Sovember 1968 overnight to yield a yellow solid. The compound was purified by recrystallization of the crude product twice from 50y0 aqueous CH30H and once from H40. After being dried a t room temperature for 4 hr and then a t 135" for an additional 16 hr the product weighed 2.3 g ( 2 2 5 yield); mp 203-205" dec (sintered at 185'). 300 mp (E 14,200), A: ' 280 m l ( e 12,900), 290 mp i e 24,000). *anal. (CISH22N~O~) C, H, N.
Acknowledgment.-The authors thank A h . Margaret Rounds and l [ r . John R. Gravatt for the analytical uiid instrumental measurements. Effect of Monoiodotyrosine Metabolites on Tyrosine Hydroxylase1" B\
m y
1211
YOTES
N. L C T S ~ YAND ' ~ NICOL-IS Zh.ivKk.n
UcpaiIiticnt of Pharmaceutzcal Chemistry, School of Phat rnncy, I'niucrsity of .\la,ylnnd, Baltimore, M a r y l a n d 21201
TABLE I AIOXOIODOTYROSINE YIETABOLITES AS
FROM
DETERMINED
RADIOIUTOQRAPHS BuOH-dioxane
Metabolitea
MIT, % metabolized Xetabolites Tyrosine LfIPbandPHPP MIA
B~OH-A~OH-H?~ -Net 70Xi R a t Rabbit
.--m40n-Rr
-?Vet Rat
%Rabbit
0.65 53.2 39.1
0 . 4 3 4 4 . 0 36.9
0.47 10.0 2 2 . 0 0.91 1.2 1.8 0.97 4 . 3 1 . 1
0 . 2 2 15.9 33.9 0.99 0 . 6 0 . 8 0.91 4.1 0.7
a The following abbreviations were used: NIP, 3-iodo-4-hydroxyphenylpyruvic acid; PHPP, 4-hydrox~phenylpyruvicacid; and AHA, 3-iodo-4-hydroxyphenylacetic acid. * The two pyruvic acids (identified by the R I values obtained for authentic compounds, uv light, and 2,4-dinitrophenylhydraziiie spray) could not be separated consistently by the first solvent system and codd not, be separated by the second; they are therefore listed together.
KPcrzLled June 19, 1968
The largest and most effective class of tyrosine hydroxylase inhibitors is made up of tyrosine analogs. llonoiodotyrosine (NIT), the most potent monohalogenated tyrosine analog i n vitro, is 100 times as d i v e as a-methyltyrosine, the most' active nonhalogenated tyrosine analog. Iji vivo, however, a-met'hyltyrosine is considerably more effective than N I T in its ability to block the synthesis of catecholamines and to produce pharmacological effects ascribed to the inhibit'ion of norepinephrine synthesis. I n this study, an appraisal of the inhibitory effect of J I I T metabolites on tyrosine hydroxylase mas made to indicate the significance of certain metabolic steps 011 the inactivation of NIT as a tyrosine hydroxylase inhibitor. Further, in order to bring such inadvation into perspective, a quantitative estimate of such metabolites was made by radioautographic studies on rat' and on rabbit liver tissue slices. When 14C-lIIT was incubated with rat and rabbit liver slices it was converted in each instance int80several iodinated and noniodinated metabolites. The location of identified metabolites arid the net percentage of each is given in Table I. Both deiodinat,ion'" and transamination*b have been suggested t o be the main path of morioiodotyrosine metabolism. While the results of Table I point to deiodination to tyrosine as t,he main pathway of M I T degradation in rat and rabbit h u e slices, the presence of 3-iodo-4-hydroxyphenylpyruvicacid (NIP) and of 3-iodo-4-hydroxyphenylaceticacid (MIA) indicate the extent to which transamination occurs; the accumulation of l I I A as an end product' of the transamination pathway is to be expected as NIP is unable to serve as substrate of p-hydroxyphenylpyruvic oxidase.3 The effect of some NIT metabolites on tyrosine hydroxylase activity is listed in Table 11. NIT, a powerful inhibitor of tyrosine hydroxylase (K1 = 9.2 X lo-', lit.43.9 X mas included as a st,andard ipported IIY Grant .ill-06480 from the National Institutes of . Puhlic Health Service. (b) I n partial fulfillment of t h e requirements tor t h e degree of Master of Science, University of Maryland, Aug 1967. ( 2 ) (a) J . Roche. R. 11ichel. 0. Michel, and 9 . Lissitzkp, Biochim. B i o p h ~ l s . . i c l n , 9 , 161 (1952); ( I ) ) G. A Johnson. E. G. Kim, W. Veldkamp, and R . Russell. B i o c h e m . L'tj(irm
