Sean M. Kerwin

Synthesis and Evaluation of Anticancer Benzoxazoles and Benzimidazoles Related to UK-1

UK-1 is a structurally unique bis(benzoxazole) natural product isolated from a strain of Streptomyces. UK-1 has been reported to possess anticancer activity but no activity against bacteria, yeast, or fungi. Previous work has also demonstrated the ability of UK-1 to bind a variety of di- and tri-valent metal ions, particularly Mg(2+) ions, and to form complexes with double-stranded DNA in the presence of Mg(2+) ions. Here we report the activity of UK-1 against a wide range of human cancer cell lines. UK-1 displays a wide spectrum of potent anticancer activity against leukemia, lymphoma, and certain solid tumor-derived cell lines, with IC(50) values as low as 20 nM, but is inactive against Staphylococcus aureus, a methicillin-resistant strain of S. aureus, or Pseudomonas aeruginosa. A series of analogues of the bis(benzoxazole) natural product UK-1 in which the carbomethoxy-substituted benzoxazole ring of the natural product was modified were prepared and evaluated for their anticancer and antibacterial properties. An analogue of UK-1 in which the carbomethoxy-substituted benzoxazole ring was replaced with a carbomethoxy-substituted benzimidazole ring was inactive against human cancer cell lines and the two strains of S. aureus. In contrast, a simplified analogue in which the carbomethoxy-substituted benzoxazole ring was replaced with a carbomethoxy group was almost as active as UK-1 against the four cancer cell lines examined but lacked activity against S. aureus. Metal ion binding studies of these analogues demonstrate that they both bind Zn(2+) and Ca(2+) ions about as well as UK-1. The non-cytotoxic benzimidazole UK-1 analogue binds Mg(2+) ions 50-fold weaker than UK-1, whereas the simple benzoxazole analogue binds Mg(2+) ions nearly as well as UK-1. These results support a role of Mg(2+) ion binding in the selective cytotoxicity of UK-1 and provide a minimal pharmacophore for the selective cytotoxic activity of the natural product.

G-quadruplexes as targets for drug design

G-quadruplexes are a family of secondary DNA structures formed in the presence of monovalent cations that consist of four-stranded structures in which Hoogsteen base-pairing stabilizes G-tetrad structures. These structures are proposed to exist in vivo, although direct confirmatory evidence is lacking. Guanine-rich regions of DNA capable of forming G-quadruplex structures are found in a variety of chromosomal regions, including telomeres and promoter regions of DNA. In this review, we describe the design of three separate groups of G-quadruplex-interactive compounds and their interaction with G-quadruplex DNA. Using the first group of compounds (anthraquinones), we describe experiments that provide the proof of concept that a G-quadruplex is required for inhibition of telomerase. Using the second group of compounds (perylenes), we describe the structure of a G-quadruplex-ligand complex and its effect on the dynamics of formation and enzymatic unwinding of the quadruplex. For the third group of compounds (porphyrins), we describe the experiments that relate the biological effects to their interactions with G-quadruplexes.

G-Quadruplex DNA as a target for drug design.

Telomeres are structures on the ends of chromosomes that are required for chromosomal stability. Telomeric DNA contains a single-stranded G-rich DNA overhang, which may adopt a G-quadruplex structure. Telomere shortening has been implicated in cellular senescence. Telomerase is an enzyme which synthesizes the G-rich strand of telomere DNA. Telomerase activity is highly correlated with cancer and may allow cancer cells to escape senescence. Based on these observations, telomerase has been proposed as a potential target for anticancer drug design. The targeting of telomerase is associated with potential problems, including the existence in some cancer cells of telomerase-independent mechanisms for telomere maintenance, and the long delay time between telomerase inhibition and effects on proliferation. One promising approach for inhibiting telomerase involves targeting the G-quadruplex DNA structures thought to be involved in telomere and telomerase function. Compounds that specifically bind G-quadruplex DNA may interact directly with telomeres, in addition to inhibiting telomerase, and produce more immediate antiproliferative effects. The diamidoanthraquinones, porphyrins, and perylene diimides have all been shown to bind G-quadruplex DNA and inhibit telomerase. Most of these compounds also bind double-stranded DNA and are cytotoxic at the concentrations required to inhibit telomerase; however, certain perylene diimides appear to be non-cytotoxic, G-quadruplex selective telomerase inhibitors. Biological characterization of such compounds may provide validation for the concept of the G-quadruplex as a target in drug design.

New transition metal ion complexes with benzimidazole-5-carboxylic acid hydrazides with antitumor activity

Metal complexes of 2-methyl-1H-benzimidazole-5-carboxylic acid hydrazide (4a; L(1)) and its Schiff base 2-methyl-N-(propan-2-ylidene)-1H-benzimidazole-5-carbohydrazide (5a; L(2)) with transition metal ions e.g., copper, silver, nickel, iron and manganese were prepared. The complexes formed were 1:1 or 1:2 M:L complexes and have the structural formulae [Cu(L(1))Cl(H(2)O)]Cl x 3 H(2)O (6), [Ag(L(1))NO(3)(H(2)O)] (7), [Ni(L(1))Cl(2)(H(2)O)(2)] x H(2)O (8), [Fe(L(1))Cl(3)(H(2)O)] x 3 H(2)O (9) and [Mn(L(1))(2)Cl(H(2)O)]Cl x 3 H(2)O (10) for ligand L(1), and [Cu(L(2))Cl(2)(H(2)O)(2)] x H(2)O (11), [Ag(L(2))(2)]NO(3) x H(2)O (12), [Ni(L(2))(2)Cl(2)] x 5 H(2)O (13), [Fe(L(2))(2)Cl(2)]Cl x 2 H(2)O (14) and [Mn(L(2))Cl(2)(H(2)O)(2)] x H(2)O (15) for ligand L(2). The antitumor activity of the synthesized compounds has been studied. The silver complex 7 was found to display cytotoxicity (IC(50)=2 microM) against both human lung cancer cell line A549 and human breast cancer cell line MCF-7.

