Development of a counter-selection method for phenylalanine auxotrophy could be a useful tool in the repertoire of yeast genetics. Fluorinated and sulfurated precursors of phenylalanine were tested for toxicity in Saccharomyces cerevisiae. One such precursor. 4-fluorophenylpyruvate (FPP). https://parisnaturalfoodes.shop/product-category/maca-powder/