Synthesis of analogues of Eunicea γ-cembranolides containing cyclic ethers via saponification

Article abstract of DOI:10.1021/jo001025j

A method for the synthesis of derivatives of the lead structures euniolide (1), 12,13-bisepieupalmerin (2), and eupalmerin acetate (3) containing tetrahydrofuran and tetrahydropyran ring systems was developed on the basis of alkali-induced intramolecular oxacyclizations. Representatives of the new analogues were submitted to the in vitro antitumor cell-line-screening program of the National Cancer Institute (NCI). While it was shown that a variety of structural modifications are possible, these transformations led typically to nontoxic synthetic cembranoids.

Full text of DOI:10.1021/jo001025j

648
J . Org. Chem. 2001, 66, 648-658
Syn th esis of An a logu es of Eu n icea γ-Cem br a n olid es Con ta in in g
Cyclic Eth er s via Sa p on ifica tion †
Abimael D. Rodr´ıguez,* Ivette C. Pin˜a,‡ Ana L. Acosta,§ Catherine Ram´ırez,§ and
J avier J . Soto|
Department of Chemistry, University of Puerto Rico, P.O. Box 23346,
U.P.R. Station, San J uan, Puerto Rico 00931-3346
arodrig@goliath.cnnet.clu.edu
Received J uly 8, 2000
A method for the synthesis of derivatives of the lead structures euniolide (1), 12,13-bisepieupalmerin
(2), and eupalmerin acetate (3) containing tetrahydrofuran and tetrahydropyran ring systems was
developed on the basis of alkali-induced intramolecular oxacyclizations. Representatives of the new
analogues were submitted to the in vitro antitumor cell-line-screening program of the National
Cancer Institute (NCI). While it was shown that a variety of structural modifications are possible,
these transformations led typically to nontoxic synthetic cembranoids.
Caribbean gorgonian octocorals of the Eunicea genus
represent an abundant source of structurally interesting
cembranolide diterpenes.1-3 Naturally occurring cembra-
noids such as euniolide (1),4 12,13-bisepieupalmerin (2),5
and eupalmerin acetate (3)6 have been shown to possess
potent in vitro antitumor activity (Figure 1).3 In addition,
a series of analogues of Eunicea cembranolides containing
cyclic ethers was reported to possess potent antileukemic
activities.7 To develop agents with useful biological prop-
erties, we have synthesized a series of unusual analogues
of cembranolides 1-3 containing cyclic ether ring sys-
tems. Concomitant hydrolysis and intramolecular oxacy-
clization of these abundant R-methylene-γ-lactones me-
diated by alkali were the key steps for the present syn-
theses. These studies have helped to establish a database
of sufficient size to be useful in future efforts directed at
1
the H and 13C NMR based structure elucidations of new
cembranoids.
Resu lts a n d Discu ssion
The Caribbean gorgonian species E. succinea and E.
mammosa contain substantial amounts of extractable
F igu r e 1. Cembrane carbon skeleton and absolute structures
of euniolide (1), 12,13-bisepieupalmerin (2), and eupalmerin
acetate (3).
* Corresponding author: Tel no. (787)-764-0000 ext 4799, fax no.
(787)-751-0625.
† Taken in part from the graduation theses of I. C. Pin˜a (1995), A.
L. Acosta (1997), and C. Ram´ırez (2000).
organic matter and grow in shallow waters; they are
hence easily collected. The hexane extracts obtained from
each species were chromatographed to give euniolide (1),
12,13-bisepieupalmerin (2), and eupalmerin acetate (3)
as white crystalline solids in multigram amounts. The
complete structural assignments of all the synthetic
cembranoid analogues described in the present work were
accomplished on the basis of comprehensive 2D NMR
experiments involving 1H-1H COSY, DEPT, 1H-13C
COSY (CSCMBB), HMQC, and HMBC measurements.
In most cases, these 2D NMR spectra provided both the
structure and the complete proton and carbon atom
assignments. Since starting materials 1-3 were optically
pure without ambiguity in the absolute configuration, the
absolute configurations of the synthetic analogues are as
depicted.
‡ Visiting graduate student from the Universidad Central de
Venezuela, Caracas.
§ Graduate student sponsored by the NIH-MBRS and NSF-MRCE
Programs of the University of Puerto Rico.
| Undergraduate student sponsored by the NIH-MBRS Program of
the University of Puerto Rico.
(1) Faulkner, D. J . Nat. Prod. Rep. 2000, 17, 7-55, and previous
reports in this series.
(2) Wahlberg, I.; Eklund, A.-M. Prog. Chem. Org. Nat. Prod. 1992,
59, 141-294.
(3) Rodr´ıguez, A. D. Tetrahedron 1995, 51, 4571-4618.
(4) (a) Morales, J . J .; Espina, J . R.; Rodr´ıguez, A. D. Tetrahedron
1990, 46, 5889-5894. (b) Marshall, J . A.; Karas, L. J .; Coghlan, M. J .
J . Org. Chem. 1982, 47, 699-701. (c) Marshall, J . A.; Andrews, R. C.;
Lebioda, L. J . Org. Chem. 1987, 52, 2378-2388.
(5) Gopichand, Y.; Ciereszko, L. S.; Schmitz, F. J .; Switzner, D.;
Rahman, A. Hossain, M. B.; Van der Helm, D. J . Nat. Prod. 1984, 47,
607-614.
(6) (a) Ealick, S. E.; Van der Helm, D.; Weinheimer, A. J . Acta
Crystallogr. 1975, B31, 1618-1626. (b) Van der Helm, D.; Ealick, S.
E.; Weinheimer, A. J . Cryst. Struct. Commun. 1974, 3, 167-171. (c)
Fonta´n, L. A.; Yoshida, W. Y.; Rodr´ıguez, A. D. J . Org. Chem. 1990,
55, 4956-4960.
(7) Rodr´ıguez, A. D.; Pin˜a, I. C.; Barnes, C. L. J . Org. Chem. 1995,
60, 8096-8100.
