Abietanoid acid from Lepechinia caulescens

Phyrochmiistry, Vol. 31,No. 9, pp. 3159-3161, 1992 Printedin GroatBritain.

ABIETANOID

0031-9422/92 SS.OO+O,OO 0 1992PergamonPressLtd

ACID FROM LEPECHINIA

GUILLERMG DELGADO,~ ENRIQUE SANCHEZ, JULIO HERN~~NDEZ, MA&A ESTEBAN MART~NEZ$

CAULESCENS* ISABELCHAVEZ,LAURA ALVAREZ$and

Instituto de Quimica, Universidad National Aut6noma de Mbxico, Circuito Exterior, Ciudad Universitaria, Coyoa&, 04510, Mixico, D.F.; $Departamento de Quimica Orgcinica,Facultad de Ciencias Quimicas e Industriales de la Universidad Autbnoma dcl Estado de Morelos, Av. Universidad 1001, Cuernavaca, Morelos, M&co; $Centro de Ecologia, Universidad National Aut6noma & MBxico, Circuit0 Exterior, Ciudad Universitaria, Coyoac&n, 04510, MQico, D.F. (Receiwd in rev~d~~

16 December 1991)

Key Word Index--Lepechiniu caulescens; Labiatae; aerial part%diterpene; abietauoid acid.

Abstract-The aerial parts of Lepechinia cuulescens provided the new diterpene 7#?-hydroxy-abietan-8(14)-en-Woic acid 9a,l3a_endoperoxide which decomposes to 7~-hy~oxy-8a,9a,i3~l~-die~xy-abie~n-l8-oic acid. Several known acids and flavonoids were also isolated from this species.

INTRODUCTION

Lepechinia species (Labiatae) have been a source of several terpenoids [l], some with cytotoxic activity [2]. In continuation of our work on Mexican plants [3, 41, and in particular on the chemical constituents of this genus [S], we have analysed a population of L. cuulescens (Ort.) Epl, an annual herb widely distributed in central Mexico. RESULTSAND DISCUSSION The new compound (1) was isolated from an acetone extract of L. caulescens along with the known compounds salvigenin [6], cirsimaritin [7J ursolic, oleanolic, maslinic (2a-hydroxy-oleanolic acid) [S], euscafic [9], 2ahydrox-y-ursolic [ 101 and 7a-hy~oxydehydroabietic acids [ll], whose identities were anon by direct comparison with authentic samples. 7fl-Hydroxy-abieta-8 (14)-en-l&oic acid Pa,l3a-endoperoxide (1) analysed for C,,H,,O, (mass spectrometry and elemental analysis). The IR data suggested the presence of acid and hydroxyl groups, which were confirmed by chemical conversion of 1 into 2,3 and 4. In addition, the IR spectrum of f displayed peroxide group absorption (1187 cm- ‘). This function was supported by the loss of oxygen from the molecular ion in the mass spectra of compounds 1-4. The presence of an allylic secondary alcohol was established by the signals at 86.48 (H-14) and 4.61 (H-7) in the ‘HNMR spectrum (Table l), due to vinylic and carbinolic protons, respectively. Double resonance experiments demonstrate that these hydrogens were reciprocally coupled. The multiplicity and coupling constant values of the carbinolic proton (Table 1) established its vicinity with a methylene and its equatorial orientation. The above data, in combination with the singlets at 680.6 and 79.1 observed in the 13C NMR

*Contribution No. 1119 from Institute de Qufmica, UNAM. TAuthor to whom correspondence should be addressed. Ptlrlo 31-9-o

spectrum (Table 2), established the presence of an endoperoxide located between C-9 and C-13. The a~nfi~ration of the peroxide was determined by comparative analysis of the 3CNMR data of this sub-

& & a

R’ OH

R’ 1

H

2 3

Me OH

4

Me OAc

H

6

OAc

5H

H

Table 1. ‘HNMR data of compounds 1-4 (SOMHz) and 6 (300 MHz)

H

1

2

3

4

6

7 14 16 17 19 20 -COOMe -QCOMe

4.61 ddd 6&d 0.98 d 0.98 d 1.28 s 1.02 s -

4.61 ddd 6.48 d 0.98 d 0.98 d 1.29 s 1.01 s 3.60s -

5.76 ddd 6.23 d 0.96 d 0.96 d 1.27 s 1.06s 212 6

5.73 dd 6.23 d 0.96 d O.% d 1.27 s 1.01 s 3.60s 2.12s

4.02 d 3.12 s 0.93 d 0.93 d 1.14 s Cl.998

-

Compounds I,2 and 4 in CDCl, + DMSO, 3 and 6 in CD&. J (Hz) compounds l-4: 6#?,7a=lO; 6a,7a=7,7a,14-3; 15,16 =15,17=7; J(Hz) mmpound 6: 68,7a=6; 6a,7a=@ l&l6 = 15,17=7.

