Dendritic supports in organic synthesis

An overview is presented of the recent developments in the use of dendritic supports in organic synthesis. Examples are presented of the application of dendritic supports in both liquid- and solid-phase organic synthesis. In liquid-phase synthesis, soluble dendrimers are used as the substrate support, while in solid-phase synthesis, 'dendronized' insoluble resins are used for this purpose. Selected examples of the synthesis of compound libraries on dendritic supports via combinatorial techniques are discussed.     

Combinatorial solid phase peptide synthesis and bioassays

Solid phase peptide synthesis method, which was introduced by Merrifield in 1963, has spawned the concept of combinatorial chemistry. In this review, we summarize the present technologies of solid phase peptide synthesis (SPPS) that are related to combinatorial chemistry. The conventional methods of peptide library synthesis on polymer support are parallel synthesis, split and mix synthesis and reagent mixture synthesis. Combining surface chemistry with the recent technology of microelectronic semiconductor fabrication system, the peptide microarray synthesis methods on a planar solid support are developed, which leads to spatially addressable peptide library. There are two kinds of peptide microarray synthesis methodologies: pre-synthesized peptide immobilization onto a glass or membrane substrate and in situ peptide synthesis by a photolithography or the SPOT method. This review also discusses the application of peptide libraries for high-throughput bioassays, for example, peptide ligand screening for antibody or cell signaling, enzyme substrate and inhibitor screening as well as other applications.     

多组分反应在吡咯衍生物合成中的应用进展

多组分反应(Multicomponent Coupling Reactions,MCRs)是将三种或三种以上的相对简单的原料加入"一锅煮"反应中,不经过中间体分离而直接得到结构复杂的分子的方法。具有操作简单、原料易得、环境友好等优点。多组分反应发展至今,已经在包括药物合成的多个领域中起到了重要作用。吡咯衍生物作为一类在自然界中广泛分布、有着重要生物医药价值和材料科学价值的重要化合物,其合成方法一直是有机合成研究中的热点之一。近年来用于合成吡咯衍生物的多组分反应也不断地被报道。多组分反应能够很好地解决传统吡咯合成路线中取代基引入的问题并能提高反应收率,为吡咯衍生物的合成与研究带来便利。本文从合成方法上概述了近年来多组分反应在吡咯合成中的应用,为合成已有吡咯衍生物和探寻全新结构的吡咯衍生物提供合成方法上的新思路。     

Seaweeds: A resource for marine bionanotechnology

Marine bionanotechnology is one of the most promising areas of research in modern science and technology. Although there are multitude methods for the synthesis of nanoparticles (NPs), there is an increasing attention in developing high-yield, low-cost, non-toxic and eco-friendly procedures. The vital advantages of greener synthesis are cost-effective, reduced usage of toxic chemicals and abundant availability of resources. During the last ten years, there have been many biological entities used to elevate novel, greener and affordable methods for the metal NPs synthesis. Rate of synthesis and stability are higher for plant material mediated NPs. However, in comparison with terrestrial resources, marine resources have not been fully explored for synthesis of noble metal NPs. Our present review is designed to speculate the importance of usage of vast marine resources and its mediated NPs synthesis, in particular seaweed-mediated NPs synthesis to overcome the limitations involved in physical and chemical methods. Finally, recent advancements in greener synthesis of metal NPs, their size, distribution, morphology and applications such as antimicrobial, antifouling and anticancer potentials are briefly described along with portraying the prospective scope of research in this field without any negative impact on the environment.     

A review on the biosynthesis of metallic nanoparticles (gold and silver) using bio-components of microalgae: Formation mechanism and applications

The synthesis of nanoparticles (NP) using algae has been underexploited and even unexplored. In recent times, there are few reports on the synthesis of NP using algae, which are being used as a bio-factory for the synthesis. Moreover, the algae are a renewable source, so that it could be effectively explored in the green synthesis of NP. Hence, this review reports on the biosynthesis of NP especially gold and silver NP using algae. The most widely reported NP from algae are silver and gold than any other metallic NP, which might be due to their enormous biomedical field applications. The NP synthesized by this method is mainly in spherical shape; the reports are revealing the fact that the cell free extracts are highly exploited for the synthesis than the biomass, which is associated with the problem of recovering the particles. Besides, mechanism involving in the reduction and stabilization is well demonstrated to deepen the knowledge towards enhancement possibilities for the synthesis and applications.     

