Bernard L. Flynn

Discovery of 7-Hydroxy-6-methoxy-2-methyl-3-(3,4,5- trimethoxybenzoyl)benzo[b]furan (BNC105), a Tubulin Polymerization Inhibitor with Potent Antiproliferative and Tumor Vascular Disrupting Properties

A structure-activity relationship (SAR) guided design of novel tubulin polymerization inhibitors has resulted in a series of benzo[b]furans with exceptional potency toward cancer cells and activated endothelial cells. The potency of early lead compounds has been substantially improved through the synergistic effect of introducing a conformational bias and additional hydrogen bond donor to the pharmacophore. Screening of a focused library of potent tubulin polymerization inhibitors for selectivity against cancer cells and activated endothelial cells over quiescent endothelial cells has afforded 7-hydroxy-6-methoxy-2-methyl-3-(3,4,5-trimethoxybenzoyl)benzo[b]furan (BNC105, 8) as a potent and selective antiproliferative. Because of poor solubility, 8 is administered as its disodium phosphate ester prodrug 9 (BNC105P), which is rapidly cleaved in vivo to return the active 8. 9 exhibits both superior vascular disrupting and tumor growth inhibitory properties compared with the benchmark agent combretastatin A-4 disodium phosphate 5 (CA4P).

Allosteric modulators of the adenosine A1 receptor: synthesis and pharmacological evaluation of 4-substituted 2-amino-3-benzoylthiophenes.

A series of 4-substituted 2-amino-3-benzoylthiophenes was screened using a functional assay of A(1)AR-mediated phosphorylation of ERK1/2 in intact CHO cells to identify both potential agonistic effects as well the ability to allosterically modulate the activity of the orthosteric agonist, R-PIA. More detailed concentration-response experiments were subsequently performed on two compounds (9a and 9o) utilizing both the ERK1/2 assay as well as a second assay of [(35)S]GTPgammaS binding to activated G proteins.

BNC105: A novel tubulin polymerization inhibitor that selectively disrupts tumor vasculature and displays single-agent antitumor efficacy

Vascular disruption agents (VDA) cause occlusion of tumor vasculature, resulting in hypoxia-driven tumor cell necrosis. Tumor vascular disruption is a therapeutic strategy of great potential; however, VDAs currently under development display a narrow therapeutic margin, with cardiovascular toxicity posing a dose-limiting obstacle. Discovery of new VDAs, which display a wider therapeutic margin, may allow attainment of improved clinical outcomes. To identify such compounds, we used an in vitro selectivity screening approach that exploits the fact that tumor endothelial cells are in a constant state of activation and angiogenesis and do not undergo senescence. Our effort yielded the compound BNC105. This compound acts as a tubulin polymerization inhibitor and displays 80-fold higher potency against endothelial cells that are actively proliferating or are engaged in the formation of in vitro capillaries compared with nonproliferating endothelial cells or endothelium found in stable capillaries. This selectivity was not observed with CA4, a VDA currently under evaluation in phase III clinical trials. BNC105 is more potent and offers a wider therapeutic window. CA4 produces 90% vascular disruption at its no observed adverse event level (NOAEL), whereas BNC105 causes 95% vascular disruption at 1/8th of its NOAEL. Tissue distribution analysis of BNC105 in tumor-bearing mice showed that while the drug is cleared from all tissues 24 hours after administration, it is still present at high concentrations within the solid tumor mass. Furthermore, BNC105 treatment causes tumor regressions with complete tumor clearance in 20% of treated animals. Mol Cancer Ther; 9(6); 1562–73. ©2010 AACR.

Alternating iodonium-mediated reaction cascades giving indole- and quinoline-containing polycycles.

A simple two-step convergent protocol gives direct access to synthetic intermediate A from ortho-iodoanilines. Intermediate A can be treated with NIS in CH2Cl2 to induce novel iodonium mediated domino reaction cascade, which provides direct access to ring-fused indole compounds B. Simply by changing the reaction conditions, this protocol can be directed down an alternative domino reaction cascade to give various ring fused quinoline compounds C.

A convenient two step protocol for the synthesis of cyclopentenones and indanones, including an asymmetric variantElectronic supplementary information (ESI) available: synthetic procedures and spectral data for all compounds 7 and 8. See http://www.rsc.org/suppdata/cc/b2/b211845a/

A one-pot palladium mediated hydrostannylation/cross-coupling protocol is used to give direct access to cross-conjugated dienones that can be utilized in Nazarov cyclizations to afford highly substituted cyclopentenones and indanones, including an asymmetric variant.

