During blooms, cyanobacteria produce diverse modified peptides. Among these are the microginins, which inhibit zinc-containing metalloproteases. Ten microginins, microginins KR767 (
), KR801(
), ...KR835 (
), KR785 (
), KR604 (
), KR638 (
), KR781 (
), KR815 (
), FR3 (
), and FR4 (
), were isolated from the extract of a bloom material of
sp. (IL-405) collected from the Kishon Reservoir, Israel in the fall of 2009. The structures of the pure compounds were elucidated using 1D and 2D NMR techniques and high-resolution mass spectrometry. The absolute configuration of the chiral centers of the amino acids were determined by Marfey's and advance Marfey's methods and by comparison of ¹H and
C NMR chemical shifts of the Ahda derivatives with those of known microginins. These microginins differ in sequence and absolute configuration of the chiral centers of the Ahda moieties and by
-methylation of the Ahda amine group and extent of chlorination of the Ahda terminal methyl group. The compounds were evaluated for inhibition of the zinc metalloprotease, aminopeptidase M, and exhibited low- to sub-nanomolar half maximal inhibitory concentration (IC
) values.
Anabaenopeptins are common metabolites of cyanobacteria. In the course of reisolation of the known aeruginosins KT608A and KT608B for bioassay studies, we noticed the presence of some unknown ...anabaenopeptins in the extract of a
cell mass collected during the 2016 spring bloom event in Lake Kinneret, Israel. The
H NMR spectra of some of these compounds presented a significant difference in the appearance of the ureido bridge protons, and their molecular masses did not match any one of the 152 known anabaenopeptins. Analyses of the 1D and 2D NMR, HRMS, and MS/MS spectra of the new compounds revealed their structures as the hydantoin derivatives of anabaenopeptins A, B, F, and
Dht-anabaenopeptin A and oscillamide Y (
,
,
,
, and
, respectively) and a new anabaenopeptin,
Dht-anabaenopeptin A (
). The known anabaenopeptins A, B, and F and oscillamide Y (
,
,
and
, respectively) were present in the extract as well. We propose that
-
and
are the possible missing intermediates in the previously proposed partial biosynthesis route to the anabaenopeptins. Compounds
-
were tested for inhibition of the serine proteases trypsin and chymotrypsin and found inactive at a final concentration of ca. 54 μM.
Thirteen new and eighteen known natural products were isolated from a bloom material of an assembly of various Microcystis spp. collected in November, 2008, from a commercial fishpond near Kibbutz ...Kfar Blum, the Jordan Valley, Israel. The new natural products included the prenylated aeruginosin KB676 (1), microphycin KB921 (2), anabaenopeptins KB906 (3) and KB899 (4) and micropeptins KB928 (5), KB956 (6), KB970A (7), KB970B (8), KB984 (9), KB970C (10), KB1048 (11), KB992 (12) and KB1046 (13). Their structures were elucidated primarily by interpretation of their 1D and 2D nuclear magnetic resonance spectra and high-resolution mass spectrometry. Marfey's and chiral-phase high performance liquid chromatography methods were used to determine the absolute configurations of their chiral centers. Aeruginosin KB676 (1) contains the rare (2S,3aS,6S,7aS)-Choi and is the first prenylated aeruginosin derivative described in the literature. Compounds 1 and 5-11 inhibited trypsin with sub-μM IC50s, while Compounds 11-13 inhibited chymotrypsin with sub-μM IC50s. The structures and biological activities of the new natural products and our procedures of dereplication are described.
Two new natural products, micropeptin TR1058 (
) and aeruginosin TR642 (
), were isolated from the hydrophilic extract of bloom material of
sp. collected from the Timurim water reservoir in Israel. ...The structures of compounds
and
were determined using 1D and 2D NMR spectroscopy and HR ESI MS and MS/MS techniques. Micropeptin TR1058 (
) was extremely unstable under the isolation conditions, and several degradation products were identified. NMR analysis of aeruginosin TR642 (
) revealed a mixture of eight isomers, and elucidation of its structure was challenging. Aeruginosin TR642 contains a 4,5-didehydroaraginal subunit that has not been described before. Micropeptin TR1058 (
) inhibited chymotrypsin with an IC
of 6.78 µM, and aeruginosin TR642 (
) inhibited trypsin and thrombin with inhibition concentration (IC
) values of 3.80 and 0.85 µM, respectively. The structures and biological activities of the new compounds are discussed.
is a fairly common inhabitant of reefs throughout the Indian and Pacific Oceans. Metabolomic analyses of samples of
collected in different depths in the Gulf of Aqaba revealed two chemotypes ...differing in the profiles of the theonellamides they produce, some of which seem to be unknown. Driven by this finding, we examined a sample of
collected more than 40 years ago in the southern part of the Gulf of Aqaba. Large-scale extract of this sample yielded four theonellamides, the known theopalauamide (
), as the major component, and three new metabolites, theonellamide J (
), 5-
-Apoa-theopalauamide (
), and theonellamide K (
), as the minor components. The planar structure of these complex cyclic glycopeptides was elucidated by combination of 1D and 2D NMR techniques and HRESIMS. The absolute configuration of the amino acids was established by Marfey's and advanced Marfey's methods, and the absolute configuration of its galactose unit using "Tanaka's method" for monosaccharides. The biological activity of the pure compounds was tested for antibacterial activity and for cytotoxicity to HTC-116 cell line. The compounds presented significant cytotoxicity against the HTC-116 cell line, illuminating the importance of the Apoa subunit for the activity.
