Iron(II) and Copper(I) Control the Total Regioselectivity in the Hydrobromination of Alkenes.

A new method that allows the complete control of the regioselectivity of the hydrobromination reaction of alkenes is described. Herein, we report a radical procedure with TMSBr and oxygen as common reagents, where the formation of the anti-Markovnikov product occurs in the presence of parts per million amounts of the Cu(I) species and the formation of the Markovnikov product occurs in the presence of 30 mol % iron(II) bromide. Density functional theory calculations combined with Fukui's radical susceptibilities support the obtained results.

Synthetic molecules for disruption of the MYC protein-protein interface.

MYC is a key transcriptional regulator involved in cellular proliferation and has established roles in transcriptional elongation and initiation, microRNA regulation, apoptosis, and pluripotency. Despite this prevalence, functional chemical probes of MYC function at the protein level have been limited. Previously, we discovered 5a, that binds to MYC with potency and specificity, downregulates the transcriptional activities of MYC and shows efficacy in vivo. However, this scaffold posed intrinsic pharmacokinetic liabilities, namely, poor solubility that precluded biophysical interrogation. Here, we developed a screening platform based on field-effect transistor analysis (Bio-FET), surface plasmon resonance (SPR), and a microtumor formation assay to analyze a series of new compounds aimed at improving these properties. This blind SAR campaign has produced a new lead compound of significantly increased in vivo stability and solubility for a 40-fold increase in exposure. This probe represents a significant advancement that will not only enable biophysical characterization of this interaction and further SAR, but also contribute to advances in understanding of MYC biology.

Crystallography Coupled with Kinetic Analysis Provides Mechanistic Underpinnings of a Nicotine-Degrading Enzyme.

Nicotine oxidoreductase (NicA2) is a bacterial flavoenzyme, which catalyzes the first step of nicotine catabolism by oxidizing S-nicotine into N-methyl-myosmine. It has been proposed as a biotherapeutic for nicotine addiction because of its nanomolar substrate binding affinity. The first crystal structure of NicA2 has been reported, establishing NicA2 as a member of the monoamine oxidase (MAO) family. However, substrate specificity and structural determinants of substrate binding and/or catalysis have not been explored. Herein, analysis of the pH-rate profile, single-turnover kinetics, and binding data establish that pH does not significantly affect the catalytic rate and product release is not rate-limiting. The X-ray crystal structure of NicA2 with S-nicotine refined to 2.65 Å resolution reveals a hydrophobic binding site with a solvent exclusive cavity. Hydrophobic interactions predominantly orient the substrate, promoting the binding of a deprotonated species and supporting a hydride-transfer mechanism. Notably, NicA2 showed no activity against neurotransmitters oxidized by the two isoforms of human MAO. To further probe the substrate range of NicA2, enzyme activity was evaluated using a series of substrate analogues, indicating that S-nicotine is the optimal substrate and substitutions within the pyridyl ring abolish NicA2 activity. Moreover, mutagenesis and kinetic analysis of active-site residues reveal that removal of a hydrogen bond between the pyridyl ring of S-nicotine and the hydroxyl group of T381 has a 10-fold effect on KM, supporting the role of this bond in positioning the catalytically competent form of the substrate. Together, crystallography combined with kinetic analysis provides a deeper understanding of this enzyme's remarkable specificity.

Mining a Kröhnke Pyridine Library for Anti-Arenavirus Activity.

