Stereographic projection path-integral simulations of (HF)n clusters

We perform several quantum canonical ensemble simulations of (HF)(n) clusters. The HF stretches are rigid, and the stereographic projection path-integral method is employed for the simulation in the resulting curved configuration space. We make use of the reweighted random series techniques to accelerate the convergence of the path-integral simulation with respect to the number of path coefficients. We develop and test estimators for the total energy and heat capacity based on a finite difference approach for non-Euclidean spaces. The quantum effects at temperatures below 400 K are substantial for all sizes. We observe interesting thermodynamic behaviors in the quantum simulations of the octamer and the heptamer.     

Synthesis and application of functionally diverse 2,6,9-trisubstituted purine libraries as CDK inhibitors.

BACKGROUND: Purines constitute a structural class of protein ligands involved in mediating an astonishing array of metabolic processes and signal pathways in all living organisms. Synthesis of purine derivatives targeting specific purine-binding proteins in vivo could lead to versatile lead compounds for use as biological probes or drug candidates. RESULTS: We synthesized several libraries of 2,6, 9-trisubstituted purines using both solution- and solid-phase chemistry, and screened the compounds for inhibition of cyclin-dependent kinase (CDK) activity and human leukemic cell growth. Lead compounds were optimized by iterative synthesis based on structure-activity relationships (SARs), as well as analysis of several CDK-inhibitor cocrystal structures, to afford several interesting compounds including one of the most potent CDK inhibitors known to date. Unexpectedly, some compounds with similar CDK inhibitory activity arrested cellular proliferation at distinctly different phases of the cell cycle and another inhibitor directly induced apoptosis, bypassing cell-cycle arrest. Some of these compounds selectively inhibited growth of cells derived from specific tumors. CONCLUSIONS: 2,6,9-Trisubstituted purines have various and potent biological activities, despite high concentrations of competing endogenous purine ligands in living cells. Purine libraries constitute a versatile source of small molecules that affect distinct biochemical pathways mediating different cellular functions.     

Rate constants for O(3P) recombination and association with N(4S)

It is shown that N(⁴S) and O(³P) atom quenching effects upon chemiluminescence from NO(B²π) (θ = 0) are of importance when this emissio Values of k₂ = (1.74 ± 0.13) × 10⁹ and (4.05 ± 0.17) × 10⁹ &² mole^-2 sec^-1 are found at 298 and 196°K respectiv     

Total synthesis of hybocarpone and analogues thereof. A facile dimerization of naphthazarins to pentacyclic systems

The total synthesis of the lichen-derived antitumor agent hybocarpone (1) and related compounds is described. The successful route to hybocarpone features a novel radical-based dimerization/hydration cascade which generates the bridging hindered carbon-carbon bond of the molecule in a stereocontrolled manner, setting the relative configurations of the four contiguous stereocenters in a single step. The conjecture is made that this process may not be so dissimilar to the biosynthetic pathway leading to the formation of hybocarpone in nature. The developed sequence to these molecular frameworks also features the first example of a synthetically useful Diels-Alder trapping of a photochemically generated hydroxy-o-quinodimethane species with a 1,1-disubstituted olefin to form a quaternary center, and includes an efficient route to hydroxynaphthoquinone-type structures represented by the monomeric subunit of the natural product.     

The synthesis of cholest-5-ene-3beta-carboxylates and a comparison of their mesomorphic behaviour with isomeric cholesterol esters with a reversed ester linkage

The syntheses of seven esters of cholest-5-ene-3beta-carboxylic acid are reported and the melting points, transition temperatures and mesophase morphologies of the esters are compared with those of the isomeric 3beta-cholesterol compounds which have the ester link reversed. For the examples reported, the cholest-5-ene-3beta-carboxlates always have significantly lower melting points, but the differences in clearing temperatures for the two series of esters are usually much less. Several of the new compounds give an increased chiral nematic phase range and an intense selective reflection of light. They therefore represent a novel type of chiral nematic material for use in thermochromic applications.