[CONTRIBUTION FROX THE DEPARTXENT OF BIOCHEMISTRY, CORNELL UNIVERSITY MEDICALCOLLEGE, AND THE LEDERLE LABORATORIES]
BIOTIN. 111. 2-(6-CARBOXYBUTYL)THIOPHANE-3,4DICARBOXYLIC ACID1 GEORGE BOSWORTH BROWN, MARVIN D. ARMSTRONG, A. W. MOYER, AND WILLIAM P. ANSLOW, JR.; B. R . BAKER, MERLE V. QUERRY, SEYMOUR BERNSTEIN, AND S. R . SAFIR Received July 20, 1946
It was recently demonstrated (1)that hydrobromic acid hydrolysis of a 2-(7phenoxypropy1)thiophane substituted by amine or carboxyl groups in the 3 and 4 positions (I) failed to give the expected 2-(y-bromopropyl)thiophane derivatives (11) because the latter apparently suffered ring closure t o sulfonium bromides (111).
x x
x x
x x ----+
I / CH2-CHz I\
I
I1
Br I11
Since the valeric acid side chain of biotin could not be completed by a method involving the halogenated thiophane, 11,it became apparent that the proper side chain should be present in the molecule before introducing the sulfur atom.2 The synthesis of 2-(6-carboxybutyl)thiophane-3,4-dicarboxylicacid (IV) was accomplished by one of the general methods recently described (1).
COOH I-;-COOH
IV Rosenmund reduction of ethyl adipyl chloride (Y) took place readily to ethyl 5-formylvalerate (VI). By condensation of the aldehyde with malonic acid, 7-carbethoxy-2-heptenoicacid (VII) was obtained as an oil. It was best purified by saponification to the corresponding diacid, VIII. Esterification gave pure methyl 7-carbomethoxy-2-heptenoate (IX) , which added methyl thioglycolate Because of the pressure of certain researches necessitated by the war effort the Cornel1 group suspended work on the problem a t this point. 2After completion of this work, Griissner, Bourguin, and Schnider (Qa) published a synthesis of two empirical isomers of dl-biotin as well as dl-biotin in minute yield by the use of a methoxybutyl side chain. These isomers were not structural isomers of biotin (Qb). This may possibly be explained by formation of a thiophanium bromide (1) and subsequent ring opening t o an isomeric structure. c j . Bennet and Hock (10). 160
161
BIOTIN. I11
smoothly in the presence of piperidine to give a good yield of methyl 3-(carbomethoxymethy1thio)suberate (X).
-4
CZHjOO C-(CI-Iz)a--COCl
-
C~H~OOC-(CHZ)~-CHO
V VI CZH~OOC-(CHZ)~-CH=CHCOOH + HOOC-(CHz)4-CH=CHCOOH VI1 VI11
---f
---f
SCHzCOOCH, CI&O 0 C-(CHz)a-CH=CH
CO 0 CH,
I
CHaO 0 C- (CHJ 4-CH CH, CO 0 CHj
4
IX
X
It was previously shown (1, 2) that Dieckmann cyclization of an ester of type XI, which can form either XI1 or XIII, gave predominately XI1 when R was -C3HT(n), - (CH2)sOCBHs or H provided the reaction was carried out in boiling benzene. CH2 C 00 CHI CH300C-CH2
I
\/
CHR
S
0
I
-1
0
I L
cHIOOC B OXI1 o c H 3
I
i, JR
XI11 However, when R was - (CH2)&OOCH3the cyclization with sodium methoxide in hot toluene gave two fractions, one an insoluble crystalline sodium enolate and the other a soluble sodium enolate in yields of 61y0 and 13% respectively. The soluble fraction gave a keto ester which was mainly X I I , while the crystalline insoluble fraction appeared to be XIII. These conclusions were supported by the following evidence : The keto ester from the soluble sodium enolate fraction was converted to the cyanohydrin with liquid hydrogen cyanide and dehydrated with phosphorus oxychloride and pyridine in benzene to 2-(d-~arbornethoxybutyl)-3carbomethoxy-4-cyanodihydrothiophene. Acid hydrolysis followed by sodium amalgam reduction gave crystalline 2-(6-carboxybutyl)thiophane-3,4-transdicarboxylic acid (IV). The choice between IV and 2-(d-carboxybutyl)thiophane-4,5-dicarboxylic acid (derived from XIII) was established by the identity of the product with a sample of the triacid (IV) synthesized by an unequivocal method (3). When the keto ester from the insoluble crystalline sodium enolate fraction was carried through the same sequence of reactions, no crystalline triacid could be isolated.