10.1021/jo001025j CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/13/2000

Synthesis of Analogues of Eunicea γ-Cembranolides
J . Org. Chem., Vol. 66, No. 3, 2001 649
Sch em e 1a
(A) Sa p on ifica tion of Eu n iolid e (1). Our first at-
tempt at structural modification of euniolide (1) involved
tandem base-induced hydrolysis of the γ-lactone and
rearrangement of the epoxide to form an oxa-bridge
between C-3 and C-14 (eq 1). Thus, euniolide was treated
with KOH/THF-MeOH at 0 °C for 24 h, followed by 0.1
N HCl, giving the desired furan ether 4 and products 5-7
in 61% overall yield, with 38% of the starting material 1
also recovered. It is especially noteworthy that in no
instance was direct conversion of the C-3,4 epoxide to a
diol functionality observed. A mechanistic rationale for
the unexpected formation of R,â-epoxy-γ-lactone 5 (iso-
lated in 13% yield) invoking the intervention of THF-
hydroperoxide has been outlined as Supporting Informa-
tion. Conjugate additions furnished a 2:1 mixture of
epimeric lactones 6 and 7 in moderate yield (35%).
Nucleophilic attack on the lactone carbonyl left an alkoxyl
anion at C-14, which after a regiospecific attack at C-3
of the epoxide, furnished eunioloic acid methyl ester (4)
in 13% yield.
a
Reaction conditions: (a) KOH, H2O, 90-100 °C, 22 h; (b) 5 N
HCl, 25 °C, 63%; (c) benzene, AcOH, 65-70 °C, 120 h, 98%; (d)
CH2N2, ether-CH2Cl2, 25 °C, 30 min, 100%; (e) toluene, AcOH,
110-120 °C, 4.5 h, 51%.
to be essential. To confirm the structure of translacton-
ization product 10 we treated it with acetic anhydride
in the presence of pyridine in CH2Cl2 at 25 °C for 24 h to
afford the known δ-cembranolide crassin acetate (11) in
71% isolated yield (eq 2).10
(B) Sa p on ifica tion of 12,13-Bisep ieu p a lm er in (2).
Next was a synthetic pathway leading to analogues of
12,13-bisepieupalmerin (2) possessing a cyclic ether
array. The saponification of 2 with aqueous KOH,
outlined in Scheme 1, surprisingly afforded only one of
several possible products, but it was not the translac-
tonized cembra-16,3-olide analogue. Instead, furan ether
12,13-bisepieupalmeroic acid (12) was isolated in 63%
yield. Through acid-promoted cyclization of carboxylic
acid 12, which has the favorable 1S,13S configuration,
we efficiently achieved the synthesis of 12,13-bisepieu-
palmerolide (13) in 98% yield. Compound 12 gave pyra-
zoline adducts 14a ,b with diazomethane at 25 °C for 30
In sharp contrast, hot aqueous KOH reacted very
cleanly with euniolide (1), affording a 1.4:1.3:1 mixture
of eunioloic acid (8), isocrassin alcohol (9),4b and crassin
alcohol (10)8 in very good overall yield (78%) after
neutralization with 0.1 N HCl (eq 2).9 To ensure repro-
(8) (a) Marshall, J . A.; Royce, R. D., J r. J . Org. Chem. 1982, 47, 693-
698. (b) McMurry, J . E.; Dushin, R. G. J . Am. Chem. Soc. 1990, 112,
6942-6949. (c) McMurry, J . E.; Dushin, R. G. J . Am. Chem. Soc. 1989,
111, 8928-8929.
(9) During a series of lactone interconversion studies, Marshall and
co-workers saponified crassin alcohol (10) and isolated isocrassin
alcohol (9) by a sequence involving several steps. They also found that
treatment of isocrassin alcohol with aqueous potassium hydroxide
followed by acidification leads cleanly to crassin alcohol (10); see ref
4b.
(10) (a) Martin, G. E.; Matson, J . A.; Turley, J . C.; Weinheimer, A.
J . J . Am. Chem. Soc. 1979, 101, 1888-1890. (b) Look, S. A.; Fenical,
W.; Qi-tai, Z.; Clardy, J . J . Org. Chem. 1984, 49, 1417-1423.
ducible high yields in our reaction, sonication of a
suspension of euniolide in 3% aqueous KOH turned out

650 J . Org. Chem., Vol. 66, No. 3, 2001
Rodr´ıguez et al.
min in quantitative yield as a 1:1.5 mixture.11 In turn,
the derived esters were smoothly cyclized to δ-lactones
15 and 16 in good overall yield (51%) through AcOH-
promoted lactonization and thermolysis in refluxing
toluene.
(C) Sa p on ifica tion of Eu p a lm er in Aceta te (3).
Interestingly, our initial run of 3 through a similar
saponification sequence produced a 14:11:3:1 mixture of
3,14-eupalmeroic acid (17), 4,14-eupalmeroic acid (18),
eucrassin alcohol (19), and isoeucrassin alcohol (20) in
44% yield (eq 3). These results stand in sharp contrast
reaction conditions the formation of 19 and 20 was
completely suppressed. Instead, an easily separable
mixture of pyrazolines 21 and 22 (obtained in a 1.7:1
ratio, respectively) and 23 and 24 (obtained in a 1.5:1
ratio, respectively) was obtained. Surprisingly, 25 was
isolated as a single diastereomer in 24% yield. A third
saponification trial afforded a 1:1 mixture of eupal-
merolide (26) and carboxylic acid 27 in moderate isolated
yield (40%) upon treatment of the crude with a mixture
of acetic anhydride and pyridine at 25 °C for 1.5 h (eq
5). Starting material 3 was also recovered. In the latter
attempt, which ran for only 12 h at a lower temperature
(45 °C), carboxylic acid 3,14-eupalmeroic acid (17), the
kinetic product, predominated.
In our last saponification, we ran the reaction at 45
°C again, but allowed a longer reaction time (18 h). In
this run, however, after neutralization with 5 N HCl, we
subjected the products without further purification to the
ozonolytic protocol outlined in Scheme 2. This afforded
the C18 carboxylic acids 28 and 29 in 30 and 54% isolated
yield, respectively. Because it was expected that esteri-
fication of these highly functionalized carboxylic acids
would lead to more manageable products (the chromato-
graphic separation of 28 and 29 was problematic and 29
was sparingly soluble in most organic solvents), each
product was treated separately with diazomethane at 25
°C, thereby avoiding subsequent yield-lowering chroma-
tography. An attempt to purify the former crude by
chromatography through a short plug of silica gel (Sep-
Pak) led in nearly quantitative yield to 30, a structurally
interesting furan ether containing a γ-lactone and a cyclic
hemiacetal. Crude 31 (obtained in 96% yield) was ana-
lyzed without further purification. No attempt was made
at this time, however, to further cyclize diester 31
through successive acid-mediated intramolecular trans-
esterifications.
to our previous findings with the saponification of
12,13-bisepieupalmerin (2, Scheme 1). Our principal
concern was whether carboxylic acids such as 17 and 18,
possessing the seemingly unfavorable 1S,13R stereo-
chemistry, would undergo further intramolecular cycliza-
tion to their corresponding lactones (vide infra). We
suspected that translactonization of kinetic isoeucrassin
alcohol (20) afforded the thermodynamically more stable
δ-lactone eucrassin alcohol (19).
