Coleone C,D, I,I′ aus einer madegassischen Plectranthus sp. nov. Interkonversion von cis- und trans-A/B-6,7-Diketoditerpenen

Coleons C, D, I, I′, obtained from a Madagascan Plectranthus sp. nov.. Interconversion of cis- and trans-A/B-6,7-Diketoditerpenes. Fairly large amounts of Coleons C and D, as well as Coleons I and I′ (3-O-formyl derivative of Coleon I) can bc isolated from the orange glands of an unclassified North Madagascan Plectranthus sp. A reversible transformation of cis- and trans-A/B-6,7-dioxo-abietane via its diosphenol has been achieved for the first time. CD.-Spectra of these compounds are presented. Hydrogenolysis of Coleon D leads to 6β,16-dihydroxy-royleanone.     

Diterpenoide Drüsenfarbstoffe: Coleon L,ein neues Diosphenol aus Coleus somaliensis S. MOORE; Revision der Strukturen von Coleon H,I, I′ und K

Leaf-gland Pigments: Coleon L, a New Diosphenolic Compound from Coleus somaliensis, S. MOORE ; Revision of the Structures of Coleon H, I, I′ and K From leaf-glands of C. somaliensis a new, highly oxidized diosphenolic hydroquinone belonging to the abietane series was isolated in minute quantities. The new compound, coleon L ( 4c ; C₂₄H₃₀O₁₀), is very labile and transformed into its tautomer coleon K (5d) on standing in solution. ¹H-NMR. spectra of coleon L showed clearly that the points of attachment of the two acetoxy groups are at C(3) and C(16) contrary to the positions expected from our previously published structure 3 for coleon K. Application of a recently elaborated conversion of trans-A/B-6,7-diketones of type 5 into the cis-isomers 6 allowed to assign unambiguously the β-configuration to the hydroxyl group at C(3) using pyridin induced solvent shifts. This confirmed structure 4c and 5d for coleon L and K, respectively. Based on similar reasons, the configuration at C(3) of coleon H, I and I′ had to be revised, the structures of these coleons being 4b , 5b and 5c , respectively.     

Diterpenoide Drüsenfarbstoffe: Coleone S und T aus Plectranthus caninus ROTH(Labiatae), ein neues Diosphenol/trans-A/B-6,7-Diketon-Paar aus der Abietanreihe

Leaf-gland Pigments: Coleons S and T from Plectranthus caninus ROTH (Labiatae), New Hydroquinones of the Abietane Series with a Diosphenol/trans-A/B-6,7-Diketone Structure. Coleons S and T were isolated from the more polar fractions from extracts of the above mentioned plant. Coleon S, C₂₀H₂₆O₆, has been shown to have structure 1a , and coleon T, C₂₀H₂₆O₆, structure 2 .     

Struktur und Partialsynthese von dimerem Coleon F

Structure and Partial Synthesis of Dimeric Coleon F Coleon F ( 1a ), on standing in solution, slowly dimerizes to the labile C(7)-epimeric spiro-dihydrofuranes 2a/2b whose structures were elucidated by spectroscopic methods. Oxydative addition of 1a to another molecule of 1a in the presence of Fétizon's reagent rapidly yields 2a/2b , thus confirming their structures as (4bS,9RS,10′aS)4,4a,10′,10′a-tetrahydro-1′,6-dihydroxy-1,2,4a,7′,8′,10′a-hexamethyl-3′,7-bis(2-propenyl)-spiro[3H,9H-phenanthren-9,5′-5′H-phenanthro[1,10-bc]furan]-2,3,5,8,9′-pentone.     

Spirocoleone: Synthese und Charakterisierung von vier diastereomeren Spiro (methylcyclopropan)-Substrukturen; Revision der Konfiguration an C(12) und C(15) von Coleon P und Derivaten sowie von Coleon-Z-Derivaten; Röntgenstrukturanalysen von Lanugon J und weiteren Spirocoleonen

