Potent sepiapterin reductase (SPR) inhibitor (IC50 = 53 - 74 nM for human SPR). Inhibits BH4 synthesis pathway and attenuates proliferation in naive CD4+ T cells. Suppresses proliferation of human effector CD4+ T cells following stimulation. Reduces SPR activity in mouse primary cultures of sensory neurons (IC50 = 450 nM). Ameliorates colitis, suppressing the intestinal infiltration of T cells and other immune cells in vivo. Also reduces immune-cell infiltration into mouse lungs. Reduces neuropathic and inflammatory pain in mouse models. Purity 98%. MW (observed): 262.3