A second trial, where the same saponification sequence
was run for only 2 h followed by workup and treatment
with diazomethane, gave a mixture in 85% yield of
pyrazolines 21-25 (eq 4). Interestingly, under these
Photolysis of pyrazoline 23 at 25 °C for 2.5 h afforded
derivative 32 as the only isolated product in quantitative
yield (Scheme 3). Sadly, treatment of 32 with PTSA‚H2O
in refluxing chloroform resulted in a high (80%) recovery
of the starting material and none of the desired lactone
33. Considerable experimentation with a wide range of
acid catalysts led to partial or complete decomposition
of 32 or no reaction. Pyrazoline 25 was likewise subjected
to the photolytic protocol depicted in Scheme 4. Like its
pyran ether counterpart 23, pyrazoline 25 underwent
rapid and quantitative conversion to 34. If, on the other
hand, a 7-59 Corning filter was used at 25 °C for 13 h,
34 was once again produced, but only in 88% yield, and
smaller amounts of photoproducts 35 and 36 were also
obtained. When 25 was decomposed thermally in benzene
and glacial acetic acid at 90-100 °C, a 3:1 mixture of
(11) Black, T. H. Aldrichimica Acta 1983, 16, 3-10.

Synthesis of Analogues of Eunicea γ-Cembranolides
J . Org. Chem., Vol. 66, No. 3, 2001 651
Sch em e 2a
Sch em e 4a
a
Reaction conditions: (a) EtOAc-hexane, hν (320-400 nm), 25
°C, 30 min, 100%; (b) EtOAc-hexane, hν (320-400 nm), 7-59
Corning filter, 25 °C, 13 h, 100%.
Sch em e 5a
a
Reaction conditions: (a) KOH, H2O, 45 °C, 18 h; (b) 5 N HCl,
25 °C; (c) EtOAc, O3, -78 °C; (d) H2O2, H2O, ∆, 18 h, 84%; (e)
CH2N2, 25 °C, 30 min, Sep-Pak, 90%; (f) CH2N2 in ether, MeOH-
CHCl3, 25 °C, 30 min, 96%.
Sch em e 3
a
Reaction conditions: (a) CH2N2 in ether-CH2Cl2, 25 °C, 30
min, 76%; (b) toluene, AcOH, 115 °C, 4.5 h, 42%.
sults stand in sharp contrast to our previous finding with
the mixture of pyrazolines 14a ,b (Scheme 1).
products 34 and 36 was obtained in 75% overall yield. It
was subsequently found that exposure of ester 34 to
either glacial acetic acid or PTSA‚H2O in refluxing
benzene did not produce the desired cyclization product
37 (Scheme 4). Furthermore, treatment of 25 with PTSA‚
H2O in benzene using temperatures varying from 25 to
65 °C also failed to furnish the corresponding δ-lactone.
Thus, ester derivatives 25, 32, and 34, each having the
1S,13R configuration, did not undergo further cyclization
through intramolecular transesterifications. These re-
The reaction of 4,14-eupalmeroic acid (18) with diazo-
methane was carefully reexamined using not crude but
pure starting material. Using the same temperature and
reaction time as in carboxylic acid 12, isomer 18 fur-
nished a 1:1 mixture of 23 and 24 in 76% overall yield
(Scheme 5). The latter mixture of pyrazolines was re-
fluxed for 4.5 h in toluene and acetic acid to give, in 42%
overall yield, a 15:12.5:1 mixture of 32, 38, and 39. This
was a one-pot reaction in which a solution of 18 and

652 J . Org. Chem., Vol. 66, No. 3, 2001
Rodr´ıguez et al.
diazomethane in ether-CH2Cl2 was stirred at ambient
temperature for 30 min. After the reaction mixture was
concentrated, the pyrazolines were dissolved in a mixture
of toluene and acetic acid, and the solution was heated
to 115 °C for 4.5 h, cooled, and concentrated under
vacuum. The oily residue obtained was purified by col-
umn chromatography. Under these reaction conditions,
no tricyclic products arising from further acid-catalyzed
intramolecular transesterification were formed.
With the failure of esters 32, 34-36, 38, and 39 to
deliver the desired δ-lactones, we turned to δ-hydroxy
carboxylic acids 17 and 18 as plausible lactone precur-
sors. Interestingly, acid-induced esterification of 3,14-
eupalmeroic acid (17) with catalytic amounts of PTSA‚
H2O in refluxing benzene for 2 h resulted in the tricyclic
δ-lactones 40 and 41 in 80% overall yield as a 3:1 mixture
of isomers, respectively (eq 6). To our surprise, double
bond isomerization to the C-8 position was a major
reaction pathway. On the other hand, our attempts to
dehydrate 4,14-eupalmeroic acid (18) using a variety of
solvents and protic acids at temperatures ranging from
25 to 80 °C failed to produced the desired R-methylene-
δ-lactone 42 (eq 7). Furthermore, ditrifluoroacetate 43
was the sole product (isolated in 44% yield) when 18 was
treated with trifluoroacetic anhydride in benzene-d6 at
25 °C in an attempt to obtain 42 upon dehydration.
Biologica l Stu d ies. The compounds listed in Table 1
were tested in the NCI's 60 cell-line human tumor screen.
The results with 14 representative cell-lines are shown.
