Synthesis of four tritium‐labelled aminowarfarin methyl ketal regioisomers

6‐Bromo‐4′‐nitro‐, 4′‐bromo‐6‐nitro‐, 4′‐bromo‐7‐nitro‐ and 4′‐bromo‐8‐nitrowarfarin methyl ketals were prepared and together subjected to catalytic tritiation over palladium on charcoal to produce tritium‐labelled aminowarfarin methyl ketals. The four regioisomers were separated by thin‐layer chromatography to yield pure compounds of high (24.9–29.8 Ci/mmol) specific activity.