- Email: [email protected]
The triterpenoid acids of Schinus molle
~h,~m&mtstry.
1978. Vol. 17. pp. 2107-21 IO 0
Prrgamon Press Ltd Prmted m England
THE TRITERPENOID TE~D~RO PO~Y~-BALRI, lstituto di Chimica
Farmaceutica
0031.9422,‘78~1201-2107 $02OC!O
ACIDS OF SCHINUS
MOUE
LUCIANO NOBILE, GIANCARL~ SCAPINI* and MAURIZIO CINI
e Tossicologica.
Facolta di Farmacia dell’Universiti &Bologna, Italy
degli Studi di Bologna,
Via Belmeloro,
(Received 20 May 1978) Key Word Index- -Schinur molle; Anacardiaceae;
triterpenes:
3-epi-isomasticadienolalic
acid.
Abstract-From the acidic fraction of the oleoresin obtained from the berries of Schinur molfe was isolated isomasticadienonic, isomasticadienonalic, masticadienonic and 3-epi-isomasticadienolic acids. In addition the new 3-epi-isomasticadienolalic acid was isolated. Both isomasticadienonalic and 3-epi-isomasticadienolalic acids had an aldehydic group attached to C-20. The absolute configuration of this centre was established. The PMR study of the isolated compounds, of their reduction products and O-acetyl derivatives is reported.
INTRODUCTION
RI I
In
a previous note El] two main ketoacids, isolated from the acidic fraction of an oleoresin obtained from berries of an Anacardiacea (Schinus molle) were identified as the known isomasticadienonic acid (1) [2] and isomasticadienonalic acid (2) and also a new a,/?-unsaturated triterpenoid acid carrying an aldehydic group in the side chain (C-20). The structure of 2 was confirmed by X-ray analysis [3]. The present note reports the isolation of a new triterpenoid acid (5) and the conligurational assignment at C-20 for both acids 2 and 5. The correlation between structural and PMR parameters [1] have been extended to the whole series of acids and their derivatives.
G@+ I
,,\@
\
R
,,G
: ii
COOR2
1 R = 0; R, = Me; R, = H IaR = O;R, = R, = Me
2 R = 0; R, = CHO; R, = H 2aR = O;R, = CHO;R, = Me
RESULTS AND DlSCUS!SlON
From the total acidic portion of the oleoresin, a fraction containing normal chain fatty acids, ranging from 22 to 28 C atoms (even C-number members predominating) was isolated. Furthermore, another fraction was obtained, which afforded, besides 1 and 2 [ 11. three other triterpenoid acids, two of which proved to be the known masticadienonic acid (3) [4] and 3-epi-isomasticadienolic acid (4) [S]. The third was hitherto unknown. We have named it 3epi-isomasticadienolalic acid and shown the structure to be (13a,l4~,17a,20S,242)-3ahydroxy-21-oxolanosta-8,24-dien-26-oic acid (5). By reduction of isomasticadienonalic acid methyl ester (2a) with NaBH,, the new (13a,l4/?,17a,20&242)(isomasticadiene3b-hydroxylanosta-8,24-dien-26-oic diolic) acid methyl ester (7a) was stereoselectively obtained, which, after monotosylation to 8a and reductive detosylation with NaBH,CN in hexamethylphosphoric triamide [6], gave isomasticadienoIic acid methyl ester (6a) [2]. Similarly, 3-epi-isomasticadienolalic acid methyl ester (5a) afforded by reduction with NaBH, the new (13a,l4~,17a,20S,24Z)-3a,2ldihydroxylanosta-8,24-dien
3 R=O;R,=Me;R,=H 3aR=O;R,=R,=Me
4
* Present address: Istituto di Chimica degli Intermedi, Facolth di Chimica Industriale, Viale Risorgimento, 4-40136 Bologna, Italy. 2107
4a & 5 5a 5b
R=H;R,=OH;R,=Me;R,=H R = H; R, = OH; R, = R, = Me R = H; R, = OAc; R, = R, = Me R = H; R, = OH; R, = CHO; R, = H R = H; R, = OH; R, = CHO; R, = Me R = H; R, = OAc: R, = CHO: R, = Me
T.
2108 Table
(‘ompound
Solvent and I-II+ 126. .___~._._~._
4-MC
4.Me
3.COOMe
(IIXI
3 42 h l2Yh +u I? 4 6X h 4RSh 017
4 67 h 4 R2 h -015
4 6X h 4 X9 h 0.21
27.MelI -.-
59s,q 5841; ,000
3 74 \ 345, ‘"2Y
I OS T 0.83 .> -022
1.055 I."6> -""I
110, 099x +"I1
, OO?
07R * 0?6<
093s 0895 + 0.04
9541 9496 to.ns
SU9,q 573rq 1016
373, 345, +02x
IYOJ lU6d -004
0 96 \ IWS ,004
079 9 OUR> -"W
n x9 s 0 90 \ -001
604rq SYI," +ni3
3 ?? \ 14I\ +032
1 UMd I Xhd + 0 02
37Sr 3 44 5 + 031
IUUd I91 d 00.1 I9Od IYOd no0
>
OV" "95, -005
.-.
