Syntheses of new fluorine-containing taxoids by means of β-Lactam Synthon Method

An Overview of Recent Advances in Biological and Pharmaceutical Developments of Fluoro-containing Drugs

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This review article provides a brief assessment of the biological and pharmaceutical developments of fluorinated drugs. It also discusses possible impacts on the further development of new fluoro-containing pharmaceuticals. Structural aspects of new drug-candidates currently under development and their biological properties, therapeutic potential and syntheses are critically evaluated

Differential metabolism of 3FDT and docetaxel in RLMs, rats, and HLMs

3FDT, an analog of docetaxel with a blocked metabolism at its 3'-N-tert-butyloxyl group with three fluorine atoms, exhibits more potent cytotoxicity than docetaxel both with human cancer cell line SK-OV-3 in vitro and with human non-small cell lung cancer A549 xenografts in vivo. To further develop pharmacodynamically and pharmacokinetically favorable fluorinated docetaxel analogs as anticancer agents, we chose 3FDT as the model compound to identify the metabolites of 3FDT in RLMs, rats, and HLMs and the cytochrome P450 enzymes responsible for the metabolism of 3FDT. Our findings indicated that the major metabolic site switched from the C3' appendage for docetaxel to the taxane ring for 3FDT, and the main metabolizing P450 enzymes switched from CYP3A to CYP3A4 and CYP2E1.

Fluorine-Containing Taxoid Anticancer Agents and Their Tumor-Targeted Drug Delivery

A long-standing problem of conventional chemotherapy is the lack of tumor-specific treatments. Traditional chemotherapy relies on the premise that rapidly proliferating cancer cells are more likely to be killed by a cytotoxic agent. In reality, however, cytotoxic agents have very little or no specificity, which leads to systemic toxicity, causing undesirable severe side effects. Consequently, various "molecularly targeted cancer therapies" have been developed for use in specific cancers, including tumor-targeting drug delivery systems. In general, such a drug delivery system consists of a tumor recognition moiety and a cytotoxic "warhead" connected through a "smart" linker to form a conjugate. When a multi-functionalized nanomaterial is used as the vehicle, a "Trojan Horse" approach can be used for mass delivery of cytotoxic "warheads" to maximize the efficacy. Exploitation of the special properties of fluorine has proven successful in the development of new and effective biochemical tools as well as therapeutic agents. Fluorinated congeners can also serve as excellent probes for the investigation of biochemical mechanisms. ¹⁹F-NMR can provide unique and powerful tools for mechanistic investigations in chemical biology. This account presents our recent progress, in perspective, on the molecular approaches to the design and development of novel tumor-targeted drug delivery systems for new generation chemotherapy by exploiting the unique nature of fluorine.

Exploration of fluorine chemistry at the multidisciplinary interface of chemistry and biology

Over the last three decades, my engagement in "fluorine chemistry" has evolved substantially because of the multidisciplinary nature of the research programs. I began my research career as a synthetic chemist in organometallic chemistry and homogeneous catalysis directed toward organic synthesis. Then, I was brought into a very unique world of "fluorine chemistry" in the end of 1970s. I started exploring the interface of fluorine chemistry and transition metal homogeneous catalysis first, which was followed by amino acids, peptides, and peptidomimetics for medicinal chemistry. Since then, I have been exploring the interfaces of fluorine chemistry and multidisciplinary fields of research involving medicinal chemistry, chemical biology, cancer biology, and molecular imaging. This perspective intends to cover my fruitful endeavor in the exploration of fluorine chemistry at the multidisciplinary interface of chemistry and biology in a chronological order to show the evolution of my research interest and strategy.

Thiacremonone augments chemotherapeutic agent-induced growth inhibition in human colon cancer cells through inactivation of nuclear factor-{kappa}B

