COMMUNICATIONS TO THE EDITOR
936
In the second sequence p r ~ p a r g y l a c e t o n ewas ~ converted in 8070 yield into its cyclic ketal ( V I ) , j b.p. 75-76' (15 mm.), and this was then alkylated (sodamide-liquid ammonia) with n-amyl bromide to give VII, identical with the product from the first route. When the acetylenic ketone (V) was hydrated by refluxing with hot aqueous methanolic sulfuric acid in the presence of mercuric sulfate excliisive joymation of the 1,4-diketone, the known B,5-undecanedione6 (IV, R ' = C H 3 ; R = CH3(CH2)4)was observed, b.p. 80-85' (0.1 mm.), 85Y0 yield. The structure of the 1,4-dione was proved by its almost quantitative cyclization to dihydroj asrnone (2-n-amyl-3-methyl-a2-cyclopentenoneV I I I ) , b.p. 79-81' ((1.2m m . ) . single peak on gas chromatography (20yGSE-30 a t lis'), 237 mp ( E 12,000); further identified as its semicarbazone, m.p. l7S-17(i0 as reported.' The exclusive formation of a 1,l-diketonerequires carbonyl participation in the hydration step via a kinetically and geometrically favored five-membered ring. Participation via a six-membered ring should however be possible in acetylenic ketones of type I X , thus leading specifically to 1 ,&liketones X . This turned out also to be the case: A41kylation of the cyclic ketal of 6-heptyn-%-one (made by alkylation of sodium 0
R'C
/I
CCHzCHzCHZC -R IX
C O CHB (CHz)3C Z C C HzC HIC HzC CH3 XI
::
B
R'CHzCCHzCHzCHzCR
X
0
XI1
acetylide in liquid ammonia with the dioxolane of 3bromopropyl methyl ketone) with butyl iodide, using sodamide in liquid ammonia, gave the corresponding disubstituted acetylene ( X I ) in 607, yield. Deketalization with aqueous perchloric acid a t room temperature led to the required 6-undecyn-2-one ( I X , R = CH,; R' = CH3(CH2)3) in 9370 yield, b.p. 85-87' ((1.3m m . ) . The acetylenic ketone was transformed on refluxing with aqueous methanolic sulfuric acid and mercuric sulfate into a single diketone (one peak on 2UYGCraig column a t 190°), the structure of which as 2,B-undecanedione (X, R = C H 3 ; R ' = C H , ( C H Z ) ~ ) was confirmed by its base-catalyzed cyclization to 2-butyl-3-methyl-A2-cyclohexenone ( X I I , 82yG yield from the acetylenic ketone), b.p. (53-65' ( 0 . 2 m m . ) , 242 mp ( E 13,4(10),only one peak on gas chromatography (Craig, 190°), 2,4-dinitrophenylhydrazone m . p . 142-1-43' as reported.8 Specific hydration of acetylenes to 1,5-diketones via &carbonyl participation can thus also take place, but it is significant that this hydration is, as expected, markedly slower than with the y-carbonyl analog. This is shown by the fact that it is possible to define conditions which will result in complete hydration of y-ketoacetylenes while leaving the &keto compounds unchanged. (4) J . Colonge and R . Gelin, Bull soc chim F y a i i c e , 208 (1954)
( 5 ) X different synthesis of this ketal has recently been published by C . Feugeas. tbtd , 2379 (1963). (6) H Hunsdiecker, Ber , 7 5 , 447 (1942) ( 7 ) W Tieff and H . Werner, ibid , 68, 640 (1935) 8) X J B Edgar. J H Harper, and hl A Kazi, J Chem. S o c , 1083 ) Predoctoral Fellow, Sational Institutes
of Health.
