Studies on biologically active pteridines. III. The absolute configuration at the C-6 chiral center of tetrahydrobiopterin cofactor and related compounds.

Tetrahydrobiopterin, the natural pteridine cofactor for aromatic amino acid hydroxylases, was produced stereopecifically with reference to the C-6 chiral center from 7,8-dihydrobiopterin by the action of dihydrofolate reductase. Similarly, 7,8-dihydro-6-methylpterin was reduced to tetrahydro-6-methylpterin having the same 6-configuration by the same enzyme. The absolute configuration of these tetrahydropterins at the C-6 chiral center was determined to be L, as in (2S)-1,2,3,4-tetrahydro-2-methylquinoxaline, which was servied from L-alanine, by comparison of the CD spectra.