IDENCE FOR THE STRUCTURE OF 6-PYRUVOYLTETRAHYDROPTERIN, AN INTERr>1EDIATE IN THE BIOSYNTHESIS OF TETRA HYDROBIOPTERIN

• Rect~t reports on the biosynthesis of tetrahydrobiopterin (BH4) have led to the recognition of 6-pyruvoyl tetrahydropterin (PPH4) as an intermediate of key importance (1-7). Its exact chemical structure has long resisted elu­ cidation; this was partly due to its instability and to the difficulties in obtaining substantial quantities of material. In fact, the only known pro­ cedure for the preparation of PPH4 requires purified PPH4-synthase (PPH4S) and purified dihydroneopterin triphosphate (NH2TP), the latter also having to be prepared enzymatically from GTP (8). Although the body of evidence presented in favour of the 6-pyruvoyl tetrahydropterin structure is convin­ cing, it is mainly of secondary nature. In view of this, we consider it important to obtain further information about this intermediate's chemical properties and constitution. In a preliminary report at the 1986-meeting on "Chemistry and Biology of Pteridines", we presented IH-NMR experiments designed to follow directly the PPH4S catalyzed conversion of NH2TP in the NMR-tube (7). These data coul d correl ate the di sappearance of the NH2TP signals with the appearance of a new signal which was attributed to the (3' )-CH3 group of PPH4 (7). Unfortunately, the signals of the hydrogens at position 7 of the pterin nucleus of PPH4 could neither be assigned nor identified. This was due to the relatively low signal to noise ratio, as well as to the interference of