Synthesis and anti-HIV-1 activity of a series of imidazo[1,5-b]pyridazines.

A series of substituted imidazo[1,5-b]pyridazines have been prepared and tested for inhibitory activity against the reverse transcriptase of HIV-1 (RT) and their ability to inhibit the growth of infected MT-4 cells. Crystal data are reported on two compounds, 15c and 33. From the structure-activity relationships developed within this and other series, it is proposed that key features of the interaction with RT include hydrogen-bond acceptor and aromatic pi-orbital bonding with the imidazopyridazine nucleus and a benzoyl function separated from the heterocycle by a suitable spacer group. Exceptional activity against the reverse transcriptase of HIV-1 (IC50 = 0.65 nM) was obtained with a 2-imidazolyl-substituted derivative, 7-[2-(1H-imidazol-1- yl)-5-methylimidazo-[1,5-b]pyridazin-7-yl]-1-phenyl-1-heptanone (33) which is attributed to additional binding of the imidazole sp2 nitrogen atom. A number of the compounds in this series also inhibit the replication of HIV-1 in vitro in MT-4 and C8166 cells at levels observed with the nucleoside AZT.

Novel glucocorticoid antedrugs possessing a 17beta-(gamma-lactone) ring.

The chemical synthesis and structure-activity relationships of a novel series of 17beta-glucocorticoid butyrolactones possessing either a 16alpha,17alpha-isopropylidene or -butylidene group are described. The sulfur-linked gamma-lactone group was incorporated onto the 17beta-position of the androstane nucleus via Barton ester decarboxylation and trapping the generated 17-radical with butyrolactone disulfides. The glucocorticoid butyrolactones were hydrolyzed in human plasma by the enzyme paraoxonase to the respective hydroxy acids, which were very weak glucocorticoid agonists. The rate of hydrolysis in plasma was very rapid (t1/2 = 4-5 min) in the case of lactones possessing a sulfur atom in the alpha-position of the butyrolactone group, whereas carbon-linked lactones were stable in plasma. 16alpha,17alpha-Butylidenes were more potent glucocorticoid agonists than the corresponding isopropylidene derivatives. Similarly, 1,4-dien-3-ones were more potent than the corresponding 4-en-3-ones. The butyrolactones linked to the steroidal nucleus via the beta-position were more potent glucocorticoid agonists than those linked through the alpha-position of the lactone. The most potent compounds were also shown to be stable in human lung S9 fraction, showed much lower systemic effects than budesonide in the thymus involution test, and possessed topical antiinflammatory activity in the rat ear edema model.

A figure of merit for the assessment of image intensifier systems.

A dimensionless figure of merit (F), which combines key aspects of the performance of image intensifier systems, is derived. This figure is ideally independent of input air kerma rate and field size and relates to the fundamental characteristics of the image reception chain. In practice it is calculated from measurements of the threshold contrast (noise) and limiting resolution using the Leeds test objects and the input air kerma rate. Several practical examples illustrate its usefulness in simple performance assessment and quality assurance procedures. A comparison is made with the use of detection index diagrams.

6,6'-Bis(2-hydroxyphenyl)-2,2'-bipyridine manganese(III) complexes: a novel series of superoxide dismutase and catalase mimetics.

A series of novel manganese(III) complexes is described based on a 6,6'-bis(2-hydroxyphenyl)-2,2'-bipyridine template. These complexes show superoxide dismutase and catalase activity. The effect of the aromatic substitution pattern on the SAR is described.