CH XRXCT E R I Z,4T IO N 0F SWEET I 9I NE, -4 C0N STI TU E N T O F STI'EE T I A ELEG-4 S S , AS THE OR3IOSIA 4 L K A LO1 D , ( + ) -6-E PI P0D OP ET ALI N E ~ I . ~ S V EF.I ,B . ~ L . \ s D ~and ~ I s-4. ~ DOUGLIS KIXGHORS D e p a r t m e n t of P h a rm a c o g n o sy and Ph(irmncology, College of P h a r m a c y , l'nksersity o j I l l i n o i s at the M e d i c a l Center, Chicago, I L 60612
Sweetinine iq an alkaloid first isolated from the bark of Szmdia punam p ~ s i sBenth. (Leguminoqae) b>- Beal and coworker. (1). Thiq group establidied the molecular formula of the compound aq C 2 0 H 3 3 S 3and demonstrated the presence of one tertiary and two secondary amino groups in the molecule (1). Although complete structural details of sweetinine were not determined at the time of its original isolation, it n-as suggested that the compound may be an Ormosiatype quinolizidine alkaloid (1).
sn-eetinine by chromatographic and spectral comparison with an authentic sample3 ( 2 ) . We now wish t o report further spectral data for sn eetinine and its formaldehyde adduct, homos~ eetinine. I n addition, primarily on the basis of the interpretation of the pmr hpectra of these two compounds, we have identified sweetinine as (*)-6epipodopetaline (1) .4 The pmr spectrum of sweetinine showed the presence of an olefinic proton, and its mass spectral fragmentation pattern indicated that the 17
1
2 N
During a screening program for legume alkaloids, several closely related Ormosia alkaloids were detected by gc ms in an extract of the stem bark of S. elegans (Vog.) Benth. One of the major components of this alkaloidal mixture has been shou-n by us previously to be identical to
compound is a monounsaturated pentacyclic Ormosia alkaloid of the podopetalinej type (3, 4). I r spectra of sweetinine in both KBr (1) and in solution (CDCl,) exhibited a strong trans-band a t 2760 cm-', indicating that the compound is a trans-quinolizidine alkaloid with H-6 cis to the
'Part of this work was presented a t the 20th Annual Meeting of the American Society of Pharmacognosy, held a t Purdue University, West Lafayette, Indiana, July 29-August 3, 1979. *American Foundation for Pharmaceutical Education Sydnor Barksdale Penick Memorial Fellow, 1978-1981.
3A generous sample of sweetinine was kindly provided by Prof. J . L. Beal. 4Structures 1 and 2 represent only one of the enantiomers of ( * )-6-epipodopetaline (sweetinine) and ( * )-homo-6-epipodopetaline (homo-sweet inhe), respectively. W e are grateful t o Dr. J. A. Lamberton for a sample cf (-)-podopetaline. 619
620
.Jouriial of Satural I'roduct~
C-7, C-9 methylene bridge ( 5 , 6). The relative stereochemistry of the protons a t C-11 and C-18 \vas deduced by examination of the pmr spectra of homo-siveetinine in several solvents. The two C-23 aminal protons of this compound appeared a t 6 3.43 as a 2H singlet in CDCI, and remained unresolved even a t 270 1IHz. In acetone-ds, these protons exhibited an AB pattern ( 6 ~3.34, b~ 3.43, 2JAB = -7.9). These data suggest that H-11 and H-18 are aiifi in homosweetinine since analysis of the pmr spectra of model aminal compounds indicates that an AX pattern would be expected for the C-24 protons if H-11 and H-18 were syii ( i ) . Further det,ailsof the relative stereochemist,ry of H-6, H-11 and H-18 in homo-sn-eetinine were obtained in the following manner. A 1H doublet of doublets centered a t 6 3.95 (2J10r,1~n= -11.4, 4Jloe,8=1.9) in the