L Tetrahedron L&es. VoL32. No.26. pp 3083-3086.1991

Printed in Great Britain

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FAVELINES, NOVEL TRICYCLIC BENZOCYCLOHEPTENES WITH CYTOTOXIC

ACTIVITIES FROM BRAZILIAN PLANT, Cnidoscolus phyllacanthus

Yuichi Endo, Tomihisa Ohta, and Shigeo Nozoe’

Faculty of Pharmaceutical Sciences, Tohoku University,

Aoba-ku, Sendai 980, Japan

Abstract: Novel cytotoxic benzocycloheptene derivatives, faveline methyl ether (l), faveline (2) and deoxofaveline (3) have been isolated from the bark of Cnidoscotus phyllacanthus. Those structures were determined on the basis of spectroscopic analysis.

Favela is a thorny tree, Cnidoscolus phyllacanthus (MART.) PAX et K.HOFFM.

(Euphorbiaceae), which grows in the semiarid northwestern part of Brazil. In spite of the use

as folk medicine, there have been no previous phytochemical study on extracts of these

species’. In the course of our investigation on antitumor compounds from natural sources,

the MeOH extract of the dried bark of Favela was found to show an activity against P-388

lymphocytic leukemia in cell culture. Bioactivity-guided fractionation has led to the isolation

of three novel tricyclic benzocycloheptene derivatives, faveline methyl ether (1) faveline (2)

and deoxofaveline (3). We report herein the structural elucidation of these compounds on

the basis of the spectroscopic analysis.

The combined n-hexane and EtOAc soluble fractions from the MeOH extract of the dried

bark of Favela (30 g), which showed cytotoxic activity, was subjected to silica gel

chromatography with rrhexane-EtOAc mixtures of increasing polarity (100:0 to 0:lOO).

Repeated chromatography on silica gel with similar elution system and recrystallization from

n-hexane gave faveline methyl ether (1, 1 .iOg)z, mp 135136 “C, and deoxofaveline (3, 1.08

g)s, mp 149-151 “C. Faveline (2, 243 mg)” was obtained by normal phase HPLC (CHCl3

elution) on lnertsil PREP-SIL (Gasukuro Kogyo) as colorless needles, mp 192-194 “C, after

recrystallization from n-hexane-CHCls.

1 R=CH3

2 R=H

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Faveline methyl ether (1) ClQH2402 determinated by HREIMS (m/z 284.1778, M+, A 0.2

mmu) has a carbonyl group (Sc 201.3) involved in a conjugated system (v 1885 cm-l). The

1H and 1% NMR spectra of 1 showed signals due to three tertiary methyls (Sri / Sc : 0.78 /

20.7;1.12/28.9;2.18/15.8),amethoxyl(6H3.87/6c55.4),amethine(6~2.37/&51.3),

andfourmethylenes(S~/Sc:1.45/43.1 ;1.87,1.74/25.1 ;2.31,2.40/41.2;3.01,3.04/

42.5). Eight degree of unsaturation derived from the molecular formula, and signals indicating eight spQ carbons in the system (Sc 112.9, d ; 124.7, s ; 125.5, d ; 129.7, s ; 131.2,

d ; 136.3, s ; 147.7, s ; 160.8, s) suggested that 1 was tricyclic compound having a benzene

ring and a double bond. Two aliphatic systems, CHQ-CH and CHQ-CHQ-CHQ, shown on the

‘H -1H COSY spectrum, were indicated to be joined with a quaternary carbon (SC 38.4) by

COLOC5 experiment. Namely, the connectivities of two methyls (SH 0.76 and 1.12) to a

quaternary carbon (Sc 38.4) a methylene (Sc 43.1), and a methine (Sc 51.3) were found on

the COLOC spectrum. The methine (SH 2.37 / Sc 51.3) and the neighboring methylene (Sri

3.01 and 3.04) were indicated to be connected to a carbonyl carbon (Sc 201.3). Partial

structure A was thus deduced from the above data. The COLOC spectrum also indicated the connectivity of the sp2 conjugated system in the partial structure 6 ; H-l (6 7.62) to C-5 (6

136.3) and C-3 (S 160.9) ; H-4 (6 6.58) to C-2 (6 124.7) C-6 (S 129.7) and C-l 1 (6 125.5) ; H-

11 (6 6.28) to C-4 (6 112.9) and C-6 ; an O-methyl (6 3.87) to C-3 ; a methyl (6 2.18) to C-l

and C-3.

Fig. 1

NOE’s for 1

Two units A and B, which accounted for all atoms in the molecular formula, were linked

together with the observed COLOC peaks for C-g and C-l 2 to H-l 1 ; C-l 1 to H-g ; C-l 0 to H-

8 and H-12 ; C-6 to H-8. In addition to those connectivities, HMBCQ spectrum showed the 2D

peak for H-l to C-7. This denoted the gross structure 1 for faveline methyl ether. Finally,

differential NOE experiment confirmed the aromatic system and the conformation of 1 as

shown in Fig.1. The coupling constants between 8- and 9-hydrogen% Jsa.Q=5.OHz,

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Jsb.s=6.OHz, indicated dihedral angle of approxymately 30-40”, which suggested that the

seven membered ring took envelope form of the cornformation.

