Guaianolides from Centaurea glastifolia

Pergamon

Phyrochemutry.

Vol

37. No

2. pp 487490.

1994

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GUAIANOLIDES

FROM CENTAUREA SEVIL ~)KS~Z and GULACTI

Faculty of Pharmacy,

University

Sciences. Department

of Chemistry,

of Istanbul

Istanbul. Turkey; TUBITAK,

P.O. 21.41470.

Basic Sciences, Department

TOPCU* Marmara

lTUBITAK,

Gebze, Turkey;

of Chemistry,

Research Center, Research Institute for Basic

Marmara

P.O. 21.41470,

(Received in revised form 9 March

Key Word Index-Cenraurea gfusrfolia; Compositae; soxypicrolide A; 15-deschloro-15-hydroxyepisolstiolide;

GLASTlFOLZA

R-arch

Center. Research Institute for

Gebze, Turkey

1994)

sesquiterpene lactones; epicebellin J.

guaianolides;

19-de-

Abstract-From the whole plant of Centaurea g/asri/olia, three new guaianolides. 19-desoxypicrolide A, lS-deschloro15-hydroxyepisolstiolide and epicebellin J. and nine known guaianolides, cebellin J. episolstiolide, 19desoxy-15chlorojanerin, I S-deschloro-15-hydroperoxychlorojanerin. 17,18_desoxyrepin, centaurepensin, epicentaurepensin, repdiolide trio1 and aguerin B were obtained. The structures were determined by spectroscopic methods.

lNlRODLCnON

Centaurea species (tribe Cynarea) contain various types of sesquiterpene lactones, particularly guaianolides. In a continuation of our investigations on Centauren species we have now studied Centaurea glastifilia L. [Syn. Charfolepis glusrijolia (L.) Cass.]. In a previous study, Nowak reported on the presence of centaurepensin, cynaropicrin, janerin. acroptilin, repin, chlorojanerin, cebellin D and cebellin F in Chartolepsis glastifolia. In this study, we report on the presence in this plant of three new guaianolides, 19-desoxypicrolide A (I), 15-deschloro- I5hydroxyepisolstiolide (2) and epicebellin J (3). and nine known ones, cebellin J (4) [2, 33, episolstiolide (5) [4, 51, 19-desoxy-15-chlorojanerin (6) [6], 15-deschloro-15hydroperoxychlorojanerin (7) [7], 17.18-desoxyrepin (8) [8], centaurepensin (9) [S, 93, epicentaurepensin (10) [S], repdiolide trio1 (I I) [8, IO] and aguerin B (12) [ 111. All the isolates were highly oxygenated and esterified at C-8 and, among them 7 previously isolated from C. hermanii [q, has a hydroperoxy group.

RESULTS AND Dl!XXJSSION

The ‘HNMR spectrum of I (Table 1, Me&O-dd) showed four pairs of methylene protons. The first pair at 66.03 (d, J = 3.5 Hz) and 5.56 (d. J = 3.2 Hz) were indicative of a lactone methylene at C-13, the second pair at 65.14 and 4.83 (d. J = 2 Hz) were assigned to an exocyclic methylene at C-14. The third pair with a large coupling constant at 64.86 and 4.50 (d, J= 12.1 Hz) indicated an aliphatic methylene at C-15, the last pair at 66.18 (dd, J = 1.7 and 1.9 Hz) and 5.73 (dd, J= 1.5 and 1.7 Hz) was attributed to the methacrylate ester protons. The presence of the methacrylate ester was confirmed by the PHY 37:2-N

