Discovery and Structure Relationships of Salicylanilide Derivatives as Potent, Non-acidic P2X1 Receptor Antagonists.

Antagonists for the ATP-gated ion channel receptor P2X1 have potential as antithrombotics and for treating hyperactive bladder and inflammation. In this study, salicylanilide derivatives were synthesized based on a screening hit. P2X1 antagonistic potency was assessed in 1321N1 astrocytoma cells stably transfected with the human P2X1 receptor by measuring inhibition of the ATP-induced calcium influx. Structure-activity relationships were analyzed, and selectivity versus other P2X receptor subtypes was assessed. The most potent compounds, N-[3,5-bis(trifluoromethyl)phenyl]-5-chloro-2-hydroxybenzamide (1, IC50 0.0192 µM) and N-[3,5-bis(trifluoromethyl)phenyl]-4-chloro-2-hydroxybenzamide (14, IC50 0.0231 µM), displayed >500-fold selectivity versus P2X2 and P2X3, and 10-fold selectivity versus P2X4 and P2X7 receptors, and inhibited collagen-induced platelet aggregation. They behaved as negative allosteric modulators, and molecular modeling studies suggested an extracellular binding site. Besides selective P2X1 antagonists, compounds with ancillary P2X4 and/or P2X7 receptor inhibition were discovered. These compounds represent the first potent, non-acidic, allosteric P2X1 receptor antagonists reported to date.

Decarboxylative borylation.

The widespread use of alkyl boronic acids and esters is frequently hampered by the challenges associated with their preparation. We describe a simple and practical method to rapidly access densely functionalized alkyl boronate esters from abundant carboxylic substituents. This broad-scope nickel-catalyzed reaction uses the same activating principle as amide bond formation to replace a carboxylic acid moiety with a boronate ester. Application to peptides allowed expedient preparations of α-amino boronic acids, often with high stereoselectivity, thereby facilitating synthesis of the alkyl boronic acid drugs Velcade and Ninlaro as well as a boronic acid version of the iconic antibiotic vancomycin. The reaction also enabled the discovery and extensive biological characterization of potent human neutrophil elastase inhibitors, which offer reversible covalent binding properties.

Total Synthesis of Leupyrrins A1 and B1 , Highly Potent Antifungal Agents from the Myxobacterium Sorangium cellulosum.

Full details on the design, elaboration, and application of efficient strategies for the high-yielding total syntheses of leupyrrins A1 and B1 , unique antifungal agents from the myxobacterium Sorangium cellulosum, are reported. A sequential zirconocene-mediated diyne-cyclization, and regioselective opening of the zirconacyclopentadiene intermediate enabled a concise entry into the unique dihydrofuran fragment, whereas another domino reaction was developed for the butyrolactone involving a one-pot lactol opening, stereoselective aldehyde addition and in situ lactonization. Furthermore, an innovative sp2 -sp3 -cross-coupling for pyrrole functionalization and an optimized HATU-mediated amide coupling protocol of two elaborate fragments were established. In addition, an unusual protective group strategy, involving a Teoc-acetonide protected amine in combination with tert-butyl and acetate esters, was successfully elaborated. These tactics and strategies are generally useful and may be also applied in the synthesis of other functionalized compounds. It is expected that the material which was obtained by these total syntheses will enable the further exploration of the biological profile of these potent antifungal agents.

11-Step Total Synthesis of Araiosamines.

A concise route to a small family of exotic marine alkaloids known as the araiosamines has been developed, and their absolute configuration has been assigned. The dense array of functionality, high polarity, and rich stereochemistry coupled with equilibrating topologies present an unusual challenge for chemical synthesis and an opportunity for innovation. Key steps involve the use of a new reagent for guanidine installation, a remarkably selective C-H functionalization, and a surprisingly simple final step that intersects a presumed biosynthetic intermediate. Synthetic araiosamines were shown to exhibit potency against Gram-positive and -negative bacteria despite a contrary report of no activity.

Stereochemical determination of the leupyrrins and total synthesis of leupyrrin A1.

The stereochemical determination of the potent antifungal agents leupyrrin A1 and B1 and the total synthesis of leupyrrin A1 are reported. The relative and absolute configuration was determined by a combination of high field NMR studies, molecular modeling, and chemical derivatization. The expedient total synthesis involves a one-pot sequential Zr-mediated oxidative diyne-cyclization/regioselective opening sequence for preparation of the unique dihydrofuran ring, a highly stereoselective one-pot approach to the butyrolactone, a challenging sp(2)-sp(3) Suzuki coupling and a high-yielding Shiina macrolactonization.

Switching off the charge transfer and closing the S1-T1 ISC channel in excited states of quinolizinium derivatives: a theoretical study.

Excited states of benzo[b]quinolizinium (BQ) derivatives that show efficient pH-responsive fluorescence switching properties were studied quantum-chemically by employing the CASSCF/CASPT2 and TD-DFT methods. Protonation of aminophenyl-BQ at the electron-donor amine moiety converts the nitrogen lone pair into a σ bond and the HOMO into a lower-lying orbital that is no longer involved in the excitation, thereby rationalizing the suppression of the charge transfer. An S1-T1 seam between the vertically excited Franck-Condon (FC) point and the S1 equilibrium geometry favors intersystem crossing (ISC). The T1 state of the protonated form remains well below S1 (1.5 eV) because of favorable exchange interactions, whereas the T1 state of the unprotonated form does not experience any analogous stabilization because of the difference in the spatial domains of the singly occupied orbitals in the S1 and T1 states. The S1 surface from the FC point until the equilibrium geometry for the protonated species is energetically downhill. Calculations on models and available experimental data suggest design principles for similarly functioning pH-responsive species, namely, an amine lone pair as the electron donor and a cationic ring of moderate size as the electron acceptor that are structurally separated by virtue of a spacer.

