Showing papers in "Helvetica Chimica Acta in 2016"

Identifying Sn Site Heterogeneities Prevalent Among Sn-Beta Zeolites

Abstract: In recent years, various protocols on preparing Lewis acidic Sn-β zeolite hydrothermally and post-synthetically have been reported. However, very little is known about the effects of different synthesis protocols on the SnIV speciation in the final material. Even the effects of individual synthesis parameters within a certain preparation method have not been studied systematically. Here, we demonstrate that hydrothermally synthesized Sn-β zeolites prepared via very similar recipes show significantly different 119Sn NMR spectra, suggesting different Sn site speciation. Among post-synthetically prepared Sn-β zeolites, less variation in the resulting 119Sn NMR spectra have been observed, indicating a more reproducible synthesis procedure compared to hydrothermal synthesis in fluoride media. This work highlights the importance of 119Sn NMR measurements to elucidate the precise local geometry of the Sn heteroatoms in Sn-β, and the need to quantify the number of reactive Sn sites on each sample that participate in a given catalytic reaction, in order to accurately compare materials prepared by different routes. This article is protected by copyright. All rights reserved.

Trifluoromethylpyridine‐Substituted N‐Heterocyclic Carbenes Related to Natural Products: Synthesis, Structure, and Potential Antitumor Activity of some Corresponding Gold(I), Rhodium(I), and Iridium(I) Complexes

Abstract: This work presents the synthesis, characterization, and application of several new metal(I) complexes with trifluoromethylpyridine-containing N-heterocyclic carbene (NHC) ligands. The metal of choice was gold(I) for compounds 7 – 10, rhodium(I) for 11 – 12, and iridium(I) for 13 – 14, respectively. The trifluoromethylpyridine moiety was incorporated, along with other biologically active moieties, with the intention of modifying the lipophilicity of the complexes, so that the transport of the active units (M–NHC) through the cell wall barrier is facilitated. The biological activity of the complexes was investigated. In vitro assessment of antitumor activity in a panel of 12 human tumor cell lines by a monolayer assay revealed good potency (mean IC50 12.6 μm) and tumor selectivity for one compound. The solid-state structures of two solvates of compound 7, one with MeOH and one with THF, were determined by X-ray diffraction analysis.

Chemical Constituents from the Fermented Mycelia of the Medicinal Fungus Xylaria nigripes

Abstract: Nineteen compounds mainly including pyrrole-containing alkaloids and phytosterols were isolated from the EtOH extract of the fermented mycelia of Xylaria nigripes, a precious medicinal fungus known as Wuling Shen in Chinese. On the basis of spectroscopic methods, the structures of the new naturally occurring compounds were determined to be (4S)-3,4-dihydro-4-(4-hydroxybenzyl)-3-oxo-1H-pyrrolo[2,1-c][1,4]oxazine-6-carbaldehyde (1), methyl (2S)-2-[2-formyl-5-(hydroxymethyl)-1H-pyrrol-1-yl]-3-(4-hydroxyphenyl)propanoate (2), and 3-{4-[(2R)-(2,3-dihydroxy-3-methylbutoxy]phenyl}-7-hydroxy-4H-chromen-4-one (3), respectively. The absolute configurations of 1 and 2 were deduced by the observed Cotton effects in their circular dichroism (CD) spectra, whereas that of the 1,2-diol moiety in 3 was determined using the Snatzke's method. Their biological activities such as neuroprotective, anti-neuroinflammatory, and cytotoxic properties were also reported.

Photoprotected Peptide α‐Ketoacids and Hydroxylamines for Iterative and One‐Pot KAHA Ligations: Synthesis of NEDD8

Abstract: The convergent synthesis of proteins by multiple ligations requires segments protected at the N- and/or C-terminus with masking groups that are orthogonal to the acid and base labile protecting groups used in Fmoc-SPPS. They must be stable to solid phase peptide synthesis, HPLC purification, and ligation conditions and easily removed in the presence of unprotected side chains. In this report, we document photolabile protecting groups for both α-ketoacids and hydroxylamines, the key functional groups employed in the α-ketoacid–hydroxylamine (KAHA) ligation. The novel photoprotected α-ketoacid is easily installed onto numerous different C-terminal peptide α-ketoacids and removed by UV light under aqueous conditions. These advances were applied to the one-pot synthesis of NEDD8, an important modifier protein, by three different convergent routes. These new protecting groups provide greater flexibility in the order of fragment assembly and reduce the number of reaction and purification steps needed for protein synthesis with the KAHA ligation. This article is protected by copyright. All rights reserved.

