Oxidative degradation of dihydrofolate and tetrahydrofolate

Abstract

7,8-Dihydrofolate has been degraded oxidatively using ferricyanide under anaerobic conditions. Three reaction pathways have been found for this oxidation, and these pathways can be controlled by variation of the pH and by the nature of the buffer anion. At pH 9, treatment of dihydrofolate with two equivalents of ferricyanide leads to quantitative formation of folate. At pH 5.6 in morpholinoethanesulfonic acid buffer, the same reactants produce p-aminobenzoylglutamate, dihydroxanthopterin, and formaldehyde. Each of these products has been identified, and isolated in high yield. 6-Formyldihydropterin can be isolated by oxidation of dihydrofolate in either phosphate or carboxylic acid buffers. This compound does not appear to be an intermediate in the formation of dihydroxanthopterin under the conditions of our experiments. Tetrahydrofolate was also degraded oxidatively using ferricyanide. Although it is more susceptible to cleavage than is dihydrofolate, tetrahydrofolate gives similar products. In addition, moderate quantities of pterin were isolated from oxidation of tetrahydrofolate at pH 5.6.