Search

Using the palladium(II)-catalyzed oxidative cyclization of a diarylamine and the annulation of a dimethylpyran ring by Lewis acid promoted reaction with prenal as key steps, the total syntheses of the 6-oxygenated pyrano[3,2-a]carbazole alkaloids koenine and koenimbine, and of the 6,7-dioxygenated pyrano[3,2-a]carbazole alkaloids koenigine and koenigicine (koenimbidine, koenidine) were achieved. Moreover, these studies led to an improved synthetic route to the 2,6-dioxygenated carbazole alkaloid glycozolidol. Mukonicine, originally published as 6,8-dimethoxypyrano[3,2-a]carbazole, was found to be identical with koenigicine. [ABSTRACT FROM AUTHOR]

We describe efficient synthetic routes to murrayamine A (mukoenine C), O-methylmurrayamine A, mahanine, O-methylmahanine, and murrayamine D and the first total syntheses of murrayamine E, I, and K. Key steps are a palladium-catalyzed construction of the carbazole framework and an annulation of the pyran ring, which is either catalyzed by phenylboronic acid or promoted by a Lewis acid. [ABSTRACT FROM AUTHOR]

Desamino tyrosine (DAT) and desamino tyrosyl tyrosine (DATT) can be used to functionalize the end groups of water soluble polymers. The phenolic groups may enable physical interactions by p-p interaction and hydrogen bonds, which might lead to the formation of a hydrogel by physical crosslinking. However, using star-shaped oligo(ethylene glycols) (sOEG) with a molecular weight of 5 kDa for functionalization with DAT or DATT resulted in the formation of surfactants and not in hydrogels. As the molecular weight of the sOEG polymer chain can have an influence on forming physical cross links, DAT(T)- fuctionalization of sOEGs with higher molecular weight was investigated, the polymers were structurally characterized and for their mechanical properties were evaluated by rheological measurements. Aqueous solutions ofDAT(T)-sOEGs with 10 and 20 kDa showed lower storage and loss moduli compared to unfunctionalized sOEGs indicating also the formation of surfactants. Cell-based assays showed that all sOEG solutions did not impair cell viability and were free of endotoxins, which could otherwise induce uncontrolled immune responses. Conclusively, our data suggested that the sOEG solutions have surface active properties without inducing unwanted cellular responses, which is required e.g. in pharmaceutical applications to solubilize hydophobic substances. [ABSTRACT FROM AUTHOR]

Using a palladium(II)-catalyzed oxidative cyclization of an N,N-diarylamine, we have achieved the total synthesis of the 2,8-dioxygenated carbazole alkaloids carbalexin B, clausine A, clauszoline M, and 2,8-dihydroxy-3-methylcarbazole. [ABSTRACT FROM AUTHOR]

A Buchwald-Hartwig amination and palladium(II)-catalyzed oxidative cyclization reaction sequence provided efficient access to a series of oxygenated tricyclic carbazoles. In the present work, this approach was applied to the total syntheses of the naturally occurring carbazole alkaloids 2-hydroxy-7-methylcarbazole, glycozolicine, mukoline, mukolidine, sansoakamine, glycozolidine, clausine-H (clauszoline-C), clausine-K (clauszoline-J), and methyl 2-hydroxy-7-methoxycarbazole-3-carboxylate, which was originally proposed as the structure of clausine-TY. The synthesis of the latter led to the structural reassignment of clausine-TY. [ABSTRACT FROM AUTHOR]

The boronic acid-catalyzed annulation of citral opens up a short route to oxygenated cyclized monoterpenoid pyranocarbazole alkaloids. Thus, murrayamine-D is available in only three steps and 55% overall yield from the corresponding carbazole precursor. [ABSTRACT FROM AUTHOR]

Side chain functionalization of gelatin with tyrosine-derived moieties, desaminotyrosine (DAT) or desaminotyrosyl tyrosine (DATT), has been reported to lead to physical networks stabilized by aromatic interactions and hydrogen bonds, while the inherent ability of gelatin chains to organize in helices is suppressed. Here, the treatment of DAT and DATT gelatin films at defined temperatures (drying at 5 °C, freeze-drying, and freeze-thawing) were explored for the potential to additionally stabilize the hydrogels by increasing the content of helical domains as additional physical netpoints. The influence of the drying procedures on the hydrogel properties such as network morphology and mechanical properties were analyzed by WAXS, swelling, and rheological measurements. The triple helix content had a stabilizing effect on gelatin-based hydrogels at temperatures below the helix-to-coil transition. However, this effect was less pronounced at physiological conditions above the transition temperature, resulting in rapid dissolution of the physical gelatin networks. [ABSTRACT FROM AUTHOR]

