Nov. 5, 1962
COMMUNICATIONS TO THE EDITOR
incorporation into the lactone, 3 may now be represented as the diacetate of 5. CH3,
/
CO
0-CO
I
CH
I
I (rH2)3-CO-xH-
[C,Hi,(OH),]
4163
to an oxygen or nitrogen atom not bearing hydrogen. On alkaline hydrolysis the fragment gives rise to one molecule of formic acid and to glycine. On Raney nickel and other catalytic reduction, i t suffers hydrogenolysis to give alaninec2,.l 1 These facts are mandatory for the grouping -CO-C-
(-NTUNICBTIONSTO
THE
1-01,s1
EDITOR
stereospecific h y d r ~ l y s i s . ~In a variety of these mixed 1n.p. with an authentic sample, 136-147", substrates, of the asymmetric type Cabde and of the [ aJ% 48.(i0,2.22% in chloroform. symmetric type Cabdd, the absolute steric sense We suggest that ethyl a-acetoxypropionate rrlity of the hydrolysis, where determined, was2 L. associate as an extended tetrahedron with aWe are studying the effect of the alpha and beta chymotrypsin in two conformations. In both, acetoxyl substituent in place of the acetamido the a-hydrogen assumes its normal orientation, group in this reaction, and wish to report an in- presumably fitting into a restricted space, determinversion of antipodal reactivity in the hydrolysis ing the sense of approach of the other three groups of ethyl a-acetoxypropionate, CH&H(OCOCHa)- to the enzyme, E. In one conformation, which is COzCzHs. preferred, I-L and I-D, the acetoxyl group (Ao), Ethyl dl-a-acetoxypropionate was subjected to lacking the polar N-H of a typical acetamido the action of a-chymotrypsin, 12 mg./ml., a t pH substrate, associates with the non-polar site (a) Ao a Ao a 7.8 in a pH-stat for 12 hours, hydrolysis stopping after about 50% reaction. Unhydrolyzed ester was recovered iii S:S% yield, a o b s d -2.32', [ C Y ] * ~ D -22', 5.3% in chloroform. Negative rotation also was observed in acetone, ethyl acetate and in I- L I-I3 ethyl dl-a-acetoxypropionate. Since the L-ester C & a has negative r ~ t a t i o n [, ~a ] % -48', this indicates more rapid hydrolysis of the D-enantiomorph than the L from the racemate, and by a ratio of about Ao COzEt am 2.7 to 1. The product of hydrolysis, a-acetoxypropionic acid, was isolated from the hydrolysate 11-L in S5% yield aobsd 1.77', [ a I z 2 ~ 23.3', 3.8% of the enzyme a t which the @-aryl groups of the in chloroform; i t was characterized as the substi- natural substrates7 normally associate. The Ltuted ureide from 1,3-bis-(p-dimethylaminopheny1)- enantiomorph does this more effectively than the carbodiimide, m.p. 149-151°, [ a ] 2 2 D - 17'. Anal. D, but only with the D enantiomorph does this asCalcd. for C22H2804N4: C, 64.06; H, 6.84; N, sociation place the ester group near the nucleo13.58. Found: C, 63.94; H, 6.95; N, 13.62. philic site (n) which leads to hydrolysis. In the D-a-ACetOxyprOpiOniC acid has positive rotationj5 second, somewhat less favored mode of association, [ C ~ ] ~ * D 49', and this confirms the more rapid hy11-L,the acetoxyl group associates with the acyldrolysis of the D-enantiomorph by a ratio of about amido site (am) and this leads to hydrolysis of the 2.5 to 1. L enantiomorph, but not of the D. A similar analySince such experiments with racemates may lead sis of the inversion of antipodal reactivity in the to results different from those found in study of the hydrolysis of 1-keto-3-carbomethoxytetrahydroisoquinoline,s indicates that the benzamido moiety individual enantiomorphs6asbthe D( +) and L( -) ethyl a-acetoxypropionates were prepared and in that substrate may be associating with ahydrolyzed separately by a-chymotrypsin, 5 mg./ chymotrypsin a t the @-arylsite, the phenyl group ml. a t pH 7.2 in 0.1 N NaC1. The initial zero being dominant in effecting association, leading order rates of hydrolysis were determined a t several to a rotation of 120' and a situation similar to that concentrations, the first numbers in each set being of I-D,as has been proposed by Hein and Niemann." the concentration, the second the rate: L : 2.84 ( 7 ) H. Neurath and G. W. Schwert, C h e m . Rcu., 46, 69 (19,50). X -11,0.646 X lo-' mole/l./sec.; 4.30, (8) G. E. Hein, R. B. McGriff and C. S i e m a n n , J . A m . C h e m Soc., 0.800; 6.67, 0.969. D : 2.99 X M , 1.08 X 82, 1830 (19GO). (9) G. E. Hein and C. Niemann, Pvoc. N d . A c a d . Sci.,47, 1341 IO-' mole/l./sec.; 5.26, 1.27; 6.19, 1.76; 7.34, (1961). 2.38. The separate enantiomorphs also lead to SAUL G. COHEN OF CHEMISTRY JOHX CROSSLEY more rapid hydrolysis of the D compound, with the DEPARTMEXT EZRAKHEDOCRI ratio in rates approaching a value in excess of 2 BRASDEISUXIVERSITY ,54, MASSACHUSETTS ROBERT ZAND with increasing concentration of substrate, con- WALTHAM RECEIVED JUSE 8, 1962 sistent with the results of the isolation experiments, which had been carried out on saturated solutions RADON FLUORIDE' of the racemate. The data indicate that the LSir: enantiomorph has a more favorable K , and a less Shortly after Bartlett? reported the reaction of favorable k 3 ; the absolute values of these kinetic parameters will require more extensive kinetic xenon with platinum hexafluoride, Claassen, Selig experiments. Enzymatic hydrolysis of the ethyl and Malm3 prepared xenon tetrafluoride by direct L-a-acetoxypropionate in a preparative experi- combination of the elements. l y e have studied ment led to L-a-acetoxypropionic acid, character- the reaction of trace amounts of radon with fluorine ized as its ureide derivative from 1,3-bis-(p- and found that radon forms a stable fluoride which dimethylaminopheny1)-carbodiimide, m.p. and is less volatile than XeF4. Gaseous radon (RnZZ2), collected from an aque( 3 ) S. G. Cohen, Y.Sprinzak and E. Khedouri, J . A m . Chem. Soc., ous solution of radium chloride, was passed through 83, 4225 (1961).
+
j-
+
+
+
(4) J. Kenyon. H. Phillips and H. G. Turley, J . Chem. SOL.,127, 399 1925). ( 5 ) C. If,Bean, J. Kenyon and H. Phillips, i b i d . , 303 (1936). (G) (a) P. Rona and R. Ammon, Biochem. Z., 181, 49 (1927) ; ( b ) P. Rona a n d E . Chain, ibid., 258, 4800 (1933).
(1) Based on work performed under t h e auspices of the U. S. Atomic Energy Commission. (2) N. Bartlett, Proc. Chem. SOL,218 (1962). (3) H. H. Claassen, H. Selig and J. G. Malm, J . A m . Cheni. SOL., 84, 3693 (1902).
