Nov. 5, 1960
COMMUNICATIONS TO THE EDITOR
(8.58 and 8.59) for these compounds probably result from shielding of the absorbing methyl rotons by the T electrons of the other ring double &mdls; the occurrence of such shielding limits the number of configurations which must be considered for these compounds. It is noteworthy that this diamagnetic shielding is absent in pyrethrosin,l9 which exhibits absorption a t 8.14; in this case, a paramagnetic shift derived from the attachment of an acetate function is observed. We wish to express our sincere thanks to the Goodyear Tire and Rubber Co. and Dr. H. S. Gutowsky (rubber samples), Drs. F. Sorm and L. Dolejg (germacrone and costunolide), Dr. S. M. McElvain (caryophyllene), Dr. S. C. Bhattacharyya (costunolide), Dr. D. H. R. Barton (pyrethrosin), Mr. 0. Norton (n.m.r. spectra), and the National Science Foundation (Undergraduate Fellowship to D.M.G.). (17) V. Herout and F. h r m , Chsm. ond I n d . , 1067 (1959); A. S. Rao, G . H. Kelkar and S. C. Bhattacharyya, Tdrohcdron, 9, 275 (1960).
(18) L. M. Jackman, ref. 1, p. 129. (10) D. H. R. Barton. 0. C. Blickman and P. de Mayo, J . Chcm. SOL, 2263 (1960).
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R CHEMICAL ENGINEERING R. B.BATES D. M. GALE now wish to report unambiguous evidence in supR E C C S ~ D SEPTEMBER 21,1960
DEPARTMENT OF CHEMISTRY AND UNIVERSITY OF ILLINOIS URBANA. ILLINOIS
THE STEREOCHEMISTRY OF THE ENZYMIC DECARBOXYLATION OF AMINO ACIDS
Sir: The recently acquired strategic importance of asymmetrically deuterated biogenic amines in the field of pharmacology' and in mechanism studies with amine oxidases2 has made it imperative to establish the absolute stereochemistry of the enzymic decarboxylation of amino acids. This ubiquitous biochemical reaction which is known to be pyridoxal phosphate (PPa1)-depended is of practical value2in preparing optically pure a-deuterated amines. The work of Mandeles, Koppelman and Hanke' (in collaboration with F. Westheimer) has served to establish that tautomerization of the postulated Schiff base intermediate ( 1 ) L to give (11) must be stereospecific but it is not known whether the overall reaction proceeds with retention or inversion of configuration (I11 -+ IV). It might be expected, however, that the transition state for the release of carbon dioxide should resemble that for protonation of the a-carbon (I) since in all probability the same active site accommodates the R group (I) in both transition states. Accordingly, over-all retention of configuration may be expected in the enzymic decarboxylation of amino acids (111 + IV). We
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port of this view. The chemical synthesis of both R- and S-a-dtyramine6 (VI and VII, respectively) from asymmetric intermediates of known absolute configuration has been accomplished. The relative rates of oxidation of these synthetic substrates by monoamine oxidase has allowed assignment of an absolute confQuration to enzymically prepared a-d-tyramine.23' Hydroxylation of p-allylanisole (esdragol) with performic acid7 gave 1,2-dihydroxy-3-(p-methoxyphenyl)-propane (b.p. 158'(2.5 mm.)), which was cleaved with lead tetraacetate in benzene to p-methoxyphenylacetaldehyde, b.p. 78-79' (0.1 mm.)s (65% over-all yield). Reduction of dcamphor with lithium aluminum deuteride in ether a t -70' gave 1-d-isoborneolg a t least 97% labeled on the carbinol carbon.10 The deuterioisoborneol was converted to the bromomagnesium salt l 1 and treated with p-methoxyphenylacetaldehyde according to Streitwieser's procedure.I2 There resulted a 40y0 yield of l-d-p-methoxyphenethyl alcohol (V, R = p-methoxybenzyl), b.p. 95' (1 ".)la [ a J 2 ' -1.44' ~ (neat).14 Ac-
