A NEWROUTETO &NITROSTEROID HORMONES
July 20, 1959
[ COSTRIBUTION FROM
THE
3707
RESEARCH LABORATORIES OF SYNTEX, S.A.]
Steroids. CX.I Studies in Nitro Steroids (Part Z).l A New Route to 6-Nitro Steroid Hormones. 6a-Nitro-17cr-acetcrxyprogesterone and 6 ~ N i t r o c o r t i s o n e ~ BY A. BOWERS,LAURACUBLLAR IBASEZ AND H. J. RINGOLD RECEIVED NOVEMBER 3, 1958 -4 new method for the transformation of steroid A4-3-ketones into their 6p- and 6a-nitro analogs by the direct nitration of their derived A3,5-dienylacetatesis described. Application of this method led t o a new synthesis of 6a-nitrotestosterone and the syntheses of 6a-nitro-17a-acetoxyprogesteroneand 6a-nitrocortisone. 6p-Sitro-A4-3-ketonesundergo mutarotation in methanol solution t o an equilibrium mixture of the 6 a and 6p-nitro-A4-3-ketones. The fission of a steroid 5a,Ba-epoxide with fuming nitric acid is described.
Previous publications from these laboratories3s4 have described the syntheses of several C-6 fluorosteroid hormones. A remarkable enhancement of biological activity in many of these compounds was noted and in particular the high oral progestational activity of 6a-fluoro-17a-acetoxyprogesteronel and the high antiinflammatory activity of the Ga-fluorocortical hormones4s5may be mentioned. I t was thus of considerable interest to establish whether this enhancement of biological activity was an inherent feature of the fluorine atom or whether the introduction of other strongly electronegative groups a t C-B(a) would have a similar effect on biological activity. In this connection we wished to extend our work on nitro steroids to the synthesis of 6a-nitro-17a-acetoxyprogesterone(XIa) and 6anitrocortisone (XIb). In the preceding paper’ we described the synthesis of the 6a-nitro and 6P-nitro analogs of testosterone and progesterone by a route which appears to be generally applicable for the synthesis of 6-nitro-A4-3-ketones from the corresponding A5-3P-hydroxy acetates. However, adoption of this route for the synthesis of Ga-nitrocortisone required an 1l-oxygenatedA5-3/3-hydroxy derivative such as the triester I. Such a compound was not readily available when CHZOAC I
w
AcO
this work was initiated,6 thus an alternate method for the preparation of 6-nitro steroid hormones utilizing the parent hormone as the starting material was investigated.
Several years ago it was shown in these laboratories that the peracid oxidation of a steroid A3s5dienyl acetate (11) yielded directly the 6P-hydroxyA4-3-ketoneIIIa. This reaction is very probably a concerted reaction initiated by electrophilic attack a t C-6 by the peracid as depicted in the formulas I1 111. The 6P-(axial) configuration for the intro-
&-
6 ‘
R’
I1
x+
a,X=OH b, X =NO*
I11
X
duced hydroxyl group is in accord with current view on the stereochemistry of processes involving electrophilic attack on cyclic enolate anions, enols or enol esterss In addition we have demonstrated recently that reaction of steroid A3s5-dienyl-3-ethylethers with Clf directly yields 6~-chloro-A4-3-ketones. Thus, it seemed to us, that mechanistically it was feasible to visualize the direct formation of 6P-nitro-A*-3-ketones by treatment of a A3a5-dienylacetate or dienyl ether system (11) with a source of electrophilic nitronium ions (NOz+); I1 + IIIb. Indeed, this was the case. A suitable source of nitronium ions was fuming nitric acidla and studies with the enol acetate of testosterone acetatell (IV) led to satisfactory conditions being established for the direct obtention of 60-nitrotestosterone acetate (V) (Fig. 1). The reaction involved adding a large excess of fuming nitric acid to an ether solution of the enol acetate a t 0”. Isolation of the product and direct crystallisation of the reaction mixture afforded 6/3-nitrotestosterone acetate (V) in 20% yield, 234-236 mp, r 10,000. In the infrared it exhibited bands a t 1730, 1680, 1615 and 1.545
(1) Steroids C I X and P a r t 1 , A. Bowers, Maria Blanca Sanchez and H. J. Ringold, THIS JOURNAL, 81, 3702 (1959). (2) Presented in part by A. B. a t the Steroids and Natural Prod(7) J. Romo, G. Rosenkranz, C. Djerassi and F. Sondheimer, J . ucts Section of the Gordon Research Conference, August, 1958. Org. Ckem., 19, 1509 (1954). (3) A. Bowers and H. J. Ringold, Telrahedron, 3, 14 (1958). (8) See for example (a) W. S. Johnson, Chemistry & I n d u s t r y , 107 (4) A. Bowers and H. J. Ringold, THIS JOURNAL, 80, 4423 (1958). (1956); (b) J. L. Beton, T. G . Halsall, E. R. H. Jones and D . C. (5) Simultaneous with our communication a preliminary announcePhillips, J . Chem. SOC.,753 (1957); (c) R. Howe and F. J. McQuillin, ment from t h e Upjohn Laboratories also described a series of 6aibid., 1194 (1958). fluoro-steroid hormones: J. A. Hogg, G. B. Spero, J. L. Thompson, (9) H.J. Ringold, 0. Mancera, C. Djerassi, A. Bowers, E . Batres, B. J. Magerlein, W. P . Schneider, D . H. Peterson, 0. K. Sebek, H. C. H . Martinez, E. Necoechea, J. Edwards, M. Velasco and R . I. DorfMurray, J. C. Babcock, R. L. Pederson and J. A. Campbell, Ckemisfry man, THISJ O U R N A L , 80, 6484 (1958). b I n d u s f r y , 1002 (1958). (IO) At - 10” absolute nitric acid has been shown t o ionize t o t h e (6) E. S. Rothman and M. E. Wail, THIS JOURNAL, 81, 411 (1959), extent of 4.1%, acrording to the equation 2HKOa = KOz+ NOSreport t h e synthesis of AJ-pregnene-3p,l7a,21-triol-ll,20-dioneHz0; D. J. Millen and W. H. Lee, private communication t o C. K. (private communication from Dr. Monroe E. Wall); 0. Halpern and Ingold; cf. “Structure and Mechanism in Organic Chemistry,” CorC. Djerassi, ibid., 81, 439 (1959) report the synthesis of As-pregnenene11 Univ. Press, Ithaca, N. y..1953,p. 277,footnote 107. 3P,lla,l7a-triol-20-one (private communication from Dr. Carl (11) L. Ruzicka and W. H. Fischer, Helv. Chim. A c f a , 19, 1371 Djerassi). (1936).
+
+
i701. si
A. BOWERS,LAURA CUBLLAR IBAREZ AND 15. J , RINCOLU
3708 0.k
0:ic
IV
OH
pear to offer a method for converting cyclic or alicyclic a,P-unsaturated ketones into their y-nitro analogs via the nitration of their derived enol esters. Application of this method led to a facile synthesis of Ga-nitro-170-acetoxyprogesterotie(XIn) (Fig. 2 ) . Treatment of 17a-acetoxyprogesteroue (VIIIa) with acetyl chloride and acetic anhydride smoothly afforded the corresponding A3.5-dieiiyl-acet:~te IXa. Xtration of this enol acetate (IXa) yielded a crude product which, without purification, was treated with alkali under very mild conditions to afford Ga-nitro-l7a-acetoxyprogesterone (XIa), 232--224 inp, E 14,130.
Fig. 1.
