Helen Stoeckli-Evans

Antibacterial phloroglucinols and flavonoids from Hypericum brasiliense

Three known phloroglucinols (japonicine A, uliginosin A and isouliginosin B) and a new phloroglucinol (hyperbrasiol A) have been isolated from a petrol extract of the leaves and flowers of Hypericum brasiliense. Their structures were established by spectroscopic methods (UV, DCI-MS, 1H and 13CNMR, including SINEPT, HMBC, HSQC, DQFCOSY experiments). The substitution pattern of hyperbrasilol A was confirmed by X-ray crystallography. All four phloroglucinols were antibacterial against Bacillus subtilis in a TLC bioautographic assay. The flavonoids, kaempferol, luteolin, quercetin, quercitrin, isoquercitrin, hyperoside and guaijaverin, were isolated from a methanol extract of the same organs.

Antifungal and antibacterial naphthoquinones from Newbouldia laevis roots.

From a dichloromethane extract of Newbouldia laevis roots, four new (6-hydroxydehydroiso-alpha-lapachone, 7-hydroxydehydroiso-alpha-lapachone, 5,7-dihydroxydehydroiso-alpha-lapachone and 3-hydroxy-5-methoxydehydroiso-alpha-lapachone) and six known naphthoquinones have been isolated. Their structures were established by spectroscopic methods (UV, EI mass spectrometry, 1H and 13C NMR) and that of 7-hydroxydehydroiso-alpha-lapachone was confirmed by X-ray crystallography. All naphthoquinones showed antifungal activity against Cladosporium cucumerinum and Candida albicans, and activity against the bacteria Bacillus subtilis and Escherichia coli.

An antifungal γ-pyrone and xanthones with monoamine oxidase inhibitory activity from Hypericum brasiliense

A new gamma-pyrone (hyperbrasilone), three known xanthones (1,5-dihydroxyxanthone, 5-hydroxy-1-methoxyxanthone and 6-deoxyjacareubin) and betulinic acid have been isolated from a dichloromethane extract of stems and roots of Hypericum brasiliense. Their structures were established by spectroscopic methods (UV, EI-MS, 1H and 13C NMR) and that of the gamma-pyrone was confirmed by X-ray crystallography. Hyperbrasilone and the xanthones were all antifungal against Cladosporium cucumerinum, while the three xanthones showed differing degrees of inhibition of monoamine oxidase A and B.

Significant antiferromagnetic exchange in copper(II) and nickel(II) dinuclear complexes of the substituted pyrazine ligand 2,3,5,6-tetra(2-pyridyl)pyrazine (TPPZ): magnetic properties, synthesis and crystal structure

Abstract The dinuclear compounds [Cu 2 (TPPZ)Cl 4 ]∗d5H 2 O ( 1 ), [Ni 2 (TPPZ)(H 2 O) 6 ](NO 3 ) 4 ∗d2.5H 2 O ( 3 ) and [Ni 2 (TPPZ)(H 2 O) 6 [-(squarate) 2 ∗d5H 2 O ( 4 ), where TPPZ is the ligand 2,3,5,6-tetra(2-pyridyl)pyrazine, have been synthesised and characterised crystallographically. [Cu 2 (TPPZ)Cl 4 ]∗d5H 2 O ( 1 ) crystallises in the monoclinic system, space group P2 1 /c, a = 15.030(3), b = 13.224(2), c = 15.320(2) A , β = 105.40(1)°, V = 2935.62(8) A 3 , Z = 4, R1 = 0.035 (observed data). [Ni 2 (TPPZ)(H 2 O) 6 ](NO 3 ) 4 ∗d2.5H 2 O ( 3 ) crystallises in the monoclinic system, space group I2/a, a = 20.660(2), b = 13.724(1), c = 25.436(3) A , β = 91.89(1)°, V = 7208.1(12) a 3 , Z = 8, R1 = 0.070 (observed data). [Ni 2 (TPPZ)(H 2 O) 6 ] (squarate) 2 ∗d5H 2 O ( 4 ) crystallises in the monoclinic system, space group A2/n, a = 19.014(2), b = 10.518(1), c = 19.131(2) A , β = 94.22(1)°, V = 3815.6(7) A 3 , Z = 4, R1 = 0.035 (observed data). Magnetic measurements show significant antiferromagnetic coupling for pyrazine bridged compounds: 2 J = −34.1 cm −1 , g = 2.05 for 1 ; 2 J = −7.6 cm −1 , D = −13.3 cm −1 , g = 2.16 for 3 ; 2 J = −7.5 cm −1 , D = −10.4 cm −1 , g = 2.17 for 4 . The magnetic behaviour of the related published compound [Cu 2 (TPPZ)(H 2 O) 4 ](ClO 4 ) 4 ∗d2H 2 O ( 2 ) has also been measured: 2 J = −61.6 cm −1 , g = 2.13. The possibility of a σ superexchange mechanism in these compounds is discussed.