Several arenaviruses cause hemorrhagic fever (HF) disease in humans and represent important public health problems in their endemic regions. In addition, evidence indicates that the worldwide-distributed prototypic arenavirus lymphocytic choriomeningitis virus is a neglected human pathogen of clinical significance. There are no licensed arenavirus vaccines, and current antiarenavirus therapy is limited to an off-label use of ribavirin that is only partially effective. Therefore, there is an unmet need for novel therapeutics to combat human pathogenic arenaviruses, a task that will be facilitated by the identification of compounds with antiarenaviral activity that could serve as probes to identify arenavirus-host interactions suitable for targeting, as well as lead compounds to develop future antiarenaviral drugs. Screening of a combinatorial library of Krönhke pyridines identified compound KP-146 [(5-(5-(2,3-dihydrobenzo[ b][1,4] dioxin-6-yl)-4'-methoxy-[1,1'-biphenyl]-3-yl)thiophene-2-carboxamide] as having strong anti-lymphocytic choriomeningitis virus (LCMV) activity in cultured cells. KP-146 did not inhibit LCMV cell entry but rather interfered with the activity of the LCMV ribonucleoprotein (vRNP) responsible for directing virus RNA replication and gene transcription, as well as with the budding process mediated by the LCMV matrix Z protein. LCMV variants with increased resistance to KP-146 did not emerge after serial passages in the presence of KP-146. Our findings support the consideration of Kröhnke pyridine scaffold as a valuable source to identify compounds that could serve as tools to dissect arenavirus-host interactions, as well as lead candidate structures to develop antiarenaviral drugs.

An enzymatic advance in nicotine cessation therapy.

A nicotine-degrading enzyme termed NicA2 was altered (NicA2-J1) through fusion of an albumin binding domain to increase its half-life. Examination of NicA2-J1 in vivo demonstrated a complete blockade of brain nicotine access, which in turn blunted nicotine's psychoactive effects. These data further support development of pharmacokinetic nicotine cessation therapeutics.

Direct Access to 2,3,4,6-Tetrasubstituted Tetrahydro-2H-pyrans via Tandem SN2'-Prins Cyclization.

A new, direct, and diastereoselective synthesis of activated 2,3,4,6-tetrasubstituted tetrahydro-2H-pyrans is described. In this reaction, iron(III) catalyzed an SN2'-Prins cyclization tandem process leading to the creation of three new stereocenters in one single step. These activated tetrahydro-2H-pyran units are easily derivatizable through CuAAC conjugations in order to generate multifunctionalized complex molecules. DFT calculations support the in situ SN2' reaction as a preliminary step in the Prins cyclization.

Influencing Antibody-Mediated Attenuation of Methamphetamine CNS Distribution through Vaccine Linker Design.

Active vaccination examining a single hapten engendered with a series of peptidic linkers has resulted in the production of antimethamphetamine antibodies. Given the limited chemical complexity of methamphetamine, the structure of the linker species embedded within the hapten could have a substantial effect on the ultimate efficacy of the resulting vaccines. Herein, we investigate linker effects by generating a series of methamphetamine haptens that harbor a linker with varying amino acid identity, peptide length, and associated carrier protein. Independent changes in each of these parameters were found to result in alterations in both the quantity and quality of the antibodies induced by vaccination. Although it was found that the consequence of the linker design was also dependent on the identity of the carrier protein, we demonstrate overall that the inclusion of a short, structurally simple, amino acid linker benefits the efficacy of a methamphetamine vaccine in limiting brain penetration of the free drug.

Prins Cyclization Catalyzed by a Fe(III) /Trimethylsilyl Halide System: The Oxocarbenium Ion Pathway versus the [2+2] Cycloaddition.

The different factors that control the alkene Prins cyclization catalyzed by iron(III) salts have been explored by means of a joint experimental-computational study. The iron(III) salt/trimethylsilyl halide system has proved to be an excellent promoter in the synthesis of crossed all-cis disubstituted tetrahydropyrans, minimizing the formation of products derived from side-chain exchange. In this iron(III)-catalyzed Prins cyclization reaction between homoallylic alcohols and non-activated alkenes, two mechanistic pathways can be envisaged, namely the classical oxocarbenium route and the alternative [2+2] cycloaddition-based pathway. It is found that the [2+2] pathway is disfavored for those alcohols having non-activated and non-substituted alkenes. In these cases, the classical pathway, via the key oxocarbenium ion, is preferred. In addition, the final product distribution strongly depends upon the nature of the substituent adjacent to the hydroxy group in the homoallylic alcohol, which can favor or hamper a side 2-oxonia-Cope rearrangement.

Continuous-flow enantioselective α-aminoxylation of aldehydes catalyzed by a polystyrene-immobilized hydroxyproline.

