Preparation of pteroylglutamic acid‐3′,5′‐²H₂ by acid catalyzed exchange with deuterium oxide

Abstract

Abstract Pteroylglutamic acid was labeled with deuterium by trifluoroacetic acid‐catalyzed exchange with deuterium oxide. The product, pteroylglutamic acid‐3′,5′‐ 2 H 2 , was selectively labeled with deuterium in the 4‐aminobenzoyl portion of the molecule; there was no evidence for isotope incorporation at C 7 or C 9 of the pteridine ring or at the glutamate residue. Isotope composition of the pteroylglutamates was determined by chemical ionization mass spectrometry following a base‐catalyzed, oxidative cleavage to either 4‐aminobenzoic acid or 4‐aminobenzoylglutamic acid. Products from the exchange reaction typically contained 1% 2 H 0 , 9% 2 H 1 , and 90% 2 H 2 isotopic species.