Antimicrobial Activity of Depsidones and Macrocyclic Peptides Isolated from Marine Sponge-Derived Fungus Aspergillus nidulans M256.

Chemical study on marine sponge-derivated fungus Aspergillus nidulans resulted in the isolation of seven depsidones (1-7) and two macrocyclic peptides (8 and 9). Their chemical structures were elucidated by extensive analyses of HRESIMS and NMR spectral data, as well as comparison with the literature. Compound 1 was an undescribed depsidone. All compounds exhibited significant antimicrobial activity (MICs: 2-128 µg/mL) towards at least one of seven microbial strains, including Bacillus cereus, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, and Candida albicans. Of these, chlorinated depsidones (1-3, and 5) displayed potential antimicrobial activity. Nidulin (2) possessed good activity against tested strains except for S. enterica with MIC values in range of 2-16 µg/mL. Interestingly, undescribed depsidone 1 was selectively bioactive on the Gram-positive bacteria (MICs: 2-4 µg/mL) and yeast (MIC: 8 µg/mL) but inactivity on the Gram-negative bacteria (MICs: >256 µg/mL). Macrocyclic peptides, 8 and 9, displayed modest activity against E. faecalis strain with MIC values of 32 and 128 µg/mL, respectively.

Anti-Inflammatory Properties of Longifuran A, a New Benzofuran from the Stems of Amomum longiligulare.

In this study, the following compounds were isolated from the dichloromethane fraction of the stems of Amomum longiligulare and then characterized: a new benzofuran, namely, longifuran A (1); five other phenolic compounds, namely, 4-methoxycinnamic acid (2), 2,5-dimethoxyphenol (3), eudesmic acid (4), 1,7-bis(4-hydroxyphenyl)-1,4,6-heptatrien-3-one (5), and 4,4'-dihydroxychalcone (6); and two triterpenoids, namely, 24-methylcycloartan-3ß-ol (7) and 24-methylencycloartan-3ß-ol (8). They were evaluated in terms of their inhibitory effects on NO production in LPS-stimulated RAW 264.7 macrophages. Results indicated that 1 and 5 exhibited promising inhibitory activities against NO generation with IC50 of 10.47±1.02 µM and 8.51±1.14 µM, respectively. Enzymatic assays demonstrated that they remarkably suppressed the secretion of two pro-inflammatory cytokines (i. e., IL-6 and TNF-α). They also dose-dependently inhibited the expression of inducible nitric oxide synthase and cyclooxygenase-2, two important enzymes modulating inflammation. Therefore, 1 and 5 could be targets for the development of new anti-inflammatory therapeutics.

Cytotoxic steroidal alkaloids from Kibatalia laurifolia.

Four new steroids, 3-epi-gitingensine (1), N-acetylgitingensine (6), kibalaurifoline (7) and kibalaurifenone (8), along with the known paravallarine (2), 7α-hydroxyparavallarine (3), gitingensine (4), and N-methylgitingensine (5) were isolated from the leaves of Kibatalia laurifolia. Their structures were determined primarily from mass spectrometry and 2D NMR analyses. On the basis of the known absolute configurations of 2 and 4, the absolute configurations of the new compounds were proposed. Due to the structural relationships of compounds 1-8, a biosynthetic pathway was suggested. Compound 2 was cytotoxic to KB cells (IC50 12.8 µM), followed by 1 with IC50 21.2 µM.

Structure-activity relationships in the acronycine and benzo[b]acronycine series: role of the pyran ring.

In order to explore the structure-activity relationships in the acronycine series, simplified analogues of cis-1,2-diacetoxy-1,2-dihydroacronycine and cis-1,2-diacetoxy-1,2-dihydrobenzo[b]acronycine (S23906-1, under clinical trials) lacking the fused pyran ring, but possessing an acetoxymethyl leaving group at position 4 were prepared. These new analogues only displayed marginal antiproliferative activity compared to the parent compounds. The presence of the angularly fused dimethylpyran ring appears as an indispensable structural requirement to observe significant cytotoxic activity in this series.

Structure-activity relationships and mechanism of action of antitumor benzo[b]pyrano[3,2-h]acridin-7-one acronycine analogues.

The cytotoxic and antitumor activities of cis-1,2-diacyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one derivatives 3, 6-9 were strongly correlated with their ability to give covalent adducts with purified, as well as genomic, DNA. Such adducts involve reaction between the exocyclic N-2 amino group of guanines exposed in the minor groove of double helical DNA and the leaving ester group at the benzylic position 1 of the drug. A transesterification process of the ester group from position 2 to position 1 in aqueous medium accounted for the intense activity of the cis-1-hydroxy-2-acyloxy-6-methoxy-3,3,14-trimethyl-1,2,3,14-tetrahydro-7H-benzo[b]pyrano[3,2-h]acridin-7-one derivatives 10-13. Compounds without acyloxy or hydroxy group at position 1, such as 15, 17, 18, and 22, were inert with respect to DNA and almost devoid of significant cytotoxic activity. Condensation of 5-amino-2,2-dimethyl-2H-chromene (26) with 3-bromo-2-naphthoic acid (27), followed by cyclization, gave access to 6-demethoxy analogues. Diacetate 32 and cyclic carbonate 33, both belonging to the latter series, were less reactive toward DNA and less cytotoxic than their 6-methoxy counterparts 3 and 34. DNA alkylation appears thus to play an important role in the antitumor properties of benzo[b]pyrano[3,2-h]acridin-7-one derivatives.

Covalent binding to glutathione of the DNA-alkylating antitumor agent, S23906-1.

The benzoacronycine derivative, S23906-1, was characterized recently as a novel potent antitumor agent through alkylation of the N2 position of guanines in DNA. We show here that its reactivity towards DNA can be modulated by glutathione (GSH). The formation of covalent adducts between GSH and S23906-1 was evidenced by EI-MS, and the use of different GSH derivatives, amino acids and dipeptides revealed that the cysteine thiol group is absolutely required for complex formation because glutathione disulfide (GSSG) and other S-blocked derivatives failed to react covalently with S23906-1. Gel shift assays and fluorescence measurements indicated that the binding of S23906-1 to DNA and to GSH are mutually exclusive. Binding of S23906-1 to an excess of GSH prevents DNA alkylation. Additional EI-MS measurements performed with the mixed diester, S28053-1, showed that the acetate leaving group at the C1 position is the main reactive site in the drug: a reaction scheme common to GSH and guanines is presented. At the cellular level, the presence of GSH slightly reduces the cytotoxic potential of S23906-1 towards KB-3-1 epidermoid carcinoma cells. The GSH-induced threefold reduction of the cytotoxicity of S23906-1 is attributed to the reduced formation of lethal drug-DNA covalent complexes in cells. Treatment of the cells with buthionine sulfoximine, an inhibitor of GSH biosynthesis, facilitates the formation of drug-DNA adducts and promotes the cytotoxic activity. This study identifies GSH as a reactant for the antitumor drug, S23906-1, and illustrates a pathway by which GSH may modulate the cellular sensitivity to this DNA alkylating agent. The results presented here, using GSH as a biological nucleophile, fully support our initial hypothesis that DNA alkylation is the major mechanism of action of the promising anticancer drug S23906-1.