Guaianolides, pseudoguaianolides and an aliphatic lactone from Hymenoxys scaposa var. Villosa

Phytochemistry, Vol. 29, No. 3, pp. 895-899, 1990 Printed in Great Britain.

0031-9422/X %3.00+0.00 1990 Pergamon Press plc

0

GUAIANOLIDES, PSEUDOGUAIANOLIDES AND AN ALIPHATIC TONE FROM HYMENOXYS SCAPOSA VAR. VILLOSA

LAC-

FENG GAO, HUIPING WANG, TOM J. MABRYand MARK W. BIERNER* Department of Botany, University of Texas at Austin, Austin, TX 78713 U.S.A.; *Department of Biology, Southwest University,

San Marcos,

Texas State

TX 78666 U.S.A.

(Received 23 May 1989) , Key Word Index-Hymenoxys scaposa var. uillosa;Asteraceae;sesquiterpene lactones; guaianolides; pseudoguaianolides; aliphatic lactone.

Abstract-Six guaianolides, seven pseudoguaianolides and an aliphatic lactone were isolated from Hymenoxys scaposa var. uillosa. Six of these compounds, villosin A, villosin B, 4-acetyl-chamissonolide, 2-desacetyl-2-isobutyrylchamissonolide, 2-desoxypleniradin and 2-desoxy-14-acetoxy-pleniradin, are reported for the first time.

INTRODUCTION The perennial weedy species Hymenoxys scaposa (DC.) Parker belongs to the family Asteraceae, tribe Heliantheae, subtribe Gaillardiinae [l, 23. Four varieties of the species, all of which are widespread in Texas, are currently recognized: H. scaposa var. argyrocaulon Parker, H. scaposa var. glabra (Nutt.) Parker, H. scaposa var. scaposa and H. scaposa var. oillosa Shinners [3]. In previous work, H. scaposa var. scaposa yielded three highly oxygenated flavone aglycones (hymenoxin [4], demethoxysudachitin and scaposin [SJ) as well as four flavonol glycosides (quercetagietrin, patulitrin and patuletin 3-O-rutinoside and 3-O-glucoside [6]). Sesquiterpene lactones were isolated from a plant collected ‘en la Sierra de Arteaga (Estado de Coahuila)’ in Mexico that was identified as Hymenoxis [sic] linenris T. & G. [7], and was probably H. scaposa var. scaposa. In agreement with the treatments of Turner and Powell [l], Stuessy [2] and Correll and Johnston [3], we treat here scaposa var. uillosa as a taxon in Hymenoxys Cass.

2D COSY. The complete ‘HNMR and the unreported “CNMR data are provided in Tables 3 and 4 for compound 12; this is the first report of its natural origin. The guaianolide pleniradin (8) was the major constituent of H. scuposa var. uillosa, and NOE experiments confirmed that the lactone ring was C-7, 8 cis-fused, the C-4 methyl group was b-oriented and the C-2 hydroxyl

.

1

RESULTSAND DISCUSSION extract of H. scaposa var. (1-14) were isolated. Six of these (3-6,9, and 10) are new to the literature. Helenalin (1) [8] and mexicanin I (2) [9], which are C-6 and C-8 diastereoisomers, are well known. Because of the unexpected solubility differences (compound 1 was readily soluble in CDCl, whereas 2 was not) both were analysed by X-ray crystallography. These studies confirmed their structures (W. Watson, pers. commun.), but did not shed light on the solubility differences. Chamissonolide (7), previously isolated from the flowers of Arnica chamissonis Less. subsp. genuina Maguire [lo] and as an acetylation product of 8a-hydroxyneopulchellin [ll], was identified by high field ‘H NMR, 2D COSY, EIMS and CIMS. Compound 12, reported previously as an aqueous alkaline hydrolysis product of inuchinenolide B [12], was identified by ‘HNMR and From the dichloromethane

uillosa, fourteen compounds

3

R’

R2

R3

5

AC

AC

H

6

i-But

H

H

6U

i-But

k

AC

AC

H

H

0 7

896

F.

