SYNTHESIS OF a-HYDROXYTRYPTOPHAN
Nov., 1950
nitropropane. A trace of N-(2-nitroisobutyl)piperidine was obtained by means of an acid catalyzed amine exchange. This investigation has revealed no exception
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to the proposal that alkylation of nitroparaffins by amines must proceed through an eliminationaddition mechanism. URBANA, ILLINOIS
RECEIVED MARCH 16, 1950
[CONTRIBUTION FROM THE INSTITUTE OF POLYTECHNICS, UNIVERSITY OF CITY OSAKA]
Studies on Amino Acids. 111. The Synthesis of a-Hydroxytryptophan BY MUNIOKOTAKE,TAKEO SAKAN AND TOSHIO MIWA
Y. Kotake,’ et al., have demonstrated the pres- recently, by Witkop6 to be identical with that ence of kynurenine, as well as kynurenic acid, obtained from phalloidin. In our investigations, we found that o-nitroin the urine of rabbits which have been fed tryptophan. They have postulated the following phenylacetic acid ethyl ester undergoes the sequence of reactions in the intermediary metab- Michael condensation with diethyl methylenemalonate in the presence of sodium ethoxide. olism of tryptophan. The product was treated with 48% hydrobromic acid and decarboxylation took place, giving an @cH -oH ,2----f acid compound with formula CIIHIIOGN. When the condensation product was treated with ethyl H nitrite and sodium ethoxide, a corresponding I oximino ester was produced with 60% yield. -CH2--CH--COOH Since o-nitrophenylsuccinic acid was obtained m J 0 ~ --+ by hydrolyzing this ester with hydrochloric acid, the oximino ester must have the structural formula H (VI) and thus the chemical structure of the conI1 densation product must be (V). The acid with the empirical formula C l l H ~ l O ~ N is therefore shown to be o-nitrophenylglutaric acid (VII). On reducing the oximino ester (VI) a t 0” with stannous chloride and hydrochloric acid in I11 glacial acetic acid, the amino ester crystallized OH I out with tin chloride as a double salt. After removing the tin with hydrogen sulfide, the product was hydrolyzed with hydrochloric acid and concentrated in an atmosphere of carbon dioxide: The hydrochloride of the amino acid was obIV tained in a crystalline form, which after recrysa-Hydroxytryptophan, which is postulated as tallization from water decomposes a t 208’. an intermediary in the above scheme, was isolated The free amino acid, decomposition point 248by Wieland and Witkop2 from the hydrolysis 249”, was obtained from this hydrochloride. product of phalloidin, a toxic principle found in a The analytical results obtained for this compoisonous mushroom, Amanita phalloides. The pound closely agree with the data calculated for yield of amino acid was too small to permit a-hydroxytryptophan and furthermore a violet biological experiments. Later, Butenandt3 was color shown by the ninhydrin test characterizes able to show that this compound possesses a the compound as an a-amino acid. In the Millon hereditary-controlling gene hormone activity, and Folin-Denis reactions the compound gave a though weaker than kynurenine, in producing the yellowish-orange and a dark blue color, respeccolor of eyes of Drosophila melanogaster; in this tively. An aromatic amine, which was liberated respect a-hydroxytryptophan acts as pro-kynur- only when the amino acid was warmed with enine. alkali, could be diazotized and coupled with Previous attempts to synthesize a-hydroxy- @-naphthol to produce a dye. The positive tryptophan proved uns~ccessful.~JThe opti- “Pine splint reaction” was shown when the amino cally active a-hydroxytryptophan which has been acid was dry distilled with zinc dust. These obtained by oxidizing L-tryptophan with per- facts indicate the presence of oxindole residue in acetic acid under controlled conditions is proved, the molecule. The results obtained by these (1) Y. Kotake, Z.physiol. Ckem., 196, 158 (1931). tests agree with those reported by Wieland for (2) Wieland and Witkop, Ann., 643, 171 (1940). the a-hydroxytryptophan, which has been iso(3) Butenandt, Nafuvwuiss., Is,447 (1940). lated from phalloidin. The amino acid we have (4) Fischer and Smeykal, Be?., 68, 2368 (1923).
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a-cooH
(5) Julian, Pikl and Wantz, THIS JOURNAL, 67, 2026 (1935).
(6) Witkop, Ann., 668, 9 8 (1947).
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MUNIOKOTAKE, TAKEO SAKAN AND TOSHIO MIWA
Vol. 72
over calcium chloride, and the solvent removed. When the sides of the container were rubbed with a glass rod, the /\l--CH3-C02C&I, SdOC?Hk
