• A selective 3-acylation of tetramic acids and the first synthesis of ravenic acid.

      Schlenk, Andrea; Diestel, Randi; Sasse, Florenz; Schobert, Rainer; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2010-02-22)
      3-Acyltetramic acids, including delicate 3-oligoenoyl derivatives, such as the Penicillium metabolite ravenic acid, were prepared in two high-yielding steps. Reaction of tetramic acids with the ylide Ph(3)PCCO afforded exclusively the corresponding 3-acylylidenetetramic acids. These were amenable to Wittig olefinations with aliphatic, aromatic, saturated and unsaturated aldehydes after deprotonation with KOtBu. Due to its simplicity, selectivity and tolerance of pH-sensitive groups this method is superior to the established acylation protocols by Jones and Yoshii. It is also applicable to the synthesis of 3-acyltetronic acids. The new 3-oligoenoyl tetramic acids exhibited structure-dependent antimicrobial and cytotoxic activity.