pmr spectrum of this compound in CDC13 was assigned to H-lOeq, which in the proposed structure, 2, is deshielded not only by 1-1, but also by the sp-diaxial electron lone pairs 'rabbit ears") (8) of K-12 and 5 - 2 3 . For such an effect to be observed, H-11 must be cis t,o the C-7, C-9 bridge in homo-sn-eetinine. I n support of this argument it was observed that in t'he pmr spectrum of homo-sv-eetinine in pyridine-dj t'he H-1Oeq doublet of doublets was shifted downfield to 6 4.43, possibly due t o solute-solvent complexation involving the aminal nitrogen lone pairs. Thus t.he struct,ure of homo-sn-eetinine n-as deduced to be 2, and, by analogy, the structure of sweetinine is 1. Structure 1 corresponds to G-epipodopetaline, an alkaloid isolated from Podopetalum ormoiidii F. Aluell. (Leguminosae), whose structure 11-as determined by X-ray crystallography (9). Confirmation of t'he identification of sm-eetinine as 6-epipodopetaline (I
[J'ol. 44, s o . 3
( l ) , and homo-s\veetinine as homo-6epipodopetaline (2), \vas obtained b?direct spectroscopic and chromatographic comparison of the However, it should be pointed out that Beal's sweetinine and the homosweetinine isolated in this \vorl; from S . elegaus are racemic, xliile the material isolated from P . ormoiidii is levorotatory. These observations explain the discrepancies in mp determinations- for sn-eetinine (mp, 1 i 4 1 i j O ) (1) and (-)-6-epipodopetaline (mp, 118-119') (9). To avoid the unnecessary proliferation of trivial nomenclature in the literature, ]!-e propose the designation of si\-eetinine as ( * )-6-epipodopetaline (1). The root bark of S . elegaiis was formerly an official drug in Brazil (IO), and extracts of this plant have been patented under its syionyni Leptolobium elegaiis for their reputed sedative, antispasmodic and analgesic effects (11). Since certain Ormosia alkaloids have been claimed to possess hypnotic and analgesic ("morphinelike") properties (12), we are currently evaluating ( *)-6-epipodopetaline (1) and related isolates for these pharmacological activities.
EXPEK11\IESTAL7 PL.\ST JI.\TERIhL.-The
s t e m bark
of
W e are grateful to Dr S AlcLean for a sample of (- )-Gepipodopetaline M e l t i n g points a e r e determined using a Xofler hot-stage instrument and are uncorrected Optical rotations mere measured on a Perkin-Elmer 241 polarimeter C v spectra were obtained on a C a r y 118 CY-] isible spectrophotometer I r spectra were obtained with a Perkm-Elmer model 337 and a Beckman model IR-18.4 spectrophotometers, with polyst) rene calibration a t l G O l cm-l P m r spectra S e r e recorded on a 1 arian T-BOA instrument operating at GO MHz a i t h a Nicolet model TT-7 Fourier Transform attachment and a Bruker 270 MHz instrument Tetramethylsilane was used as internal standard and chemical shifts are reported on t h e 6 (ppm) scale Low resolution mass spectra mere obtained on a 1-arian RIAT 1125 double focusing mass spectrometer operating a t 70 eT'
Sep-Oct 19Sl]
Balandrin and Kinghorn: Sweetinine
.Si;.eetiri elegrins i\-og. 1 Benth. (Leguminosae), collected in Brazil in February, 1972, was supplied through t h e Drug Research and Development Program ( S a t u r a l Products B r a n c h ) of t h e S a t i o n a l Cancer Institute, Bethesda, Maryland. -1voucher specimen representing this collection is deposited a t t h e Herbarium of t h e S a t i o n a l Arboretum, V.S. Department of Agriculture, Washington, D . C .