"XX 7 0.X?\ I n"6
2"Ks I 7" \ -0,x
" x9 .\ 0825 -1007
0x2, 096s 0 I4 " 9" , "Y5, - "05
0 Yo .l n94r 004 lOl$ lo"\ +001
0 xor. "Ul \ "01
"YYS 095x + 0.04 1.017 l"4r -001
0775 082~ --00s
IOlS 0949 +0"6
077T
\
n.Yx 09Je too3
0.99s OY3r -006
0.84s 007 n79., 0x5, -0”h “X2, "ROT + 0.02
?"X,T
l.9Od IYOJ 0M
O‘m r 0X9\ + 0.01
+"3n
5Y21q 5x1 ,q 1011
0885 IN5 \ +003
097d OYhd -001
5941q JX2,q +012
375s 344< toil
09O.s O.XY .% +001
OYOd 092d -002
5.95rq 5a3:q +nl2
3 74 \ 345s ,029
I'Md 191 d -001
0 89 I 08RS - 0 0,
"Yxd 0.97 d fool
59414 5 x2 1; +0.0x
3 75 \ 3.46\ ro29
IYld IXXd +on3
OX*\ OYJ \ 004
OY3d OY?d -001
5Y4,q 5x1 'q f"l3
1.74> IJJ\ C!30
I 78\*
IYOd
I XX,/ i "02
"RhT "RI\ f no5
"Vhr " Y4 \ + 0 "2
"Y6\ OY6\ +0UJ
“7115 OUOI
0 u9 \ ORh\ ,003
953d Y46d +I307
5 X",q 5 69,q t-0II
172, 343\ + n2v
l9"d I RSd -005
092s 0 79 s ,013
"Y2, 0897 ,003
09R\ 090s +0.08
0x31
IMY < ou4, coo5
YS3d 94Sd - 0 OX
5901y 569ru +021
373s 344s ~"29
IYld lx5d -+"."6
0x2s
OYOI 0 xx I + 0.02
60S1q 5 R9 rq s-016
3 74 \ 341, 1031
IuOd l95d + 0.05
0x7, 0.9 I 5 -"c-l
s92,q 5 7R rq co14
? 72 \ 342, -029
I91 d 1.X8d f "03
OUU\ n.uls -007 ?"X\ I ?I \ t u.17
COOMe
24-H<
OU7d OUUd -""I
" Y" s "94T -004
iJ311 1 :, h *Ol’
JO-R:
091s OU9r -002
2.06\ 1x0s +026
2.0x\ 171, +077
l4Mc
0.77I 1).7Y s 002
"97 \ 104s 0 I):
34’11 3“h . I, I -
13-Y?,
III\ lOI> -010
-007
724dd.h 1 W dd. h I"15
IO-MC
I 07 \ 107s 0.w
I “XI
2 "II% Ikl, +02s
IWI
I 07 < OR7\ + 0.20
I "I \
4 5: dd.h 4 66 dd. b -0 I4
VI rrl.
I NMR chemical shifts for the triterpenoid acids from Schinus molle
._
4?.?dd.h 4.64rid. h -0 I2
POLIO-BAI.ISI
"'XI\ "829 t ".0X
0995 " YY .s "0" 0 Y" I 0 9 1\ -001
00’
077% -006
"995 "99 \ 0""
-013
0975 0.91> , "06
tO"l
095.\ 0x3, 0 Ml\
+ A6 = 6,,,., - b, D ; + = shielding. - = deshielding. t For 7a. 7b.br and db: (3a -- H)W z IS--25Hz: for 4s, 4b, 5, Sb. 9s and 9b (3/I - H)W = 58 HZ [S]. - 7.4-7.6 Hz; J,;,, .,,” = 4.5 Hz. - 1.3 H7: J,, ~,, = 7.5 Hz.
26-oic (3-epi-isomasticadienediolic) acid methyl ester (%I), which, tosylated to 10a and then reductively detosylated, lead to 3-epi-isomasticadienolic acid methyl ester (4a) [S], present also in the oleoresin. As the configuration at C-20 for 6a and 4a is S [2, 51, the same chirality at this carbon can be attributed to both acids 2 and 5. In fact, 6a and its epimer 4a were obtained with 93 and 7% yields, respectively, by reduction with NaBH, of isomasticadienonic acid methyl ester (la) having the known 20Sconfiguration. We have measured the PMR spectra of all the isolated
or synthetic methyl esters in order to confirm their structures, and to strengthen and extend the useful correlations described in the previous note [ 11. We have also prepared the acetyl derivatives of the hydroxylated compounds at C-3 and or at C-21 to study their PMR spectra. The PMR parameters in CDCI, and C,D, are presented in Table 1. Some points merit attention: (I) The angular methyls at C-IO. C-13 and C-14 are markedly shielded by the X.9-unsaturation. being steritally very close to the z axis of the n-bond. In the 3-0~0 derivatives la and 2a a significant ASIS effect is observed for the C-IO methyl group [I], but the reduction of the 3-0~0 group (3~ and 3b-OH derivatives) minimizes this effect, as it does in the C-3 acetyl derivatives. Me
7a R = OH: K, = H: R, = OH 7b R = OAc: R, = H: R, = OAc 8a R = OH; R, = H: R, = OTos 9a R = H: R, = OH: R, = OH 9b R = H; RI = OAc: R, = OAc
lOa R = H. R, = OH: R, = OTos
6aR = OH:R,
= H
6h R = OAc: R, = H
Triterpenoid
acids of Schimu molle
(2) When the 3-0~0 moiety is present, the methyls at C-4 show in CDCI, identical chemical shifts in agreement with Bhacca [7], whereas in the 3-hydroxyl derivatives these methyls are not magnetically equivalent: the /?-OH and a-OH groups deshield the Caxial and Cequatorial methyl, respectively. The acylation of the 3-hydroxyl group (a or 8) minimizes this effect. In C,D,, the collision complexes of the carbonyl at C-3 for compounds la and 2a cause shielding of the Caxial methyl [l], while in the 3-hydroxyl (R=H or AC) derivatives the 4,4dimethyl moiety experiences a negligible ASIS effect. (3) According to Caputo and Mangoni [S], in the 3hydroxyl compounds the 3/?-H resonates at lower field than the broader 3a-H (Table 1, note t). The acetylation of the 3-hydroxyl causes a comparable deshielding of both 3a- and 3/I-H and the ASIS effect is reversed; move. over, this effect is larger (0.1 ppm) for the 3a-OCOMe methyl group than for the 3/?-OCOMe. These correlations may be useful for structural and stereochemical assignments.
