An abbreviated synthesis of tetrahydropteridines

5,6,7,8-Tetrahydrobiopterin, the naturally occurring essential cofactor for the enzymatic hydroxylations of phenylalanine, tyrosine and tryptophan, and its synthetic analog 2-amino-6-methyl-5,6,7,8-tetrahydro-4(3H)-pteridinone, have been synthesized in good yield by the direct hydrogenation of 1-(2-amino-1,6-dihydro-5-nitro-6-oxopyrimidin-4-yl-amino)-1,5-dide oxy-L- erythro-pentulose and 2-amino-6-hydroxy-5-phenylazo-4-pyrimidylamino-acetone, respectively. The reactions were carried out at room temperature in trifluoroacetic acid over a platinum catalyst at 2 atm and the products, each containing a mixture of the two possible C-6 isomers, were isolated by precipitation. The simplicity of the preparative method suggests the procedure may be applied generally to the synthesis of all tetrahydropteridines derived from similar pyrimidine precursors.