A new class of indolosesquiterpene alkaloids from polyathia suaveolens

Three new alkaloids, polyavolensin, polyavolensinol and polyavolensinone, isolated from the stem of Polyathia suaveolens are shown to belong to a new class of indolosesquiterpenes with structures 4, 5, 6 respectively by PMR, CMR and mass spectrometry. They have also been interrelated by chemical reactions.     

A family of multicyclic indolosesquiterpenes from a bacterial endophyte

Three novel indolosesquiterpenes, xiamycin B (1b), indosespene (2), and sespenine (3), along with the known xiamycin A (1a) were isolated from the culture broth of Streptomyces sp. HKI0595, a bacterial endophyte of the widespread mangrove tree Kandelia candel. Agar diffusion assays revealed moderate to strong antimicrobial activities against several bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis, while no cytotoxicity against human tumor cell lines was observed. Together with the previously reported oridamycin, the endophyte metabolites represent the first indolosesquiterpenes isolated from prokaryotes.     

Identification and characterization of xiamycin A and oxiamycin gene cluster reveals an oxidative cyclization strategy tailoring indolosesquiterpene biosynthesis

Xiamycin A (XMA) and oxiamycin (OXM) are bacterial indolosesquiterpenes featuring rare pentacyclic ring systems and are isolated from a marine-derived Streptomyces sp. SCSIO 02999. The putative biosynthetic gene cluster for XMA/OXM was identified by a partial genome sequencing approach. Eighteen genes were proposed to be involved in XMA/OXM biosynthesis, including five genes for terpene synthesis via a non-mevalonate pathway, eight genes encoding oxidoreductases, and five genes for regulation and resistance. Targeted disruptions of 13 genes within the xia gene cluster were carried out to probe their encoded functions in XMA/OXM biosynthesis. The disruption of xiaK, encoding an aromatic ring hydroxylase, led to a mutant producing indosespene and a minor amount of XMA. Feeding of indosespene to XMA/OXM nonproducing mutants revealed indosespene as a common precursor for XMA/OXM biosynthesis. Most notably, the flavin dependent oxygenase XiaI was biochemically characterized in vitro to convert indosespene to XMA, revealing an unusual oxidative cyclization strategy tailoring indolosesquiterpene biosynthesis.     

Structural and vibrational analyses of t,C,t,T,t,T,t-deca-1,3,5,7,9-pentaene

An analysis of the results of the fluorescence spectrum investigation of all-trans-deca-1,3,5,7,9-pentaene and t,C,t,T,t,T,t-deca-1,3,5,7,9-pentaene in an n-decane matrix [B.E. Kohler, V. Terpougov, J. Chem. Phys. 108 (1998) 9586–9593] has been performed using scaled quantum mechanical force field (SQM-FF) methodology at the HF/6-31G level. The measured vibronic wavenumbers were assigned taking into account the results of quantum-chemical predictions of the vibrational spectra for all-trans-deca-1,3,5,7,9-pentaene and t,C,t,T,t,T,t-deca-1,3,5,7,9-pentaene. Results from additional calculations at the MP2(FC)/aug-cc-pVDZ and B3LYP/6-311++G(d,p) levels are also reported.     

Solubilities of l-glutamic acid, 3-nitrobenzoic acid,p-toluic acid,calcium-l-lactate,calcium gluconate,magnesium-dl-aspartate,and magnesium-l-lactate in water

Solubilities of l -glutamic acid, 3-nitrobenzoic acid, p -toluic acid, calcium-l -lactate, calcium gluconate, magnesium- dl -aspartate, and magnesium- l -lactate in water were determined in the temperature range 278 K to 343 K. The apparent molar enthalpies of solution at T =  298.15 K as derived from these solubilities areΔ_solH_m (l -glutamic acid,m_sat =  0.0565 mol · kg ^− 1)  =  30.2 kJ · mol ^− 1,Δ_solH_m (3-nitrobenzoic acid, m =  0.0188 mol · kg ^− 1)  =  28.1 kJ · mol ^− 1, Δ_solH_m( p - toluic acid, m =  0.00267 mol · kg ^− 1)  =  23.9 kJ · mol ^− 1,Δ_solH_m (calcium- l -lactate tetrahydrate,m =  0.2902 mol · kg ^− 1)  =  25.8 kJ · mol ^− 1,Δ_solH_m (calcium gluconate, m =  0.0806 mol · kg ^− 1)  =  22.1 kJ · mol ^− 1, Δ_solH_m(magnesium-dl -aspartate tetrahydrate, m =  0.1469 mol · kg ^− 1)  =  11.5 kJ · mol ^− 1, andΔ_solH_m (magnesium- l -lactate trihydrate,m =  0.3462 mol · kg ^− 1)  =  3.81 kJ · mol ^− 1.     

