Cryptic Metabolites from Marine-Derived Microorganisms Using OSMAC and Epigenetic Approaches.

Marine microorganisms have proven to be a source of new natural products with a wide spectrum of biological activities relevant in different industrial sectors. The ever-increasing number of sequenced microbial genomes has highlighted a discrepancy between the number of gene clusters potentially encoding the production of natural products and the actual number of chemically characterized metabolites for a given microorganism. Homologous and heterologous expression of these biosynthetic genes, which are often silent under experimental laboratory culture conditions, may lead to the discovery of new cryptic natural products of medical and biotechnological interest. Several new genetic and cultivation-based strategies have been developed to meet this challenge. The OSMAC approach (one strain-many compounds), based on modification of growth conditions, has proven to be a powerful strategy for the discovery of new cryptic natural products. As a direct extension of this approach, the addition of chemical elicitors or epigenetic modifiers have also been used to activate silent genes. This review looks at the structures and biological activities of new cryptic metabolites from marine-derived microorganisms obtained using the OSMAC approach, the addition of chemical elicitors, and enzymatic inhibitors and epigenetic modifiers. It covers works published up to June 2021.

Metabolism of Antifungal Thiochroman-4-ones by Trichoderma viride and Botrytis cinerea.

Biotransformation of 6-methylthiochroman-4-one (1) and 6-chlorothiochroman-4-one (2) was performed using Trichoderma viride in order to obtain new derivatives with antifungal properties against the phytopathogen Botrytis cinerea. Two thiochromanone derivatives are described for the first time. Antifungal activity of these compounds was tested against two different strains of Botrytis cinerea; 1 and 2 gave 100% inhibition of Bc2100 at 100-250 µg/mL, and 3 gave a maximal inhibition of 96% of BcUCA992 at 200 µg/mL. The detoxification mechanism of 1 and 2 by B. cinerea was also investigated.

Bio-Guided Isolation of New Compounds from Baccharis spp. as Antifungal against Botrytis cinerea.

Baccharis genus Asteraceae is widely used in traditional treatment against fever, headache, hepatobiliary disorders, skin ulcers, diabetes, and rheumatism, as well as an antispasmodic and diuretic. Its phytochemistry mainly shows the presence of flavonoids and terpenoids such as monoterpenes, sesquiterpenes, diterpenes, and triterpenes. Some of them have been evaluated for biological activities presenting allelopathic, antimicrobial, cytotoxic, and anti-inflammatory properties. In this paper, our research group reported the isolation, characterization, and antifungal evaluation of several molecules isolated from the dichloromethane extract from Baccharis prunifolia, Baccharis trinervis, and Baccharis zumbadorensis against the phytopathogen fungus Botrytis cinerea. The isolated compounds have not previously been tested against Botrytis, revealing an important source of antifungals in the genus Baccharis. Six known flavones were isolated from B. prunifolia. The dichloromethane extracts of B. trinervis and B. zumbadorensis were subjected to a bio-guided isolation, obtaining three known flavones, an α-hydroxidihydrochalcone mixture, one labdane, one triterpene, and two norbisabolenes from the most active fractions. The compounds 4'-methoxy-α-hydroxydihydrochalcone (7A), 3ß,15-dihydroxylabdan-7-en-17-al (8), and 13-nor-11,12-dihydroxybisabol-2-enone (11) are novel. The most active compounds were the Salvigenin (5) and 1,2-dihydrosenedigital-2-one (10) with an IC50 of 13.5 and 3.1 µg/mL, respectively.

Biocatalytic preparation and absolute configuration of enantiomerically pure fungistatic anti-2-benzylindane derivatives. Study of the detoxification mechanism by Botrytis cinerea.

Enantiomerically pure 2-benzylindane derivatives were prepared using biocatalytic methods and their absolute configuration determined. (1R,2S)-2-Benzylindan-1-ol ((1R,2S)-2) and (S)-2-benzylindan-1-one ((S)-3) were produced by fermenting baker's yeast. Lipase-mediated esterifications and hydrolysis of the corresponding racemic substrates gave rise to the enantiopure compounds (1S,2R)-2-benzylindan-1-ol ((1S,2R)-2) and (1R,2S)-2-benzylindan-1-ol ((1R,2S)-2), respectively. The antifungal activity of these products against two strains of the plant pathogen Botrytis cinerea was tested. The metabolism of anti-(+/-)-2-benzylindan-1-ol (anti-(+/-)-2) by B. cinerea as part of the fungal detoxification mechanism is also described and revealed interesting differences in the genome of both strains.

