Structural studies on antifolate drugs

Single crystal X-ray structure determinations are reported for eleven compounds all of which are either biologically active or potentially biologically important. The compounds fall into two distinct classes:- 1. Substituted diaminopyrimidines 2. Substituted aminopyrimidinones The first class of compounds were all selected on the basis of their common diaminopyrimidine nucleus which has been demonstrated to be a vital requirement for antifolate activity. They may all be described as non-classical or small molecule lipophilic dihydrofolate reductase (DHFR) inhibitors, as opposed to the classical folate analogues, having the ability to cross the blood-brain barrier, enter cells via a rapid passive diffusion process, and achieve high intracellular concentrations. Thus they are an excellent choice in the search for crystallography in the solid state, providing geometrical and distance data not available from any other analytical techniques to date; supporting and enhancing data obtained in the lower resolution studies of protein crystallography. The biological importance of these compounds is discussed and an attempt is made to relate/predict their pharmacological activity to observed structural features in the crystalline environment. Special attention is focussed on hydrogen bonding, confirmational flexibility and hydrophobicity of substituents; each of which appear to make contributions to tight binding in the enzyme active site. Chapter 9 describes the use of data from the literature and the solid state modelling of an observed enzyme-substrate interaction in an attempt to define it more accurately in terms of its geometric flexibility. Of the second class, one compound (ABPP) is reported; studies in two different crystal forms. In demonstrating both antiviral and high interferon inducing activity it is possible that this compound could be useful against cancer and also viral infections.

The effects of substrate water availability on the isolation and growth of fungi

The work reported in this thesis was carried out to contribute to the knowledge of the effects of substrate water availability or water activity (a ) on fungal growth parameters and its implications in the preparationw of materials susceptible to biodeterioration. Fungi were isolated from soils of different ecological sites at a range of substrate aw levels controlled by sodium chloride (NaCl). Three groups of fungi were isolated : firstly, those isolated only at high a (aw about 0.997).secondly, those isolated at high and decreasing aw (aw 0.997 to 0.85) and finally, those isolated at only decreased aw (aw O.95 to 0.80). From these isolations, test fungi were selected to study the effects of pH, temperature, exo-enzyme production and biocide efficacy at decreased aw levels, with glycerol and NaCl as a controlling solutes. The linear extension rates of the fungi increased at all test pH values near optimum a of growth. Test fungi of the Aspergillus glaucus group were found to be most resistant to low aw. Growth and survival of vegetative and fruiting bodies at elevated temperatures were enhanced with the addition of a controlling solutes. A. flavus, A. fumigatus displayed high heat resistance and A. amstelodami, A. versicolor and Penicillium citrinum displayed low heat resistance at high aw levels and vice versa at low aw levels. Amylase, lipase and protease activities were studied at lowered aw , using modifications of the test tube method of Raute11a and Cowling. Amylase and protease production in most xerophilic fungi ceased around 0.80 aw , but lipase production in some xerophilic fungi, including A. glatlcus fungi, was up to and including 0.70 aw with g1ycero1.