The application of polystyrene-immobilized proline-based catalysts in packed-bed reactors for the continuous-flow, direct, enantioselective α-aminoxylation of aldehydes is described. The system allows the easy preparation of a series of ß-aminoxy alcohols (after a reductive workup) with excellent optical purity and with an effective catalyst loading of ca. 2.5% (four-fold reduction compared to the batch process) working at residence times of ca. 5 min.

Synthesis and biological evaluation of pyrimidine analogs of antimycobacterial purines.

Pyrimidine analogs of antimycobacterial 6-aryl-9-benzylpurines have been synthesized and screened for antibacterial activity against Mycobacterium tuberculosis H(37)Rv in vitro. Several active compounds were identified and the best results were observed for 5-formamidopyrimidines. These compounds generally displayed IC(90) values < or =1microg/mL, and they exhibited low toxicity towards mammalian cells. Imidazolylpyrimidines, which may be regarded as fleximer analogs of the parent purines, were also synthesized and one of them was found to be quite a potent inhibitor of M. tuberculosis (IC(90) 14microg/mL).

Synthesis of imidazole derivatives with antimycobacterial activity.

4-Substituted 1-(p-methoxybenzyl)imidazoles were designed and synthesized in order to mimic parts of the structure of highly potent antimycobacterial 6-aryl-9-(p-methoxybenzyl)purines. 4-Haloimidazoles were subjected to Pd-catalyzed cross-coupling in order to introduce a (hetero)aryl group, or they were converted to Grignard reagents and reacted with (hetero)arylaldehydes. Further transformations of the adducts gave a variety of potential antimycobacterials with different "spacers" between the imidazole and (hetero)aryl group. The adduct from furfural was rearranged to a cyclopentenone derivative when treated with methanol under acidic conditions. Several target compounds exhibited antimycobacterial activity in vitro (IC(90 )13 microg/mL for the best inhibitors), but they were not as active as the most potent purines and pyrimidines synthesized before.

A new catalytic Prins cyclization leading to oxa- and azacycles.

A new Prins cyclization process that builds up one carbon-carbon bond, one heteroatom-carbon bond, and one halogen-carbon bond, (in an oxa- and azacycle) relies on an iron catalyst system formed from Fe(acac)3 and trimethylsilyl halide. The method displays a broad substrate scope and is economical, environmentally friendly, and experimentally simple. This catalytic method permits the construction of chloro, bromo and iodo heterocycles, by the suitable combination of iron(III) source, the corresponding trimethylsilyl halide and the solvent, in high yields.

beta'-Hydroxy-alpha,beta-unsaturated ketones: A new pharmacophore for the design of anticancer drugs. Part 2.

Novel antiproliferative beta'-acyloxy-alpha,beta-unsaturated ketones were obtained by means of an iron(III)-catalyzed multicomponent domino process (ABB' 3CR). The most active derivatives displayed GI(50) values in the range of 0.5-3.9 muM against a panel of representative human solid tumor cell lines: A2780, SW1573, HBL-100, T-47D and WiDr. Analysis of cells following 24 h exposure to these drugs showed cell cycle arrest in the S and G(2)/M phase, in a dose-dependent manner. Our data indicate that the beta'-acyloxy-alpha,beta-unsaturated ketones cause permanent damage to the cells and induce apoptosis.

Factors controlling the alkyne prins cyclization: the stability of dihydropyranyl cations.

The relative stability of the intermediates involved in the alkyne Prins cyclization and the competitive 2-oxonia-[3,3]-sigmatropic rearrangement was studied. This rearrangement was shown to occur slowly under typical alkyne Prins cyclization conditions when the allenyl oxocarbenium ion that results from the rearrangement is similar to or higher in energy than the starting alkynyl oxocarbenium ion. The formal 2-oxonia-[3,3]-sigmatropic rearrangement may be disfavored by destabilizing the resultant allenyl oxocarbenium ion or by stabilizing an intermediate dihydropyranyl cation. The trimethylsilyl group as a substituent at the alkyne and electron-withdrawing groups (CH2Cl and CH2CN) located at the alpha-position to the carbinol center are shown to be effective. DFT calculations suggest that these substituents stabilize the dihydropyranyl cations, thus leading to a more uniform reorganization of the electronic density in the ring, and do not have a direct effect on the formally positively charged carbon atom.

