Compounds obtained from natural sources such as plants or microorganisms still cover about 25% of the top 35 worldwide selling ethical drug sales either as the original isolated substance or after synthetic modification1. The misconception that natural products research has failed to deliver new lead compounds is taken ad absurdum: 15 natural product derived drugs have been launched in the key markets of the United States, Europe and Japan 2000 – 2003 and 15 compounds were on Phase III clinical trails at the end of 2003.

Polyketides as low molecular weight products (< 2 kDa) from microorganisms are a rich source of significant pharmaceuticals2. Especially the genus Streptomyces is called a “talented" producer of bioactive metabolites. From a soil sample collected close to our institute, we isolated strain Gö C4/4 (Streptomyces bottropensis) and provided it to our CD-Screening approach3. With a conspicuous CD-Spectrum (fig. 1), the novel metabolite mensacarcin could be isolated.

Figure 1.  X-ray structure and CD-Spectra of mensacarcin – absolute configuration top above.

Here we present the structure elucidation, biosynthetic studies and the high potent cytotoxic activity of mensacarcin, as well as the data of some semi-synthetic derivates4. The latest results show an interesting, unusual behaviour for these kinds of compounds in the used FACS scan and mammalian cell cultures.