Glaucolides and related sesquiterpene lactones from Vernonia nudiflora and Chrysolaena propinqua

003 l-9422/92 $5.00 + 0.00 (“8 1992 Pergamon Press plc

Pkytockemistry, Vol. 31, No. 2, pp. 609 613, 1992 Printed in Great Britain.

GLAUCOLIDES

AND RELATED

VERNONIANUDIFLORA

SESQUITERPENE LACTONES AND CHRYSOLAENAPROPINQUA

DE PONCE DE WERNER HERZ*

ALICIA BARDON, NORMA I. KAMIYA, CAROLINA A.

LEON,

CI%AR

FROM

A. N. CATALAN, Jljsus G.

D~Az*

and

Instituto de Q&mica Organica, Facultad de Bioquimica, Quimica y Farmacia, Universidad National de Tucumin, Ayacucho 491. 4000 S. M. de Tucuman, Argentina; *Department of Chemistry, The Florida State University, Tallahassee, FL 32306, U.S.A. (Received

in rerised,form

Key Word Index-Vernonia nudijbra; Chrysolaena cadinanolides; sesquiterpene lactones.

propinqua;

18 June 1991) Compositae; Vernonieae; glaucolides; hirsutinolides;

Abstract-Aerial parts of Vernonia mAflora furnished glaucolides A and B, one known and one new glaucolide derivative, one known and three new hirsutinolide derivatives and two new cadinanolides as well as several flavonoids and other common slant constituents. Aerial parts of Chrysolaena propinqua gave glaucolide B, one known and one new hirsutinolide and common plant constituents. 1

1

INTRODUCTION

In continuation of our work on Argentine Vernonieae [ 1] we have studied collections of Vernonia nudijora Less. and Chrysolaena propinqua (Hieron.) H. Robinson. Previous work on V. nudi$ora is limited to the mention that glaucolide A (la) and apigenin could be detected in a sample from an undisclosed location in Argentina [2, 31 and to a report that the roots of V. nudifora of unspecified provenance furnished a germacradienolide vernudifloride and a related guaianolide [4, 51. Our own work on the aerial parts of a collection from San Luis Province resulted in the isolation of glaucolide A (la) and glaucolide B (lb), both common constituents of Vernonia species, the known analogue lc [6], 2 (previously known from Stilpnopappus tomentosus [7] and Critoniopsis bogotana [8]), 3,4a (previously found in V. noueboracensis [9] and V. polyanthes [lo]), 4b, 5 (earlier found in V. cineren [8]), 6a, 7a, 8, the flavones velutin, genkwanin, apigenin, chrysoeriol and common triterpenes and plant sterols. Chrysolaena propinqua (Hieron.) H. Robinson [ 1 l] (syn. Vernonia propinqua Hieron. [ 121 and V. lepidifera Chod. [13]) also contained glaucolide B as well as 9a [14], 9b and common triterpenes and plant sterols.

RESULTS AND DISCUSSION

Lactone 3 is new and is the tiglate analogue of a methacrylate from Critoniopis huaircajana [8] and an angelate from V. patens [14]. Like the ‘H NMR spectra of these and other glaucolide derivatives its ‘HNMR spectrum at room temperature exhibited broad signals due to conformational equilibrium; hence measurements were carried out at elevated temperature (Table 1) although even then several of the signals remained broad. The mass spectrum and comparison of the ‘HNMR spectrum with the spectra of the analogues together with decoupling experiments clearly established the gross