Table 1. l3C and 1H NMR Spectral Data for Faveline methyl ether (l), Faveline (2) and Deoxofaveline (3) in CDC13a

1 2 3

No. ‘3Cb ‘H ‘3Cb ‘H ‘3Cb ‘H

1 131.2 d 7.62 s 131.1 d 7.63s 2 124.7 s 122.1 s 3 160.9 s 157.9 s 4 112.9 d 6.59 s 118.1 d 6.61 s 5 136.3 s 136.6 s 6 129.7 s 130.0 s 7 201.3 s 201.2 s

6

9

10 11 12

42.5 t 3.02 dd (12.5,5.5) 3.05 dd

(12.5,5.0) 51.3 d 2.36 m

42.5 t 3.01 dd (12.5,6.0) 3.04 dd

(12.5, 5.0) 51.3 d 2.37 dd

(6.0,5.0) 147.7 s 125.5 d 6.29 s 41.2t 2.31 ddd

(12.5, 12.5,5.0) 2.40 m

147.7 s 125.0 d 6.19 s 40.2 t 2.29 m

2.38 m

13 25.1 t 1.67 m 1.74 m

14 43.1 t 1.45 m 15 36.4 s 16(15Me) 20.7 q 0.76 s 17(15-Me) 28.9 q 1.12 s 18(2-Me) 15.6 q 2.18 s OMe 55.4 q 3.87 s

25.0 t 1.65 m 1.74 m

43.0t 1.45m 37.9 s 20.7 q 0.75 s 29.oq 1.11 s 15.1 q 2.22 s

130.4 d 6.76 s 120.9 s 151.6 s 116.6 d 6.54 s 135.4 SC 135.3 SC 32.7 t 2.56 dd

(13.0,lO.O) 2.64 dd

(13.0,8.0) 30.4 t 1.47 br ddd

(13.0, 13.0,8.0) 2.22 m

54.9 d 2.27 m

145.1 s 124.7 d 6.24 s 41.2t 2.16 m

2.36 br d (14.0)

24.5 t 1.62 m

42.4 t 1.40 m 36.7 s 20.4 q 0.69 s 30.4 q 0.97 s 15.4 q 2.18 s

a 13C and 1H NMR spectra were recorded at 125 MHz and 500 MHz, respectively. Coupling constants (Hz) are given in parentheses. 6 Multiplicities were determined by DEPT experiments. c Assignments may be interchanged.

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Faveline (2) C18H2202 given by HREIMS (m/z 270.1609, M+, A -1.1 mmu), showed

hydroxyl absorption at v 3270 cm-l. The ‘H and 1% NMR spectra were simitar to those of 1.

However, the decrease in the molecular weight by 14 (CH2) and the loss of a methoxyl signal

indicated that 2 was the demethyl form of 1. The 1 H -1 H COSY and COLOC spectra allowed

a complete assignment of all proton and carbon signals as shown in Table 1, leading to the

gross structure 2 for faveline.

Deoxofaveline (3) has the molecula formula C18H240 which was determined by

HREIMS (m/z 256.1840, M+, A 1.3 mmu). The IR spectrum of 3 showed the absorption of a

hydroxyl group (v 3370 cm-l). The 1H and 1% NMR spectra implied that the structure of 3

was similar to those of 2. The l H -l H COSY spectrum indicated the presence of two partial

structures CH2-CHs-CH and CHs-CH2-CH2. These observation as well as the absence of

the 13C NMR spectrum led to the structure of deoxofaveline as 3, which was confirmed by the

precise analysis of the COLOC spectrum.

Diphenolic diterpene, rosmaridiphenol, having similar structure to faveline methyl ether

(1) and faveline (2) has been isolated from Rosmarinus officinalis 7. Faveline methyl ether

(l), faveline (2), and deoxofaveline (3) showed activity against P-388 murine leukemia cells

with I&o’s of 1.8, 18.6, and 1 .O ug/ml, respectively.

Acknowledements: We wish to thank Dr. Toshihiko Naito (Botanical Garden, Faculty of

Science, Tohoku University) for collection of the bark of the plant, and Fuji Chemical Industry

Co.,Ltd. for carrying out the biological assay.

1.

2.

3.

4.

5.

6.

7.

References and Notes

J. K. Dawn, L. D. Burch, R. Tkachuk, and H. H. Mundel, J. Am. Oil. Chem. Sot., 64,880

(1987)

1 : mp 135136 “C (n-hexane) ; [a], -344.2” (c=O.91, CHCI3) ; UV (MeOH) kmax 342

(log E 3.78), 299 (3.94) 259 (4.54) 253 nm (sh., 4.50) ; IR (CHC13) 2940, 2860, 1665,

1600 cm-1 ; EIMS m/z 284 (M+), 215,202,173.

2 : mp 192-l 94 “C (n-hexane-CHCls) ; [a], -303.9“ (c=O.73, CHC13) ; UV (MeOH) hmax

340 (sh., log E 3.66) 302 (3.94) 260 nm (4.53) ; IR (CHC13) 3580, 3270(br.), 2930, 2850,

1665,1605 cm-1 ; EIMS m/z 270 (M+), 257,201,188.

3 : mp 149-151 “C (n-hexane) ; [a], +242.1” (c=O.60, CHCl3) ; UV (MeOH) hmax 308

(sh., log E 3.81) 300 (3.85) 270 (sh.,4.28), 263 (4.33) 220 nm (4.47) ; IR (CHCl3) 3605,

3370(br.), 2935,2870, 1617 cm-1 ; EIMS m/z 256 (M+), 241, 213, 167, 171.

H. Kessler, C. Griesinger, J. Zarbock, and H. R. Loosli, J. Magn. f&on., 57, 331 (1984).

A. Bax, and M. F. Summers, J. Am. Chem. Sot., 108, 2093 (1986).

C. M. Houlihan, C. -T. Ho, and S. S. Chang, J. Am. Oil. Chem. Sot., 61, 1036 (1984).

(Received in Japan 22 February 1991)