The Biochemistry of Bakanae Fungus

In the preceeding paper of this series, it has been reported that the function of 3 oxygen atoms in gibberic acid, C19H22O3, was identified as being one carbonyl and one carboxyl. In this paper, the results of oxidation of gibberic acid by selenium dioxide are described which were attempted in order to acertain the position of the ketone group. The oxidation does not take place by the usual method, but advances smoothly when the alcoholic solution of gibberic acid is heated at 144° during 3 hours in a sealed tube using six times of the theoretical amount of selenium dioxide. By this oxidation, gibberic acid gives a substance named “gibberdionic acid” Gibberdionic acid, crystallizing into yellowish plates, mp 188°, has an empirical formula, C19H20O4, and shows an absorption spectrum of ultraviolet ray very similar to that of gibberic acid. This fact shows that there occurs no change in the mother nucleus of gibberic acid but oxidation occurs in one of the side chains introducing a new carbonyl group at the position of the next carbon atom of the ketone group which existed originally. Gibberdionic acid is negative against Schiff's reagent, the reaction of Tschugaef's diketone-Ni-dioxime, but -positive for the reaction of tolidine-acetate, showing the existence of an aldehyde group. Moreover, this acid gives the ppt. of cadmium-yellow and colourless crystals when recrystallized from alcohol containing water, showing just the same reactions of phenylglyoxal. By treating gibberdionic acid with hydrogen peroxide in an alkaline solution, we obtain one mole of a hydroxy-dicarboxylic acid and one mole of carbon dioxide, but no aldehyde and volatile acid. This acid has been named “gibberdicarboxylic acid” and it crystallizes out in the form of colourless needles and decomposes at 145° We propose as the empirical formula of gibberdicarboxylic acid C17_??_18H22_??_24O6, and its absorption spectrum of ultraviolet ray is observed to be very similar to that of gibberic acid. Therefore, gibberdionic acid must be an acid which contains a glyoxal, -CO-CHO. From these results, it is ascertained that the position of ketone group in gibberic acid is located not in the mother nucleus but in one of side chains and, moreover, adjacent to the terminal methyl group of its side chain.