structure and the relative stereochemistry. Lactone 4b has been prepared previously by dehydration of 9d from Chresta sphaerocephala [15], although its C-10 stereochemistry was misrepresented, but is new as a natural product. The structure was clear from the mass and ‘H NMR spectra (Table 1). Lactone 6a, possibly an artefact derived from 6b, was obviously the ethyl ether of a lo-deoxyhirsutinolide or lo-deoxypiptocarphol diester and an intermediate in the biogenetic route leading from glaucolides of type 2 to compounds of type 5. This was apparent from the mass and from ‘H NMR spectra (Table 1) which instead of the usual vinylic singlet of H-5 near 66 (in CDCI,) exhibited two mutually coupled doublets at 63.43 (H-5) and 5.13 (H-6) indicative of an a-orientated hydroxyl group (J,, 6 =9 Hz) on C-5, as well as the usual sequence of signals arising from the protons attached to C-8, C-9, C-10 and C-14 which was established by sequential decoupling. The a-orientation of the C-5 hydroxyl group is that expected for epoxide ring opening of lb as in the standard formulas C-5 of the glaucolides is reentrant and C-5 of the hemiacetals of type 5 is apical. In an earlier review of the literature [16] we pointed out that the ‘HNMR spectra of such hemiacetals and their 1-alkoxy derivatives indicate the existence of two distinct groups-group A where J,,,, and J, 9b differ widely in magnitude (l-3 and 8811 Hz, respectively) and group B in which these two coupling constants are nearly equal and relatively small (- 3 Hz). In members of group A the H-8 resonance is unusually far downfield (in CDCl, 66.336.5), whereas the H-8 signal of group B is found more upfield, usually in the vicinity of 65.5. Since the relative configuration of members of group A is definitely that shown in formulae 5 or 9ad, we suggested for the reasons cited in [16] that the C-l stereochemistry of members of group B might be the reverse. The ethyl ether isolated from V. nudifora, with J,,, =4 and 2 Hz and with the H-8 signal at 65.82, clearly belongs to group B and is, therefore, formulated as 6a. 609

610

A. BARD~Net

al.

OAc 0 1 a R=MeAcr b R=Ac c R=Tig

OAc

OAc

4 a R=MeAcr b R=Tig

6a R=Et b R=H

7 a R’=Ac, R’=Tig b R ‘=H, R2=Ac

8

9

a R’, R2=Ac, R3=H b R’=H, R’=Ac, R3 =XHO

OAc

10 Lactone 7a which contained three acetates and a tiglate, the latter obviously on C-8, was related to several c&fused cadin-7(11)-en-6,12-olides isolated earlier [14] from V. jalcana. One of the acetates was on C-13 as shown by the chemical shifts of H-13a, b, the second was attached to C-5 because the chemical shift of H-5 corresponded to the shift of H-5 in the analogue 7b [14], and the third was attached to C-10 because the chemical shift of H-15 showed that the hydroxyl group on C-4 was not esterified,

again as in 7b. In all other respects the ‘H NMR (Table 2) and the NOE difference spectrum (Table 3) of 7a corresponded to literature values for 7b. A possible biogenetic route to compounds of this type involving, in the case of V. nudiflora, initial attack of acetate on the /I-face of lactone 10 has been suggested L-141. Alternate attack of acetate on the cl-face of a lactone such as 3 should give rise to a c&fused cadin-7( 1l)-en-6, 1Zolide (8) with opposite stereochemistry at C-5, C-6 and

611

Sesquiterpene lactones from Vernonia and Chrysolaena Table 1. ‘H NMR spectra data of compounds 3,4b and 6a (500 MHz, CDCI,) H

3 (60”)

3 (C,D,,

2a 2b 3a 3b

2.5 m 2.4 m 2.05 m obsc. 5.41 brs

2.10 M 1.95 m 1.72 ddd (15, 11, 2)

5 6 8 9a 9b 10 13a 13b

14t 1st Act

3’

4’t 57 -OH

5.58 2.52 obsc. 2.87 5.03 4.97 1.08 1.50 2.07 6.93 1.85 1.86 3.08

*CH,CH, tIntensity

65”)

1.60 m 5.0 m

dd (11, 2.5) m m d (12.5) d (12.5) d (7.5) brs s qq (7.1) dq (7, 1) q (1) br

5.45 2.42 1.50 2.10 5.07 4.97 0.58 1.18 1.66 6.98 1.47 1.79

m ddd (13, 11, 11) ddd (13, 5.5, 2.5) m d d d s s qq dq q

4b

4b (C,D,,

4.1 m 2.8 m 2.4 m 5.90 br s

4.12 br s 2.1 m 1.8 m 5.55 brs

6.60 brd (9, 2) 2.60 m 1.96 m

6.42 brd 2.32 dd (15, 9) 1.77 dd (15, 2)

5.30 4.90 1.23 1.57 2.06

5.25 5.03 1.06 1.31 1.67 6.94

74“)

6* 2.07 1.78 1.78 1.42 3.42 5.13 5.82 1.99 1.72 2.57 4.87 4.79 0.92 1.42 2.03 6.11 5.65 1.94

br d brd s s s qq 1.39 dq 1.68 q

brd (13) brd (13) s s s

7.00 44 1.81 dq 1.82 q

m m m m d (9) d (9) dd (4, 2) ddd (16, 2.5, 2) ddd (16, 11, 4) ddq (11, 2.5, 7) d (12.5) d (12.5) d (7) s s quint (1.5) (H-2’a) quint (1.5) (H-2’b) br st (H-3’)

3.67 q (7), 3.50 q (7), 1.71 t (7) three protons.