162
QEORGE B. BROWN, B. R. BAKER, et
al.
Subsequently, Woodward and Eastman (4) observed that 3-keto-4-carbomethoxythiophane (XII, R = H) gave a permanent red-violet color with ferric chloride, whereas 2-carbomethoxy-3-ketothiophane(XIII, R = H) gave a transitory color with ferric chloride. They showed that the latter was quantitatively oxidized by ferric chloride to a double compound, Cl2HI4OBS2. When these observations were applied to the keto ester fractions obtained by cyclization of methyl 0-(carbomethoxymethy1thio)suberate (X), it was found that the keto ester obtained from the insoluble sodium enolate fraction gave a transitory green color with ferric chloride and 97y0 of the theoretical amount necessary to cause oxidation to a double compound was consumed before a permanent color was obtained (using acetoacetic ester as an indicator), indicating that this keto ester fraction was pure XIII. The keto ester from the soluble sodium enolate fraction, which gave a transitory purple color with ferric chloride, was titrated in the same manner. Only 45% of the theoretical amount of ferric chloride was consumed, thus indicating that this fraction was a mixture of XI1 and XI11 in a ratio of about 1:1. The keto ester, XII, remaining after the oxidation was isolated by means of its solubility in alkali. It gave a permanent purple color with ferric chloride3 and formed a semicarbazone, m.p. 127-129'. This was isomeric with the semicarbazone, m.p. 128-129", of the keto ester, XIII, obtained from the insoluble sodium enolate fraction. A mixture of the two gave a depression in the melting point. The crystalline triacid, IV, was shown to have a trans configuration of the carboxyl groups by treatment successively with thionyl chloride and aniline. A trianilide was obtained. If the configuration were cis, a mono acid chloride anhydride mould have been formed (1) which mould result in an alkali-soluble monoanilide anilic acid derivative on subsequent treatment with aniline. The crystalline triacid, IV, was also obtained via conversion of 7-carbethoxy-2heptenoic acid (VII) to the diethyl ester. However, no insoluble sodium enolate fraction was obtained in the Dieckmann cyclization. The crystalline triacid, IV, was difficult to isolate and in some runs none could be crystallized. Acknowledgment. The authors wish to thank Drs. Vincent duVigneaud and Y. SubbaRow for their helpful suggestions and Messers Louis Brancone, Louis Dorfman, J. R. Rachele, and Roscoe C. Funk, Jr. for the microanalyses. EXPERIMENTAL
Ethyl hydrogen adipate. The method of Swann, Oehler, and Buswell (5) was modified for large runs in order to avoid the fractional distillation. A much purer product, m.p. 2529", was obtained. 8 Of the nine derivatives of 3-carboxalkyl-4-ketothiophane of known structure described in the literature or prepared in this laboratory, all give red-brown, red-violet, or purple colors with ferric chloride. On the other hand, eight derivatives of 2-carboxalkyl-3-ketothiophane all give green or blue ferric chloride tests. No exceptions have yet been observed. This color test may possibly be used to distinguish between structurally isomeric keto esters. Application to the keto esters under consideration gave results which are in agreement with the other lines of evidence for their structures.
BIOTIN.
