Total synthesis of maremycins A,B, C1/C2, D1, and D2

The total synthesis of maremycins A, B, C₁/C₂, D₁, and D₂ is achieved starting from the natural amino acids l-isoleucine and S-methyl-l-cysteine, in which the total synthesis of maremycins B, C₁/C₂, and D₂ is accomplished for the first time. The synthesis features a position-selective intramolecular bromination process for the synthesis of key chiral building block, a Pd-catalyzed indole synthesis for the preparation of (2S,3S)-β-methyltryptophan and hydroxylation of oxindoles by molecular oxygen. In addition, the protocol for conversion of maremycins A and B to maremycins C and D was improved.     

Determination of vitamins A,B1, B2, D3 and C by densitometry of thin-layer chromatograms

Summary A method for densitometric determination of vitamins A, B₁, B₂, D₃, and C separated by t. l. c. is described. A silica gel layer is used with a solvent system of acetone-methanol-benzene (128). The spots are evaluated by direct densitometric light emission measurements. Preliminary separation of the vitamins one from another or from other pharmaceuticals is not necessary. The accuracy of the method is about 6%. The accuracy for vitamin A is up to 12%.

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Zusammenfassung Ein Verfahren zur Bestimmung der dünnschichtchromatographisch getrennten Vitamine A, B₁, B₂, D₃ und C wurde beschrieben. Dazu dient eine Kieselgelschichte mit Aceton Methanol Benzol (128) als Lösungsmittel. Die Flecken werden densitometrisch gemessen. Eine vorhergehende Trennung der einzelnen Vitamine voneinander bzw. von anderen pharmazeutischen Begleitstoffen ist nicht nötig. Die Methode ist auf etwa 6% genau, für Vitamin A auf 12%.

     

Superconductivity in the intermetallic borocarbides YPd2B2C,YPt2B2C and LaPt2B2C

We report a detailed study of the thermodynamic properties of the conventional phonon-mediated superconductors YPd₂B₂C, YPt₂B₂C and LaPt₂B₂C. Our calculations conducted within the framework of the Migdal-Eliashberg formalism show that the experimental values of the critical temperature cannot be properly reproduced using commonly accepted value of Coulomb pseudopotential. Moreover, we proved that the values of universal ratios of conventional superconductivity appearing in the Bardeen-Copper-Schrieffer (BCS) theory are inconsistent with our results obtained from the investigated borocarbides. The observed differences are connected with the strong/medium-coupling and retardation effects existing in the studied systems.     

Photoionization and photodissociation dynamics of the B 1sigmau + and C 1Piu states of H2 and D2

The photoionization and photodissociation dynamics of H(2) and D(2) in selected rovibrational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states have been investigated by velocity map ion imaging. The selected rotational levels of the B (1)Sigma(u) (+) and C (1)Pi(u) states are prepared by three-photon excitation from the ground state. The absorption of fourth photon results in photoionization to produce H(2)(+) X (2)Sigma(g)(+) or photodissociation to produce a ground-state H(1s) atom and an excited H atom with n >or= 2. The H(2) (+) ion can be photodissociated by absorption of a fifth photon. The resulting H(+) or D(+) ion images provide information on the vibrational state dependence of the photodissociation angular distribution of the molecular ion. The excited H(n >or= 2) atoms produced by the neutral dissociation process can also be ionized by the absorption of a fifth photon. The resulting ion images provide insight into the excited state branching ratios and angular distributions of the neutral photodissociation process. While the experimental ion images contain information on both the ionic and neutral processes, these can be separated based on constraints imposed on the fragment translational energies. The angular distribution of the rings in the ion images indicates that the neutral dissociation of molecular hydrogen and its isotopes is quite complex, and involves coupling to both doubly excited electronic states and the dissociation continua of singly excited Rydberg states.     

The total synthesis of coleophomones B, C, and D

Members of the coleophomone family of natural products all possess several intriguing and challenging architectural features, as well as exhibit unusual biological activity. They, therefore, constitute attractive targets for synthesis. In this Article, we describe the total synthesis of coleophomones B (2), C (3), and D (4). The highly strained and congested 11-membered macrocycle of coleophomones B (2) and C (3) was constructed using an impressive olefin metathesis reaction. Furthermore, both of the requisite geometric isomers of the Delta(16,17) within the macrocycle could be accessed from a common precursor, facilitating a divergence that lent the coleophomone B (2)/C (3) synthesis an unusually high degree of efficiency. The synthesis of coleophomone D (4) confirmed that it exists as a dynamic mixture of isomeric forms with a different aromatic substitution pattern from the other family members.     

Planar D 2h B26H8, D 2h B26H8 2+, and C 2h B26H6: Building Blocks of Stable Boron Sheets with Twin-Hexagonal Holes

The most stable mono-layer boron sheets were predicted to have both the isolated hexagonal hole and the twin-hexagonal hole. Previous investigations indicate that planar B₁₈H _n ^q (n = 3–6, q = n ? 4) are the building blocks of boron sheets with isolated hexagonal holes. Extensive DFT investigations performed in this work show that D _2h B₂₆H₈, D _2h B₂₆H₈ ²⁺, and C ₂ B₂₆H₆, may serve as the building blocks of boron sheets with twin-hexagonal holes. These bicyclic clusters possess planar or quasi-planar geometries at B3LYP/6-311+G(d,p) level, with 16, 14, and 14 delocalized π electrons, respectively. Detailed analyses indicate that they are overall aromatic in nature, with the formation of islands of both σ and π aromaticity. They are analogous to D _2h C₁₆H₁₄ and D _2h C₁₆H₁₄ ²⁺ in π bonding patterns, respectively, but fundamentally different from the latter in σ-bonding. Remarkably, all of them appear to be energetically the lowest-lying isomers obtained, which are promising targets for future gas phase syntheses. These hydroboron clusters, together with B₁₈H _n ^q clusters, establish the molecular basis for modeling the short-range structures, nucleation, and growth processes of monolayer boron sheets. The results obtained in this work enrich the chemistry of boron hydride clusters and expand the analogy relationship between hydroborons and hydrocarbons.     

