Sabine Mika

Combined action of enzymes: the first domino reaction catalyzed by Agaricus bisporus

The enzymes tyrosinase and laccase from a crude extract of the button mushroom (Agaricus bisporus) can be employed to catalyze the domino reaction between phenol and various cyclic 1,3-dicarbonyls using atmospheric oxygen as the oxidizing agent and yielding annulated benzofuranes in a highly efficient and sustainable manner.

Flavonoid Glucuronides and a Chromone from the Aquatic Macrophyte Stratiotes aloides

The first phytochemical analysis of the aquatic macrophyte Stratiotes aloides afforded two new flavonoid glucuronides, luteolin 7-O-beta-D-glucopyranosiduronic acid-(1-->2)-beta-D-glucopyranoside (1) and chrysoeriol 7-O-beta-D-glucopyranosiduronic acid-(1-->2)-beta-D-glucopyranoside (2), as well as the new 2-(2-hydroxypentyl)-5-carboxy-7-methoxychromone (5) and chrysoeriol 7-O-beta-(6-O-malonyl)glucopyranoside (3), which has been assigned via NMR data for the first time. Additionally, free amino acids such as tryptophan, arginine, leucine, isoleucine, phenylalanine, and tyrosine along with choline, cis-aconitic acid, the phenolic glycoside alpha-arbutine, the chlorophyll derivative phaeophorbide a, and the flavonoid glycoside luteolin 7-O-beta-(6-O-malonyl)glucopyranoside (4) were isolated. Despite the low quantities obtained in some cases (between 50-300 microg), the structures of all compounds were unambiguously elucidated by extensive NMR and MS experiments. With a delay of 2 days compound 1 (10 and 50 microM test concentration) strongly inhibited the growth of human SH-SY5Y neuroblastoma cells in a dose-dependent manner, whereas only a moderate growth inhibition of human Patu 8902 carcinoma cells could be observed. Compounds 1 and 2 showed no activities against the bacteria Escherichia coli BW25113, Pseudomonas pudida KT2440, and Enterobacter cloacae subsp. dissolvens.

Laccase-catalyzed stereoselective oxidative ring opening of 2,5-dialkylfurans into 2-ene-1,4-diones using air as an oxidant

The laccase-catalyzed ring opening of 2,5-dimethylfuran using air as an oxidant stereoselectively yields (Z)- or (E)-3-hexene-2,5-dione depending on the mediator employed: with TEMPO the (Z)-3-hexene-2,5-dione is formed, while a combination of TEMPO and violuric acid gives (E)-3-hexene-2,5-dione. The (Z)-selective ring cleavage was extended to a variety of symmetrical and unsymmetrical 2,5-dialkylfurans.

Preparation of the geranyl-α-pyrone (±)-aurantiacone via a new pyrone synthesis

The structure of the leaf resin geranyl-α-pyrone auranti-acone isolated from Mimulus ( = Diplacus) aurantiacus (Curtis) Jeps. (Scrophulariaceae) was confirmed through synthesis. The key step is lactonization of the sensitive 5-hydroxy-3-oxopent-4-enoic acid under mild conditions, which can be released from the corresponding bispotassium salt. The latter is accessible in a few steps from an N-acyl aziridine and an ethyl acetoacetate.

Efficient Lewis Acid Mediated Epoxyolefin Cyclizations with Pyrones as Terminators in Liquid SO2 as a Solvent

Lewis acids like BF 3 ·OEt 2 , TiCl 4 , ZnCl 2 ·OEt 2 , ZnI 2 , and InCl 3 in liquid SO 2 as a solvent at low temperatures have been found to be highly efficient in epoxyolefin cyclizations with pyrones as terminators.