Diterpenoids of Halimium viscosum

Phytochemistry, Vol. 29, No. 9, pp. 2927.-2930,1990.

003l-9422/90 $3.00+ 0.00 fJ 1990Pergamon Press plc

Printed in Great Britain.

DITERPENOIDS JULIO

OF HALIMIUM

VlSCOSUM*

G. URONES, ISIDRO SANCHEZ MARCO& NARCISO MARTIN GARRIDO and PILAR BASABE BARCALA

Departamento de Quimica Orginica, Facultad de Quimicas, Universidad de Salamanca, Plaza de 10s Caidos l-5,37008 Salamanca, Spain (Received in revised form 9 February

Key Word Index--Halimium

viscosum; Cistaceae;

1990)

diterpenes.

Abstract-From the neutral part of H. uiscosum a new diterpene with a labdane skeleton was isolated in the form of its diacetyl derivative. It was characterized as 3P-methoxy-8-labden-7/?,15-diol by spectroscopic methods and synthesis.

INTRODUCTION Continuing the study we have been carrying out on the hexane extract of H. uiscosum collected at La Fregeneda (Salamanca, Spain), we report the isolation, structural determination and hemisynthesis of a new diterpene with a labdane skeleton. RESULTS AND

DISCUSSION

The neutral part of the hexane extract of H. viscosum (La Fregeneda) principally contains esters which are difficult to separate [Z]. From the unsaponifiable part, beside the components reported previously [3], two acetyl derivatives with a methoxyl group were isolated: 3p,15-diacetoxy-7a-methoxy-8-labdene [4] and an isomer of the former, compound 2. In its 13C NMR spectrum (Table 1), compound 2 (IR 1750, 1250 cm-‘) showed signals of 25 carbon atoms: eight methyl groups (one of them corresponding to an OMe at S57.55), seven methylenes, four methines (two CH-0 at 677.21 and 88.27) and six totally substituted carbons (four of them sp’, two of these with a double tetrasubstituted bond). The ‘H NMR spectrum showed signals corresponding to the following groupings: HC-OAc (65.32, lH, t) which according to its shift must be allylic to a double bond; CH,XH,OAc (64.11,2H, t), HC-OMe (63.37,3H, sand 62.66, lH, dd), and four methyl groups (three Me-C and one Me-CH) and a Me-C= (61.66, 3H, s). Alkaline hydrolysis of compound 2 afforded the dio13 (IR: 3440 rm-‘) which in its ‘H NMR spectrum showed signals of a hydrogen atom geminal to a secondary hydroxyl group (64.05, lH, t) and a shielded signal at (63.70, 2H, m) of a primary hydroxyl group. In contrast, the signals at 63.37 (3H, s) and 2.66 (lH, dd) remained at the same shift as in the spectrum of compound 2. The mass spectrum of 2 ([Ml’ at m/z 422, C,,H,,O,) corresponded to a bicyclic diterpene with a methoxyl group, a tetrasubstituted double bond and two acetoxyl groups. The base peak at m/z: 187 [C,,H,,O,-(60

*Part 9 in the series ‘Constituents Part 8 see ref. [l].

