Pterin Chemistry. Part 92. Loading Experiments with 6α,β- Tetrahydro-L-(3′-2H1)biopterin

6α,β-Tetrahydro-L-[3′-2H1]biopterin ([3′-2H1]-1) was administered orally to two primapterinuric patients in order to investigate the biosynthetic pathway of 7-substituted pterins in humans. L-Primapterin (2) and L-biopterin were isolated from urine after loading and measured by GC/MS. L-Biopterin and L-primapterin were labelled with 2H to an equal extent. From this result, one can conclude that L-primapterin is formed from tetrahydro-L-biopterin, very probably via an intramolecular rearrangement.