Examination of the structure of an unknown green fluorescent compound, compound G2, accumulated in non-growing cells of Eremothecium ashbyii by the addition of dimeric diacetyl.

The addition of dimeric diacetyl to Eremothecium ashbyii caused simultaneous accumulation of two green fluorescent compounds with the inhibition of riboflavin formation in non-growing cells. One compound, referred to as Compound G1, was identified as 6, 7-dimethyl-8-ribityllumazine as reported previously and the other is referred to as Compound G2. The latter compound was considered to be 6-methyl-7-(2-hydroxy-2-methyl-3-oxobutyl)-8-ribityllumazine because a violet fluorescent compound, 6-methyl-7-hydroxy-8-ribityllumazine was derived from Compound G2 in the presence of p-quinone and because the known action mechanism of dimeric diacetyl as a trapping agent of possible intermediates in the biosynthetic pathway. The results indicate that an immediate intermediate to 6, 7-dimethyl-8-ribityllumazine in the biosynthetic pathway of riboflavin is 4-ribitylamino-5-amino-2, 6-dihydroxypyrimidine, whose pyrimidine portion is derived by the elimination of a dimeric diacetyl fragment from the molecule of the isolated lumazine.