EXPERIMENTAL
Mps are uncorr. UV spectra were taken in EtOH soln and IR spectra in Nujol. PMR chemical shifts (Table I) are given in ppm (a) ( t0.02) from TMS as internal standard and the coupling constant, .I, in Hz (kO.5). Sample concns were cu 10:; in CDCI, or in C,D,. Optical rotations were determined in CHCI,. For CC the sample/absorbent ratio was always l/30. For TLC, Si (7:3) was used: visualigel HF254 Merck and hexane_EtOAc zation was with lo”/, H,SO, in EtOH at 130” and with dinitrophenylhydrazine (DNPH). For PLC 2 mm Si gel PFIs, Merck and C,H,-Et,0 (9:l) was used (UV visualisation). GLC was carried”o;t using dual FID: 1 m x 3 mm glass column packed with 2.5 “/, SE 30 on Chromosorb CS; column temp. 250’. Injector t&p. 320”: He carrier gas flow rate 40 ml/min ior fatty acid esters, 80 mljmin for fatty and triterpemc acid esters, 120 mlimin for triterpcnic acid esters. Extraction oj oleoresin and separation of the acidic fracrion. Dried. coarsely mllled berries of S. molle (400 g) were extracted in a Soxhlet apparatus for 24 hr with petrol (bp 4&70”) and the extract was evapd to given an oleoresinous residue (36 g). The residue was taken in 175 ml Me,CO and left overnight to 0’. By fiItration,awax-likematerialwasobtained(0.75g),crystalli~tion from Me,CO. mp 77-79’. soluble in 5 ;b Na,CO, (see ‘Fatty acids’). The Me,CO filtrate was evapd to dryness, the residue dissolved in Et,0 and extracted with 5% Na,CO,, affording after usual treatment the acid fraction (s~~below). Fart?, acids. The fraction insoluble in cold Me,CO (0.75 g), mp77-79”. was methylated in Et,0 with CH,N,. The esters mixture (R,0.70: mp ca 63‘ from Me,CO) was examined by GLC. The 7 oeaks obtained were identified as normal chain fatty acids by’successive co-injection with authentic samples or by MS (Table 2). Triterpenoid acids. The Me,CO soluble acid fraction, obtained by solvent evapn (14g). was methylated in Et,0 with CH,N, and the isolated esters chromatographed over neutral AI,O, Grade II and eluted successively with increasing polarity solvents. Frocfion Aa. Eluted with petrol-C,H, (1: 1);TLC R, 0.70 and 0.61: contained qualitatively the same mixture as the above described fatty acids (GLC analysis) and the known isomasticadienonic acid methyl ester (la) (R, 0.61) [I, 41.
*The mmp 14@-141” with an authentic sample obtained from the reactionbf(la) with NaBH, was not depressed. This reaction yields as main product (93%) isomasticadienolic acid methyl ester (6a), but 4a may be isolated as the pure substance (7 “/,) by
PLC [2,5].
2109
Table 2. Composition Chain length 22 23 24 25 26 27 28
of the fatty acids fraction
Identification GLC GLC MS GLC MS
GLC GLC
Peaks areas
(%)
10.5 0.3 63.3 1.4 22.7 0.3 10.5
Fraction Ab. Eluted with C,H,. The R 0.61 residue, by crystallization from MeOH, afforded furt h er la, mp 111”; [a], + 36”. and another product (mp lOf%lOS”; [a], +22.8”). which on GLC showed 2 peaks (R, 32 and 38 min) with areas ratio 9: 1. The main peak (R, 32 mm) corresponded to la (confirmed by GLC coinjection) while the highest R, compound was masticadienonic acid methyl ester (3a), present as the acid in commercial gum mastic [4]. Its identity was confirmed by GLC (co-injection with an authentic sample), and from the [a], of a synthetic mixture (9: 1) of the methyl esters of la and 3a. which gave results in good accordance with the value + 22.8”; moreover, a sample of product. mp lO&lOS”, isomerized according to Seoane [2] and crystallized from MeOH, alTorded a single substance with mp and [a],, corresponding to that of la and having a single peak (R, 32 min) on GLC. Fraction B. Eluted with C,H,-Et,0 (95:s to 8:2), 2 TLC spots. one at R, 0.50reacted with the sulfuric acid only, whereas the R, 0.45 spot reacted also with DNPH. In order to separate the two compounds, 1 g of the residue from fraction B, dissolved in 18 ml dry EtOH. was treated with 1.27 g of Girard P reagent and 3.7 ml 98% HOAc. After refluxing 90 min. the reaction mixture was poured in 320ml iced H,O containing 2.35g NaOH and left 30 min. The unreacted product was extracted with Et,0 and the ethereal soln, evapd to dryness (0.45 g). By repeated crystallization from hexane and then from EtOH, 3-epi-isomasticadienolic acid methyl ester (4a) was obtained: 3408(OH). 1718(z$-unsaturated mp 14&141”*; IR vcrn-‘: ester CO), 1646 (conjugated -C=C-_); PMR: see Table 1: (Found:C,78.9;H,l0.6.Calc.forC,,H,,O,:C,79.l;H,10.7”,). A further sample of the product was oxidized with Jones’ reagent and gave, after crystallization from MeOH, la: [a]., + 36”; mp 1 lo’, not depressed after mixture with an authenuc sample. Fraction C. Elutted with C,H,-Et,0 (7: 3 to 1: 1). From this fraction (single spot by TLC; RC 0.45) only the previously described isomasticadienonalic agd methyl ester (2a) [l] was isolated. Fracbon D. Eluted with C,H,-Et,0 (1: 1 to pure Et,O). The residue, purified by CC on AI,O, Grade II (eluents C,H,-EtOH from 95:5 un to 90: 10) and crystallization with MeOH-H,O. afforded 3-ipi-isomasticadienolalic acid methyl ester (Saj as needles mp 151- 152”: [a],, +9.1” (c = 0.88). The product was positive to the Liebermann-Burchard test; UV i,,,,. nm (log E): 212 (4.07): IR vcm -I: 3538 and 3405 (OH), 1715 (sh) and 1709 (a&unsaturated ester and aldehydic CO), 1640 (conjugated -C=C-);PMR:seeTablel;(Found:C,76.4;H,9.9.C,,H,,O, requires: C, 76.8; H, 10.0 7”). Absolute conjiyuration at C-20 of 2s and Sa. I.somasticadienediolic acid melhyl ezfer (7a). 