Table 2. ‘H NMR spectra data of compounds 7a and 8 (500 MHz) H

7a (CDCI,)

2c( 28 3a 38 5 8

2.34 1.66 2.34 1.86 5.82 5.74 3.09 3.44 5.23

;; 10 13a

m ddd (15, 15, 5) m m s dd (4, 2.5) dd (16, 4) dd (16, 2.5)

13b

d (12.5) 4.82 d (12.5)

l4.t 1st

1.70 s 1.38 brs

3’

6.68 1.79 1.78 2.15 2.05 1.94 2.70

4’t

5’t Act

-OH

44 (7, 1) brd (7) brs s s s br

7a (C,D,)

8 (CDCI,)

8 (GD,)

1.86 ddd (15, 4.5, 3)

2.00 1.96 1.90 1.57 5.15 6.04 1.90 2.09 2.16 4.89 4.78 1.03 1.19

ddd (14, 14, 4) m m ddd (14, 14, 4)

1.81 ddd (14, 14, 4)

6.89 1.81 1.84 2.07 1.96

44 (7, 1) brd (7) br s s

1.19 2.23 1.60 5.91 5.60 1.95 3.37 -

ddd (15, 15, 5) ddd (15, 15, 4.5) m s ddd dd dd

5.36 4.94 1.51 1.47 6.71 1.42 1.77 1.93 1.65 1.59 2.58

d (13) d (13) s s qq dq (7, 1) brs s s s br

C-10. That this was the structure

of our remaining lactone from V. nudijlora was apparent from the ‘H NMR spectrum (Table 2) which, aside from the presence of a secondary methyl group on C-10, differed most significantly from the spectrum of 7a in the chemical shifts of the H-5 singlet (64.92 vs 5.91 in C,D,), the H-8 dd (66.16 vs

5.60) and the H-15 singlet (61.14 vs 1.38) as well as in the coupling constants involving H-8, H-9~7and H-9p (12 and 6.5 Hz vs 4 and 2.5 Hz). The diamagnetic shifts of H-5 and H-15 are attributable to the fact that H-5 is no longer cis to the C-4 hydroxyl and that the C-4 methyl groupin

dd (12,6.5) m ddd (13, 7, 3.5) ddq (13.5, 4, 7) brd (12) d (12) d (7) s

3.03 br

1.44 1.56 0.97 4.92 6.16 1.84 1.76 1.16 4.98 4.95

ddd (14, 44, 4) ddd (14, 4, 4) ddd (14, 14, 4) s dd (12, 7) ddd (13, 13, 12) ddd (13, 7, 3.5) ddq (13, 4, 7) brd (12)

1.14 6.81 1.42 1.75 1.71 1.56

s qq dq (7, 1) quint (1.5) s s

dd (12, 0.5) 0.62 d (6.5)

3.29 br, 2.17 br

the conformation imposed on 8 equatorial instead of axial as in ‘la-is no longer cis to the C-5 acetoxy and to the C-O bond of the lactone group. The change in the H8, H-9 coupling constants similarly reflects the conformational change in going from 7a to 8 which makes the aorientated substituent on C-8 of 8 equatorial rather than axial as in 7a, while the coupling constants involving H-9 and H-10 (13 and 4 Hz) indicate that the C-10 methyl group is a and equatorial. These conclusions were confirmed by the NOE spectrum (Table 3) which revealed pronounced interactions between axial H-5 and axial H-

612

et al.

