Dec. 20, 1957
~,~,8-~UBSTITUTED-~-AZA-~,~-DIOXABICYCLO[~,~,~]O~TANES
The product was recrystallized from n-pentane to yield 0.77 g. (47%) of (-)-a-lipoic acid as blunt yellow needles, m.p. 47-52', -63' (c 1.6, benzene). The (-)-alipoic acid was recrystallized again from n-pentane, m.p. 50-53'. I t s infrared spectrum (4yo in carbon tetrachloride, 0.127-mm. path) was identical to that of (+)-a-lipoic acid3 and of DL-(Y-lipOiC acid.' I t s activity in enzymatic POF assays was 39% of that of DL-a-lipoic acid.ll Anal. Calcd. for C8HI402&: C, 46.55; H , 6.84; S, 31.05; neut. equiv., 206. Found: C, 46.37; H, 6.90; S, 30.63; neut. equiv., 200 * B. From DL-a-Lipoic Acid.-In the preparation of (+)a-lipoic acid ( - )-cinchonidine salt described above, the filtrate remaining after removal of the crystalline salt from the original reaction mixture was reduced in volume by stages by distillation under reduced pressure at 35". At each stage, additional crystalline material which formed by cooling the solution to -18" was removed by filtration. There finally remained 4.5 g. of a yellow sirup which did not crystallize, [ a ] z 4 . -79.6" 7~ (c 1, ethyl alcohol). The sirup was treated with 50 ml. of 5 % hydrochloric acid, and the mixture extracted three times with ether. The ether extract was washed five times with water and dried over sodium sulfate in the cold. Removal of drying agent and ether left a yellow solid. Recrystallization of the solid from n-pentane yielded 2.29 g. of (-)-a-lipoic acid as yellow leaflets, m.p. 57-59', [ a ] z 4 . -50" 4~ (c 1, benzene). Its activity in the POF assayzO was %yoof that of DL-a-lipoic acid, 2 z DL-a-Lipoic Acid-SZ35 (VIII).-A solution of 1.015 mg. (50 mc.) of elemental sulfur-35 in 2.9 ml. of benzenez3was transferred from a sealed tube to a 500-ml. round-bottomed flask using 75 ml. of benzene for rinsing. A 1.75-g. (0.0545 (21) T h e optical rotation and POF assay values for this sample of (-)-a-lipoic acid indicated t h a t it contained 15-20% of (+)-a-lipoic acid. (22) The optical rotation a n d POF assay values for this sample of (-)-or-lipoic acid were not in good agreement b u t indicated t h a t the sample contained 13-22'% of (+)-a-lipoic acid. (23) Elemental sulfur-35 was obtained from Oak Ridge Nntional 1,aboratory.
[CONTRIBUTION FROM
THE
6487
gramatom)portionof elemental sulfur (USP precipitated) was added to the solution, which was then heated to dissolve the sulfur in the benzene. The benzene was then distilled to leave crystalline elemental sulfur containing 50 mc. of sulfur-35. A 13.1-g. (0.0545 mole) portion of sodium sulfide (NaZS.9HzO) and 125 ml. of 95y0 ethyl alcohol were added and the mixture stirred and refluxed under nitrogen to form a yellow-brown solution. To this refluxing solution was added during the course of three hours, a cold solution prepared by adding 7.3 ml. of 5.82 N sodium hydroxide solution (0.0425 mole of NaOH) t o a cold solution of 9.29 g . (0.0436 mole) of ~~-6,8-dichlorooctanoic acid in 140 ml. of absolute ethyl alcohol. After another 30 minutes of refluxing, about one-half of the alcohol was distilled, and a solution of 1.75 g. (0.0436 mole) of sodium hydroxide in 100 ml. of water was added. The mixture was refluxed under nitrogen for 15 minutes to decompose complex sulfides. The reaction mixture was then cooled, acidified with 140 ml. of 5% hydrochloric acid and extracted four times with a total of 500 ml. of benzene. The benzene was washed four times with saturated sodium chloride solution and dried over anhydrous sodium sulfate in the cold. After removal of drying agent and benzene, the remaining oil was distilled in a small vapor bath still under reduced pressure (0.2 mm.) and vapor temperature up to BO", to give a yellow oil which crystallized. The crystals were recrystallized from n-pentane to yield 4.05 g. (45%) of DL-a-lipoic acid-SP as yellow prisms, m.p 59-60'. I t s specific activity, determined by combustion to barium sulfate, was approximately 4 mc./g. (theoretical specific activity, 4.4 mc./g.). Its infrared spectrum (470 in carbon tetrachloride, 0.127-mm. path) was identical with that of DL-a-lipoic acid.4 I t s assay for POF activity was 109% of that of DL-a-lipoic acid.