In comparative testing against these human tumor cell-
lines, euniolide (1) and 12,13-bisepieupalmerin (2) ex-
hibited IC50 values of 0.1-43 µg/mL. Eupalmerin acetate
(3) exhibited IC50 values from 0.3-16 µg/mL. All the
synthetic analogues screened in this bioassay were less
toxic than their prototypes, suggesting that the present
structural modifications were generally deleterious to the
cytotoxicity of precursors 1-3. Thus, analogues 5, 8, 12,

Synthesis of Analogues of Eunicea γ-Cembranolides
J . Org. Chem., Vol. 66, No. 3, 2001 653
Rea ction of Eu n iolid e (1) w ith Alk a lies. P a th A. A
mixture of 1 (1.16 g, 0.0037 mol) and NaOH (1.14 g, 0.028 mol)
in 50 mL of undistilled 1:1 MeOH/THF was stirred at 0 °C for
24 h before it was neutralized with 0.1 N HCl and then diluted
with water (50 mL), extracted with CH2Cl2 (3 × 50 mL), and
concentrated. The resulting oil was chromatographed on silica
gel (85 g, 1:9 (v/v) ethyl acetate in hexane) to give 102 mg (13%)
of eunioloic acid methyl ester (4), 97 mg (13%) of 15(S),17-
epoxyeuniolide (5), 278 mg (35%) of a 2:1 mixture of 6 and 7,
and 437 mg of 1. The mixture of 6 and 7 was separated by
silica gel chromatography (10 g, elution with 10% ether in
CHCl3).
17, 19, 27, 28, 30, and 32 were nontoxic; several of the
cell-lines gave IC50 values of 20-80 µg/mL, while others
were not responsive at 100 µg/mL. On the other hand,
R-methylene-δ-lactones 13 and 40 showed a character-
istic pattern of differential cytotoxicity and were ap-
proximately equipotent (e.g., mean panel GI50's ∼ 1-16
nM). As a matter of interest, the eupalmerin acetate (3)
isolated in this study was utilized in a Hollow Fiber
Assay for in vivo antitumor activity.12 Using a high dose
of 40 mg/kg against 12 human tumor cell-lines implanted
subcutaneously and intraperitoneally in athymic mice,
we observed some activity against several of the cell-lines.
While these data require confirmation, they are sugges-
tive of in vivo antitumor activity. Further pharmacologi-
cal evaluation of this series of nontoxic compounds in
relevant in vitro tests is currently in progress.
Da ta for 4: yellowish oil; [R]25 -15.9° (c 6.4, CHCl3); IR
D
(neat) 3430, 1718, 1626, 1258, 1148, 1073 cm-1; UV (MeOH)
1
λmax 209 nm (ꢀ 11700); H NMR (CDCl3, 300 MHz) δ 2.86 (m,
1H, H-1), 1.79 (m, 1H, H-2), 2.07 (m, 1H, H-2′), 3.84 (t, 1H, J
) 7.8 Hz, H-3), 1.71 (m, 2H, H-5), 2.07 (m, 2H, H-6), 5.24 (br
t, 1H, J ) 6.9 Hz, H-7), 2.12 (m, 2H, H-9), 2.15 (m, 2H, H-10),
5.03 (br t, 1H, J ) 7.5 Hz, H-11), 1.73 (m, 1H, H-13), 2.30 (dd,
1H, J ) 2.7, 14.1 Hz, H-13′), 3.90 (m, 1H, H-14), 5.64 (br s,
1H, H-17), 6.27 (br s, 1H, H-17′), 1.12 (s, 3H, Me-18), 1.52 (s,
3H, Me-19), 1.60 (s, 3H, Me-20), 3.77 (s, 3H, OCH3); 13C NMR
(CDCl3, 75 MHz) δ 45.0 (d, C-1), 33.7 (t, C-2), 83.5 (d, C-3),
73.9 (s, C-4), 39.8 (t, C-5), 22.2 (t, C-6), 128.4 (d, C-7), 132.5
(s, C-8), 39.1 (t, C-9), 25.2 (t, C-10), 128.0 (d, C-11), 130.6 (s,
C-12), 42.7 (t, C-13), 80.9 (d, C-14), 141.1 (s, C-15), 167.3 (s,
C-16), 124.5 (t, C-17), 23.2 (q, C-18), 15.2 (q, C-19), 17.0 (q,
C-20), 51.9 (q, OCH3); HREI-MS m/z [M]+ calcd for C21H32O4
348.2301, found 348.2292, 348 (7), 346 (8), 331 (13), 330 (50),
192 (87), 155 (100).
Exp er im en ta l Section
Gen er a l Exp er im en ta l P r oced u r es. Infrared spectra
were determined as thin films and were referenced to poly-
styrene. 1H NMR, 13C NMR, DEPT, HMQC, HMBC, 1H-1H
COSY, RCT COSY, and 2D-NOESY spectra were recorded
either at 300 and 500 MHz for 1H or at 75 and 125 MHz for
13C. Column chromatography was carried out with silica gel
(35-75 mesh). HPLC was performed using a 10 µm silica gel
Partisil 10 semipreparative column (9.4 mm × 50 cm) or a 10
µm Ultrasphere-CN semipreparative column (10 mm × 25 cm).
Unless otherwise noted, ether and THF were freshly distilled
from sodium wire and sodium benzophenone ketyl, respec-
tively. Samples were photolyzed externally using a Xe (Hg)
ozone free 1000 W UV lamp with a 7-51 Corning filter.
Reactions were monitored by TLC on silica gel plates (0.25
mm) and visualized using UV light and I2 vapors. Diazo-
methane was prepared in-house.13 Reagents from commercial
suppliers were used as provided. Yields refer to chromato-
graphically and spectroscopically pure materials.
Extr a ction a n d Isola tion of Eu n icea γ-Cem br a n olid es
1-3. The Caribbean gorgonian octocorals E. succinea and E.
mammosa were collected at 25 m depth by SCUBA from Mona
Island, Puerto Rico. The gorgonians were stored at 0 °C
immediately after collection and then were frozen at -10 °C
upon arrival, freeze-dried, and kept frozen until extraction.
The dried E. succinea (2.5 kg) was blended with MeOH:CHCl3
(1:1), and after filtration the crude extract was evaporated
under vacuum to yield a residue (322.9 g) which was parti-
tioned between hexane and H2O. The hexane extract was
concentrated to yield 170.9 g of a dark green oily residue,
which was later dissolved in toluene and filtered. The resulting
filtrate was concentrated (168.9 g), loaded onto a large size
exclusion column (Bio-Beads SX-3), and eluted with toluene.
