KEITHS . BROWN,J R . ,
4414
AND
reaction product was virtually identical with t h a t of the protonated (uncharged) Form of K-propionyl-0-cinnamoylhydroxylamine. This spectrum was independent of pH in the p H range 1-9. Preparation of N-Propionyl-0-cinnamoylhydroxylamine .-Two methods of preparation of this compound were employed-the reaction of S-propionylhydroxamic acid with cinnamoyl chloride in anhydrous pyridine, and the reaction of the same hydrosamic acid with cinnamoylimidazole in anhydrous dioxane. Following reaction (which appeared t o be nearly instantaneous in both instances) the organic solvent was removed by a flash evaporation in Tumu. T h e residual solid was extracted with acetate buffer, p H 5.5, and with H 2 0 . The crude sticky solid was extracted with ethyl acetate, and the ethyl acetate extract was evapoL-ated to dryness. 'The resultant solid was recrystallized from hot water-dioxane; m . p . 119' (cor.); neut. equiv. calcd. 219, found 221. Methods. p H Measurements.--XlI potentiometric titrations reported herein were carried out in 0.1 , I4KC1 as solvent, employing KOH as titrant. A Radiometer precision p H meter (Model 2RSE) was used throughout. All buffers were calibrated against Sational Bureau of Standards p H standards employing a Kadiometer Model p H m-4 precision p H meter. XI1 pH measurements were carried out in thermostated water-jacketed vessels maintained a t 25.0 f 0.1". Spectral Measurements.-=\ Cary Model 14 recording spectrophotometer was used in all measurements reported herein. Inner and outer cell compartments were thermostated a t 25.0 =k 0.1". Kinetics of acylation arid deacylation of cinnamoylimidazole were followed essentially according t o the methods of Bender,
[COSTRIBUTIOSFROM
THE
DEPARTMENT OF
PHARMACEUTICAL
Buxus Alkaloids.
111.'
S . MORRISKUPCHAN
Vol. X f i
Schonbaum, and Zerner.3 The hydroxamates were all transparent above 270 mp a t p H 6.86 or below a t the concentration levels employed, obviating the need for highly precise matching of reference and sample. .It high p H (near or above the p K . 4 ' ) significant absorption was noted below 280 nip (although n o new absorption peaks were detected above 230 m p ) and precise blanks were prepared in such experiments as well as in all experiments involving furoyl- or acetyl-acylating agents. D,O Experiments.-Reactions in DpO were compared t o reactions in H 2 0 by dilution of concentrated aqueous phosphate buffer with either DpO or H 2 0 . The final concentration of D p O was 977, in every DaO experiment. The phosphate buffers maintained the p H (or p D ) such t h a t all measured rates were within jnc of the optimal rates (in the respective solvents) a t this temperature. FeC13 Test for Hydroxamates.-AI stock solution containing 1.33'7, FeC13, 0.013 ,M HCI, and 0.53 M monochloracetic acid was used in all hydroxamate tests. This solution has the advantages of yielding stable (nonfading) ferric-hydroxamic acid complexes which are insensitive to dilution over the dilution range eniployed. In typical experiments, 10-500 X Inl. of sample was mixed with 3 ml. of stock solution and the optical density read a t ,520 tnp with a Beckrnan Model D U spectrophotometer. Xliphatic acylhydroxamates all gave the same extinction, v i s . , 1.09 X 103 O.D./cm. X, Forrnohydroxarnate gave a considerably lower extinction (0.85 X l o 3 ) .
Acknowledgment.-This work was supported by research grants from the U. S. Public Health Service and the National Science Foundation.
CHEMISTRY
O F THE
UNIVERSITY
O F \vISCONSIN,
LfADISON
6,
\VIS.]
The Structure of Cyclobuxine
BY KEITHS. BROWN,J R . , ~A N D S. MORRISK U P C H A X ~ RECEIVED APRIL6, 1964 Physical and chemical evidence have led to the assignment of structure Ia (3,20-bis(methylamino)-4-methylenel4-methyl-9,19-cyclopregnan-16-01) to cyclobuxine, the major alkaloid of the acetone-insoluble portion of the bases of Aurus sernperzsirens L. The gross skeletal structure for cyclobuxine was indicated by the structures suggested for the products of selenium dehydrogenation (naphthalenes I11 and \:I, phenanthrene 17, and anthracene IV); dehydrogenation of decyclized cyclobuxine ( X I a ) gave only phenanthrene-related material. Key degradation products in the structure assignment were a conjugated diene ( V I I I a ) produced by Hofmann degradation; a mixture of cis- and trans-cisoid cyclopentenones (XT-Ia and b ) arising from oxidation followed by facile e l h i n a t i o n of methylamine; and the product from the ozonolysis of cyclobuxine followed by alkali treatment of the thus resultant a-aminoketone, the diosphenol X I I I a , which showed additional conjugation in the ultraviolet spectrum.
