Showing papers on "Bicyclic molecule published in 2012"
TL;DR: This work reports the first total synthesis of aplyviolene, and undesirable aspects of this first-generation synthesis are the lengthy preparation of the cis-perhydroazulene unit and the need to remove the extraneous ketone carbonyl group from the product of the fragment-coupling step.
Abstract: Aplyviolene (1) and macfarlandin E (2, Figure 1A) are representative of the more complex members of the rearranged spongian diterpene class of natural products.[1,2] These diterpenes are structurally defined by attached cis-perhydroazulene and 6-acetoxy-2,7-dioxabicyclo[3.2.1]octan-3-one fragments. The substantial challenge in assembling these structures centers on the construction of the sensitive bicyclic lactone subunit and the formation of the C8–C14 σ-bond joining the two ring systems, a challenge augmented by the quaternary nature of C8.[3] We previously reported preparation of the lactone subunits of 1 and 2 by the synthesis of truncated congeners 3 and 4 (Figure 1A),[4] as well as the first total synthesis of aplyviolene (outlined in Figure 1B).[5] In this latter effort, the key C8–C14 σ-bond was formed by Michael addition of tertiary enolate 5 to enone 6.[6] Subsequent elaboration of product 7 provided intermediate 8, which was converted to (−)-aplyviolene along the lines of our earlier synthesis of 3. Undesirable aspects of this first-generation synthesis are the lengthy preparation of the cis-perhydroazulene unit and the need to remove the extraneous ketone carbonyl group from the product of the fragment-coupling step.
219 citations
TL;DR: In this article, the major progress in the field of enantioselective one-, two-, and multi-component domino reactions promoted by chiral metal catalysts, covering the literature since the beginning of 2012, is discussed.
Abstract: This review updates the major progress in the field of enantioselective one-, two-, and multi-component domino reactions promoted by chiral metal catalysts, covering the literature since the beginning of 2012. It illustrates how enantioselective metal-catalyzed processes have emerged as outstanding tools for the development of a wide variety of fascinating one-pot asymmetric domino reactions, allowing complex and diverse structures to be easily generated from simple materials in a single step. During the last 4 years, a myriad of already existing as well as completely novel and powerful asymmetric domino processes have been developed on the basis of asymmetric metal catalysis, taking economical advantages, such as avoiding costly protecting groups and time-consuming purification procedures after each step. Abbreviations: acac: acetylacetonate; Ad: 1-adamantyl; Ar: aryl; BArF: tetrakis[3,5-bis(trifluoromethyl)phenyl]borate; BBN: 9-borabicyclo[3.3.1]nonane; BINAP: 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl; BINAP(O): 2-diphenylphosphino-2′-diphenylphosphinyl-1,1′-binaphthalene; BINOL: 1,1′-bi-2-naphthol; BIPHEP: 2,2′-bis(diphenylphosphino)-1,1′-biphenyl; Bipy: bipyridine; Bn: benzyl; Boc: tert-butoxycarbonyl; bod: bicyclo[2.2.2]octane-2,5-diene; Box: bisoxazoline; bpe: 1,2-bis(2-pyridyl)ethane; Bs: p-bromobenzenesulfonyl (brosyl); Bz: benzoyl; Cat: catalyst; Cbz: benzyloxycarbonyl; CMOF: chiral mixed metal-organic framework; cod: cyclooctadiene; coe: cyclooctene; Cp: cyclopentadienyl; CPME: cyclopentyl methyl ether; Cy: cyclohexyl; DABCO: 1,4-diazabicyclo[2.2.2]octane; dba: (E,E)-dibenzylideneacetone; DBDMH: 1,3-dibromo-5,5-dimethylhydantoin; DCE: dichloroethane; de: diastereomeric excess; Dec: decyl; DET: diethyl tartrate; DIPEA: diisopropylethylamine; DME: 1,2-dimethoxyethane; DMF: N,N-dimethylformamide; DTBM: di-tert-butylmethoxy; ee: enantiomeric