Roseophilin的合成研究进展

Roseophilin是一种从灰绿链霉菌中分离出来的、由一个十三元大环并一个杂环组成的具有抗肿瘤活性的新型抗生素的活性物质。Roseophilin独特的结构及活性引起了很多学者对其合成的兴趣。通过十三元大环和杂环合成Roseophilin,其中十三元大环的主要合成方法有末端双键的RCM关环、扩环、烷基化关环三种反应类型。     

Effect of the sequence of the introduction of foreign substances on the action of papain

Summary In general, aniline, aniline hydrochloride, aniline sulfate, and triethylamine act as inhibitors in the hydrolysis of casein or of a suspension of flour from grain of Cicer arietinum by means of papain. The order in which the enzyme and the substrate is added to the inhibitor often has a significant effect. As a rule, there is a greater retardation when the enzyme is added last to a complex of the substrate and the inhibitor.     

Prediction of the effects of imperfect construction of a QMS filter

Modelling techniques have previously predicted the observed behaviour of perfectly manufactured QMS mass filters. These methods are extended to examination of the behaviour of imperfect QMS filters; this examination considers the behaviour of QMS filters with one rod displaced radially inward as this is a simple manufacturing defect that arises when a rod does not fit correctly into the mounting.The results demonstrate the well known, but poorly documented property, that exchanging the connections of a poorly performing QMS device sometimes improves performance. This is shown to arise because only a displacement of a y-rod produces a large effect. The results also show that displacement of a y-rod may produce a spurious additional peak known as a precursor. More detailed investigation suggests that precursors are not separate peaks but are formed because a section of the main peak is removed causing an apparent double peak.Finally results confirm that adjustment of the voltage applied to a displaced rod can be used to significantly improve the QMS behaviour. A small change by a fraction alpha in the position of a single rod may be compensated by a change of 2 x alpha in the voltage applied to that rod.     

Influence of the stereochemistry of sugars on the selectivity of formation of carbohydrate-derived cyclopentadienyl and indenyl ligands

Interaction of lithium cyclopentadienide with a suitable partially protected alpha-D-allofuranose triflate, 4, epimer at C3 of glucose, gives as a major product, besides the expected glucose-cyclopentadiene, 5, a glucose-disubstituted cyclopentadiene, 6. This unprecedented behaviour, which does not occur with alpha-D-glucofuranose and other sugars, is tentatively explained by a complexation of LiCp and the oxygen atoms of the isopropylidene function of one molecule of 4 and one of 5, giving a termolecular structure as the result of a template effect. The results of other experiments, such as the use of MgCp2 in place of LiCp or the complexation of oxygen atoms by lithium triflate, which changed the selectivity of the reaction largely in favour of the monosubstitution product 5, support this hypothesis. When lithium indenide is reacted with 4, glucose-monosubstituted and glucose-disubstituted indenes, 8 and 9, respectively, are formed, and 9 is obtained with almost total diastereoselectivity. This result can also be rationalised by a stereoselective complexation of lithium, as shown by separate experiments and by molecular mechanics calculations. Methyltricarbonyl molybdenum(II) complexes have been synthesised and characterised from glucose-monosubstituted 5 and glucose-disubstituted 6 cyclopentadienes.     

Modification of the pitch of chiral nematic liquid crystals by means of photoisomerization of chiral dopants

New photoisomerizable chiral dopants have been studied. The dopants used were menthone derivatives, a chiral stilbene derivative and a nematic copolymer of a menthone derivative and a benzoyloxybenzonitrile derivative. NMR, HPLC and UV results showed that the E-Z-isomerization of all the compounds indicated proceeded rapidly upon UV exposure, without the formation of undesired by-products. Isomerization of the menthone derivatives, including the copolymer, induced a substantial decrease in the helical twisting power. The changes in helical twisting power induced by the isomerization of the chiral stilbene derivative were limited to a factor of 2. In mixtures of the photoisomerizable dopants with commercial dopants of opposite twisting senses and a nematic host mixture, the sign of the twisting sense could be reversed by illuminating the mixture with UV light. The viewing angle dependence of irradiated regions of a 90 -twisted nematic cell was rotated 90 with respect to the viewing angle dependence of the non-irradiated regions. It is expected that this approach may be useful in the preparation of dual domain TN cells with a reduced viewing angle dependence.     

Study of the mechanism of formation of transparent polyacrylonitrile

The kinetics of bulk polymerization of acrylonitrile, leading to a transparent polymer, was studied. The reaction was followed by a dilatometer specially designed for high degrees of conversion and for continuous supply of monomer during the reaction. The last stages of polymerization were followed by density determinations. It was found that the kinetic scheme did not show any irregularities, and that the major condition for obtaining a transparent polymer is a continuous supply of monomer to fill up the gaps formed by the contraction during the polymerization process.     

