Synthesis and characterization of n=5, 6 members of the La4Srn−4TinO3n+2 series with layered structure based upon perovskite

Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La₄Sr_n−4Ti_nO_3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)₅Ti₅O₁₇] and [(La,Sr)₆Ti₆O₂₀] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]_p. The n=5 member is similar to the previously reported n=5 member of other A_nB_nO_3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this A_nB_nO_3n+2 series.     

Selective N-debenzylation of amides with p-TsOH

N-Benzylamides were debenzylated efficiently with 4 equiv. of p-TsOH in refluxing toluene. Good to quantitative yields of the desired primary amides were obtained within 2-4 h from a wide variety of N-2,4-dimethoxybenzylamides. N-4-Methoxylbenzyl amides and N-benzylamides were also debenzylated cleanly. In the case of N-2,4-dimethoxylbenzylamides, selective N-debenzylation was possible in the presence of N-Fmoc, N-t-BOC or N-trityl-protection. Protected amino acid amides survived these conditions without any detectable epimerization.     

Crystal Structure of Pseudorhombohedral InFe1−xTixO3+x/2 (x=2/3)

The structure of pseudorhombohedral-type InFe_1−xTi_xO_3−x/2 (x=2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO₃-In₂Ti₂O₇ including incommensurate structures. The structure with the unit cell of a=5.9188(1), b=10.1112(2), and c=6.3896(1) Å, β=108.018(2)°, and a space group P2₁/a is the alternate stacking of an edge-shared InO₆ octahedral layer and an Fe/Ti-O plane along c^*. Metal sites on the Fe/Ti-O plane are surrounded by four oxygen atoms on the Fe/Ti-O plane and two axial ones. Electric conductivities of the order 10⁻⁴ S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell.     

Synthesis, characterization and crystal structures of cyclometallated palladium (II) compounds containing difunctional ligands with [P,P], [As,As], [N,N], [P,As], [P,N] and [P,O] donor atoms

Treatment of the chloro-bridged dinuclear complex [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}(μ-Cl)]₂ (1) with homobidentate [P,P], [As,As], [N,N], and heterobidentate [P,As], [P,N] ligands in a 1:1 molar ratio gave the dinuclear complexes [{Pd[3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N](Cl)}₂{μ-L}] (L = Ph₂PC₄H₆(NH)CH₂PPh₂ (2); Ph₂As(CH₂)₂AsPh₂ (3); 1,3-(NH₂CH₂)₂C₆H₄ (4); Ph₂P(CH₂)₂AsPh₂ (5); Ph₂P(CH₂)₂NH₂ (6)), with the bidentate ligands bridging the two cyclometallated fragments.The reaction with the homobidentate ligands in a 1:2 molar ratio in the presence of NaClO₄ afforded the mononuclear compounds [[Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-P,P}][ClO₄] (L = Ph₂PC₄H₆(NH)CH₂PPh₂ (7); (o-Tol)₂P(CH₂)₂P(o-Tol)₂ (8)), [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{Ph₂As(CH₂)₂AsPh₂-As,As}][ClO₄] (9) and [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-N,N}][ClO₄] (L = NH₂(CH₂)₃NH₂ (10); NH₂(C₆H₈)CH₂(C₆H₈)NH₂ (11); 1,3-(NH₂CH₂)₂C₆H₄ (12); 1,3-(NH₂)₂C₅H₃N (13); NH₂(C₆H₄)O(C₆H₄)NH₂ (14); NMe₂(CH₂)₂NMe₂ (15)), in which the chloro ligands are absent and the bidentate ligands are chelated to the palladium atom.Reaction of 1 with Ph₂P(CH₂)₂AsPh₂ in 1:2 molar ratio in acetone in the presence of NH₄PF₆ afforded the analogous mononuclear compound [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{Ph₂P(CH₂)₂AsPh₂-P,As}][PF₆] (16); whereas reaction with Ph₂P(CH₂)₃NH₂ gave [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{Ph₂P(CH₂)₃N(CMe₂)-P,N}][PF₆] (17), derived from intermolecular condensation between the aminophosphine and acetone. Condensation of the NH₂ group was precluded by change of solvent, using dichloromethane.Iminophoshines also reacted with 1 in 1:2 molar ratio in acetone to give a new series of mononuclear cyclometallated complexes: [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-P,N}][ClO₄] (L = Ph₂PC₆H₄C(H)NCy (20); Ph₂PC₆H₄C(H)NC(CH₃)₃ (21); Ph₂PC₆H₄C(H)NNMe₂ (22); Ph₂PC₆H₄C(H)NNHMe (23); Ph₂PC₆H₄C(H)NNHPh (24)). Analogous complexes with a stable P,O-chelate were obtained using bidentate [P,O] donor ligands: [Pd{3,4-(MeO)₂C₆H₂C(H)N(Cy)-C6,N}{L-P,O}][Cl] (L = 2-(Ph₂P)C₆H₄CHO (25); Ph₂PN(Me)C(O)Me (26)).The crystal structures of compounds 1, 5, 15, 16, 18, 20 have been determined by X-ray crystallography.     

