Kainic acid, C
10H
15O
4N⋅H
2O, the anthelmintic principle, was extracted from
Digenea simplex Ag., in 0.02-0.06% yield. Kainic acid is soluble in water, forming an acid solution, and is sparingly soluble or insoluble in ethanol, acetone, ether, and benzene. Molecular weight, 213; pK′, 2.16, 4.57, 10.42; [α]
D25: -12.7°. It gives positive reaction for secondary amine, colors yellow with ninhydrin, and this yellow substance possesses the absorption maximum at 429mμ. The dry distillation of kainic acid resulted in evolution of carbon dioxide, formation of a pyrrole-like substance giving positive pine splinter and Ehrlich reactions, and needle crystals of m.p. 140°, corresponding to the formula C
16H
18O
2N
2. Kainic acid possesses one double bond and forms dihydrokainic acid, m.p. 285° (decomp.), C
10H
17O
4N, [α]
D25: -37°. Acetylation of kainic acid with acetic anhydride gives N-acetylkainic anhydride, C
12H
15O
4N, and the same with dihydrokainic acid gives N-acetyldihydrokainic anhydride, C
12H
17O
4N. Esterification of kainic and dihydrokainic acid respectively yields the dimethyl ester of b.p
3 133° and b.p
3 140°. Kainic acid does not show a marked absorption in the ultraviolet region but the absorptions of -NH, -COOH, and -COO- appear in the infrared region. From the foregoing results, a structure of unsaturated imido acid of (C
8H
12) (COOH)
2⋅NH⋅H
2O with one double bond has been proposed.
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