A. BARD& Table

3. NOE difference

spectra

of compounds

7a

7a and 8 8

Irradiated

Observed

Irradiated

Observed

H-3u

H-3/I (lO.l), H-5 (3.5) H-13b (1.2) H-3a (2.4), C-5 AC (3.7)

H-5

H-3fl (2.2), H-8 (14.2) H-10 (7.8), H-15 (3.8) H-5 (9.1) H-9/I (5.6)

H-5 H-8 H-9/l

H-9a (4.5), H-9B (2.3) H-13a (5.3) H-8 (4.8), H-9a (23.9) H-14 (3.2)

H-8

H-13a

H-14 H-15 H-4

H-2a + H-~G( (4.8) H-98 (1.3) H-~/J’ (l.S), H-5 (1.0) H-3’ (3.4) H-5’ (2.1)

8, H-3b, H-10 and neighbouring H-15 and between axial H-8 and axial H-9/I. The 13C NMR spectrum listed in the Experimental is in accord with the postulated structure. The aerial parts of Chrysoluena propinqua also furnished glaucolide B as well as 9a [14], 9b and very small amounts of lactones closely related to 9a in the form of mixtures which could not be identified satisfactorily. The genus Chrysolaena recently created by H. Robinson [ll], encompasses seven species, six of them former members of Vernonia series Flexuosae including V. propinqua Hieron. and V. platensis (Spreng.) Less. According to Jones [12] the former is synonymous with V. lepidifera Chod., while the latter is synonymous with V. cognata Less. which has been studied twice previously [16, 171. The chemistry of these two species appears to be essentially identical although not particularly distinctive when compared with the chemistry of other species traditionally included within Vernonia. EXPERIMENTAL

General. For sepn of mixts HPLC was used. Columns employed were (A) Alltech RSil Cl8 (10 p, 10 x 500 mm), B) Phenomenex Ultremex Cl8 (5 p, 10 x 250mm), and C) Phenomenex Maxsil lOC8 (10 p. 10 x 500 mm). R,s were measured from the solvent peak. PIant material. Aerial parts of V. nudijlora Less. were collected at the flowering stage in December 1989 in the Departamento Capital, San Luis, Argentina. A voucher specimen (Del Vitto No. 4293) is deposited in the Herbarium of the Universidad National de San Luis, Argentina. Aerial parts of Chrysolaena propinqua (Hieron.) H. Robinson were collected in December 1987 in Missiones, Argentina. A voucher specimen (P. R. Legname No. 9270 as V. lepidifera Chodat) is deposited in the Herbarium of the Instituto Miguel Lillo, Tucuman, Argentina. Extraction of V. nudiflora. Flowers and leaves (585 g) were extracted with CHCI, (2 x 6 1) room temp. for 7 days to give 72 g (12.3%) of crude extract which was suspended in 620 ml of EtOH at 5%55”, diluted with 460 ml of Hz0 and extracted successively with hexane (3 x 250 ml) and CHCI, (3 x 250 ml). Evapn of the hexane extract gave 23 g of residue a portion of which (5 g) was chromatographed over silica gel using hexane containing in-

H-13b H-14 H-15

H-13b (30.4) H-2’ (6.2) H-4’ (1.9) H-13a (29.3) H-2b (2.5), H-15 (3.3) H-10 (2.6) H-5 (3.3)

creasing amounts of Et,0 followed by hexane-EtOAc (25100%). This gave 1.5 g of material with the same R, as /I-amyrin, 90 mg of material with R, close to cholesterol and 900 mg of material with lower R, whose IR spectrum indicated the presence of sesquiterpene lactones. HPLC of a portion (100 mg) of the triterpene fr. (column B, MeOH, 2 ml min - i) gave 15 mg of lupeol (R, 29 min), 7 mg of /Gamyrin (R, 36 min) and in the later frs unidentified triterpene mixts. Purification of the sterol fr. by CC over Florisil (hexane-Et,O, 4: 1) followed by HPLC (column B, MeOH, 2 mlmin-‘) gave mixtures of sitosterol and stigmasterol and an unidentified A”-3-hydroxyoleanane. HPLC of the sesquiterpene lactone fr. (column B, MeOH-H,O, 4:3, 2.3 ml min ‘) furnished 6.2 mg of 4a (R, 29 min), 25 mg of 4b (R, 43 min) and 6.9 mg of 5 (R, 50 min). Evapn of the CHCl, extract gave 21 g of residue which was flash chromatographed on silica gel using CHCI, with increasing amounts of Et,0 (&SO%) and CHCI,-EtOAc (3@-lOO%), 21 fractions being collected and monitored by TLC. Frs 6-15 were combined and taken up in CHCI,. Undissolved material was filtered and recrystallized from MeOH-H,O (2: 1) to give 5.9 mg of velutin (5,4’-dihydrydoxy-7,3’dimethoxyflavone) identified by UV, MS and ‘H NMR spectrometry including data from NOE spectrometry to locate the methoxy groups. The filtrate was rechromatographed (silica gel, CHCI,-EtOAc, 5-100%) to give 55 frs. Frs 1621 of the rechromatogram were combined and processed by HPLC (column A, MeOH-H,O, 3:2,2 ml min-i) to give 3 (1 mg, R, 28 min), 2 (6.5 mg, R, 30 min), lc (26.7 mg, R, 40 min) and 4.5 mg of unidentified material (R, 63 min). Frs 22-35 of the rechromatogram were combined and taken up in CHCI,. The undissolved material (10 mg) was again identified as velutin (10 mg); HPLC of the filtrate (column C, MeOH-H,O, 3:2; 2 ml min-‘) gave la (3.1 mg, R, 7 min), 2 (9.5 mg, R, 10 and 11 min), and 20 mg of lc after further purification by HPLC on column A. HPLC of frs 38-40 (column C, MeOH-H,O, 4:3, 1.8 ml min ‘) gave 12.2 mg of a mixt. of unidentified glaucolides (R, 16 min), 4a (27.5 mg, R, 25 min), 4b (12 mg, R, 34 min), Ic (20 mg, R, 43 min), 5 (6.9 mg, R, 50 min) and 6 (2.6 mg, R, 65 min). HPLC of frs 4145 (column C, MeOH-H,O, 4:3, 2 ml min- ‘) gave more 4a (10 mg, R, 18 min), more 4b (84 mg, R, 23 min) and more lc (11.6 mg, R, 38 min). Frs 4655 gave unidentified mixts. Frs 1619 from the flash chromatogram after repeated CC and prep. TLC gave 2 mg of genkwanin, 1.6 mg of a