GAOet al Table 1. ‘H NMR data for compounds 3 and 4 [recorded at 500 MHz. 6ppm (J, HZI in CDCl,. TMS] ___H

3

4

1 2 3 3’ 6 7 8 9 9’ IO 13 13’ 14* 15*

2.98 drld (2. 3, 12) 7.69 Jd (2. 6) 6.12 dd (3. 6)

2.41 I (10) 4.30 dddd (6. 7. 8. 10) 2.88 JJ (8. 1X) 2.08 JJ (7. IX) 4.29 hr .\ 3.57 dq (2.6, 8) 4.93 ddd (2, 6. 8) 2.lOdJd(1.7. 5. 15) 1.95 ddd (2.10. 15) 2.10 01 6.16 d (2.7) 5.78 (1 (3.3, 1.25 i/ (7) 0.66 .$ OH 4.01 ti (6) (2-OH) 4.52 d 14) (6-OH)

--_____

12

0

4.02 dd ( 1.4, 4) 3.32 hr d (7.3) 5,19ddd(3. 7.3, 11) 7.31 ddd (6. II. IS) 1.96 ddd i3. _i. 15) 2.05 m 3.2X d (5.6) 3.25 d (5.6) 1.32 d (6.8) 1.13 s OH 2.51 rl (4) (6-OH)

*Intensity for three protons.

l-l

group was r-oriented. The C-l and C-5 chiral centres were not identical to those of 2a-acetoxy helenium lactone [l3], but were the same as those of pleniradin [14, 151. The structure of neogaillardin (11) [16] was determined by comparison of its ‘H NMR data with those of compound 8 and with those previously reported for pleniradin [ 161. Florilenalin 2-O-acetate (13) [ 17) was identified by high field ‘H NMR, 2D COSY and mass spectroscopy. The aliphatic lactone, 38-hydroxy-icosan1,5fl-olide (14), recently isolated from Hymenoxys odorata by direct comparison of DC. [18], was identified ‘H NMR and CIMS data [18]. Compound 3 had a protonated molecular ion in its CIMS at mj-_ 279 (100%) in accord with a formula of C,,H,,O,. The fragments at m/z 261 [M+H-H,O]+ in the CI mass spectrum and 260 [M-H,01 ’ in the EIMS indicated that a hydroxyl group was present, and the ‘H NMR data (Table 1) suggested that compound 3 differed from 1 in that an epoxy group was present at C11,13 in 3. The assignment of a C-l 1,13 epoxy group in 3 was in accord with the H-7 signal at b 3.32 appearing as a br d (J= 7.3 Hz); 2D COSY spectrum indicated that this signal was coupled with the H-8 signal at 65.19 (ddd, J = 3, 7.4, 11 Hz) as well as the H-6 signal at ii4.02 (dd, J = 1.4,4 Hz). All other signal assignments were confirmed by a 2D COSY spectrum. The small coupling constant (1.4 Hz) between H-6 and H-7 indicated that the hydroxyl group at C-6 was p-oriented. The asymmetric centres at C-l, C-5, and C-10 were assigned as in helenalin (1) and mexicanin I (2) on the basis of ‘H NMR data plus biogenetic analogy. Stereochemistries for the cis C-7, 8 lactone ring and the C-11x,13 epoxy functional group were assigned from difference NOE experiments conducted in acetone-d,. Irradiation of the H-8 signal at S5.29 enhanced the signals of H-7 (63.25), H-l and H-9%: irradiation of the H-7 signal enhanced the H-8 signal and, to some extent. the H-6 signal. These data suggested that

the lactone ring was &-fused and that H-l was roriented. Irradiation of the H-13a signal enhanced the H13b and H-6 signals, and irradiation of the H-13b signal enhanced the H-13a signal. Because of the similar chemical shifts of H-7 and H- 13a.b in both CDCl, and acetoned, another irradiation of the H-7 signal (63.36) was recorded in pyridine-d,, a solvent in which the H-7 signal was clearly separated from other signals. In pyridine-d,, irradiation of the H-7 signal enhanced the H-8 and H-6 signals, but not the signals for H-13a,b. Therefore, the epoxy group at C-l 1.13 was assigned an x-orientation, which was supported by the chemical shift of H-7: 63.32 in CDCl, when compared with the H-7 signal (~52.85)for 1 lp,l3-epoxy-11,13-dihydroaromatin [19]. Compound 3 is named here villosin A. Compound 4, villosin B, had a peak at m, I 28 1 (100%) in its CIMS suggesting a formula of C1sH2005. The fragments at miz 263 and 245 in its CIMS and nt’: 262 and 244 in its EIMS were in accord with the presence of two hydroxyl groups. Comparison of the ‘H NMR data of4 with those of 3 indicated that 4 was the C-l 1.13 deoxy and C-2,3 hydrated form of 3. A 2D COSY spectrum allowed assignment of all proton signals. The 13C NMR data (Table 4) also supported this structure assignment for 4. Compound 5 had a molecular formula of C,,H,,O(base peak in its CIMS at m:; 367) consistent with the presence of one hydroxyl and two acetyl groups on a pseudoguaianolide skeleton. The 13C NMR spectrum exhibited 19 signals also in accord with such a structure (Table 4). The oxygenated positions were determined by ‘H NMR (Table 2) and a 2D COSY spectrum. The only significant differences between the ‘HNMR signals of this compound and those for 7 [ 10. 1 l] were for the H-4 signals (6 5.06, br d .I = 5 Hz for 5 and 64.08, dd. J = 2.5 Hz for 7) and signals for two acetyl methyl groups in the spectrum for 5. The small coupling constants between H7 and H-13a.b were in accord with a C-7.8 cis-lactone ring Cl 11.