PHA stimulation of human lymphocytes during amino acid deprivation. Protein,RNA and DNA synthesis

Resting lymphocytes are in the G₀ phase of the cell cycle. Upon activation by PHA, they progress into G₁ with accompanying increased protein and RNA synthesis, initiate DNA synthesis and divide. We have studied the kinetics of inhibition of macromolecular synthesis during activation in the absence of single amino acids. Three types of kinetics are observed. In the absence of tryptophan or isoleucine, stimulated lymphocytes show a normal increase in protein and RNA synthesis during the first 30 hours of stimulation, initiate DNA synthesis but are subsequently inhibited. In phenylalanine-deficient medium, no DNA synthesis occurs in spite of a slight increase in protein synthesis. No increase in macromolecular synthesis is observed in medium lacking any one of the other essential amino acids (eg: lysine). Our results indicate that the kinetics of macromolecular synthesis in tryptophan-deficient medium is the result of a limited reserve of protein-bound tryptophan which becomes exhausted after 30 hours. On the other hand, delayed inhibition of synthesis in isoleucine-deficient medium probably reflects an initially low requirement for this amino acid followed by inhibition of the synthesis of isoleucine-rich proteins involved in some late event of stimulation. Partial deprivation of lysine results in kinetics of protein synthesis similar to that in tryptophan- or isoleucine-deficient media. The results indicate that the kinetics of macromolecular synthesis during activation of lymphocytes in the absence of an essential amino acid is a function of the quantitative requirement for that amino acid, at a given time during stimulation. Upon replacement of lysine, lymphocytes inhibited by lysine deficiency begin RNA and protein synthesis immediately and at a rate faster than that of unstimulated cultures to which PHA is added. They also initiate DNA synthesis earlier and therefore, are closer to the S phase than resting lymphocytes. It is concluded that lymphocytes stimulated in the absence of lysine are activated even though no overall increase in macromolecular synthesis is observed. Furthermore, the kinetics of DNA synthesis following reversal of inhibition by phenylalanine suggests that lymphocytes stimulated during phenylalanine deprivation become arrested at most six hours before S. These results indicate that amino acid deficiencies lead to arrest of activated lymphocytes at various stages of stimulation, depending on how stringent these deficiencies are.     

DNA合成技术及应用

DNA从头合成技术是指以寡核苷酸链为起始的合成DNA片段的技术,其不断进步是合成生物学快速发展的基石之一。常规使用的连接介导的DNA合成技术和PCR介导的DNA合成技术日益成熟,精确合成长度已经达到0．5—1kb。微阵列介导的DNA合成技术不断发展,其低成本、高通量的特点吸引了人们的注意;而酵母体内DNA合成技术的成功探索也为体外DNA合成提供了一种补偿方法。DNA合成在优化密码子用于异源表达、构建异源代谢途径、合成人工基因组以及合成减毒病毒用于疫苗研制等方面有广泛应用。综述了DNA从头合成技术的研究进展,并介绍了DNA合成的前沿应用。     

A novel, cellulose synthesis inhibitory action of ancymidol impairs plant cell expansion

The co-ordination of cell wall synthesis with plant cell expansion is an important topic of contemporary plant biology research. In studies of cell wall synthesis pathways, cellulose synthesis inhibitors are broadly used. It is demonstrated here that ancymidol, known as a plant growth retardant primarily affecting gibberellin biosynthesis, is also capable of inhibiting cellulose synthesis. Its ability to inhibit cellulose synthesis is not related to its anti-gibberellin action and possesses some unique features never previously observed when conventional cellulose synthesis inhibitors were used. It is suggested that ancymidol targets the cell wall synthesis pathway at a regulatory step where cell wall synthesis and cell expansion are coupled. The elucidation of the ancymidol target in plant cells could potentially contribute to our understanding of cell wall synthesis and cell expansion control.     

Protein synthesis in homologous and heterologous cell-free systems from chick embryo connective tissues.

Two homologous systems for cell-free protein synthesis from chick embryo connective tissues are described. Both the skin polysomes and the wing-leg polysomes are active in collagen synthesis, but they have different requirements for optimum protein synthesis. Protein synthesis was not dependent on tissue-specific factors, since heterologous preparations of supernatant enzymes or initiation factors were able to stimulate maximum protein synthesis with each fraction of polysomes.     