Sesquiterpene

lactones

from Vernonia and Chrysolaena

2:3 mixt. of velutin and apigenin, 1.6 mg of a 2:3 mixt. of apigenin and chrysoeriol (all flavones were identified by UV, MS and ‘H NMR spectrometry, including NOE spectra) and additional fractions which were processed by HPLC (column B, MeOH-H,O, 4: 3, 1.5 ml min-‘) to give 7a (5.1 mg, R, 28 min) and 8 (25 mg, R, 33 min) as well as mixt of 7a and two unidentified lactones (28 mg, R, 18 and 22 min). Extraction ofC. propinqua. Flowers and leaves (1.60 kg) were extracted with CHCI, (2 x 6 I) at room temp. for 7 days to give 105 g (6.6%) of crude extract. A 30 g portion was suspended in 250 ml of EtOH at 50’,diluted with 190 ml of H,O and extracted successively with hexane (3 x 200 ml) and CHCI, (3 x 200 ml). A portion (4 g) of the residue from the hexane extract (16 g) was chromatographed over silica gel using hexane with increasing amounts of Et,0 (G-25%) followed by hexane with increasing amounts of EtOAc ( IWOo/,). This gave 0.320 g of material with the same R, as fi-amyrin and 0.106 g of material with R, close to cholesterol. HPLC of a portion (80 mg) of the triterpene fraction (column B, MeOH, 2.2 ml min-‘) gave 10 mg of lupeol (R, 32 min), 13.8 mg of P-amyrin (R, 38 min), 7.6 mg of cc-amyrin (R, 43 min) and 3 mg of germanicol (R, 47 min). HPLC of the sterol fr. gave 3.8 mg of lupeol (R, 29 min), 11.2 mg of stigmasterol (R, 36 min) and 9 mg of sitosterol (R, 41 min). Flash chromatography of the CHCI, extract (11 g, CHCI, with increasing amounts of EtOAc, CrlOO%) gave 54 frs. Frs 8-14 were combined (0.6 g) and rechromatographed CHCI, with followed by amounts of EtOAc, &50%, increasing 1: 1,32 frs. HPLC (column A, MeOH-H,O, 6:5, CHCI,-EtOAc 2.5 ml min-‘) of frs 17-24 from the second chromatogram gave 9b (2.2 mg, R, 32 min) while repeated HPLC of fr. 25 gave 9a (11.2 mg) and small amounts of mixts containing analogues of 9a. CC and HPLC of frs 15-26 from the flash chromatography gave lb (9 mg). Attempts to purify frs 27-54 from the flash chromatography by CC and PTLC resulted in extensive decomposition (4R*,8S*,lOR*)-l-Oxo-4-hydrox~-8-tiglyloxy-13-acetoxygermucru-5E,7(13)-dien-6,12-elide (3). Gum; IR v,,, cm-‘: 1770, nm 218; MS PC1 m/z (rel. int.) 421 [M 1740,1025 cm-‘; UV/.,,, + l]+, 22.6.404 (14.5); 403 (81.9) 361 (29.9), 343 (16.6), 321(19.4); 303 (42.1). 277 (100). 261 (53.4) 243 (42.1); ‘H NMR spectrum in Table 1. (4R*,8S*,lOR*)-1,4-Epoxy-8-tiglyloxy-lO-~ydroxy-l3-acetoxvgermacra-1,5E,7( 13)-trien-6,12-elide Gum; IR (4b). v,,, cm-‘: 3473,30!4, 1767, 1712, 1647, 1233,1122,1060, 1023, 986,971,948; UV A,,, nm 286,216 nm; PC1 MS m/z (rel. int.) 419 [M + I]+, 100); ‘H NMR spectrum in Table 1. (lR*,4R*.5R*,8S*,lOR*)-1,4-Epoxy-l-ethoxy-5-~ydroxy-8methacryloxy- 13-acetoxygermacra-SE, 7(1 l)-dien-6,12-elide (6a). Gum, contaminated by ca 20% of an unknown impurity; 3471, 1761, 1722, 1666, 1637, 1159, 1113, 1086, IR 1:marcm-‘: 1068, 1034,997,865; PC1 MS-m/z (rel. int.) 453 ([M + l]‘, 37.2), 425 (5.5) 407 (14.1) 393 (7.7) 368 (16.4), 367 (100) 307 (16.9) 279 (33.1) 261 (15.4); ‘H NMR spectrum in Table I. (1S*,4R*,5S*,6S*,8S*,1OR*)-1,4-Dihydroxy-5,10,!3-triaceroxy 8-tiglylo.xy-cadin-7( I l)-en-6,12-elide Gum; IR (7a). v,,, cm -‘: 3437, 1746, 1644, 1445, 1266; PC1 MS-m/z (rel. int.) 539 ([M + !] +, 100) 521 (39.0) 497 (33.6) 479 (56.7) 461(8.7), 439 (6.!), 419 (5.1) 377 (15.7); ‘H NMR spectrum in Table 2. (IR*,4R*,5R*,6R*,8S*,!OR*)-1,4-Dihydroxy-5,13-diaceroxy-

