Andreas Speicher

Syntheses of Cyclic Bisbibenzyl Systems

The cyclic bisbibenzyl systems Marchantin I (3), Riccardin C (4) and Isoplagiochin C (5) representing unique types of bryophyte constituents were prepared by a flexible, efficient and general synthetic approach involving the construction of biphenyl and bibenzyl units using Suzuki and Wittig protocols.

Bisbibenzyls, a New Type of Antifungal Agent, Inhibit Morphogenesis Switch and Biofilm Formation through Upregulation of DPP3 in Candida albicans

The yeast-to-hypha transition plays a crucial role in the pathogenesis of C. albicans. Farnesol, a quorum sensing molecule (QSM) secreted by the fungal itself, could prevent the formation of hyphae and subsequently lead to the defect of biofilm formation. The DPP3, encoding phosphatase, is a key gene in regulating farnesol synthesis. In this study, we screened 24 bisbibenzyls and 2 bibenzyls that were isolated from bryophytes or chemically synthesized by using CLSI method for antifungal effect. Seven bisbibenzyls were found to have antifungal effects with IC80 less than 32 µg/ml, and among them, plagiochin F, isoriccardin C and BS-34 were found to inhibit the hyphae and biofilm formation of C. albicans in a dose-dependent manner. To uncover the underlying relationship between morphogenesis switch and QSM formation, we measured the farnesol production by HPLC-MS and quantified Dpp3 expression by detecting the fluorescent intensity of green fluorescent protein tagged strain using Confocal Laser Scanning microscopy and Multifunction Microplate Reader. The DPP3 transcripts were determined by real-time PCR. The data indicated that the bisbibenzyls exerted antifungal effects through stimulating the synthesis of farnesol via upregulation of Dpp3, suggesting a potential antifungal application of bisbibenzyls. In addition, our assay provides a novel, visual and convenient method to measure active compounds against morphogenesis switch.

Stereoselective oxidoreductase type bioconversions of exogenous substrates by cell suspension cultures of bryophytes

Abstract We established green cell suspension cultures of Marchantia polymorpha, Marchantia plicata, Riccia fluitans and Asterella blumeana. Whole cell biotransformations of the oxidoreductase type were studied using different exogenous substrates. The results show that cell cultures of liverworts can serve as effective tools in bioconversion reactions for the enantio- or diastereoselective reduction of simple ketones, β-ketoesters and α,β-unsaturated carbonyl compounds. The reduction of ketones and β-ketoesters resulted in products according to Prelog’s rule.

3,4-dihydroxy-3′-methoxystilbene, the first monomeric stilbene derivative from bryophytes

Abstract 3.4-Dihydroxy-3′-methoxystilbene, the first monomeric stilbene derivative to be discovered in bryophytes was isolated from the neotropic liverwort Marchesina bongardiana . Its structure has been elucidated on the basis of NMR spectral evidence and independent chemical synthesis of this hitherto unknown compound.

Ring strain and total syntheses of modified macrocycles of the isoplagiochin type

Summary Macrocycles of the bisbibenzyl-type are natural products that are found exclusively in bryophytes (liverworts). The molecular framework of the subtype “isoplagiochin” is of substantial structural interest because of the chirality of the entire molecule, which arises from two biaryl axes in combination with two helical two-carbon units in a cyclic arrangement. From a structural as well as a synthetic point of view we report on the total synthesis of compounds which possess more rigid two-carbon biaryl bridges like stilbene (E or Z) or even tolane moieties which were introduced starting with a Sonogashira protocol. The McMurry method proved to be a powerful tool for the cyclization to these considerably ring-strained macrocycles.

First detection of a chloroperoxidase in bryophytes.

Chlorinated cyclic bisbibenzyls of the isoplagiochin type are the first verified halometabolites from bryophytes. They could be obtained by in vitro chlorination of isoplagiochin C with chloroperoxidase from Caldariomyces fumago. Furthermore, an enzyme of this type was detected for the first time in bryophytes namely in the liverwort Bazzania trilobata using the monochlorodimedon assay.

Carboxylated α-pyrone derivatives and flavonoids from the liverwort Dumortiera hirsuta

Abstract Three new carboxylated α-pyrone derivatives, dumortins A-C, and a new flavone glycoside have been isolated from the liverwort, Dumortiera hirsuta , together with the known flavonoids, luteolin, luteolin -5-O-β- d -glucuronide and luteolin -7-O-β- d -glucuronide . The structures of the new α-pyrones were confirmed spectroscopically as 4-(3′,4′-dihydroxy- E -styryl)-6-carboxy-α-pyrone,4-[2-(3′,4′-dihydroxyphenyl)-ethyl]-6-carboxy-α-pyrone and 3-[1-hydroxy-2-(3′,4′-dihydroxyphenyl)-ethyl]-6-carboxy-α-pyrone. The new flavonoid was elucidated as luteolin -5-O-β- d -glucuronide-6″-methyl ester. The structures of dumortins A and B were confirmed by independent chemical synthesis.

Atroposelective Heck macrocyclization: enantioselective synthesis of bis(bibenzylic) natural products.

The Heck protocol was applied for the first time to the atroposelective synthesis of macrocyclic natural products. As ring closure to bis(bibenzyls) of the isoplagiochin type leads to a configurationally stable biaryl axis in the molecule, cyclization could be conducted atroposelectively in the presence of a chiral BINAP ligand.

Rapid detection of chlorinated bisbibenzyls in Bazzania trilobata using MALDI-TOF mass spectrometry.

Chlorinated bisbibenzyls of the bazzanin type are detected in crude bryophyte plant extracts of Bazzania trilobata from different locations using MALDI-TOF mass spectrometry. These results show that these chlorinated compounds are not artefacts of an incidental occurrence or of the sample preparation but are genuine and produced by the liverwort or an endosymbiotic metabolism. Further experiments were performed concerning the in vitro chlorination of the halogen free basic unit isoplagiochin C.

Chemical and In Vitro Syntheses of Brominated and Chlorinated 3,4′-Dihydroxybibenzyls (Halogenated Lunularins)

Ten halogenated lunularins 16, 17, 26, 27, 30, 31, 36, 37, 42 and 43 as model substances for a new class of halometabolites isolated from bryophytes are prepared by chemical total syntheses according to a Wittig-protocol using halogenated aldehydes and phosphonium salts and/or by an in vitro halogenation of lunularin using potassium halide and hydrogen peroxide in the presence of a chloroperoxidase. The results confirm the need for a haloperoxidase in the in vitro chlorination of lunularin 6.