Spirocoleons: Synthesis and Characterization of Four Diastereomeric Spiro (methylcyclopropane) Substructures; Revision of the Configuration at C(12) and C(15) of Coleon P and Derivatives and Coleon-Z Derivatives; X-Ray Analysis of Lanugon J and of Further Spirocoleons X-ray analyses show the correctness of the previously published structure of coleon Q (1) , establish the structure of lanugon J (4a) , and necessitate a revision of the configuration at C(12) and C(15) in coleon P (3a) and its derivatives 3b and 3c , and furthermore of the coleon Z derivatives 11a–11d . Two further diastereomeric spiro (methylcyclopropane) substructures have been generated by photoisomerization of lanugon J (4a) and 12-O-desacetylcoleon N (8) ; they represent the novel cis-type B with (12R, 13R, 15S)- and the novel trans-type D with (12R, 13R, 15R)-configuration (Scheme 1). The structures of the photoproducts 5a ((12R, 13R, 15R)-lanugon J) and 7a ((12R, 13R, 15S)-lanugon J) were established by X-ray analysis. So far, only two of the eight possible diastereomers of the spiro-(methylcyclopropane) substructure I have been detected in nature, i.e. the trans-type A with (12R, 13S, 15S)- and the cis-type C with (12R, 13S, 15R)-configuration. The four diastereomers A-D , all possessing (12R)-configuration, show very similar properties. However, careful comparison of spectral and chiroptical data allow a differentiation, even in the case of functionalization of H₃C(17). The (12S)-counter-parts could not yet be prepared.     

Cyclopeptid-Antibiotika aus Aspergillus-Arten. Struktur der Echinocandine C und D

Cyclopeptide antibiotics from Aspergillus species. Structure of echinocandins C and D The echinocandins B, C and D are antifungal antibiotics produced by a strain of Aspergillus rugulosus. All three metabolites are closely related representing cyclic oligopeptides composed of six amino acids and a linolic acid residue in an amide linkage. The complete structure of echinocandin B ( 1 ) has recently been established by X-ray analysis. Structural assignments to the new minor metabolites C and D have now been made by hydrolytic and oxidative cleavage reactions, formation of N-acyl-α-aminoethers as well as by chemical correlations and extensive NMR. examinations. Echinocandin C ( 2 ), C₅₂H₈₁N₇O₁₅, contains 3-hydroxyhomotyrosine in the place of 3, 4-dihydroxyhomotyrosine present in 1 . Echinocandin D ( 3 ), C₅₂H₈₁N₇O₁₃, differs in two amino acids: 3, 4-dihyroxyhomotyrosine and 4, 5-dihydroxyornithine, unusual units of 1 being replaced by 3-hydroxyhomotyrosine and ornithine.     

Electron-Nuclear Double Resonance Study of Flavodoxin from Peptostreptococcus Elsdenii

The proton electron-nuclear double resonance (ENDOR) of the semiquinone of Peptostreptococcus elsdenii flavodoxin has been studied at – 155°. Studies with flavodoxin derivatives in which the natural coenzyme has been replaced by C(8)? CD₃,? C(9)? D? , C(6,9)? D₂? , and iso-FMN² have made it possible to unequivocally assign the ENDOR lines to C(8)? CH₃ and C(6)? H.     

Oligonucleotide Analogues with a Nucleobase‐Including Backbone:, Part 6, 2‐Deoxy‐D‐erythrose‐Derived Phosphoramidites: Synthesis and Incorporation into 14‐Mer DNA Strands

Two modified DNA 14‐mers have been prepared, containing either a 2‐deoxy‐D ‐erythrose‐derived adenosine analogue carrying a C(8)−CH₂O group (deA*), or a 2‐deoxy‐D ‐erythrose‐derived uridine analogue, possessing a C(6)−CH₂O group (deU*). These nucleosides are linked via a phosphinato group between O−C(3′) (deA* and deU*) and O−C(5′) of one neighbouring nucleotide, and between C(8)−CH₂O (deA*), or C(6)−CH₂O (deU*) and O−C(3′) of the second neighbour. N⁶‐Benzoyl‐9‐(β‐D ‐erythrofuranosyl)adenine ( 3 ) and 1‐(β‐D ‐erythrofuranosyl)uracil ( 4 ) were prepared from D ‐glucose, deoxygenated at C(2′), and converted into the required phosphoramidites 1 and 2 . The modified tetradecamers 31 and 32 were prepared by solid‐phase synthesis. Pairing studies show a decrease in the melting temperature of 7 to 8 degrees for the duplexes 31 ⋅ 30 and 32 ⋅ 29 , as compared to the unmodified DNA duplex 29 ⋅ 30 . A comparison with the pairing properties of tetradecamers similarly incorporating deoxyribose‐ instead of the deoxyerythrose‐derived nucleotides evidences that the CH₂OH substituent at C(4′) has no significant effect on the pairing.     