I11
163
A mixture of 1160 g. of adipic acid, 940 g. of ethyl adipate, 620 cc. of commercial absolute ethanol, 400 cc. of dibutyl ether, and 200 cc. of concentrated hydrochloric acid was refluxed for four and one-half hours. Volatile material was removed on the steam-bath in vacuo, the hot residue was diluted with 1 liter of benzene, then cooled overnight a t 5". The white crystals of adipic acid were washed with 500 cc. of benzene in portions; weight, 310 g. The filtrate was added in a thin stream to a stirred mixture of 850 g. of sodium bicarbonate and 6 1. of water. After being stirred an additional ten minutes, the layers were separated. Distillation of the benzene'layer gave 850 g. of unchanged ethyl adipate. The aqueous bicarbonate solution was covered with 500 cc. of benzene and acidified with 900 cc. of concentrated hydrochloric acid with stirring. Distillation of the benzene extract gave 920 g. (66% or %4r, based on the adipic acid and ethyl adipate not recovered) of white crystals, m.p. 28-29', b.p. 140-145" (2 mm.). Rlaise and Koehler (6) give the m p. 29" and b.p. 160' (7 mm.). Ethyl adipyl chloride (V). This was prepared in the usual manner with thionyl chloride in 99% yield, b.p. 120" (15 mm.). Blaise and Koehler (6) record b.p. 128" (17 mm.). Ethyl 5-formylvalerate (VZ). A mixture of 300 g. of ethyl adipyl chloride, 28 g. of 5% palladium-barium sulfate catalyst, 1 cc. of quinoline-sulfur poison (7) and 1liter of xylene was stirred under reflux a t a bath temperature of 130-140" while a stream of hydrogen was bubbled through the solution. At the end of four hours 85% of the theoretical amount of hydrogen chloride had been evolved and reduction was slow. After removal of the catalyst, the xylene was removed in vacuo and the residue distilled until the distillation became slow, b.p. 90-93" (2 mm.) ; yield, 147 g. (58%) of a colorless liquid. A similar preparation had the following physical constants: b.p. 111-116" (14 mm.); rib' 1.4300; d:: 1.000; MD (Calc'd) 40.8; M, (found), 40.8. By continued distillation impure aldehyde was slowly obtained which was dissolved in ether, washed with aqueous sodium bicarbonate, dried, and redistilled. I n this way another 10-15% of aldehyde was obtained. The aldehyde is 60% polymerized after one week a t 5" and should be used as soon as possible. The 2,4-dinitrophenylhydrazonewas obtained as either one of two modifications from ethanol, m.p. 59-60' or 74-75", The lower-melting form after melting is converted t o the higher-melting form. A mixture of the two melts at 74-75". Anal. Calc'd for CI4H18NlO~: X, 16.6. Found (m.p. 59-60'): N, 16.7. Found (m.p. 74-75'): Y, 16.7. After this compound was prepared Baer (8) synthesized it by another method. He gives the physical constants of the aldehyde, b.p. 97-98' (10 mm.), n: 1.4280, and m.p. 74-75" for its 2,4 -dinitrophenylhydrazone. 7-Ca,Boxy-2-heplenoic acid (VZZZ). T o a mixture of 124 g. of ethyl 5-formylvalerate (VI), 160 g. of malonic acid, and 180 cc. of pyridine was added 4 cc. of piperidine. After standing overnight the solution was poured into dilute hydrochloric acid and extracted with benzene. The benzene extract was extracted in turn with aqueous sodium bicarbonate. Acidification gave an oil which was taken up in benzene and washed with water. Evaporation gave 90 g. (57%) of 7-carbethoxy-2-heptenoic acid (VII) as an oil. A solution of 86 g. of the monoester in 500 cc. of water containing 90 g. of sodium hydroside was heated on the steam-bath for two hours, then poured into ice and 200 cc. of concentrated hydrochloric acid. The white solid was washed with water; yield, 48.7 g. (66%), m.p. 186-189" (uncor.). Recrystallization from water raised the m.p. to 196-198" (cor.) .4naZ. Calc'd for CgHl204: C, 55.8; H, 7.0. Found: C, 55.2; H, 6.9. This acid was characterized by catalytic reduction in ethanol with Adams catalyst to suberic acid, m.p. and mixed m.p. 141.5-143" (cor.). Methyl 7-carbo?nethoxy-2-heptenoate(ZX) . A solution of 48.7 g. of 7-carboxy-2-heptenoic acid (VIII) in 200 cc. of chloroform and 150 cc. of methanol containing 2 cc. of concentrated sulfuric acid was refluxed for sixteen hours under a Soxhlet apparatus containing
164
GEORGE B. BROWN, B. R. BAKER,
et al.
