Maya Mitova

Marine bacteria associated with sponge as source of cyclic peptides

Two bacteria associated with the marine sponge Ircinia variabilis were isolated using commercial and experimental media. The use of media containing marine derived proteins improved the growth of both isolated bacteria, showing that marine bacteria need of marine derived proteins for a better growth. The composition of free and total fatty acids of both strains cultivated under different carbon source was investigated. Several diketopiperazines were isolated from both bacteria and the hypothesis of their role in the bacterial-spongy interaction is discussed.

Cyclic peptides from a Ruegeria strain of bacteria associated with the sponge Suberites domuncula.

Two new cyclic peptides, cyclo-(glycyl-L-seryl-L-prolyl-L-glutamyl) and cyclo-(glycyl-L-prolyl-L-glutamyl), have been isolated from the cell extract of a Ruegeria strain associated with cell cultures of Suberites domuncula. Three other cyclopeptides have been isolated for the first time from a natural source. Additionally, a new diastereoisomer of a known compound is reported. The structures of isolated compounds have been elucidated by means of spectroscopic data (1D-, 2D-NMR, HRESIMS) and chiral HPLC analysis. The new cyclopeptides exhibited moderate antimicrobial activity against Bacillus subtilis.

Exocellular Cyclic Dipeptides from a Ruegeria Strain Associated with Cell Cultures of Suberites domuncula

From cell cultures of Suberites domuncula was isolated a bacterial strain, SDC-1, which was identified by 16S ribosomal RNA sequence analysis as an α-Proteobacterium of the genus Ruegeria. The occurrence of the strain in sponge cell culture could be explained by its resistance to the antibiotics used in the isolation of sponge cell cultures or by the preservation of SDC-1 by host sponge cells. The fatty acid composition of SDC-1 is characterized by branched C-12 methyl fatty acids. Two new and 8 known cyclic dipeptides were isolated and characterized from the fermentation broth of SDC-1. Cyclodipeptides are one of the families of cell-cell signaling compounds and may have some role to play in sponge-bacteria interactions.

Subinhibitory concentrations of antibiotics induce phenazine production in a marine Streptomyces sp.

Subinhibitory concentrations of antibiotics were found to enhance and modulate the production of new phenazines, streptophenazines A-H, in a marine Streptomyces isolate. The streptophenazines differ in length and substitution of an alkyl chain. The pattern of metabolites formed depends on the antibiotic used. In the presence of tetracycline, streptophenazines F and G were induced and the production of streptophenazines A-D was increased. When using bacitracin, mainly streptophenazine H was produced. Streptophenazines C and H showed moderate activity against Bacillus subtilis, while streptophenazine C was also active against Staphylococcus lentus.

Triterpene saponins and iridoid glucosides from Galium rivale

Three new glycosides of the oleanene-type triterpenes, rivalosides C-E (1-3), along with three known triterpene saponins, momordin IIb (4) and rivalosides A-B (5-6), and five known iridoid glucosides: monotropein, scandoside, deacetylasperulosidic acid, geniposidic acid and asperulosidic acid, were isolated from aerial parts of Galium rivale. The structures of the new compounds were elucidated by spectral methods and chemical means as 2alpha-acetoxy-3alpha, 19alpha-dihydroxy-olean-12-en-28-oic acid 28-O-beta-D-glucopyranosyl-(1--> 6)-beta-D-glucopyranoside, 2alpha,3alpha, 19alpha-trihydroxy-olean- 12-en-28-oic acid 28-O-beta-D-glucopyranosyl-(1 --> 6)-beta-D-glucopyranoside and 3-O-beta-D-glucuronopyranosyl-24-hydroxy-olean-12-en-28-oic acid 28-O-beta-D-glucopyranoside, for rivalosides C-E, respectively. The taxonomic significance of the rivalosides in G. rivale was discussed.

Exocellular peptides from Antarctic psychrophile Pseudoalteromonas Haloplanktis.

A novel diketopiperazine, named cyclo-(D-pipecolinyl-L-isoleucine) (DKP 1), and 7 known diketopiperazines were isolated from the cell-free culture supernatant of the Antarctic psychrophilic bacterium Pseudoalteromonas haloplanktis TAC125. Two diketopiperazines containing pipecolinyl moiety were isolated for the first time from a natural source. Two new linear peptides, stable to bacterial proteolytic enzymes, were also characterized. The structures of the isolated compounds were elucidated by means of spectroscopic data (1D-, 2D-NMR, EIMS, FABMS, and ESIMS/MS) and chiral high-performance liquid chromatography. The potential antioxidant activity of the isolated compounds was evaluated by a DPPH free radical scavenging assay.

Bioactive Phenolics from Carthamus lanatus L.

Abstract Two flavonoid aglycons, eight flavonoid glycosides, chlorogenic acid and syringin were isolated from aerial parts of Carthamus lanatus. Isorhamnetin 3-O-β-ᴅ-glucoside and chlorogenic acid were found for the first time in the genus Carthamus and respectively, quercimeritrin, astragalin, kaempferol 3-O-β-ᴅ-sophoroside and syringin in the species. The ethyl acetate fraction of the methanol extract exhibited a higher antioxidant activity than the butanol fraction measured by the α,α-diphenyl-β-picrazylhydrazyl (DPPH) free radical scavenging assay. Cytotoxicity and antioxidant activities of the main constituent, luteolin 7-O-β-D-glucoside, were evaluated.

Iridoid glucosides from Galium album and G. lovcense

Abstract The iridoid composition of Galium album ssp. album, G. album ssp. pychnotrichum and G. lovcense was studied. Eleven known iridoids were isolated and identified. Two new iridoids, 7- O -acetyl-10-acetoxyloganin and 7β-hydroxy-11-methyl forsythide, were isolated from G. lovcense , and their structure elucidated.

GC-MS of Crinum latifolium L. Alkaloids

A GC-MS analysis of underivatized alkaloids from leaves of Crinum latifolium was performed. From the identified 15 alkaloids, 9 were found for the first time in this plant. Almost all alkaloids belonged to the crinane type. Substantial changes in the methylation and oxidation pattern of the alkaloids at and after flowering were observed

Antimicrobial activity and cytotoxicity of Carthamus lanatus.

Total dichloromethane, methanol and water extracts, their fractions as well as volatiles of Carthamus lanatus aerial parts were phytochemically screened and evaluated for antibacterial, antifungal and cytotoxic activity. The H(2)O/MeOH fraction of the CH(2)Cl(2) extract exhibited noticeable antibacterial activity. The same fraction and the volatiles showed significant cytotoxic activity.