Solid‐State Structural Transformations and Photoreactivity of 1D‐Ladder Coordination Polymers of PbII

An attempt has been made to design double‐stranded ladder‐like coordination polymers (CPs) of hemidirected Pb^II. Four CPs, [Pb(μ‐bpe)(O₂C‐C₆H₅)₂] ? 2H₂O ( 1 ), [Pb₂(μ‐bpe)₂(μ‐O₂C‐C₆H₅)₂(O₂C‐C₆H₅)₂] ( 2 ), [Pb₂(μ‐bpe)₂(μ‐O₂C‐p‐Tol)₂(O₂C‐p‐Tol)₂] ? 1.5 H₂O ( 3 ) and [Pb₂(μ‐bpe)₂(μ‐O₂C‐m‐Tol)₂(O₂C‐m‐Tol)₂] ( 4 ) (bpe=1,2‐bis(4′‐pyridyl)ethylene), have been synthesised and investigated for their solid‐state photoreactivity. CPs 2 – 4 , having a parallel orientation of bpe molecules in their ladder structures and being bridged by carboxylates, were found to be photoreactive, whereas CP 1 is a linear one‐dimensional (1D) CP with guest water molecules aggregating to form a hydrogen‐bonded 1D structure. The linear strands of 1 were found to pair up upon eliminating lattice water molecules by heating, which led to the solid‐state structural transformation of photostable linear 1D CP 1 into photoreactive ladder CP 2 . In the construction of the double‐stranded ladder‐like structures, the parallel alignment of C?C bonds in 2 – 4 is dictated by the chelating and μ₂‐η²:η¹ bridging modes of the benzoate and toluate ligands. The role of solvents in the formation of such double‐stranded ladder‐like structures has also been investigated. A single‐crystal‐to‐single‐crystal transformation occurred when 4 was irradiated under UV light to form [Pb₂(rctt‐tpcb)(μ‐O₂C‐m‐Tol)₂(O₂C‐m‐Tol)₂] ( 5 ).     

Online H/D exchange liquid chromatography as a support for the mass spectrometric identification of the oxidation products of melatonin

The hydrogen–deuterium exchange of protonated melatonin and its in vitro oxidation end‐products have been examined by liquid chromatography coupled with ion‐trap mass spectrometry. Specific H/D scrambling of protons in the C2 and C4 positions of the indole ring during gas‐phase fragmentation process was observed for both melatonin and its oxidation products. Collision‐induced dissociation spectra showed losses of variably deuterated NH₃, H₂O and CH₃CONH₂. In addition, a similar H/D scrambling behaviour was observed for the oxidation products, obtained from the opening of the indole ring by oxidative attack. Fragmentation pathways are proposed and H/D scrambling has been employed as a fingerprint, allowing identification of N¹‐acetyl‐5‐methoxykynurenin (AMK), N¹‐acetyl‐N²‐formyl‐5‐methoxykynurenin (AFMK), dehydro‐AFMK and hydroxymelatonin as the oxidation products of melatonin in vitro. Copyright © 2008 John Wiley & Sons, Ltd.     

Phase equilibria in water-protein-polysaccharide systems

Summary Phase separation and thermodynamic stability of water (W) — casein (C) — neutral polysaccharide (NPS) systems have been studied. Dextrans of different molecular weights D40, D150, D500 and D2000 (10^–3 M _w =40, 150, 500, 2000), ficoll (10^–3 M _w =400) and amylopectin (10-^–6 M _w = 38) have been used as neutral polysaccharides. Phase diagrams of W-C-NPS systems, as well as their effect on the thermodynamic stability of the molecular weight and structural features of polysaccharides, low-molecular salts, pH and temperature have been considered. There has been shown the similarity of conditions under which the stability of W-C-NPS systems is disturbed, resulting in their separation, as well as conditions favorable to self-association of casein. A decrease in the pH value, an increase in the ionic strength and a rise in temperature are favorable both to self-association of casein and separation of W-C-NPS systems. Proceeding from this fact and from the results obtained earlier for W-C-acidic polysaccharide and W-albumin-D-glucan systems, a conclusion is drawn as to the common nature of the relationship between self-association of polymers and their compatibility. At constant temperature and pH, the stability limit of W-C-NPS systems is determined by the concentrations of polymers (w ₂ andw ₃) and salt (C₄). The totality of cloud points C ₄ ^* (pH) at givenw ₂ andw ₃ being considered as the stability limit. It is also shown that the relationship C ₄ ^* (pH) is an increasing function within the range of pH values from 6.5 to 11.5 and in all cases where lim C ₄ ^* (pH)=0. The sequence of values 947-1PHPH IEP C ₄ ^* is determined by the nature of the low-molecular salt (Na₂SO₄ NaCl KSCN) and the specific nature of the polysaccharides (D2000 amylopectin < D 150 < ficoll < D 40).W-C-NPS-NaCl have been found to possess a lower critical point in a system of coordinates: temperature-composition. W-C-NPS-urea (6M) systems feature, in a system of coordinates: pH-polymer concentration, two areas of separation, overlapping at sufficiently high total concentrations. This fact is indicative of the specific nature of interaction of casein macromolecules capable of association near the isoelectric point due to interaction of charge fluctuations and, in the acid region, due to interaction of non-ionized carboxyl groups. The obtained results are discussed with the stability limit being expressed in terms of second virial coefficients.With 13 figures and 2 tables     