The combined terpenoid-rich fractions (TLC guided) were
concentrated to a dark yellow oil (118.6 g) and chromato-
graphed over a large silica gel column (3 kg) using 30% EtOAc
in hexane. From this column, 14 fractions were obtained, the
less polar of which consisted of complex mixtures of unidenti-
fied sterols and fatty acid derivatives, and the known cem-
branolide diterpenes euniolide (1)4 (24 g) and eupalmerin
acetate (3)6 (12.9 g). The more polar portion of the extract was
divided roughly into fractions 6-14 on the basis of TLC
analyses. From some of these fractions several known cem-
branolides were identified among which 12,13-bisepieupalm-
erin (2)5 (5.0 g) stood out as the most abundant. The identi-
fication of 1-3 was accomplished through detailed comparisons
with the physical and chemical data previously reported for
these compounds. A similar extraction procedure was followed
with the dried E. mammosa specimens.
Da t a for 5: yellowish oil; [R]25 +9.5° (c 1.9, CHCl3); IR
D
(neat) 1790, 1262, 1105, 972 cm-1; UV (MeOH) λmax 209 nm (ꢀ
1
4500); H NMR (CDCl3, 300 MHz) δ 2.58 (m, 1H, H-1), 1.30
(ddd, 1H, J ) 2.1, 5.1, 9.6 Hz, H-2), 2.03 (m, 1H, H-2′), 2.88
(dd, 1H, J ) 4.2, 9.6 Hz, H-3), 1.48 (m, 1H, H-5), 1.92 (m, 1H,
H-5′), 1.86 (m, 1H, H-6), 2.11 (m, 1H, H-6′), 4.94 (br t, 1H, J
) 6.6 Hz, H-7), 1.97 (m, 1H, H-9), 2.16 (m 1H, H-9′), 2.06 (m,
1H, H-10), 2.32 (m, 1H, H-10′), 5.03 (m, 1H, H-11), 2.45 (br d,
1H, J ) 10.2 Hz, H-13), 2.61 (m, 1H, H-13′), 5.03 (m, 1H, H-14),
3.03 (d, 1H, J ) 5.1 Hz, H-17), 3.23 (d, 1H, J ) 5.1 Hz, H-17′),
1.23 (s, 3H, Me-18), 1.56 (s, 3H, Me-19), 1.70 (s, 3H, Me-20);
13C NMR (CDCl3, 75 MHz) δ 38.9 (d, C-1), 26.3 (t, C-2), 58.2
(d, C-3), 60.3 (s, C-4), 36.7 (t, C-5), 22.2 (t, C-6), 125.3 (d, C-7),
134.9 (s, C-8), 39.0 (t, C-9), 24.9 (t, C-10), 126.7 (d, C-11), 129.9
(s, C-12), 37.9 (t, C-13), 80.3 (d, C-14), 60.1 (s, C-15), 172.4 (s,
C-16), 49.1 (t, C-17), 17.4 (q, C-18), 15.7 (q, C-19), 17.8 (q, C-20);
HREI-MS m/z [M]+ calcd for C20H28O4 332.1988, found 332.2014,
332 (14), 318 (11), 133 (46), 119 (58), 107 (76), 93 (100).
Da t a for 6: yellowish oil; [R]25 -5.8° (c 7.6, CHCl3); IR
D
(neat) 1777, 1260, 1163, 1046 cm-1; UV (MeOH) λmax 209 nm
(ꢀ 4900); 1H NMR (CDCl3, 300 MHz) δ 2.80 (m, 1H, H-1), 1.71
(m, 1H, H-2), 1.81 (dd, 1H, J ) 6.8, 9.9 Hz, H-2′), 2.91 (t, 1H,
J ) 6.7 Hz, H-3), 1.46 (m, 1H, H-5), 1.98 (m, 1H, H-5′), 1.94
(m, 1H, H-6), 2.17 (m, 1H, H-6′), 4.96 (br t, 1H, J ) 7.2 Hz,
H-7), 2.15 (m, 2H, H-9), 2.23 (m, 2H, H-10), 5.10 (m, 1H, H-11),
2.45 (d, 2H, J ) 6.5 Hz, H-13), 4.78 (dd, 1H, J ) 6.8, 13.3 Hz,
H-14), 2.61 (dt, 1H, J ) 3.7, 10.5 Hz, H-15), 3.63 (dd, 1H, J )
3.4, 9.8 Hz, H-17), 3.75 (dd, 1H, J ) 4.0, 9.8 Hz, H-17′), 1.27
(s, 3H, Me-18), 1.57 (s, 3H, Me-19), 1.70 (s, 3H, Me-20), 3.34
(s, 3H, OCH3); 13C NMR (CDCl3, 75 MHz) δ 38.1 (d, C-1), 27.4
(t, C-2), 59.3 (d, C-3), 59.7 (s, C-4), 37.2 (t, C-5), 22.5 (t, C-6),
125.4 (d, C-7), 134.3 (s, C-8), 39.1 (t, C-9), 24.6 (t, C-10), 126.8
(d, C-11), 130.7 (s, C-12), 39.2 (t, C-13), 80.1 (d, C-14), 45.2 (d,
C-15), 176.3 (s, C-16), 68.7 (t, C-17), 17.3 (q, C-18), 15.5 (q,
C-19), 16.9 (q, C-20), 59.2 (q, OCH3); HREI-MS m/z [M]+ calcd
for C21H32O4 348.2301, found 348.2327, 348 (12), 330 (5), 109
(86), 107 (75), 93 (85), 68 (100).
Da ta for 7: yellowish oil; [R]25 +18.9° (c 6.2, CHCl3); IR
D
(neat) 1771, 1260, 1176, 1098 cm-1; UV (MeOH) λmax 208 nm
(ꢀ 4700); 1H NMR (CDCl3, 300 MHz) δ 2.67 (m, 1H, H-1), 1.31
(m, 1H, H-2), 1.80 (m, 1H, H-2′), 2.68 (m, 1H, H-3), 1.12 (m,
1H, H-5), 2.05 (m, 1H, H-5′), 2.37 (m, 2H, H-6), 4.87 (br d, 1H,
J ) 10.1 Hz, H-7), 2.03 (m, 2H, H-9), 1.96 (m, 1H, H-10), 2.38
(m, 1H, H-10′), 5.05 (br t, 1H, J ) 6.7 Hz, H-11), 2.43 (m, 1H,
H-13), 2.71 (m, 1H, H-13′), 4.75 (dt, 1H, J ) 3.6, 12.0 Hz, H-14),
(12) Hollingshead, M. G.; Alley, M. C.; Camalier, R. F.; Abbott, B.