cm.-' (characteristic of a nitro group attached to a saturated carbon atom) . I 2 The structure and stereochemistry assigned to V followed from its mode of preparation, elemental analysis, spectral data, its characteristically high negative rotation a t the sodium ~7h e ([a]D - 120') and the marked similarity of its rotatory dispersioti curve with that of GP-nitrotestosterone and complete disimilarity with that of Ga-nitrotestosterAttempts to prepare crystalline V by the room temperature acetylation of Gp-nitrotestosterone with acetic anhydride in pyridine were unsuccessful. It appears that neither 6p- nor 6a-nitro-A43-ketones are stable to mild acetylation conditions since both 6a-nitrotestosterone and Ga-nitrocortisone also failed to afford recognizable products after treatment with acetic anhydride in pyridine a t room temperature. Hydrolysis of the 17P-acetoxy group of V with zc; methanolic potassium hydroxide for 18 hours a t room temperature followed by acidification with acetic acid and precipitation with water led to a mixture of both cia- and GP-nitrotestosterone as evidenced by the rotation of the crude product. Crystallization of the mixture led only to the isolation of GP-nitrotestosterone (VI), identical in every respect with an authentic sample.' Very mild alkaline treatment of V I afforded Ga-nitrotestosterone (\-TI),identical with an authentic sample.' The isolation of the thermodynamically less stable GP-nitrotestosterone (VI) by a relatively vigorous alkaline hydrolysis of the 17-acetate V (which involves formation of the salt of the aci form of the nitro group) and the isolation of Ga-nitrotestosterorie (X'II) by a lei-)- mild alkali treatment of 6pnitrotestosterone (VI) 19 analogous to the case described in the previrus paper.' Thme results with the enol acetate of testosterone clearly established the feasibility of obtaining G-nitro-A"-3-ketones from the corresponding A43-ketones by the direct nitration of their derivecl enol acetates. Although we have not eqloited this method in other than the steroid nucleus i t d should be capable of wide application and w ~ l ap(12) For a well documented account of t h e infrared spectra of nitro compounds see J. F. Brown, TEISJ O U R N A L , 77, 6341 (1955) (13) For a discussion of t h e difference in t h e rotatorv dispersiori c t i n e s of ( a -and 6p-nitro A4- 3-ketones 5ee ref. 1.
b , X - - = O . R - O A c . R'=H THPR
b,X=-O,R=OAc /HNO, CH,I'I
7 Y
Po
@OR'
I=00 . 4 ~
1-
0
OH- -O +
NO: H XIa.);- con\ erbim of li8-nitroprogestrruiir t o its 60-nitro epimer readily
+
July 20, 1959
A NEW ROUTETO NITRO STEROID HORMONES
the composition of the mixture could not be confirmed by either paper or column chromatography and we cannot rule out the possibility of complete inversion with partial decomposition, or of a rotationally significant amount of aci form being present a t equilibrium. In connection with a general study of the fission of steroid epoxides being carried out in these laboratoriesi5 we investigated the reaction of fuming nitric acid in anhydrous ether solution on 5a,6a-oxidopregnane-3P-ol-2O-one3-acetate3 (XII) (Fig. 3). As was to be expected from the known course of ionization of absolute nitric acidlo nucleophilic attack a t C-GP by the nitrate ion afforded in good yield the diaxial glycol mononitrate ester, pregnane3&5a,BP-triol-20-one %acetate &nitrate (XIII). The structure of XI11 followed from elemental analysis, a strong band in the infrared a t 1640 cm.-' (characteristic of a nitrate ester)" its stability toward oxidation with 8 N chromic acid and its transformation into the known 3,&hydroxy-&~,Gaepoxide (XIV) upon treatment with alkali. Acetylation of XIV afforded pregnenolone acetate a-epoxide (XII). I n the ease with which the nitrate ester undergoes nucleophilic displacement to form the epoxide it closely resembles mesylate or tosylate esters.I6 I n the Clauberg assay, oral route, Ga-nitro-17aacetoxyprogesterone exhibited 3-4 times the oral progestational activity of 17a-acetoxyprogesterone. l7