Sesquiterpenes

of Hymenoxys

scaposa

897

Table 2. ‘H NMR data for compounds $6 and 6a (5 and 6 were recorded 500 MHz, and 6a was recorded at 200 MHz, 6 ppm in CDCI,, TMS)*

at

H

5

6

6a

1 2 3 3’ 4 6 I 8 9 9’ 10 13 13’ 14t 1st OR 2’

2.30 dd (9, 11) 4.94 ddd (3, 9, 9) 2.81.ddd (6, 9, 15) 1.45 dd (3, 15) 5.06 brd (5) 3.70 brd (10) 3.60 brdd (8, 10) 4.85 ddd (4, 8, 11) 1.9 1.9 1.9 6.37 d (2) 5.77 d (1) 1.10 d (7) 1.02 s

2.36 4.85 2.12 1.42 4.09 3.70 brd (9) 3.55 brdd (8, 9) 4.82 ddd (5, 8, 10) 1.9 1.9 1.9 6.34 5.83 1.08 0.93 Oi-But 2.54 44 (7, 7) 1.16 d (7) 1.15 d (7)

2.32 4.93 2.16 1.39 5.02 5.14 d (12) 3.75 brdd (8, 12) 4.85 2.0 2.0 2.0 6.28 5.54 1.12 1.03 Oi-But 2.52 1.16 1.15 2.02 2.13

37 4’1 OAct OAct

2.05 s 2.09 s

*Coupling patterns and coupling constants (Hz, in parentheses) repeated if identical with those in preceding column. tIntensity for three protons.

The molecular formula for compound 6 (C19H2806) as suggested by a peak at m/z ([M + H], 100%) in its CIMS was in accord with an isobutyryl group in 4 instead of an acetyl group as in 7. Moreover, a fragment at m/z 265 was consistent with the loss of a C,H,02 sidechain. Fragments at m/z 247 and 229 suggested that, as in 7, two hydroxyl groups were present in 6. The isobutyrate group in 6 was further indicated by the ‘H NMR signals at 62.54 (dq,J=7,7Hz),1.16(d,J=7Hz)andl.l5(d,J=7Hz).A 2D COSY experiment allowed the assignment of all signals. The downfield signal at 64.85 assigned to H-2 by 2D COSY indicated that the isobutyrate sidechain was attached to C-2. This was further supported by acetylation, which yielded a diacetate (6a); relative to the spectrum of 6, the signals for H-4 (6 5.02, br d, J = 5 Hz) and H-6 (65.14, d, J = 12 Hz) in 6a shifted to lower field, while the H-2 signal remained almost unchanged. The C4 hydroxyl group was assigned an a-orientation based on the broadened doublet signal of H-4/?; in similar compounds, H-4a gives a doublet of doublets signal [ZO]. The 13C NMR data (Table 4) were in accord with the structure assignment. An EIMS peak at m/z 248 for 9 suggested, as did the ‘H NMR data, that 9 had a structure similar to that of 8. A 2D COSY spectrum allowed the assignment of all proton signals. Four signals for H-2 and H-3 at 6 1.57-1.90 indicated that 9 did not have the C-2 hydroxyl group present in 8. Since the stereochemistry of 8 had already been determined by NOE, the stereochemistry of 9 could be assigned the same as for 8 based on NMR data. Compound 10 had a protonated molecular ion at m/z 307 in its CIMS in accord with a molecular formula of C,,H,,O,. A fragment at m/z 246 indicated the loss of acetic acid. The EIMS of 10 also indicated the presence of

are not

one acetyl and one hydroxyl group (m/z 246 and 228). ‘H NMR data (Table 3) suggested that 10 had a structure similar to that of 9, with the only difference being an oxygenated C-14 in 10 as indicated by an AB quartet at 64.51 (br d, 13.4 Hz) and 4.45 (br d, 13.4 Hz) and the absence of a vinylic methyl signal. A 2D COSY spectrum allowed assignment of all signals except those for H-2 and H-3. The presence of an acetyl group was confirmed by a three-proton singlet at 62.09, and it was assigned to the C-14 position based on the chemical shift of an AB quartet as well as the ’ %ZNMR signals for C-14 (667.07). All the ‘H and 13CNMR spectral data supported a structure of 10 with stereochemistry as in 8. EXPERIMENTAL

