Novel 6-formylpterin derivatives: chemical synthesis and O2 to ROS conversion activities

Abstract

6-Formylpterin (6FP) has been demonstrated to have strong neuroprotective effects against transient ischemia-reperfusion injury in gerbils. Also it has been shown that in rats, 6FP protected retinal neurons even when it was administered after the ischemic insult. Since there is a significant need for such a compound that effectively suppresses the events caused by the lack of oxygen supply, 6FP has attracted further investigation. Unfortunately, however, 6FP is hardly soluble in water at neutral pH and in organic solvents because of its self-assembling ability. Although a several mM solution of 6FP is available in alkaline water, it is unstable. In the present study, a novel chemical derivatization of 6FP has been developed which maintains the formyl group on the 6-position of 6FP, which is essential for the physiological activities of 6FP, and increases solubility in water and organic solvents. In the method, the 2- and 3-positions of 6FP were modified by a three component coupling reaction: 6FP was subjected to the reaction with acid chloride and N,N-dimethylformamide. The derivatives synthesized here, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-pivaloylpteridine-4-one 1, 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-isobutyrylpteridine-4-one 2, and 2-(N,N-dimethylaminomethyleneamino)-6-formyl-3-o-toluoylpteridine-4-one 3, showed high solubility in water (1.0–5.6 mM) and organic solvents. The O₂ conversion property has also been determined for the derivative 1. Using an oxygen electrode, it has been found that O₂ is consumed in the presence of 1 and NADH at around pH 7.4 and that the rate of O₂ consumption is enhanced by UV-A irradiation. Electron paramagnetic resonance (EPR) analysis coupled with DMPO spin trapping has also revealed that in the presence of NADH, 1 converts O₂ to ˙O₂⁻, which is further reduced to ˙OH. By UV-A illumination in the analogous systems, ¹O₂ formation was observed. These results are similar to those reported previously for 6FP.