T H ECHASDLERLABORATORY GILBERT STORK COLUXBIA USIVERSITY RICHARD BORCHg SEIV YORK2T, N E W YORK RECEIVED J A N U A R Y 28, 1961
Vol. 86
A Synthesis of cis-Jasmone
Sir: I t was demonstrated by Hunsdiecker * t h a t 2-alkyl 3-methyl-A2-cyclopentenones (I) are readily prepared by base-catalyzed cyclization of I ,4-diketones of the general formula 11, which were themselves available by a variety of classical methods. The discovery in our laboratory of a new synthesis of 1,4-diketones2 suggested the possibility of its use for the preparation of diketone 111, the precursor of the well-known jasmone (IV), the important constituent of the essential oil of j a ~ m i n e . ~
&
H H CH~C=CCHZC& I 1
-CH3
-CH3
I
IV 0
0
0
II
It
II
n
RC HzCCHz CHzCCH3 CHsCHzC =C-CHzCHz CCHzCHz CCHB I
A H
11
I11
We first demonstrated the feasibility of the synthesis for the preparation of 3-methyl-A2-cyclopentenones with an unsaturated side chain in the %position by synthesizing I (R = allyl). Alkylation of the magnesium halide complex of V with allyl chloride in the presence of cuprous chloride led to cyclic ketal V1 obtained in 61% yield (b.p. 78-81' a t 0.5 mm.) and deketalized (917,) as usual t o VII, b.p 70-77' (0.5 m m . ) , semicarbazone m.p. 99-101'. Hydration in the standard manner gave 837, of 8-nonene-2,5-dione (11, R = allyl), b.p. 75-77' ( 0 . 5 mm.), cyclized in 9:3Y0 yield to the known %-allyl 3-methyl-A2-cyclopentenone( I , R = allyl), b.p. 71-73', A,, E t O H 236 mp ( E 12,000), 2,4dinitrophenylhydrazone m.p 174-175' 0 , o , HCECCHzCH1CCHa
0, $ CH2= CHCHzCeCCH2CHzCCH3
V
VI 0 II CHZ =CHCH2 C =CCHZCHzCCHa VI1
In the synthesis of diketone 111, the precursor of jasmone, two problems were faced which are absent with the simple allyl derivative just described. The first of these was the occurrence of rearrangements, which we could not suppress, in the formation of cis-1-halo 2-pentene. This was solved when it was found that cis-2-pentene-1-o15 (VIII) could be transformed in 937, yield, upon treatment with toluenesulfonyl chloride and powdered sodium hydroxide in the cold, into a crude tosylate which was satisfactory for use in the alkylation of V. In that alkylation, the use of the magnesium complex of \.' proved unsatisfactory, but success was achieved by the use of the lithium salt of V in liquid ammonia which gave ketal IX in 457, yield, b.p. 100-103'. Deketalization of IX with aqueous perchloric acid (947, yield) a t room (1) H Hunsdiecker, Be?.. 76, 447 (1942). (2) G Stork and R Borch, J A m , C h r m S o c , 86, 93a (1984) (3) For a review see E. L Saul, A m Puvfumer, 4 6 , 27 (1913) (1) L . Crombie. 4 . J B. Edgar, S H Harper, M . U' I.owe, and I). Thompson, J Chem S O L ,3,552 (19.50) ( 5 ) Cf J Colonge and J . Poilane, Bull. SOL. chim. F r a n c e , 953 (1Y.55).
March 5 , 1964
COMMUNICATIONS TO THE EDITOR
n 57 0. 9 CH3CHzC= CCHzCECCHaCHzCCHs
937
At p H 7, the catalytic rate constants (of the turnover, kzk3/(k2 k 3 ) ) of the a-chymotrypsin-catalyzed CHaCHzC= CCHzOH hydrolysis of the ethyl and p-nitrophenyl esters of Nacetyl-L-tryptophan were shown to be equivalent to VJII IX one another.2 The catalytic rate constants of these two reactions are essentially identical from pH 7 down to pH 2 (see Fig. 1). Since the enzyme contains CH3CHZC =C C H ~ C E C C H Z C H ~ C C H ~ many carboxylate ions, the protonation of these groups X should electrostatically perturb the ionization constant of the basic group of pKa = 7. Thus, whereas ionic temperature gave pure cis-8-undecen-5-yn-2-one (X), strength effects on the rate are negligible near neutralb.p. 81-84' (0.2 m m . ) , one peak on V.P.C. (20% Craig, ity, they are important a t low pH because of the large 215"), no ultraviolet absorption, and no trans double positive charge on the enzyme.? The intrinsic pKa bond peak a t 10.3 p . The p-nitrophenylhydrazone of the group, on which both these ester hydrolyses had m.p. 95-96'. are dependent, is 7.2, using data from pH 2 to 7 . FurThe second problem came from the fact that it was thermore, titration of the concentration of enzymatic now necessary to hydrate the acetylenic link in X active sites by N-trans-cinnamoylimidazole around without affecting the cis double bond. Here the reneutrality is exactly equivalent to titration of that markable acceleration of the rate of hydrolysis b y ysame solution by the burst of p-nitrophenol in the recarbonyl participation became crucially important. action of N-acetyl-L-tryptophan p-nitrophenyl ester5 Whereas the usual hydration conditions (hot aqueous a t p H 2.3, using pure a-chymotrypsin. Thus the relamethanolic sulfuric acid and mercuric ion) led to almost tive rates of reaction, titration of active sites, and the complete cis-trans isomerization, i t was possible to pH dependence of the enzyme appear to be normal as effect the desired reaction without any involvement of low as p H 2 , and thus it is feasible to