The glycosides of the leaves from Isoplexis isabelliana (Webb) Masf

The isolation, characterisation and chemical investigation of the cardiac glycosides of the dried leaves of Isoplexis isabelliana (WEBB ) MASF . are described. 7 glucosides B, D, E, J (monoside), K, M, and 1 (monoside) could be obtained in homogenous form, 3 others were mixtures (“A” = A₁ + A₂, “C” = C₁ + C₂, and “G” = G + K). The substances B (gluco-evatromonoside), D (cheiroside A), E (digitoxigenin-glucosido-6-deoxyglucoside), J (digitoxigenin glucoside), and M (digitalinum verum) could be identified with known substances. The new glycosides are derived from 3 genins: digitoxigenin, uzarigenin, and xysmalogenin, which are directly bound to one of the following sugars: 6-deoxyglucose, 2-O-acetyl-6-deoxy-D -glucose, 2,6-dideoxy-D -arabinohexose (= D -canarose), and 2,6-dideoxy-D -ribohexose (= D -digitoxose), terminated by a glucose unit. –Canarobiose, a new crystalline disaccharide of D -glucose and D -canarose, has also been obtained. –Apart from these cardiac glycosides 3 C₂₁-steroids have been isolated (in addition to the 2 known genins γ-digiprogenin and purpnigenin), and their structures elucidated. The presence of 2 sapogenins has been detected.     

Cationic ring‐opening polymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐allyl‐β‐D‐glucopyranose as a convenient synthesis of dextran

For the convenient synthesis of (1→6)‐α‐D ‐glucopyranan, i. e., dextran ( 4 ), ring‐opening polymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐allyl‐β‐D ‐glucopyranose ( 1 ) has been carried out using BF₃·OEt₂. With a ratio of [BF₃·OEt₂]/[ 1 ] = 0.5 at 0 °C for 140 h, the yield and M_n of the obtained polymer are 84.0% and 21 700, respectively. The polymer consists of (1→6)‐α‐linked 2,3,4‐tri‐O‐allyl‐D ‐glucopyranose ( 2 ) which is similar to the results for the cationic ring‐opening polymerization of 1,6‐anhydro‐2,3,4‐tri‐O‐methyl‐β‐D ‐glucopyranose and 1,6‐anhydro‐2,3,4‐tri‐O‐ethyl‐β‐D ‐glucopyranose. Polymer 2 was isomerized using tris(triphenylphosphine)‐chlororhodium as the catalyst in toluene/ethanol/water to yield polymeric 2,3,4‐tri‐O‐propenyl‐(1→6)‐α‐D ‐glucopyranan ( 3 ). Deprotection of the propenyl ether linkage of 3 was then performed using hydrochloric acid in acetone to give 4 .     

Lanthanide-Ion Complexation by D-Glucuronic and D-Galacturonic Acids

To assess the potential of naturally occurring substances in the treatment of heavy-metal intoxication, the interaction between D -galacturonic and D -glucuronic acids with several trivalent lanthanide ions has been studied in aqueous solutions by means of a spectrophotometric method (27°; 0.1M NaClO₄; pH 4.0). Values for the overall stability constants for [LnL] and [LnL₂] (Ln = La, Ce, Pr, Nd, Gd, or Lu) complexes are presented and discussed. The interpretation of the data shows that, similarly to acetates, the COOH group coordinates metal ions in both [LnL] and [LnL₂] complexes. The 1:1 complexation is supplemented by the ring C(5)? O-atom. Moreover, the C(4)? O-atom seems to play an important role in the steric hindrance of the chelating ligand molecules.     

