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Andreas Kirschning

Publications and source records attributed to Andreas Kirschning.

7 recordsLinked to original sources
PubMed2003

Polymer/carrier composites as materials and reactors for organic synthesis.

In this work new polymer/carrier composites are described which serve as novel materials in flow-through reactors for polymer-supported organic solution-phase synthesis. Monolithic polymer/carrier columns are prepared by a new precipitation polymerization process inside the void pore volume of megaporous glass carrier materials. Chemical functionalization of the internal polymer phase with chlorosulfonic acid or trimethylamine generates small, interconnected ion-exchange resin beads with a diameter of 1-3 microm which can be used for a large variety of organic syntheses. These monolithic rods are incorporated into an appropriate casing and can conveniently be operated in the flow-through mode. Important successful applications are polymer-assisted solution-phase reductions, oxidations and Horner-Emmons olefinations. Additionally, the use of these monolithic columns as catalytic microreactors and their performance in selected reactions are described.

Catalysis↗
PubMed2002

First preparation of spacer-linked cyclic neooligoaminodeoxysaccharides.

The preparation of novel cyclic 1,4-butanediol-linked oligoaminodeoxysugars 3-5 and 7 is described which are potential binders to polynucleotides. Neooligosaccharides 3-5 are assembled by two consecutive metathesis protocols. In the first phase metathesis-mediated dimerization of an aminodeoxymonosaccharide which was either allylated at the anomeric center or at C4 led to E/Z mixtures of C2-symmetric homodimers which were transformed into the corresponding 1,4-butanediol linked disaccharides by catalytic hydrogenation of the central olefinic double bond. Double Q-allylation of the head-to-head dimer set the stage for macrocyclization by means of ring-closing metathesis. This ring-closing process was highly dependent of the configuration in the carbohydrate moieties. arabino-Configured homodimer 15 directly yielded the macrocycle 32 which contains two sugar units while under the same metathesis conditions the corresponding ribo-configured starting homodimer 19 afforded cyclic neotetra- and neohexasaccharides 34 and 35 after a preceding dimerization and trimerization step, respectively. In addition, homodimer 23 was coupled with silylglycoside 14a under Lewis-acid promoted glycosidation conditions to furnish the doubly glycosylated homodimer 31. Ring-closing metathesis afforded the macrocyclic neoaminodeoxyoligosaccharide 36 with alternating 1,4-butanediol linkage and glycosidic bond. The primary cyclization products were finally transformed into the respective cyclic neoaminodeoxyoligosaccharides 3-5 and 7 by catalytic hydrogenation and standard deprotection conditions.

Amino Sugars↗
PubMed2001

Functionalized Polymers-Emerging Versatile Tools for Solution-Phase Chemistry and Automated Parallel Synthesis.

As part of the dramatic changes associated with the need for preparing compound libraries in pharmaceutical and agrochemical research laboratories, industry searches for new technologies that allow for the automation of synthetic processes. Since the pioneering work by Merrifield polymeric supports have been identified to play a key role in this field however, polymer-assisted solution-phase synthesis which utilizes immobilized reagents and catalysts has only recently begun to flourish. Polymer-assisted solution-phase synthesis has various advantages over conventional solution-phase chemistry, such as the ease of separation of the supported species from a reaction mixture by filtration and washing, the opportunity to use an excess of the reagent to force the reaction to completion without causing workup problems, and the adaptability to continuous-flow processes. Various strategies for employing functionalized polymers stoichiometrically have been developed. Apart from reagents that are covalently or ionically attached to the polymeric backbone and which are released into solution in the presence of a suitable substrate, scavenger reagents play an increasingly important role in purifying reaction mixtures. Employing functionalized polymers in solution-phase synthesis has been shown to be extremely useful in automated parallel synthesis and multistep sequences. So far, compound libraries containing as many as 88 members have been generated by using several polymer-bound reagents one after another. Furthermore, it has been demonstrated that complex natural products like the alkaloids (+/-)-oxomaritidine and (+/-)-epimaritidine can be prepared by a sequence of five and six consecutive polymer-assisted steps, respectively, and the potent analgesic compound (+/-)-epibatidine in twelve linear steps ten of which are based on functionalized polymers. These developments reveal the great future prospects of polymer-assisted solution-phase synthesis.

Journal Article↗