1.3 g of 2a in 330 ml MeOH were treated with 1.8 g NaBH, in 18 ml,H,O. After 12 hr at room temp., the mixture was acidified with HOAc and extracted with Et,O. The product, obtained by evapn of the solvent, was purified by CC on Al,O, Grade 111. eluting from C,H6-E!,O (9: 1) up to Et,O. The mam fraction (R 0 13) was crystalhzed from Et-O-hexane to afford thin needles mp 135-137”: [z],, nm (loge): 208 (4.04): IR v cm- *: 3295 + 2.9” (c’= 1.0); UV i (hr. OH) 1722 (a&uE:turated ester CO). 1640 (conjugated &=Cl); PM‘R’I see Table 1; (Found: C, 76.4; H, 10.7. C,,H,,O, requires: C. 76.5; H, 10.4 %). 3-epi-lsomasticadiene-
2110
T. Pozzo-BALOI
diolicacid methylester(9a).0.3108ofSawere treated withNaBH, as above described for 28. 0.158 g of crystallme product were obtamed: mp 14&141’ from Et,0 -hcxane, [a], + lO.71’ (c = O.YX): uv i.,,, nm (log E): 212 (4.06); IR r-cm ‘: 3540 and 33YO (OH), 1700 (n,@msaturated ester CO), 1640 (conjugated -C=C-); PMR: see Table 1; (Found: C. 76.2; H. 10.5. C,,H,,O, requires: C. 76.5: H. 10.4“;,). ‘~~u~i~fffs~~ufz~~~~ ftf o.~lcm 7a rrnrf 9s. 0.730 g of 7a in 7.5 ml of Py were treated with 0.288~ tosyl chloride (initial cooling). The soln. left at room temp. overnight. was poured in aq. 5”;, NaHCO,, and after shaking for 45 min. extracted with Et20. The ethereal extract was washed with 2 M HCI, with H,O, and then drted. the solvent rvap and the residue chromatographcd on AI,O, Grade HI. Elution with C,H, gave 0.145 g of product, which, by crystallization from Et,O. afforded needles mp 127-129’. R, 0.33: UV *1,_ nm (log a): 225 (4.46): IR vcm-‘: 1720 (a,&unsaturated ester CO), IMS (conjugated -C=C-). The absorption spectra suggest it to be the ditosyl derivative of 7a. Further elution with C,H, and then with C,H; Et,0 up to (9: I). yielded 0.420 g ofthe monotosyl derivattve Xa: thin needles by crystallization from Et,O, mp 131-133’; R 0.18; UV i. (log E): 223 (4.28). 210 (sh): IR vcm ‘: 3574 (Ok). 1720 (n,p-~? saturated ester CO). 1640 (conjugated -C=C--); (Found: C, 70.8: H. 8.X: S. 4.7. C,,H,,O,S requires. C. 71.2: ft. 8.X; s. 5.0 “I). Simcarly. from 0.140 p of ester (Pa) were obtained 0.070 g of the corresponding monotosyl derivative IOa: needles mp 108I IO’ from Et,&hcxane: R, 0.16; UV i.,,,_ (log I:): 223 (4.31). ?lO(sh);lR vcm ’ 3555 _ and 3440 (OH). 1720 (br. a&unsaturated ester CO), 1640 (conJugaled --C=C-): (Found’ C, 71.3, H. Y.0: S. 4.8. C>aH,,O,S requtrcs: C, 71.2: H. X.8: S 50”;) Rcduciwc ~~fus~i~u[f~~~~ o/ mctnr)ros)Idr*rit:uf~~~,.~ 8a cznd 10% ro yield isomasticudienolic acid methyl ester (6s) and 3-epi-isomastic~adicnolic ucrd me&g/ PSCP~(4a). 0.400 g of 8a in 5 ml hcxamethylphosphoric triamide were treated with 0.200 g NaRH,CN at 7W for I3 hr. The reaction mixture was poured into H,O and extracted with EtzO. After evapn of the solvent, the residue was chromatographed on Al,O,% Grade II elutrng with C,H, and then with increasing polartty mixtures of C,H,-Et,0 up IO EtZO. From the first 6 fractions. 0.125 g of R, 0.41 product were
ef (11.
obtamed; further elution afforded the starting product. PLC of rhc R ( 0.41 product gave 0.097 g of isomasticadrenolic acid methyl ester (6a): mp 148-149. (EtOH). identical (mmp. IR. PMR) to a sample prepared by NaBH, reduction of la [5] (see Fraction B). By the same methodised for 8a, from 0.052g of 1Oa. were obtained 0.013 g of a product which was identical to both extracted and synthetic (see Fraction B) 3-cpi-isomasticadlenollc acid methyl ester (4a) (mmp, IR). O-rr~rrl clericxztices. The mono- and di-O-acctyl derivatives of the following hydroxylated acid methyl esters were also prepared by Ac,O m Py (4b) 3-ept-isomasticadienolic; mp 93--95 (from dry EtOH). (Found: C. 77.1; H, 10.6. C3_%H,,0, requires: C, 77.3; H, 10.2 *‘) (Sb) 3-epi-~somasticadtenolalic: mp 9t?-93” (from EtOH). (Found: C. 75.1; H. 9.8 C,~,ll.OO~ requires: C. 75.2. H,9.6):,). (6b) isomasticadienolic: mp 101.5 102.5’ (from dry EtOH). (Found: C. 77.9: H. 10.6. C,,H,,O, requires: C. 77.3, Il. IO.2 “;,). (‘lb) ~sornast~~ad~enediol~c; mp 83-X5, (from MeOHl. (bound: C. 73.0. H. 9.8. C,,11,,0, requires: C. ‘73.6: H. 9.5’:~. (98) 3-ept-tsomasticadienedioltc: homogeneous oil by TLC. (Found: C. 73.3: H. 9.4. C,,H,,O,> requires: C. 73.6; H, 9.5 “;,). REFERENCFS T., Nobtle. I... Seapini. G and Ctm. M. (1976) Gozz.Chim. Irof. 106.785. Seoane. E. (1956) _f. Chmi. Snc. 4158. Manotti-Lanfredi. A. M.. Tiripicchio. A. Tiripicchio-Camellini. M. and Scapini. G (1975) Crys~. SIW.I. Cornmum 4. 551. Barton, B. H. R. and Scoanc. E. (lY65) J. L’/ICWI. Svc. 4150. Caputo. R. and Mangom. L. (lY70) &I;;. (‘him Itul. 100, 317. Hutchins. R. 0.. Maryanoff. B. E. and Milewski, C. A. (1971). .I. Chrm. Sot. D. 1097.