presence in the MS spectrum of a prominent peak at m/z 69. The proton signal at 64.27 with J values of 2 and 6 Hz was indicative of an z-carbinolic methine proton at C-3. The proton assignments were made by COSY and spindecoupling experiments. The 13C NMR spectrum by an APT experiment displayed one methyl, six methylene, four aromatic and six aliphatic methines, and nine quaternary carbon atoms (Table 2). The presence of a p hydroxybenzoyl group followed from ‘HNMR and 13CNMR signals as well as the base peak at m/z 121 in the EIMS spectrum (see Experimental). Its location at CI5 followed from downfield shifts of the C-l 5 methylene protons (64.86 and 4.50). While the acetylation of I’under normal conditions yielded a diacetyl derivative (In), more forcing conditions gave a triacetyl derivative (lb. Table 1). In the ‘H NMR spectrum of lb, the carbinolic methine proton (H-3) at 65.19 and C-15 methylene protons at 64.83 and 4.58 were shifted to 65.53, 5.37 and 4.87, respectively, while the other signals remained almost unchanged compared to the corresponding signals in the spectrum of la. Thus, the third hydroxyl group had to be tertiary and could only be placed at C-4. The a-position of the hydroxyl group at C4 was established by the upfield shift (ca 0.3-0.4 ppm) of H-6 compared to the /I-hydroxy epimers; in the case of the /?-OH at C-4, there is probably a I-3 diaxial interaction between H-68 and the hydroxyl group [ 123. Based on the spectral data, I was identified as a new derivative of picrolide A [ 133 and named 19-desoxypiaolide A. The EIMS spectrum of 2 did not give a molecular ion peak but a peak at m/z 349 [M-CH,OH]+. The ‘H NMR spectrum (Table 1) showed a pair of doublets for an a-methylene-y-lactone group at 66.28 (J = 3.5 Hz, H-l 3) and 5.86 (J = 3.1 HI H-l 3). two broadened singlets at 65.17 and 4.97 for C-14 exocyclic methylene protons 487

488

S. oKSO. and G. TOPCU

R2

R’

R2 18

16 17

+

6

a

7

CXIH

19

2

OH 0 cl OH

OH

9

cl KG 0

OH

10

cl 0

5

cl

and a broadened singlet of two protons at 64.01 which could be attributed to the methylene protons at C-15. The relationship between the protons was established by sequential spin-decoupling experiments, and the presence of epoxymethacrylate ester moiety was deduced by the signals at 63.19 and 2.82 (d, J=5 Hz). The EIMS spectrum supported this finding giving a peak at m/z 57 [C,H,O] + as a base peak along with a prominent peak at m/z 279 [M -epoxymethacrylate]‘. The stereochemistry of the epoxy group on the side chain was deduced mainly on the basis of the exocyclic methylene shifts of C13 and C-14. When 2 was compared to similar compounds bearing an epoxymethacrylate ester group, at C8, e.g. solstiolide and episolstiolide, the chemical shifts of C-13 and C-14 methylene protons were in good agreement with episolstiolide indicating a-orientation of the epoxy group in the ester moiety [4. 51. Cebellin J (4) and its C-17 epimer (3) could not be separated. However, they were co-characterized by

11

OH

means of some chemical shift differences in the ‘H NMR spectrum as well as by the duplicities as seen in the “CNMR spectrum (Tables I and 2). In the ‘HNMR spectrum, all protons of the epimers 3 and 4 resonated at the same ppm, but two sets of signals were observed for the C-13 and C-14 protons: one set at 66.23,5.63 and 5.17. 5.06 for cebellin J and the other set at 66.26.5.87 and 5.18. 4.91 for epicebellin J. After acetylation. the C-13 methylene protons of both epimers were much closer. appearing at 66.28 and 5.82 for cebellin J and at S6.29 and 5.85 for epicebellin J (Table I). The EIMS spectrum of the acetylated epimers gave a molecular ion peak at m/r 585 corresponding to a molecular formula Cz,HJJO,,CI, and peaks at m/z 524. 464, 404 and 344 due to the successive loss of four acetoxy groups from the [M - I] + ion (see Experimental). Based on all the spectral data, 3 and 4 were determined as epicebellin J and cebellin J [2. 33. the former has not been reported before as a natural compound.

