Identification of novel antitumor agents from mixture-based synthetic combinatorial libraries using cell-based assays

A new strategy is presented here which integrates combinatorial library technology with the antitumor in vitro screening system at the National Cancer Institute in the search for novel antitumor agents. Mixture-based synthetic combinatorial libraries (SCLs) representing hundreds of thousands to millions of individual compounds were screened against the cell-based assay, which evaluates compounds for their ability to inhibit the growth of 60 different human tumor cell lines. Five different SCLs, composed of peptides, peptidomimetics, polyamines or small molecules were first tested against three cell lines to identify the most active SCLs. Two SCLs, namely the N-perbenzylated pentamine and the N-acylated permethylated triamine, were deconvoluted to yield individual compounds having significant activities against the 60 tumor cell lines. Active compounds were tested in mice to determine the maximum tolerated dose, followed by in vivo testing in a hollow fiber assay. Using this strategy, three different compounds identified directly from SCLs are currently being evaluated in human tumor xenografts. This study demonstrates for the first time the use of in vitro cell-based assays to identify antitumor lead compounds from mixture-based combinatorial libraries.     

Comparison of the effects of symmetric versus asymmetric H bonding on 2H and 17O nuclear quadrupole coupling constants: Application to formic acid and the hydrogen diformate anion

In this paper, we analyse the effects on the nuclear quadrupole coupling behaviour of ²H and ¹⁷O nuclei of a shift in H-bond character from asymmetric to symmetric. Using ab initio methods, the coupling amplitudes (nuclear quadrupole coupling constant e²_qQ/h) coupling anisotropies (asymmetry parameter η), and orientations of the electric field gradient (EFG) principal axis (PA) system of the H-bonded deuterium and oxygen nuclei in the formic acid dimer and related monomers, and the deuterium diformate anion are calculated. In addition, the relative contributions to the ²H and ¹⁷O EFGs of nuclear and electronic terms, and also the convergence of the EFG as a function of contributions from increasingly distant nuclei in the molecule are investigated. The trends in the calculated ¹⁷O EFGs on going from an asymmetric to a symmetric H-bonded environment are correlated with experimental nqr data in order to establish the hitherto unknown e²qQ/h sign, EFG assignments and PA orientation of symmetrically H-bonded oxygen. The possibility that the e²qQ/h value of deuterium is negative for symmetric H bonds is discussed, and difficulties in the computation of ²H EFGs for symmetric - as distinct from asymmetric - H-bonded systems are pointed out. In strong disagreement with assumptions in the literature, it is found that nearest neighbour terms do not dominate the ²H EFG in symmetrically H-bonded systems.     

Terminal acetylene-silver trifluoromethanesulfonate π complexes. Synthesis, stoichiometry, and activation of the terminal carbon---hydrogen bond

Terminal acetylene---silver(I) trifluoromethanesulfonate π complexes have been isolated. They are of 1 : 1 stoichiometry in the solid state and solution with all carbon---carbon triple bonds coordinated to silver ion. Their stability constants as measured by proton NMR are strongly solvent dependent and decrease in the order 1,5-hexadiyne> 1,7-octadiyne> 1-hexyne, 3-methyl-1-pentyne> 3,3-dimethyl-1-butyne. IR and NMR analysis indicates weakening and polarization of the terminal carbon---hydrogen bond upon silver ion coordination. In solution terminal acetylenes π coordinated to silver ion undergo deuterium exchange approximately 10⁵ times faster than uncoordinated acetylenes. The mechanism of deuterium exchange does not involve silver acetylides as intermediates.     

Computational strategies for the optimization of equilibrium geometries and transition-state structures at the semiempirical level