1. Pozzo-Balbi. 2. 3 4. 5. 6.
1978. Vol. 17. pp. 2107-21 IO 0
Prrgamon Press Ltd Prmted m England
THE TRITERPENOID TE~D~RO PO~Y~-BALRI, lstituto di Chimica
Farmaceutica
0031.9422,‘78~1201-2107 $02OC!O
ACIDS OF SCHINUS
MOUE
LUCIANO NOBILE, GIANCARL~ SCAPINI* and MAURIZIO CINI
e Tossicologica.
Facolta di Farmacia dell’Universiti &Bologna, Italy
degli Studi di Bologna,
Via Belmeloro,
(Received 20 May 1978) Key Word Index- -Schinur molle; Anacardiaceae;
triterpenes:
3-epi-isomasticadienolalic
acid.
Abstract-From the acidic fraction of the oleoresin obtained from the berries of Schinur molfe was isolated isomasticadienonic, isomasticadienonalic, masticadienonic and 3-epi-isomasticadienolic acids. In addition the new 3-epi-isomasticadienolalic acid was isolated. Both isomasticadienonalic and 3-epi-isomasticadienolalic acids had an aldehydic group attached to C-20. The absolute configuration of this centre was established. The PMR study of the isolated compounds, of their reduction products and O-acetyl derivatives is reported.
INTRODUCTION
RI I
In
a previous note El] two main ketoacids, isolated from the acidic fraction of an oleoresin obtained from berries of an Anacardiacea (Schinus molle) were identified as the known isomasticadienonic acid (1) [2] and isomasticadienonalic acid (2) and also a new a,/?-unsaturated triterpenoid acid carrying an aldehydic group in the side chain (C-20). The structure of 2 was confirmed by X-ray analysis [3]. The present note reports the isolation of a new triterpenoid acid (5) and the conligurational assignment at C-20 for both acids 2 and 5. The correlation between structural and PMR parameters [1] have been extended to the whole series of acids and their derivatives.
G@+ I
,,\@
\
R
,,G
: ii
COOR2
1 R = 0; R, = Me; R, = H IaR = O;R, = R, = Me
2 R = 0; R, = CHO; R, = H 2aR = O;R, = CHO;R, = Me
RESULTS AND DlSCUS!SlON
From the total acidic portion of the oleoresin, a fraction containing normal chain fatty acids, ranging from 22 to 28 C atoms (even C-number members predominating) was isolated. Furthermore, another fraction was obtained, which afforded, besides 1 and 2 [ 11. three other triterpenoid acids, two of which proved to be the known masticadienonic acid (3) [4] and 3-epi-isomasticadienolic acid (4) [S]. The third was hitherto unknown. We have named it 3epi-isomasticadienolalic acid and shown the structure to be (13a,l4~,17a,20S,242)-3ahydroxy-21-oxolanosta-8,24-dien-26-oic acid (5). By reduction of isomasticadienonalic acid methyl ester (2a) with NaBH,, the new (13a,l4/?,17a,20&242)(isomasticadiene3b-hydroxylanosta-8,24-dien-26-oic diolic) acid methyl ester (7a) was stereoselectively obtained, which, after monotosylation to 8a and reductive detosylation with NaBH,CN in hexamethylphosphoric triamide [6], gave isomasticadienoIic acid methyl ester (6a) [2]. Similarly, 3-epi-isomasticadienolalic acid methyl ester (5a) afforded by reduction with NaBH, the new (13a,l4~,17a,20S,24Z)-3a,2ldihydroxylanosta-8,24-dien
3 R=O;R,=Me;R,=H 3aR=O;R,=R,=Me
4
* Present address: Istituto di Chimica degli Intermedi, Facolth di Chimica Industriale, Viale Risorgimento, 4-40136 Bologna, Italy. 2107
4a & 5 5a 5b
R=H;R,=OH;R,=Me;R,=H R = H; R, = OH; R, = R, = Me R = H; R, = OAc; R, = R, = Me R = H; R, = OH; R, = CHO; R, = H R = H; R, = OH; R, = CHO; R, = Me R = H; R, = OAc: R, = CHO: R, = Me
T.
2108 Table
(‘ompound
Solvent and I-II+ 126. .___~._._~._
4-MC
4.Me
3.COOMe
(IIXI
3 42 h l2Yh +u I? 4 6X h 4RSh 017
4 67 h 4 R2 h -015
4 6X h 4 X9 h 0.21
27.MelI -.-
59s,q 5841; ,000
3 74 \ 345, ‘"2Y
I OS T 0.83 .> -022
1.055 I."6> -""I
110, 099x +"I1
, OO?
07R * 0?6<
093s 0895 + 0.04
9541 9496 to.ns
SU9,q 573rq 1016
373, 345, +02x
IYOJ lU6d -004
0 96 \ IWS ,004
079 9 OUR> -"W
n x9 s 0 90 \ -001
604rq SYI," +ni3
3 ?? \ 14I\ +032
1 UMd I Xhd + 0 02
37Sr 3 44 5 + 031
IUUd I91 d 00.1 I9Od IYOd no0
>
OV" "95, -005
.-.