Stachartins A – E, Phenylspirodrimanes from the Tin Mine Tailings‐Associated Fungus Stachybotrys chartarum

Abstract: Eight phenylspirodrimane-type analogues, including five new compounds, named stachartins A – E (1, 3, 6 – 8), were isolated from cultures of the tin mine tailings-associated fungus Stachybotrys chartarum. Their structures were elucidated by spectroscopic methods including extensive 2D-NMR techniques.

Anti‐inflammatory Activity of Two New Indole Alkaloids from the Stems of Nauclea officinalis

Abstract: Two new indole alkaloid derivatives (1, 2), together with six known indole alkaloids (3 – 8) were isolated from the 70% EtOH/H2O extract of the stem of Nauclea officinalis. Their structures were determined on the basis of extensive analyses of spectroscopic data (IR, MS, 1D- and 2D-NMR). All the isolates were evaluated for their anti-inflammatory activities on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7, and all the compounds showed significant inhibitory activities with the IC50 values of 0.82, 6.45, 9.75, 1.34, 3.40, 2.69, 1.58, and 1.96 μm, compared to the positive drug control group aminoguanidine with an IC50 value of 1.80 μm, especially compound 1 had the most significant activity.

A Structure–Activity Study of Nickel NNN Pincer Complexes for Alkyl‐Alkyl Kumada and Suzuki–Miyaura Coupling Reactions

Abstract: A new series of nickel NNN pincer complexes were synthesized and characterized. The main difference among these complexes is the substituents on the side arm amino group(s). No major structural difference was found except for the C-N-C angle of the various substituents and the “pseudo bite angle” of the complexes. Four new complexes were efficient for the alkyl-alkyl Kumada reaction of primary alkyl halides and among them, one complex was also efficient with secondary alkyl halides. The influence of the substituents on the catalytic performance of the nickel complexes in alkyl-alkyl Kumada and Suzuki-Miyaura cross-coupling reactions was systematically investigated. No correlation was found between the catalytic activity and the key structural parameters (C-N-C angle and “pseudo bite angle”), redox properties or Lewis acidity of the complexes. This article is protected by copyright. All rights reserved.

Tricoordinate Organochromium(III) Complexes Supported by a Bulky Silylamido Ligand Produce Ultra-High-Molecular Weight Polyethylene in the Absence of Activators

Abstract: Low-coordinate organoCr(III) complexes supported by the silylamido ligand –N(SiMe3)DIPP (DIPP = 2,6-diisopropylphenyl) are ethylene polymerization catalyst precursors without the need of additional cocatalyst. The reaction of CrCl3(THF)3 with 3 or 2 equiv. of LiN(SiMe3)DIPP yields either a four-membered cyclometalated Cr complex or Cr[N(SiMe3)DIPP]2Cl, respectively, with no trace of Cr[N(SiMe3)DIPP]3. Addition of 1 equiv. of LiN(SiMe3)DIPP to Cr[N(SiMe3)DIPP]2Cl also leads to the four-membered metallacycle, which upon heating transforms to a new six-membered Cr metallacycle, likely via a σ-bond metathesis step. Cr[N(SiMe3)DIPP]2Cl can be readily converted to bis(amido)Cr(III) vinyl and alkyl complexes Cr[N(SiMe3)DIPP]2R (R = vinyl, Bn, and Me). All of these structurally characterized low-coordinate Cr(III) complexes with a Cr–C bond initiate the polymerization of ethylene in the absence of activators or cocatalysts, producing ultra-high-molecular weight polyethylene.

Synthesis and Characterization of Heterobimetallic Tantalum–Rhodium and Tantalum–Iridium Complexes Connected by a Tantalacyclopentadiene Fragment

Abstract: We report the synthesis of heterobimetallic Ta–Rh and Ta–Ir complexes bridged by a 2,5-di-tert-butyltantallacyclopentadiene fragment. A mononuclear 2,5-di-tert-butyltantallacyclopentadiene complex 2 was prepared by the reaction of (η2-Me3SiC≡CSiMe3)TaCl3(dme) (1) with excess amounts of 3,3-dimethyl-1-propyne in the presence of AlCl3. The tantallacyclopentadiene moiety of complex 2 served as a η4-diene undium centers: treatment of 2 with [M(μ-Cl)(cod)]2 (M = Rh and Ir: cod = 1,5-cyclooctadiene) in tolueit for coordinating to the rhodium and irine gave TaRh(μ-C4H2tBu2)Cl4(cod) (3) and [TaIr(μ-C4H2tBu2)Cl4]2 (5), respectively. X-ray diffraction study of 3 revealed a dative bond from an electron-rich rhodium toward an electron-deficient tantalum. Upon dissolving 3 in THF, [(thf)TaRh(μ-C4H2tBu2)Cl3]2(μ-Cl)2 (4) was isolated together with free 1,5-cyclooctadiene. When complex 5 was treated with 1,2-bis(diphenylphosphino)ethane (dppe), a monomeric Ta–Ir complex, TaIr(μ-C4H2tBu2)Cl4(dppe) (6), was isolated. Ta—Rh and Ta—Ir heterobimetallic complexes 3 and 6 were reduced by a two-electron process upon reaction with 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (7a: Me4BTDP) or 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine (7b: Me2BTDP) to afford the corresponding complexes TaM(μ-C4H2tBu2)Cl2(L) (8: M = Rh, L = cod, 9: M = Ir, L = dppe), where the metallacycle moiety was assigned to have a tantallacyclopentadiene fragment with a large contribution of a tantallacyclopentatriene canonical form. This article is protected by copyright. All rights reserved.

