Our aim is to modify this side chain to suppress the high hydrophobicity and the development of resistance. Within an ongoing research program we are searching for more suitable analoges of taxol by developing bioreductive approaches to optically pure C-13 side chain precursors. One appealing strategy in this context is the utilization of [alpha]-keto-[beta]-lactams, which can be coupled with Baccatin III.In this PhD thesis we present the elaboration of a recently outlined facile and efficient method for the synthesis of [alpha]-keto-[beta]-lactams by extension to diverse substituents R and various protecting groups (PG) at the nitrogen atom.These precursors were tested of their suitability as substrates for yeast reductases. The results were promising, because every substrate could by transform in the biotransformation. However, no enantiopure compound could be obtained; only racemic products or products with limited optically purity could be prepared.
Due to the fact, that only optically pure products are interesting for the C-13 side chain, some other experiments were realized. A collection of 15 reductases originating from yeast have been overexpressed in Escherichia coli (E. coli) as gluthatione (S)-transferase fusion proteins (GST-Fusion Protein). With these reductases we checked their ability as enantioselective reducing agents.
The aim of this PhD-Thesis was the detailed study of the 23 synthesized educts for substrate acceptance by the 15 yeast reductases by means of whole cell systems as well as with purified GST-Fusion-Proteins.