J .; Mayo, J . G.; Malspeis, L.; Grever, M. R. Life Sci. 1995, 57, 131-
141.
(13) Hudlicky, M. J . Org. Chem. 1980, 45, 5377.

654 J . Org. Chem., Vol. 66, No. 3, 2001
Rodr´ıguez et al.
3.19 (m, 1H, H-15), 3.46 (t, 1H, J ) 10.1 Hz, H-17), 3.77 (dd,
1H, J ) 5.1, 10.1 Hz, H-17′), 1.27 (s, 3H, Me-18), 1.57 (s, 3H,
Me-19), 1.64 (s, 3H, Me-20), 3.35 (s, 3H, OCH3); 13C NMR
(CDCl3, 75 MHz) δ 37.8 (d, C-1), 22.5 (t, C-2), 60.9 (d, C-3),
61.1 (s, C-4), 39.1 (t, C-5), 23.2 (t, C-6), 125.4 (d, C-7), 135.3
(s, C-8), 38.8 (t, C-9), 25.3 (t, C-10), 123.6 (d, C-11), 129.7 (s,
C-12), 35.8 (t, C-13), 80.3 (d, C-14), 46.8 (d, C-15), 174.7 (s,
C-16), 67.5 (t, C-17), 18.1 (q, C-18), 15.8 (q, C-19), 15.9 (q, C-20),
58.9 (q, OCH3); HREI-MS m/z [M]+ calcd for C21H32O4 348.2301,
found 348.2294, 348 (26), 330 (14), 285 (5), 245 (10), 134 (42),
120 (48), 93 (91), 67 (100).
residue that was subjected to chromatography (SiO2, 10% ethyl
acetate in hexane) to give 12 mg (71%) of known crassin
acetate (11).10
Sa p on ifica tion of 12,13-Bisep ieu p a lm er in (2) w ith
Aqu eou s KOH. A suspension of 2 (619 mg, 1.85 mmol) in 3%
aqueous KOH (15 mL) was stirred vigorously at 90-100 °C
for 22 h and then cooled, diluted with water (50 mL), quenched
with 5 N HCl, and extracted with chloroform (4 × 100 mL).
The combined organic extracts were washed with saturated
NaCl, dried, and concentrated. The crude white foam obtained
(597 mg) was chromatographed on silica gel (24 g) using a 98:
2:0.5 mixture of chloroform/MeOH/acetic acid as eluant to yield
413 mg (63%) of 12,13-bisepieupalmeroic acid (12).
P a th B. A suspension of 1 (325 mg, 1.03 mmol) in 3%
aqueous KOH (50 mL) was stirred vigorously at 70 °C for 4 h,
cooled to room temperature, neutralized with 0.1 N HCl, and
extracted with CHCl3 (3 × 50 mL). The combined organic
layers were dried and concentrated to leave a residue (369 mg)
that was chromatographed on silica gel (15 g). Elution with
2% MeOH in CHCl3 yielded 99 mg (29%) of eunioloic acid (8),
96 mg (28%) of isocrassin alcohol (9),4b and 71 mg (21%) of
crassin alcohol (10).8
Da ta for 12: white foam; [R]32 -11.6° (c 2.1, CHCl3); IR
D
(neat) 3596, 3580-3200 (broad), 1701, 1623, 1287, 1162, 1084,
1056 cm-1; UV (MeOH) λmax 208 (ꢀ 9300) and 270 nm (ꢀ 1700);
1H NMR (CDCl3, 300 MHz) δ 3.32 (br d, 1H, J ) 8.4 Hz, H-1),
3.96 (dd, 1H, J ) 6.0, 10.2 Hz, H-3), 5.34 (t, 1H, J ) 7.5 Hz,
H-7), 3.18 (br d, 1H, J ) 9.9 Hz, H-13), 3.70 (dd, 1H, J ) 2.7,
9.6 Hz, H-14), 5.74 (br s, 1H, H-17), 6.38 (br s, 1H, H-17′),
1.07 (s, 3H, Me-18), 1.54 (s, 3H, Me-19), 0.78 (d, 3H, J ) 6.6
Hz, Me-20), 5.42 (br s, exchangeable, OH); 13C NMR (CDCl3,
75 MHz) δ 43.3 (d, C-1), 31.3 (t, C-2), 86.4 (d, C-3), 73.2 (s,
C-4), 36.3 (t, C-5), 21.6 (t, C-6), 129.2 (d, C-7), 132.1 (s, C-8),
37.4 (t, C-9), 21.2 (t, C-10), 32.2 (t, C-11), 30.5 (d, C-12), 79.0
(d, C-13), 84.6 (d, C-14), 141.8 (s, C-15), 170.7 (s, C-16), 125.5
(t, C-17), 25.7 (q, C-18), 14.7 (q, C-19), 10.9 (q, C-20); HREI-
MS m/z [M]+ calcd for C20H32O5 352.2250, found 352.2261, 352
(1), 334 (15), 316 (45), 298 (16), 95 (83), 55 (100).
Da ta for eu n ioloic a cid (8): colorless oil; [R]25 -18.8° (c
D
19.4, CHCl3); IR (neat) 3600-3000 (broad), 1697, 1624, 1260,
1095, 1022 cm-1; UV (CHCl3) λmax 244 nm (ꢀ 750); 1H NMR
(CDCl3, 300 MHz) δ 2.83 (m, 1H, H-1), 1.81 (dd, 1H, J ) 7.8,
14.4 Hz, H-2), 2.12 (m, 1H, H-2′), 3.87 (br t, 1H, J ) 7.8 Hz,
H-3), 1.73 (br t, 2H, J ) 6.0 Hz, H-5), 5.22 (t, 1H, J ) 6.6 Hz,
H-7), 5.03 (t, 1H, J ) 6.9 Hz, H-11), 1.99 (dd, 1H, J ) 8.4,
13.8 Hz, H-13), 2.28 (br d, 1H, J ) 13.8 Hz, H-13′), 3.91 (m,
1H, H-14), 5.71 (br s, 1H, H-17), 6.39 (br s, 1H, H-17′), 1.13 (s,
3H, Me-18), 1.51 (s, 3H, Me-19), 1.59 (s, 3H, Me-20), 6.64 (br
s, 1H, exchangeable, COOH); 13C NMR (CDCl3, 75 MHz) δ 44.7
(d, C-1), 33.6 (t, C-2), 83.3 (d, C-3), 74.4 (s, C-4), 40.0 (t, C-5),
22.2 (t, C-6), 128.2 (d, C-7), 132.4 (s, C-8), 39.1 (t, C-9), 25.1 (t,
C-10), 127.9 (d, C-11), 130.5 (s, C-12), 42.7 (t, C-13), 80.8 (d,
C-14), 140.6 (s, C-15), 171.1 (s, C-16), 126.3 (t, C-17), 22.8 (q,
C-18), 15.1 (q, C-19), 16.9 (q, C-20); HREI-MS m/z [M]+ calcd
for C20H30O4 334.2144, found 334.2141, 334 (7), 316 (15), 298
(2), 192 (45), 109 (59), 81 (100).
