ihydroxypropyl)-2-[2-(4-hydroxyphenyl)ethylamino]pteridi ne of the formula (Va) is synthesized which can then be labeled with a radioactive iodine as described below and the resulting radioiodinated compound of the formula (VIa) is usedas a tracer.The compound of the formula (IXa) prepared above can then be conjugated with tyramine or a protein such as bovine serum albumin (BSA), rabbit serum albu