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Using a multiscale (dual resolution) approach combining an atomistic (GROMOS96) and coarse-grain (MARTINI) force field, we have been able to simulate the process of drug–polymer nanoparticle assembly by nanoprecipitation from mixed solvents. Here, we present the development and application of this method to the interaction of three poly(glycerol adipate) polymer variants with the anticancer drug dexamethasone phosphate. Differences in encapsulation efficiency and drug loading between the polymers are in agreement with the experimental trend. Reference atomistic simulations at key points along the predicted aggregation pathway support the accuracy of the much more computationally efficient multiscale methodology.

Two short routes to novel methylated pentacyclic quinoacridinium salts have been devised. New compounds display telomerase-inhibitory potency (<1 μM) in the TRAP assay. 3,11-Difluoro-6,8,13-trimethyl-8H-quino[4,3,2-kl]acridinium methosulfate (12d, RHPS4, NSC 714187) has a higher selectivity for triplex and quadruplex DNA structures than the 3,6,8,11,13-pentamethyl analogue (12c, RHPS3, NSC 714186) and a low overall growth-inhibitory activity in the NCI 60 cell panel (mean GI50 13.18 μM); in addition, the activity profile of 12d does not COMPARE with agents of the topoisomerase II class. Compound 12d is soluble in water, stable in the pH range of 5−9, efficiently transported into tumor cells, and is currently the lead structure for further elaboration in this new class of telomerase inhibitor.

The enantioselectivity ratio (()-:(-)-forms) of three substituted 1-[(benzofuran-2-yI) phenylmethyl] imidazoles as inhibitors of aromatase (P450AROM) was 2.16, 12.3 and 1.0 for the 4-methyl-, 4-fluoro- and 4-chloro-substituted compounds, respectively. The (±)-compounds were all >1000 times more potent than (±)-aminoglutethimide (IC50 12 × 103nM). High potency (5.3–65.0 nM) for all the enantiomers studied is unusual since activity usually resides in one form for chiral inhibitors of P450AROM- The 4-methyl derivative was fitted into the model [Furet, P., Batzl, C., Bhatnager, A.S., Francotte, E., Rihs, G. and Lang, M. (1993) J. Med. Chem.36, pp. 1393–1400] for binding of S-(-)-fadrazole to the active site and the (R)- and (S)- forms both gave a good fitting pattern with (S)-(-)-fadrazole so accounting for their close activity. Docking of both forms into the active site model for P450AROM[Laughton, C.A., Zvelebil, M.J.J.M. and Neidel, S. (1993) J. Steroid Biochem. Mol. Biol.44, pp. 399–407], using the orientation of (S)-(±)-fadrazole, gave similar strong binding along the position of the C and D rings of the steroid substrate and in the hydrophobic cavity below the A/B rings. The site was probed for group size accommodation using the less potent 4-phenyl analogue (IC50(±) 242nM): the (S)-form showed restricted access to the region under the A ring due to the extended bulk of the biphenyl group.

The triazenyl-pyrimethamine derivative 3a (TAB), a potent and selective inhibitor of Pneumocystis carinii DHFR, was selected as the starting point for a lead optimization study. Molecular modeling studies, corroborated by a recent crystal structure determination of the ternary complex of P. carinii DHFR−NADPH bound to TAB, predicted that modifications to the acetoxy residue of the lead inhibitor could exploit binding opportunities in the vicinity of an active site pocket bounded by residues Ile33, Lys37, and Leu72. Substitutions in the benzyl moiety with electron-donating and electron-withdrawing groups were predicted to probe face−edge interactions with amino acid Phe69 unique to the P. carinii enzyme. New triazenes 10a−v and 12a−f were prepared by coupling the diazonium tetrafluoroborate salt 6b of aminopyrimethamine with substituted benzylamines or phenethylamines. The most potent of the new inhibitors against P. carinii DHFR was the naphthylmethyl-substituted triazene 10t (IC50:  0.053 μM), but a more substantial increase in potency against the rat liver DHFR led to a reduction in selectivity (ratio rat liver DHFR IC50/P. carinii DHFR IC50:  5.36) compared to the original lead structure 3a (ratio rat liver DHFR IC50/P. carinii DHFR IC50:  114).