δ-La cton iza tion of 12,13-Bisep ieu p a lm er oic Acid (12).
To a solution of 12 (48 mg, 0.13 mmol) in dry benzene (10 mL)
was added glacial acetic acid (2 drops). The solution was heated
to 65-70 °C for 120 h using a Dean-Stark apparatus, cooled,
and concentrated, and the residue was subjected to silica gel
chromatography (2.0 g, 30% ethyl acetate in hexane), giving
44 mg (98%) of 12,13-bisepieupalmerolide (13).
Da ta for 13: colorless oil; [R]32 -63.5° (c 1.15, CHCl3); IR
D
(neat) 3462 (sharp), 1712, 1638, 1263, 1238, 1149, 1099 cm-1
;
Da ta for isocr a ssin a lcoh ol (9): yellowish oil; [R]25
UV (MeOH) λmax 209 nm (ꢀ 18500); 1H NMR (CDCl3, 500 MHz)
δ 2.56 (m, 1H, H-1), 1.88 (m, 1H, H-2), 2.17 (m, 1H, H-2′), 4.01
(dd, 1H, J ) 1.0, 9.6 Hz, H-3), 5.26 (t, 1H, J ) 7.6 Hz, H-7),
4.02 (dd, 1H, J ) 6.3, 9.3 Hz, H-13), 3.18 (dd, 1H, J ) 9.3,
11.1 Hz, H-14), 5.48 (dd, 1H, J ) 0.7, 2.7 Hz, H-17), 6.38 (dd,
1H, J ) 0.7, 3.0 Hz, H-17′), 1.15 (s, 3H, Me-18), 1.58 (s, 3H,
Me-19), 1.12 (d, 3H, J ) 6.7 Hz, Me-20); 13C NMR (CDCl3, 125
MHz) δ 46.2 (d, C-1), 28.1 (t, C-2), 84.3 (d, C-3), 73.3 (s, C-4),
41.3 (t, C-5), 21.4 (t, C-6), 126.9 (d, C-7), 133.2 (s, C-8), 36.9 (t,
C-9), 24.7 (t, C-10), 28.4 (t, C-11), 38.7 (d, C-12), 86.4 (d, C-13),
81.1 (d, C-14), 136.8 (s, C-15), 164.4 (s, C-16), 124.6 (t, C-17),
23.2 (q, C-18), 16.6 (q, C-19), 17.5 (q, C-20); HREI-MS m/z [M]+
calcd for C20H30O4 334.2144, found 334.2151, 334 (7), 316 (25),
208 (13), 164 (29), 109 (34), 93 (61), 81 (91), 55 (100).
D
-0.12° (c 1.2, CHCl3); IR (neat) 3467, 1763, 1662, 1274, 1165,
1090 cm-1; UV (CHCl3) λmax 244 nm (ꢀ 300); 1H NMR (CDCl3,
500 MHz) δ 3.41 (m, 1H, H-1), 3.36 (m, 1H, H-3), 5.02 (br t,
1H, J ) 6.5 Hz, H-7), 5.26 (m, 1H, H-11), 2.24 (dd, 1H J )
12.0, 16.0 Hz, H-13), 2.73 (br d, 1H, J ) 16.0 Hz, H-13′), 4.79
(ddd, 1H, J ) 4.0, 6.2, 12.0 Hz, H-14), 5.69 (d, 1H, J ) 0.5 Hz,
H-17), 6.28 (d, 1H, J ) 0.7 Hz, H-17′), 1.06 (s, 3H, Me-18),
1.62 (s, 3H, Me-19), 1.70 (s, 3H, Me-20); 13C NMR (CDCl3, 125
MHz) δ 38.3 (d, C-1), 27.6 (t, C-2), 74.8 (d, C-3), 73.9 (s, C-4),
38.3 (t, C-5), 21.7 (t, C-6), 127.0 (d, C-7), 135.2 (s, C-8), 38.4 (t,
C-9), 24.4 (t, C-10), 127.5 (d, C-11), 129.5 (s, C-12), 38.7 (t,
C-13), 78.2 (d, C-14), 138.8 (s, C-15), 170.1 (s, C-16), 123.2 (t,
C-17), 28.1 (q, C-18), 16.3 (q, C-19), 17.0 (q, C-20); HREI-MS
m/z [M]+ calcd for C20H30O4 334.2144, found 334.2148, 334 (3),
316 (11), 298 (4), 107 (49), 93 (71), 81 (100).
Tr ea tm en t of 12,13-Bisep ieu p a lm er oic a cid (12) w ith
Dia zom eth a n e F ollow ed by th e Th er m olysis of P yr a zo-
lin es 14a ,b. A solution of diazomethane in ether (30 mL) was
added to a solution of 12 (94 mg, 0.27 mmol) in CH2Cl2 (10
mL). The reaction mixture was stirred at room temperature
for 30 min prior to being concentrated and stored under high
vacuum. The resulting oil (108 mg, 100%), which consisted of
a 1:1.5 epimeric mixture of two pyrazolines as established by
TLC and NMR spectroscopic analyses, was used in the next
step without further purification. HREI-MS (crude mixture of
epimers) m/z [M]+ calcd for C22H36N2O5 408.2624, found
408.2619, 408 (11), 380 (7), 362 (52), 331 (16), 209 (25), 195
(37), 169 (100), 123 (64), 109 (76), 95 (90), 81 (93). A solution
of pyrazolines 14a ,b (110 mg, 0.27 mmol) in toluene (30 mL)
was treated with glacial acetic acid (10 mL), warmed to 110-
120 °C for 4.5 h, cooled, and concentrated to leave a crude oil
that was purified by means of silica gel chromatography (4.3
g, eluted with 25% ethyl acetate in hexane), giving 17 mg (19%)
of δ-lactone 15 and 30 mg (32%) of δ-lactone 16.
