Enantiodivergence in small-molecule catalysis of asymmetric phosphorylation: concise total syntheses of the enantiomeric D-myo-inositol-1-phosphate and D-myo-inositol-3-phosphate

Peptide-based catalysts have been found that catalyze the enantiodivergent phosphorylation of a meso myo-inositol-derived triol (1). The sequential screening of random peptide libraries, followed by the evaluation of a focused library, led to the identification of two peptides (2 and 24) that are complementary in producing enantiomeric D-myo-inositol-1-phosphate and D-myo-inositol-3-phosphate derivatives. The catalysts were then used to complete efficient total syntheses of both D-I-1P and D-I-3P in optically pure form. Additional information is gleaned from relative rate experiments that unambiguously show the catalysts to afford enantioselection through rate accelerative pathways with respect to simple achiral alkylimidazole catalysts. Furthermore, solvent effect studies show that the two enantiodivergent catalysts exhibit different tolerances of polar media. The systematic discovery of site-selective catalysts establishes a basis for future studies of chiral catalysts that differentiate unique functional groups in polyfunctional molecules.     

How to Make Drugs Orally Active: A Substrate Template for Peptide Transporter PepT1

By building key structural features into hydrophilic drugs, they can be recognized by the PepT1 transporter system of the small intestine and rendered orally active. The model shown provides, for the first time, a 3D template for all known substrates of PepT1.     

In situ preparation of a highly active N-heterocyclic carbene-coordinated olefin metathesis catalyst

Highly active N-heterocyclic carbene-coordinated catalysts may be synthesized and used in situ, without requiring prior isolation of the catalyst. Activation of this in situ catalyst with ethereal HCl dramatically reduces the reaction times required for high conversions. A variety of alpha,beta-unsaturated carbonyl-containing substrates participate readily in cross and ring-closing metathesis reactions using this preparation.     

MiniMax: What has been learned thus far

Summary A small experiment, ?MiniMax?, has been set up in the C0 intersection region of the Fermilab Tevatron to seek evidence for disoriented chiral condensates and to study other forward physics phenomena. The experiment consists of a proportional wire chamber telescope accompanied by scintillation (trigger) counters, a lead converter, and followed by an electromagnetic calorimeter. The solid angle accepted is a cone centered at pseudorapidity (η) of 4.1 and of radius (in η-ϕ space) of about 0.6. Over 2.5 million events thus far have demonstrated the successful operation of the apparatus, however to date the analysis has not progressed sufficiently to permit any conclusions concerning disoriented chiral condensates. presented byL. W. Jones Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Modelling flow over a backward–facing step using the F.E.M. and the two-equation model of turbulence

Flow over a downstream-facing step is predicted using the F.E.M. A two-equation model of turbulence is employed where the transport of turbulence kinetic energy and dissipation rate are depicted using transport-type equations, i.e. the two-equation model of turbulence. The results obtained are compared with other models and experimental results. Generally, the model was found to be under-predictive with regard to the reattachment length when previous empirical data was used in the transport equations.     

On the evaluation of ion source conditions for optimum sensitivity of chemical ionization

The best operating conditions that yield maximum sensitivity at minimum source pressure have been evaluated for the chemical ionization source in a Kratos MS-25 mass spectrometer. The best reagent gas pressure is shown to be different for each gas and is significantly lower than is usually reported in the literature.     

13C NMR spectra of 1,3,4-thiadiazole/thiadiazoline isomeric pairs

The ¹³C NMR spectra of four pairs of 1,3,4-thiadiazole/thiadiazoline isomers have been recorded using broad band and off-resonance proton decoupling techniques and in the coupled mode. Differences in the chemical shifts of the heterocyclic ring and the carbonyl carbons allow identification of the isomer present. Their IR and UV spectra are in agreement with literature reports for azole/azoline analogues.     

A linear algorithm for a core of a tree

A core of a graph G is a path P in G that is central with respect to the property of minimizing d(P) = Σ_υ?V(G)d(υ, P), where d(υ, P) is the distance from vertex υ to path P. We present a linear algorithm for finding a core of a tree. Since the core of a graph is not necessarily unique, we also output a list of all the vertices which are in some core.