An efficient synthesis and substitution of 3-Aroyl-2-bromobenzo[b]furans.

A convenient method for the synthesis of 2-bromo-3-aroyl-benzo[b]furans from readily accessible precursors has been developed. The 2-bromo group has been employed as a versatile synthetic handle in both palladium-mediated couplings and direct nucleophilic substitutions to give access to a wide range of 2-substituted-3-aroyl-benzo[b]furans.

2-Aminothienopyridazines as novel adenosine A1 receptor allosteric modulators and antagonists

A pharmacophore-based screen identified 32 compounds including ethyl 5-amino-3-(4- tert-butylphenyl)-4-oxo-3,4-dihydrothieno[3,4- d]pyridazine-1-carboxylate ( 8) as a new allosteric modulator of the adenosine A1 receptor (A1AR). On the basis of this lead, various derivatives were prepared and evaluated for activity at the human A 1AR. A number of the test compounds allosterically stabilized agonist-receptor-G protein ternary complexes in dissociation kinetic assays, but were found to be more potent as antagonists in subsequent functional assays of ERK1/2 phosphorylation. Additional experiments on the most potent antagonist, 13b, investigating A1AR-mediated [(35)S]GTPgammaS binding and [(3)H]CCPA equilibrium binding confirmed its antagonistic mode of action and also identified inverse agonism. This study has thus identified a new class of A1AR antagonists that can also recognize the receptors allosteric site with lower potency.

A reductive-coupling plus Nazarov cyclization sequence in the asymmetric synthesis of five-membered carbocycles.

Palladium-mediated hydrostannylation of alkynoyl compounds is combined with Stille-Scott cross-coupling (reductive-coupling) to give one-pot access to divinyl and aryl vinyl ketones, which undergo Nazarov cyclization to give cyclopentenones upon treatment with acid. This reaction sequence has been studied with a variety of different substitution patterns, including the use of oxazolidinone auxiliaries to achieve torquoselectivity in the Nazarov cyclization. Through a combination of good yields and moderate to good levels of stereochemical induction, this approach affords efficient, convergent, and asymmetric access to a variety of different cyclopentanoid systems.

Opposing auxiliary conformations produce the same torquoselectivity in an oxazolidinone-directed Nazarov cyclization

Most applications of chiral oxazolidinone auxiliaries in asymmetric synthesis operate through a common set of stereocontrol principles. That is, the oxazolidinone is made to adopt a specific, coplanar conformation with respect to the prochiral substrate, and reaction occurs preferentially at whichever stereoheterotopic face is not blocked by the substituents on the oxazolidinone. In contrast to these principles, we report here the discovery of an alternative mechanism of oxazolidinone-based stereocontrol that does not require coplanarity and is driven instead by allylic strain. This pathway has been uncovered through computational studies of an asymmetric Nazarov cyclization. Chiral oxazolidinone auxiliaries provide essentially complete control over the torquoselectivity of ring closure and the regioselectivity of subsequent deprotonation. Density functional theory calculations (M06-2X//B3LYP) reveal that in the transition state of 4π electrocyclic ring closure, the oxazolidinone ring and the cyclizing pentadienyl cation are distorted from coplanarity in a manner that gives two transition state conformations of similar energy. These two conformers are distinguished by a 180° flip in the auxiliary orientation such that in one conformer the oxazolidinone carbonyl is oriented toward the OH of the pentadienyl cation (syn-conformer) and in the other it is oriented away from this OH (anti-conformer). Surprisingly, both conformations induce the same sense of torquoselectivity, with a 3-5 kcal/mol preference for the C5-β epimer of the ring-closed cation. In both conformations, the conrotatory mode that leads to the C5-α epimer is disfavored due to higher levels of allylic strain between the oxazolidinone substituent and adjacent groups on the pentadienyl cation (R(4) and OH). The excellent torquoselectivities obtained in the oxazolidinone-directed Nazarov cyclization suggest that the allylic strain-driven stereoinduction pathway represents a viable alternative mechanism of stereocontrol for reactions of sterically congested substrates that lie outside of the traditional coplanar (N-acyloxazolidinone) paradigm.

A New Approach to Highly Substituted Cyclopentanoids from a Concise Formal Synthesis of (+)-Roseophilin

A convergent reaction sequence involving a reductive coupling and a chiral Brønsted acid catalyzed Nazarov reaction is utilized in a concise formal synthesis of (+)-roseophilin (11 steps via longest linear sequence, 10.2% yield, 95% ee).