Efficient syntheses of 13C‐ and 14C‐labelled 5‐benzyl and 5‐indolylmethyl L‐hydantoins

Robust and straightforward methods are described for the first syntheses of highly pure ¹³C‐ and ¹⁴C‐labelled L‐5‐benzylhydantoin (L‐BH) and L‐5‐indolylmethylhydantoin (L‐IMH) by cyclizing the amino acids L‐phenylalanine and L‐tryptophan, respectively, with potassium cyanate. [3‐¹³C]‐L‐phenylalanine was used to prepare [6‐¹³C]‐L‐BH and [indole‐2‐¹³C]‐L‐tryptophan was used to prepare [indole‐2‐¹³C]‐L‐IMH, which we required for solid‐state NMR experiments with a hydantoin transport protein. The successful incorporation and integrity of the ¹³C labels was confirmed by solution‐state NMR spectroscopy. [¹⁴C]Potassium cyanate was used to prepare [2‐¹⁴C]‐L‐BH and [2‐¹⁴C]‐L‐IMH, which we required for transport assays with the protein. Copyright © 2010 John Wiley & Sons, Ltd.