of Halimium viscosum’. For

+32)] appeared as the result of the rupture of a side chain, as in labdanes which contain a primary acetoxyl group [S] and the loss of the oxygenated functions on the decaline system. The presence in a labdane skeleton of a methyl group born by a tetrasubstituted double bond is only possible by locating the unsaturation at C-8 and therefore the allylic acetoxyl must be located on C-7 and B because of the multiplicity of the signal (J = 8.3 Hz, t). The presence of two methyl groups slightly deshielded at 61.02 and 0.98 and the multiplicity of the geminal hydrogen to the methoxyl group dd(J = 11.7 and 4.4 Hz) suggest that this group must be located at C-3fi. This agrees with other compounds with a labdane skeleton which we have found in this neutral part, they are always functionalized at C-3 on the A-ring. The structure of compound 2 can be established by hemisynthesis, as detailed below, from 1 (7-labdene3fi,15-diol) [3], which is the major product of this extract. Reaction of 1 with S,C-NaH-Me1 yielded 4 (4.6%) and 5 (54.0%) [6]. The IR spectrum of 5 shows band of a hydroxyl group at 3450 cm-’ while in 4 this band does not appear. In the ‘H NMR spectrum of 4 the signals of H-3 (6, 5.29, dd) and H-15 (4.62, t) are prominent; and in the ‘H NMR spectrum of 5 they appear at 6,3.20 (m, H-3) and 4.62 (t, H-15), showing that they are di- and monoxanthate, respectively. This is corroborated by the 13CNMR spectra of 4 and 5 which show 22 and 24 signals, respectively (Table 1). Methylation of 5 with Me1 in the presence of NaH afforded 6. Its IR spectrum did not show the signal of the hydroxyl group and its ‘HNMR spectrum showed the signal of a methoxyl group at 3.36 (3H, s). Alkaline hydrolysis of compound 6 yielded 7 (IR; 3360 cm- ‘). Its ‘HNMR spectrum showed a signal corresponding to the hydrogens geminal to a primary hydroxyl group at 63.63 (2H, m). Acetylation of 7 afforded 8, which is also obtained by methylation under mild conditions of 9 with CH,N, on silica gel [7]. The monoacetyl derivative 9 was obtained by chemoselective acetylation of the primary hydroxyl group by heating 1 with ethyl acetate over alumina [S]. Compound 9 was identical to a minor natural product previously isolated in this neutral part [3]. Heating of 8 with I, quantitatively yielded 10 (the signal of the olefinic H disappears; Me-C= remains at

2927

J. G. URONES et al.

1

R’ H

Rz H

4

xt

5

H Me

Xt Xt Xt

6 7 8 9

Table C 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Me-S Me-S Me-S(IS Me-SCS OMe Me
Me

H

Me

AC

H

AC

1. 13C NMR data of compounds

Xt = CSSMe

10 11

RZ R’ AC @OAc H BOH H AC AC =o

12

AC

2 3

130”

1, 2, 4, 5 and 7-12 (50.3 MHz, CDCI,,

TMS as int. standard)*

1

2

4

5

7

9

8

10

11

36.82 27.47 79.20 38.72 49.79 23.55 122.01 135.35 55.44 37.41 24.46 39.69 30.59 39.98 61.23 19.82 21.95 27.94 15.09 13.68

36.90 22.53 88.27 39.46 49.32 25.88 77.21 124.99 146.69 38.66 25.55 35.50 31.17 35.05 62.93 19.31 20.09 28.15 16.11 14.70

34.92 23.03 91.39 38.52 50.05 23.30 121.77 135.28 55.10 36.72 24.28 39.53 27.89 36.91 72.61 18.68 22.01 30.85 16.98 13.77 19.01 19.84 215.50 216.65

36.95 27.52 79.22 38.82 50.01 23.35 122.11 135.46 55.61 36.65 23.94 39.56 27.91 36.9 1 72.68 18.72 21.99 28.04 15.11 13.75 19.55

37.37 22.31 89.06 38.67 50.34 23.43 122.15 135.32 55.49 36.87 24.45 39.75 30.57 39.99 61.27 19.84 21.97 28.03 15.82 13.64

37.44 27.30 79.31 38.73 49.76 23.64 122.08 135.26 55.38 36.62 24.42 39.85 30.86 36.32 63.85 19.89 21.93 27.94 15.86 13.68

37.38 22.30 89.02 38.68 50.33 23.41 122.2 1 135.23 55.43 36.85 24.38 39.67 30.85 35.34 63.05 19.71 21.93 28.01 15.82 13.65