Patterns of protein synthesis in livers of Xenopus laevis during metamorphosis: Effects of estrogen in normal and thyrostatic animals

Two-dimensional gel electrophoresis has been used to analyse protein synthesis in the livers of Xenopus laevis larvae during metamorphosis. The patterns found at different developmental stages have been characterised and compared to those found in developmentally static tadpoles and estrogen-treated tadpoles. The results suggest that the majority of proteins synthesized by the larval liver during metamorphosis can be divided equally into three main categories: those which are synthesized continuously, those whose synthesis is lost, and those whose synthesis is gained during development. The synthesis of proteins tends to be lost earlier in metamorphosis than it is gained. The pattern of liver protein synthesis in thyrostatic animals is not characteristic of any single stage of normal development, and displays features characteristic of many different stages. About half the changes in protein synthesis which occur during normal metamorphosis are dependent upon it. All the stages examined are responsive to estrogen, and each has a characteristic response. Half of the estrogen-induced changes in protein synthesis are independent of metamorphosis, while the other half require metamorphosis.     

Histone synthesis is not coupled to the replication of adenovirus DNA

Histone synthesis decreases approximately in parallel with the decrease in cellular DNA synthesis when KB cell monolayers are productively infected with adenovirus type 2 and does not occur in coordination with the later surge of viral DNA synthesis. The synthesis of histones is not, therefore, required for all replicative DNA synthesis in the nuclei of mammalian cells.     

Timing of ethylene and polygalacturonase synthesis in relation to the control of tomato fruit ripening

A critical role in the initiation of ripening has been proposed for pectolytic enzymes which are known to be involved in fruit softening. The hypothesis that tomato (Lycopersicon esculentum Mill.) ripening is controlled by the initial synthesis of the cell-wall-degrading enzyme polygalacturonase (EC 3.2.1.15), which subsequently liberates cell-wall-bound enzymes responsible for the initiation of ethylene synthesis and other ripening events, has been examined. A study of kinetics of ethylene evolution and polygalacturonase synthesis by individual fruits in a ripening series, employing an immunological method and protein purification to identify and measure polygalacturonase synthesis, showed that ethylene evolution preceded polygalacturonase synthesis by 20h. Exogenous ethylene stimulated the synthesis of polygalacturonase and other ripening events, when applied to mature green fruit, whereas the maintenance of fruits in a low ethylene environment delayed ripening and polygalacturonase synthesis. It is concluded that enhanced natural ethylene synthesis occurs prior to polygalacturonase production and that ethylene is responsible for triggering polygalacturonase synthesis indirectly. Possible mechanisms for ethylene action are discussed.     

Kinetics of DNA and histone messenger RNA synthesis in CV-1 monkey kidney cells infected with simian virus 40.

Histone messenger RNA has been identified in CV-1 monkey kidney cells and its synthesis during the simian virus 40 (SV40) productive cycle has been correlated with the synthesis of cellular DNA and viral DNA. In cultures of CV-1 cells that have reached confluence, infection with SV40/5 (a high-yield clone of SV40) promotes an increase in the rate of cellular DNA synthesis followed by a decline. During this decline the rate of viral DNA synthesis continues to rise and eventually surpasses that of cellular DNA.The synthesis of histone mRNA rises concomitantly with the increase in the synthesis of cellular DNA. This occurs in a fashion similar to that observed when confluent CV-1 cultures are stimulated by the addition of fresh serum to the growth medium. However, whereas in cells stimulated with serum the synthesis of histone mRNA closely parallels that of cellular DNA, in cells infected with SV40, histone mRNA synthesis continues at a high rate even after the decline of cellular DNA synthesis. The rate of histone mRNA synthesis thus appears to he coupled to the total (cellular plus viral) DNA synthesis and not to the synthesis of the host DNA alone. The high rate of synthesis of the F1 histone at late times after infection suggests that histone genes are transcribed co-ordinately.     

Deficient heme synthesis as the cause of noninducibility of hemoglobin synthesis in a Friend erythroleukemia cell line.