Structural,Thermal, and Electronic Properties of Two-Dimensional Gallium Oxide (β-Ga2O3) from First-Principles Design

Two-dimensional (2D) materials with exotic electronic, optical and mechanical properties have attracted tremendous attention in the last two decades, due to their potential applications in electronics, energy storage and conversion technologies. However, only a few dozen 2D materials have been successfully synthesized or exfoliated. Motivated by the recent discovery of 2D gallenene, we have explored new 2D allotropes of β-Ga₂O₃, an emerging wide-band gap transparent conductive oxide (TCO) with a wide range of semiconducting applications. All the possible 2D allotropes of β-Ga₂O₃ with high energetic stability have been predicted using particle swarm optimization, combined with density functional theory calculations. The structural and dynamical stability of the predicted 2D allotropes has been analyzed. Although β-Ga₂O₃ is not a van der Waals material, results predict that one or two allotropes of β-Ga₂O₃ are stable. In addition, the accurate band structures of these 2D semiconducting oxides have been calculated using both the GGA and LDA-1/2 approach. Remarkably, monolayer Ga₂O₃(100) has a larger indirect band gap of 4 eV, demonstrating a new avenue for the discovery of 2D β-Ga₂O₃ based nano-devices with enhanced electronic properties.     

Two‐Dimensional Semiconductors Grown by Chemical Vapor Transport

Developing controlled approaches for synthesizing high‐quality two‐dimensional (2D) semiconductors is essential for their practical applications in novel electronics. The application of chemical vapor transport (CVT), an old single‐crystal growth technique, has been extended from growing 3D crystals to synthesizing 2D atomic layers by tuning the growth kinetics. Both single crystalline individual flakes and continuous films of 1 L MoS₂ were successfully obtained with CVT approach at low growth temperatures of 300–600 °C. The obtained 1 L MoS₂ exhibits high crystallinity and comparable mobility to mechanically exfoliated samples, as confirmed by both atomic resolution microscopic imaging and electrical transport measurements. Besides MoS₂, this method was also used in the growth of 2D WS₂, MoSe₂, Mo_x W_1−x S₂ alloys, and ReS₂, thus opening up a new way for the controlled synthesis of various 2D semiconductors.     

Novel and Stereospecific Synthesis of (2S)‐3‐(2,4,5‐Trifluorophenyl)propane‐1,2‐diol from D‐Mannitol

A stereospecific synthesis of (2S)‐3‐(2,4,5‐trifluorophenyl)propane‐1,2‐diol from D ‐mannitol has been developed. The reaction of 2,3‐O‐isopropylidene‐D ‐glyceraldehyde with 2,4,5‐trifluorophenylmagnesium bromide gave [(4R)‐2,2‐dimethyl‐1,3‐dioxolan‐4‐yl](2,4,5‐trifluorophenyl)methanol in 65% yield as a mixture of diastereoisomers (1 : 1). The Ph₃P catalyzed reaction of the latter with C₂Cl₆ followed by reduction with Pd/C‐catalyzed hydrogenation gave (2S)‐3‐(2,4,5‐trifluorophenyl)propane‐1,2‐diol with >99% ee and 65% yield.     

The Crystal and Molecular Structure of 3-Oxo-17β-acetoxy-Δ4-14α-methyl-8α, 9β, 10α, 13α-estrene

The crystal and molecular structure of 3-oxo-17β-acetoxy-Δ⁴-14α-methyl-8α, 9β, 10α, 13α-estrene, C₂₁H₃₀O₃, has been determined by X-ray diffraction analysis. The crystals belong to the orthorhombic space group P2₁2₁2₁, with the cell dimensions a = 12.093 Å, b = 19.667 Å, c = 7.746 Å; Z = 4. Intensity data were collected at room temperature with an automatic four-circle diffractometer. The structure was solved by direct methods and the parameters were refined by least-squares analysis. All the hydrogen atoms were included in the refinement. The final R value was 0.038 for 1413 observed reflections. The conformation of ring A is intermediate between a half-chair and a 1, 2-diplanar form. The hydrogens at C(9) and C(10) are anti, the B/C ring junction is trans, and rings B and C adopt chair conformations. Ring D is cis fused and is halfway between C₂ and C_s forms.