THE TOTAL SYNTHESIS OF UK-1

A concise, five-step total synthesis of UK-1, a novel bis(benzoxazole) metabolite of Streptomyces sp. 517-02, was accomplished. The methyl ether of UK-1 was also synthesized in 3 steps using the same methodology. Both syntheses are accomplished by the sequential construction of two benzoxazole rings derived from 3-hydroxyanthranilic acid.

Evaluation of Binding of Perylene Diimide and Benzannulated Perylene Diimide Ligands to DNA by Electrospray Ionization Mass Spectrometry

Electrospray ionization mass spectrometry (ESI-MS) and spectroscopic studies in solution were used to evaluate the self-association, G-quadruplex DNA binding, and selectivity of a series of perylene diimides (PDIs) (PIPER, Tel01, Tel11, Tel12, and Tel18) or benzannulated perylene diimide ligands (Tel34 and Tel32). Fluorescence and resonance light scattering spectra of Tel01, Tel12, Tel32, and Tel34 reveal that these analogs undergo self-association in solution. UV-Vis and fluorescence titrations with G-quadruplex, duplex, or single-stranded DNA demonstrate that all the analogs, with the exception of Tel32, bind to G-quadruplex DNA, with those PDIs that are self-associated in solution showing the highest degree of selectivity for binding G-quadruplex DNA. Parallel ESI-MS analysis of the stoichiometries demonstrates the ability of the ligands, with the exception of Tel32, to bind to G-quadruplex DNA. While most ligands show major 1:1 and 2:1 binding stoichiometries as expected in the case of end-stacking, interestingly, three of the most quadruplex-selective ligands show a different behavior. Tel01 forms 3:1 complexes, while Tel12 and Tel32 only form 1:1 complexes. Collisional activation dissociation patterns are compatible with ligand binding to G-quadruplex DNA via stacking on the ends of the terminal G-tetrads. Experiments with duplex and single strand DNA were performed to assess the binding selectivities of the ligands. PIPER, Tel11, and Tel18 demonstrated extensive complexation with duplex DNA, while Tel11 and Tel18 bound to single strand DNA, confirming the lack of selectivity of these two ligands. Our results indicate that Tel01, Tel12, and Tel34 are the most selective for G-quadruplex DNA.

The para-toluenesulfonic acid-promoted synthesis of 2-substituted benzoxazoles and benzimidazoles from diacylated precursors

The synthesis of benzoxazoles and benzimidazoles is accomplished by treating N,O-diacylated 2-aminophenols or N,N′-diacylated 1,2-phenylenediamines with p-toluenesulfonic acid under reflux in xylenes or toluene. These reactions are operationally simple and proceed in excellent yield.

Synthesis of a DNA-cleaving bis(propargylic) sulfone crown ether

Abstract The prototypical bis(propargylic) sulfone crown ether 5 was synthesized in six steps and 26 % overall yield from readily available starting materials. In alkaline aqueous buffer, compounds 5 cleaves supercoiled DNA.

Coupling reactions of bromoalkynes with imidazoles mediated by copper salts: Synthesis of novel N-alkynylimidazoles

A cross-coupling reaction of imidazoles with bromoalkynes in the presence of a catalytic amount of CuI is reported. This protocol allows an access to novel N-(1-alkynyl)imidazoles in moderate to good yields.

Pharmacokinetics of caffeic acid phenethyl ester and its catechol-ring fluorinated derivative following intravenous administration to rats.

The pharmacokinetic profiles of caffeic acid phenethyl ester (CAPE) and its catechol‐ring fluorinated derivative (FCAPE) were determined in rats after intravenous administration of 5, 10 or 20 mg/kg for CAPE and 20 mg/kg for FCAPE, respectively. The plasma concentrations of CAPE and FCAPE were measured using a validated liquid chromatography tandem mass spectrometric method. The pharmacokinetic parameters were estimated using non compartmental analysis (NCA) and biexponential fit. The results showed that the area under the plasma concentration‐time curve for CAPE treatment increased in a proportion greater than the increase in dose from 5 to 20 mg/kg of CAPE. Total body clearance values for CAPE ranged from 42.1 to 172 ml/min/kg (NCA) and decreased with the increasing dose of CAPE. Similarly, the volume of distribution values for CAPE ranged from 1555 to 5209 ml/kg, decreasing with increasing dose. The elimination half‐life for CAPE ranged from 21.2 to 26.7 min and was independent of dose. That FCAPE was distributed extensively into rat tissues and eliminated rapidly was indicated by a high value of volume of distribution and similar short elimination half‐life as that of CAPE. Copyright