Endophytic Fungi as Efficient Biocatalysts in Obtaining Chiral Building Blocks

Recently, great attention has been given to enantioselective synthesis of optically pure compounds using environmental friendly methodologies due to the increasing demand for modern drugs, food ingredients and agrochemicals1. Optically pure alcohols are useful as building blocks for the synthesis of bioactive compounds and they can be transformed into other functionalities without racemization2. Chemical transformations mediated by whole cells of microorganisms have some advantages over classical chemical procedures including their low cost, high versatility and efficiency with chemo-, regio- and stereoselectivities3. The aim of this study was to identify new endophytic strains that could be used as biocatalysts in the reduction of prochiral ketones into chiral phenylethanols with excellent enantiomeric excess (e.e.) and high yields. Seven endophytic fungi strains were isolated from Handroanthus impetiginosus leaves and showed stereoselectivity in the conversion of acetophenone into 1-phenylethanol. Initially, the results showed that all strains reduced the acetophenone, however at different conversion and stereoselectivity degrees. Among all evaluated strains, Talaromyces purpurogenus H4 displayed an excellent performance with very high conversion percentage (>99.9%) and satisfactory e.e. (82.8%). T. purpurogenus H4 revealed a preference for the formation of (S)-1-phenylethanol, which demonstrated high application as precursor to natural aromas synthesis. When the bioreduction was tested with substituted acetophenones as substrates, it was demonstrated a relationship between the reactivity and the electronic nature of the substituent groups. In fact, T. purpurogenus H4 efficiently reduced both substituted acetophenones with electron attractor or donor groups but the substrates which contained electron-donating groups were less reactive than those with attractors groups. Next, the effect of some parameters in the asymmetric reduction of acetophenone by T. purpurogenus H4 was investigated: substrate concentration, reaction temperature, pH of culture medium, co-solvent, inoculum charge, stirring speed and reaction time. Due to the interesting results obtained in the bioreduction of acetophenone by T. purpurogenus H4, a preparative scale reaction was performed by using the optimized conditions. The extraction of the product was carried out with ethyl acetate. As result of purification, (S)-1-phenylethanol was isolated with 73% of yield and 96% of e.e. The bioreduction potential of the endophyte T. purpurogenus H4 makes this fungus an interesting candidate for further studies to expand its use as an environmentally friendly tool for the synthesis of other desired chiral synthons.