Synthesis of Amaryllidaceae alkaloids, siculine, oxocrinine, epicrinine, and buflavine

Three crinane type of alkaloids isolated from Amaryllidaceae family were synthesized by taking advantage of the PIFA-mediated intramolecular p-p′ diphenol coupling reaction of norbelladine derivatives. Furthermore, buflavine was also prepared by using the p-p′ diphenol coupling followed by dienone-phenol rearrangement as a key step.     

Mild, powerful, and robust methods for esterification, amide formation, and thioesterification between acid chlorides and alcohols, amines, thiols, respectively

We developed two efficient practical methods for esterification, amide formation, and thioesterification between acid chlorides and alcohols, amines, thiols, respectively. The present mild and robust reaction was performed by two separate methods both by combining cheap and readily available amines, N-methylimidazole, and N,N,N′,N′-tetramethylethylenediamine (TMEDA). Method A uses catalytic N-methylimidazole and TMEDA with an equimolar amount of K₂CO₃, whereas Method B uses equimolar amounts of N-methylimidazole and TMEDA. The salient features are as follows. (i) With regard to reactivity, Method B was superior to Method A for esterification and thioesterification, whereas cost-effective Method A was superior to Method B for amide formation. (ii) Amide formation proceeded smoothly between acid chlorides and less nucleophilic and stereocongested amines such as 2,6-dichloroaniline. (iii) This protocol was applied to the successful synthesis of two agrochemicals, bromobutide and carpropamid.     

Synthesis, structure, and properties of four ternary compounds: CaSrTt, Tt=Si, Ge, Sn, Pb

The title compounds were synthesized and characterized by structural measurements and electronic structure calculations. Single-crystal X-ray diffraction analyses established that they all have the orthorhombic inverse-PbCl₂-type structure (Pnma, Z=4, a=8.108(2), 8.124(2), 8.421(2), 8.509(2) Å; b=4.944(1), 4.949(1), 5.168(1), 5.189(1) Å; c=9.170(2), 9.184(2), 9.685(2), 9.740(2) Å, respectively). The tetrel (Tt) atoms are situated in tricapped trigonal prisms of ordered Sr and Ca atoms in which the smaller Ca atoms play a distinctive role. The structure is distinguishable from the Co₂Si type by its more nearly ideal 6+3 (TCTP) environment about Tt rather than a higher coordination by cations. Other representations of the two structural types are also considered. Electronic band structure calculations suggest that the compounds are semiconductors, in agreement with literature data on their Ae₂Tt analogues.     

Preparation,structure, and magnetic properties of isostructural La3MAlS7 and La3MFeS7 (M = Mg,Mn, Fe,Co, Ni,or Zn)

A series of quaternary metal sulfides of the general formula La₃MM′S₇ (M = Mn, Fe, Co; M′ = Al and M = Mg, Mn, Fe, Co, Ni; M′ = Fe) consisting of linear chains of face shared MS₆ octahedra and isolated M′S₄ tetrahedra has been prepared and studied. The aluminium compounds La₃MAlS₇ (M = Mn, Fe, Co) exhibit linear chain antiferromagnetism. Magnetic behavior of other La₃MFeS₇ sulfides has been examined in detail. The magnetic susceptibility of La₃MgFeS₇ shows that tetrahedral site Fe³⁺ undergoes a transition from $\text{S =}\text{5}\text{2}$ to S = 2 spin state around 150 K.     

Total synthesis of (4R,5S,6E,14S)- and (4R,5S,6E,14R)-cystothiazoles F

Total synthesis of (4R,5S,6E,14S)- and (4R,5S,6E,14R)-cystothiazoles F 3 was achieved from the chiral bithiazole-type primary alcohols [(S)- and (R)-4-ethoxycarbonyl-2′-(1-hydroxymethylethyl)-2,4′-bithiazoles 8], which were obtained based on the enzymatic resolution of racemic alcohol 8 and its acetate 9. From a direct comparison by means of chiral HPLC between natural cystothiazole F 3 and synthetic compounds [(4R,5S,6E,14S)- and (4R,5S,6E,14R)-cystothiazoles 3], natural cystothiazole F 3 was found to be a 33:67 diastereomeric mixture [(4R,5S,6E,14S)-3:(4R,5S,6E,14R)-3 = 33:67].     

