Stereochemistry of biopterin cofactor and facile methods for the determination of the stereochemistry of a biologically active 5,6,7,8-tetrahydropterin.

The structure of (-)-tetrahydrobiopterin, the cofactor for phenylalanine, tyrosine, and tryptophan hydroxylases, was determined as (6R, 1'R, 2'S)-6-(1',2'-dihydroxypropyl)-5,6,7,8-tetrahydropterin by X-ray crystallographic analysis. The CD spectra of (-)-tetrahydrobiopterin exhibits a negative Cotton effect at 290-240 nm in pH 3.2 solution. The relationship of the negative Cotton effect and the 6R configuration was supported by the application of CD analysis with 2-methyltetrahydronaphthalene as a model compound. The stereochemistries at the C(6) position of various biologically active 6-substituted tetrahydropterins were determined from the CD spectra. The relative configuration of two asymmetric centers, C(6), and C(1'), was determined by HPLC analysis on a strong cation exchange column.