Flavacol, obtained together with aspergillic acid from culture filtrates of Aspergillus flavus, is shown by synthesis to be 3-hydroxy-2 : 5-diisobutylpyrazine (I). Culture filtrates of the mould Aspergillus flavus grown on a medium containing a casein hydrolysate and sodium chloride give a crude acidic product separable into two components, one of which, aspergillic acid, is soluble in sodium hydrogen carbonate solution; the other, which we now name flavacol, C₁₄H₂₄ON₂, is soluble in sodium hydroxide solution but insoluble in sodium hydrogen carbonate solution. Flavacol does not give a coloration with ferric chloride and in its general properties, particularly its ultra-violet absorption spectrum, it resembles the isomeric deoxyaspergillic acid and 3-hydroxy-2 : 5-di-sec.-butylpyrazine. It is, however, not identical with either of these two compounds nor is it identical with racemic deoxyaspergillic acid (Dunn, Gallagher, Newbold, and Spring, this vol., p. 126). The method selected for this synthesis was that developed by Baxter and Spring (J., 1947, 1179) in which a diketopiperazine is treated with phosphoryl chloride to yield a 2-chloropyrazine (together with a 2 : 5-dichloropyrazine), treatment of which with alkali, or better with sodium ethoxide followed by reaction of the 2-ethoxypyrazine with mineral acid, yields the required 2-hydroxypyrazine. Flavacol has now been identified by synthesis as 3-hydroxy-2 : 5-diisobutylpyrazine (I). Treatment of DL-leucine anhydride (II) with phosphoryl chloride gives a mixture of products from which 3-hydroxy-2 : 5-diisobutylpyrazine (I) was directly isolated. It is identical with flavacol.