Evans O. Onyango

Synthetic Studies on Furanosteroids: Construction of the Viridin Core Structure via Diels–Alder/retro-Diels–Alder and Vinylogous Mukaiyama Aldol-Type Reaction

The synthesis of the viridin class of furanosteroids core skeleton from the readily available 2,3-dihydro-4-hydroxyinden-1-one (6) is described. Our strategy was broken down into three parts: (1) Synthesis of functionalized alkyne oxazoles of type 5; (2) intramolecular Diels-Alder/retro-Diels-Alder reaction of 5 followed by tautomerization and elaboration of R to give silylated furanonaphthols 4 bearing an aldehyde side chain; and (3) annulation of ring A by intramolecular vinylogous Mukaiyama aldol-type cyclization. Two major challenges were faced in the last step: (i) furanonaphthol derivatives bearing a β-hydroxyaldehyde functionality (R(1) = OH) suffered from dehydration to the E-enal, which is geometrically incapable of cyclization, and (ii) the functionality at C17 had a strong influence on the conversion of 4 to 3, as exemplified by the failure of the free ketone (X = O) or its derivatives (X = H, OH; X = H, OAc) to cyclize. In the end, success was realized with the analogous C17-norketone (X = H, H).

Synthesis of a dicyano abietane, a key intermediate for the anti-inflammatory agent TBE-31.

The synthesis of dicyano abietane 11, a potential precursor to the biologically active tricyclic bis-cyano enone 6 (TBE-31), was accomplished in eight steps from epoxide 13. The synthesis features a Lewis acid promoted stereoselective cyclization of epoxide 13 to generate the tricyclic ring system 12 in one step.

Synthesis and biological evaluation of amino acid methyl ester conjugates of 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid against the production of nitric oxide (NO)

2-Cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO, 2) was condensed with various amino acid methyl esters at the C-28 carboxylic acid. The new amide conjugates were evaluated for their inhibition of nitric oxide (NO) production in RAW264.7 cells stimulated with interferon-γ (IFNγ). Of these new compounds, CDDO conjugates with alanine, valine, and serine are nearly equipotent to CDDO-ethyl amide (4), a triterpenoid with promising biological activity in numerous disease models. Some of these conjugates also induce the in vitro expression of heme oxygenase-1, and inhibit the proliferation of Panc-1343 pancreatic cells.

A new class of inhibitors of the AraC family virulence regulator Vibrio cholerae ToxT

Vibrio cholerae is responsible for the diarrheal disease cholera that infects millions of people worldwide. While vaccines protecting against cholera exist, and oral rehydration therapy is an effective treatment method, the disease will remain a global health threat until long-term solutions such as improved sanitation and access to clean water become widely available. Because of this, there is a pressing need for potent therapeutics that can either mitigate cholera symptoms, or act prophylactically to prevent the virulent effects of a cholera infection. Here we report the design, synthesis, and characterization of a set of compounds that bind and inhibit ToxT, the transcription factor that directly regulates the two primary V. cholerae virulence factors. Using the folded structure of the monounsaturated fatty acid observed in the X-ray structure of ToxT as a template, we designed ten novel compounds that inhibit the virulence cascade to a greater degree than any known inhibitor. Our findings provide a structural and functional basis for the development of viable antivirulence therapeutics that combat cholera and, potentially, other forms of bacterial pathogenic disease.

Triple Benzannulation of Naphthalene via a 1,3,6-Naphthotriyne Synthetic Equivalent. Synthesis of Dibenz[a,c]anthracene.

A new synthesis of dibenzo[a,c]anthracene (4) is described that features the generation, from tetrabromo-bis-triflate 1 and phenyllithium, of a 1,3,6-naphthotriyne (2) synthetic equivalent that is trapped with 3 equiv of furan to form Diels-Alder tris-adduct 3. A subsequent two-step deoxygenation of 3 represents the first synthesis of dibenz[a,c]anthracene (4) that involves a tandem aryne Diels-Alder cycloaddition-deoxygenation strategy.

Constructing the Heterocyclic Core of Viridin and Wortmannin

Abstract The furanosteroids are a class of novel fungal metabolites, several of which are potent inhibitors of phosphatidylinositol 3-kinase (PI-3 kinase), an enzyme that plays a key role in the life cycle of cells. The inhibitory activity of these compounds stems from their ability to selectively block certain intracellular signaling pathways, in particular those associated with cell growth and development. As such they hold promise as a new class of therapeutic agents for diseases characterized by rapid cell proliferation, as is the case in cancer. However, the known members of this class are far too toxic and nonselective for development as antitumor agents. Because of this there is intense interest in developing new synthetic pathways to both the naturally occurring compounds, and simpler analogs, in order to better evaluate structure-activity relationships. This chapter outlines a concise synthetic approach to the furanosteroid skeleton that should apply equally well to preparing the biologically important natural products as well as structural analogs.

Syntheses of 1-Bromo-8-methylnaphthalene and 1-Bromo-5-methylnaphthalene.

The Diels-Alder reaction between 2-methylfuran and 3-bromobenzyne (3), which was generated under mild conditions from 1,3-dibromobenzene and lithium diisopropylamide (LDA), gives a mixture of regioisomeric 1,4-dihydro-1,4-epoxynaphthalenes 4 and 5. A subsequent two-step deoxygenation affords the corresponding 1-bromo-8-methylnaphthalene (1) and 1-bromo-5-methylnaphthalene (2) in high yields.