Friend cells of the line Fw are not induced to accumulate substantial amounts of hemoglobin and to become benzidine-positive when treated with butyric acid or other inducers, except in the presence of exogenous hemin. The cells are shown to have a deficiency in heme synthesis since they require exogenous hemin during the period of maximal hemoglobin synthesis; since endogenous heme synthesis cannot be induced to the level found in normal inducible Friend cells, even after hemoglobin synthesis has been induced by hemin and butyric acid and the hemin has then been withdrawn; since they are not inducible for ferrochelatase (heme synthetase) activity; and since they accumulate free globin chains after stimulation with butyric acid in the absence of hemlin. Comparison of globin synthesis and globin mRNA content of the cells shows that globin synthesis is not controlled by the hemin-controlled repressor of protein synthesis (HCR) nor by any specific translational control of globin synthesis by hemlin.     

DNA and protein synthesis in cultured lens epithelial cells. II. Activity of synthetic effectors]

Cultivated bovine lens epithelium cells are highly susceptible to inhibitors of DNA-, RNA- and protein synthesis. The strict correlation between inhibition by puromycin of protein and DNA synthesis suggests that, in the cell system investigated, protein synthesis is essential for DNA synthesis to occur. Studies with actinomycin D have shown that in cultivated lens epithelium cells, part of protein synthesis is accomplished through a relatively long-lived mRNA. In long-term cultivation experiments, no further stabilization of mRNA, which is typical of lens fibre cells, could be demonstrated. There are indications that high doses of actinomycin D produce direct inhibition of DNA synthesis. By means of cytosine arabinoside a linear relationship was established between concentration of the effector and inhibition of DNA synthesis. Protein synthesis remains virtually unaffected even after high doses. The strong inhibition of DNA synthesis with protein synthesis continuing ("unbalanced growth") could not be utilized for the synchronization of lens epithelium cells, because it was only partly reversible after changing the medium and applying deoxycytidine.     

Bacteriophage phiX174 single-stranded viral DNA synthesis in temperature-sensitive dnaB and dna C mutants of Escherichia coli.

We asked if phiX174 single-stranded DNA synthesis could reinitiate at the nonpermissive temperature in dnaB and dnaC temperature-sensitive host mutants. The rates of single-stranded DNA synthesis were measured after the removal of chlorampheicol that had been added at various times after infection to specifically stop this stage of phiX174 DNA synthesis. Reinitiation was not defective in either mutant host. Our data suggested that the reinitiation of the single-stranded stage of phiX174 DNA synthesis in these experiments was analogous to the normal initiation of this stage of phiX174 DNA synthesis in infections without chloramphenicol. Assuming this to be the case, we conclude that the host cell dnaB and dnaC proteins are not essential for the normal initiation of the single-stranded synthesis stage of phiX174 DNA synthesis. In related experiments we observed that in the dnaC mutant host at the permissive temperature, phiX174 replicative form DNA synthesis continued at its initial rate even during the single-stranded DNA synthesis stage. This indicates that these two stages of phiX174 DNA synthesis are not necessarily mutually exclusive.     

Control of ribulose 1,5-bisphosphate carboxylase synthesis in the cotyledons of Citrullus lanatus

White light completely inhibits the germination of Citrullus lanatus (Thunb.) Matsumara & Nakai seeds. Under these conditions light does not induce ribulose bisphosphate carboxylase (Rubisco) synthesis in the cotyledons. Although the seeds apparently are capable of attaining sufficient levels of the far-red light absorbing form of phytochrome, Pfr, in the dark to permit germination this does not induce Rubisco synthesis. However, it appears that a substantial amount of synthesis of the small subunit (SSU) takes place in the dark. The synthesis of the two subunits is therefore not tightly coordinated in this tissue, and in none of the treatments were equimolar concentrations of the two subunits present in the cotyledons. However, if the seeds are allowed to start germination in the dark and are then transferred to continuous light, Rubisco synthesis is induced. This induction of Rubisco synthesis in the cotyledons is dependent on the presence of the elongating radicle. Kinetin induces synthesis of Rubisco in isolated cotyledons in both the light and the dark, while 2-chloroethanephosphonic acid (Ethrel) only restores the sensitivity towards light activation of Rubisco synthesis. Synthesis of Rubisco in isolated cotyledons in the presence of these two compounds differs from that of the intact tissue in that the synthesis of the SSU is stimulated more than the synthesis of the large subunit (LSU).