New tri- and tetranuclear transition metal spin clusters incorporating a versatile polydentate Schiff base ligand

Abstract A trinuclear Fe(III) complex [Fe3(OAc)3L3] (1), a tetranuclear Mn(III) complex [Mn4Cl4L4] (2) and a tetranuclear Ni(II) complex [Ni4(MeOH)4L4] (3) have been synthesized from the reaction of simple metal salts with ligands derived from salicylidene-2-ethanolamine (H2L). Structural characterization of the three complexes reveals distinctly different topologies, despite the similar coordination modes of the ligand L2−. Preliminary magnetochemical studies have been performed and reveal spin ground states of S=1/2,8 and 4 for complexes 1, 2 and 3, respectively.

Ring-tilted ferrocenophanes. the crystal and molecular structures of (1,1′-ferrocenediyl)diphenylgermane and (1,1′-ferrocenediyl)phenylphosphine

Abstract The structures of (1,1′-ferrocenediyl)diphenylgermane (B) and (1,1′-ferrocenediyl)phenylphosphine (C) have been determined from a three-dimensional X-ray analysis using diffractometer data. Crystals of compound B are orthorhombic, space group, Pnma , with Z = 4 in a unit cell of dimensions a 14.867(9), b 12.522(7) and c 9.373(6) A. Full matrix least-squares refinement has given a final R -factor of 0.069 for 956 reflections for which I > 3 σ ( I ). The structure is isomorphous with (1,1′-ferrocenediyl)diphenylsilane [3]. The molecule has crystallographic m symmetry, with atoms Fe and Ge lying in the mirror plane, which bisects the two phenyl groups. The planar cyclopentadienyl rings are bridged by a single Ge atom and are inclined at an angle of 16.6° to one another. The bridge angle, C(1)GeC(1′) is 93.6° and the shortest inter-ring distance, C(1)C(1′), is 2.86 A. the exocyclic C(1)Ge bond makes an angle of 38° with the plane of the cyclopentadienyl ring. Crystals of compound C are orthorhombic, space group Pbca , with Z = 8 in a unit cell of dimensions a 27.130(10), b 12.701(8) and c 7.380(5) A. Full matrix least-squares refinement converged at R = 0.059 for 996 reflections for which I > 3 σ ( I ). The molecule has only an approximate mirror plane, close to which lie atoms Fe, P, C(6) and C(9). The planar cyclopentadienyl rings are bridged by a single P atom and are inclined at an angle of 26.7° to one another. The bridge angle C(1)PC(1′) is 90.6° and the shortest inter-ring distance, C(1)C(1′), is 2.62 A. The exocyclic C(1)P and C(1′)P bonds make angles of 32° and 33° to their respective cyclopentadienyl rings.

Crystal and molecular structures of Cu(II) and Zn(II) complexes of 2,3,5,6-tetra(2-pyridyl)pyrazine (TPPZ): an old ligand revisited

