The glycolipid flocculosin-A from the fungus <i>Anthracocystis flocculosa</i> , or how to deal with cotton-wool-like crystals

Flocculosin A is a strong antifungal metabolite secreted by the Basidiomycota fungus Anthracocystis flocculosa (formerly Pseudozyma flocculosa). It crystallizes in the form of long, soft cotton-wool-like needles, usually observed together with the mycelium in liquid culture conditions. Many crystallization tests were carried out. Among them, only a very slow cooling technique was able to yield suitable crystals, which were needle-like with a maximum thickness of 5 µm and several millimetres long. These crystals permitted us to record single-crystal X-ray diffraction data and solve the crystal structure as well as to determine the absolute configurations of the three chiral centres present in the two lipid chains.