3709
----R H
W XIV
O
6 Fig. 3.
hydroxide (1.2 g . j was kept a t room temperature for 18 hours. After neutralizing the reaction mixture with acetic acid, concentration of the solution t o 30 cc. and careful addition of water afforded a crystalline product (1.16 g.),z2 m.p. 180-190", [ a ] -88", ~ raised by three crystallizations from methanol t o 202-204" (310 mg.), [ a ]-144', ~ 234-236 mp, e 10,800. T h e m.p. was undepressed on admixture with a n authentic sample of 6P-nitrotestosterone.' The infrared spectra of the two compounds were identical. T h e conversion of the above product (m.p. 202-204') into 6a-nitrotestosterone (VII) was carried out as previously described and afforded a product identical in every respect with an authentic samp1e.l A3p5-Pregnadiene-3,17a-diol-20-one 3,17-Diacetate (IXa). -17a-A~etoxyprogesterone~~(10 g.) (VIIIa) in acetic anhydride (30 cc.) and acetyl chloride (30 cc.) was heated under reflux in a n atmosphere of nitrogen for 2 hours. After cooling the reaction mixture in ice for 2 hours, filtration afforded A~,~-pregnadiene-3,17a-diol-20-one 3,17-diExperimental acetate ( I X a ) (4.9 g.), m.p. 193-195", raised by several 60-Nitro-A4-androstene-17@-01-3-one 17-Acetate (V).crystallizations from methanol t o 205-206', [ a ]D - 127', Fuming nitric acid (75 cc.)lQwas added during 1 hour m4th 234 mp, e 20,000; : : :A 1760(s), 1740(s), l575(m) good stirring t o a solution of A3,5-androstadiene-3,17P-diol and 1540(m) cm.-I. diacetate (IV) (10 g . ) in anhydrous ether (300 cc.), keeping Anal. Calcd. for C95H3405: C, 72.43; H,8.27; 0, 1 9 . N . the temperature a t Oo.20 After keeping a t 0" for a further 2 hours, ice-water (350 cc.) mas added in one portion and Found: C, 72.41; H,8.46; 0, 19.20. 6~-Nitro-l7a-acetoxyprogesterone(XIa) .-Fumiug nithe product isolated with ether. The ether solution was washed with cold 555 sodium bicarbonate solution until the tric acid (15 cc.) was added over 30 minutes with good alkaline solution just turned brown and then several times stirring t o a solution of A3s6-pregnadiene-3,17a-diol-20-one 3,li-diacetate ( I X a ) (2.2 9.) in anhydrous ether (60 cc.) a t with water: The dried solution (xapS04) was evaporated 0'. After a further two hours a t 0' ice-water (100 cc.) t o dryness zn z'ucuo and the product crystallized from etherethyl acetate-hexane t o afford 6P-nitro-A4-androstene-17@- was added in one portion and the product isolated wit11 ol-3-one 17-acetate (V) (1.96 g.), n1.p. 163-171', raised by ether. The ether solution was washed with 5% sodium bicarbonate solution until the alkaline solution just turned several crystallizations from ethyl acetate-hexane t o 170173", [a]D -120', 234-236 mp, e 10,000; 1730, brown and then several times with water. After drying (Na2SO4) the solvent was removed in vacuo and the residue 1680, 1615 and I545 cni.-'; rotatory dispersion curve (c 0.0570 in dioxane): [o~];~u --21.l0, [ulsas -73' , lffl307.5 triturated with hexane t o afford an amorphous solid (1.56 g.), m.p. 102-120', [N]D -80". I n the ultraviolet i t dis-3,255', [ a 1 3 0 5 -3065'. Anal. Calcd. for C21Hd3aS: C, 67.18; H, 7.79; X, played a n inflection a t 230-234' mp, e 7,890. All attempts to crystallize this product were unsuccessful and chromatog3.73. Found: C, 67.58; H, 7.54; N,3.81. raphy over alumina or silica gel failed t o yield a pure prod6P-Nitrotestosterone (VI).