Abstract Copper and zinc complexes of 2,3,5,6-tetra(2-pyridyl)pyrazine (TPPZ) have been prepared. The reaction of Cu(ClO4)2 with TPPZ leads to a dinuclear complex where the ligand is bis-tridentate (crystal data: C24H28N6O22Cl4Cu2, monoclinic, space group P21/n, a=7.855(4), b=16.267(6), c=14.860(3) A, β=102.91(3)°, Z=2, 2522 reflections with I>2.5σ(I), R=0.053). In an acidic medium the same reaction gave a mononuclear dimeric complex where TPPZ is mono-tridentate. The Cu…Cu separation in the dimer is 3.446(3) A and the Cu…Cl bridging bond is 2.682(2) A. The molecules are stacked up the a axis with a short Cu…Cu inter-stacking distance of 3.854(4) A. One of the non-coordinated pyridine N atoms is protonated and hydrogen bonded to a perchlorate O atom (crystal data: C24H17N6O8Cl3Cu, triclinic, space group P 1 , a=6.873(7), b=12.753(5), c= 16.252(7) A, α=69.29(3), β=90.10(4), γ=83.57(4)°, Z=2, 3436 reflections with I>3σ(I), R=0.050). The reaction of TPPZ with an excess of ZnCl2 gave a neutral mononuclear five-coordinate complex where TPPZ is mono-tridentate (crystal data: C24H16N6Cl2Zn, monoclinic, space group P21/n, a=14.744(1), b=7.245(1), c= 21.253(2) A, β=104.51(1)°, Z=4, 3340 reflections with I>2.5σ(I), R=0.036).

Enantioselective catalytic cyclopropanation of styrenes by copper complexes with chiral pinene-[5,6]-bipyridine ligands

Abstract Substituted mono- and bis-pinene-[5,6]-bipyridines are useful ligands in asymmetric copper-catalyzed cyclopropanation by styrenes. Copper complexes were prepared either in situ or prior to the reaction. The catalytic reaction of styrene with ethyl diazoacetate and Cu – 11b yields ethyl trans -phenylcyclopropane carboxylate in >99% yield and 87% e.e. at 0°C. The corresponding cis -configured cyclopropane was produced with an e.e. of 90%. The cis / trans ratio is 22:78. Other ligands of this series are less effective. Various olefins were tested as substrates but exo -methylene olefins show the best results.

Diastereoisomerically Pure Fulleropyrrolidines as Chiral Platforms for the Design of Optically Active Liquid Crystals

Incorporation of [60]fullerene (C(60)) within self-organizing systems is conceptually challenging but allows us to obtain materials which combine the characteristics (anisotropy, organization) of condensed mesophases with the properties of C(60) (photo- and electrochemical activity). Here, we report on the synthesis, characterization, and liquid-crystalline properties of four optically active fullerodendrimers, which are chiral at the point of conjunction between the fullerene scaffold and the mesogenic moieties. Thus, the novelty of this study is to take advantage of the asymmetric carbon atom created during the 1,3-dipolar cycloaddition reaction on C(60) in order to induce mesoscopic chirality in the materials. Four diastereoisomeric fulleropyrrolidines ((R,S)-1, (R,R)-1, (S,R)-1, and (S,S)-1) were synthesized and associated with a second-generation nematic (N) dendron to give fullerodendrimers ((R,S)-2, (R,R)-2, (S,R)-2, and (S,S)-2) which display chiral nematic (N*) phases. The absolute configurations of the stereogenic centers were determined by X-ray crystallography, 1D and 2D NMR experiments, and circular dichroism (CD) spectroscopy. The liquid-crystalline properties of the fullerodendrimers were studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). The fulleropyrrolidine derivatives 2 exhibit supramolecular helicoidal organizations with a right-handed helix for the (R,S)-2 and (R,R)-2 diastereoisomers and a left-handed helix for the (S,R)-2 and (S,S)-2 diastereoisomers. This result suggests that the self-organization of such supermolecular materials can be controlled at the molecular level by the introduction of only one chiral center.

Di- and trinuclear CoII complexes of a bis-β-diketone ligand with variable conformation: structure and magnetic studies

The bis-β-diketone-phenol ligand H3L reacts with Co(OAc)2 to become part of di- or trinuclear complexes in various conformations, depending on the nature of the co-ligand present in the reaction. Thus, the following series of complexes have been synthesized: [Co2(HL)2(Solv)4] (Solv = py, 1; MeOH, 2), [Co2(HL)2(LL)2] (LL = bpy, 3; bpya, 4; Ph2bpy, 5; phen, 6) and [Co3(HL)3] (7), of which 1, 3, and 7 have been crystallographically characterized. The solvent-controlled interconversion between the trinuclear complex and dinuclear complexes 1 or 2 has been demonstrated. The distortion of the CoII coordination geometry within 1, 3, and 7 has been evaluated through Continuous Shape Measures, whereas their magnetic data have been treated with models that include spin–orbit coupling effects.