"XX 7 0.X?\ I n"6
2"Ks I 7" \ -0,x
" x9 .\ 0825 -1007
0x2, 096s 0 I4 " 9" , "Y5, - "05
0 Yo .l n94r 004 lOl$ lo"\ +001
0 xor. "Ul \ "01
"YYS 095x + 0.04 1.017 l"4r -001
0775 082~ --00s
IOlS 0949 +0"6
077T
\
n.Yx 09Je too3
0.99s OY3r -006
0.84s 007 n79., 0x5, -0”h “X2, "ROT + 0.02
?"X,T
l.9Od IYOJ 0M
O‘m r 0X9\ + 0.01
+"3n
5Y21q 5x1 ,q 1011
0885 IN5 \ +003
097d OYhd -001
5941q JX2,q +012
375s 344< toil
09O.s O.XY .% +001
OYOd 092d -002
5.95rq 5a3:q +nl2
3 74 \ 345s ,029
I'Md 191 d -001
0 89 I 08RS - 0 0,
"Yxd 0.97 d fool
59414 5 x2 1; +0.0x
3 75 \ 3.46\ ro29
IYld IXXd +on3
OX*\ OYJ \ 004
OY3d OY?d -001
5Y4,q 5x1 'q f"l3
1.74> IJJ\ C!30
I 78\*
IYOd
I XX,/ i "02
"RhT "RI\ f no5
"Vhr " Y4 \ + 0 "2
"Y6\ OY6\ +0UJ
“7115 OUOI
0 u9 \ ORh\ ,003
953d Y46d +I307
5 X",q 5 69,q t-0II
172, 343\ + n2v
l9"d I RSd -005
092s 0 79 s ,013
"Y2, 0897 ,003
09R\ 090s +0.08
0x31
IMY < ou4, coo5
YS3d 94Sd - 0 OX
5901y 569ru +021
373s 344s ~"29
IYld lx5d -+"."6
0x2s
OYOI 0 xx I + 0.02
60S1q 5 R9 rq s-016
3 74 \ 341, 1031
IuOd l95d + 0.05
0x7, 0.9 I 5 -"c-l
s92,q 5 7R rq co14
? 72 \ 342, -029
I91 d 1.X8d f "03
OUU\ n.uls -007 ?"X\ I ?I \ t u.17
COOMe
24-H<
OU7d OUUd -""I
" Y" s "94T -004
iJ311 1 :, h *Ol’
JO-R:
091s OU9r -002
2.06\ 1x0s +026
2.0x\ 171, +077
l4Mc
0.77I 1).7Y s 002
"97 \ 104s 0 I):
34’11 3“h . I, I -
13-Y?,
III\ lOI> -010
-007
724dd.h 1 W dd. h I"15
IO-MC
I 07 \ 107s 0.w
I “XI
2 "II% Ikl, +02s
IWI
I 07 < OR7\ + 0.20
I "I \
4 5: dd.h 4 66 dd. b -0 I4
VI rrl.
I NMR chemical shifts for the triterpenoid acids from Schinus molle
._
4?.?dd.h 4.64rid. h -0 I2
POLIO-BAI.ISI
"'XI\ "829 t ".0X
0995 " YY .s "0" 0 Y" I 0 9 1\ -001
00’
077% -006
"995 "99 \ 0""
-013
0975 0.91> , "06
tO"l
095.\ 0x3, 0 Ml\
+ A6 = 6,,,., - b, D ; + = shielding. - = deshielding. t For 7a. 7b.br and db: (3a -- H)W z IS--25Hz: for 4s, 4b, 5, Sb. 9s and 9b (3/I - H)W = 58 HZ [S]. - 7.4-7.6 Hz; J,;,, .,,” = 4.5 Hz. - 1.3 H7: J,, ~,, = 7.5 Hz.
26-oic (3-epi-isomasticadienediolic) acid methyl ester (%I), which, tosylated to 10a and then reductively detosylated, lead to 3-epi-isomasticadienolic acid methyl ester (4a) [S], present also in the oleoresin. As the configuration at C-20 for 6a and 4a is S [2, 51, the same chirality at this carbon can be attributed to both acids 2 and 5. In fact, 6a and its epimer 4a were obtained with 93 and 7% yields, respectively, by reduction with NaBH, of isomasticadienonic acid methyl ester (la) having the known 20Sconfiguration. We have measured the PMR spectra of all the isolated
or synthetic methyl esters in order to confirm their structures, and to strengthen and extend the useful correlations described in the previous note [ 11. We have also prepared the acetyl derivatives of the hydroxylated compounds at C-3 and or at C-21 to study their PMR spectra. The PMR parameters in CDCI, and C,D, are presented in Table 1. Some points merit attention: (I) The angular methyls at C-IO. C-13 and C-14 are markedly shielded by the X.9-unsaturation. being steritally very close to the z axis of the n-bond. In the 3-0~0 derivatives la and 2a a significant ASIS effect is observed for the C-IO methyl group [I], but the reduction of the 3-0~0 group (3~ and 3b-OH derivatives) minimizes this effect, as it does in the C-3 acetyl derivatives. Me
7a R = OH: K, = H: R, = OH 7b R = OAc: R, = H: R, = OAc 8a R = OH; R, = H: R, = OTos 9a R = H: R, = OH: R, = OH 9b R = H; RI = OAc: R, = OAc
lOa R = H. R, = OH: R, = OTos
6aR = OH:R,
= H
6h R = OAc: R, = H
Triterpenoid
acids of Schimu molle
(2) When the 3-0~0 moiety is present, the methyls at C-4 show in CDCI, identical chemical shifts in agreement with Bhacca [7], whereas in the 3-hydroxyl derivatives these methyls are not magnetically equivalent: the /?-OH and a-OH groups deshield the Caxial and Cequatorial methyl, respectively. The acylation of the 3-hydroxyl group (a or 8) minimizes this effect. In C,D,, the collision complexes of the carbonyl at C-3 for compounds la and 2a cause shielding of the Caxial methyl [l], while in the 3-hydroxyl (R=H or AC) derivatives the 4,4dimethyl moiety experiences a negligible ASIS effect. (3) According to Caputo and Mangoni [S], in the 3hydroxyl compounds the 3/?-H resonates at lower field than the broader 3a-H (Table 1, note t). The acetylation of the 3-hydroxyl causes a comparable deshielding of both 3a- and 3/I-H and the ASIS effect is reversed; move. over, this effect is larger (0.1 ppm) for the 3a-OCOMe methyl group than for the 3/?-OCOMe. These correlations may be useful for structural and stereochemical assignments.