excess; EWG: electron-withdrawing group; Fesulphos: 1-phosphino-2-sulfenylferrocene; Hept: heptyl; Hex: hexyl; HFIPA: hexafluoroisopropyl alcohol; HMPA: hexamethylphosphoramide; JohnPhos: (2-biphenyl)di-tert-butylphosphine; Josiphos: 1-[2-(diphenylphosphino)ferrocenyl]ethyldicyclohexylphosphine ethanol adduct; L: ligand; Mandyphos: 1,1′-bis[(dimethylamino)benzyl]-2,2′-bis(diphenylphosphino)ferrocene; Me-DuPhos: 1,2-bis(2,5-dimethylphospholano)benzene; MOM: methoxymethyl; Ms: mesyl; MS: molecular sieves; MTBE: methyl tert-butyl ether; Naph: naphthyl; NBS: N-bromosuccinimide; Ns: nosyl (4-nitrobenzenesulfonyl); Oct: octyl; Pent: pentyl; Phos: phosphinyl; Phox: phosphinooxazoline; Pin: pinacolato; PG: protecting group; Phth: phthalimido; Piv: pivaloyl; PMB: p-methoxybenzyl; PMP: 1,2,2,6,6-pentamethylpiperidine; PTAD: 4-phenyl-1,2,4-triazoline-3,5-dione; Py: pyridyl; Pybox: 2,6-bis(2-oxazolyl)pyridine; QUINOX: (quinolin-2-yl)-oxazoline; rs: regioselectivity ratio; r.t.: room temperature; SDS: sodium dodecyl sulfate; Segphos: 5,5′-bis(diphenylphosphino)-4,4′-bi-1,3-benzodioxole; SES: β-trimethylsilylethanesulfonyl; Taniaphos: [2-diphenylphosphinoferrocenyl](N,N-dimethylamino)(2-diphenylphosphinophenyl)methane; TBS: tert-butyldimethylsilyl; TEA: trimethylamine; Tf: trifluoromethanesulfonyl; TFA: trifluoroacetic acid; THF: tetrahydrofuran; TIPS: triisopropylsilyl; TMG: 1,1,3,3-tetramethylguanidine; TMS: trimethylsilyl; Tol: tolyl; Ts: 4-toluenesulfonyl (tosyl); VANOL: 3,3′-diphenyl-2,2′-bi-1-naphthol; Walphos: 1-{2-[2′-(diphenylphosphino)phenyl]ferrocenyl}ethyldi[3,5-bis(trifluoromethyl)phenyl]phosphine; Xyl: 3,5-dimethylphenyl.
175 citations
TL;DR: From a large combinatorial library of chemically constrained bicyclic peptides, a selective and potent inhibitor of human urokinase-type plasminogen activator is isolated and crystallized, revealing an extended structure of the peptide with both peptide loops engaging the target to form a large interaction surface.
Abstract: From a large combinatorial library of chemically constrained bicyclic peptides we isolated a selective and potent (K(i) = 53 nM) inhibitor of human urokinase-type plasminogen activator (uPA) and crystallized the complex. This revealed an extended structure of the peptide with both peptide loops engaging the target to form a large interaction surface of 701 A(2) with multiple hydrogen bonds and complementary charge interactions, explaining the high affinity and specificity of the inhibitor. The interface resembles that between two proteins and suggests that these constrained peptides have the potential to act as small protein mimics.
149 citations
TL;DR: The key structural feature in Boceprevir, Merck's new drug treatment for hepatitis C, is the bicyclic [3.1.0]proline moiety "P2", which is an enzymatic oxidative desymmetrization of the prochiral amine substrate.
Abstract: The key structural feature in Boceprevir, Merck’s new drug treatment for hepatitis C, is the bicyclic [3.1.0]proline moiety “P2”. During the discovery and development stages, the P2 fragment was produced by a classical resolution approach. As the drug candidate advanced through clinical trials and approached regulatory approval and commercialization, Codexis and Schering–Plough (now Merck) jointly developed a chemoenzymatic asymmetric synthesis of P2 where the net reaction was an oxidative Strecker reaction. The key part of this reaction sequence is an enzymatic oxidative desymmetrization of the prochiral amine substrate.
136 citations
TL;DR: In this article, the acid-promoted intramolecular cycloadditions of activated cyclo-propanes were systematically described, and the potential of this strategy has been demonstrated by the synthesis of natural products.
