• First Syntheses of Melophlins P, Q, and R, and Effects of Melophlins on the Growth of Microorganisms and Tumor Cells

      Biersack, Bernhard; Diestel, Randi; Jagusch, Carsten; Rapp, Georg; Sasse, Florenz; Schobert, Rainer; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2008-11)
    • Novel peptidomimetic compounds containing redox active chalcogens and quinones as potential anticancer agents.

      Shaaban, Saad; Diestel, Randi; Hinkelmann, Bettina; Muthukumar, Yazh; Verma, Rajeshwar P; Sasse, Florenz; Jacob, Claus; Helmholtz Centre for infection research, Inhoffenstr. 7, 38124 Braunschweig, Germany. (2012-12)
      Many types of cancer cells are associated with a disturbed intracellular redox balance and oxidative stress (OS). Among the various agents employed to modulate the intracellular redox state of cells, certain redox catalysts containing quinone and chalcogen moieties have shown considerable promise. Passerini multicomponent reaction has been developed for the synthesis of agents combining two, three or even four redox centers in one molecule in a good yield. When incubated with cancer cells these agents inhibited cell proliferation and induced apoptotic cell death. Interestingly, some of these redox active compounds exhibited quite low toxicity with normal cells. The cause was obviously OS, which was reflected by significant decrease in reduced glutathione, subsequently cell cycle arrest and induction of apoptosis.
    • 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.