carry out mechthe cis double bond by keeping X a t room temperature anistic investigations a t low P H . ~ for 1.5 hr. with dilute aqueous methanolic sulfuric The object of such investigations is to spectrophotoacid-mercuric sulfate.6 The resulting 1,&diketone I11 metrically observe the individual steps of eq. 1, which was then cyclized with dilute aqueous base, in the usual are not discretely observable a t pH 7 . The a-chymomanner, to jasmone (75yo over-all from ketal IX). trypsin-catalyzed hydrolysis of N-acetyl-L-tryptophan This showad only one peak on v.p.c. (20% Craig, p-nitrophenyl ester a t pH 2.3 shows a typical initial 220') and was identified as cis-jasmone by its ultraburst followed by a steady-state production of p violet spectrum [ X ~ 237 ~ ~ mp " ( e ll,OOO)],the identity nitrophenol. This observation can only be interpreted of its infrared spectrum with t h a t of authentic main terms of the rapid formation and slow decomposition terial,? and by its 2,4dinitrophenylhydrazone, m . p . of an N-acetyl-L-tryptophanyl-a-chymotrypsin inter117.5' as reported.7 mediate.7 The formation of this intermediate is (6) Under these conditions, t h e 6-ketoacetylenes are completely unstoichiometric, as mentioned above, by comparison changed. with titration of the enzymatic sites with N-trans(7) I* Crombie and S. H . Harper, J Chem Sac., 869 (1952). cinnamoylimidazole. THECHANDLER LABORATORY GILBERTSTORK The technique of the observation of the acyl-enzyme COLUMBIA UZIVERSITY RICHARD BORCH in the hydrolysis of N-acetyl-1,-tryptophan methyl KEWYORK27, SEW YORK ester consisted in spectrophotometrically observing RECEIVED JANUARY 28, 1964 the time course of the reaction under conditions of (E)o > ( S ) Oand (E)o > K m , so that two consecutive first-order processes are observed. When the subThe Observation of Acyl-Enzyme Intermediates in strate is saturated with enzyme [sic] and when the the a-Chymotrypsin-Catalyzed Hydrolysis of Specific enzyme is in greater concentration than the substrate, Ester Substrates at Low pH1 the initial first-order process measures kz and the final first-order reaction measures k 3 (if kz > Sir : These are approximately the conditionsg under which The a-chymotrypsin-catalyzed hydrolyses of the the a-chymotrypsin-catalyzed hydrolysis of N-acetylethyl, methyl, and p-nitrophenyl esters of N-acetylL-tryptophan methyl ester was carried out a t pH L-tryptophan were shown by means of an indirect values of 2.3, 3.4, and 4.3. A typical spectrophotokinetic argument t o proceed through the formation of a common N-acetyl-L-tryptophanyl-a-chymotrypsin metric experiment is shown in Fig. 1 of the accompanying communication.lo In each experiment, the initial intermediate. For the methyl ester, the half-lives absorbance of the ester decreased rapidly, reached a a t p H 7 for the formation, kz, and decomposition, minimum, and then slowly rose, reaching an infinity k3, of this intermediate (eq. 1) were calculated to be (4) Evidence for a functional carboxyl group [J A Stewart, H. S Lee, 1 and 30 msec., respectively, too fast for ordinary and J E. Dobson, ibid , 86, 1.537 (1963)l is probably related t o these large or even most stopped-flow instrumentation to measure ionic strength effects. (a) The m-ester was used a t an !E)o'(S)o ratio high enough t o obviate directly. However, both kz and k0 are dependent on H I
H I
PI:
+
R
a basic group with a p K a of ca. 7 . 3 Therefore, a t pH 3, the half-lives of the above individual steps should be of the order of seconds rather than milliseconds, and thus amenable to direct measurement. f l ) This research was supported by grants from the National Institutes of Health, part XXV in the series: T h e Mechanism of Action of Proteolytic Enzymes (2) B. Zerner and M . L Bender, J . A m . Chem. S O L ,86,356 (1963). (3) M . 1, Bender, G E. Clement, F J. Kezdy, and B. Zerner, %bid, 8 6 , 358 (1963)
the side reaction of the D-compound noted earlier 2 (6) T h e enzyme is stable a t p H values of 2 to 3 : i n fact p H 2 is often used to crystallize a-chymotrypsin [ M Laskowski, 'Methods in Enzymology," Val 2 , S. P. Colowick and N 0 Kaplan, E d , Academic Press, New York, N Y . , 1955, p 121 ( 7 ) H Gutfreund and B l i Hammond [Biochem J , 75, 526 ( 1 9 5 ~ ) ] report a similar phenomenon in the n-chymotrypsin-catalyzed hydrolysis of N-benzyloxycarbonyl-1,-tyrosine0-nitrophenyl ester a t p H 7 2 , but do not indicate that the reaction is stoichiometric. (8) Sf 1,. Bender and B. Zerner, J . A m Chem SOC..8 4 , 2.550 ( 1 8 6 2 ) , F. J. K6zdy and M . I, Bender, Biochrin , 1, 1007 (1962) (9) Although the requirement of (IT)" > !S)o was always obeyed, the requirement of (E)n > K , is problematical because of experimental limitations so that some rate constants may not be true maximal rate constants a t s a t u ration conditions (10) F. J K6zdy and 51. L. Bender, J . A i n Chrm SOC, 8 6 , 938 (1'161)