-The crude non-crystalline uct. nitration productz1 from t h e preceding experiment ( [ a ) ~ T h e crude nitration product (950 mg.) was dissolved in -60"), (2.0 g.) in methanol (60 cc.) containing potassium methanolic potassium hydroxide solution (50 cc. of lyG) and __-______ kept a t 5-10' for 2 minutes. The solution was then neudetectable. T h e measurements were made m-ith a Rudolph Spectrotralized with acetic acid, diluted with water and extracted polarimeter with a xenon arc suurce. with ether. The extract was washed well with water, dried (15) Cf. refs. 3 and 4 and forthcoming publications from these (PiazSO4) and evaporated to the point of crystallization to laboratories. afford 6a-nitr0-17a-acetoxyprogesterone ( X I a ) (570 mg. j , (16) See for exnrnrtle .'. I h r s t and 1'. Koller. Helo. Chrnz. Acta, SO, m.p. 201-203', raised by two crystallizations from acetoile-1454 (1947). 232-234 nip, E 14,130; hexane to 203-205', [ a ]+5~4'," : :A (17) Biological assays b y Endocrine Laboratories, Madison, Wisc. : 1730, 1695(infl.), 1680, 1620 and 1550 cm.-'; rotatory (18) For general directions see the preceding paper. All crystalliza- : : A dispersion curve (c 0.0590 in dioxane): [a1700+30.5', tions of nitro steroids were carried o u t a s rapidly a s possible in an a t [ ~ l l m +55.9', [ a 1 3 9 0 +203.5", [ c Y ] ~+164.5", ~o [U]SO~.S mosphere of nitrogen. +2,230", [ a ] 3 0 0 +1740". (19) T h e nitric acid used in this work had a density a t 20" between Anal. Calcd. for C23H3,OcN: C, 66.16; H, 7.48; N , 1.5015 and 1.5040. F o r details of its preparation see t h e preceding 3.36. Found: C, 66.51; H , 7.73; N, 3.65. paper footnote 21. (20) T h e importance of temperature control in nitrations of this type is discussed in ref. 1, footnote 23. (21) Due t o t h e low yield of 6i3-nitrotestosterone acetate which could be isolated by direct crystallization. it was found advantageous to hydrolyze t h e total crude nitration product.
(22) T h e yield of crystalline material mas not constant a n d varied from 2 0 4 6 % . (23) Prepared according to the method of H. J Kingold. B . I.okeu, G. Kosenkranz and F. Sondheimer, THISJ O U R N A L , 78, 816 (1950).
3710
A. BOWERSAND H. J. RINGOLD
Vol. 81
i13J-Pregnadiene-3, 17a,21-triol-1 1,20-dione 3,17,2 1-Trineth ha no^ t o 230-232", [ a ] +149" ~ (dioxane); ;:A: 3450, acetate (IXb).--I stirred suspension of cortisone acetate 1710, 1670, 1625 and 1550 cni.?; 228-230 r n p L t 0 e ( I - I I I b ) (10 g . ) in acetic anhydride (500 cc.) containing p 14,130; rotatory dispersion curve (c 0.0560): [a1700+ l o 0 , toluenesulfonic acid monohydrate (7.0 g.) was kept at room [.~1m +150°, [ a l a 1 5 +2,390", [a1300 +1,535'. temperature for 7 2 hours (after 1 hour a complete solution A n d . Calcd. for C21H2707?j: C, 62.21; H , U.71; N , \\-as obtained). T h e reaction mixture was then added with 3.46. Found: C,61.95; H , 6 . 6 3 ; N, 3.31. stirring t o 3.5 kg. of ice and water. After keeping overnight Pregnane-38,5a,6/3-triol-20-one 3-Acetate 6-Nitrate at 5' filtration afforded a product (10.25 g.), m . p . 123nitric acid (5.0 cc.) was added with stirring 128",which after one crystallization from methanol con- t(XIII).-Fuming o a solution of 5a,6a-oxidopregnane-3/3-01-2O-one 3-acetate taining a few drops of pyridine yielded A3J-pregnadiene3,17a,2l~triol-11,20-dione triacetate ( I X b ) (7.0 g.), m .p. ( X I ) (1.0 g.) in anhydrous ether (30 cc.) at 0 ' . d f t e r keeping a t 0-5' for 17 hours the precipitate which had !5?