Dibenzo-30-crown-10 (DB30C10) is one of the first-generation macrocyclic hosts discovered by Pedersen. Crown ethers originally attracted attention due to their ability to encapsulate metal cations and render them soluble in organic solvents. These studies helped to launch host-guest chemistry as a discipline within supramolecular chemistry. Crown ethers form complex molecules containing organic cations and neutral organic molecules. Additionally, they form components in supramolecular architectures such as catenanes, rotaxanes, and supramolecular polymers. They have been used as selective hosts in diverse applications such as wastewater treatment, switchable catalysis, therapeutic agents, sensors, molecular machines, and stimuli responsive materials "smart polymers". Despite the vigorous research activity in the field, DB30C10 has received surprisingly little attention. DB30C10 was reported in 1967 and has been commercially available since 1992; however, it has been mostly overlooked as a host in favour of smaller crown ethers such as DB24C8, B15C5, 18C6 and 15C5. Herein we present an improved synthetic route that improves the yield of the cyclization step in the synthesis of DB30C10 from 25% to 88% enabling us to prepare multiple grams of the material without the use of pseudo high-dilution techniques. The same methodology was applied to three other crown ethers with similar improvement in yield. Four new rotaxanes based on the DB30C10-paraquat binding motif were used to investigate the binding conformation of DB30C10 and paraquat. The new rotaxanes were characterized by 1H, 13C and 2D-NOESY NMR, mp, and HRMS. A single crystal X-ray structure of one of the [2]rotaxanes was obtained. To our knowledge, this is the first crystal structure of a rotaxane based on this particular binding motif. This result illustrated that DB30C10 was a suitable host for the construction of supramolecular systems and polymers. Our eventual goal is to use DB30C10 in the construction of supramolecular polymers with novel topologies. Therefore, the relative threading efficiency of DB30C10 in solution had to be determined. A series of segmented polyurethane poly(pseudorotaxanes) with paraquats in the backbone were synthesized with different crown ether or cyptand hosts. The threading efficiency was determined by 1H NMR. / Ph. D.

Paclitaxel was isolated from the bark of <i>Taxus brevifolia</i> in the late 1960s. It exerts its biological effect by promoting tubulin polymerization and stabilizing the resulting microtubules. Paclitaxel has become one of the most important current drugs for the treatment of breast and ovarian cancers. Studies aimed at understanding the biologically active conformation of paclitaxel bound on β–tubulin are described. In this work, the synthesis of isotopically labeled taxol analogs is described and the REDOR studies of this compound complexed to tubulin agrees with the hypothesis that palictaxel adopts T-taxol conformation. Based on T-taxol conformation, macrocyclic analogs of taxol have been prepared and their biological activities were evaluated. The results show a direct evidence to support T-taxol conformation. (+) Discodermolide is a polyketide isolated from the Caribbean deep sea sponge <i>Discodermia dissoluta</i> in 1990. Similar to paclitaxel, discodermolide interacts with tubulin and stabilizes the microtubule <i>in vivo</i>. Studies aimed at understanding the biologically active conformation of discodermolide bound on β–tubulin are described. In this work, the synthesis of fluorescent labeled discodermolide analogs is described and their biological activities were evaluated. Synthetic approaches to fluorescent labeled and isotopically labeled discodermolide analogs discodermolide are also described. / Ph. D.

Prostate cancer is the most common non-skin cancer for men in America. The androgen receptor exerts transcriptional activity and plays an important role for the proliferation of prostate cancer cells. Androgen receptor ligands bind the androgen receptor and inhibit its transcriptional activity effectively. However, prostate cancer can progress to hormone refractory prostate cancer (HRPC) to avoid this effect. Chemotherapies are currently the primary treatments for HRPC. Unfortunately, none of the available chemotherapies are curative. Among them, paclitaxel and docetaxel are two of the most effective drugs for HRPC. More importantly, docetaxel is the only form of chemotherapy known to prolong survival in the HRPC patients. We hypothesized that the conjugation of paclitaxel or docetaxel with an androgen receptor ligand will overcome the resistance mechanism of HRPC. Eleven conjugates were designed, synthesized and biologically evaluated. Some of them were active against androgen-independent prostate cancer, but they were all less active than paclitaxel and docetaxel. Discodermolide is a microtubule interactive agent, and has a similar mechanism of action to paclitaxel. Interestingly, discodermolide is active against paclitaxel-resistant cancer cells and can synergize with paclitaxel, which make it an attractive anticancer drug candidate. Understanding the bioactive conformation of discodermolide is important for drug development, but this task is difficult due to the linear and flexible structure of discodermolide. Indirect evidence for the orientation of discodermolide in the tubulin binding pocket can be obtained from fluorescence spectroscopy of the discodermolide tubulin complex. For this purpose, we designed and synthesized a simplified fluorescently labeled discodermolide analog, and it was active in the tubulin assembly bioassay. In addition, a conformationally constrained discodermolide was designed to mimic the bioactive conformation according to computational modeling. The synthetic effort was made, but failed during one of the final steps. / Ph. D.

Taxol (1) was first isolated from the bark of the Pacific yew about 35 years ago by Drs. Wall and Wani. Although its development as an anticancer agent was delayed by numerous reasons, including its scarcity and insolubility, the discovery of its tubulin-assembly activity and other factors motivated oncologists to overcome these problems. It has since become one of the most important current drugs for the treatment of several cancers, including breast and ovarian cancers. Like almost all anticancer drugs taxol does have some toxic side effects and many tumors also show significant resistance to therapy with taxol. Drug targeting studies aimed at improving its selectivity and efficacy is described. Two targeting methods, the estrogen receptor (ER) directed targeting and colloidal gold (cAu)directed targeting, were used in our research. In this dissertation, a series of estradiol-taxol conjugates (ETCs) were synthesized. They were active in four cytotoxicity assays and tubulin polymerization assay, but less active than taxol. One of them showed the desired selectivity for ER positive cancer cells. Recently, several studies have attempted to elucidate the bioactive binding conformation of taxol on microtubules. Three models have been proposed for this conformation. The T-taxol conformation was proposed by Dr. Snyder based on electron crystallographic density and molecular modeling. In this dessertation, a series of cyclopropyl-containing taxol analogs and macrocyclic taxol lactones were synthesized. The bioassay results showed they are less active than taxol. The molecular modeling studies suggested that the cyclopropyl-containing taxol analogs could not adopt the T-taxol conformation, which would result in the loss of bioactivities. It is an indirect evidence to support T-taxol conformation. As for macrocyclic taxol lactones, it is proposed that they would have a close contact between the ester moiety on the C-3' phenyl ring and Phe272 of the β-tubulin protein when they adopt T-taxol conformation. It will push the macrocyclics out of the binding pocket and lead to the lost of bioactivities. / Ph. D.