37.65 22.70 88.79 38.92 51.72 18.79 33.90 125.75 140.42 38.88 25.58 35.53 31.12 35.22 63.06 19.39 20.23 28.24 16.24 19.39

35.36 25.62 88.89 38.95 52.01 34.05 199.22 130.19 167.08 37.98 27.21 34.72 31.21 35.25 62.81 19.28 18.48 27.98 16.22 19.43

36.96 22.53 88.38 39.73 49.51 29.61 73.13 128.57 144.46 38.52 25.83 35.26 31.17 35.51 ‘62.97 19.34 20.31 28.11 16.22 14.63

21.38

57.51 20.96

57.54 20.98

57.54 20.93

57.54 20.79

171.72

170.85

171.08

170.72

171.08

57.55 20.93 21.25 170.52 171.01

12

215.80 57.54

*Assignments based on DEPT experiments and, particularly in the case of 1, on C/H (HCCORR) normal and long range dimensional correlations. Assignation of the signals of other compound was done by comparison with those of 1.

two

1.54 ppm). Its ‘%NMR spectrum showed the signal of Reduction of compound 11 with NaBH, yielded 12, two tetrasubstituted olefinic atoms at 6 128.57 and 144.46. whose “C NMR spectrum showed a signal of 23 carbon Treatment of 10 with Na,CrO, afforded compound 11, atoms. At 673.13 the signal of a carbon bearing a which contains an acetoxyl group (IR; 1745, 1240 cm- ’ ) secondary hydroxyl group, whose geminal hydrogen in and an r&unsaturated carbonyl (IR; 1670, 1675 cm- ‘; the ‘HNMR spectrum appears at 64.07, partially overUV 244 nm). The signal in the ‘H NMR spectrum of the laps with the hydrogens geminal to the primary acetoxyl group at 4.10. The multiplicity of the signal shows that the Me-C= (6 1.75,3H, s) now appeared deshielded because the methyl is not at LYwith respect to the carbonyl group. hydroxyl group is /%in agreement with the entrance of the

Diterpenoids

of Halimium uiscosum

reductant on the a side, which shows the least hinderance. Acetylation of compound 12 afforded 2, with the structure 3P-methoxy-7b,15-diacetoxy-8-labdene. EXPERIMENTAL