EXPERIMENTAL
Mps are uncorr. UV spectra were taken in EtOH soln and IR spectra in Nujol. PMR chemical shifts (Table I) are given in ppm (a) ( t0.02) from TMS as internal standard and the coupling constant, .I, in Hz (kO.5). Sample concns were cu 10:; in CDCI, or in C,D,. Optical rotations were determined in CHCI,. For CC the sample/absorbent ratio was always l/30. For TLC, Si (7:3) was used: visualigel HF254 Merck and hexane_EtOAc zation was with lo”/, H,SO, in EtOH at 130” and with dinitrophenylhydrazine (DNPH). For PLC 2 mm Si gel PFIs, Merck and C,H,-Et,0 (9:l) was used (UV visualisation). GLC was carried”o;t using dual FID: 1 m x 3 mm glass column packed with 2.5 “/, SE 30 on Chromosorb CS; column temp. 250’. Injector t&p. 320”: He carrier gas flow rate 40 ml/min ior fatty acid esters, 80 mljmin for fatty and triterpemc acid esters, 120 mlimin for triterpcnic acid esters. Extraction oj oleoresin and separation of the acidic fracrion. Dried. coarsely mllled berries of S. molle (400 g) were extracted in a Soxhlet apparatus for 24 hr with petrol (bp 4&70”) and the extract was evapd to given an oleoresinous residue (36 g). The residue was taken in 175 ml Me,CO and left overnight to 0’. By fiItration,awax-likematerialwasobtained(0.75g),crystalli~tion from Me,CO. mp 77-79’. soluble in 5 ;b Na,CO, (see ‘Fatty acids’). The Me,CO filtrate was evapd to dryness, the residue dissolved in Et,0 and extracted with 5% Na,CO,, affording after usual treatment the acid fraction (s~~below). Fart?, acids. The fraction insoluble in cold Me,CO (0.75 g), mp77-79”. was methylated in Et,0 with CH,N,. The esters mixture (R,0.70: mp ca 63‘ from Me,CO) was examined by GLC. The 7 oeaks obtained were identified as normal chain fatty acids by’successive co-injection with authentic samples or by MS (Table 2). Triterpenoid acids. The Me,CO soluble acid fraction, obtained by solvent evapn (14g). was methylated in Et,0 with CH,N, and the isolated esters chromatographed over neutral AI,O, Grade II and eluted successively with increasing polarity solvents. Frocfion Aa. Eluted with petrol-C,H, (1: 1);TLC R, 0.70 and 0.61: contained qualitatively the same mixture as the above described fatty acids (GLC analysis) and the known isomasticadienonic acid methyl ester (la) (R, 0.61) [I, 41.
*The mmp 14@-141” with an authentic sample obtained from the reactionbf(la) with NaBH, was not depressed. This reaction yields as main product (93%) isomasticadienolic acid methyl ester (6a), but 4a may be isolated as the pure substance (7 “/,) by
PLC [2,5].
2109
Table 2. Composition Chain length 22 23 24 25 26 27 28
of the fatty acids fraction
Identification GLC GLC MS GLC MS
GLC GLC
Peaks areas
(%)
10.5 0.3 63.3 1.4 22.7 0.3 10.5
Fraction Ab. Eluted with C,H,. The R 0.61 residue, by crystallization from MeOH, afforded furt h er la, mp 111”; [a], + 36”. and another product (mp lOf%lOS”; [a], +22.8”). which on GLC showed 2 peaks (R, 32 and 38 min) with areas ratio 9: 1. The main peak (R, 32 mm) corresponded to la (confirmed by GLC coinjection) while the highest R, compound was masticadienonic acid methyl ester (3a), present as the acid in commercial gum mastic [4]. Its identity was confirmed by GLC (co-injection with an authentic sample), and from the [a], of a synthetic mixture (9: 1) of the methyl esters of la and 3a. which gave results in good accordance with the value + 22.8”; moreover, a sample of product. mp lO&lOS”, isomerized according to Seoane [2] and crystallized from MeOH, alTorded a single substance with mp and [a],, corresponding to that of la and having a single peak (R, 32 min) on GLC. Fraction B. Eluted with C,H,-Et,0 (95:s to 8:2), 2 TLC spots. one at R, 0.50reacted with the sulfuric acid only, whereas the R, 0.45 spot reacted also with DNPH. In order to separate the two compounds, 1 g of the residue from fraction B, dissolved in 18 ml dry EtOH. was treated with 1.27 g of Girard P reagent and 3.7 ml 98% HOAc. After refluxing 90 min. the reaction mixture was poured in 320ml iced H,O containing 2.35g NaOH and left 30 min. The unreacted product was extracted with Et,0 and the ethereal soln, evapd to dryness (0.45 g). By repeated crystallization from hexane and then from EtOH, 3-epi-isomasticadienolic acid methyl ester (4a) was obtained: 3408(OH). 1718(z$-unsaturated mp 14&141”*; IR vcrn-‘: ester CO), 1646 (conjugated -C=C-_); PMR: see Table 1: (Found:C,78.9;H,l0.6.Calc.forC,,H,,O,:C,79.l;H,10.7”,). A further sample of the product was oxidized with Jones’ reagent and gave, after crystallization from MeOH, la: [a]., + 36”; mp 1 lo’, not depressed after mixture with an authenuc sample. Fraction C. Elutted with C,H,-Et,0 (7: 3 to 1: 1). From this fraction (single spot by TLC; RC 0.45) only the previously described isomasticadienonalic agd methyl ester (2a) [l] was isolated. Fracbon D. Eluted with C,H,-Et,0 (1: 1 to pure Et,O). The residue, purified by CC on AI,O, Grade II (eluents C,H,-EtOH from 95:5 un to 90: 10) and crystallization with MeOH-H,O. afforded 3-ipi-isomasticadienolalic acid methyl ester (Saj as needles mp 151- 152”: [a],, +9.1” (c = 0.88). The product was positive to the Liebermann-Burchard test; UV i,,,,. nm (log E): 212 (4.07): IR vcm -I: 3538 and 3405 (OH), 1715 (sh) and 1709 (a&unsaturated ester and aldehydic CO), 1640 (conjugated -C=C-);PMR:seeTablel;(Found:C,76.4;H,9.9.C,,H,,O, requires: C, 76.8; H, 10.0 7”). Absolute conjiyuration at C-20 of 2s and Sa. I.somasticadienediolic acid melhyl ezfer (7a). 