-161 . The analytical sample had m.p. 168-169", settled out was removed by filtration t o afford prcgnane-33,L a j -@lo, ~ A"?: 234 mp, e 20,890. 5a,6P-triol-20-one 3-acetate 6-nitrate ( X I I I ) (650 iiig.), .1nuZ. Calcd. for C2iHa1O8:C, 66.65; H , 7.04. Found: n1.p. 182-186', raised by several crystallizations frtitn C , 66.56; H , 7.08. ~ ; : :A 3425, 1730, 16'35 niethanol t o 194-196', [ a ] -37'; 6,3-Nitro-l4-pregnene-l7a,2 l-diol-3,11,20-trione 17,2 1- and 1640 cm.-'. Diacetate (60-Nitrocortisone Diacetate) (Xb).-Fuming ,2naZ. Calcd. for C 2 a H 3 5 0 7 SC : , 63.14; H , 8.(16;S , nitric acid (75 cc.) was added over 2 hours with good stirring 3.20. Found: C , 63.02; H , 7.99; S , 3.28. t o a suspension of ~3~5-pregnadiene-.3,17m,21-triol-11,20-1 solution of XI11 (500 mg.) in acetone ( 3 1 c c . ) 1v:is tliune 3,17,%1-triacetate ( I X b ) (10 g.) in anhydrous ether (:XI!) cc.) a t 0 " . Most of the steroid had dissolved after treated with an excess of 8 2V clironiic acidz1at 1.5' for 5 this time. T h e solution was then stirred at 0 " for a further minutes. Addition of water and filtration afforded unchaiigcd itiirt2 hours when ice-water (400 cc.) was added in one portion. ing material in high yield. Ethyl acetate (250 cc.) was then added and the combined Treatment of Pregnane-3P,S~~,6P-triol-20-one 3-Acetate cirganic phase was washed with cold 5% sodium bicarbonate hvdroxide ( 100 solution until t h e alkaline solution just turned brown and 6-Nitrate (XIII) with Alkali.-Potassium added tci a solution of t h e nitrate eitcr SI11 (250 then several times with water. T h e dried solution (Naz- nig.) was in methanol (12 cc.) and heated under rcflus ill :til a t Sod) was evaporated i n Vacuo a t 40"and the residue crystal- ing.) mosphere of nitrogen for 45 iniriutes. *1fter ncutralizatioii lized from ethyl acetate-ether t o afford 6P-nitrocortisone with acetic acid, addition of ice-water ;inti filtraticiii af17,21-diacetate ( S b ) (3.97 g.), m.p. 220-223", [ W I D -56", 5a,6a-or;idopregnane-39-ol-20-one (XI\.) (170 mg. ), and a second crop (960 mg.), m.p. 219-223'. T h e ana- forded m.p. 183-185", raised by cr)-stallizations frciin eth>-l:tcctatelytical sample from ethyl acetate-hexane had m . p . 226228', [ m ] D -Si", k",t,"," 226-228 mp, e 11,480; 1748- hexane to 185-1Sio, [ a ] D -5". =1rzaZ. Calcd. for C21HJP03: C, 75.86; H , '3.70;0,14.44 (sh.), 1735, 1710, 1680, 1625 and 1555 cm.-'; rotatory dispersion curve (c 0.0615 in dioxaue): [a1700-30.9", [a120 Found: C, 75.54; H , 9 . 7 9 ; 0, 14.82. -9.750, [cy]5s; -37.40, [ c Y ] i 2 5 -lo2.5°, [0(]400 -73.2 , hcetylation of this product (acetic atiliytiride-p?ridine, 16 hours, 20') afforded 5a,6cr-oxidopregnane-3~-ol-20-~~11e [ a 1 3 0 2 5 -3340 . Anal. Calcd. for C ~ L H J I O S SC, : 61.34; €1, 6.38; S , 3-acetate ( X I I ) , n1.p. 167-168",undepressed on admixturc with a11 authentic sainple, [ a ] D +14", :::A! 1737 and 1708 2.86. Found: C, 61.70; H,6.55; S , 2 . 7 9 . 6m-Nitrocortisone (XIb).-60-Sitrocortisotic tliacetatc c m - l . The infrared spectra were ideiiticul. . I d . Calcd. for C23Ha,01: C, 78.70; €1, 9.15; 0 , ( S b ) (500 mg.) was added t o a solution of potassium hy17.09. Found: C, 74.05; H, 8.87; 0, 17.40. droxide (100 nig.) in methanol ( 5 cc.) a t 0" and stirred for 2 hours under nitrogen. The steroid dissolved readily and after 90 minutes a precipitate began to settle out. Xfter (24) See for example A . Binvers, T. C . Iialsall, E. I