NMR analysis and molecular dynamics simulations of d(GGTAATTACC)(2) and its complex with a tetrahydropyrimidinium analogue of Hoechst 33258 suggest that DNA minor groove recognition in solution involves a combination of conformational selection and induced fit, rather than binding to a preorganised site. Analysis of structural fluctuations in the bound and unbound states suggests that the degree of induced fit observed is primarily a consequence of optimising van der Waals contacts with the walls of the minor groove resulting in groove narrowing through: (i) changes in base step parameters, including increased helical twist and propeller twist; (ii) changes to the sugar-phosphate backbone conformation to engulf the bound ligand; (iii) suppression of bending modes at the TpA steps. In contrast, the geometrical arrangement of hydrogen bond acceptors on the groove floor appears to be relatively insensitive to DNA conformation (helical twist and propeller twist). We suggest that effective recognition of DNA sequences (in this case an A tract structure) appears to depend to a significant extent on the sequence being flexible enough to be able to adopt the geometrically optimal conformation compatible with the various binding interactions, rather than involving 'lock and key' recognition.

Hoechst 43254 (H43254), a 2,3,4,5-tetrahydropyrimidin-1-ium analogue of the bis-benzimidazole minor groove binding agent Hoechst 33258 (H33258), has been studied by NMR and restrained molecular dynamics in its complex with d(GGTAATTACC)2. We investigate the origin of the enhanced complex stability afforded by the replacement of the N-methylpiperazine ring of H33258 with the tetrahydropyrimidinium ring of H43254, the latter presenting the opportunity for specific minor groove-directed recognition through a pyrimidinium NH. A set of 25 drug-DNA NOEs define the binding site with some precision and are used as part of the structural analysis using restrained molecular dynamics simulations considering explicit solvation and the treatment of electrostatic interactions using the particle mesh Ewald method within AMBER 4.1. Starting with three different initial structures with the drug located at different sites in the groove (pairwise RMSD 4.3-12.6 A) we arrive at three very similar structures (pairwise RMSD 0.80-1.34 A) representing one converged binding site at the centre of the AATT tract. Two of the three structures show the tetrahydropyrimidinium ring to be suitably positioned for an -NH to adenine N3 hydrogen bond suggesting that electrostatic interactions may play an important role in the enhanced affinity as well as imparting additional A-T specificity. The NMR data show that the pyrimidinium NH interaction is dynamic since signal averaging from the two sides of the ring indicate rapid rotations in the bound form.

<it>Objectives</it>: To investigate the variability in antimicrobial susceptibility of <it>Pseudomonas aeruginosa</it> from sputa of patients with cystic fibrosis, to compare testing individual colonies of the same morphotype either separately or combined and to study the reproducibility of testing antimicrobial susceptibility within and between laboratories. <it>Methods</it>: One hundred and one sputa were cultured. Four colonies of each <it>P. aeruginosa</it> morphotype were suspended. Susceptibility to 12 agents by disc diffusion was tested individually or by pooling the four suspensions. A sputum sample containing four morphotypes of one genotype of <it>P. aeruginosa</it> was used to study reproducibility. Susceptibility was tested in duplicate by eight biomedical scientists in one laboratory and by routine procedures in seven different laboratories. <it>Results</it>: There was a mean of four morphotypes of <it>P. aeruginosa</it> per sputum and three antibiograms per morphotype. In some cases, all four colonies of a single morphotype had different antibiograms. The susceptibility profiles of single isolates of <it>P. aeruginosa</it> correlated poorly with pooled cultures, with the pooled tests missing resistance. Results from one sample tested in duplicate by eight biomedical scientists in one laboratory and in seven other laboratories did not correlate well. The wide range of zone sizes in disc diffusion tests illustrated the variation in susceptibility of 48 colonies from one sputum sample. <it>Conclusions</it>: The role of conventional antimicrobial susceptibility testing is questionable once <it>P. aeruginosa</it> chronically infects the cystic fibrosis lung. A range of susceptibility patterns is seen, even within a morphotype. Routine test results are not reproducible and underestimate resistance.

The cyclohexenol (I) is protected by reaction with the chlorosilane (II) to form the siloxycyclohexene (III).

Coordination of benzyl ethers to tricarbonylchromium as in (V) (from (I) via (III)) allows α‐substitution via the corresponding α‐carbanions using the electrophiles (VI)‐(X) (→ (XI)).

Abstract: A suite of application benchmarks, designed to be broadly representative of UK HPC usage, has been developed to stress a broad range of architectural features of large scale parallel HPC resources. A generic methodology to investigate application performance and scaling characteristics has been defined, resulting in a detailed understanding of the performance of these applications. This methodology is transferable to other applications and systems: it is of practical value to developers and users who are aiming for optimal utilisation of HPC resources. An understanding of the performance characteristics of a range of large-scale HPC resources has been obtained using low-level synthetic benchmarks. A relatively simple, qualitative mechanism to assess and predict application performance on current and future architectures using synthetic benchmark results together with application performance analysis results is explored. [Copyright &y& Elsevier]