Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs).

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)-based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

Identification of a quadruple mutation that confers tenofovir resistance in chronic hepatitis B patients.

BACKGROUND & AIMS: Tenofovir disoproxil fumarate (TDF) is one the most potent nucleot(s)ide analogues for treating chronic hepatitis B virus (HBV) infection. Phenotypic resistance caused by genotypic resistance to TDF has not been reported. This study aimed to characterize HBV mutations that confer tenofovir resistance. METHODS: Two patients with viral breakthrough during treatment with TDF-containing regimens were prospectively enrolled. The gene encoding HBV reverse transcriptase was sequenced. Eleven HBV clones harboring a series of mutations in the reverse transcriptase gene were constructed by site-directed mutagenesis. Drug susceptibility of each clone was determined by Southern blot analysis and real-time PCR. The relative frequency of mutants was evaluated by ultra-deep sequencing and clonal analysis. RESULTS: Five mutations (rtS106C [C], rtH126Y [Y], rtD134E [E], rtM204I/V, and rtL269I [I]) were commonly found in viral isolates from 2 patients. The novel mutations C, Y, and E were associated with drug resistance. In assays for drug susceptibility, the IC50 value for wild-type HBV was 3.8 ±â€¯0.6 µM, whereas the IC50 values for CYE and CYEI mutants were 14.1 ±â€¯1.8 and 58.1 ±â€¯0.9 µM, respectively. The IC90 value for wild-type HBV was 30 ±â€¯0.5 µM, whereas the IC90 values for CYE and CYEI mutants were 185 ±â€¯0.5 and 790 ±â€¯0.2 µM, respectively. Both tenofovir-resistant mutants and wild-type HBV had similar susceptibility to the capsid assembly modulator NVR 3-778 (IC50 <0.4 µM vs. IC50 = 0.4 µM, respectively). CONCLUSIONS: Our study reveals that the quadruple (CYEI) mutation increases the amount of tenofovir required to inhibit HBV by 15.3-fold in IC50 and 26.3-fold in IC90. These results demonstrate that tenofovir-resistant HBV mutants can emerge, although the genetic barrier is high. LAY SUMMARY: Tenofovir is the most potent nucleotide analogue for the treatment of chronic hepatitis B virus infection and there has been no hepatitis B virus mutation that confers >10-fold resistance to tenofovir up to 8 years. Herein, we identified, for the first time, a quadruple mutation that conferred 15.3-fold (IC50) and 26.3-fold (IC90) resistance to tenofovir in 2 patients who experienced viral breakthrough during tenofovir treatment.

Novel 5,6-disubstituted pyrrolo[2,3-d]pyrimidine derivatives as broad spectrum antiproliferative agents: Synthesis, cell based assays, kinase profile and molecular docking study.

Two new series of 5-subtituted and 5,6-disubstituted pyrrolo[2,3-d]pyrimidine octamides (4a-o and 6a-g) and their corresponding free amines 5a-m and 7a-g have been synthesized and biologically evaluated for their antiproliferative activity against three human cancer cell lines. The 5,6-disubstituted octamides 6d-g as well as the amine derivative 7b have shown the best anticancer activity with single digit micromolar GI50 values over the tested cancer cells, and low cytotoxic effects (GI50 > 10.0 µM) against HFF-1 normal cell. A structure activity relationship (SAR) study has been established and disclosed that terminal octamide moiety at C2 as well as disubstitution with fluorobenzyl piperazines at C5 and C6 of pyrrolo[2,3-d]pyrimidine are the key structural features prerequisite for best antiproliferative activity. Moreover, the most active member 6f was tested for its antiproliferative activity over a panel of 60 cancer cell lines at NCI, and exhibited distinct broad spectrum anticancer activity with submicromolar GI50 and TGI values over multiple cancer cells. Kinase profile of compound 6f over 53 oncogenic kinases at 10 µM concentration showed its highly selective inhibitory activity towards FGFR4, Tie2 and TrkA kinases. The observed activity of 6f against TrkA (IC50 = 2.25 µM), FGFR4 (IC50 = 6.71 µM) and Tie2 (IC50 = 6.84 µM) was explained by molecular docking study, which also proposed that 6f may be a type III kinase inhibitor, binding to an allosteric site rather than kinase hinge region. Overall, compound 6f may serve as a promising anticancer lead compound that could be further optimized for development of potent anticancer agents.

Synthesis and in vitro antiproliferative activity of C5-benzyl substituted 2-amino-pyrrolo[2,3-d]pyrimidines as potent Hsp90 inhibitors.