地耳苯抗疟有效成份的研究—地耳苯系A、B、C、D的分离和结构

从地耳草中分离到四个间苯三酚衍生物, 定名为地耳草素A、B、C、D. 通过紫外、红外、核磁和质谱分析以及化学反应, 推定其结构分别为4、8、12和14. 4和8对鼠疟原虫有显著抑制作用.     

Concise syntheses of cystothiazoles A, C, D, and melithiazol B

A convergent synthesis of cystothiazoles C 1 and D 3 was achieved based on Julia coupling between the functionalized aldehyde 5b, corresponding to left half of the final molecule, and aryl sulfone 6 or 7, bearing a bithiazole moiety, corresponding to right half. Methylation of 1 and 3 gave cystothiazole A 2 and melithiazol B 4, respectively. The overall yield (5 steps from (2R,3S)-3-methylpent-4-yne-1,2-diol 10; 57%) of 5b via the present route was improved in comparison to that of the previously reported functionalized aldehyde 5a (7 steps from 10; 13%). By applying the modified Julia coupling method, selectivity (6E/6Z=20 : 1-26 : 1) toward the (6E)-form of the coupled products (15 or 19) against the corresponding (6Z)-form was improved in comparison to the Wittig method (6E/6Z=4 : 1-6.9 : 1).     

高效液相色谱法同时测定扁桃仁中的水溶性维生素C,B1,B2和B6

建立了用高效液相色谱同时测定扁桃仁中4种水溶性维生素C,B1,B2和B6的方法。以酸水解法处理样品,在Inertsil ODS-3柱(25 cm×4.6 mm i.d., 5.0 μm)上,以0.05 mol/L KH2PO4 (pH 6.0)-甲醇(体积比为70∶30)为流动相进行等度洗脱,检测波长265 nm条件下,对陕西蒲城扁桃仁中的水溶性维生素C,B1,B2和B6的含量进行了同时测定。4种水溶性维生素在其质量浓度为5.0~50 mg/L时线性良好(r=0.9990~0.9997);添加水平为5.0~20.0 mg/kg时,平均回收率为91.77%～99.30%,相对标准偏差(n=3)为0.31%～1.98%。测得陕西蒲城产扁桃仁中维生素B2的含量为4.27～4.53 mg/kg,维生素B1的含量为0.799～0.838 mg/kg,未检出维生素C和维生素B6。该法简便、快速,准确性和重现性均较好,对果仁中水溶性维生素的测定具有一定的参考价值。     

Synthesis of xyloketal A, B, C, D, and G analogues

A series of demethyl analogues of the natural products xyloketal A, B, C, D, and G have been prepared in a notably direct manner from 3-hydroxymethyl-2-methyl-4,5-dihydrofuran and a series of corresponding phenols. These syntheses featured a boron trifluoride diethyl etherate-promoted electrophilic aromatic substitution reaction as a key step. In the case of the synthesis of analogues of xyloketal A, the process was found to be highly efficient (up to 93% yield). The optimized isolated yield of these reaction products is remarkable in view of the fact that this transformation involves, minimally, six individual reactions. Moreover, these synthetic studies provide significant insight into the possible biogenic origin of the xyloketal natural products.     

Interaction of vitamins A,B1, C,B3 and D with zigzag and armchair boron nitride nanotubes: A DFT study

In this work, based on the density functional theory, the interaction of vitamins A, B1, C, B3 and D with (5, 5) armchair and (9, 0) zigzag single-walled boron nitride nanotubes (BNNTs) are studied. It is found that binding of vitamins A, B1, C, B3 and D with (9, 0) and (5, 5) BNNTs is thermodynamically favorable. Calculated solvation energies show that the solubility of functionalized (9, 0) BNNTs is higher than that of functionalized (5, 5) BNNT, and both dissolutions in water are spontaneous. The results showed that BNNTs can act as a suitable drug delivery vehicle for vitamins A, B1, C, B3 and D within biological systems. This study may provide a new insight into the development of the functionalized boron nitride nanotubes as drug delivery systems for virtual applications.     

Medicinal foodstuffs. XIX. Absolute stereostructures of canavalioside, a new Ent-kaurane-type diterpene glycoside, and gladiatosides A1, A2, A3, B1, B2, B3, C1, and C2, new acylated flavonol glycosides, from sword bean, the seeds of Canavalia gladiata

A new ent-kaurane-type glycoside, canavalioside, and eight new acylated flavonol glycosides, gladiatosides A1, A2, A3, B1, B2, B3, C1, and C2, were isolated from the seed of Canavalia gladiata together with robinin, kaempferol 3-O-beta-D-galactopyranosyl-7-O-alpha-L-rhamnopyranoside, and kaikasaponin III. The absolute stereostructures of canavalioside and gladiatosides A1, A2, B1, B2, B3, C1, and C2 were elucidated on the basis of chemical and physicochemical evidence.