( 6 ) Specification of asymmetric configuration according to R. S Cahn, C. K. Ingold and V. Prelog, Ex@cricntia,12, 81 (1956). (7) D . Swern, "Organic Reactions," Roger Adams, Ed., John Wiley and Son$, Inc., New York, N. Y., 1953, Vol. VII, p. 378. ( 8 ) H. Plieninger and B. Kiefer. C h e w . Bcr., 90, 617 (1957). reported the preparation of this aldehyde using different methods which proved unsatisfactory in our hands. (1) B. Belleau, J. Burba, M. Pindell and J. Reiffenstein, forthcoming (9) A. Streitwieser. Jr., and W. D . Schaeffer, THISJOURNAL, 79,6233 publication in Science. (1957). (2) B . Belleau, M.Fang, J. Burba and J. Moran, THISJOURNAL, (10) Determined by n.m.r. analysis. We are grateful to Dr. R . R . 83, 5752 (1960). Fraser for the interpretation of the n.m.r. spectra and for stimulating (3) A. E . Braunstein,"The Enzymes,'' Vol. 2, 2nd Ed., P. D . Boyer, discussions. H. Lardy and K. Myrbkk, Ed., Academic Press, New York. N. Y., (11) G. Vavon and A. Antonini, Compt. rend., 291, 1120 (1951). 1960, p. 113. (12) A. Streitwieser, Jr., and J. R. Wolfe, Jr., Tars JOURNAL, 79, (4) S. Mandeles, R. Koppelman and M. E. Hanke, J . B i d . Chcm., 803 (1957). 209, 327 (1954). (13) C.H. DePuy and R. E. Learp, ibid., 79, 3710 (1957). T6, (5) D . E. Metzler, M. Ikawa and E. E. Snell, THISJOURNAL, (14) In a recent paper, Streitweisetlr h a noted that with the 648 (1954). possible exception of enzymically prepared 1-d-ethsnol, all optically
COMMUNICATIONS TO THE EDITOR
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cording to Streitwieser's interpretation,l6 this alcohol should be of near optical purity. The wel1established mechanism for the Meerwein-Ponndorf reductionl6 allows the assignment of absolute configuration (S)16shown in (V) (R = p-methoxybenzyl). The alcohol (V) was converted to the t ~ s y l a t e ,m.p. '~~~ 5 8~O , which was converted to the corresponding azide by reaction with excess sodium azide. This type of displacement by azide is known to proceed with complete inversion of configuration. Reduction of the crude azide with lithium aluminum hydride in ether and hydrolysis with hydrobromic acid gave (R)-1-dtyramine (VI) isolated as the crystalline hydrochloride. It follows that its deuterium content must be the same as that of the starting deuterioisoborneol. The preparation of (S)-1-d-tyramine (VII) was accomplished by first treating the alcohol (V) with phosphorus tribromide in the presence of collidine. Under these conditions (presence of collidine) , virtually complete inversion of configuration should The bromide thus obtained (b.p. 140°(13 35% yield) was submitted to the same reaction sequence already applied to the above tosylate to give the desired (S)-1-d-tyramine (VII). The rates of oxidation by rat liver monoamine oxidase of these two synthetic substrates were measured using tyramine as a standard.20 The active deuterio alcohols of absolute contigaration (V) are dextrorotatory. I n view of t h e existence of *-hydrogen bonding in our atcohol (see I . M. Goldman and R. 0. Crisler, J . Org. Chem., 23, 731 (195811, the sign of the rotation may lose significance. (1.5) A. Streitwieser, J r . , a'.D . Schaeffer and J . R . Wolfe, Telrakedy o n . 6 , 338 (1959). (16) W. E. Doering and R. W. Young, ibrd., 72, 631 (1950); H. S. Mosher and E. L a c o m h e , i b i d . , 72, 3994 (1950). (17) R. S. Tipson, J . Org. Chem., 9, 235 (1944). (18) A. Streitwieser. Jr., and W. D . Schaeffer, THISJOURNAL, 78, 5597 (1956). (191 A. Streitwieser, Jr., ibid., 76, 5014 (1953) ( 2 0 ) S. Udenfriend and J. R. Cooper, J . B i d . C h z m . , 196, 227
(1952).