Mps: uncorr, ‘H NMR: 200 MHz, CDCl,, TMS as int. standard, 13CNMR: 50.3 MHz. Extraction and isolation. The neutral fraction from saponification of the hexane extract of H. viscosum, as described in ref. [4], was fractionated on CC yielding four fractions (I-IV). Acetylation of fraction II and CC on silica gel and prep. TLC eluting 3 x with hexan+Et,O provided 3/?,15-diacetoxy-7amethoxy-8-labdene [4] and 2 (15 mg). 7B.15-Diacetoxy-3B-methoxy-7-la6dene (2). Oil. [a];’ + 16.0” (CHCI,; c 1.11); IRv~~:ccm-‘: 1750, 1630, 1240, 1130, 1030. ‘HNMR: 65.32 (lH, t, J=8.3 Hz, H-7), 4.11 (2H, t, J=6.8 Hz, H-15), 2.66 (lH, dd, J,=11.7 and J,=4.4 Hz, H-3), 3.37 (3H, s, Me-O), 2.08 (3H, s, Me-CO,), 2.05 (3H, s, Me-CO,), 1.51 (3H, s, Me-17), 1.03 (3H, s, Me-18), 0.98 (3H, s, Me-19), 0.95 (3H, d, J = 6.8 Hz, Me-16), 0.78 (3H, s, Me-20). EIMS 70 eV m/z (rel. int.): 422 [M] + (5), 380 (12), 362 (6), 348 (6), 330 (7), 315 (8), 237 (8), 227 (19), 203 (26), 187 (lOO), 173 (lo), 161(12), 119 (32); Anal. Calcd for C,,H,,O,: C, 71.05; H, 10.02; Found C, 71.07; H, 9.98. Alkaline hydrolysis of 2. Compound 2 (15 mg) was treated with 1 ml NaOH in MeOH (10%) for 24 hr at room temp. Usual work-up gave 3 (12 mg). Oil. IR ~2~: cm-‘: 3420, 1640, 1180, 1050. ‘HNMR: 64.05 (lH, t, J=8.1 Hz, H-7), 3.70 (2H, t, J =6.8 Hz, H-15), 3.37 (3H, s, Me-O), 2.66 (lH, dd, J, =11.7 and J, = 3.4 Hz, H-3), 1.66 (3H, s, Me-17), 1.01 (3H, s, Me-18), 0.98 (3H, s, Me-19), 0.94 (3H, d, J=6.3 Hz, Me-16), 0.80 (3H, s, Me20). Reaction oj 1 with S,C. Compound 1 (1.36 g) was added dropwise to a stirred suspension of 500 mg NaH (80% by weight in oil) in 10 ml Et,0 and the reaction mixture refluxed for 2 hr under N,. Then 0.2 ml S,C, freshly distilled and dried over CaCl,, was added dropwise. The resulting mixture was heated under reflux for an additional 30 min. The reaction mixture was cooled in an ice bath and 2 ml freshly distilled Me1 was added. The mixture was refluxed for 72 hr and then cooled in an ice bath and ice water was added to the mixture. After separation of the Et,0 layer, it was washed with 0.5 M HCI, twice with aq. NaCI, once with H,O and then dried over Na,SO,. The filtered Et,0 soln was coned, giving 1.80 g of reaction product. By silica gel CC of the reaction mixture, 4 (80 mg, n-hexane-EtOAc, 19: l), 5 (734 mg, n-hexane-EtOAc, 9:l) and 1 (552 mg, Et,O) were obtained. Compound 4. Oil. IR v$T cm- I: 1740(weak), 1260,1240,1210, 1080, 880; ‘HNMR: 65.35 (lH, m, H-7), 5.29 (lH, dd, J1=11.7 and J1 = 3.4 Hz, H-3), 4.62 (2H, t, J = 6.4 Hz, H-15), 2.53 (6H, s, S-Me), 1.66 (3H, br s, Me-17), 1.02 (3H, s, Me-18), 0.99 (3H, d, J =6.8 Hz, Me-16), 0.89 (3H, s, Me-19), 0.79 (3H, s, Me-20). Compound 5. Oil. IR ~2:: cm-‘: 3450,173O (weak), 1240,1070, 870; ‘HNMR: 65.35 (lH, m, H-7), 4.62 (2H, t, J=6.4 Hz, H-15), 3.20(1H,m,H-3),2.53(3H,s,S-Me), 1.66(3H,s,Me-17),0.99(3H, s, Me-18), 0.93 (3H, d, J=6.8 Hz, Me-16), 0.82 (3H, s, Me-19), 0.72 (3H, s, Me-20). Methyl&on of 5 with MeI. Me1 (2 ml) was added under dry N, and then 260 mg 5 dissolved in 4 ml Et,0 to 150 mg NaH (80%) in 1 ml Et,O. The mixture was refluxed for 2 days. After this icewater was added and the mixture extracted with Et,O. The Et,0 was washed with H,O, dried and evapd to give 330mg of reaction product. CC of the reaction product on 40 g silica gel gave 142 mg of a mixture, which was purified by TLC to give 6 (90mg). Oil. IR vt:‘crn-‘: 1750, 1240, 1160, 1070, 870; ‘HNMR:65.38(1H,brs,H-7),4.63(2H,t,J=6.5Hz,H-15),3.36