1.3 g of 2a in 330 ml MeOH were treated with 1.8 g NaBH, in 18 ml,H,O. After 12 hr at room temp., the mixture was acidified with HOAc and extracted with Et,O. The product, obtained by evapn of the solvent, was purified by CC on Al,O, Grade 111. eluting from C,H6-E!,O (9: 1) up to Et,O. The mam fraction (R 0 13) was crystalhzed from Et-O-hexane to afford thin needles mp 135-137”: [z],, nm (loge): 208 (4.04): IR v cm- *: 3295 + 2.9” (c’= 1.0); UV i (hr. OH) 1722 (a&uE:turated ester CO). 1640 (conjugated &=Cl); PM‘R’I see Table 1; (Found: C, 76.4; H, 10.7. C,,H,,O, requires: C. 76.5; H, 10.4 %). 3-epi-lsomasticadiene-
2110
T. Pozzo-BALOI
diolicacid methylester(9a).0.3108ofSawere treated withNaBH, as above described for 28. 0.158 g of crystallme product were obtamed: mp 14&141’ from Et,0 -hcxane, [a], + lO.71’ (c = O.YX): uv i.,,, nm (log E): 212 (4.06); IR r-cm ‘: 3540 and 33YO (OH), 1700 (n,@msaturated ester CO), 1640 (conjugated -C=C-); PMR: see Table 1; (Found: C. 76.2; H. 10.5. C,,H,,O, requires: C. 76.5: H. 10.4“;,). ‘~~u~i~fffs~~ufz~~~~ ftf o.~lcm 7a rrnrf 9s. 0.730 g of 7a in 7.5 ml of Py were treated with 0.288~ tosyl chloride (initial cooling). The soln. left at room temp. overnight. was poured in aq. 5”;, NaHCO,, and after shaking for 45 min. extracted with Et20. The ethereal extract was washed with 2 M HCI, with H,O, and then drted. the solvent rvap and the residue chromatographcd on AI,O, Grade HI. Elution with C,H, gave 0.145 g of product, which, by crystallization from Et,O. afforded needles mp 127-129’. R, 0.33: UV *1,_ nm (log a): 225 (4.46): IR vcm-‘: 1720 (a,&unsaturated ester CO), IMS (conjugated -C=C-). The absorption spectra suggest it to be the ditosyl derivative of 7a. Further elution with C,H, and then with C,H; Et,0 up to (9: I). yielded 0.420 g ofthe monotosyl derivattve Xa: thin needles by crystallization from Et,O, mp 131-133’; R 0.18; UV i. (log E): 223 (4.28). 210 (sh): IR vcm ‘: 3574 (Ok). 1720 (n,p-~? saturated ester CO). 1640 (conjugated -C=C--); (Found: C, 70.8: H. 8.X: S. 4.7. C,,H,,O,S requires. C. 71.2: ft. 8.X; s. 5.0 “I). Simcarly. from 0.140 p of ester (Pa) were obtained 0.070 g of the corresponding monotosyl derivative IOa: needles mp 108I IO’ from Et,&hcxane: R, 0.16; UV i.,,,_ (log I:): 223 (4.31). ?lO(sh);lR vcm ’ 3555 _ and 3440 (OH). 1720 (br. a&unsaturated ester CO), 1640 (conJugaled --C=C-): (Found’ C, 71.3, H. Y.0: S. 4.8. C>aH,,O,S requtrcs: C, 71.2: H. X.8: S 50”;) Rcduciwc ~~fus~i~u[f~~~~ o/ mctnr)ros)Idr*rit:uf~~~,.~ 8a cznd 10% ro yield isomasticudienolic acid methyl ester (6s) and 3-epi-isomastic~adicnolic ucrd me&g/ PSCP~(4a). 0.400 g of 8a in 5 ml hcxamethylphosphoric triamide were treated with 0.200 g NaRH,CN at 7W for I3 hr. The reaction mixture was poured into H,O and extracted with EtzO. After evapn of the solvent, the residue was chromatographed on Al,O,% Grade II elutrng with C,H, and then with increasing polartty mixtures of C,H,-Et,0 up IO EtZO. From the first 6 fractions. 0.125 g of R, 0.41 product were
ef (11.
obtamed; further elution afforded the starting product. PLC of rhc R ( 0.41 product gave 0.097 g of isomasticadrenolic acid methyl ester (6a): mp 148-149. (EtOH). identical (mmp. IR. PMR) to a sample prepared by NaBH, reduction of la [5] (see Fraction B). By the same methodised for 8a, from 0.052g of 1Oa. were obtained 0.013 g of a product which was identical to both extracted and synthetic (see Fraction B) 3-cpi-isomasticadlenollc acid methyl ester (4a) (mmp, IR). O-rr~rrl clericxztices. The mono- and di-O-acctyl derivatives of the following hydroxylated acid methyl esters were also prepared by Ac,O m Py (4b) 3-ept-isomasticadienolic; mp 93--95 (from dry EtOH). (Found: C. 77.1; H, 10.6. C3_%H,,0, requires: C, 77.3; H, 10.2 *‘) (Sb) 3-epi-~somasticadtenolalic: mp 9t?-93” (from EtOH). (Found: C. 75.1; H. 9.8 C,~,ll.OO~ requires: C. 75.2. H,9.6):,). (6b) isomasticadienolic: mp 101.5 102.5’ (from dry EtOH). (Found: C. 77.9: H. 10.6. C,,H,,O, requires: C. 77.3, Il. IO.2 “;,). (‘lb) ~sornast~~ad~enediol~c; mp 83-X5, (from MeOHl. (bound: C. 73.0. H. 9.8. C,,11,,0, requires: C. ‘73.6: H. 9.5’:~. (98) 3-ept-tsomasticadienedioltc: homogeneous oil by TLC. (Found: C. 73.3: H. 9.4. C,,H,,O,> requires: C. 73.6; H, 9.5 “;,). REFERENCFS T., Nobtle. I... Seapini. G and Ctm. M. (1976) Gozz.Chim. Irof. 106.785. Seoane. E. (1956) _f. Chmi. Snc. 4158. Manotti-Lanfredi. A. M.. Tiripicchio. A. Tiripicchio-Camellini. M. and Scapini. G (1975) Crys~. SIW.I. Cornmum 4. 551. Barton, B. H. R. and Scoanc. E. (lY65) J. L’/ICWI. Svc. 4150. Caputo. R. and Mangom. L. (lY70) &I;;. (‘him Itul. 100, 317. Hutchins. R. 0.. Maryanoff. B. E. and Milewski, C. A. (1971). .I. Chrm. Sot. D. 1097.
1. Pozzo-Balbi. 2. 3 4. 5. 6.