Chemotherapeutic strategies commonly use multiple agents to overcome drug resistance and to lower drug toxicity. Activation of nuclear factor-kappaB (NF-kappaB) is implicated in drug resistance in cancer cells. Previously, we reported that thiacremonone, a novel sulfur compound isolated from garlic, inhibited NF-kappaB and cancer cell growth with IC(50) values about 100 microg/mL in colon cancer cells. In the present study, we tested whether thiacremonone could increase susceptibility of cancer cells to chemotherapeutics through inactivation of NF-kappaB. Colon cancer cells were cotreated with thiacremonone (50 microg/mL, half dose of IC(50)) and lower doses of each chemotherapeutic agent (half dose of IC(50)) for 24 hours. NF-kappaB activity was completely abrogated in cells treated with a combination of thiacremonone and docetaxel, whereas thiacremonone on its own did not alter NF-kappaB activity. This combined drug effect was also found with other anticancer drugs in colon cancer and in other cancer cells. In good correlation with inhibition of cell growth and NF-kappaB activity, the combination treatment also regulated NF-kappaB target genes. Oral treatment of mice with thiacremonone (1 mg/kg) by administering it in drinking water for 4 weeks significantly augmented docetaxel (1 mg/kg, i.p., four times)-induced decrease of tumor growth accompanied with regulation of NF-kappaB activity and NF-kappaB target genes. These results warrant carefully designed clinical studies investigating the combination of thiacremonone and commonly used chemotherapeutic agents for the treatment of human cancers.

Recent advances in the chemistry and biology of new generation taxoids

Among the numerous chemotherapeutic drugs, paclitaxel and docetaxel are among the most widely used against various types of cancer. However, these drugs cause undesirable side effects as well as drug resistance. Therefore, it is essential to develop "taxane" anticancer agents with better pharmacological properties and improved activity especially against drug-resistant cancers. Several laboratories have performed extensive SAR studies on paclitaxel. Our SAR studies have led to the development of numerous highly potent novel second- and third-generation taxoids with systematic modifications at the C-2, C-10, and C-3' positions. The third-generation taxoids showed virtually no difference in potency against drug-resistant and drug-sensitive cell lines. Some of the new generation taxoids also exhibited excellent cytotoxicity against pancreatic cell lines expressing multidrug-resistant genes. We have also designed taxoids with strategic fluorine incorporation to investigate their effects on the cytotoxicity and the blockage of known metabolic pathways. Furthermore, we have successfully employed computational biology analysis to design novel macrocyclic taxoids to mimic the bioactive conformation of paclitaxel. This account describes our work on the design, synthesis, and biological evaluation of these novel taxoids, which has led to the discovery of very promising candidates for further preclinical studies.

Syntheses and Structure-Activity Relationships of Novel 3'-Difluoromethyl and 3'-Trifluoromethyl-Taxoids

A series of novel 3'-difluoromethyl-taxoids and 3'-trifluoromethyl-taxoids with modifications at the C2 and C10 positions were synthesized and evaluated for their in vitro cytotoxicities against human breast carcinoma (MCF7-S, MCF7-R, LCC6-WT, LCC6-MDR), non-small cell lung carcinoma (H460) and colon adenocarcinoma (HT-29) cell lines. These second-generation fluoro-taxoids exhibited several times to more than 20 times better potency than paclitaxel against drug-sensitive cancer cell lines, MCF7-S, LCC6-WT, H460, and HT-29. These fluoro-taxoids also possess two orders of magnitude higher potency than paclitaxel against drug-resistant cancer cell lines, MCF7-R and LCC6-MDR. Structure-activity relationship study shows the importance of the C10 modification for increasing the activity against multidrug-resistant cancer cell lines. Effects of the C2-benzoate modifications on the potency in the 3-difluoromethyl-taxoid series are very clear (i.e., F < MeO < Cl < N(3)), while those in the 3-trifluoromethyl-taxoid series are less obvious. Also, different trends in the sensitivity to the C2-substitution are observed between drug-sensitive cell lines and drug-resistant cancer cell lines that overexpress efflux pumps.

Synthesis of Novel C2−C3‘N-Linked Macrocyclic Taxoids by Means of Highly Regioselective Heck Macrocyclization

[reaction: see text] Novel C2-C3'N-linked macrocyclic taxoids are synthesized using intramolecular Heck reaction in the key step. Macrocyclization proceeds with high regioselectivity in good yield. Taxoids bearing an olefin moiety at C2 and an iodide at C3'N give exo-products exclusively. However, the endo-products are formed with up to 100% regioselectivity just by switching the positions of the olefin and the iodide moieties. Some of these macrocyclic taxoids are significantly cytotoxic.