2929

(3H,s, Me-O),2.64(1H,dd, J,=11:4and J,=4.3 Hz, H-3), 2.52 (3H,s, S-Me), 1.67(3H,s, Me-17),0.98(3H,s, Me-18), 0.96(3H,d, J=6.8 Hz, Me-16), 0.84 (3H, s, Me-19), 0.74 (3H, s, Me-20). Alkaline hydrolysis of6. Compound 6 (90 mg) was treated with 3 ml 2M NaOH in MeOH for 24 hr at room temp. Usual workup gave 8 (70 mg). Oil; IR vt:; cm-‘: 3360, 1180, lOQ0, 960; ‘HNMR: 65.38 (lH, m, H-7), 3.63 (2H, t, J=7.3 Hz, H-15), 3.36 (3H,s,Me-0),2.67(1H, dd, J,=11.2and J,=3.4 Hz,H-3), 1.67 (3H, s, Me-17), 0.95 (3H, s, Me-18), 0.92 (3H, d, J=6.4 Hz, Me16), 0.83 and 0.76 (3H, s, each one, Me-19 and Me-20). Acetylation of7. Compound 7 (70 mg) was treated with Ac,O (1 ml) and pyridine (1 ml) for 24 hr at room temp. Usual work-up afforded 8 (70 mg). Oil; IR ~2:: cm- ‘: 1740, 1240, 1185, 1100, 1060, 1040, 960; ‘HNMR: 65.38 (lH, br s, H-7), 4.09 (2H, t, J =6.4 Hz, H-15), 3.36 (3H, s, Me-O), 2.67 (lH, dd, J, = 11.6 and J,=3.3 Hz, H-3), 1.66 (3H, s, Me-17), 0.95 (3H, s, Me-18), 0.93 (3H, d, J=6.8 Hz, Me-16), 0.83 (3H, s, Me-19), 0.76 (3H, s, Me20). Chemoselectiue ncetylation of 1. Neutral chromatographic alumina (Ref. 1077, activity I; Merck) (15 g) were added to a soln of l(459 mg) in EtOAc (45 ml) and this was refluxed under N, for 84 hr. After this, the reaction product was filtered and the EtOAc evapd off to afford 9 (337 mg). Oil; [alo -3.6” (CHCl,; c 0.55); IR vti: cm- 1: 3440, 1745, 1730, 1640, 1240, 1060, 1050, 1040, 1020 and 960. ‘HNMR: 65.40 (lH, br s, H-7), 4.05 (2H, t, J =6.4 Hz, H-15), 3.21 (lH, m, H-3), 2.02 (3H, s, MeCO,), 1.65 (3H, s, Me-17), 0.95 (3H, s, Me-18), 0.90 (3H, d, J=6.8 Hz, Me16), 0.83 (3H, s, Me-19), 0.74(3H, s, Me-20). EIMS 70 eV, m/z (rel. int.):350[M]+(2),207(4),189(5),150(12), 149(100),140(2),121 (15), 107 (7), 83 (8), 81 (lo), 69 (9). Methylation of 9 with CH,N,. Compound 9 (300mg) absorbed on silica gel (log) was treated with gaseous CH,N, generated from 8 g N-methyl-N-nitroso-p-toluene-sulphonamide. CC of the reaction product, on 10 g silica gel, afforded 8 (18 mg, n-hexane-EtOAc, 9:l) and 9 (165 mg, hexane-EtOAc, 1:l). Isomerizntion of 8 with iodine. Compound 8 (159 mg) in dry C,H, (10 ml) and I, (10 mg) was refluxed for 3.5 hr. ‘H NMR spectroscopy of the reaction mixture showed that compound 8 was completely transformed. The reaction mixture was purified on silica gel CC yielding 10 (90 mg). Oil. IR vt!; cm-’ : 1750, 1240, 1180, 1100, 1050, 1030, 880. ‘HNMR: 64.10 (2H, t, J =6.4 Hz, H-15), 3.37 (3H, s, Me-O), 2.66 (lH, dd, J, = 11.2 and J2 = 3.9 Hz, H-3), 2.04 (3H, s, Me-CO,), 1.54 (3H, s, Me-17), 0.98 (3H, s), 0.95 (3H, s), 0.93 (3H, d, J=6.8 Hz, Me-16), 0.78 (3H, s). Oxidation of10 with Na,CrO,. Dry Na,CrO, (120 mg), 0.5 ml Ac,O, 0.4 ml glacial HOAc and 100 mg dry NaOAc were added to 125 mg 10 dissolved in 3 ml C,H,. The mixture was kept at 40” for 15 hr. Then H,O was added and after 1 hr the mixture was extracted with Et,O. The ethereal extract was washed with NaHCO, and H,O to give 110 mg, that by CC on 30 g silica gel, eluting with n-hexane-EtOAc (41) yielded 85 mg 11. Oil; UV IEzHnrn (loge)=244 (4.15); IR vth’crn-‘: 1750, 1680, 1615, 1250, 1030, 880. ‘HNMR: 64.10 (2H, t, J=6.4Hz, H-15), 3.39 (3H, s, Me-O), 2.72 (lH, dd, J,=9.8 and J,=3.2 Hz, H-3), 2.04 (3H, s, Me-CO,), 1.75 (3H, s, Me-17), 1.08 (3H, s, Me-20), 0.97 (3H, d, J=6.8 Hz, Me-16), 0.98 and 0.87 (3H, s, each one Me-18 and Me-19). Reduction of 11 with NaBH,. NaBH, (930 mg) was added to 11 (50 mg) dissolved in MeOH (10 ml). The mixture was then kept at room temp. for 50 hr after which H,O and a few drops of HCl were added. The mixture was then extracted with Et,0 and washed with H,O. Evaporation of the solvent yielded 40 mg of material. By silica gel CC of the reaction mixture, 12 (29 mg, hexane-EtOAc, 4: 1) and 3 (17 mg, hexane-EtOAc, 1:l) were obtained.

