 The starting material for the reaction sequence was uric acid (8), which had been isolated from kidney stones by Carl Wilhelm Scheele in 1776.Uric acid (8) was reacted with PCl5 to give 2,6,8-trichloropurine (10), which was converted with HI and PH4I to give 2,6-diiodopurine (11).The product was reduced to purine (1) using zinc dust.