Synthesis of methyl (5Z,8Z,10E,12E,14Z)-eicosapentaenoate

The first total synthesis of methyl (5Z,8Z,10E,12E,14Z)-eicosapentaenoate has been achieved in seven steps and in 16% overall yield. The synthesis confirmed the assigned structure of this polyunsaturated natural product.     

Hupermine A,a novel C16N2-type Lycopodium alkaloid from Huperzia phlegmaria

A novel C₁₆N₂-type Lycopodium alkaloid consisting of a quinolizidine with a 6-dimethylaminohexyl side chain, hupermine A (1), was isolated from the club moss of Huperzia phlegmaria, and the structure and relative stereochemistry were elucidated on the basis of spectroscopic data.     

Local environment in Ba2In2−xWxO5+3x/2 oxide ion conductors

The actual oxygen environment of the tungsten dopant in the Ba₂In_2−xW_xO_5+3x/2 solid solution was revealed by combining X-ray absorption spectroscopy at the tungsten L_I and L_III edges and at the indium L_I edge. Whatever the substitution ratio, the tungsten atoms exhibit a regular octahedral environment. When the substitution ratio increases, the oxygen vacancies are progressively filled until their total occupancy for x=2/3. For x?0.3, the perovskite structure is stabilised; the tungsten atoms are randomly distributed in the structure. Although X-ray diffraction revealed a cubic symmetry for these compositions, a local distortion of the indium environment is observed when a tungsten atom is in its surrounding.     

Conformational analysis of bridgehead-substituted bicyclo[m.m.m]alkanes and bicyclo[8.8.n]alkanes

Conformational analyses of bicyclo[m.m.m]alkanes where m=1-10 and of bicyclo[8.8.n]alkanes where n=1-7 bearing methyl groups on the bridgeheads were carried out using a Monte Carlo search strategy. In the bicyclo[m.m.m]alkane series, greater variability was observed for the inter-bridgehead distance for larger values of m. This suggests that properly substituted bicyclo[8.8.8]hexacosanes or larger ring systems might serve as molecular springs.     

Synthesis and properties of the Co7Se8−xSx and Ni7Se8−xSx solid solutions

We report the synthesis and elementary properties of the Co₇Se_8−xS_x (x=0-8) and Ni₇Se_8−xS_x (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni₇Se_8−xS_x system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co₇Se_8−xS_x system, as well as Ni₇Se₈ and Ni₇SeS₇, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/mol_CoK² and ∼7 mJ/mol_NiK² for Co₇Se_8−xS_x and Ni₇Se_8−xS_x, respectively.     

Fingerprint quality control of Angelica sinensis (Oliv.) Diels by high-performance liquid chromatography coupled with discriminant analysis

High-performance liquid chromatography (HPLC) was employed in the fingerprint analysis of Angelica sinensis (Oliv.) Diels. A chromatographic profile of A. sinensis (Oliv.) Diels from the Dingxi District of Gansu province, China, was established as the characteristic fingerprint. The feasibility and advantages of employing chromatographic fingerprint combined with discriminant analysis were investigated and demonstrated for the evaluation of A. sinensis (Oliv.) Diels for the first time. Our results showed that the chromatographic fingerprint combining with discriminant analysis can efficiently distinguish A. sinensis (Oliv.) Diels from various areas.     

Castanolide and epi-castanolide, two novel diterpenoids with a unique seco-norabietane skeleton from Salviacastanea Diels f. pubescens Stib.

Castanolide (1) and epi-castanolide (2), two novel diterpenoids possessing a unique seco-norabietane skeleton, were isolated from Salviacastanea Diels f. pubescens Stib. Their structures and relative stereochemistry were elucidated by extensive NMR analysis and confirmed by single-crystal X-ray diffraction study. A possible biosynthetic pathway of these two compounds was also proposed.     

6,7-Seco-ent-kaurane-type diterpenoids from Isodon eriocalyx var. laxiflora

Twenty nine 6,7-seco-ent-kaurane-type diterpenoids including 18 new ones, laxiflorolides C–T (1–18), along with 21 known ones were obtained from Isodon eriocalyx var. laxiflora. Laxiflorolides E–G (3–5) are the first identified naturally occurring 6,7-seco-ent-kauranoids that feature a 3,6-epoxy unit, and laxiflorolide M (11) is the first identified naturally occurring 6-nor-6,7-seco-ent-kauranoid. The absolute configurations of compounds 1, 3, 6, and 11 were determined by single-crystal X-ray diffraction analyses. The cytotoxic activity of the isolates was evaluated by an MTT assay.     