J. G. URONES et al.

2930

Compound 12. Oil; IR v:g; cm-i: 3420,1750,1240,1180,1105, 1020; ‘HNMR: 64.10 (2H, t, 5=6.3 Hz, H-15), 4.07 (IH, I, J =8.2Hz,H-7),3.36(3H,s,Me-O),2.66(1H,dd,J,=11.2andJ, =3.9 Hz, H-3), 2.04 (3H, s, Me-CO,), 1.66 (3H, s, Me-17). 1.01 (3H, s), 0.99 (3H, s), 0.94 (3H, d, J=6.0 Hz, Me-16) 0.80 (3H, s). Acetylation qf‘ 12. Compound 12 (10mg) was treated with pyridine (1 ml) and Ac,O (1 ml) for 5.5 hr at room temp. LJsual work-up gave 2 (10 mg).

2. Pascual Teresa, J. de, Urones, J. G., Carrillo, H. and Gonzalez Mufioz, M. A. (1979) An. Quim 75. 140. 3. Pascual Teresa, J. de. Uroncs. J. G., Basabe, P., Carrillo, H., Gonzalez Muiioz, M. A. and Marcos, 1. S. (I 985) Phytochemistry 24. 791.

4. Urones, J. G., Marcos, Phytockrmistry

I. S.. Basabe,

P., Garrido,

N. M. (1988)

27, 501.

5. Enzell, C. R. and Ryhage, R. (1964) Arkiv,for Kemi 23, 367. 6. Wilcox, C. F. and Whitney, G. C. (1967) J. Org. Chem. 32, 2933. 7. Ohno.

REFERENCES 1. Urones,

Lithgow,

J. G., Marcos, I. S., Sexmero, J. J., Basabe, A. M. (1990) Phytochemistry 29, 1247.

Letters

P. and

8. Posner, 5003.

K., Nishiyama.

H. and Nagase,

H. (1979) Tetrahedron

45, 4405.

G. H. and Oda,

M. (1981) Tetrahedron

Letters

22,