Solubilities of terephthalaldehydic,p-toluic,benzoic, terephthalic and isophthalic acids in N,N-dimethylformamide from 294.75 to 370.45 K

Using a laser monitoring observation technique, solubilities of terephthalaldehydic, p-toluic, benzoic, terephthalic and isophthalic acids in N,N-dimethylformamide have been measured as a function of temperature in the temperature range 294.75–370.45 K. The experimental data are correlated with the λh equation. The calculated results show good agreement with the experimental solubilities. The molar mixing enthalpy of solution H^E is estimated from the h parameter to discuss the properties of solution. In the terephthalic acid-N,N-dimethylformamide system a repulsive interaction exists between solute and solvent, which leads to an endothermic effect during dissolution. The strongest attractive interaction exists in the p-toluic acid-N,N-dimethylformamide system, causing a significant exothermic effect.     

Copper-indium ordering in RECu6In6 (RE=Y, Ce, Pr, Nd, Gd, Tb, Dy)

The rare earth metal-copper-indides RECu₆In₆ (RE=Y, Ce, Pr, Nd, Gd, Tb, Dy) were synthesized from the elements by arc-melting. Well-crystallized samples were obtained by slowly cooling the melted buttons from 1320 to 670 K in sealed silica tubes in a muffle furnace. They were investigated by X-ray diffraction on powders and single crystals: ThMn₁₂ type, space group I4/mmm, Z=2, a=916.3(2), c=535.8(2) pm, wR₂=0.063, 216 F² values, 15 variables for YCu₆In₆, a=926.5(4), c=543.5(3) pm, wR₂=0.064, 314 F² values, 15 variables for CeCu₆In₆, a=925.7(4), c=540.1(3) pm, wR₂=0.075, 219 F² values, 15 variables for PrCu₆In₆, a=923.1(4), c=540.3(3) pm, wR₂=0.071, 218 F² values, 15 variables for NdCu₆In₆, a=917.7(4), c=540.2(3) pm, wR₂=0.076, 207 F² values, 15 variables for GdCu₆In₆, a=917.0(5), c=540.5(4) pm, wR₂=0.062, 215 F² values, 15 variables for TbCu₆In₆, a=915.2(8), c=540.7(7) pm, wR₂=0.108, 218 F² values, 15 variables for DyCu₆In₆. The structures have been refined with a split position (50% Cu+50% In) for the 8j site. They can be explained by a tetragonal body-centered packing of CN 20 polyhedra (10Cu+10In) around the rare earth atoms. The ordering models of the copper and indium atoms and the limitations/resolution of X-ray diffraction for this topic are discussed.     

Synthesis of cyclohexane derivatives including Br,Cl, N,O, and S at 1,2,4,5-positions: selectivity in addition reactions

Brominations of mono addition products of 1,4-cyclohexadiene with 2,4-dinitrobenzenesulfenyl chloride (RSCl) selectively gave 1R(S),2R(S),4R(S),5R(S)-4,5-dibromo-2-(2,4-dinitrophenylthio)cyclohexyl acetate and 1R(S),2R(S),4R(S),5R(S)-4,5-dibromo-2-chlorocyclohexyl)(2,4-dinitrophenylthio)sulfane. From series reactions 7-oxabicyclo[4.1.0]hept-3-ene with reagents, such as RSCl, NaN₃, and H₂SO₄/Ac₂O, six 1,2,4,5-tetrasubstituted cyclohexane derivatives including S, O, N, Cl, and Br were selectively obtained. Formations and structures of the products were discussed.     

Protonation,deuteration, and formylation of aceperidazylenes

1H-1,2-Diazaphenalene derivatives in which the pyridazine ring is ortho- and peri-fused to acenaphthene and acenaphthylene (1H-indeno[6,7,1-def]cinnolines) have been synthesized. It has been found that electrophilic attack on these compounds is directed at C⁶.     

Synthesis, structure and physical properties of LnNi(Sn,Sb)3 (Ln=Pr, Nd, Sm, Gd, Tb)

Five new analogues of the β-CeNiSb₃ family have been synthesized and found to be LnNi(Sn,Sb)₃ and isostructural to the previously reported β-CeNiSb₃. LnNi(Sn,Sb)₃ (Ln=Pr, Nd, Sm, Gd, or Tb) crystallizes in the orthorhombic space group, Pbcm, with lattice parameters of a∼12.9 Å, b∼6.1 Å, c∼12.0 Å. The structure consists of layers of nearly square nets of X (X=Sn/Sb) atoms and highly distorted NiX₆ octahedra. Lanthanide atoms are located between layers of X and NiX₆ octahedra. All analogues are metallic and experimental effective magnetic moments are in agreement with the respective Ln³⁺ calculated moments.     