613

8-riylyloxycadin-7( 1 I)-en-6,12-elide (8). Gum; IR Y,_ cm- I: 3447,3014, 1748, 1649,1452,1377; PC1 MS m/z (rel. int.) 481 ([M + l]‘, 100); ‘H NMR spectrum in Table 2; ‘sC NMR spectrum (67.89 MHz, CDCI,, multiplicities by DEPT pulse sequence) 6 170.53s, 170.05s, 169.64s (two acetate carbonyls and C-12) 166.01s (C-l’), 162.96s (C-7), 139.03d (C-3’), 127.91s (C-2’), 122.29s (C-l l), 90.79s (C-6), 75.82s and 70.70s (C-4 and C-lo), 72.67d (C-5), 69.34d (C-8), 55.28t (C-l 3), 36.27r, 33.32r and 27.80t (C-2, C-3 and C-9), 31.38d (C-lo), 26.97q (C-15) 20.32q and 19.83q (acetate methyls), 14.38q (C-4’) 13.12q (C-14) 11.96q (C5’). (!S*,4R*,8S*,10R*)-!,4-Epox~~-8,lO-diacetoxy-l~orm~~ox~~13-hydroxygermacra-5E,7(1 I)-dien-6,!2-elide (9b). Gum; PC1 MS m/z (rel. int.) 383 ([M + l]‘, 100). The very dilute ‘H NMR spectrum (CDCI, + D,O, room temp.) exhibited sharp peaks at 6 1.22 (s, 3p, H-14) 1.58 (a 3p, H-15) 2.10 (s, 3p, AC) and broad signals at 62.40 and 2.55 (H-9a and H-9b), 65.95 (H-5), 66.4 (H-8) and 68.2 (formyl H).

Acknowledgements~Work from the Consejo de (Argentina), Fundacion ciones de la Universidad the government and the Islands for a fellowship.

in Tucuman was supported by grants Investigaciones Cientificas y Tecnicas Antorchas and Consejo de InvestigaNational de Tucuman. J. G. D. thanks Caja General de Ahorros of the Canary

REFERENCES

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