Syntheses and structures of zinc and tin(II) compounds with hemilabile N-silyl-tert-butylamido and N-silyl-p-tolylamido ligands that contain pendent tert-butoxy groups

Syntheses and solid-state structures of zinc and tin(II) compounds, containing the N-silyl-amide ligands (O^tBu)(NR)SiMe₂, R = ^tBu (L^tBu), or R = p-tolyl (L^pTol), are reported. The N-silyl amines were synthesized by modified published procedures from commercially available Me₂SiCl₂, ^tBuOH, and ^tBuNH₂, or p-Me-C₆H₄NH₂, respectively. Treatment of SnCl₂ with LiL^pTol furnished Sn(L^pTol)₂, which was X-ray structurally characterized and shown to contain two covalent Sn-N bonds and two asymmetrical O → Sn donor bonds. The single-crystal X-ray structure of Sn(L^tBu)₂ revealed a much more symmetrically-coordinated, pseudo-trigonal-bipyramidal tin atom. Aminolysis of diethylzinc with HL^pTol produced [EtZn(L^pTol)]₂, which crystallized as a centrosymmetric dimer, containing four-coordinate zinc atoms connected by bridging amides. Zinc dichloride, by contrast, reacted with two equivalents of LiL^tBu to produce the homoleptic, pseudo-spirocyclic Zn(L^tBu)₂.     

Novel ent-kaurane dimers from Isodon rubescens var. rubescens

Three novel asymmetric ent-kaurane dimers xindongnins M-O (1-3) were isolated from Isodon rubescens var. rubescens. Their structures were elucidated by spectroscopic methods including 2D NMR analysis. The relative stereochemistry of 1 was determined by single crystal X-ray diffraction, which also confirmed the unique linkage of a single carbon-carbon bond between the two subunits of this dimer. A biogenetic pathway was proposed for the formation of these dimers.     

Diastereoselective synthesis of homo-N,O-nucleosides

A new class of homo-N,O-nucleosides has been designed, based on the 1,3-dipolar cycloaddition of C-substituted nitrones with allyl nucleobases. The N-methyl-C-ethoxycarbonyl nitrone 1, and the C-α-silyloxymethyl-N-methyl nitrone 7 have been exploited: the stereochemical features of the obtained nucleosides are dependent on the nature of the dipole. The results obtained with DFT calculations fully agree with the experimental results and successfully reproduce the experimentally observed reversal of endo/exo selectivity for nitrones 1 and 7.     

Three new Lycopodium alkaloids from Huperzia carinata and Huperzia squarrosa

Eleven Lycopodium alkaloids with lycodine-type, lycopodine-type, and fawcettimine-related skeletons were isolated from the whole plants of Huperzia carinata (Desv. Ex. Poir.) Trevis and Huperzia squarrosa (G. Forst) Trevis (Huperziaceae). Among them, 8,15-dihydrohuperzine A (2), lycocarinatine A (3), and lycoposerramine U N-oxide (11) are new compounds. The structures of these new alkaloids were elucidated on the basis of 2D NMR correlations. Some of these isolated alkaloids were assayed for acetylcholinesterase (AChE) inhibitory activity.     

Polyhydroxylated macrolide isolated from the endophytic fungus Pestalotiopsis mangiferae

A new polyhydroxylated macrolide, named mangiferaelactone (1) was isolated from a solid culture of the endophytic fungus Pestalotiopsis manguiferae, together with ten known compounds [(6S,1′S)-LL-P880α; (6S,1′S,2′R)-LL-P880β; (1′S,2′R)-LL-880γ; (1′R)-dehydropestalotin; (−)-5-carboxylmellein; (−)-5-methylmellein; (−)-5-hydroxylmethylmellein; arabenoic acid; 5,6-dihydro-4-methoxy-2H-pyran-2-one; and the (−)-2-hexylidene-3-methylsuccinic acid]. P. manguiferae was isolated from Hyptis dilatata, a small shrub common in the central region of Panama. The structure of compound 1 was elucidated by a combination of spectroscopic methods (IR, MS, optical rotation, 1D and 2D NMR spectroscopy). The absolute configuration of 1 was established as 4R,7R,8R,9S by application of vibrational circular dichroism (VCD). Compound 1 showed a minimum inhibitory concentration (MIC) of 1.6863 mg/mL against Listeria monocytogenes, and 0.5529 mg/mL against Bacillus cereus. No activity was observed for compound 1 against Plasmodium falciparum or Trypanosoma cruzi; likewise, no cytotoxic activity was observed against A2058 and H522-T1 cells.     

Crystal structures of RPt3−xSi1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) studied by single crystal X-ray diffraction

The crystal structures of ternary compounds RPt_3−xSi_1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt_3−xSi_1−y arises from defects: x≈0.20, y≈0.14. The crystal structure of RPt_3−xSi_1−y can be considered as a packing of four types of building blocks which derive from the CePt₃B-type unit cell by various degrees of distortion and Pt, Si-defects.