Extracts of Buxus sempervirens L. have been used since ancient times in the treatment of a wide variety of diseases, including malaria and venereal disease. More recently an alkaloidal extract of the plant has been reported to possess antitubercular properties5 Previous chemical studies have indicated the rnulticomponent nature of the alkaloidal e ~ t r a c t6-E. ~ We (1) P a r t s I and 11: Keith S.Brown, J r , and S Morris K u p c h a n , J A m C h e w L O G ,84, 4690, 1592 (1962) T h e material presented i n this paper mas first outlined in P a r t I. ( 2 ) National Science Foundation Cooperative Predoctoral Fellow in Chemistry, 1960-1962. 13) T o whom inquiries concerning this paper should he directed. This investigation was supported in p a r t by research grants from t h e Kational I n s t i t u t e s of Health (H-2952 and CY-4500) (4) E Schlittler. K . Heusler, and W Friedrich, Helv Chim A d a , 32, 2209 (1949) ( 5 ) I, E. Weller. C . T Redemann, R Y.Gottshall, J XI Roberts, E H Lucas, and H hl Sell, Anlibioi. Chemolhel,npy, 3 , 603 (1953); Merck and C u , Tnc , British P a t e n t 782,469 (1957) ( 6 ) ( a ) K . Heusler and E Schlittler, Heiv C h i m A d o , 32, 2226 (1949), l b ) W Friedrich and E Schlittler. ibid.. 3 3 , 873 (1950) (c) E. Schlittler arid W Friedrich. ibzd.,33, 878 (1950). (7) l< L a u r e n t , lloctoral llissertation, University of Toulouse, 1947, pp 17-34, These in\-estigations were published in (a) 13. Vincent and T h l a t h o u . C o m p l y r n d , 220, 474 (1945): ( b ) 11. Vincent, I S&ro,and R . L a u r e n t . l ' h t u o p w 3 , 29 (1948) (c) I) Vincent and X I , P a r a n t . Compt. i~e,id soc. biol., 148, 1878 11964) (8) K . S Brown, J r . . and S. M Kupchan. .I Chromatog., 9 , 71 (1962) ~
have isolated four alkaloids from the acetone-insoluble portion of the strong bases of B . sempervirens, and have elucidated the structures of the three major bases. This paper reports the structure of the major alkaloid, cyclobuxine (Ia), the first steroidal alkaloid recognized to contain a cyclopropane ring and the first having a substitution pattern a t C-4 and C-14 which is intermediate in the biogenetic scheme between lanosteroland cholesterol-type steroids. The configuration of cyclobuxine'o and the constitutions of the remaining two alkaloidsll,l?will be presented in future communications. Cyclobuxine (Ia), C2iH420N2, demonstrated infrared bands for a terminal methylene (6.09 and 11.20 f i ) and n.m.r.I3 peaks for the terminal methylene in an elec(9) Cyclobuxine is band 11, t h e alkaloid of Rr 0 68 in column 1 of Table 11, ref 8 I t is most prohably t h e same as "alkaloid A" of ref 6 a , a l ~ though no comparison sample of "A" is available, t h e physical constants o f cyclobuxine a n d its derivatives correspond closely t o those of ".4" and t h e respective derivatives (10) K S Brow.n, J r , and S. 51 K u p c h a n , J A m C h e m Soc., 86, 4124 (1964) i l l ) Cyclobuxamine, K . S. Brown, Jr , and S M Kupchan. tbid , 8 6 , 1480 (1964) (12) Cyclovirobuxine; K S.Brown. J r . , and S M. K u p c h a n , Trlvnheiivon L e l l e r s , in press.
STRUCTURE OF CYCLOBUXINE
Oct. 20, 1964 /
R
Nx CH3
4415
ene peaks in the infrared and n.m.r. spectra, and showing in the latter a signal for a new secondary methyl group (9.22 T) as well as considerable deshielding of the cyclopropyl methylene (9.43 and 9.73 7 ) .