Several improvements have been made to the gradient algorithms commonly used to optimize equilibrium and transition-state geometries at the semiempirical level. A gradient algorithm derived from a combination of a variable metric method (Davidon–Fletcher–Powell/Broyden–Fletcher–Goldfarb–Shanno) and Pulay's direct inversion in the iterative subspace method for geometry optimization (GDIIS) is compared with the variable metric method combined with an accurate linear search algorithm. The latter method is used routinely in the standard semiempirical program packages, MNDO, MOPAC, and AMPAC. The combined variable metric and GDIIS algorithm is also compared with GDIIS which uses a static metric. The performance of these algorithms is examined for a wide range of systems with respect to both choice of coordinate system (for cyclic molecules) and guess for the initial Hessian. The results show that the GDIIS method is up to ca. 40% more efficient than the variable metric combined with accurate line search algorithm: however, the exact savings vary depending on the coordinate system and initial Hessian. For noncyclic systems, variable-metric GDIIS is usually equal or superior to static-metric GDIIS, and consistently performs ca. 30% more efficiently than the variable metric combined with accurate line search algorithm. For the optimization of cyclic molecules, an improved estimate of the initial Hessian has increased the efficiency by at least a factor of two. Greater efficiencies (usually >40%) are also obtained when static-metric GDIIS is used to refine the geometry after the initial application of a transition-state search based on the variable metric combined with line search algorithm. On the basis of these results, we recommend several changes to the algorithms as currently implemented in the standard semiempirical program packages.     

Voice F0 responses to pitch-shifted auditory feedback: a preliminary study

Auditory feedback has been suggested to be important for voice fundamental frequency (F₀) control. The present study featured a new technique for testing this hypothesis by which the pitch of a subject's voice was modulated, fed back over earphones, and the resultant change in the emitted voice F₀ was measured. The responses of 67 normal, healthy young adults were recorded as they attempted to ignore intermittent upward or downward shifts in pitch feedback while they sustained steady vowel sounds (/a/) or sang musical scales. Ninety-six percent of subjects increased their F₀ when the feedback pitch was decreased, and 78% of subjects decreased their F₀ when the pitch feedback was increased. Latencies of responses ranged from 104 to 223 ms. Results indicate people normally rely on pitch feedback to control voice F₀.     

Maximum principles for the polyharmonic equation on Lipschitz domains

The Agmon-Miranda maximum principle for the polyharmonic equations of all orders is shown to hold in Lipschitz domains in ℝ³. In ℝn,n≥4, the Agmon-Miranda maximum principle andL ^p-Dirichlet estimates for certainp>2 are shown to fail in Lipschitz domains for these equations. In particular if 4≤n≤2m+1 theL ^p Dirichlet problem for Δ ^m fails to be solvable forp>2(n−1)/(n−3). Supported in part by the NSF.     

Actinophyllic acid, a potent indole alkaloid inhibitor of the coupled enzyme assay carboxypeptidase u/hippuricase from the leaves of Alstonia actinophylla (Apocynaceae)

Bioassay-guided fractionation of the aqueous extract of the leaves of Alstonia actinophylla with use of a coupled enzyme assay, CPU/hippuricase, to detect carboxypeptidase U inhibitors led to the isolation of a novel indole alkaloid, actinophyllic acid (1). The structure of 1 was determined from detailed 2D NMR studies. Actinophyllic acid was found to be a potent inhibitor of the coupled enzyme assay with an IC(50) of 0.84 microM. Actinophyllic acid possesses a unique 2,3,6,7,9,13c-hexahydro-1H-1,7,8-(methanetriyloxymethano)pyrrolo[1',2':1,2]azocino[4,3-b]indole-8(5H)-carboxylic acid skeleton.     

A diterpene related to cladiellin from a pacific soft coral

A new diterpene $\text{2}$ from a soft coral collected at Majuro Atoll has been related to cladiellin ($\text{1}$.     

Guanidinium-Type resonance stabilization and its biological implications. I. the guanidine and extended-guanidine series

An unusual type of π-electron delocalization in Y-shaped molecules related to guanidine and its protonated form, the guanidinium ion, has been studied by ab initio methods at the STO -3G and 3-21G levels. Results are reported for tautomeric, rotameric, and protonated forms of the oxygen-substituted guanidine series (urea, carbamic, and carbonic acids); “extended-guanidine” (aminomethylene guanidine) including pseudocyclic forms; and simple ring systems in which the extended-guanidine group is incorporated (3-amino-1,2,4-triazole, 2,4-diaminopyrimidine). Both the guanidine and guanidinium type stabilizations have been characterized in terms of a number of structural and energetic parameters: degree of single/double bond character from bond lengths and π-bond orders, electron distributions, and protonation energies. The major finding is that the structural and energetic properties of the isolated extended-guanidinium group resemble those of the group when incorporated within 6-membered heterocyclic or heterobicyclic rings, although the details vary with the nature of the ring and possibility of reinforcement or interference with the substructure resonance from overall ring delocalization. The implications for stabilization of the protonated forms of some biologically important pteridines is discussed.