anhydrous magnesium sulfate in the thimble. The solution, washed with water, was distilled. The product was a water-white liquid, b.p. 148" (11 mm.); yield, 52.5 g. (93%). Anal. Calc'd for CloHla04:C, 60.0; H, 8.1. Found: C, 60.4; H, 8.1. Methyl 8-(carbomethoxymethy1thio)suberate ( X ) . To a mixture of 52 g. of methyl 7carbomethosy-2-heptenoate (IX) and 28 cc. of methyl thioglycolate was added 0.5 cc. of piperidine. The temperature was maintained a t 43-48" by adequate cooling. After standing for fifteen hours, the mixture was distilled; colorless oil, b.p. 198" (1 mm.) (bath 230"); yield, 71.1 g. (93%). The b.p. varied considerably with the bath temperature. -4naZ. Calc'd for C13H2201S: C, 50.9; H, 7.3. Found: C, 50.2; H, 6.9. 2-(b-Carbomethoxybutyl)-4-keto-3and 6-carbomethoxythiophane [ X U and X I Z I , R = -(C&)&OOCH3]. To a suspension of 5.4 g. of sodium methoxide (Mathieson) in 50 cc. of toluene was added 25 g. of methyl 8-(carbomethoxymethy1thio)suberate (X) in 25 cc. of toluene. The solution was refluxed on the steam-bath for one hour. In a few minutes a crystalline sodium enolate had separated from solution. The mixture was cooled, the solid removed and washed with toluene. The solid was shaken with iced hydrochloric acid and benzene containing a little toluene until solution was complete. The organic layer was separated, washed with aqueous sodium bicarbonate and water. Removal of the solvent i n vacuo left 13.7 g. (61%) of XI11 as a colorless oil, which gave a transitory green color with alcoholic ferric chloride. The semicarbazone formed white crystals from 50% methanol, m.p. 128-129". Anal. Calc'd for C13H21N30SS: C, 47.1; H, 6.4; N, 12.7. Found: C, 36.7;H, 6.7;N, 12.7. The toluene filtrate from the insoluble sodium enolate was cooled in an ice-bath and extracted twice with ice-water. The extracts -were immediately acidified and extracted with benzene. After being washed with aqueous sodium bicarbonate and water, the solution was evaporated t o dryness in vacuo. The residue of X I 1 and XI11 (R = - (CH2)rCOOCHs) was a light yellow oil; yield, 3 g. (13%). It gave a transitory purple color with ferric chloride. Anal. Calc'd for C12H1806S: C, 52.6; H, 6.5. Found: C, 52.9; H, 7.1. Ferric chloride titration of the keto ester fractions. To a solution of 1.03 g. of 2-(b-carbomethoxybutyl) 4-keto-5-carbomethoxythiophane(XIII) from the insoluble sodium enolate fraction and 2 drops of methyl acetoacetate in 20 cc. of methanol was added 0.37 h' ferric chloride in 80% methanol until a permanent (one hour) color was obtained. This required 9.8 cc. of the reagent or 97% of that required for oxidation to a double compound. The latter was obtained as an oil on dilution with water. A solution of 0.90 g. of the keto ester from the soluble sodium enolate fraction was titrated in the same manner and 4.0 cc. of 0.37 N ferric chloride taken up in order to obtain a purple color which did not bleach after one hour. This corresponds to 45% of 2-(b-carbomethoxybutyl)-4-keto-5-carbomethoxythiophane(XIII) and 55% of 2-(b-carbomethoxy)3-carbomethoxy-4-ketothiophane (XII). The solution was diluted n-ith several volumes of water and extracted with benzene containing a little ether. The organic layer was cooled in an ice-bath and extracted with iced 3% sodium hydroxide. The aqueous extract was immediately acidified and the keto ester, X I I , isolated in the usual manner; yield, 0.19 g. It gave a permanent purple color with alcoholic ferric chloride. The semicarbazone formed white crystals from 50% methanol, m.p. 127-129". A mixture with the semicarbazone of X I I I , described above, melted at 102-105". Anal. Calc'd for C13H12N30SS: N, 12.7. Found: hT, 12.5. To a misture of 13.7 2-(b-Car6omethoxybutyl)-~-cyano-6-carbomethox~d~h~drothiophene. g. of 2-(6-carbomethoxybutyl)-4-keto-5-carbomethovythiophane (XIII, from the insoluble sodium enolate) and 5 cc. of hydrogen cyanide cooled in an ice-bath was added 0.05 CC.of 50% potassium hydroxide. After fifteen hours a t Oo, the mixture was acidified with 0.15
BIOTIN.