Acknowledgments.-We are indebted to Mrs. Sonia Schorr Sloan and Dr. C. W. de Fiebre for carrying out enzymatic POF assays, to Mrs. Doris H. Hahn and Miss Naomi E. Schlichter for infrared spectral data and t o Dr. J. H. Peterson for specific radioactivity determinations. WILMINGTON, DELAWARE
PRODUCTS DEVELOPMENT LABORATORIES, PARKE,DAVIS& Co.]
Chloramphenicol. 2,4,8-Subs tituted- 1-aza-3,7-dioxabicyclo [3.3.O ]octanes BY WILLIAMH. EDGER TON,^ JAMES R. FISHER AND GEORGE W. MOERSCH RECEIVED JUNE 24, 1957
A series of l-aza-3,7-dioxabicyclo[3.3.0]octanes derived from the chloramphenicol skeleton was prepared. A novel series of isomers, believed related by a cis-trans relationship, was isolated and characterized. The structure of a by-product was demonpreviously reported from the reaction of benzaldehyde with ~-threo-2-amino-l-(p-aminophenyl)-1,3-propanediol strated to be ~-threo-4-(p-benzylideneaminophenyl)-2,8-diphenyl-l-aza-3,7-dioxabicyclo[3.3.0] octane.
During the preparation of ~-threo-2-benzylideneamino -1-(p-benzylideneaminopheny1)-l13-propanediol (11) by treating benzaldehyde with Lthreo - 2 - amino - 1-(9- aminopheny1)- 1,3- propanediol
dene derivative with a 1,3-dioxane structure (III).2 This assumption was made on the ease of preparation and the ready decomposition of the compound to the known dibenzylidene derivative CBHS I CH
/\
OH
I
NH~-~-CHCHCH~OH ~
I
I
2CeH5CHO
+
NHz
111
I
N=CHC&6
(I) in refluxing ethanol, a by-product was obtained which was reported to be a cyclic tribenzyli-
11. Subsequent study of this by-product has proved it to be ~-threo-4-(p-benzylideneamino-
(1) Smith, Kline a n d French Laboratories, 1530 Spring Garden Street, Philadelphia 1, Penna.
(2) W. H. Edgerton and J. R . Fisher, J . Oug. Chem., 19, 593 (1954).
Vol. 79
WILLIAM H. EDGERTON, JAMES R . FTSIIER AND GFORGEW.MOERSCII
6488
N O ~ - C j ! H - C f H - ~ 2
O
X
VI
N
\/\/ CH CH
--+
NHz-
C6H6CH=X-
0
0
SI
0
h-
',/\/ CII
CI-I
0 --+
IV
N
0
\/\/ c11
cri
VI I
phenyl)-2,8-diphenyl-l-aza-3,7-dioxahicyclo[3.3.0]- with a suggestion by Bergmann* and was later conoctane (IV). firmed by Pedrazzoli and Tricerri.6 The configuraHydrogenation of I V under less stringent condi- tion of the erythro series would lead one to expect tions than those reported by Senkus3 gave L- that the erythro bicyclic compounds would form threo - 1- ( p - benzylaminophenyl) - 2 - dibenzylamino- with difficulty. 1,3-propanediol (V). Although V could not be puriPedrazzoli and Tricerr? isolated a small quantity fied satisfactorily because of its labile nature, it was of by-product from the bicyclooctane formation to proved, by comparison of the infrared spectra, which they assigned a dioxane structure similar to identical to a compound prepared by the reductive 111, largely on the basis of spectral data. No such alkylation of ~-threo-2-dibenzylamino-l-(p-nitroby-product was found under the somewhat milder phenyl)-l13-propanediol(VII). reaction conditions employed for the preparation L-threo -4(p-nitrophenyl)-:! &diphenyl- 1-aza-3,7- of the bicyclooctanes of the present study. The indioxabicyclo [3.3.0]octane (X) was hydrogenated frared and ultraviolet curves of the bicyclooctanes until three molar equivalents of hydrogen was ab- of the normal series described in the present work sorbed. A 39% yield of the p-aminophenyl deriva- agree quite well with those reported by the Italian tive XI was isolated. Examination of the other workers. The 4-phenyl-l-aza-3,7-dioxabicyclo [3.3.0]products of hydrogenation indicated that an abnormal reaction4 had taken place with IV, I1 and octanes formed hydrochlorides which were stable in ~-threo-l-@-aminophenyl)-2-benzylideneamino-l,3-a dry atmosphere. Neutralization