A novel series of heat shock protein 90 (Hsp90) inhibitors was identified by X-ray crystal analysis of complex structures at solvent-exposed exit pocket C. The 2-amino-pyrrolo[2,3-d]pyrimidine derivatives, 7-deazapurines substituted with a benzyl moiety at C5, showed potent Hsp90 inhibition and broad-spectrum antiproliferative activity against NCI-60 cancer cell lines. The most potent compound, 6a, inhibited Hsp90 with an IC50 of 36nM and showed a submicromolar mean GI50 value against NCI-60 cell lines. The interaction of 6a at the ATP-binding pocket of Hsp90 was confirmed by X-ray crystallography and Western blot analysis.

Chiral environment of catalytic sites in the chiral metal-organic frameworks.

Chiral metal-organic frameworks are considered a useful platform in heterogeneous catalysis for enantioselective chemical transformations. However, it has been observed that the enantioselectivity is sensitive to the site at which the reaction takes place, even in a single crystal, since the chiral environment of the catalytic site varies according to its location, e.g., that of the surface is anisotropic, whereas that of the interior is isotropic.

Synthesis and in vitro evaluation of the antitubercular and antibacterial activity of novel oxazolidinones bearing octahydrocyclopenta[c]pyrrol-2-yl moieties.

A novel series of oxazolidinone-class antimicrobial agents with 5-substituted octahydrocyclopenta[c]pyrrole moieties at the C-ring of linezolid and an acetamide or 1,2,3-triazole ring as the C-5 side chain of the oxazolidinone ring were prepared. The resulting series of compounds were evaluated for in vitro antimicrobial activity against Mycobacterium tuberculosis and a panel of clinically important resistant Gram-positive and -negative bacteria. Among them, endo-alcohol 2a and exo-alcohol 2b showed potent inhibitory activity against M. tuberculosis H37Rv, which was superior to that of linezolid. Several analogues in this series showed potent in vitro antibacterial activity against the clinically important vancomycin-resistant bacteria and showed similar or better potency against linezolid-resistant methicillin-resistant Staphylococcus aureus (MRSA) strains. The hydroxyl group in the azabicyclic C-ring interacted with the same hydrophobic pocket as linezolid based on a docking study. Selected compounds with high antimicrobial activity showed good human microsomal stability and low CYP isozyme and monoamine oxidase (MAO) inhibition.

Exploration of 3-Aminoazetidines as Triple Reuptake Inhibitors by Bioisosteric Modification of 3-α-Oxyazetidine.

For a development of broad spectrum antidepressant 3-aminoazetidine derivatives, two series of compounds were explored by bioisosteric modification of 3-α-oxyazetidine. We synthesized 166 novel 3-aminoazetidine derivatives in series A and B, starting from Boc-protected 3-azetidinone (3) and Boc-protected 3-azetidinal (9) respectively, through parallel syntheses. The inhibitory reuptake activities against serotonin (5-HT), norepinephrine (NE), and dopamine (DA) neurotransmitters were measured by the Neurotransmitter Transporter Uptake Assay Kit using the human embryonic kidney 293 (HEK293) cells stably transfected with the respective three kinds of human transporters (hSERT, hNET, and hDAT). Our study aimed to identify compounds having relative inhibitory activities against hSERT > hNET > hDAT. Lead optimization including microsomal stability, CYP, hERG assay, Ames test, BBB, and PK study resulted in the identification of compound 10dl as a candidate for further studies.

Synthesis and biological evaluation of 1-(isoxazol-5-ylmethylaminoethyl)-4-phenyl tetrahydropyridine and piperidine derivatives as potent T-type calcium channel blockers with antinociceptive effect in a neuropathic pain model.

New tetrahydropyridinyl and piperidinyl ethylamine derivatives were designed with hypothetical mapping on pharmacophore model generated from ligand-based virtual screening. The designed compounds were synthesized, and their inhibitory activities on T-type calcium channel were assayed using FDSS and patch-clamp assay. Among them, compounds 7b and 10b showed potent T-type calcium current blocking activity against Ca(v)3.1 (α(1G)) and Ca(v)3.2 (α(1H)) channel simultaneously. With hERG and pharmacokinetics studies, compounds 7b and 10b were evaluated for the antinociceptive effect on rat model of neuropathic pain. They were significantly effective in decreasing the pain responses to mechanical and cold allodynia induced by spinal nerve ligation. These results suggest that modulation of α(1G) and α(1H) subtype T-type calcium channels may provide a promising approach for the treatment of neuropathic pain.

Assessing the guest-accessible volume in MOFs using two-photon fluorescence microscopy.

