7,8-dihydro-l-biopterin (BH2), an analogue of the natural cofactor BH4, is a precursor in the synthesis of BH4 [1].

Tetrahydrobiopterin (BH4) is a key redox-active cofactor involved in endothelial isoform of NO synthase (eNOS) catalysis. BH4 is an important determinant of NO-dependent signaling pathways. Oxidation of BH4 has been observed in vascular cells in the setting of the oxidative stress associated with diabetes [1,2].

In cultured aortic endothelial cells, supplementation with BH2 abolished VEGF-induced NO production. DHFR but not GTPCH1 knockdown increased reactive oxygen species (ROS) production. BH2 abolished the increase in ROS production induced by DHFR knockdown. Intracellular BH2, as well as the relative concentrations of BH4 and BH2, together play a determining role in the redox regulation of eNOS-modulated endothelial responses [2]. 7,8-dihydro-L-biopterin was a reduced form of pterins. Pterins noncompetitively inhibited rat liver GTP cyclohydrolase I activity. 7,8-dihydro-L-biopterin exhibited approximately 12-times more potent than oxidized pterins. The Ki values for 7,8-dihydro-L-biopterin was 14.4 μM [1].

References:
[1] Shen R, Alam A, Zhang Y.? Inhibition of GTP cyclohydrolase I by pterins[J]. Biochimica et Biophysica Acta (BBA)-General Subjects, 1988, 965(1): 9-15.
[2] Sugiyama T, Levy B D, Michel T.? Tetrahydrobiopterin recycling, a key determinant of endothelial nitric-oxide synthase-dependent signaling pathways in cultured vascular endothelial cells[J]. Journal of Biological Chemistry, 2009, 284(19): 12691-12700.