G. DELGAW et ai.

3160 Table 2. ‘sCNMR

chemical shifts of com-

pounds 1,5 and 6 (75 MHz, CDCI,) C

1

5*

6

1 2

30.8 17.4 36.5 45.9 38.4 32.1 64.7 147.8 80.6 38.9 21.7 24.7 79.1 125.4 32.1 17.3 17.3 180.8 17.0 19.5

30.9 17.6 36.7 46.8 38.2 19.9 25.0 144.3 80.8 39.2 21.8 24.3 79.2 127.0 32.2 17.5 17.1 178.5 17.9 19.2

32.7 17.5 35.9 46.1 34.2 30.0 65.8 67.2 62.2 36.5 20.4 23.2 61.4 55.7 33.1 16.5 16.1 180.3 17.7 17.9

3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

found in other Labiatae species previously investigated, in particular from SaEoiu [20,21] and Hyptis [22] species.

*Taken from ref. [14].

stance [12--l

with

those

published

for

similar

formation of diepoxides from epidioxides has been accomplished previously be treatment with Fe (II) [17, 181 as well as thermally [19]. In this case, traces of acid present in the CDCl, may catalyse the rearrangement. It is worth noting that substance 1 may be the biogenetic precursor of abietanoid diterpenes highly oxidized at ring C, some of which have been found to display certain antitumour activity [Z]. The secondary metabolites isolated from L. caulescens were similar to those

compounds

53. In particular, the upfield shift of C-l (S30.8) and C-5 (638.4) of 1 (Table 2) with respect to C-l and C-5 of methyl dehydro abietate (638.0 and 644.9, respectively [16]) is due to the y-gauche effect caused by the aorientated C(9)-C(13) endoperoxide. In addition, the steric compression between C-11 and C-20 causes a diamagnetic shift on C-11 of 1 (621.7) since this carbon resonates at 623.6 in methyl 9fi,13&epidioxy 8(14)abietan-1%oate [14, 1Sj. Finally, comparison of r3CNMR data of 1 with those of 5 (Table 2), recently published [14], ailowed us to confirm the structure of this new compound. The absolute configuration depicted in 1 was proposed by comparison of the sign of the specific rotation of the natural product with reported data for similar substances [14, 151 which show laevorotatory activity, such as 1. It was observed that the natural compound (I), recovered from the NMR sample, partially decomposed to a less polar substance, identified as 8a,Pa,13a,14adiepoxy-abietan-18-oic acid (6) as follows: the composition C20H3005 for 6 was established on the basis of the mass spectral, ‘H NMR (Table 1) and l 3C NMR (Tabie 2) data. The IR spectrum showed absorptions at 3559-2538 and 1696 cm-r indicating the presence of hydroxyl and carboxylic groups, respectivefy. The presence of a diepoxide was evident by inspection of tht i3C NMR spectrum (Table 2), which showed the presence of three singlets at 867.3,62.2 and 61.4 that were assigned to C-8, C-9 and C13, respectively. The doublet at 655.7 was assigned to C14. The a contiguration of the epoxides was in agreement with the upfield shift of C-l (6327) and C-5 (634.2, Table 2) with respect to the same carbons of methyl dehydro abietate [16]. Therefore, the structure of the transformation product of 1 should be represented as 6. The

