Feb. 5 , 1955
BROMINATION O F 7-KETOCHOLESTANOL
[CONTRIBUTION FROM THE PHARMACEUTICAL INSTITUTE,
665
AND 7-KETOCHOLESTENOL
MEDICAL FACULTY, UNIVERSITY
OF KYUSHU]
Cholesterol and Related Compounds. 11. Bromination of 7-Ketocholestanol and 7-Ketocholestenol BY KYOSUKE TSUDA AND RYOICHI HAYATSU' RECEIVED MARCH 23, 1954 Reaction of 7-ketocholestanyl acetate ( I ) with N-bromosuccinimide under infrared irradiation gives the 6,8-dibromide, which on dehydrohalogenation yields as the primary product a n acetoxydienone, considered to be 7-keto-A6~8(g)-cholestadienyl acetate (111). Bromination of 7-ketocholestenyl acetate under the same conditions gives the 8-bromo derivative, IX. The two products have been related by conversion to common reaction products.
When 7-ketocholestanyl acetate (I) is treated with two moles on N-bromosuccinimide with concomitant infrared irradiation, an unstable dibromide 11, m.p. SO", is formed. I1 readily loses hydrogen bromide when refluxed with pyridine. Three products have been separated by chromatography from this reaction. One of these, m.p. 152-153', 239.5 mp2 ( E 26,650), is identical with a substance described by us in a previous paperI3and to which we assigned the structure of 7-ket0-A~~~(~)-cholestadienyl acetate (111,see below). A second product, V, m.p. 119-120°, Amax 281 mp (E 25,300), has the empirical formula C27Hto0, and consequently we considered t h a t it probably is formed from I11 by loss of the elements of acetic acid with extension of the unsaturated system to give 7-keto-A3~S~x~9~-~holestetriene. And indeed we converted I11 into V by saponification to the free alcohol, conversion to the tosylate and detosylation with dimethylaniline. Presumably V is not an initial product but is formed from I11 during chromatography on a l ~ m i n a . ~ Indeed the crude dehydrohalogenation product, m.p. 125-135", shows ultraviolet absorption maxima a t 239 mp (0.862 optical density) due to 111, and a t 278-280 mp (optical density, 0.190), due to V. The difference in intensity shows that I11 is the predominant product. In addition to these two products, a small amount of another substance, IV, m.p. 109-llOo, was obtained, but it has been characterized only by ultraviolet absorption data, Amax 241 mp (E 5020), 278 mp ( E 14,500). Since our first paper3 in which we assigned the structure of 7-ket0-A~~~(~)-cholestadienyl acetate to 111, Inhoffen5 has assigned this structure to a substance which clearly differs from I11 both in melting point, m.p. 169-171", and in the absorption maximum, 248 mp ( E 12,800). Substances believed to have structures corresponding to I11 and to V but in the ergosterol series have recently been described by Glaxo Laboratories6 and also differ from our products in ultraviolet absorption characteristics. Thus the substance assigned structure I11 (but with the ergosterol side chain) by the English group has an absorption maximum a t 246
AEzoH
(1) Takamine Research Laboratory, Sankyo Co., Ltd., Tokyo, Japan.
(2) An earlier value of 238 mp8 is now corrected t o 239.5 mp. (3) Part I, K. Tsuda, K. Arima and R. Hayatsu, THISJOURNAL, 76, 2933 (1954). (4) A similar reaction has been reported by J. Elks, e1 oi., J. Chem. SOC..463 (1954). (5) H . H.Inhoffen and W.hlengel, Ber., 87, 146 (1954). (6) J. Elks. e1 a!.. J . Chem. SOL. 451. 463 (1954).