Carbamazepine derivatives with P2X4 receptor-blocking activity.

Antagonists for the P2 receptor subtype P2X4, an ATP-activated cation channel receptor, have potential as novel drugs for the treatment of neuropathic pain and other inflammatory diseases. In the present study, a series of 47 carbamazepine derivatives including 32 novel compounds were designed, synthesized, and evaluated as P2X4 receptor antagonists. Their potency to inhibit ATP-induced calcium influx in 1321N1 astrocytoma cells stably transfected with the human P2X4 receptor was determined. Additionally, species selectivity (human, rat, mouse) and receptor subtype selectivity (P2X4 vs P2X1, 2, 3, 7) were investigated for selected derivatives. The most potent compound of the present series, which exhibited an allosteric mechanism of P2X4 inhibition, was N,N-diisopropyl-5H-dibenz[b,f]azepine-5-carboxamide (34, IC50 of 3.44µM). The present study extends the so far very limited knowledge on structure-activity relationships of P2X4 receptor antagonists.

Fluorimetric detection of Mg2+ and DNA with 9-(alkoxyphenyl)benzo[b]quinolizinium derivatives.

A benzo[b]quinolizinium-benzo-15-crown-5 ether conjugate 2a is presented that enables the fluorimetric detection of Mg(2+) and DNA by a significant light-up effect, along with a change of the emission wavelength with different analytes (Mg(2+): 495 nm; DNA: 550 nm). The mechanism of the excited-state deactivation of 2a was investigated by steady-state fluorescence spectroscopy in media of varied viscosity and compared with the photophysical properties of methoxyphenyl-substituted benzo[b]quinolizinium 2b (m,p-diOMe), 2c (m-OMe), and 2d (p-OMe) as reference compounds. Compounds 2a-c, which share the m-alkoxyphenyl substituent as the common feature, have low emission quantum yields (Φ(F) < 10(-2) in water) but exhibit a significant increase of their fluorescence intensity in viscous glycerol solutions. In contrast, the viscosity of the medium does not influence the emission properties of the parent phenyl-substituted benzo[b]quinolizinium 2e and of the p-methoxyphenyl-substituted derivative 2d. Based on these observations it is concluded that the excited-state deactivation in 2a-c is mainly due to the rotation of the m-alkoxy group about the C(ar)-O bond. The interaction of 2a-c with DNA or Mg(2+) ions was studied by spectrophotometric titrations and CD spectroscopy. Notably, the association of 2a or 2b with DNA or 2a with Mg(2+) ions induces a strong fluorescence enhancement (15- and 40-fold for DNA, 450-fold for Mg(2+)), which is rationalized by the suppression of the torsional-relaxation of the alkoxy-substituent in the excited state. Additionally, the cation-induced light-up effect of 2a is selective towards Mg(2+) ions as compared with other cations such as NH(4)(+), Li(+), Na(+), K(+) and Ba(2+).

DNA cleavage by the Cu(II) complex of the DNA-intercalating 9-bis(pyridin-2-ylmethyl)aminobenzo[b]quinolizinium.

The synthesis and the investigation of the Cu(II)-binding, the DNA-binding, and the DNA-damaging properties of a conjugate between the benzo[b]quinolizinium ion and the bis(pyridin-2-ylmethyl)amino receptor are presented. Photometric and fluorimetric titrations as well as CD spectroscopic analysis reveal that the 9-bis(pyridin-2-ylmethyl)aminobenzo[b]quinolizinium ligand intercalates into DNA (K(b) = 1.9 x 10(4) M(-1)) and exhibits a high selectivity towards complexation of Cu(2+) in water (K(b) = 4.3 x 10(4) M(-1)). This combination of functionalities allows to localize Cu(2+) in close proximity of DNA, where these metal ions induce efficient DNA damage, as shown by the single-strand cleavage of supercoiled plasmid DNA. Notably, the DNA cleavage does not require additional reagents nor light.

Selective detection of Hg2+ in the microenvironment of double-stranded DNA with an intercalator crown-ether conjugate.

9-[2-(1,4-Dioxa-7,13-dithia-10-azacyclopentadecyl)phenyl]amino-benzo[b]quinolizinium enables the unambiguous fluorimetric and polarimetric detection of Hg(2+) in the close proximity of double-stranded nucleic acids without interfering background signals from the complexes of this compound with Hg(2+) or DNA alone.

Selective ratiometric detection of mercury(II) ions in water with an acridizinium-based fluorescent probe.

The integration of a selective Hg2+ receptor unit, 1,4-dioxa-7,13-dithia-10-azacyclopentadecane, into the 9-aminoacridizinium fluorophore provides a fluorescent probe which allows a selective ratiometric detection of Hg2+ in water.

Synthesis of 6-amino-3,4-dihydroisoquinolinium derivatives by ring-opening reactions of acridizinium ions.

The reaction of the 9-fluoroacridizinium (9-fluorobenzo[b]quinolizinium) or the 9-aminoacridizinium (9-aminobenzo[b]quinolizinium) ion with primary alkyl amines gives with high diastereoselectivity 6-amino-3,4-dihydroisoquinolinium derivatives as main products, which exhibit pronounced absorption and fluorescence properties. It is proposed that the reaction proceeds via a nucleophilic ring-opening followed by an aza Diels-Alder reaction.