Each year, infections caused by fungal pathogens claim the lives of about 1.6 million people and affect the health of over a billion people worldwide. Among the most recently developed antifungal ...drugs are the echinocandins, which noncompetitively inhibit β-glucan synthase, a membrane-bound protein complex that catalyzes the formation of the main polysaccharide component of the fungal cell wall. Resistance to echinocandins is conferred by mutations in FKS genes, which encode the catalytic subunit of the β-glucan synthase complex. Here, we report that selective removal of the benzylic alcohol of the nonproteinogenic amino acid 3S,4S-dihydroxy-l-homotyrosine of the echinocandins anidulafungin and rezafungin, restored their efficacy against a large panel of echinocandin-resistant Candida strains. The dehydroxylated compounds did not significantly affect the viability of human-derived cell culture lines. An analysis of the efficacy of the dehydroxylated echinocandins against resistant Candida strains, which contain mutations in the FKS1 and/or FKS2 genes of the parental strains, identified amino acids of the Fks proteins that are likely to reside in proximity to the l-homotyrosine residue of the bound drug. This study describes the first example of a chemical modification strategy to restore the efficacy of echinocandin drugs, which have a critical place in the arsenal of antifungal drugs, against resistant fungal pathogens.
Bioassay-guided fractionation of the 7:3 MeOH/water extract of a cultured cyanobacterium strain identified as Fischerella sp. yielded nine isonitrile-containing alkaloids. Three of the compounds, ...ambiguine H isonitrile (1), ambiguine I isonitrile (2), and ambiguine J isonitrile (3), are new, while the other six, 12-epi-hapalindole H, ambiguine A isonitrile, ambiguine B isonitrile, ambiguine D isonitrile, ambiguine E isonitrile, and ambiguine F isonitrile, have been previously isolated from Fischerella ambigua. The structures of the compounds were determined by 1D and 2D NMR techniques and mass spectrometric data. Ambiguine H isonirile and ambiguine I isonirile possess antibacterial and antimycotic activity.
The extract of a sample of the sponge Theonella aff. swinhoei collected in Madagascar exhibited promising in vitro antiplasmodial activity. The antiplasmodial activity was ascribed in part to the ...known metabolite swinholide A. Further investigation of the extract afforded three unusual cyclic peptides, cyclotheonellazoles A–C (1–3), which contain six nonproteinogenic amino acids out of the eight acid units that compose these natural products. Among these acids the most novel were 4-propenoyl-2-tyrosylthiazole and 3-amino-4-methyl-2-oxohexanoic acid. The structure of the compounds was elucidated by interpretation of the 1D and 2D NMR data, HRESIMS, and advanced Merfay’s techniques. The new compounds were found to be nanomolar inhibitors of chymotrypsin and sub-nanomolar inhibitors of elastase, but did not present antiplasmodial activity.
Eight new and four known peptaibols were isolated from a strain of the fungus, Trichoderma atroviride (NF16), which was cultured from an Axinellid sponge collected from the East Mediterranean coast ...of Israel. The structures of the pure compounds were determined using HRMS, MS/MS and one- and two-dimensional NMR measurements. The isolated compounds belong to the trichorzianines, a family of 19-residue linear hydrophobic peptides containing a high proportion of α-aminoisobutyric acid (Aib), an acetylated N-terminus and a C-terminal amino alcohol. These new peptaibols exhibited antimicrobial activity against environmental bacteria isolated from the Mediterranean coast of Israel.
Microcystins constitute a serious threat to the quality of drinking water worldwide. These protein phosphatase inhibitors are formed by various cyanobacterial species, including Microcystis sp. ...Microcystins are produced by a complex microcystin synthetase, composed of peptide synthetases and polyketide synthases, encoded by the mcyA-J gene cluster. Recent phylogenetic analysis suggested that the microcystin synthetase predated the metazoan lineage, thus dismissing the possibility that microcystins emerged as a means of defence against grazing, and their original biological role is not clear. We show that lysis of Microcystis cells, either mechanically or because of various stress conditions, induced massive accumulation of McyB and enhanced the production of microcystins in the remaining Microcystis cells. A rise in McyB content was also observed following exposure to microcystin or the protease inhibitors micropeptin and microginin, also produced by Microcystis. The extent of the stimulation by cell extract was strongly affected by the age of the treated Microcystis culture. Older cultures, or those recently diluted from stock cultures, hardly responded to the components in the cell extract. We propose that lysis of a fraction of the Microcystis population is sensed by the rest of the cells because of the release of non-ribosomal peptides. The remaining cells respond by raising their ability to produce microcystins thereby enhancing their fitness in their ecological niche, because of their toxicity.
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