The three dimensional structure of both a ligand and its cognate receptor are required for the success of structure-assisted drug design. This thesis reports the crystal structure of hectochlorin, a small, bioactive molecule, and the steps toward determining the crystal structure of an RNA molecule that is an attractive target for drug design. The absolute structure of hectochlorin, a cytotoxic, secondary metabolite isolated from Lyngbya majuscula, is reported herein. Specifically, the absolute configuration of hectochlorin, as determined by x-ray crystallography, is reported as 6S, 7S, 10S, 31S. Marine natural products are interesting as a source of novel chemical compounds that are potentially valuable as therapeutic agents, or have industrial applications. The absolute structure provides a model that serves as a starting point for rational drug design synthesis. In a second study, results are reported from attempts to crystallize a biologically important RNA structure, the trans-acting response element, (TAR), for the determination of its structure by x-ray diffraction, and ultimately, providing an initial model for structure-assisted drug design targeted against HIV. Crystals, of biologically relevant TAR sequences, greater that 0.1 x 0.1 x 0.1 mm�� in size, both in the presence and absence of a cognate ligand analogue, have been obtained. These crystals have been shown to be of poor diffraction quality, but the initial crystallization conditions provide a starting point for optimization that may yield higher quality crystals. / Graduation date: 2001

Investigation on the synthesis of the C-13 side chain of taxol was carried out in order to prepare modified taxol derivatives by coupling of the side chain acid chloride to a suitably protected baccatin III. The side chain was prepared by the Darzens condensation. Acylation of baccatin III was performed with simple acylating agents and extensive studies of the ¹H NMR and ¹³C NMR spectra of various acylbaccatins III were carried out aided by homonuclear and heteronuclear COSY experiments. This work led to the unambiguous assignment of the ¹H NMR and ¹³C NMR spectra of these compounds. Coupling of more bulky side chains to 7-(2,2,2-trichloroethyloxycarbonyl) baccatin III was difficult and yields were poor. Conventional methods, using triethylamine or pyridine with 4-dimethylaminopyridine in the coupling reaction of 3- phenylpropanoyl chloride and 7-(2,2,2-trichloroethyloxycarbonyl) baccatin III led to the desired coupled product in low yield together with two coupled compounds possessing more than one phenylpropanoyl group on the C-13 side chain. When the coupling reaction was performed in the presence of silver cyanide in refluxing toluene, only 13-(3-phenylpropanoyl) baccatin III was obtained. However, these two methods were not successful in the coupling reaction of 2-acetyl-3- phenyllactyl chlorlde with 7-(2,2,2-trichloroethyloxycarbonyl) baccatin III. Preliminary studies on the cleavage of the N-acyl group at the C-3' position of taxol and cephalomannine were performed. Taxol reacted with zinc bromide in chloroform-methanol solution to produce 10- deacetyl-7-epitaxol and 10-deacetyltaxol. No cleavage of the N-acyl group was detected in this case and in other reactions in which taxol was treated with various selective reagents. Other attempts involved the conversion of cephalomannine to its ozonolysis products with a pyruvyl group at the 3’-NH group. A method of cleavage of the N-pyruvyl group has not yet been found, however. / Ph. D. / incomplete_metadata

Copies of author's previously published articles inserted / Describes the exploratory clinical development of tucaresol, consisting of three studies performed on humans and subsequent in vitro and animal studies investigating the possible effects on the immune system. Demostrates that rational drug design may be an efficient way of selecting potential therapeutic candidates. / xxi, 265 leaves : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (M.D.)--University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 1995

Human African Trypanosomiasis (HAT) is an infectious, vector-borne protozoal disease which is amongst the so-called neglected diseases. In 2000, at a summit of the United Nations, eight Millennium Development Goals (MDGs) were set, to be achieved by 2015. MDG 6 states “to combat HIV/AIDS, malaria & other diseases”. With just under 2 years to go before the end of 2015, HAT is still thriving in developing countries. The drugs currently used for the treatment of HAT are in short supply, have severe side effects and those used to treat late stages of the disease are very difficult to administer. The aforementioned challenges call for research into this neglected disease in order to develop new, safe and easy-to-use medicines. Naphthoquinones are a class of compounds shown to possess anti-parasitic activity, amongst a variety of other biological activities, and therefore this pharmacophore was selected for this study. The purpose of this study was to synthesise derivatives of 2,3-dichloro-1,4- naphthoquinone to be tested for anti-trypanosomal activity and thereafter conduct structureactivity relationship studies. A series of reactions were carried out using thiophenol, phenol and aniline nucleophiles to synthesise thioether (-S-), ether (-O-) and amino (-NH-) derivatives of 2,3-dichloro-1,4-naphthoquinone with various halogen or methyl substituents. Purification of the products was carried out by recrystallisation. Nuclear magnetic resonance (NMR), infra-red (IR) and high pressure liquid chromatography coupled to an electro-spray ionisation mass spectrometer (HPLC-ESI-MS) were the analytical methods used for structural confirmation of the products. There were eighteen 1,4-naphthoquinone derivatives that were successfully synthesised using ethanolic solutions. Unfortunately, attempts to synthesise 1,4-naphthoquinones in reactions involving 2-(trifluoro-methyl)aniline and 2-isopropyl-5-methylphenol were unsuccessful, presumably due to steric hindrance by the bulky ortho-substituents. Although the aims of the synthetic procedures were to obtain both mono- and disubstituted products by nucleophilic displacement of the chlorine atom(s) of 2,3-dichloro-1,4- naphthoquinone, only monosubstituted products were obtained from substitution with aniline and phenol nucleophiles. Thiol nucleophiles, however, selectively yielded disubstituted products only. Synthesised naphthoquinone derivatives were tested against Trypanosoma brucei and calculation of the EC₅₀ values from the obtained dose-response curves was carried out using the four parametric equation. All the 1,4-naphthoquinones showed a degree of potency, except compounds 1b, 3c and 3e, which had little or lack of potency. Structure-activity relationship studies (SARs and QSARs) were carried out to determine which structural features or functional group substituents of the naphthoquinone derivatives contribute or take away from the desired anti-trypanosomal activity. It was found that compounds with the best in vitro anti-trypanosomal potencies in the series of analogous 1,4-naphthoquinone derivatives had EC₅₀ values in the range 2.137 to 2.884 μM. The most potent compound in the series was 2-chloro-3-(4-(trifluoromethyl)phenylamino)-1,4- naphthoquinone 1e; but it was 142-fold less potent than the reference standard of melarsoprol.