All NOE and 2D COSY data were recorded at 500 MHz. Hymenoxys scaposa (DC.) Parker var. villosa Shinners was collected by Mark W. Bierner on 18 May 1988, in Jeff Davis County, Texas along Hwy 166, 14.5 miles west of Hwy 17. A voucher specimen (Bierner 88-52) is deposited in the Plant Resources Center of the University of Texas at Austin. The plant material (614 g) was extracted with 6 1. of CH,Cl, for 15 min ( x 2). The combined extracts were evapd under red. pres. After work-up, 18.3 g of crude residue was obtained. Purification, which was carried out as described before [18] by combined silica gel CC, Sephadex LH-20 CC and semi-prep. HPLC, yielded: helenalin (1) (160 mg), mexicanin I(2) (352 mg), 3 (6 mg), 4 (80 mg), 5 (13 mg), 6 (112 mg), 7 (275 mgb 8 (800 mgb 9 (11 mg), 10(10 mg), 11(12 mg), 12(60 mg), 13(32 mg), 14(9 mg). Villosin A (3). EIMS (probe) 70 eV, m/z (rel. int.): 278 [M]’ (C,,H,,O,=278) (13), 260 [M-H,O]+ (19X 245 [260-Me]+ (28), 124 (100). CIMS (methane, 0.4 torr, probe) m/z (rel. int.): 279 [M+H]+ (lOO), 261 [M+H-H,O]+ (72).

F. GAO et al.

898

3. ‘H NMR data for compounds 9,10 and 12 recorded (J, Hz) in CDCI,, TMS

Table

H

9

1 2 2 3 3’ 5 6 6 7 8 9a 9b 10 13 13’ 14a 14b 15 OAc

2.20 1.82 1.58 1.90 1.82 1.82 2.26 1.38 3.40 5.33 5.34

6.21 d (3.1) 5.56 d (2.8) 1.73 br s* 1.18 s*

*Intensity

2.20 1.82 1.58 1.90 1.82 1.82 2.33 1.38 3.49 5.42 5.63

br m m m -dd (7.7, 14) ddd (10, 12, 14) m br d (9) br s

6.23 5.58 4.51 4.45 1.21 2.09

d (3.2) d (3) br d (13.4) br d (13.4) s* s*

5

4

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 OR 1’ 2’ 3’ 4

53.39 69.48 49.52 215.13 59.16 17.57 47.08 79.86 40.65 28.00 140.70 170.66 122.97 22.22 15.77

“-‘These

50.31 77.21” 39.09 76.02b 50.90 76.42b 45.71 77.95” 28.27 35.70 136.94 170.46 125.69 19.78’ 20.34’ OAc 169.46 21.16 169.46 21.39 signals

6 49.00 79.02” 40.14 76.47b 51.57 76.61b 46.91 79.78” 28.57 35.87 137.05 170.05 126.13 19.88’ 20.50’ O&But 176.98 34.16 18.88 18.79

may be interchanged

4.59 br t (8) 2.29 dd (8, 13) 1.81 br dd (8, 13) 2.71 br d (11) 2.22 ddd (2, 6, 13) 1.45dr(ll, 11, 13) 3.29 m 4.84 ddd (3, 9, 12) 2.54 dd (3, 13) 2.25 dd (3, 13) 6.30 d (3.4) 5.64 d (3.1) 1.83 d (1.5)* 1.03 s*

for three protons.

46, 10 and 12 (reTable 4. 13CNMR data for compounds corded at 90 MHz, 6 ppm, TMS; 5,6, and 10 were recorded in CDCI,; 4 and 12 were recorded in acetone-d,) c

12

IO br m m m dd (7.7, 14) ddd (10, 12, 14) In br d (9) br s

at 500 MHz, S ppm

10

12

47.96 27.91 38.81 79.09 51.11 26.24 43.96 78.50 124.03 137.38 139.79 170.03” 121.26 67.07 24.32 OAc 170.56” 20.93

142.80 70.28 51.07 76.83 53.03 25.92 43.03 79.70 37.49 129.00 140.74 170.07 121.00 21.71 22.87

within each column.