Biocatalytic Preparation of Chloroindanol Derivatives. Antifungal Activity and Detoxification by the Phytopathogenic Fungus Botrytis cinerea.

Indanols are a family of chemical compounds that have been widely studied due to their broad range of biological activity. They are also important intermediates used as synthetic precursors to other products with important applications in pharmacology. Enantiomerically pure chloroindanol derivatives exhibiting antifungal activity against the phytopathogenic fungus Botrytis cinerea were prepared using biocatalytic methods. As a result of the biotransformation of racemic 6-chloroindanol (1) and 5-chloroindanol (2) by the fungus B. cinerea, the compounds anti-(+)-6-chloroindan-1,2-diol (anti-(+)-7), anti-(+)-5-chloroindan-1,3-diol (anti-(+)-8), syn-(+)-5-chloroindan-1,3-diol (syn-(+)-8), syn-(-)-5-chloroindan-1,3-diol (syn-(-)-8), and anti-(+)-5-chloroindan-1,2-diol (anti-(+)-9) were isolated for the first time. These products were characterized by spectroscopic techniques and their enantiomeric excesses studied by chromatographic techniques. The results obtained in the biotransformation seem to suggest that the fungus B. cinerea uses oxidation reactions as a detoxification mechanism.

Conversion of the mycotoxin patulin to the less toxic desoxypatulinic acid by the biocontrol yeast Rhodosporidium kratochvilovae strain LS11.

The infection of stored apples by the fungus Penicillium expansum causes the contamination of fruits and fruit-derived products with the mycotoxin patulin, which is a major issue in food safety. Fungal attack can be prevented by beneficial microorganisms, so-called biocontrol agents. Previous time-course thin layer chromatography analyses showed that the aerobic incubation of patulin with the biocontrol yeast Rhodosporidium kratochvilovae strain LS11 leads to the disappearance of the mycotoxin spot and the parallel emergence of two new spots, one of which disappears over time. In this work, we analyzed the biodegradation of patulin effected by LS11 through HPLC. The more stable of the two compounds was purified and characterized by nuclear magnetic resonance as desoxypatulinic acid, whose formation was also quantitated in patulin degradation experiments. After R. kratochvilovae LS11 had been incubated in the presence of (13)C-labeled patulin, label was traced to desoxypatulinic acid, thus proving that this compound derives from the metabolization of patulin by the yeast. Desoxypatulinic acid was much less toxic than patulin to human lymphocytes and, in contrast to patulin, did not react in vitro with the thiol-bearing tripeptide glutathione. The lower toxicity of desoxypatulinic acid is proposed to be a consequence of the hydrolysis of the lactone ring and the loss of functional groups that react with thiol groups. The formation of desoxypatulinic acid from patulin represents a novel biodegradation pathway that is also a detoxification process.

Global antifungal profile optimization of chlorophenyl derivatives against Botrytis cinerea and Colletotrichum gloeosporioides.

Twenty-two aromatic derivatives bearing a chlorine atom and a different chain in the para or meta position were prepared and evaluated for their in vitro antifungal activity against the phytopathogenic fungi Botrytis cinerea and Colletotrichum gloeosporioides. The results showed that maximum inhibition of the growth of these fungi was exhibited for enantiomers S and R of 1-(4'-chlorophenyl)-2-phenylethanol (3 and 4). Furthermore, their antifungal activity showed a clear structure-activity relationship (SAR) trend confirming the importance of the benzyl hydroxyl group in the inhibitory mechanism of the compounds studied. Additionally, a multiobjective optimization study of the global antifungal profile of chlorophenyl derivatives was conducted in order to establish a rational strategy for the filtering of new fungicide candidates from combinatorial libraries. The MOOP-DESIRE methodology was used for this purpose providing reliable ranking models that can be used later.