S45: Enzymatic Total Syntheses, Tailored Enzymes and Chemo-enzymatic Syntheses - New Aspects of Natural Product Drug Discovery and Design

Many currently used drugs are either natural products or – more often – are derived from natural products, because the natural products themselves have various disadvantages. Biosynthesis studies set the stage for the design of natural product analogues by combinatorial biosynthesis, precursor-directed biosynthesis of mutasynthesis.  This involves incorporation experiments with isotope-labeled precursors, cloning, sequencing and analyzing of gene clusters of biosynthetic pathways, typically followed by gene-inactivation experiments and studies of single, overexpressed enzymes. The latter is essential to understand their mechanism of action and their substrate specificities, crucial for future design of analogues. However, incorporation experiments only allow the identification of basic building block molecules, often not useful for analogue design. Gene inactivation experiments often yield shunt products rather than pathway intermediates useful for enzyme studies, and consequently enzyme studies are often restricted to enzymes initiating a pathway, or to the last enzyme/s of a given pathway. Further complications arise from the formation of complexes of co-dependent enzymes necessary to pass on instable pathway intermediates. As a possible solution, entire pathways can be studied and be reconstituted using mixtures of overexpressed enzymes, and protein structures of key enzymes can be investigated and redesigned to be suitable, e.g. for mutasynthesis. As an example, a report of our studies on gilvocarcin-type anticancer natural products will be presented, for which the investigation of key biosynthetic steps and the design of analogues with improved drug properties was hampered by the above mentioned complications.