&OR R
Ia, H b, CH3 C , CH3 d, COCHI e , COCHI f , CHO g, p-NO2C6HdCW20CO
R'
H H COCHj COCH, H CHO H
tronically unsymmetrical environment (5.20 and 5.43 T),14 the grouping CH2-CHOH-CH (5.29 T , octet, J 3, 7, and 9.5 c./sec.), two N-methyls (7.53 and 7.57 7), two tertiary C-methyls (8.87 and 9.03 T ) , one secondary C-methyl (8.92 T ) , and a cyclopropyl methylene (9.72 and 9.95 .),I5 A number of disalts of cyclobuxine could be prepared by standard methods,6a showing both nitrogens to be present as basic amino groups. Formaldehyde-formic acid methylation gave an N,N'-dimethyl derivative Ib,6a with a characteristic strong sharp band for the dimethylamino group a t 3.60 p in the infrared spectrum, in addition to the strong terminal methylene bands a t 6.09 and 11.10 p. The n.m.r. spectrum of I b showed a marked shift in the signal of the secondary methyl group from t h a t of the parent alkaloid Ia (to 9.13 7 ) , indicating its proximity to one of the amino functions. O-AcetylN,N-dimethylcyclobuxine (IC)6a showed the expected infrared band a t 5.81 p j and n.m.r. signals for the grouping CH~-CH(OAC)-CH (4.95 T ) and 0-acetate (8.03 7).
Acetic anhydride-pyridine acetylation of cyclobuxine gave the O,N,N'-triacetyl derivative Id,6a showing strong bands in the infrared for an ester (5.78 p ) and two tertiary amide (6.14 p, very strong) functions, as well as the terminal methylene (11.08 p). The n.m.r. spectrum of the triacetyl derivative Id showed restricted internal rotation16 of both N-methyl groups and of one N-acetyl group, which varied with the solvent. Milder acetylation of cyclobuxine (Ia) with acetyl chloride and potassium carbonate in benzene, l7 or mild hydrolysis of triacetylcyclobuxine Id gave the N,N'-diacetyl derivative Ie, lacking the 5.78 ~1 band in the infrared spectrum and showing in the n.m.r. spectrum restricted rotation of the N-acetyl group and of only one N-methyl group. An O,N,N'triformyl derivative If (Amax 5.78, 6.00, and 11.05 p ) was also prepared from cyclobuxine. Hydrogenation of cyclobuxine with platinum in ethanolic acetic acid gave in 97y0 yield the single dihydro compound IIa,6a* l l lacking the terminal methyl(13) We thank Mr. R. Matsuo and Mr. A. Krubsack for t h e n.m.r. determinations. All chemical shifts are reported in r-values ( p . p . m . ) . (14) Cf. M . D. Piair and R. A d a m s , J. A m . Chem. SOC.,83, 922 (1961). (15) R. McCrindle and C. Djerassi, J . Chem. Soc., 4034 (1962); this assignment was made in this work independently on the basis of the coupling constant of t he A B doublets (4 c./sec.); cf. H . S. Gutowsky, M . Karplus, and D . M. G r a n t , J . Chem. P h y s . . 31, 1278 (1959). (16) Cf.J. A. Pople, W. G. Schneider, and H J. Bernstein, "High-resolution Nuclear Magnetic Resonance," McGraw-Hill Book Co., Inc., New York, N. Y . , 1959, pp. 366-371. (17) Cf. W. J. Hickinbottom, "The Reactions of Organic Compounds," 3rd. E d . , Longmans, Green and Co., New York, N. Y., 19.57, pp. 404-405.
