Facile synthesis of 14C‐nitrofurazone from 14C‐urea

The veterinary drug nitrofurazone (5‐nitro‐2‐furaldehyde semicarbazone) exhibits excellent antimicrobial properties but its application in food‐producing animals is prohibited. The illegal use of nitrofurazone is regularly monitored by food regulatory agencies. Currently, semicarbazide (SEM) is used as a marker of nitrofurazone exposure. However, the use of SEM as a marker of nitrofurazone is under scrutiny after evidence of a high incidence of false positive tests. To overcome the current dilemma, it is necessary to identify a nitrofurazone‐specific marker analyte which requires conducting nitrofurazone metabolism studies in food‐producing animals. The use of carbon‐14 labeled nitrofurazone would facilitate metabolism studies and structural elucidation of nitrofurazone metabolites of possible utility as a marker compound. In the present work, a synthetic method is described to procure radiolabeled nitrofurazone that incorporates 14 C‐ carbon at the semicarbazide moiety. The method incorporates 14 C‐carbon via employing readily available and more economically affordable [ 14 C]‐urea compared with [ 14 C]‐semicarbazide. To the best of our knowledge, there is no report on the synthesis of 5‐nitro‐2‐furaldehyde [ 14 C]‐semicarbazone from 14 C‐urea. The developed method involves monoamination of [ 14 C]‐urea followed by a condensation reaction with 5‐nitro‐2‐furaldehyde to produce 5‐nitro‐2‐furaldehyde [ 14 C]‐semicarbazone in 85% yield with greater than 98% radiochemical purity.