Abstract: In this account we have systematically described the acid-promoted intramolecular cycloadditions of activated cyclopropanes, which were conceptually classified into intramolecular cross-cycloadditions (IMCC) and intramolecular parallel-cycloadditions. The IMCC provided a general and efficient strategy for construction of structurally complex and diverse bridged bicyclic skeletons. The potential of this strategy has been demonstrated by the synthesis of natural products. 1 Introduction 2 [3+2]IMCC of Cyclopropane 1,1-Diester with C=O 3 [3+2]IMCC of Cyclopropane 1,1-Diester with C=N 4 [3+2]IMCC of Cyclopropane 1,1-Diester with C=C 5 [3+3]IMCC of Cyclopropane 1,1-Diester with Nitrones 6 [3+2]IMCC of Mono-donor/Mono-acceptor Cyclopropane with C=O 7 Lewis Acid Regulated Domino Cycloisomerization/[4+2]IMCC or [3+2]IMCC of Alkynylcyclopropane Ketone with C=O and C=N 8 Conclusions and Outlook
117 citations
TL;DR: Analysis of the alkyne-insertion transition states revealed that the serious steric repulsion between the substituents in theAlkyne moiety of the substrates and the rigid H(8)-BINAP backbone is responsible for not generating the disfavored [3 + 2] cycloadducts.
Abstract: A highly enantioselective Rh(I)-catalyzed intramolecular [3 + 2] cycloaddition of 1-yne-VCPs to bicyclo[3.3.0] compounds with an all-carbon chiral quaternary stereocenter at the bridgehead carbon was developed. DFT calculations of the energy surface of the catalytic cycle (complexation, cyclopropane cleavage, alkyne insertion, and reductive elimination) of the asymmetric [3 + 2] cycloaddition reaction indicated that the rate- and stereo-determining step is the alkyne-insertion step. Analysis of the alkyne-insertion transition states revealed that the serious steric repulsion between the substituents in the alkyne moiety of the substrates and the rigid H(8)-BINAP backbone is responsible for not generating the disfavored [3 + 2] cycloadducts.
117 citations
TL;DR: A highly enantioselective [3 + 2] annulation of MBH carbonates and maleimides catalyzed by chiral phosphines has been developed and functionalized bicyclic imides were prepared in excellent yields, and with high diastereoselectivities and nearly perfect enantiosity.
98 citations
TL;DR: The cyclic α-imino gold carbene intermediate B is most likely generated in situ via regioselective nitrene transfer from an azido group to a tethered terminal alkyne in the presence of a gold catalyst and at ambient temperature.
95 citations
TL;DR: D-Threonine-L-tert-leucine-derived bifunctional phosphine, Cat.
92 citations
TL;DR: High diastereodivergence was achieved through unusual hydrogen-bonding interactions of multifunctional primary-amine catalytic systems, and the Michael addition intermediates were successfully isolated in some cases, indicating that the above reaction via dienamine catalysis may proceed by a stepwise Michael-Michael cascade rather than by a concerted Diels-Alder cycloaddition pathway.
Abstract: Switchable reaction patterns of β-substituted cyclic enones via amine-based dienamine activation are reported. While γ-regioselective vinylogous Michael addition was observed with alkylidenemalononitriles, a completely different [4 + 2] cycloaddition was obtained with allylidene- or alkynylidenemalononitrile substrates, affording densely substituted bicyclo[2.2.2]octanes or analogous architectures with moderate to excellent diastereo- and enantioselectivity by the catalysis of primary amines from natural quinidine or quinine. Importantly, high diastereodivergence was achieved through unusual hydrogen-bonding interactions of multifunctional primary-amine catalytic systems. Endo cycloadducts were efficiently produced using a combination of 9-amino-9-deoxyepiquinidine and salicylic acid, while exo variants were obtained using 6′-hydroxy-9-amino-9-deoxyepiquinidine. Moreover, we successfully isolated the Michael addition intermediates in some cases, indicating that the above [4 + 2] reaction via dienamine cat...
91 citations
TL;DR: The development of linkers for the generation of genetically encoded bicyclic peptides and testing whether the peptides cyclised by them have significant variations in their backbone conformations suggest that application of different cyclisation linkers in a combinatorial fashion could be an attractive means to generate topologically diverse macrocycle libraries.
Abstract: Combinatorial libraries of structurally diverse peptide macrocycles offer a rich source for the development of high-affinity ligands to targets of interest. In this work we have developed linkers for the generation of genetically encoded bicyclic peptides and tested whether the peptides cyclised by them have significant variations in their backbone conformations. Two new cyclisation reagents, each containing three thiol-reactive groups, efficiently and selectively cyclised linear peptides containing three cysteine moieties. When the mesitylene linker of the bicyclic peptide PK15, a potent inhibitor of plasma kallikrein (Ki=2 nM), was replaced by the new linkers, its inhibitory activity dropped by a factor of more than 1000, suggesting that the linkers impose different conformations on the peptide. Indeed, structural analysis by solution-state NMR revealed different NOE constraints in the three bicyclic peptides, indicating that these relatively small linkers at the centres of bicyclic peptide structures significantly influence the conformations of the peptides. These results demonstrate the prominent structural role of linkers in peptide macrocycles and suggest that application of different cyclisation linkers in a combinatorial fashion could be an attractive means to generate topologically diverse macrocycle libraries.