CH.\R.WTERIZITIOSOF
S\VEETISISE.(==)-0-epipodopetaline, 11, kindly donated bj- Prof. J . L. Beal, exhibited X= t h e following d a t a : mp, 174-175'; 589, 578, 540, 436 and 305 nm, 0.0" (e 0.4;) E t O H ) ; iiv, apparent A m a s (cj-clohexane) 193 (log c 4.20) and 210 nm (log c 3.86); ir, Y ma'; ICDC13j 3170 ( S H ) , 2800, 2760 em-' ftrctis-bands): pnir (GO MHz, CDCI,) 6 3.17 ( l H , bs, H-11) and 5.43 ( l H , d: j J 1 ;;=6.1, H-17): nis, 117 z 315 ill-, 23(;), 287 ( 3 ,243 '31, 231 (28), 217 (81, 189 ( S i , 149 120), 122 (15), 98 148), 97 (21), 96 (10), 84 (1001, 50 (14 I and 41 (10,. >lass measnrement: Found, 315.26760, Calcd. for Cz,,Hs,S,, 315.26744.
$ iueetinine .
PREP.LR.~TIOS OF
HOMC-S\\ EETISISE 12) l.-Ilomo-sweet inine [. ( + 1-honio-6epipodopetaline, 2) was quantitatively prepared from 1 (20 nigj b y treatment with formaldehyde according t o published procedures (1, 13, 14). T h e product 121 m g i was purified b>- preparative tlc on silica gel C;HLFj in methylene chloride-methanol2 8 5 ammoniiini h>-droxidesoliit ion (85:15:11 ( R , , 0.581 and recrystallization from acetone. This compound pshibited t h e folloxing d a t a : nip, 148-151 (lit. 149-151") (1); [a; , A?3, X=589, 578, 546, 436 and 305 nm, 0.0" (e 0.38, E t O H ) : ir, Y m a s ICIIClj) 2800, 2760 cm-I i f r a w h a n d s ) ; pmr (270 N H z , 2763 em-1 iiriins-hands): pnir 1270 NHz, ?JI,,., I # ? = -11.4, : J 1 , ,,,=1.9, H-lOeq'i, 5.27 :=G.O, H-17): 160 LIHz, acetone-de) ibd, 3J1; 6 3.34 ( l H , d , i)J240 ,,.=-7.9, H-24ax), 3.43 -7.9! H-24eq), 4.00 i l H , ( l H , d , ?J2i'.2iR= ,,=1.8, H-l@eq), d d , 2 J l i ,3,=l- l l . 0 , = 1 . 9 , H-lOeq), 5.36 ilH. h d . 3J - - = 6 . 1 . H-171: ms. ?1r z 327 OI-: GS'Ti, 312 1111,284 ( 9 1 ,244 ( 2 3 1 , 243 128,, 22:) i55i, 161 (151, 134 ( 1 4 ) , 122 (35j, 98 1100), 97 1221, 96 i2G), 84 ( 3 2 ) and 41 (201.
fRO1i
ISOL.\TIOS OF s\\ EETISISE I*)-~-EPIPODOPET.\LISE, 1 1 .IS I T S H O l l O DEI leaving a residue 193 g ) which was taken up i n 200 nil of 5(; aqueous HCl and *.\naltech, Inc., S e w a r k , Delaware
Gel
filtered. T h i s solution was made basic (pH 9 ) by t h e addition of concentrated >H,OH and was extracted 7 times with 300 ml portions of chloroform. T h e organic extracts were collected, dried over anhydrous SazSO, and filtered. Removal of t h e solvent in riiczlo left a reddish-brown gum (7.1 g) which was taken up in 150 nil of 5'; aqueous HC1. This aqueous solution was washed with several portions of diethyl ether, alkalinized ipH 9 ) with concentrated S H , O H and extracted with diethyl ether ( 1 0 x 3 m l ) . T h e combined diethyl e t h e r extracts were dried, filtered and reduced t o a volume of 40 ml. On standing for several hours, t h e solution deposited a colorless crystalline material (99 mgj which was recrystallized several times from acetone. Gc;ms showed this material t o be a mixture of several (2%"Orniosici-type quinolizidine alkaloids, one of the main components of n-hich was identical (tlc, gc nisi t o an authentic sample of sweetinine3 (21. The problem of separating sweetinine [ 1*)-Gepipodopetaline, 1 1 from the other alkaloids in the crystalline mixture obtained from S. elegcins stem bark was overcome b y preparation of t h e homo derivative b y reaction with formaldehyde and subsequent purification as described above. Pure ( * ) homo-6-epipodopetaline (2) 112 nig I derived from .S. e l e g o u s was identical (nip, pmr, nis, t l c ) t o the homo derivative of an authentic sample of sweetinine from S. piinn111 e n sis . .