R
R'
Selenium dehydrogenation of cyclobuxine6",' a t 350-370' gave in 36y0 yield an exceedingly complex mixture of hydrocarbons, which could be separated by chromatography on silica gel and acetylated cellulose18 into fractions roughly consisting of tetrahydroanthracenes, tetrahydrophenanthrenes, trisubstituted anthracenes, and 1,2,8-trisubstituted phenanthrenesLg (in order of decreasing percentage of the mixture). These were then further purified through the formation of crystalline complexes with 1,3,5-trinitrobenzene20; only one hydrocarbon was obtained in fully purified form, an 8-methyltetrahydrophenanthrene derivative, for which structure I11 is suggested on the basis of elemental analysis (C21H28) and the spectral properties : A,, 12.21 p (two adjacent aromatic protons21); X E " 233.5, 280.5, 285 sh, 290.5, and 325.5 mp; n.m.r. spectrum showed the presence of: (1) two a- and three paromatic protons, 2 2 supporting the 1,2,5-trisubstituted naphthalene structure ; (2) an aromatic methyl group, the grouping Ar-CH2-CH2, and no additional protons on carbons directly attached to the aromatic nucleus ; and (3) two tertiary methyl groups, and two primary (ethyl) methyl groups, one strikingly deshielded (8.08 T).23
In an effort to isolate and characterize members of the other hydrocarbon classes detected in the dehydrogenation mixture from cyclobuxine, a mother-liquor fraction in which cyclobuxine was a t least 30% of the weight was dehydrogenated on a larger scale. Similar work-up gave a mixture nearly identical with that obtained from pure cyclobuxine, from which were isolated the pure tetrahydrophenanthrene derivative I11 and three additional pure hydrocarbons (one (18) T. M. Spotswood, J . Chromatog., 3 , 101 (1960). (19) F. A. Askew, J . Chem. S O C ,509 (1935); E Heilbronner, H . U Daniker, and P. A . Plattner, Helu. Chim A c t a , 31, 1723 (1949); H Dannenberg and W. Steidle, 2. Nalurforsch., 9b, 294 (1954). (20) Picrate complexes of these aromatic hydrocarbons were highly unstable, possibly because of steric interaction of the picric acid with t h e aliphatic portions of the aromatic donors, (21) Cf,L. J. Bellamy, "The Infrared Spectra of Complex Molecules," 2nd Ed., John Wiley and Sons, Inc., New York, N. Y . , 1958, p p . 75-79 (22) See ref. 16, pp. 247-254. (23) Examination of a Dreiding model of 111 (assuming the configuration10 unchanged from that of cyclobuxine) reveals t h a t t h e methyl of the e t h y l group nearest the aromatic nucleus, owing to interaction with the other ethyl and two methyl groups, may most favorably occupy a position near the plane of the aromatic nucleus adjacent to the C-X proton, in accord w i t h t h e observed anomalous n.m.r. spectral signal position (ref 16, p p . 180-183, J. S . Waugh and R. W. Fessenden, J . A m . Chem S O L . ,1 9 , 846 (1.%7), H Conroy in "Advances in Organic Chemistry-Methods and Results ," Vol. 11, R. A . Raphael, E . C Taylor, and H. Wynberg, E d . , Interscience Publishers, Inc., New York, S. Y . , 1960, pp 282-284.
KEITHS.BROWN,J R . ,
4416
AND
representing each of the additional classes of compound produced in the reaction), for which stmctures IV, V, and VI are suggested on the basis of elemental analyses and spectral properties. The 5-methyl-
III
N
v
VI
cyclopentenoanthracene derivative IV (Cz1H22) showed Amax 11.36 (lone aromatic protons a t C-9 and C-1OZ1), 12.53 (two adjacent aromatic protonsz1),and 13.50 (in cyclohexane ; three adjacent aromatic protonsz1) p ; AEtOH msx 259.5, 334, 350, 367, and 385.5 mp; n.m.r. spectrum showing the presence of (1) the 9- and 10-protons, and 2a- and 3P-aromatic protons,22supporting 1,2,5trisubstitution; (2) an aromatic methyl group, the grouping Ar-CHz-CH,, and no additional protons on carbons bound directly to the aromatic nucleus; (3) a tertiary C-ethyl group, a tertiary C-methyl group, and the grouping CHz-CH2-C. The other trinuclear aromatic hydrocarbon, the 8-methyl-l,2-cyclopentenophenanthrene derivative V, was highly crystalline : C Z I H ~Amax ~ , 12.22 (two adjacent aromatic protons2') ; EtOH Amax 261, 284, 294.5, 307 mp; n.m.r. spectrum showing the presence of (1) the C-4,5,9,and 