TL;DR: It is presented that 1,n-enynes and diynes containing propargylic esters are highly reactive and useful starting materials for the cycloisomerization catalyzed by a transition metal catalyst.
TL;DR: DFT calculations at the M06-2X/6-311++G(d,p) level of theory revealed that CO(2) fixation by 1 and formation of the adduct 3 is strongly exothermic and proceeds with a low energy barrier of approximately 7.3 kcal mol(-1) via an intermediate van der Waals complex.
Abstract: The bifunctional frustrated Lewis pair 1-[bis(pentafluorophenyl)boryl]-3,5-di-tert-butyl-1H-pyrazole (1) was employed for small molecule fixation by reaction with carbon dioxide, paraformaldehyde, tert-butyl isocyanate, tert-butyl isothiocyanate, methyl isothiocyanate and benzonitrile, affording the adducts 3–8 as zwitterionic, bicyclic boraheterocycles. Treatment of 1 with tert-butyl isocyanide gave the isocyanide–borane complex 9, whereas the zwitterionic alkynylborate 10 was formed by C–H bond activation of phenylacetylene. The molecular structures of all products 3–10 were established by X-ray diffraction analyses. DFT calculations at the M06-2X/6-311++G(d,p) level of theory revealed that CO2 fixation by 1 and formation of the adduct 3 is strongly exothermic and proceeds with a low energy barrier of approximately 7.3 kcal mol−1via an intermediate van der Waals complex.
TL;DR: The first stereoselective annulation reaction between α-cyano-1,4-diketones and ynals, mediated by catalytic amounts of a triazolium salt precatalyst and cocatalytic amount of a weak carboxylate base, is disclosed.
TL;DR: A distinct approach for the total synthesis of these natural products empowered by a unique, reagent-driven pinacol rearrangement and substrate-specific oxidation chemistry is described, which has potential for scaleability as well as biogenetic implications.
Abstract: Although the stilbene resveratrol is simple in terms of its size and functional group array, it possesses high chemical reactivity, a property that enables its conversion into hundreds of architecturelly diverse bioactive oligomeric natural products.[1–3] Among recent dimeric isolates, hopeanol and hopeahainol A (1 and 2, Scheme 1) are two of the most intriguing given their constrained, partially dearomatized bicyclic cores and potent activity in antitumor and acetyl-cholinesterase inhibition assays.[4] Indeed, these molecules have already been the subject of synthetic interest, with reports by Nicolaou, Chen, and co-workers describing racemic and enantioselective syntheses of 1 and 2 in 15 linear steps.[5] Their route featured several cascade-based bond constructions[6] and the discovery that hopeahainol A (2) could be converted into hopeanol (1) upon treatment with base, an idea counter to the original biosynthetic proposal.[4b] In this communication, we describe a distinct approach for the total synthesis of these natural products empowered by a unique, reagent-driven pinacol rearrangement and substrate-specific oxidation chemistry. Significantly, it has potential for scaleability as well as biogenetic implications.
TL;DR: There are many readily available methods for the preparation of enantiopure carbonyl compounds containing aand bchiral centers, but the selective functionalization of the g position has been met with more difficulties and less progress.
Abstract: Various β,γ-unsaturated thioacids are subjected to the title reaction in the presence of the bicyclic guanidine catalyst BCG
Patent•
11 Dec 2012
TL;DR: A compound of formula (I) is defined in this article, where I is a salt-forming cation and Y is OR 1 or NR 2R3, and R1,R2, R3 and M are as defined herein.
Abstract: A compound of formula (I), wherein: M is hydrogen or a pharmaceutically acceptable salt-forming cation; Y is OR1 or NR2R3, and R1,R2, R3 and M are as defined herein. Also, methods of treating bacterial infection, pharmaceutical compositions, molecular complexes and processes for preparing compounds.
TL;DR: 6d is a promising RAF/VEGFR2 inhibitor showing potent anticancer activity and maximized its oral absorption in rats and showed significant suppression of ERK1/2 phosphorylation in an A375 melanoma xenograft model in rats by single administration.