New Cytotoxic Meroterpenoids from the Plant Endophytic Fungus Pestalotiopsis fici

Abstract: Pestalofones I – K (1–3), three new dimeric meroterpenoids with 2-(7-benzoyl-2,3-dihydrobenzofuran-2-yl)-1-phenylethan-1-one (in 1) and 2-(7-benzoyl-2,3-dihydrobenzofuran-2-yl)-1-(3,8-dioxatricyclo[5.1.0.02,4]oct-4-yl)ethan-1-one (in 2 and 3) skeletons, were isolated from the solid cultures of the plant endophytic fungus Pestalotiopsis fici. The structures of 1–3 were elucidated by NMR experiments. Compound 1 was found to be present as a racemic mixture. The absolute configurations of 2 and 3 were deduced by analogy to the previously isolated metabolites pestalofones G and H (4 and 5) from the same fungus. Biogenetically, compounds 1–3 are derived from the same precursors (co-isolated compounds 9 and 10) as the previously isolated compounds 4–8. Compounds 2 and 3 showed weak cytotoxic activities against four human tumor cell lines T24, HeLa, A549, and MCF-7.

A Convenient 1,3‐Dipolar Cycloaddition Reaction for the Synthesis of Spirooxindoles and Some Other Spirocompounds Containing the 1,3,4‐Oxadiazole Moiety

Abstract: A series of spiro[indoline-3,2′-[1,3,4]oxadiazol]-2-ones were prepared from the reaction of isatin derivatives and hydrazonoyl chlorides through the 1,3-dipolar cycloaddition reaction. This method has some important aspects, such as mild reaction condition, easy purification, and high yield of products. Also, the synthesis of spiro[acenaphthylene-1,2′-[1,3,4]oxadiazol]-2-one and spiro[[1,3,4]oxadiazole-2,9′-phenanthren]-10′-one were studied under the same condition. The structures were confirmed spectroscopically (IR, 1H- and 13C-NMR, and EI-MS) and by elemental analyses. A plausible mechanism for this reaction is proposed.

3D-Printing inside the Glovebox: A Versatile Tool for Inert-Gas Chemistry Combined with Spectroscopy.

Abstract: 3D-Printing with the well-established ‘Fused Deposition Modeling’ technology was used to print totally gas-tight reaction vessels, combined with printed cuvettes, inside the inert-gas atmosphere of a glovebox. During pauses of the print, the reaction flasks out of acrylonitrile butadiene styrene were filled with various reactants. After the basic test reactions to proof the oxygen tightness and investigations of the influence of printing within an inert-gas atmosphere, scope and limitations of the method are presented by syntheses of new compounds with highly reactive reagents, such as trimethylaluminium, and reaction monitoring via UV/VIS, IR, and NMR spectroscopy. The applicable temperature range, the choice of solvents, the reaction times, and the analytical methods have been investigated in detail. A set of reaction flasks is presented, which allow routine inert-gas syntheses and combined spectroscopy without modifications of the glovebox, the 3D-printer, or the spectrometers. Overall, this demonstrates the potential of 3D-printed reaction cuvettes to become a complementary standard method in inert-gas chemistry.

Functionalized Ionic (Poly)Styrenes and their Application as Catalysts in the Cycloaddition of CO2 to Epoxides

Abstract: Valorization of CO2, an abundant C(1) synthon, into platform chemicals is of growing interest. In this context, a key reaction is the cycloaddition of CO2 to epoxides to form carbonates (CCE). A series of organocatalysts for this reaction, based on imidazolium salts modified with a styrene functional group and a second variable functional group, were prepared and characterized. Both the ionic salts and ionic polymers derived from the salts were evaluated in this reaction. In general, the monomers perform slightly better than the polymers; however, the latter are considerably more convenient to use. Of the catalysts studied, the ionic polystyrene imidazolium salt with an ammonium functionality shows highest activity, tolerates a range of epoxides, and can be recycled multiple times without loss of activity.