Vol. 82
results are shown in Fig. 1 where it can be seen that the slope ratio (at initial velocities) is 2.00 when (VI) is compared with tyramine and 1.25 when (VII) is compared. Keeping in mind that slope ratios of 2.3 and 1.0 have been observed with the enzymically prepared enantiomers of a-d-tyramine,2 it follows that the a-d-tyramine obtained by decarboxylation of L-tyrosine in D2O as the solvent has the same absolute configuration (VI) as the synthetic sample, giving rise to an isotope effect of 2.0. The smaller isotope effect obtained with (VI) indicates that this preparation is optically impure. On the basis of these experiments, it is clear that the enzymic decarboxylation of tyrosine and presumably of other amino acids proceeds with retention of configuration. Acknowledgments.-Financial assistance from the National Research Council of Canada is gratefully acknowledged. Appreciation is expressed to AUrs.Maureen Triggle for technical assistance. DEPARTMENT OF CHEMISTRY UNIVERSITY OF OTTAWA OTTAWA,ONTARIO RECEIVED JULY20, 1960
B. BELLEAU J. BURBA
THE ABSOLUTE OPTICAL SPECIFICITY OB MONOAMINE OXIDASE
Sir: The widely distributed enzyme monoamine oxidase has been shown in recent years to play an important role in adrenergic mechanisms especially in the inactivation of catecholamines and serotonin in the central nervous system.' The subject of the occurrence, nature and role of monoamine oxidase has been reviewed2 and it is apparent that little is known about its mechanism of action although Zeller and his group3 have offered some interesting speculations concerning the nature of the active sites. A most striking feature of monoamine oxidase is the relative lack of optical specificity4in addition to the well-known lack of substrate specificity. Moreover, the enzyme does not distinguish between the geometrical isomers (cis- and trans-) of phenylcyclopropylamine as judged from their virtual equipotency as inhibitors.6 In contrast with these results is our recent discovery6 of a marked increase in the potency of sympathomimetic amines produced by stereospecific deuterium substitution, an observation which led US to postulate that monoamine oxidase may be the (1) P. A. Shore, J. A. R. Mead, R . Kuntzman, S. Spector and B. B. Brodie, Science, 126, 1063 (1957); S. Spector. D. Prockop, P. A. Shore and B . B. Brodie, ibid., 127, 704 (1957); "Symposium on Monoamine Oxidase Inhibitors,'' A n n . W . Y . Acad. Science, 80, 568 (1959). ( 2 ) A . N. Davison, PhyrioZ. Rev., 38, 729 (1958); H. Blaschko, Pharmacal. Rev., 4, 415 (1952). (3) E. A. Zeller, J. Barsky, L. A. Blanksma and J . C .Lazanas, Fed. Pvoc., 16, 276 (1957): J . Barsky, W. L. Pacha, S. Sarkar and E. A. Zeller, J . B i d . Chem., 234, 389 (1959). (4) P. Pratesi and H. Blaschko, Brit. J . Pharmocol. Chemotherapy, 14, 256 (1959); J. H. Biel, A. C. Conway, F. Diperro, A. E. Daukker and P. A. Nnhfer, THIS JOURNAL, 81, 4995 (1959); H. Blaschko, D. Richter and H. Schlossmann, J . PhysioZ. ( L o n d . ) ,31, 2187 (1937). (5) S. Sarkar, R. Banerjee, M . S. Ise and E. A. Zeller, H d o . C h i m . Acta, 43, 439 (1960). (6) B. Belleau, J. Burba, hl. Pindell and J . KeiEenatein, Science, forthcoming publication.