Abstract: To develop RAF/VEGFR2 inhibitors that bind to the inactive DFG-out conformation, we conducted structure-based drug design using the X-ray cocrystal structures of BRAF, starting from an imidazo[1,2-b]pyridazine derivative. We designed various [5,6]-fused bicyclic scaffolds (ring A, 1-6) possessing an anilide group that forms two hydrogen bond interactions with Cys532. Stabilizing the planarity of this anilide and the nitrogen atom on the six-membered ring of the scaffold was critical for enhancing BRAF inhibition. The selected [1,3]thiazolo[5,4-b]pyridine derivative 6d showed potent inhibitory activity in both BRAF and VEGFR2. Solid dispersion formulation of 6d (6d-SD) maximized its oral absorption in rats and showed significant suppression of ERK1/2 phosphorylation in an A375 melanoma xenograft model in rats by single administration. Tumor regression (T/C = -7.0%) in twice-daily repetitive studies at a dose of 50 mg/kg in rats confirmed that 6d is a promising RAF/VEGFR2 inhibitor showing potent anticancer activity.
TL;DR: The Parham cyclization-intermolecular α-amidoalkylation sequence results in the facile enantioselective synthesis of 12b-substituted isoindoloisoquinolines (ee up to 95%) using BINOL-derived Brønsted acids.
Abstract: The Parham cyclization–intermolecular α-amidoalkylation sequence results in the facile enantioselective synthesis of 12b-substituted isoindoloisoquinolines (ee up to 95%) using BINOL-derived Bronsted acids. α-Amidoalkylation of indole occurs through the formation of a chiral conjugate base/bicyclic quaternary N-acyliminium ion pair.
TL;DR: The defacto barrierless formation of the 1,4-dihydronaphthalene molecule involving a single collision between a phenyl radical and 1,3-butadiene represents an important step in the formation of polycyclic aromatic hydrocarbons (PAHs) and their partially hydrogenated counterparts in combustion and interstellar chemistry.
Abstract: The crossed beam reactions of the phenyl radical (C6H5, X2A1) with 1,3-butadiene (C4H6, X1Ag) and D6-1,3-butadiene (C4D6, X1Ag) as well as of the D5-phenyl radical (C6D5, X2A1) with 2,3-D2-1,3-butadiene and 1,1,4,4-D4-1,3-butadiene were carried out under single collision conditions at collision energies of about 55 kJ mol–1. Experimentally, the bicyclic 1,4-dihydronaphthalene molecule was identified as a major product of this reaction (58 ± 15%) with the 1-phenyl–1,3-butadiene contributing 34 ± 10%. The reaction is initiated by a barrierless addition of the phenyl radical to the terminal carbon atom of the 1,3-butadiene (C1/C4) to form a bound intermediate; the latter underwent hydrogen elimination from the terminal CH2 group of the 1,3-butadiene molecule leading to 1-phenyl-trans-1,3-butadiene through a submerged barrier. The dominant product, 1,4-dihydronaphthalene, is formed via an isomerization of the adduct by ring closure and emission of the hydrogen atom from the phenyl moiety at the bridging carbo...
TL;DR: This is the first incorporation of N-benzylic α-branched succinimides into 3-disubstituted oxindole derivatives with a quaternary carbon chiral center at the 3-position in excellent yields and enantio- and diastereoselectivities.
TL;DR: The isomerization of alkynoates is smoothly catalyzed by a bicyclic guanidine-diamine catalyst to afford the trisubstituted allenoates (II) in high enantioselectivities (up to 94% e.g. as mentioned in this paper ).
Abstract: The isomerization of alkynoates is smoothly catalyzed by a bicyclic guanidine—diamine catalyst to afford the trisubstituted allenoates (II) in high enantioselectivities (up to 94% e.e.).
TL;DR: The design and the synthesis of several chemical subclasses of imidazole containing γ-secretase modulators (GSMs) is described, resulting in the identification of benzimidazoles 44a as a GSM with low nanomolar potency in vitro.
Abstract: The design and the synthesis of several chemical subclasses of imidazole containing γ-secretase modulators (GSMs) is described. Conformational restriction of pyridone 4 into bicyclic pyridone isosteres has led to compounds with high in vitro and in vivo potency. This has resulted in the identification of benzimidazole 44a as a GSM with low nanomolar potency in vitro. In mouse, rat, and dog, this compound displayed the typical γ-secretase modulatory profile by lowering Aβ42 and Aβ40 levels combined with an especially pronounced increase in Aβ38 and Aβ37 levels while leaving the total levels of amyloid peptides unchanged.
TL;DR: A new gold-catalyzed hydride transfer from an unactivated C(sp) H bond to an alkyne, and the subsequent selective cyclizations are disclosed.