Mps: uncorr. The above ground parts of L. cuulescens were collected near Xalapa, Veracruz, Mexico, on August 14, 1987. Voucher specimens (M 21777) are deposited at the National Herbarium, Instituto de Biologia de la UNAM. Extraction and isolation ofthe compounds. Air-dried leaves and stems (2.5 kg) of L, caulescens were extracted (x 2) with Me&O at room temp. The oily residue (127 g) was chromatographed on a silica gel column (1 kg, deactivated with 10% H,O), eluting with n-hexane and n-hexane_EtOAc mixtures. Repeated column and prep. TLC of the appropriate fractions gave (in order of increasing polarity) salvigenin (19 mg) [6], ursolic and oleanolic acids (315 mg mixture), 7~-hydroxy-abietat~enoic acid (220 mg) [I 11, ci~~a~tin (25 mg) [7], 1 (190 mg), maslinic acid (15 me) [8], 2~-hydroxy-ursolic acid (28 mg) [lo] and euscafic acid (19 mg) [9]. The methyl esters of the acids were obtained by treatment with ethereal CHIN,. It was noted that after ca 3 weeks the sample of 1 recovered from the NMR tube was composed of the original natural product and the less polar compound 6. The mixture (87 mg) was sepd by prep. TLC eluting with n-hexane-EtOAc (1:4, two developments), affording 49 mg of 1 and 15 mg of 6. 7B-Hydroxy-abieta-8 (lil)-en-oic acjd, 9a,13a,-endoperoxide (1). Solid, mp 147” (from I-Pr,O), Cd];’ -104.6” (EtOH; c 0.15); IR vg?: 3579,3509,3427,1698,1187,885,805 cm’; ‘H NMR: see Table 1; ‘%NMR (20 MHz, CDCI,): see Table 2; EIMS (70 ev) m/z (rel. int.): 350 EM]’ (0.4), 332 (1.Q 318 (3), 300 (25), 289 (51), 255 (27), 199 (17X 183 (17), 165 (42), 109 (32), 55 (53), 43 (lOO),41 (71). (Found C, 68.60; H, 8.54. C,,H,eO, requires: C, 68.57; H, 8.57.) Compound 2 was obtained by reaction of 1 with CH,N, in Et,O. Mp 119-121” (from i-Fr,Of; IRvz’: 3580, 2960,1720,1455 cm-‘; ‘H NMR: see Table 1; EIMS (70 ev) m/z (rel. int.): 364 [M] * (O.S),348 (3), 332 (15), 314 (15), 225 (27), 240 (17), 239 (74), 16.5(32), 123 (34), 109 (SO),107 (40), 105 (30), 91(55), 81(40), 79 (45), 69 (46), 59 (42), 55 (68),43 (100). Compound 3 is an oily product obtained via the normal acetylation of 1:IR vg$ 2960, 2935, 1733, 1465, 1450, 1386, 1150, 1080 cm-‘; RIMS (70 eV) m/z (rel. int.): 392 [M] + (0.5), 376 (0.8), 360(0.5), 300 (7.5), 239 (15), 199 (32), 183 (18), 159 (27), 146 (83), 109 (33), 91 (32), 55 (32), 43 (100); ‘HNMR: see Table i. Compound 4 is an oily product obtained via acetylation and methylation of 1: IR vz’? 2960,2870,1733,1728,1460 cm-‘: ‘H NMR: see Table 1; EIMS (75 eV) m/z (ref. int.): 406 [MI’ (0.5X 390 (2), 374 (I), 346 (31,330 (7), 146 (83), 91 (45), 55 (30), 43 (100). 7~-~~roxy-8a,9~13~,14a-d~e~x~-~b~tu~-l8-oic acid (6). Mp 180-182” (from i-Pr,Ok IRv&~‘~: 3559, 3432, 3403, 1694 1464, 1385, 1274, 1244, 1176, 1150, 1048, 1021, 964cm-‘; ‘H NMR: see Table 1; t3C NMR (75 MHz, CDCI,): see Table 2; EIMS (75 eV) m/z (rel. int.): 350 [M] + (O.l), 332 (O.Z),322 (l), 243 (S), 233 (4), 225 (3), 20S (3), 199 (ll), 183 (6), 159 (18), 105 (16), 93

(12), 91 (19), 79 (23), 55 (47), 41 (74), 43 (100). AcknowZedgements-We thank Messrs R. Villena, R. Patiiio, R. Gavifio, L. Velasco, J. CBrdenas, and F. de1 Rio, Institute de

Abietanoid acid from Lepechinia caulescens Quimica de la UNAM for the measurement of the spectra. This work was supported in part by Consejo National de Ciencia y Technologia, Mbxico. REFERENCES

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