Indiana University-Purdue University Indianapolis (IUPUI) / Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in malignant tumors, and its activation is associated with high histological grade and advanced cancer stage. STAT3 has been shown to play important roles in multiple aspects of cancer aggressiveness including proliferation, survival, self-renewal, migration, invasion, angiogenesis and immune response by regulating the expression of diverse downstream target genes. Thus, inhibiting STAT3 promises to be an attractive strategy for treatment of advanced tumors with metastatic potential. We firstly identified a STAT3 inhibitor, inS3-54, by targeting the DNA-binding site of STAT3 using an in-silico screening approach; however, inS3-54 was finally found not to be appropriate for further studies because of low specificity on STAT3 and poor absorption in mice. To develop an effective and specific STAT3 inhibitor, we identified 89 analogues for the structure-activity relationship analysis. By using hematopoietic progenitor cells isolated from wild-type and STAT3 conditional knockout mice, further studies showed that three analogues (A18, A26 and A69) only inhibited STAT3-dependent colony formation of hematopoietic progenitor cells, indicating a higher selectivity for STAT3 than their parental compound, inS3-54. These compounds were found to (1) inhibit STAT3-specific DNA binding activity; (2) bind to STAT3 protein; (3) suppress proliferation of cancer cells harboring aberrant STAT3 signaling; (4) inhibit migration and invasion of cancer cells and (5) inhibit STAT3-dependent expression of downstream targets by blocking the binding of STAT3 to the promoter regions of responsive genes in cells. In addition, A18 can reduce tumor growth in a mouse xenograft model of lung cancer with little effect on body weight. Taken together, we conclude that it is feasible to inhibit STAT3 by targeting its DNA-binding domain for discovery of anticancer therapeutics.

Indiana University-Purdue University Indianapolis (IUPUI) / ALDH isoenzymes are known to impact the sensitivity of certain neoplastic cells toward cyclophosphamides and its analogs. Despite its bone marrow toxicity, cyclophos-phamide is still used to treat various recalcitrant forms of cancer. When activated, cyclo-phosphamide forms aldophosphamide that can spontaneously form the toxic phospho-ramide mustard, an alkylating agent unless detoxified by ALDH isozymes to the carbox-yphosphamide metabolite. Prior work has demonstrated that the ALDH1A1 and ALDH3A1 isoenzymes can convert aldophosphamide to carboxyphosphamide. This has also been verified by over expression and siRNA knockdown studies. Selective small molecule inhibitors for these ALDH isoenzymes are not currently available. We hypothe-sized that novel and selective small molecule inhibitors of ALDH3A1 would enhance cancer cells’ sensitivity toward cyclophosphamide. If successful, this approach can widen the therapeutic treatment window for cyclophosphamides; permitting lower effective dos-ing regimens with reduced toxicity. An esterase based absorbance assay was optimized in a high throughput setting and 101, 000 compounds were screened and two new selective inhibitors for ALDH3A1, which have IC50 values of 0.2 µM (CB7) and 16 µM (CB29) were discovered. These two compounds compete for aldehyde binding, which was vali-dated both by kinetic and crystallographic studies. Structure activity relationship dataset has helped us determine the basis of potency and selectivity of these compounds towards ALDH3A1 activity. Our data is further supported by mafosfamide (an analog of cyclo-phosphamide) chemosensitivity data, performed on lung adenocarcinoma (A549) and gli-oblastoma (SF767) cell lines. Overall, I have identified two compounds, which inhibit ALDH3A1’s dehydrogenase activity selectively and increases sensitization of ALDH3A1 positive cells to aldophosphamide and its analogs. This may have the potential in improving chemotherapeutic efficacy of cyclophosphamide as well as to help us understand better the role of ALDH3A1 in cells. Future work will focus on testing these compounds on other cancer cell lines that involve ALDH3A1 expression as a mode of chemoresistance.