Guaianolidcs Table

H I 22 2s 3 5 6 I 8 9a 9/3 13 13’ I4 14 IS 15’ 18 I8 I9 2’,6 3’.5’ OAc OAc OAc OAc

I.

1 (CDCI, + CD,OD)

18 (CDCI,)

3.64ddd 2.54 ddd 1.61 ddd 4.27 dd 2.49 dd 5.00 dd 3.23 dddd 5.22 ddd 2.44 dd 2.80 dd 6.03 d 5.56 d 5.14d 4.83 d 4.86 d 4.5Od 6.18 dd 5.73 dd 1.99dd I.98 dd 6.90 dd

3.27 2.20 1.33 3.78 2.12 4.61 2.95 4.82 2.48 2.13 5.88 5.34 4.87 4.57 4.59 4.39 5.93 5.44 1.70 I.69 6.56

3.47 2.58 1.72 5.19 2.53 4.46 3.21 5.10 2.70 2.62 6.27 5.70 5.20 5.02 4.83 4.58 6.20 5.72 1.99 8.08 7.19 2.09 2.30

ddd m dd dd dd dddd brdd dd dd d d d br s d d br s br s brs dd dd s s

489

ghi/olio

‘H NMR spectral data of 1, la, lb, 2, 3 and 3a (200

1 (Me&O-d,)

ddd m ddd dd dd dd dddd ddd dd dd d d d d d d dd dd dd dd dd

from Cenfowea

MHZ)

lb

2

(CDCI,)

(CDCI,)

3(4). (CD%

w4@* (CDcl,)

3.44 ddd 2.59 m 1.70 m 5.53 dd 2.57 m 4.53 dd 3.20 dddd 5.10 brdd 2.56 dd 2.42 m 6.25 d 5.64 d 5.16 d 4.92 br s 5.37 d 4.87 d 6.19 brs 5.70 hr s 2.00 br s 8.03 dd 7.18 dd 2.10s 2.33 s 2.05 s

3.34 ddd 2.52 m I.68 m 4.20 dd 2.32 dd 4.51 dd 3.12dddd 4.99 ddd 2.79 dd 2.30 m 6.28 d 5.86 d 5.17 brs 4.97 br s 4.01 brs 4.01 brs 3.19d 2.82 d 1.62 brs

3.44 ddd 2.51 m 1.67 m 4.17 dd 2.32 dd 4.67 dd 4.15 dddd 5.11 ddd 2.76 dd 2.40 dd 6.26 d(6.23) 5.87 d(5.63) 5.18 brs(5.17) 4.91 brs(5.06) 4.00 br s 4.00 br s 3.87 d 3.64 d 1.55 s

3.32 ddd 2.54 m 5.43 2.35 4.46 3.15 5.16 2.52 1.68 6.29 5.85 5.17 5.03 5.01 4.73 4.11 3.84 1.71

dd dd dd dddd ddd dd dd d(6.28) d(5.82) brs br s (5.05) brs br s d(4.08) d(3.83) s

_-

-

2.02 2.07 2.10 2.13

-

s s s s

The different values for 4 and 4a are shown in paranthescs. J[Hr]:l 1.2a=10;1,2~=7.7;1,5=11.2;2~2~=14.8;~3=6;2~,3=2;5.6=11.5;6,7=9.2;7,8=10,7.13=3.5;7,13’=3.2;8.9a=5; 8,9~=2.2;9a.9~=1S;l4.14’=2;15,15’=12.1;18,18’=1.7;18,19=1.9;18’,19=1.5,2’,3’=5’,6’=9;2’,6’=3’,5’=23.Compounds1~and lb: l,2a=l~l.2~=9;l.5=l0.5;2a.3=6.2;2~,3=2.2;5,6=11.5;6,7=9.2;7,8=10.3,8,9a=5.1;8,9~=2.1;9~9~=15;14.14’=1;15,15 =12.3;2’,3’=5’,6’=8.9;2’.6’=3’,5’=2.1.Compound2:1,Za=10.5;1.2~=10;1,5=9.5;h,3=S.5;2~.3=1.8;5.6=9;6,7=II,Z;7.8=10; 7,13=3.5;7.13’=3.1;8,9a=5;8,9~=2;9a,9~=14.5;15,15’=12;18,18’=5.Compounds3and~:1.2a=9;1.2~=8;1,5=I1;2~3=6; 2~,3=2;5,6=10.5;6,7=11.5;7,8=10;7,13=7,13’=3.2;8,9a=5;8,9~=2.2;9~9~=14.5; 18,18’=11.5.