of the salts in propanediol being formed as well as the expected ether-sodium carbonate solution yielded an isoproduct XI. XI was benzalated to IV, thereby meric compound as well as considerable amounts of completing an alternate synthesis of IV. decomposition products. The elemental analyses An exhaustive hydrogenation of ~-threo-2,4,S- of the two isomers were alike, but the melting triphenyl-l-aza-3,7-dioxabicyclo [3.3.0]octane (X- points, optical rotations (where present), X-ray 11) resulted in extensive debenzylation with the diffraction patterns and infrared spectra were disisolation of primary amine as well as the mono- similar. The prominent features of the infrared benzyl and dibenzyl derivative^.^ spectra of the threo isomers were the disappearance The preparation of several l-aza-3,7-dioxabi- of a strong band a t 8.3 to 8.95 p and the appearance cyclo [3.3.0]octanes6 was successful, but i t was of a strong band a t 10.34 to 10.42 p. X and X.4, noted that the 4-p-nitrophenyl (X) and 4-phenyl respectively, mere hydrolyzed with alcoholic hy(XII) congeners could not be prepared by refluxing drogen chloride to ~-threo-2-amino-l-(p-nitroin ethanol as the parent member I V of the series phenyl)-1,3-propanediol hydrochloride. The isolawas first isolated.2 The reaction in benzene using tion of the same parent amine from both bicyclic a Dean and Stark3j6 water trap resulted in good isomers rejects any permanent alteration of the yields of the bicyclic products. Chloramphenicol7 skeletal configuration either during formation of does not react with benzaldehyde under these con- the bicyclic compound or during the formation of ditions. The bicyclic compounds were formed also the isomer. by treating the benzylidene derivatives with one 5-Ethyl-2,8-diphenyl- 1- aza - 3,7 - dioxabicyclomole of aldehyde under Dean and Stark conditions. [3.3.0]octane (XIV) was prepared in two isoRepresentatives of the D-threO and DL-erythro series meric forms whose infrared spectra resemble those were prepared in good yields. This is in accord of the 4-phenyl series in the pdints mentioned. The yield of the A isomer was much better in the 5(3) M.Senkus, THISJOURNAL, 67, 1515 (1945). ethyl series due to less decomposition. No optical (4) This reaction is similar to that previously reported in reference 2. The fact that the reduction was limited to the absorption of three molar rotation was present in these compounds. Preequivalents of hydrogen explains the isolation of the benzylidene comliminary attempts to separate optical isomers of pounds which are apparently in equilibrium in the reaction mixture. XI11 by an activated lactose column9 and by forni(5) Since the completion of this work, several members of this series ing diastereoisomeric salts were unsuccessful. 5 have been reported b y A. Pedrazzoli and S. Tricerri, Hclo. Chim.A d a , 39, 965 (1956); M. Nagawa and B. Shimizu, A n n . R c p f . Takaminc Ethyl-1-aza-3,i-dioxabicyclo [3.3.0]octane (XV) Lab., 7, 1 ( 1 9 5 5 ) , as well as W. H. Edgerton and J. R . Fisher, U. S. was prepared, but no isomeric compound could be Patent 2,777,854 (January 15, 1957). These previously reported isolated from the hydrochloride. compounds are enumerated in Table I. (6) Dean and Stark, Znd. E n g . Chcm., 12, 486 (1920). (7) Chloramphenicol is the generic name of the antibiotic for which the trademark of Pnrke, Davis & Co..is "Chloromycetin."
(8) E. D. Bergmann, Chcm. Reus., 63, 309 (1053). (9) N. J. Leonard and W. J. Middleton, Tars JOURNAL, 7 4 , 6114
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Dec. 20. 1957
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~YILLIAM H. EDGERTON, JAMES I