mp ( E 12,800), and that corresponding to V (ergosterol side chain) has two absorption maxima, 217 mk ( E 19,000) and 272 mp ( E 14,600). Unfortunately it is not yet possible to predict absorption maxima of cross-conjugated systems. Since our original assignment of structure to I11 rested mainly on catalytic hydrogenation (Pd catalysis, acetic acid) to 7-ketocholestanyl acetate, we have extended our reduction studies. Catalytic hydrogenation with Raney nickel as catalyst results in absorption of one mole of hydrogen; the product was separated by chromatography on acid-washed alumina into two products, one of which corresponded in physical properties to 7-ket0-A~(~)cholestenyl acetate, and the other to 7-ket0-A~"~)cholestenyl acetate.' The latter substance is assumed to arise by migration of the double bond
I
II1
-EL Hz AcO/&o
+ x117
1
*co,(j3:o x1117
during hydrogenation from the 8,9- to the 8,14position. I n addition to these two products, starting material was recovered. Although this result supports structure I11 which we have assigned to our dienolone, we do not consider this structure as proved in view of the discrepancies noted above and hope that further work will provide conclusive evidence. If structure I11 is correct, the dibromo derivative I1 can be considered as the 6,s-derivative. It is known that monobromination of 7-ketocholestanyl acetate leads to the 6-bromo derivative.x We have also investigated the reaction of 7ketocholesteryl acetate (VII) with N-bromosuccinimide, again under infrared irradiation. The product is a monobromo derivative IX, which retains the characteristic ultraviolet absorption maximum of VII, m.p. l52", A,, 233 mk. On dehydrohalogenation with pyridine (followed by chromatography on alumina) i t is converted into a mixture of I11 and V, and hence it is regarded as the 8-bromo derivative IX. Chromatography of this product results in loss of the elements of acetic acid; the product VI11 is regarded as the 8-bromo derivative of A3*6-cholestadiene-7-one,since the absorption maxima in the ultraviolet (A, 279 mp, E 17,100) is almost identical with that of the unsubstituted dienone (A, 277 mp, E 24,400). (7) L. F. Fieser, THIS JOURNAL, 76, 4395 (1953). (8)T. Barr, L. M. Heilbron, E. R. H. Jones and F. S. Spring, J. Chem. Soc.. 334 (1938).
666
KYOSUKE TSUDA AND RYOICHI HAYATSU
Vol. 77
Conversion of I11 to V.-A solution of 3 g. of 111in 40 cc. of ethanol was treated with 0.7 g. of potassium hydroxide, allowed to stand for 15 hours, and then poured into water and repeatedly extracted with ether. The ether layer was washed with water, dried and the solvent was removed by distillation. The residue (2.1 g.) soon solidified and was dissolved in 10 cc. of pyridine, and after drying, 1.5 g. of tosyl chloride added and the mixture was allowed t o stand The reaction mixture was poured into a mixater and dilute hydrochloric acid and extracted with ether. The ether solution was washed with 105; sodium carbonate and water, dried, and the solvent was removed under reduced pressure. The residue (1.9 g.) waz crystallized from acetone, colorless needles, m.p. 108-109 (135' clear), yield 1.4 g. Anal. Calcd. for CJIHJsOIS: C, 73.91; H , 8.69. Found: C,73.61; H,8.60. One g. of 7-ket0-A~~*(~)-cholestadiene-3-to~ylate thus obtained was refluxed for 14 hours with 40 cc. of dimethylaniline, poured into ice-cooled dilute hydrochloric acid, and Experimentallo extracted with ether. The ether layer was washed with 6,8-Dibromo-7-ketocholestanyl Acetate (II).