A multistage, one-pot procedure mediated by a single catalyst: a new approach to the catalytic asymmetric synthesis of beta-amino acids

A catalytic asymmetric procedure for the preparation of beta-amino acids (specifically beta-substituted aspartic acid derivatives) is reported. The cinchona alkaloid catalyst benzoylquinine (BQ) mediates up to five distinct steps of a reaction pathway, all in one reaction vessel. The products of this reaction, highly optically enriched beta-substituted aspartic acid derivatives, were prepared from N-acyl-alpha-chloroglycine esters and acid chlorides in the presence of the catalyst. This approach was also amenable to the synthesis of small polypeptides containing beta-substituted aspartic acid units, including a non-natural fragment of the antibiotic lysobactin. The addition of Lewis acids to this system was found to accelerate the rate of specific steps in the reaction pathway. Mechanistic aspects of this reaction, such as imine formation and Lewis acid chelation to the beta-lactam intermediate, were investigated through comparison of IR, NMR, and other physical data.

Syntheses and biological activity of C-3'-difluoromethyl-taxoids

A series of new taxoids bearing difluoromethyl group at the C-3' position and modifications at the C-10 and C-14 positions has been synthesized and their biological activities studied. The in vitro cytotoxicity assay results indicate that these newly developed taxoids exhibit comparable to several times better activity against drug-sensitive cell line LCC6-WT, and 40-70 times better activity against the corresponding drug-resistant cancer cell line LCC6-MDR as compared to that of paclitaxel. Apoptosis analysis has revealed the exceptional activity of SB-T-12843 (1e) in inducing apoptosis in both MDR-bearing and MDR-negative cancer cells.

Recent advances in the chemistry of taxol

The history of the development of the important anticancer drug taxol (1) is briefly described, and recent studies of its chemistry and tubulin-binding conformation are then presented. Topics discussed include side chain attachment to baccatin III (3a), the effect of oxygenation of the taxane ring system on bioactivity, the importance of the oxetane ring for bioactivity, the synthesis of a C-6/C-4 bridged analogue, and the conformation of the side chain when taxol is bound in a complex with polymerized tubulin.

From beta-lactams to alpha- and beta-amino acid derived peptides

The potential of beta-lactams as intermediates for the access to alpha- and beta-amino acid-derived peptides is shortly reviewed, with major focus on the technologies developed in our group. The two general strategies lie, on one side, in the oxidative ring expansion of 3-hydroxy beta-lactams to N-carboxy alpha-amino acid anhydrides or Leuch's anhydrides and subsequent coupling with alpha-amino acid esters and, on the other side, in the nucleophilic ring opening of N-Boc-beta-lactams. Both approaches have been successfully applied to the synthesis of alpha,beta-diamino acid, alpha-amino-beta-hydroxy acid, polyhydroxylated alpha-amino acid, alpha,alpha-disubstituted alpha-amino acid, beta-amino acid, beta-amino-alpha-hydroxy acid and beta,beta-disubstituted beta-amino acid derived peptides. Because of the mild reaction conditions needed for the above transformations and the highly stereoselective procedures employed for the construction of the starting beta-lactam ring, the whole process allows the production of optically pure final products.

Structural significance of the benzoyl group at the C-3'-N position of paclitaxel for nitric oxide and tumor necrosis factor production by murine macrophages

The antitumor agent paclitaxel (Taxol) mimics the actions of lipopolysaccharide (LPS) on murine macrophages (M phi). Recently, we have shown that the benzoyl group at the C-3' position of paclitaxel is the most important site to induce nitric oxide (NO) and tumor necrosis factor (TNF) production by C3H/HeN M phi (Biochem. Biophys. Res. Commun. 210, 678-686, 1996). In the present study, synthetic analogs of paclitaxel with replacement of the C-3'-N position were examined for their potencies to induce NO and TNF production by peritoneal M phi of LPS-responsive C3H/HeN mice and LPS-hyporesponsive C3H/HeJ mice, by human blood cells and human M phi. In this structure-activity relationship study, we found that (i) the p-substitution of the benzoyl group definitely affects the activity to activate C3H/HeN M phi, (ii) the analogs having a methyl or chloro group at the p-position exhibit stronger activity than that of paclitaxel, (iii) there is good correlation between NO and TNF production by the M phi in response to compounds, (iv) the compounds tested do not induce either NO or TNF production by C3H/HeJ M phi or TNF production by human cells, (v) a previous treatment of C3H/HeN M phi with the inactive compounds can hardly affect either paclitaxel- or LPS-induced TNF production by the M phi, (vi) paclitaxel and its analogs marginally affect LPS-induced TNF production by human blood cells, and (vii) there is no correlation between the NO/TNF inducibility to C3H/HeN M phi and growth inhibitory activity against M phi-like J774.1 and J7.DEF3 cells.