Versuche zur ersten Totalsynthese des Aglycons der Cripowelline A und B und erste asymmetrische Synthese von Tropional
type: CreativeWork
description: Amaryllidaceae alkaloids - and their subspecies Crinum – are traditional medicinal plants that have also become very important for modern medicine. At Bayer AG in Leverkusen two novel alkaloids – Cripowelline A and B – were isolated from extracts of Crinum powellii. Both alkaloids showed a broad insecticidal effect. Within this thesis two different strategies were developed, which should allow an efficient synthesis of the aglycon of the cripowellines A and B. According to the first synthetic concept a metathesis reaction should be used to build up the polycyclic ringsystem of the aglycon. In a first attempt the sidechain – containing the amid function - of the metathesis precursor was obtained starting from commercially available piperonal with a yield of 57% over four steps. The second sidechain should have been introduced by subsequent alpha-arylation. The arylation only led to poor yields on a test system, therefore no trials were carried out to get the target molecule. Alongside the desired metathesis precursor could be synthesized by addition of a benzyllithium species to a carbonyl compound. Although four different benzylic compounds could be synthesized in yields of 38 or 45% over 6 or 7 steps respectively, it was not possible to obtain the desired product, because no lithiation of the benzylic position could be achieved. In another effort towards the precursor the sidechain bearing the allylic ketone could be introduced starting from commercially available 3,4-(methylendioxy)phenylacetic acid in 19% yield over five steps. However, the reaction to the secondary amine by cleavage of the acetal and subsequent reductive amination was not successful. According to a second synthetic concept an alpha-arylation reaction should be used to build up the ringsystem. The synthesis of the desired arylation precursor was completed in nine steps using commercially available D-tartaric acid in an overall yield of 24%. The keysteps of this synthetic sequence were the oxidati…
abstract: Amaryllidaceae alkaloids - and their subspecies Crinum – are traditional medicinal plants that have also become very important for modern medicine. At Bayer AG in Leverkusen two novel alkaloids – Cripowelline A and B – were isolated from extracts of Crinum powellii. Both alkaloids showed a broad insecticidal effect. Within this thesis two different strategies were developed, which should allow an efficient synthesis of the aglycon of the cripowellines A and B. According to the first synthetic concept a metathesis reaction should be used to build up the polycyclic ringsystem of the aglycon. In a first attempt the sidechain – containing the amid function - of the metathesis precursor was obtained starting from commercially available piperonal with a yield of 57% over four steps. The second sidechain should have been introduced by subsequent alpha-arylation. The arylation only led to poor yields on a test system, therefore no trials were carried out to get the target molecule. Alongside the desired metathesis precursor could be synthesized by addition of a benzyllithium species to a carbonyl compound. Although four different benzylic compounds could be synthesized in yields of 38 or 45% over 6 or 7 steps respectively, it was not possible to obtain the desired product, because no lithiation of the benzylic position could be achieved. In another effort towards the precursor the sidechain bearing the allylic ketone could be introduced starting from commercially available 3,4-(methylendioxy)phenylacetic acid in 19% yield over five steps. However, the reaction to the secondary amine by cleavage of the acetal and subsequent reductive amination was not successful. According to a second synthetic concept an alpha-arylation reaction should be used to build up the ringsystem. The synthesis of the desired arylation precursor was completed in nine steps using commercially available D-tartaric acid in an overall yield of 24%. The keysteps of this synthetic sequence were the oxidati…
author: Backes, Michael
language: ger
keywords: info:eu-repo/classification/ddc/540, Cripowellin A, Aglykon, Totalsynthese, Asymmetrische Synthese, Cripowellin B, Tropional, Hydrazon-Methode, Chemie, Alkaloide, Duftstoffe, Alkylierung, SAMP/RAMP-Hydrazone
date published: 2004
date modified: 2026-07-30T19:43:19Z
provider: RWTH Aachen University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Mainz