Villosin B (4). EIMS (probe) 70 eV, m/z (rel. int.): 280 [Ml’ (C,sH2,,05=280) (l), 262 [M-H,O]+ (19), 244 [262-H,O]+ (7), 124 (100). 96 (76). CIMS (methane, 0.4 torr, probe) m/z (rel. int.): 281 [M+H]+ (lOO), 263 [M+H-H,O]+ (78), 245 [263 -HzO]+ (31). 4-Acetyl-chamissonolide (5). EIMS (probe) 70 eV, m/z (rel. int.): 306 [M-HOAc]+ (C,,H,,O,=366) (13), 288 [306-H,O]+ (2.5) 246 [306-HOAc]+ (33), 107 (lOO), 43 [AC]’ (91). CIMS

(methane, 0.4 torr, probe) m/z (rel. int.): 367 [M +H]+ (lOO), 349 [M+H-HzO]+ (15), 323 [M-AC]+ (22), 307 [M+H -HOAc]+ (36), 247 [307-HOAc]+ (96), 229 [247-H,O]+ (66). 2-DeacetyI-2-isobutyrykhamissonolide (6). CIMS (methane, 0.4 torr, probe) m/z (rel. int.): 353 [M +H]+ (C 19H 280 6 =352) (lOO), 265 [M-C,H,O,]+ (II), 247 [265-HzO]+ (49), 229 [247- H,O] + (23). Acetylation ofcompound 6. Compound 6 (40 mg) was acetylated with Ac,O-pyridine at room temp. for 4 hr. The usual workup yielded 38 mg of crude acetylation product. Pure acetate (6a, 18 mg) was obtained after silica gel prep. TLC (hexane-EtOAc, 2/l). EIMS (probe) 70 eV, m/z (rel. int.): 436 [M]’ (C,,H,,O, =436) (5), 306 [M-AC-C,H,02]+ (100). 2-Deoxypleniradin (9). EIMS (probe) 70 eV, m/z (rel. int.): 248 [M]’ (C,,H,,O,=248) (17), 230 [M-HzO]+ (47), 215 [230 -Me] + (25), 43 (100). 2-Deoxy-14-acetouy-pleniradin (10). EIMS (probe 70 eV, m/z (rel. int.): 288 [M-H,01 (C,,H,,O, =306 (2), 246 [M -HOAc]+(lOO),228[246-H,0]+(1OO),43[Ac]+(8O).CIMS (methane, 0.4 torr, probe) m/z (rel. int.): 307 [M + H] + (14), 306 [M + H] + (86), 246 [M - HOAc] + (100). Acknowledgements-We thank Dr W. H. Watson (Department of Chemistry, Texas Christian University, Fort Worth, TX) for the X-ray analysis of helenalin and mexicanin I, Dr B. A. Shoulders, Mr Steve Sorey and Mr Jim Wallin for high resolution NMR services and Dr John W. Chinn and Mr Floyd Maseles for MS service. We acknowledge support from the National Institutes of Health (Grant GM-35710) and the Robert A. Welch Foundation (Grant F-130). REFERENCES 1. Turner, B. L. and Powell, A. M. (1977) in The Biology and Chemistry of the Compositae Vol. 2 (Heywood, V. H., Harborne, J. B. and Turner, B. L.. eds), p. 722. Academic Press, London.

Sesquiterpenes of Hymenoxys scaposa 2. Stuessy, R. F. (1977) in The Biology and Chemistry of the Compositae Vol. 2 (Heywood, V. H., Harborne, J. B. and Turner, B. L., eds), p. 643. Academic Press, London. 3. Correll, D. S. and Johnston, M. C. (1970) Manual of the Vascular Plant of Texas, p. 1679. Texas Research Foundation, Renner. 4. Thomas, M. B. and Mabry, T. J. (1967) J. Org. Chem. 32, 3254. 5. Thomas, M. B. and Mabry, T. J. (1968) Tetrahedron 243675. 6. Thomas, M. B. and Mabry, T. J. (1968) Phytochemistry 7, 787. 7. Romo, J., Romo de Vivar, A. and Aguilar, M. (1969) Biol. Inst. Quim. Univ. Nacl. Auton. Mex. 21, 66. 8. Hem, W., Romo de Vivar, A., Romo, J. and Viswanathan, N. (1963) J. Am. Chem. Sot. 85, 19. 9. Doming, E. and Romo, J. (1963) Tetrahedron 19, 1415. 10. Willuhn, G., Pretzsch, G. and Wendisch, D. (1981) Tetrahedron 37, 773. 11. Bohlmann, F., Zdero, C., King, R. M. and Robinson, H.

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