10 protons, and three additional aromatic protons, supporting 1,2,8-trisubstitutionzz; and (2) aliphatic protons essentially identical with those seen in the spectrum of the anthracene IV, indicating the aliphatic portions of the two molecules to be identical. The crystalline representative of the tetrahydroanthracenes, VI (CW Hzs), showed Amax 11.35 p (lone aromatic protons a t C-9 and C-lOz1), " : :A 233.5 (weaker than in the tetrahydrophenanthrene derivative I I I ) , 277.5, 287, and 324.5 m p ; n.m.r. spectrum showing the presence of (1) 3-a- and 2P-aromatic protons,2zsupporting the 2,3,5trisubstituted naphthalene structure; ( 2 ) an aromatic methyl, the grouping rlr-CH2-CHz, and no additional protons on carbons bound directly to the aromatic nucleus; and ( 3 ) a primary methyl group, and two tertiary methyl groups, one strongly shielded (9.53 T ). 2 4 In an effort to bring some clarity into the confusing picture presented by these products, a small sample of decyclized cyclobuxine (XIa) was dehydrogenated a t 330'. Similar work-up gave a total binuclear aromatic fraction (9y0)with infrared and ultraviolet spectral characteristics identical with those of I11 (Amax 12.21 p , no trace of 11.35 p ; ":A? 233.5, 280.5, 285, 290.5, and 325.5 m p , no trace of 277.5 or 287 mp),
S.MORRISKUPCHAN
Vol. 86
and a fluorescent trinuclear aromatic fraction (7%) whose ultraviolet spectrum was typical for a n 8 - methyl- 1,2kyclopentenophenanthrene derivative l 9 262, 283, 294, and 307 mp) and showed no trace whatsoever of anthracene absorption above 840 mp. Therefore, the complexity of the hydrocarbon mixture from cyclobuxine is related to the presence of the cyclopropane ring, anthracenoid material (IV, VI) possibly resulting from initial cleavage of the 1,10- or g,ll-bond, followed by recyclization onto C-6 or C-7 and elimination of the cyclopropyl methylene. Ozonolysis of O,N,N'-triacetylcyclobuxine (Id) gave the ketone VIIa (Amax 5 79 p , stronger than in the starting material), C30H4605NZ (showing replacement of C=CHz by C=O), n.m.r confirming the loss of the methylene grouping and showing the N-acetyl group and one N-methyl group with freed rotationz5, this compound developed a deep red color under the conditions of the Zimmermann test, 26 but the spectrum of the product showed only slowly rising absorption in the 400-600 mp region (no maximum), so the test was assumed to be negative.
VIIa, R = COCH3, R' = COCHJ b, R = P - N O ~ C G H ~ C H ~ OR' C O=, H C,
R
=
H, R '
=
H
Hofmann degradation6" of a monomethiodide prepared from N,N'-dimethylcyclobuxine (Ib) led to a des-N-base VIIIa'" in addition to an appreciable recovery of N,N'-dimethylcyclobuxine (l0-20%) and a small amount of a homoannular diene isomer (presumably IX) which was also produced by acid or chlorani1 treatment of the major product VIIIa. The major product ( C Z ~ H ~ ~ O possessed N) an acylable hydroxyl group and a basic dimethylamino function (also evident in the infrared and n.m.r. spectra); the Cmethyl groups showed n.m.r. signals unchanged from those in the starting material Ib. The terminal methylene group was still present, no longer in an unsymmetrical environment (Amax 6.10, 11.15, and 11.30
CH* VIIIa, R = H b, R = COCHI
IX
X
(241 Examination of a Lkeiding model of \-I (assuming t h e configurationla
n.m.r. 5.34 T (2H)), and conjugated with a new double bond (AF,"," 229.5 mp (log t 4.22); 2 moles uptake
unchanged from t h a t of cyclobuxine) reveals t h a t t h e strain imposed b y t h e cyclopentane ring forces t h e tertiary methyl group on t h e second carbon removed from t h e 2-position t o lie nearly under t h e 2,3-bond of t h e aromatic system, in accord with the observed shielding of t h e n . m r spectral signal (see ref. 2 3 , and also 5.1. Gorman. S.S e u s s , and K Biemann. J A m . C h e m . Soc , 84, 1058 ( 1 9 6 2 ) ) .
(2.5) Examination of a Dreiding model of V I I a shows t h a t the :&acetylmethylamino group suffers much less hindrance t o rotation in t h e case of a ketone a t C ~ t4h a n when there is a bulky methylene group at t h e same position ( 2 6 ) W. Zimmermann, Z . pkysioi Chem., 300, 111 ( 1 9 5 5 ) .