The assessment of guest-accessible volume in MOFs can be reliably done by using two-photon confocal fluorescence microscopy (TPM) with a tool-box of dyes with a wide range of sizes. It would be applicable to any porous materials, whose single-crystal structures are not available, or non-crystalline materials.

Homochiral 3D metal-organic frameworks from chiral 1D rods: 6-way helical packing.

The chiral 3D MOFs resulted from the packing of chiral 1D SBBs were studied. It was demonstrated that the final packing pattern is sensitively dependent on the dimension of SBBs. In addition, we were able to identify a new plywood-like network from ligand 2H(2) exhibiting an unprecedented six-way chiral helical packing motif, which extends the list of invariant rod packings.

Exploration of novel 2-alkylimino-1,3-thiazolines: T-type calcium channel inhibitory activity.

We have developed combinatorial libraries of new 2-alkylimino-1,3-thiazolines with four diversity points, consisting of more than 500 compounds, in a parallel synthetic fashion. The synthetic strategy was based on the construction of a large library aimed at the discovery of new compounds with T-type calcium channel inhibitory activity through structure modifications of hit compound 2. The syntheses of the compounds of Chemset A with four diversity points were accomplished by the condensation of thioureas 5 with alpha-haloketones 6{1-66} having two diversity points each. A library of phthalimidyl 1,3-thiazolines 24 was synthesized to provide Chemset B, which allowed the introduction of other diversity points through the nucleophilic character of the amino nitrogen. A sublibrary, Chemset C, was constructed from the libraries of Chemset A and Chemset B by functionalization of the C-4 position of the 1,3-thiazoline ring. The products containing ester or acid groups at the C-4 position of the 1,3-thiazoline ring were used in amide synthesis to give a new sublibrary within Chemset C. Deprotection of the phthalimidyl moiety of 24 followed by the reaction with benzoyl chloride gave the corresponding sublibrary in Chemset C. Another sublibrary which includes secondary amino derivatives was obtained by reduction of the amide moiety or reductive amination of 23 with phenyl aldehyde. The selected compounds from the generated libraries were evaluated with respect to inhibition of T-type calcium channels, where some of them have exhibited promising activity.

Asymmetric Pauson-Khand-type reaction mediated by Rh(I) catalyst at ambient temperature.

An efficient asymmetric PKR mediated by Rh(I) catalyst at ambient temperature was developed. The reaction utilizing a Rh(I) catalyst bearing a (R)-3,5-diMeC4H4-BINAP ligand at 18-20 degrees C under a reduced partial pressure of CO (0.1 atm) provided PKR products in high chemical yield as well as high enantioselectivity.

Linkage of N3 dye to N3 dye on nanocrystalline TiO2 through trans-1,2-bis(4-pyridyl)ethylene for enhancement of photocurrent of dye-sensitized solar cells.

Linking of N3 dye to another TiO2-attached N3 dye rendered an enhanced short-circuit photocurrent and thereby higher efficiency for the dye-sensitized solar cell with the pertinent TiO2 film electrode.

Synthesis of chiral self-assembling rhombs and their characterization in solution, in the gas phase, and at the liquid-solid interface.

Chiral, enantiopure metallo-supramolecular rhombs self-assemble in solution through coordination of bis-pyridyl-substituted ligands with (en)M(NO3)2 (en = ethylenediamine, M = Pd(II), Pt(II)). Characterization by NMR and CD spectroscopy in solution and by ESI-FT-ICR mass spectrometry in the gas phase suggests that an equilibrium exists in water/methanol of a major 2:2 complex and a minor 3:3 complex of ligands and metal corners. In the gas phase, doubly charged 2:2 complexes fragment into two identical singly charged halves followed by metal-mediated C-H and C-C bond activation reactions within the ethylenediamine ligands. Electrochemical scanning tunneling microscopy (EC-STM) provides in situ imaging of the complexes even with submolecular resolution. Flat-lying rhombs are deposited under potential control from an aqueous electrolyte on a Cu(100) electrode surface precovered by a tetragonal pattern of chloride anions from the supporting electrolyte. Chirality induces the formation of only one domain orientation. Density functional calculations help to interpret the STM images.

Desymmetrization of meso-dienyne by asymmetric Pauson-Khand type reaction catalysts.

Desymmetrization of the meso dienynes, such as propargyl 1-vinylallyl N-tosylamides (1a-c) and propargyl 1-vinylallyl ethers (1d-e), by asymmetric Pauson-Khand type reaction catalysts was studied. The corresponding vinyl substituted bicyclic pentenones (2 and 3) were obtained with high diastereoselectivity and enantioselectivity.