Antiproliferative activity of 4-chloro-5,6-dihydro-2H-pyrans. Part 2: Enhancement of drug cytotoxicity.

The Prins reaction was the basis to synthesize functionalized alkyl chlorodihydropyran derivatives. The inexpensive, stable, and environmentally friendly FeCl(3) promotes the cyclization. The method represents an efficient and regioselective manner to obtain in a single step chlorovinyl-TMS oxacycles. The in vitro antiproliferative activities of the compounds were examined in the human solid tumor cell lines A2780 (ovarian cancer), SW1573 (non-small cell lung cancer), and WiDr (colon cancer). Overall, the results show an enhancement in the cytotoxicity exhibited by the new analogs when compared to their parental compounds.

Prins-type synthesis and SAR study of cytotoxic alkyl chloro dihydropyrans.

A series of functionalized tetrahydropyran and dihydropyran derivatives was synthesized by means of a Prins-type cyclization between unsaturated alcohols and several aldehydes. An unprecedented dimer bearing two 4-chloro-5,6-dihydro-2H-pyran scaffolds was obtained in high yield. A panel of three representative human solid tumor cells from diverse origin was used to assess the cytotoxicity of the compounds. Overall, the results show the relevance of the chlorovinyl group in the biological activity, and 2-alkyl-4-chloro-5,6-dihydro-2H-pyrans represent interesting leads for further chemical modifications and biological studies.

The silylalkyne-Prins cyclization: stereoselective synthesis of tetra- and pentasubstituted halodihydropyrans.

[reaction: see text] A new type of Prins cyclization using silylated secondary homopropargylic alcohols and aldehydes yielding tetra- and pentasubstituted dihydropyrans is described. The presence of the trimethylsilyl group in the triple bond favors the Prins cyclization and minimizes the 2-oxonia-[3,3]-sigmatropic rearrangement as a competitive alternative pathway. Ab initio theoretical calculations of the species involved in the rearrangements support the proposed mechanism. The process is highly stereoselective, affording cis-dihydropyran as the only isomer.

One-pot synthesis and SAR study of cis-2,6-dialkyl-4-chloro-tetrahydropyrans.

A series of cis-2,6-dialkyl-4-chloro-tetrahydropyrans were prepared by means of an iron(III)-catalyzed process. The in vitro antiproliferative activities were examined in the human solid tumor cell lines A2780, SW1573, and WiDr. The results show that the presence of bulky substituents favors the Prins cyclization leading to new products with better activity profile against all cell lines tested.

Beta'-hydroxy-alpha,beta-unsaturated ketones: a new pharmacophore for the design of anticancer drugs.

A series of beta'-hydroxy-alpha,beta-unsaturated ketones were prepared by means of an iron(III) catalyzed domino process. The in vitro antiproliferative activities were examined in the human solid tumor cell lines A2780, SW1573, and WiDr. The results showed that beta'-hydroxy-alpha,beta-unsaturated ketones were more potent than alpha,beta-unsaturated ketones. The best activity profiles were obtained for the derivatives bearing cyclic or branched substituents on the side chains.

Fe(III) halides as effective catalysts in carbon-carbon bond formation: synthesis of 1,5-dihalo-1,4-dienes, alpha,beta-unsaturated ketones, and cyclic ethers.

Iron(III) halides have proven to be excellent catalysts in the coupling of acetylenes and aldehydes. When terminal acetylenes were used the main products obtained were 1,5-dihalo-1,4-dienes with (E,Z)-stereochemistry contaminated in some cases with (E)-alpha,beta-unsaturated ketones. The former carbonyl derivatives were the sole products isolated when nonterminal aromatic alkynes were used. When homopropargylic alcohols were used, a Prins-type cyclization occurred yielding 2-alkyl-4-halo-5,6-dihydro-2H-pyrans. In addition, anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization with homoallylic alcohols. Isolation of an intermediate acetal, calculations, and alkyne hydration studies provide substantiation of a proposed mechanism.