Bioactive metabolites from Chaetomium aureum: structure elucidation and inhibition of the Hsp90 machine chaperoning activity.

Chemical investigation of the EtOAc extract of the fungus Chaetomium aureum, an endophyte of the Moroccan medicinal plant Thymelaea lythroides, afforded one new resorcinol derivative named chaetorcinol, together with five known metabolites. The structures of the isolated compounds were determined on the basis of one- and two-dimensional NMR spectroscopy and high-resolution mass spectrometry as well as by comparison with the literature. All compounds were tested for their activity towards the Hsp90 chaperoning machine in vitro using the progesterone receptor (PR) and rabbit reticulocyte lysate (RRL). Among the isolated compounds, only sclerotiorin efficiently inhibited the Hsp90 machine chaperoning activity. However, sclerotiorin showed no cytotoxic effect on breast cancer Hs578T, MDA-MB-231 and prostate cancer LNCaP cell lines. Interestingly, deacetylation of sclerotiorin increased its cytotoxicity toward the tested cell lines over a period of 48 h.

Synthesis, characterization and biological evaluation of some 16E-arylidene androstane derivatives as potential anticancer agents.

A series of new 16E-arylidene androstane derivatives were synthesized and characterized. The new compounds were screened for their anticancer activities against the human cancer cell lines SW480, A549, HepG2 and HeLa in vitro using the MTT assay. The results of the in vitro study showed that a number of compounds have shown IC(50) values lower than 20 µM against the four cancer cell lines.

A new colorimetric method to quantify ß-1,3-1,6-glucans in comparison with total ß-1,3-glucans in edible mushrooms.

Mushroom ß-glucans are known for their activity as biological response modifiers and anticarcinogenic agents. ß-1,3-1,6 Branched glucans with a triple helix tertiary structure are recognised as the most potent ones. In the present work, a colorimetric method for ß-1,3-1,6-glucan quantification based on the dye Congo red is introduced. This method is specific for ß-glucans with a triple helix. The ß-1,3-1,6-glucan content of mycelia and fruiting bodies from various mushrooms was determined and compared with the total ß-1,3-glucan content, measured by a fluorimetric method. The results show equal amounts of ß-1,3-1,6- and total ß-1,3-glucans in the analysed species but obvious differences between mycelia and fruiting bodies. On the average, 3% of mycelia and 8% of fruiting body dry mass consist of ß-1,3-1,6-glucans. The average percentage of ß-1,3-1,6-glucans in the total ß-1,3-glucan content differs between mycelia (46%) and fruiting bodies (87%).

Biosynthesis of the C(7)-cyclitol moiety of acarbose in Actinoplanes species SE50/110. 7-O-phosphorylation of the initial cyclitol precursor leads to proposal of a new biosynthetic pathway.

We have previously demonstrated that the biosynthesis of the C(7)-cyclitol, called valienol (or valienamine), of the alpha-glucosidase inhibitor acarbose starts from the cyclization of sedo-heptulose 7-phosphate to 2-epi-5-epi-valiolone (Stratmann, A., Mahmud, T., Lee, S., Distler, J., Floss, H. G., and Piepersberg, W. (1999) J. Biol. Chem. 274, 10889-10896). Synthesis of the intermediate 2-epi-5-epi-valiolone is catalyzed by the cyclase AcbC encoded in the biosynthetic (acb) gene cluster of Actinoplanes sp. SE50/110. The acbC gene lies in a possible transcription unit, acbKLMNOC, cluster encompassing putative biosynthetic genes for cyclitol conversion. All genes were heterologously expressed in strains of Streptomyces lividans 66 strains 1326, TK23, and TK64. The AcbK protein was identified as the acarbose 7-kinase, which had been described earlier (Drepper, A., and Pape, H. (1996) J. Antibiot. (Tokyo) 49, 664-668). The multistep conversion of 2-epi-5-epi-valiolone to the final cyclitol moiety was studied by testing enzymatic mechanisms such as dehydration, reduction, epimerization, and phosphorylation. Thus, a phosphotransferase activity was identified modifying 2-epi-5-epi-valiolone by ATP-dependent phosphorylation. This activity could be attributed to the AcbM protein by verifying this activity in S. lividans strain TK64/pCW4123M, expressing His-tagged AcbM. The His-tagged AcbM protein was purified and subsequently characterized as a 2-epi-5-epi-valiolone 7-kinase, presumably catalyzing the first enzyme reaction in the biosynthetic route, leading to an activated form of the intermediate 1-epi-valienol. The AcbK protein could not catalyze the same reaction nor convert any of the other C(7)-cyclitol monomers tested. The 2-epi-5-epi-valiolone 7-phosphate was further converted by the AcbO protein to another isomeric and phosphorylated intermediate, which was likely to be the 2-epimer 5-epi-valiolone 7-phosphate. The products of both enzyme reactions were characterized by mass spectrometric methods. The product of the AcbM-catalyzed reaction, 2-epi-5-epi-valiolone 7-phosphate, was purified on a preparative scale and identified by NMR spectroscopy. A biosynthetic pathway for the pseudodisaccharidic acarviosyl moiety of acarbose is proposed on the basis of these data.