-To a solu- water, dried and the solvent was removed under reduced tion of 5 g. of 7-ketocholestanyl acetate ( I ) in 50 cc. of car- pressure. The brown oily residue (400 mg.) was dissolved in 10 cc. of petroleum ether-benzene ( 1 : 1 ) and passed bon tetrachloride, 5 g. (2 moles) of N-bromosuccinimide (NBS) and 0.2 g. of dibenzoyl peroxide were added; the through a column of 30 g. of alumina (Brockmann Grade 11). The column was eluted with 200 cc. of petroleum ethermixture was irradiated with a 375-watt infrared lamp a t a distance of 40 cm. and refluxed on a water-bath with exclu- benzene (1 : 1 ) a n d the eluate was fr:tctionated into 40 cc. each. sion of moisture for 35-40 minutes. After filtration from Fractions 3-5 afforded a colorless oil which soon solidified succinimide, t h e solvent was removed under reduced pressure below 40", and the reddish-brown, oily residue t h a t and was crystallized from ethanol; m.p. 119-120°, A%:" solidified was recrystallized from acetone; pale yellow mi- 281 mp ( E 25,800), identical with V , yield 120 mg. 7-Keto-6-bromocholestanolAcetate (VI) .-To a solution crocrystals, m.p. 80" dec., yield 2.1 g., recovery of succinof 3 g. of I in 30 cc. of carbon tetrachloride, 3 g. (2 moles) of imide, 2.55 g. S B S and 150 mg. of dibenzoyl peroxide were added and the ilnal. Calcd. for C29HdbBr203: C, 57.80; H , 7.64. mixture was refluxed. About one mole of S B S was conFound: C, 57.64; H , 7.89. sumed in 40 minutes and further reaction did not occur 011 Dehydrobromination of the Dibromide 11.-A solution of prolonged reflus ( 1 hr.). The mixture was filtered, thc 3 g. of I1 in 30 cc. of pyridine was refluxed for 6 hr. The filtrate was evaporated to dryness under reduced pressure, reaction mixture was poured after cooling into ice-chilled and the residual oil was chromatographed through a column dilute HCl and extracted with ether. The ether layer was containing 30 g. of alumina (Brockmann Grade I I / I I I ) as a washed with loc,.; HC1 and water, dried and the ether dis- petroleum ether-benzene ( 1: 1) solution. Crystallization tilled under reduced pressure t o give 1.2 g. of brownish oil. of the oily residue from acetone yielded V I as colorless Crystallization from acetone-alcohol gave crude crystals, plates, m.p. 175", the temperature recorded in the litera1n.p. 125-135". The ultraviolet absorption measurement ture.* of this material showed Amax 239 mp (0.862 optical density) Bromination of 7-Ketocholestenyl Acetate with NBS.-To and 278-280 mp (0.190 optical density) (0.004:4 EtOH). a solution of 6 g. of VI1 in 50 cc. of CCI,, 3 g. ( 1 mole) of After chromatographic purification through alumina, the XBS and 200 mg. of dibenzoyl peroxide were added, and the amount of the substance showing " : :A 239 m p was smaller mixture was irradiated with a 375-watt infrared lamp a t a than that in the foregoing ratio. Therefore the 3-acetoxy distance of 40 cm. The reaction ended in about 10 mingroup had been eliminated during chromatographic purifi- utes. The mixture was treated in the usual manner, and cation owing to use of alumina not treated with acid. In the red oil obtained thereby was crystallized from acetone; this chromatography, 1.1 g. of the crude crystals was dis- colorless needles, m .p. 147-150". Further recrystallization solved in 300 cc. of benzene-petroleum ether (1: 1) and from acetone raised the m.p. to 152' ( I X ) , al'D -11:30° ( c placed on 50 g. of alumina (Brockmann Grade 11); the 1.01 CHCla), : : :A 233 mp ( E 14,800), yield 2.2 g. eluate was divided into 40-cc. portions. Fractions 1-1 ilnal. Calcd. for CzjHa503Br: C, 66.79; H , 8.M. afforded a colorless oil which solidified and mas crystallized Found: C , 67.32; H , 8.88. three times from ethanol; colorless needles (V),m.p. 119%h'en the bromide IX (1.7 8.) was purified by chroma120°, yield 210 mg., ultraviolet absorption: ": : :A 281 m p ( E 25,300), a l * D -260.8' ( C 1.07 CHCL), ynL,,.1670, 1642, tography through 40 g. of alumina (Brockmann Grace 11) with a 400-cc. mixture (1:2) of petroleum ether and ben162.5 and 1600 cm.-' in Kujol. Anal. Calcd. for C27H100:C , 85.20; H, 10.59. Found: zene, the eluate yielded colorless needles which melted a t I 1
