Complex sentence: Charles Heidelberger, who had earlier found that fluorine in fluoroacetic acid inhibited a vital enzyme, asked Robert Duschinsky and Robert Schnitzer at Hoffman-La Roche to synthesize fluorouracil, and in 1957 they reported its efficacy against transplated tumors in rats and mice.
Split into simpler sentences: Charles Heidelberger, who had earlier found that fluorine in fluoroacetic acid inhibited a vital enzyme. At his request Robert Duschinsky and Robert Schnitzer at Hoffman-La Roche synthsized fluorouracil, and in 1957 they reported its efficacy against transplated tumors in rats and mice.