\CKSOWLEDC;lIESTS iTe are grateful t o Dr. hI. Suffness, Head, Plant and Animal Products Section, Drug liesearch and Ilevelopment Program, S a tional Cancer Institute, Bethesda, Maryland, for supplying the plant material used in this study and t o Gudrun 11.Christenson, Economic Botanl- Laboratory, BARC-East, L-nited States Department of Agricultr!re, Beltsville, Maryland, for botanical assistance. \Ye wish t o thank Dr. J . L. Beal, T h e Ohio S t a t e L-niversit?., Columbus, Ohio, for his encouragement of this work and for a generous sample of sweetinine: Dr. S. l I c L e a n , University of Toronto, Canada, for a sample oi ( - j-Gepipodopetaline and for keeping us informed of his recent work in this area: Dr. J . h. Lamherton, CSIRO, lIelbourne, -\ustralia, for a sample of i- ) podopetaline: and Dr. C. E. Costello, l l a s s Spectrometry Facility, Massachusetts Institute of Technology, Cambridge, Massachusetts, for t h e high resolution mass spectrum. 3 I . F . B . is grateful t o the American Foundation for Pharmacentical Education for financial assistance in the form of the Sydnor Barksdale Penick Memorial Fellowship (1978-1981). Rerei:,ed 6 . I f a r c h 1981
($22
.Journal of Natural Products
LITEIIATUIIE C I T E D 1. Fitzgerald, T. .J., .J. B . LaPidris and ,J. L . Beal, Lloydzii, 27, 107 (1904). 2. Balandrin, hl. F. and A . 11. Kinghorn, J . .Tut. P r o d . , 42, 097 (1979). 3. H a r t , N.K., S.11. .Johns, .J. A. Lamberton, 31. F. Alackay, .4. AlcL. Mathieson and L . Satzke, Tetrnhedron Lett., 5333 (1972). 4. h l c l e a n , S. and 13. hlisra, Con. J . Chem., 52, 1907 (1971). 5 . l)eslongchamps, P., .J. S. Wilson and %. I-alenta, T e f r ( l h e d ro n Lett., 3893 (1904). 6. Liu, H.-J., 1’. Sato, %. Valenta, .J. S. Wilson and T. T.-J. Yu, Can. J . Chenl., 54, 97 (1976). 7. Chivers, P. ,J. and T. A . Crabb, Telmhedron, 26, 3369 (1970).
[Vol. 44, No. 5
8. Hutchins, R . O., L. 1).Kopp and E. L. Eliel, J . A m . Chenz. Soc., 90, 7174 (1968). 9. Cheng, P.-T., S. hlcLean, R. Misra and S. C. Nyburg, T elrahedron L ett., 4245 (19i6). 10. Imbesi, A , “Index Plantarum”, hlessina, 1964, p. 659. 11. Investigations Scientifiques Pharmacentiqu&, S.A., “Analgesic, sedative and antispasmodic Leptolohauni elegans extracts”, Fr. 11. 6685 (Cl. A 61k), 17 h l a r 1969, iippl. 12 .Jan 1968; C h e m . A h s t r . , 74, 5 7 2 5 7 ~(1971). 12. Hess, K. and F . hlerck, B e r . D tsch. Chem. Ges., 52B, 1976 (1919). 13. Eisner, U . and F. Sorm, Collect. Czech. Chem . C om niun., 24, 2348 (1959). 14. Naegeli, P., I:. Naegeli, W. C . Wildman and R. J . Highet, T etrahedron Left., 2075 (1963).