A Modified ToxT Inhibitor Reduces Vibrio cholerae Virulence in Vivo

We have previously designed and synthesized small-molecule inhibitors that reduce Vibrio cholerae virulence in vitro by targeting the transcription factor ToxT. Here we report the synthesis and biological activity of derivatives of our previous bicyclic, fatty acid-like inhibitors. All of the synthesized derivatives show antivirulence activity in vitro. For the most potent compounds, a concentration of 5 μM completely inhibited ToxT-mediated tcpA expression as measured in the β-galactosidase assay. One indole compound, 3-(1-butyl-1 H-indol-7-yl)propanoic acid (8), was also effective at inhibiting intestinal colonization in the infant mouse. These modified compounds may serve as good candidates for further anti-cholera drug development.

Synthesis, Crystal Structures, Density Functional Theory (DFT) Calculations and Molecular Orbital Calculations of Three New Derivatives of 1 - (phenylsulfonyl)indole

AbstractThree new derivatives of 1-(phenylsulfonyl)indole : 3-nitro-1-(phenylsulfonyl)-1H-indol-2-amine (I): C14H11N3O4S; N-(tert-butyl)-3-nitro-1-(phenylsulfonyl)-1H-indol-2-amine (II): C18H19N3O4S and tert-butyl 4-(phenylsulfonyl)-(1; Pelkey, Gribble, Tetrahedron Lett 38:5603–5606, 1997; 3)triazolo[4,5-b]indole-1(4H)-carboxylate (III): C19H18N4O4S, have been synthesized and their structures determined by single crystal X-ray crystallography. (I), C14H11N3O4S, is triclinic with space group P-1 and cell constants:a = 7.7394(8) Å, b = 12.5826(11) Å, c = 14.7280(13) Å, α = 77.259(8)°, β = 75.885(8)°, γ = 79.342(8)°, V = 1343.6(2) Å3, Z = 4. (II), C18H19N3O4S, is monoclinic with space group P21/c and cell constants:a = 16.0499(5) Å, b = 12.0196(4) Å, c = 9.7866(4) Å, β = 104.879(4)°, V = 1824.67(12) Å3, Z = 4. (III), C19H18N4O4S, is triclinic with space group P-1 and cell constants: a = 9.0391(8) Å, b = 10.3429(12) Å, c = 10.8145(11) Å, α = 75.870(9)°, β = 71.489(9)°, γ = 88.111(8)°, V = 928.64(17) Å3, Z = 2. All three compounds have the same indole nitrogen phenylsulfonyl substituent. In the crystals, the dihedral angle between the mean planes of the pyrrolyl groups of the indole ring and phenylsulfonyl groups are 86.0(8)o (IA) or 83.5(4)o(IB), and 85.0(6)o(III), forming an L-shaped molecule, while in (II) it is 52.9(5)o, forming a V-shaped molecule due in part to the puckering of the pyrrolyl ring from the nonplanar indole group. Additionally, the DFT frontier molecular orbitals of each compound are displayed and correlation between the calculated molecular orbital energies (eV) for the surfaces of the frontier molecular orbitals to the electronic excitation transitions from the absorption spectra of each compound have been proposed.Graphical AbstractSynthesis, Crystal Structures, Density Functional Theory (DFT) Calculations and Molecular Orbital Calculations of three new derivatives of 1-(phenylsulfonyl)indole: 3-nitro-1-(phenylsulfonyl)-1H-indol-2-amine (I): C14H11N¬3O4S; N-(tert-butyl)-3-nitro-1-(phenylsulfonyl)-1H-indol-2-amine (II): C18H19N3O4S and tert-butyl 4-(phenylsulfonyl)-[1,2,3]triazolo[4,5-b]indole-1(4H)-carboxylate (III): C19H18N4O4S.

Abstract 5559: Novel synthetic pyridyl analogues of CDDO-Im with improved stability and their potential use in cancer prevention

Synthetic oleanane triterpenoids are non-cytotoxic, multifunctional drugs with a broad spectrum of applications for prevention and treatment of cancer and for many other chronic diseases. CDDO-Im, 1[2-Cyano-3,12-dioxooleana-1,9(11-dien-28-oyl] imidazole, synthesized more than a decade ago, is one of the most potent triterpenoids known to date with marked anti-inflammatory, cytoprotective, antiproliferative, differentiative and proapoptotic activity on various human and murine tumor cell lines. However, pharmacokinetics of CDDO-Im are not optimal. Therefore, three new pyridyl analogues of CDDO-Im, namely CDDO-3P-Im, CDDO-2P-Im and CDDO-4P-Im, have been synthesized and screened for their possible use as chemopreventive or chemotherapeutic drugs. At low nanomolar concentrations, they were equivalent to CDDO-Im for induction of differentiation in U937 leukemia cells and at higher doses they induced apoptosis. As inflammation and oxidative stress contribute to carcinogenesis, we also assessed their cytoprotective potential. The new compounds suppressed inducible nitric oxide synthase expression in RAW264.7 macrophage-like cells and significantly induced heme oxygenase-1 and NADPH quinone reductase mRNA and protein levels in lung cancer cells as well as in various mouse tissues. Most importantly, pharmacokinetic studies performed in vitro in human plasma and in vivo revealed superior stability for each new analogue. While CDDO-Im was almost completely degraded after 30 min ( 50% still detectable. Six hours after gavage, much higher concentrations of the new derivatives were found in mouse liver, lung, pancreas and kidney in contrast to CDDO-Im. Thus, the new pyridyl analogues have better bioavailability, and because of their potent anti-inflammatory activity and improved stability, they will be tested in vivo in relevant carcinogenesis models. Citation Format: Martine Cao, Evans Onyango, Charlotte Williams, Darlene Royce, Gordon Gribble, Michael Sporn, Karen Liby. Novel synthetic pyridyl analogues of CDDO-Im with improved stability and their potential use in cancer prevention. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5559. doi:10.1158/1538-7445.AM2015-5559