Nucleoside analogues have attracted much attention due to their potential biological activities. Amongst all synthetic nucleosides, C5-modified pyrimidines and C2- or C8-modified purines have been ...particularly studied. A large variety of palladium cross-coupling reactions, with a majority of them based on the Suzuki–Miyaura reaction, have been developed for preparing the desired nucleoside derivatives. Our objective is to focus this review on the Suzuki–Miyaura cross-coupling of nucleosides using methodologies compatible with green chemistry and sustainable development for one part and bioorthogonality for the other part, which means using aqueous medium and no protection/deprotection steps.
Sporopollenin is highly cross-linked polymer composed of carbon, hydrogen and oxygen that is extraordinarily stable and has been found chemically intact in sedimentary rocks some 500 million year ...old. It is the outer shell (exine) of plant spores and pollen and when extracted it is in the form of an empty exine or microcapsule. The exines resemble the spores and pollen from which they are extracted, in size and morphology. Also, from any one plant such characteristics are incredible uniform. The exines can be used is microcapsules or simply as micron-sized particles due to the variety of functional groups on their surfaces. The loading of the exine microcapsules into their cavities is via multi-directional nano-diameter sized channels. The exines can be filled with a variety of polar and non-polar materials. Such as enzymes can be encapsulated within the shells and still remain active. In vivo studies in humans have shown that an encapsulated active substance can have a substantially increased bioavailability than if it is taken alone. The sporopollenin exine surface possesses phenolic, alkane, alkene, ketone, lactone and carboxylic acid groups. Therefore it can be derivatised in a number of ways, which has given rise to its having been used for, such as, solid supported for peptide synthesis, catalysis and ion-exchange chromatography. Also, the presence of the phenolic groups on sporopollenin endows it with antioxidant activity.
Pollen grain and spore shells are natural microcapsules designed to protect the genetic material of the plant from external damage. The shell is made up of two layers, the inner layer (intine), made ...largely of cellulose, and the outer layer (exine), composed mainly of sporopollenin. The relative proportion of each varies according to the plant species. The structure of sporopollenin has not been fully characterised but different studies suggest the presence of conjugated phenols, which provide antioxidant properties to the microcapsule and UV (ultraviolet) protection to the material inside it. These microcapsule shells have many advantageous properties, such as homogeneity in size, resilience to both alkalis and acids, and the ability to withstand temperatures up to 250 °C. These hollow microcapsules have the ability to encapsulate and release actives in a controlled manner. Their mucoadhesion to intestinal tissues may contribute to the extended contact of the sporopollenin with the intestinal mucosa leading to an increased efficiency of delivery of nutraceuticals and drugs. The hollow microcapsules can be filled with a solution of the active or active in a liquid form by simply mixing both together, and in some cases operating a vacuum. The active payload can be released in the human body depending on pressure on the microcapsule, solubility and/or pH factors. Active release can be controlled by adding a coating on the shell, or co-encapsulation with the active inside the shell.
The purpose of this work is to prepare ionically cross-linked (with CaCl2) gellan particles with immobilized yeast cells for their use in repeated fermentation cycles of glucose. The study ...investigates the influence of ionic cross-linker concentration on the stability and physical properties of the particles obtained before extrusion and during time in the coagulation bath (the cross-linker solution with different CaCl2 concentrations). It was found that by increasing the amount of the cross-linker the degree of cross-linking in the spherical gellan matrix increases, having a direct influence on the particle morphology and swelling degree in water. These characteristics were found to be very important for diffusion of substrate, that is, the glucose, into the yeast immobilized cells and for the biocatalytic activity of the yeast immobilized cells in gellan particles. These results highlight the potential of these bioreactors to be used in repeated fermentation cycles (minimum 10) without reducing their biocatalytic activity and maintaining their productivity at similar parameters to those obtained in the free yeast fermentation. Encapsulation of Saccharomyces cerevisiae into the gellan gum beads plays a role in the effective application of immobilized yeast for the fermentation process.
Three families of mono‐substituted sucrose fatty acid esters were prepared by enzymatic and classical synthetic procedures, and their self‐assembly and self‐organizational properties were ...investigated by thermal polarised light microscopy, differential scanning calorimetry and X‐ray diffraction. The properties were evaluated as a function of the fatty acid chain length. For the lower homologues of the series columnar liquid‐crystalline stacking structures were found, whereas for the higher homologues, lamellar phases predominated. A model for the columnar stacking arrangement, consisting of a unique arrangement of the molecules which could lead to the creation of multiple internal ion channels between the hydrophobic interior and the hydrophilic exterior of the columns, is suggested.
Three families of monosubstituted sucrose fatty acid esters were prepared by enzymatic and classical synthetic procedures, and their self‐assembly and self‐organizational properties (see figure) were investigated by using thermal polarised light microscopy, differential scanning calorimetry and X‐ray diffraction.
Bredinin (4-carbamoyl-1-β-
d-ribofuranosylimidazolium-5-olate,
1) was synthesised by the formation of a malonamate from 2,3-isopropylidene-
d-ribofuranosylamine and ethyl malonyl chloride, followed ...by a sequence involving amination, via reduction of an oxime, heterocycle formation and then deprotection.
We report on the self‐organizing properties of sucrose esters that are di‐(1′,6′, 1′,6, and 6,6′)‐substituted with aliphatic chains of identical or different chain lengths and levels of saturation. ...For the materials possessing two saturated aliphatic chains, the compounds exhibited thermotropic lamellar smectic A phases. A remarkable new phase transition was observed for the di‐octadecanoyl homologue in which one smectic A phase transformed into another with a continuous change in layer spacing, but with a discontinuous change in the correlation length. The incorporation of long cis‐unsaturated chains led to increased cross‐sectional areas of the chains relative to the sucrose head groups and, hence, columnar phases were observed.
Smooth transition: The self‐organizing properties of a variety of disubstituted sucrose esters are reported (see structure). Materials with two saturated aliphatic chains exhibited thermotropic, lamellar smectic A phases. A remarkable new phase transition was observed for the di‐octadecanoyl homologue, in which one smectic A phase (see polarizing light microscopy image) transformed into another with a continuous change in layer spacing, but a discontinuous change in correlation length.
The synthesis of 2′,3′-didehydro-2′,3′-dideoxynucleosides having a branching group at either of the 2′- or 3′-positions other than a proton and branching groups at both of the 2′- and 3′-positions ...other than a proton is reviewed. The report contains 81 references.
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In this article we report on the syntheses, self-organizing properties, and structures of a variety of cerebrosides and related synthetic glycolipids. The thermotropic and lyotropic liquid ...crystalline properties of the materials were evaluated in detail. All of the families of materials studied exhibited columnar mesophases. In the dry state the aliphatic chains were found to be located on the exterior of the columns, whereas in the wet state the reverse was the case with the polar headgroups on the exterior. Thus, the aliphatic chains act almost like hydrocarbon solvents in the dry state.
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