Three New Abietane-type Diterpenes from the Bark of Cryptomeria japonica

Abstract: Three new abietane-type diterpenoids, 7β-acetoxy-12-methoxyabieta-8,11,13-triene-6α,11-diol (1), 7α-acetoxy-12-methoxyabieta-8,11,13-triene-6α,11-diol (2), and 6α-acetoxy-12-methoxyabieta-8,11,13-triene-7α,11-diol (3), as well as two known abietane-type diterpenoids, 12-methoxyabieta-8,11,13-triene-6α,7β,11-triol (4) and 6α-acetoxy-12-methoxyabieta-8,11,13-triene-7β,11-diol (5), were isolated from the MeOH extract of the bark of Cryptomeria japonica. Their structures were determined by analysis of spectroscopic data and comparison of NMR data with those of related metabolites.

Synthesis of Novel Isoindolo[2,1-a]quinazolinedione Derivatives Containing a 1,2,3-Triazole Ring System

Abstract: A synthesis of isoindolo[2,1-a]quinazolinedione derivatives, coupled with a 1,2,3-triazole ring system, via the reaction of isatoic anhydride, HCCCH2NH2, and 2-formylbenzoic acid is described, which led to the formation of the isoindolo[2,1-a]quinazoline-5,11-dione scaffold having a CC bond that participated in a click reaction with various organic azides.

Paeonenoides D and E: Two New Nortriterpenoids from Paeonia lactiflora and Their Inhibitory Activities on NO Production

Abstract: Two new nortriterpenoids, paeonenoides D and E (1 and 2, resp), together with seven known compounds, were isolated from the roots of Paeonia lactiflora Their structures were elucidated on the basis of spectroscopic evidence Compounds 1–7 were screened for inhibitory effects against NO production in LPS-induced RAW2467 macrophages and for cytotoxic activities against HL-60, Hep-G2, and SK-OV-3 cell lines Compounds 1–3 and 5–7 exhibited inhibitory activities with IC50 values in the range of 96–322 μM Triterpenoids with an epoxide ring and a free COOH function, 1–3, showed effectively increased activities compared with other pentacyclic triterpenoids Compounds 1–6 showed significant cytotoxic activities against the Hep-G2 cell line and modest cytotoxic activities against HL-60 and SK-OV-3 cell lines

Synthesis of Pseudo‐Peptides Containing a Quinazolinone Skeleton via Ugi Four‐Component Reaction

Abstract: A simple and efficient synthesis of quinazolinone pseudo-peptide derivatives based on a new 3-amino-1,2,3,4-tetrahydro-4-oxoquinazoline-2-carboxylic acid via Ugi four-component reaction has been developed. This reaction was conducted under mild conditions with a broad scope of substrates.

In vitro Antioxidant Activity of Ubiquinone and Ubiquinol, Compared to Vitamin E

Abstract: Coenzyme Q10 (CoQ10) is the prevalent ubiquinone in human organism, largely present in its reduced form, ubiquinol (QH2), to which the antioxidant, free radical scavenger activity is ascribed by many authors. However, some studies indicate that also the oxidized form presents some effect in preventing the cellular oxidative stress. In this article four in vitro chemical test methods (TEAC, FRAP, DPPH, and BR) were used to assess the free radical scavenging power of CoQ10, QH2, and vitamin E. The results showed that CoQ10 is almost ineffective, while in three of the tests QH2 presents a higher antioxidant activity than vitamin E. From these results, it can be concluded that the interconversion CoQ10⇌QH2 leading to the prevalence of QH2 in biological tissues is responsible for the antioxidant action of coenzyme Q10 in living organisms.

Configurational Assignment of ‘Cryptochiral’ 10-Hydroxystearic Acid Through an Asymmetric Catalytic Synthesis

Abstract: An asymmetric catalytic total synthesis of (S)-10-hydroxystearic acid (1) for comparison of its absolute configuration to that of samples obtained by fermentative hydration of oleic acid is reported. The synthesis involves two catalytic key-steps, namely ruthenium-catalyzed anti-Markovnikov hydration of 9-decynoic acid (7) to 10-oxodecanoic acid (5), followed by titanium-mediated asymmetric catalytic addition of dioctylzinc (25) to 5 in presence of the chiral ligand N,N’-((1R,2R)-cyclohexane-1,2-diyl)bis(1,1,1-trifluoromethanesulfonamide) (6). The synthesis is short and efficient and avoids use of protecting groups. Ozonolysis of 10-undecynoic acid (9) to 5 provides an alternative entry point into the synthetic route. The double dehydrobromination of (ω,ω-1)-dibromoalkanoic acids to ω-alkynoic acids under a variety of conditions was investigated with 10,11-dibromoundecanoic acid (11) as model substrate and using qNMR to quantify all reaction products. The synthetic approaches presented here have the potential to be generalized to the asymmetric catalytic synthesis of a variety of n-hydroxy-fatty acids. This article is protected by copyright. All rights reserved.