Kribellosides, novel RNA 5'-triphosphatase inhibitors from the rare actinomycete Kribbella sp. MI481-42F6

Yeast capping enzymes differ greatly from those of mammalian, both structurally and mechanistically. Yeast-type capping enzyme repressors are therefore candidate antifungal drugs. The 5′-guanine-N7 cap structure of mRNAs are an essential feature of all eukaryotic organisms examined to date and is the first co-transcriptional modification of cellular pre-messenger RNA. Inhibitors of the RNA 5′-triphosphatase in yeast are likely to show fungicidal effects against pathogenic yeast such as Candida. We discovered a new RNA 5′-triphosphatase inhibitor, designated as the kribellosides, by screening metabolites from actinomycetes. Kribellosides belong to the alkyl glyceryl ethers. These novel compounds inhibit the activity of Cet1p (RNA 5′-triphosphatase) from Saccharomyces cerevisiae in vitro with IC50s of 5–8 μM and show antifungal activity with MICs ranging from 3.12 to 100 μg ml−1 against S. cerevisiae.