Chemoenzymatic syntheses of N-trifluoroacetyl-l-daunosamine,N-trifluoroacetyl-l-acosamine,N-benzoyl-d-acosamine,and N-benzoyl-d-ristosamine from an achiral precursor,methyl sorbate

A conjugated addition of benzylamine to methyl (4R,5S)-4,5-(isopropylidenedioxy)-(2E)-hexenoate 8a followed by lactonization under acidic condition proceeds to the formal total syntheses of l-daunosamine 4 and l-acosamine 2. On the other hand, direct conjugated addition of benzylamine to methyl (4S,5S)-4,5-epoxy-(2E)-hexenoate 5 and the subsequent intramolecular nucleophilic attack by the ester carbonyl group on the epoxy ring of the substrates leads to the formal total syntheses of d-acosamine 2 and d-ristosamine 1.     

Crystal growth, structure determination, and optical properties of new potassium-rare-earth silicates K3RESi2O7 (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu)

Single crystals of K₃RESi₂O₇ (RE=Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were grown from a potassium fluoride flux. Two different structure types were found for this series. Silicates containing the larger rare earths, RE=Gd, Tb, Dy, Ho, Er, Tm, Yb crystallize in a structure K₃RESi₂O₇ that contains the rare-earth cation in both a slightly distorted octahedral and an ideal trigonal prismatic coordination environment, while in K₃LuSi₂O₇, containing the smallest of the rare earths, lutetium is found solely in an octahedral coordination environment. The structure of K₃LuSi₂O₇ crystallizes in space group P6₃/mmc with a=5.71160(10) Å and c=13.8883(6) Å. The structures containing the remaining rare earths crystallize in the space group P6₃/mcm with the lattice parameters of a=9.9359(2) Å, c=14.4295(4) Å, (K₃GdSi₂O₇); a=9.88730(10) Å, c=14.3856(3) Å, (K₃TbSi₂O₇); a=9.8673(2) Å, c=14.3572(4) Å, (K₃DySi₂O₇); a=9.8408(3) Å, c=14.3206(6) Å, (K₃HoSi₂O₇); a=9.82120(10) Å, c=14.2986(2) Å, (K₃ErSi₂O₇); a=9.80200(10) Å, c=14.2863(4) Å, (K₃TmSi₂O₇); a=9.78190(10) Å, c=14.2401(3) Å, (K₃YbSi₂O₇). The optical properties of the silicates were investigated and K₃TbSi₂O₇ was found to fluoresce in the visible.     

Asymmetric synthesis of N,O,O,O-tetra-acetyl d-lyxo-phytosphingosine,jaspine B (pachastrissamine) and its C(2)-epimer

The highly diastereoselective conjugate addition of lithium (S)-N-benzyl-N-(α-methylbenzyl)amide to a γ-silyloxy-α,β-unsaturated ester and in situ enolate oxidation with (+)-(camphorsulfonyl)oxaziridine has been used as the key step in the asymmetric synthesis of N,O,O,O-tetra-acetyl d-lyxo-phytosphingosine, jaspine B (pachastrissamine) and its C(2)-epimer.     

Total synthesis of N,O,O,O-tetraacetyl-d-ribo-phytosphingosine and its 2-epi-congener

Total synthesis of the natural d-ribo-phytosphingosine I and its 2-epimer III in the protected form was achieved through a common strategy. The aza-Claisen rearrangement of allylic thiocyanate (Z)-V incorporated the new stereogenic centre with nitrogen and the subsequent Wittig olefination constructed a non-polar side chain. Hydrogenation, followed by removal of protecting groups, completed the syntheses of I and III.     

Ferrimagnetism in the rare earth titanium (III) oxides, RTiO3; R = Gd,Tb, Dy,Ho, Er,Tm

The series of compounds RTiO₃, R = Gd, Tb, Dy, Ho, Er, and Tm, were obtained as single-phase materials via solid state reaction between Ti₂O₃ and R₂O₃ at ca. 1500°C in welded molybdenum crucibles under argon; YbTiO₃ and LuTiO₃ could not be obtained as single-phase materials using this procedure. Lattice constants for all compounds were determined from powder X-ray data and are compared with previous results. All of these materials order magnetically between 30 and 70 K. From the appearance of the χ^?1_m vs T curve the type of order can be identified as ferrimagnetic. High-temperature susceptibility data have been fit to a two-sublattice molecular field model and the intra- and intersublattice interaction constants have been extracted. It is found that the TiTi interaction is ferromagnetic and relatively constant from R = Gd to R = Lu. Low-temperature magnetization field data suggest the existence of complex magnetic structures, large magnetocrystalline anisotropy, or both. The magnetic properties of the RTiO₃ series are compared to those of the chemically similar and better-known RMO₃ phases where M = Al, V, Cr, Mn, and Fe. The observed differences are shown to follow from the sign of the M-M interaction, which is ferromagnetic for M = Ti and antiferromagnetic for M = V, Cr, Mn, and Fe, together with the implications of the crystal symmetry for the R-M interaction.