p;
Oct. 20, 1964
STRUCTURE OF CYCLOBUXINE
upon hydrogenation, n.m.r. 3.6-4.6 T (ABX pattern)). The degradation product VIIIa would not add maleic anhydride under forcing conditions, and was not dehydrogenated to aromatic material by chloranil. 27 DecyclizationZ8of various derivatives of cyclobuxine led to mixtures (presumably X I and X I I ) exhibiting
XIa, R = H, R' = H b, R COCH3, R' = COCH3 C, R = P-KO~CGHICHTOCO, R' = H X I I a , R = H , R' = H b, R = COCHs, R' = COCHI C , R = COCH,, R' = H
a new tertiary methyl group in the n.m.r. spectra, in accord with the presence in each precursor of a cyclopropyl methylene ; the double bonds thus formed could not be hydrogenated to any appreciable extent (typical of steroid 7,8- and 8,g-double bonds, less so for 9,11-), and showed only a partial new vinyl hydrogen in the n.m.r. spectra. Ozonolysis of cyclobuxine di-p-nitrobenzylcarbamate (Ig) and hydrogenolysis of the product gave an unstable a-aminoketone (VIIc) which upon treatment with base was oxidized and hydrolyzed to the diosphenol X I I I a (analyzed as the triacetyl derivative X I I I b ) . The ultraviolet spectra of the diosphenol X I I I a (A;", 296.5 mp (log E 3.95), Xzk:H-NaoH 343.5 rnp (log E 3.81)) and of its triacetyl derivative X I I I b A(",: 277 mp (log 6 4.10)) showed additional conjugation over those of known steroidal 3,4-diosphenols (e.g., from cholesterol," : :A 278 mp, acetate 247 mp (log E 4.18)29; from cevagenine, 278 mp,
(" /
/
0
OR XIIIa, R = H b, R = COCHi
OR XIVa, R = H b , R = COCH3
EtOH-NaOH L a x
320 mfi30). The corresponding decyclized diosphenol (probably XIV) had normal spectral EtOH-NaOH characteristics: AEH277 mfi, Amax 322 mpj triacetyl derivative 247 mp (log e 4.10). These observations lent strong support to the presence of a 9@,19-cyclopropane ring in cyclobuxine. Chromic acid oxidation of a series of nitrogenprotected derivatives of dihydrocyclobuxine gave ketones (XV) showing Amax 5.78-5.80 p (five-membered(27) Cf. E. A. Braude, L. P. Jackman, R . P. Linstead, a n d G. Lowe. J . Chem. SOL.,3123 (1960). (28) Cf.D H . R . Barton and P . deMayo. ibid., 2178 (1953). (29) L. F. Fieser a n d R. Stevenson, J . A m . Chem. SOL.,1 6 , 1728 (1954). (30) E. S u n d t , 0. Jeger, and V. Prelog, Chem. Ind. (London). 1365 (1953).
4417
ring carbonyl) and strong Zimmermann testsz6 I t was not possible to move the double bond of decyclized materials into conjugation with these ketones (in accord with a skeletal structure possessing an intermediate quaternary carbon, C-14). The ketones could also be obtained by oxidation with manganese dioxide, which ordinarily attacks only allylic alcohols.3 1 The parent ketone XVd, with the nitrogens unprotected
CHJ/
~
I
XVa, R = CH3CO b,R CGH~CO C, R = O - N O ~ C G H ~ C H ~ O C O d , R = H
(prepared through N,N'-di-p-nitrobenzyloxycarbonyldihydrocyclobuxine, IId) rapidly eliminated methylamine in basic solution, giving a mixture of cis- and trans-cisoid cyclopentenones (XVIa and b) ,Amax 5.85, and 6.09 p , "A?: 244 mp (log E 3.89), which were interconvertible in basic solution and separable by partition chromatography, and gave positive Zimmermann tests26 (confirming the environment of the original alcohol as CH2-CHOH-CH) Configurations were assigned to the two isomers by their n.m.r. spectra; in the less polar compound XVIa, the vinyl methyl group signal (doublet, J 7 c./sec. a t 7.92 T ) was relatively deshielded (6 from more polar -0.27 p.p.m.), hence i t was the trans isomer as shown3*; in the more ~
I
polar (cis) isomer XVIb, the vinyl proton group signal (quadruplet, J 7.5 c./sec. a t 3.53 7) was similarly deshielded (6 from less polar -0.82 p . ~ . m . ) ,Equi~~ librium mixtures consisted of 50-70y0 of the cis isomer XVIb.34 From these data, structure Ia (3,20-bis(methylamino)-4-methylene-14-methy1-9,19-cyclo - pregnan - 1601) was assigned to cyclobuxine. Further substantiation of this structure, and evidence relating to the configuration of cyclobuxine, is in the following paper. l o (31) J. Attenburrow, A. F. B. Cameron, J . H . C h a p m a n , R M E v a n s , B. A. Hems, A . B. A . Jansen, and T. Walker, J . Chem. S O L , 1094 (1
