L-Biopterin (1), one of the most ubiquitous compounds in the class of the naturally occurring pterins, was isolated from human urine as a growth factor of Crithidia fasciculata by Patterson et al. 1 Through its 5, 6, 7, 8-tetrahydro form, 1 functions as an essential enzyme cofactor in the conversion of phenylalanine to tyrosine2 and tyrosine to DOPA, 3 in melanine synthesis, 4 and in tryptophan hydroxylation. 5 As a consequence, tetrahydrobiopterin has ...