The known compounds 5-12 were identified by comparing their spectral data with the literature values [4-l l] and the “C NMR data of 6 is given for the first time. EXPERIMENTAL

Plant material. Centaurea glastifolia L. was collected in August 1990 from eastern Turkey (Ardahan). It was identified by Dr Kerim Alpmar and deposited in the Herbarium of Faculty of Pharmacy, University of Istanbul (ISTE 65901). Extraction and isolation. Whole plants (2.5 kg) of C. glastifolia were extracted with petrol-Et,O-EtOH (1: 1: 1) at room temp. and the solvent evapd in uacuo. The extract (56.5 g) was chromatographed on a silica gel column eluting with pe.trol, a gradient of petrol-Et,0 up to 100% Et,O, followed by MeOH up to 20%. The combined frs were further purified by small CC as well as prep. TLC to obtain pure compounds. The yields were as (6 mg), 19-desoxy-15follows: 17.18 desoxyrepin chlorojanerin (15 mg), aguerin B (4.5 mg), episolstiolide (7 mg), 19-desoxypicrolide A (12 mg), cebellin J + epicebellin J (17 mg), l5-deschloro- 15-hydroperoxychloro-

(8 mg), centaurepensin (9 mg), epicentaurepensin (7 mg), repdiolide trio1 (4 mg), 15-descholoro-15hydroxycpisolstiolide (3 mg). 19-Desoxypicrolide A (1). Powder, UV i=F’ nm: 262; IR vi;: cm- ‘: 3350-3500 (OH), 1755 (&lactone), 1722 (OCOR), 1695 (OCOAr), 1612, 1595 and 1510 (aromatics); 860, 750; EIMS m/z (rel. int.): 466 [M -H,O] ’ (1.1). 347 [M-C,H,O,]+ (3.5). 316 (2.5), 242 (5.4), 163 (16.1), 137 [C,H,O,]+ (31.0), 121 [C7H,02]+ (lOO), 93 (9.5). 69 (48.2), 57 (58.2), 56 (30.5), 55 (42.4); *H and ‘-‘CNMR: Tables 1 and 2.

janerin

Triaceryl

derioatiue

o/

19-desoxypicrolide

A

(1 b).

Amorphous compound, IR vEFJ cm - I: 1760 (d-lactone), 1730 (OAc), 1720 (OCOR), 1687 (OCOAr). 1615, 1595 and 1510 (aromatics); EIMS m/z (rel. int.): 508 [M -0Ac -AC]+ (1.3). 466 [M-OAc-AC-AC]+ (0.5), 423 (1.0). 316(3.8),243(2.7).242(5.8),223(12.5), 163(15.1), 138 [M + 1-C,H,OJ]+ (27.1), 137 [C,H,O,]+ (17.4), 121 [C,H,02]+ (100). 97 (17.1), 93 (12.3). 85 [C,H502]+ (5.8), 69 [C,H50]+ (50.0), 57 (60.5), 55 (39.5), ‘H and “CNMR: Tables 1 and 2. 15-Deschloro-15-hydroxy-episolstiolide (2). IR vzFJ cm-‘: 3420-3500 (OH), 1760 (&lactone), 1730 (OCOR), 1660and 164O(C=CH,), 1255,1030,9O5,84QEIMSm/z