Pteridine studies. Part XXXIV. Nucleophilic addition reactions of pteridine-2-thiol and 2-(methylthio)pteridine
Pteridine-2-thiol was reduced by sodium borohydride to the 3,4-dihydro-derivative. Pteridine-2-thiol also reacted readily with sodium hydrogen sulphite and the following potentially carbanionic (‘Michael’) reagents; acetylacetone, ethyl acetoacetate, dimedone, and phloroglucinol. These gave 1 : 1 adducts, namely 4-substituted 3,4-dihydropteridine-2-thiols. Pteridine-2-thiol was found to undergo covalent hydration at the 3,4-double bond.
2-(Methylthio)pteridine added the following nucleophilic agents across the 3,4-double bond; sodium hydrogen sulphite, dimedone, pyrimidine-4,6-diol, barbituric acid, and thiobarbituric acid. Reduction of 2-(methylthio)-pteridine with sodium borohydride yielded the 3,4-dihydro-derivative. However 2-(methylthio)pteridine in acid solution gave a dihydrate by addition of water to the 5,6- and 7,8-double bonds (in the pyrazine ring). 4-Methylpteridine-2-thiol underwent hydration but did not react with dimedone; 4-methyl-2-(methylthio)pteridine underwent neither reaction. Pteridine-7-ol gave a 5,6-adduct with phloroglucinol.