Reprint of: Synthesis of a tricyclic core of rameswaralide

A tricyclic core containing a 5,7-fused bicyclic unit of rameswaralide was prepared starting from a 1,6-enyne. The synthetic sequence involved (i) ruthenium-catalyzed [5+2]-cycloaddition of 1,6-enyne, (ii) an acyl radical based approach to construct the lactone, and (iii) a regioselective installation of the conjugated double bond by a concomitant sulfenylation-dehydrosulfenylation sequence.     

Method of computer-aided determination of the type of normal vibrations of polyatomic molecules

Correct assignment of calculated and experimental frequencies, as well as corservation of the initial assignment in case of a random coincidence of two frequencies during the solution of an inverse spectral problem, are important problems in spectroscopy of polyatomic molecules. Vibrations are classified according to their form, which is thought to be a more reliable basis for assignment than frequency. We offer a PC program to determine the type of vibrations according to their form (obtained by solving a direct vibrational problem) in a given system of vibrational basis set functions. Optimization of systems of basis set functions for molecules with six-membered rings is discussed. L. Ya. Karpov Physicochemical Scientific Research Institute. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 298–303, March–April, 1995. Translated by L. Smolina     

Synthesis of thermochromic formazans of a number of benzazoles

In a search for compounds that have thermochromic properties, a group of formazans that contain benzimidazolyl (benzothiazolyl), methyl (phenyl), and hydroxydinitrophenyl (anthraquinoyl) groups in the 1-, 3-, and 5-positions, respectively, were synthesized. Benzimidazolylformazans with a picramic acid residue in the 5-position have thermochromic properties.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 970–973, July, 1971.     

Regularities of binary condensation of vapors when one of them is undersaturated

Simple analytical expressions are derived for the stationary concentration of a binary solution in a markedly supercritical droplet growing exothermically in diffusion or free-molecular regimes in mixed vapors when one of condensing vapors is supersaturated and present in a small amount and another vapor is slightly undersaturated and present in a large amount. The condensation of sulfuric acid and water vapors on a droplet under the conditions of Earth atmosphere is considered as an example of practical importance. Under isothermic conditions, analytical expressions are obtained for the time of establishing a power law for variations in a droplet radius with time under the diffusion and free-molecular regimes of the droplet growth. The power laws are derived in an explicit form under these regimes, which describe the rapid establishment of a stationary concentration of a solution in a growing droplet.     

Effect of stress-jump condition on electrophoretic behavior of a spherical dispersion of soft particles

The electrophoresis of a concentrated dispersion of soft particles, where a particle comprises a rigid core and an ion-penetrable membrane layer, is modeled theoretically, taking the effect of double-layer polarization into account. In particular, the influence of a stress-jump condition of the flow field at the membrane layer-liquid interface on the electrophoretic mobility of a particle is investigated. The type of particles considered mimic biocolloids, such as cells and microorganisms, and inorganic colloids covered by an artificial polymer layer such as surfactant molecules. A unit cell model is adopted to simulate the present spherical dispersion, and the governing equations and the associated boundary conditions are solved by a pseudo-spectral method based on Chebyshev polynomials. We show that while the stress-jump condition, characterized by a stress-jump coefficient, can have a significant influence on the mobility of a particle, the associated flow field is not influenced appreciably. Also, the influence of the stress-jump condition on the mobility of a particle depends largely on the nature of the membrane layer, characterized by its friction coefficient.     

Synthesis of the glycosyl lactol moiety of halichoblelide

The enantioselective synthesis of the 2-deoxy-α-l-fucosyl lactol moiety of halichoblelide, a potent cytotoxin isolated from an actinomycete of marine origin, was achieved using a diastereoselective addition of a dithianyl anion to a chiral aldehyde intermediate and a stereoselective glycosidation of a hydroxy lactone intermediate derived from the addition product with a protected l-fucal as the key steps.     

Position of coordination of the lithium ion determines the regioselectivity of demethylations of 3,4-dimethoxymorphinans with L-selectride

[reaction: see text] L-Selectride is an efficient agent for the 3-O-demethylation of opioids and is known to cleave the least hindered methoxyl group in a molecule. The treatment of a 3,4-dimethoxymorphinan containing a 6-ketal with L-Selectride gave selective 4-O-demethylation, rather than cleavage of the less hindered 3-methoxyl. In contrast, a 3,4-dimethoxymorphinan lacking a 6-ketal gave selective 3-O-demethylation, suggesting that the regiochemistry of L-Selectride-mediated O-demethylation can be manipulated through altering the position of coordination of the lithium ion.     