I11
165
cc. of 85% phosphoric acid and the volatile material removed in vacuo. The residue was dissolved in 25 cc. of benzene, dried with sodium sulfate and the drying agent rinsed with 15 cc. of benzene. The solution, diluted with 40 cc. of reagent pyridine, was treated with 10.6 cc. of phosphorus oxychloride. The temperature was maintained at 40-45" by occasional cooling. After a total of six hours, the mixture was poured oniced hydrochloric acid and extracted with benzene. The extract was washed with dilute hydrochloric acid, aqueous sodium bicarbonate, and dilute hydrochloric acid. Distillation gave 10.5 g. (75%) of a yellow oil, b.p. 189-193' (1mm.). Anal. Calc'd for ClaHlrNOJ3: N, 4.9. Found: N, 4.9. 8-(d-Carboxybutyl)thiophane-5', 4-trans-dicarboxylic acid. A mixture of 7.2 g. 2-(&carbomethoxybutyl)4-keto-3 and 5-carbomethoxythiophane (XI1 and XI11 obtained from the soluble sodium enolate fraction) was converted to a mixture of 2-(L-carbomethoxybutyl)4-cyano-3 and 5-carbomethoxydihydrothiopheneas described in the preceding experiment ; yield, 5.4 g. (73%) of a yellow oil, b.p. 178-193" (1 mm.), but mainly at 183". A solution of this mixture in 16 cc. of acetic acid and 27 cc. of concentrated hydrochloric acid was refluxed for seventeen hours, then evaporated to dryness in vacuo. The residue was extracted with acetone, filtered from ammonium chloride and again evaporated. The residue consisted of 5.2 g . (100%) of 2-(d-carboxybutyl)dihydrothiophene-3,4and 4,5dicarboxylic acids. A solution of the 5.2 g. of unsaturated triacids in 23 cc. of 10% sodium hydroxide and 33 cc. of water was stirred with 55 g. of 2% sodium amalgam at 70-80" for two hours. The decanted solution was acidified, saturated with salt and extracted twice with ethyl acetate. Dried with magnesium sulfate, the extracts were evaporated in vacuo. The residue was crystallized from 1:3 ethyl acetate-benzene; yield, 1.45 g. (28%) of white crystals, m.p. 105-109" dec. Recrystallization of a similar preparation from acetone-benzene gave solvated crystals, m.p. 11&120° dec. Anal. Calc'd for c n H ~ @ e S * C&O: c, 49.7; H, 6.2; s, 10.6; N.E., 102. Found: C, 49.7; H, 5.7; S, 10.2; N.E., 113. The material was desolvated by drying at 135" (1 mm.) over phosphorus pentoxide for three hours. An oil formed with gas evolution, and resolidified on cooling, m.p. 124-125'. Anal. Calc'd for C U H I ~ O ~C, S :47.8; H , 5.8; S, 11.6. Found: C, 47.4; H, 5.0; S, 11.9. The filtrate from the 1.45 g. of triacid was evaporated to dryness i n vacuo and heated overnight on the steam-bath with 3.5 g. of sodium hydroxide in 14 cc. of water. The solution was acidified and worked up as described above. I n this way a n additional 0.51 g. (10%) of white crystals, m.p. 112-115' dec. was obtained. The trianilide of both fractions was prepared by way of triacid chloride and aniline in the usual manner, white crystals from dilute alcohol, which shrink a t 240" and melt at 252". ~O 69.5; ~ SH, : 6.2; N, 8.4. Anal. Calc'd for C ~ Q H ~ ~ NC, Found: C, 69.5; H, 6.4; X, 8.3. When 2-(d-carbomethoxybutyl)-4-cyano-5-carbomethoxydihydrothiophene was hydrolyzed and the product treated with sodium amalgam as described above, no crystalline triacid could be isolated.
6
SUMMARY
A synthesis of 2-(b-carboxybutyl)thiophane-3,4-trans-dicarboxylicacid has been described. NEW YORK,N. Y. PEARL RIVER,X. Y.
166
GEORGE B. BROWN, B. R. BBKER, et
d.
REFERENCES (1) B.~KER, QUERRY,SAFIR, AND BERNSTEIN, J. org. Chem., 12, paper 1 of this series. (2) BROWN,BAKER,BERNSTEIN, AND SAFIR, J. o r g . Chem., 12, paper 11 of this series. (3) BAKER,QUERRY,BERNSTEIN, SAFIR,AND SUBBAROW, J . Org. Chem., 12, paper IV of this series. (4) WOODWARD AND EASTMAN, J . A m . Chem. SOC.,66,849 (1944). (5) SWANN, OEHLER, AND BUSWELL, Org. Syntheses, COll. VOl. 11, 276 (1943). ( 6 ) BLAISEAND KOEHLER, Bull. soc. chim., [4] 7, 215 (1910). (7) HERSHBERG AND CASON, OTg. Syntheses, 21, 84 (1941). (8) BAER,J . A m . Chem. SOC., 64, 1416 (1942). (9) GRUSSNER, BOURQUIN, AND SCHNIDER, (a) H e h . Chim. Acla,[29, 517 (1946) ; (b) Hela. Chim. Acta, 29, 770 (1946). (10) BENNETAND HOCK,J . Chem. SOC.,477 (1927).