Abstract: The 1,5-hydride transfer of alkynylcyclopropanes bearing a spiran core is investigated under different conditions: pentalene derivatives or bicyclic systems are formed.
TL;DR: Changing the Rh(I) catalyst effected the Cγ-H bond activation of the common 9-cyclopentyl-8-rhodabicyclo and produced the novel spiro[2.4.4]heptane skeleton in a site-selective manner.
Abstract: The unprecedented Csp3–Csp3 bond cleavage of unactivated cyclopentane has been achieved. RhI-catalyzed cycloaddition of allenylcyclopentane-alkynes produced in situ the 9-cyclopentyl-8-rhodabicyclo[4.3.0]nona-1,6-diene intermediates, which subsequently underwent [7+2] cycloaddition via β-C elimination, affording bicyclo[7.4.0]tridecatriene derivatives in good yields. Changing the RhI catalyst effected the Cγ–H bond activation of the common 9-cyclopentyl-8-rhodabicyclo[4.3.0]nona-1,6-diene intermediate to produce the novel spiro[2.4]heptane skeleton in a site-selective manner.
TL;DR: This novel approach, which uses a singlet-oxygen-mediated reaction cascade, is particularly powerful because the one-pot reaction begins from furan substrates which can be variously functionalized (A, Scheme 1) with ease, thus allowing direct access to highly substituted scaffolds of type B (frequently with excellent stereoselectivity).
Abstract: The route to the title bicyclic lactams starting from mono, di- or trisubstituted furans involves the oxidation of the furans with singlet oxygen in methanol followed by in situ reduction of the resultant hydroperoxide, the addition of an 1,2-aminoalcohol, and then a catalytic amount of TFA.
TL;DR: The first total synthesis of mycocyclosin, a diketopiperazine natural product isolated from M. tuberculosis, is described, with construction of the highly strained bicyclic framework accomplished through an intramolecular Miyaura-Suzuki cross-coupling to generate the biaryl linkage.
TL;DR: Trans-2,8-Dioxabicyclodecanes were prepared in high yield with the creation of up to three stereocenters in a single pot by the acid-mediated reaction of γ,δ-unsaturated alcohols with aldehydes to enable the stereoselective introduction of substituents at the C3, C4, C7, and C9 positions of the bicyclic framework.
Abstract: trans-2,8-Dioxabicyclodecanes were prepared in high yield with the creation of up to three stereocenters in a single pot by the acid-mediated reaction of γ,δ-unsaturated alcohols with aldehydes (see scheme, Bn=benzyl). This versatile reaction enables the stereoselective introduction of substituents at the C3, C4, C7, and C9 positions of the bicyclic framework.
TL;DR: In this paper, the UO2(H2L2H2O) complex with uranyl ions with two aromatic and one alicyclic polycarboxylic acids has been crystallographically characterized.
Abstract: The complexes formed by uranyl ions with two aromatic and one alicyclic polycarboxylic acids have been crystallographically characterized. Three complexes were obtained under hydrothermal conditions with 2,2′-bipyridine-3,3′-dicarboxylic acid (H2L1), [UO2(L1)(H2O)]·3H2O (1), [UO2(L1)(DMF)]·0.5H2O (2) and [UO2(L1)(H2L1)]·H2O (3), all of which contain one-dimensional polymeric chains with the ligand being both chelating through one oxygen atom from each carboxylate group and bridging through the remaining donor atoms, the nitrogen atoms being uncoordinated. The last coordination site is occupied by either a water (1), a dimethylformamide (2), or a monodentate, zwitterionic H2L1 molecule (3). Biphenyl-3,3′,4,4′-tetracarboxylic acid (H4L2) gives the complex [UO2(H2L2)(H2O)2]·2H2O (4) under hydrothermal conditions, which is also a one-dimensional coordination polymer with uranyl chelation by only one carboxylate group from each aromatic ring. A two-dimensional assembly is finally obtained in the complex [(UO2)3(HL3)2(H2O)6]·10H2O (5), crystallized at room temperature, in which H4L3 is the all-exo isomer of bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid. The three carboxylate groups in 5 are chelating, the ligand being thus a T-shaped node, and the layers are built from a tessellation of oblong twelve-membered rings arranged in herringbone fashion.
TL;DR: A bicyclic imidazolium ionic liquid, [b-4C-im][Br], was found to be highly effective not only for promoting PCR of GC-rich DNA by minimizing non-specific amplification, but also for facilitating PCR of normal-GC DNA under mild conditions.