Unprecedented Halogenation of Biginelli Compounds of Salicyldehyde

Unprecedented results are obtained from bromination of the normal/non-bridged and abnormal/bridged Biginelli compound of salicyldehyde. Bromination with 2,4,4,6-tetrabromocyclohexa-2,5-dienone yields a bridged monobromo-derivative and a bridged dibromo-derivative, respectively, whereas bromination with bromine and acetic acid gives a mixture of those two products in each case. Bromination with N-bromosuccinimide gives a third product, namely a tribromo-derivative, in addition to those two products. Iodination of both the substrates using iodine monochloride (Wijs solution) furnishes a bridged monoiodo-derivative only.     

Development of a general approach to the synthesis of a library of isoflavonoid derivatives

Isoflavonoids are a class of organic compounds that act primarily as antioxidants. They are produced almost exclusively by various members of the bean family including soybeans, tofu, peanuts, chick peas, and alfalfa. The antioxidant characteristics that isoflavonoids exhibit help hinder the progression of certain cancers, primarily breast, prostate, and colon cancer. We have developed a three-five step synthesis for obtaining a suite of isoflavonoid derivatives. The synthesis involves an enamine formation, a ring closure and halogenation, a Suzuki coupling, and finally a global deprotection to obtain the respective isoflavonoid derivatives.     

Non-Gaussian statistics of electrostatic fluctuations of hydration shells

This paper aims to understand the statistics of the electric field produced by water interfacing a non-polar solute of nanometer dimension. We study, by numerical simulations, the interface between SPC/E water and a Kihara solute, which is a hard-sphere core with a Lennard-Jones layer at its surface. The distribution of the interfacial electric field is monitored as a function of the magnitude of a point dipole placed close to the solute-water interface. The free energy surface as a function of the electric field projected on the dipole direction shows a cross-over with increasing dipole magnitude. While it is a single-well harmonic function at low dipole values, it becomes a double-well surface at intermediate dipole moment magnitudes, transforming into a single-well surface again, with a non-zero minimum position, at still higher dipoles. This transformation, reminiscent of a discontinuous phase transition in bulk materials, has a broad intermediate region where the interfacial waters fluctuate between the two minima. This region is characterized by intense field fluctuations, with non-Gaussian statistics and variance far exceeding expectations from the linear-response approximation. The excited state of the surface water is found to be lifted above the ground state by the energy required to break approximately two hydrogen bonds. This state is pulled down in energy by the external electric field of the solute dipole, making it readily accessible to thermal excitations. The excited state is a surface defect in the hydrogen-bond network, creating a stress in the nearby network, but otherwise relatively localized in the region closest to the solute dipole.     

Mechanism of formation of shish kebab structures

To describe the characteristic crystalline structure of polyolefins, Pennings first proposed a model consisting of a combination of an extended chain crystal (a “shish”) and folded chain crystals (“kebabs”). In Pennings' model the “shish” forms first during a crystallization process under stress and then later the “kebabs” overgrow this “shish” structure epitaxially. Because we had some doubts about such a mechanism, we undertook a series of experimental studies on linear polyethylene, particularly in regard to the crystallization process from a solution under shear. Our conclusion is that the crystals grow first by a screw dislocation mechanism, like whiskers, and then later these are deformed by the shear stress to form the shish kebab structures.     

The mechanism of reequilibration of solids in the presence of a fluid phase

The preservation of morphology (pseudomorphism) and crystal structure during the transformation of one solid phase to another is regularly used as a criterion for a solid-state mechanism, even when there is a fluid phase present. However, a coupled dissolution-reprecipitation mechanism also preserves the morphology and transfers crystallographic information from parent to product by epitaxial nucleation. The generation of porosity in the product phase is a necessary condition for such a mechanism as it allows fluid to maintain contact with a reaction interface which moves through the parent phase from the original surface. We propose that interface-coupled dissolution-reprecipitation is a general mechanism for reequilibration of solids in the presence of a fluid phase.     

Group of symmetry of the periodic system of chemical elements

The concurrence of the group of symmetry of the periodic system of elements with the group of dynamical symmetry of a hydrogenlike atom is employed in the theoretical investigation of atoms. The character of the degeneracy of the eigenvalues of a hydrogenlike atom Hamiltonian, without changing its eigenfunctions, was changed by introducing into this Hamiltonian a term which violates the symmetry in relation to transformations from the subgroup O(4) of the group SO(4, 2). In consequence, it was realized that such “reorganization” of the states of a hydrogenlike atom, which form a representation of the group SO(4, 2), effects the splitting of this representation into finite‐dimensional multiplets, first of which are in full agreement with the experimentally observable composition of electron shells of atoms, and retains the physical meaning of quantum numbers that define electron states. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 499–508, 1999