Arbeitskreis Lindel

Marine Naturstoffe - Bausteine des Lebens

Have you thought about organic synthesis lately?


Aktuelles Gruppenbild vom Arbeitskreis Lindel
 

Aktuelle Publikationen:

J. H. Lang, P. G. Jones, T. Lindel, "Total Synthesis of the Marine Natural Product Hemiasterlin by Organocatalyzed α-Hydrazination", Chem. Eur. J. 2017, 23, 12714-12717.

 
 
Inhalt:
An efficient synthesis of the potently cytotoxic marine peptide hemiasterlin is presented. The tetramethyltryptophan moiety is assembled by tert-prenylation of indole, followed by the high-yielding organocatalyzed α-hydrazination of a sterically congested aldehyde with excellent enantioselectivity. 2-Bromo-N-ethylpyridinium tetrafluoroborate (BEP)-mediated peptide coupling completes the synthesis, being the first approach that does not employ chiral auxiliaries. A novel phenonium-type rearrangement of the indole system occurred when subjecting dihydroxylated 3-tert-prenylindole to Mitsunobu conditions.

J.-N. Schäckermann, T. Lindel, "Synthesis and Photooxidation of the Trisubstituted Oxazole Fragment of the Marine Natural Product Salarin C", Org. Lett. 2017, 19, 2306-2309.

 
 
Inhalt:
The eastern section of the macrocyclic marine natural product salarin C from the sponge Fascaplysinopsis sp. was synthesized employing a halogen dance reaction to assemble the trisubstituted oxazole moiety. The synthesis was inspired by Kashman’s hypothesis on the biomimetic oxidation of salarin C to salarin A. Clean conversion to the triacylamine partial structure of salarin A occurred on treatment with photochemically generated singlet oxygen. Thus, a Wasserman-type oxidative rearrangement is chemically possible in this case.

N. E. Kanitz, T. Lindel, Photoreactivity of monofluorinated 2-azidobenzimidazoles towards carboxylic acids A", Z. Naturforsch. 2016, 71b, 1287–1300.

 
 
Inhalt:
Aiming at the development of new photolabeling agents, the synthesis and photoreactivity of all monofluorinated derivatives of 2-azido-1-methylbenzimidazole are described. In the case of 4-, 5-, or 7-fluorination, irradiation in the presence of carboxylic acids (300 nm, Rayonet) afforded the monofluorinated 2-amino-6-acyloxybenzimidazoles in a regioselective manner, presumably after conversion of the initially formed nitrene to the N-cyanodiazaxylylene. Incorporation of chloride was also possible, and yields were comparable to those observed for the non-fluorinated parent compound. When blocking the reactive 6-position by a fluoro substituent, the title reaction was not possible. The analysis of the 19F NMR chemical shifts of the 5- and 7-monofluorinated products allowed the distinction between carboxylates and other nucleophiles.