperazines is presented. The key transformation involves a selective borane amide bond reduction in the presence of a carbamate resin linkage. This synthetic route takes advantage of the large diverse pool of commercially available carboxylic acids, acid chlorides, and sulfonyl chlorides. The solid-phase approach facilitates parallel processing by eliminating the need for column chromatography after each synthetic step. The N-monosubstituted piperazines were shown to react with polymeric activated tetrafluorophenol (TFP) reagents to generate arrays of amides and sulfonamides in good purity for biological testing.     

Simultaneous analysis of caffeic acid derivatives and alkamides in roots and extracts of Echinacea purpurea by high-performance liquid chromatography-photodiode array detection-electrospray mass spectrometry

High-performance liquid chromatography (HPLC) coupled with UV photodiode-array detection and electrospray ionization mass spectrometry was developed for the simultaneous analysis of caffeic acid derivatives and alkamides in the roots and extracts of Echinacea purpurea. Caffeic acid derivatives and alkamides produced very abundant peaks in the total ion current chromatogram during negative and positive cone voltage switching. Cichoric acid and the isomer pair, dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamide, were used as a standard for quantification of caffeic acid derivatives and alkamides in E. purpurea. This novel method surpasses previously published ones in product quality control and providing the HPLC chromatographic fingerprints of biological active components in E. purpurea.     

Ligand-receptor docking with the Mining Minima optimizer

The optimizer developed for the Mining Minima algorithm, which uses ideas from Genetic Algorithms, the Global Underestimator Method, and Poling, has been adapted for use in ligand-receptor docking. The present study describes the resulting methodology and evaluates its accuracy and speed for 27 test systems. The performance of the new docking algorithm appears to be competitive with that of previously published methods. The energy model, an empirical force field with a distance-dependent dielectric treatment of solvation, is adequate for a number of test cases, although incorrect low-energy conformations begin to compete with the correct conformation for larger sampling volumes and for highly solvent-exposed binding sites that impose little steric constraint on the ligand.     

A new strategy for solid phase synthesis of a secondary amide library using sulfonamide linker via radical traceless cleavage

A new strategy for solid phase synthesis of a secondary amide library using sulfonamide linker via radical traceless cleavage is reported. Polystyrylsulfonyl chloride (1) reacted with primary amines to afford polystyryl-supported N-alkyl sulfonamides (2), which were acylated with acid chlorides and followed by radical cleavage with TiCl₄/Zn to afford secondary amides. It was interestingly found that the products released from acyl alkanesulfonamide resins are closely dependent on the substituents of benzene rings of alkyl or acyl groups on the resins. When the substituent on benzene ring of N-benzyl group of sulfonamides is an electron rich MeO-group, the products released from sulfonamide resins are dependent on the substitution position on benzene ring: para-MeO- to yield 1,2-bis (p-methoxylphenyl)ethane and N-p-methoxylbenzyl benzamide (30:1); ortho-MeO- to give 1,2-bis (o-methoxylphenyl)ethane and N-o-methoxylbenzyl benzamide (1:15); and meta-MeO- only to release N-m-methoxylbenzyl benzamide. Neither N-benzoyl sulfonamide resins on benzene ring with electron-drawing para-O₂N-, nor the one with electron-donating para-H₂N- could release any amide product, while the N-benzoyl sulfonamide resins on benzene ring with para-acetamido group released para-acetamidobenzamides. The conjugation effect to stabilize the radical groups in the radical cleaving process was observed.     

Closed path integrals and the quantum action

We suggest a closed form expression for the path integral of quantum transition amplitudes. We introduce a quantum action with parameters different from the classical action. We present numerical results for the harmonic oscillator with weak perturbation, the quartic potential, and the double well potential. The quantum action is relevant for quantum chaos and quantum instantons.     

Hadronic loop corrections to the muon anomalous magnetic moment

The dominant theoretical uncertainties in both the anomalous magnetic moment of the muon and the value of the electromagnetic coupling at the Z scale, M(Z), arise from their hadronic contributions. Since these will ultimately dominate the experimental errors, we study the correlation between them, as well as with other fundamental parameters. To this end we present analytical formulas for the QCD contribution from higher energies and from heavy quarks. Including these correlations affects the Higgs boson mass extracted from precision data.     

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber

Self-induced phase matching in stimulated four-wave mixing in a nonbirefringent single-mode optical fiber has been observed. It is shown that in a nonbirefringent single-mode fiber the phase matching that is necessary for stimulated four-wave mixing can be accomplished with a combination of self-phase modulation and cross-phase modulation induced by a pump-laser pulse.     

Asymptotic approach to the truncated cosh-Gaussian beams

The propagation behavior and M ²-factor of truncated cosh-Gaussian (ChG) beams are studied by using the asymptotic approach. Detailed numerical results are given to illustrate the dependence of M ²-factor on the beam decentered parameter , truncation fraction p and power fraction f. Our results are self-consistent and reduce to those of Pare and Belanger [Opt. Commun. 123, p. 679 (1996a); Proc. SPIE 2870, p. 104 (1996b)]. The advantage of the approach is shown, and the problems introduced by the hard-aperture diffraction and the approach used are discussed.