Biosynthesis of Riboflavin Preparation of Phosphorylated Pyrimidine Intermediates

2-Am ino-5-nitro-6-(r-D -ribityl)am ino-4(3H )-pyrim idinone (6a) was converted to the dimethoxytrityl derivative, which was subsequently acetylated. The trityl residue was then rem oved, and the compound was phosphorylated by the cyanoethyl method. Rem oval of the protecting groups yielded 2-am ino-5-nitro-6-(l'-D-ribityl)am inopyrim idinone 5'-phosphate (11a). Catalytic hy­ drogenation yielded the labile 2,5-diam ino-6-(T-D-ribityl)am ino-4(3H)-pyrim idinone 5'-phosphate (3a) which is the substrate for a deaminase from yeast. 5-Am ino-6-(l'-D -ribityl)am ino2,4(1 H ,3H )-pyrim idinedione 5'-phosphate (3b) was prepared by an analogous sequence of reac­ tions. It was further converted to 6,7-dim ethyl-8-(l'-D -ribityl)lum azine 5'-phosphate (12b). The phosphoric acid esters prepared by the present procedures contained about 20% of an undesired isomer as a consequence of insufficient selectivity o f the tritylation reaction.