The C13-C18 fragment 3 of the novel antibiotic branimycin was prepared along two highly stereocontrolled routes. The first one uses a standard Roush crotylation protocol, whereas the second one proceeds via an allenyl silane propargylation with unexpected stereochemical consequences, which are discussed in detail.

The alkyl chain in the backbone of sphingosine derivatives can be exchanged with functionalised (labelled) side chains in a single step under cross-metathesis reaction conditions.

Lipids U 0750One-Step Labelling of Sphingolipids via a Scrambling Cross-Metathesis Reaction.-An efficient procedure for the one-step labelling of sphingolipids is elaborated including cross-metathesis reaction of N-protected ceramides (I) with alkenes (II). -(NUSSBAUMER*, P.; ETTMAYER, P.; PETERS, C.; ROSENBEIGER, D.; HOEGENAUER, K.; Chem. Commun. (Cambridge) 2005, 40, 5086-5087; Novartis Inst. Biomed. Res., A-1235 Wien, Austria; Eng.) -R. Staver 10-207