Shape-memory polymers (SMPs) are stimuli-sensitive materials capable of performing complex movements on demand, which makes them interesting candidates for various applications, for example, in biomedicine or aerospace. This trend article highlights current approaches in the chemistry of SMPs, such as tailored segment chemistry to integrate additional functions and novel synthetic routes toward permanent and temporary netpoints. Multiphase polymer networks and multimaterial systems illustrate that SMPs can be constructed as a modular system of different building blocks and netpoints. Future developments are aiming at multifunctional and multistimuli-sensitive SMPs. [ABSTRACT FROM AUTHOR]

The article reflects on the use of functional polymers in medicine. Topics include step for synthesis of block copolymer which involves ring-opening polymerization of N-carboxybenzyl-protected L-ornithine N-carboxyanhydride with methoxy-polyethylene glycol (PEG)-amine followed by quantitative guanidinylation; challenges related to release of bioactive substances in drug delivery research; and use of gold nanoparticles for making biosensors.

Shape-memory hydrogels (SMH) are multifunctional, actively-moving polymers of interest in biomedicine. In loosely crosslinked polymer networks, gelatin chains may form triple helices, which can act as temporary net points in SMH, depending on the presence of salts. Here, we show programming and initiation of the shape-memory effect of such networks based on a thermomechanical process compatible with the physiological environment. The SMH were synthesized by reaction of glycidylmethacrylated gelatin with oligo(ethylene glycol) (OEG) α,ω-dithiols of varying crosslinker length and amount. Triple helicalization of gelatin chains is shown directly by wide-angle X-ray scattering and indirectly via the mechanical behavior at different temperatures. The ability to form triple helices increased with the molar mass of the crosslinker. Hydrogels had storage moduli of 0.27–23 kPa and Young's moduli of 215–360 kPa at 4 °C. The hydrogels were hydrolytically degradable, with full degradation to water-soluble products within one week at 37 °C and pH = 7.4. A thermally-induced shape-memory effect is demonstrated in bending as well as in compression tests, in which shape recovery with excellent shape-recovery rates Rr close to 100% were observed. In the future, the material presented here could be applied, e.g., as self-anchoring devices mechanically resembling the extracellular matrix. [ABSTRACT FROM AUTHOR]

The author discusses the design of advanced functional polymers for medical purposes. Topics mentioned include the utilization of porous scaffolds for tissue reconstruction, the biomedical applications of thermosensitive hydrogels and the incorporation of nanoparticles into electrospun fibers through additive electrospraying.

A space filling model of the X‐ray structure of the pyrano[3,2‐a]carbazole alkaloid mupamine is shown. Its synthesis, which involves the boronic acid‐catalyzed annulation of citral, is described in the Communication by H.‐J. Knölker et al. on page 8536 ff. [ABSTRACT FROM AUTHOR]

Front Cover: Shape‐memory polymers can be created in a modular approach, consisting of three components: chain segments, permanent netpoints and temporary netpoints. Varying these components enables the integration of several functions, as well as the implementation of multistimuli‐sensitivity in shape‐memory polymers. Further details can be found in the article by Konstanze K. Julich‐Gruner, Candy Löwenberg, Axel T. Neffe, Marc Behl, and Andreas Lendlein* on page 527. [ABSTRACT FROM AUTHOR]

Hydrophilic biopolymers display a strong tendency for self-organization into stable secondary, tertiary, and quaternary structures in aqueous environments. These structures are sensitive to changes in external conditions, such as temperature, pH or ions/salts, which may lead to molecular and/or macroscopic transitions. Here, we report on biopolymer-based stimuli-sensitive switchable matrices showing a shape-memory function as an output being alternatively switched by two different input signals, such as environmental changes in salt concentration or temperature. This was realized by implementing a shape-memory function in hydrogels based on the coil-to-helix transition of protein chains in gelatin-based networks. The hydrogels exhibited mechanical properties similar to that of soft tissue (storage modulus G ' = 1-100 kPa) and high swelling capabilities ( Q = 1000-3000 vol %). In these gelatin-based networks, the covalent netpoints defined the permanent shape while after deformation helicalization of the gelatin acted as reversible stimuli-sensitive switches providing additional crosslinks capable of fixing the deformed temporary shape. By using either chaotropic salts to suppress gelatin helicalization or kosmotropic salts to support conformational changes of gelatin toward a helical orientation, these additional crosslinks could be cleaved or formed. In bending experiments, the strain fixity ( R f ) and strain recovery ratios ( R r ) were determined. While R f ranged from 65 to 95% and was depending on the network composition, R r were independent of the hydrogel composition with values about 100%. In addition, R f and R r were independent of the type of chaotropic salt that was used in this study, showing equal R f and R r values for MgCl 2 , NaSCN, and Mg(SCN) 2 .