Da ta for cr a ssin a lcoh ol (10): colorless oil; IR (neat) 3418,
1715, 1619, 1282, 1099, 1022 cm-1; UV (CHCl3) λmax 248 nm
1
(ꢀ 800); H NMR (CDCl3, 300 MHz) δ 2.53 (m, 1H, H-1), 3.93
(d, 1H, J ) 11.1 Hz, H-3), 5.05 (t, 1H, J ) 7.5 Hz, H-7), 5.23
(m, 1H, H-11), 4.20 (ddd, 1H, J ) 2.1, 5.1, 11.1 Hz, H-14), 5.70
(d, 1H, J ) 1.5 Hz, H-17), 6.52 (d, 1H, J ) 2.1 Hz, H-17′), 1.38
(s, 3H, Me-18), 1.58 (s, 3H, Me-19), 1.64 (s, 3H, Me-20), 2.48-
1.60 (broad envelope, 12H), 2.68 (br s, 2H, exchangeable, OH);
13C NMR (CDCl3, 75 MHz) δ 39.2 (d, C-1), 19.2 (t, C-2), 82.6
(d, C-3), 74.0 (s, C-4), 38.7 (t, C-5), 22.1 (t, C-6), 125.3 (d, C-7),
135.3 (s, C-8), 40.1 (t, C-9), 24.0 (t, C-10), 127.5 (d, C-11), 130.7
(s, C-12), 44.6 (t, C-13), 71.8 (d, C-14), 138.4 (s, C-15), 168.1
(s, C-16), 127.6 (t, C-17), 24.6 (q, C-18), 14.5 (q, C-19), 14.9 (q,
C-20); HREI-MS m/z [M]+ calcd for C20H30O4 334.2144, found
334.2150, 334 (14), 316 (21), 291 (40), 109 (92), 93 (59), 68
(100).
Acetyla tion of Cr a ssin Alcoh ol (10). A mixture of 10 (15
mg, 0.045 mmol), acetic anhydride (1 mL), and pyridine (2 mL)
was stirred in CH2Cl2 (8 mL) at room temperature for 24 h,
diluted with saturated NaHCO3, and extracted with CH2Cl2.
The combined organic layers were concentrated, leaving a
Da ta for 15: colorless oil; [R]29 -66.0° (c 1.0, CHCl3); IR
D
(neat) 3448, 1726, 1710, 1141, 1096, 1022 cm-1
;
1H NMR
(CDCl3, 300 MHz) δ 2.39 (m, 1H, H-1), 3.96 (dd, 1H, J ) 5.1,
9.3 Hz, H-3), 2.15 (m, 2H, H-6), 5.26 (br t, 1H, J ) 7.2 Hz,

Synthesis of Analogues of Eunicea γ-Cembranolides
J . Org. Chem., Vol. 66, No. 3, 2001 655
H-7), 4.04 (dd, 1H, J ) 9.6, 9.9 Hz, H-13), 3.35 (dd, 1H, J )
9.3, 9.9 Hz, H-14), 1.10 (m, 2H, H-17), 1.11 (s, 3H, Me-18),
1.58 (s, 3H, Me-19), 1.10 (d, 3H, J ) 6.9 Hz, Me-20), 0.73 (m,
1H, H-21), 1.52 (m, 1H, H-21′); 13C NMR (CDCl3, 75 MHz) δ
43.3 (d, C-1), 24.8 (t, C-2), 84.0 (d, C-3), 73.3 (s, C-4), 41.1 (t,
C-5), 21.4 (t, C-6), 126.8 (d, C-7), 133.3 (s, C-8), 36.9 (t, C-9),
26.2 (t, C-10), 28.5 (t, C-11), 38.7 (d, C-12), 86.4 (d, C-13), 80.9
(d, C-14), 23.1 (s, C-15), 174.2 (s, C-16), 13.8 (t, C-17), 23.3 (q,
C-18), 16.8 (q, C-19), 17.6 (q, C-20), 13.1 (t, C-21); HREI-MS
m/z [M]+ calcd for C21H32O4 348.2300, found 348.2290, 348 (49),
330 (31), 236 (20), 155 (74), 109 (79), 95 (93), 81 (96), 55 (100).
Hz, H-17′), 1.41 (s, 3H, Me-18), 1.59 (s, 3H, Me-19), 0.86 (d,
3H, J ) 6.6 Hz, Me-20), 3.08 (br s, exchangeable, OH); 13C
NMR (CDCl3, 75 MHz) δ 38.6 (d, C-1), 21.0 (t, C-2), 83.3 (d,
C-3), 74.2 (s, C-4), 36.6 (t, C-5), 22.3 (t, C-6), 125.1 (d, C-7),
137.1 (s, C-8), 39.0 (t, C-9), 20.9 (t, C-10), 32.2 (t, C-11), 28.7
(d, C-12), 77.2 (d, C-13), 72.7 (d, C-14), 135.2 (s, C-15), 166.7
(s, C-16), 128.4 (t, C-17), 24.5 (q, C-18), 14.3 (q, C-19), 10.7 (q,
C-20); HREI-MS m/z [M]+ calcd for C20H32O5 352.2250, found
352.2249, 352 (12), 334 (11), 316 (9), 288 (4), 236 (6), 109 (44),
95 (83), 81 (100).
Da ta for 20: colorless oil; [R]21 +10.6° (c 1.7, CHCl3); IR
D
Da ta for 16: colorless oil; [R]29 -1.9° (c 1.6, CHCl3); IR
(neat) 3443, 1756, 1274, 1159, 1085, 1006 cm-1; UV (MeOH)
λmax 210 nm; 1H NMR (CDCl3, 300 MHz) δ 3.41 (m, 1H, H-1),
3.46 (d, 1H, J ) 11.1 Hz, H-3), 5.75 (br t, 1H, J ) 7.5 Hz,
H-7), 3.62 (d, 1H, J ) 10.2 Hz, H-13), 4.42 (dd, 1H, J ) 5.5,
10.2 Hz, H-14), 5.71 (br s, 1H, H-17), 6.29 (br s, 1H, H-17′),
1.06 (s, 3H, Me-18), 1.57 (s, 3H, Me-19), 0.88 (d, 3H, J ) 6.6
Hz, Me-20), 2.86 (br s, 1H, exchangeable, OH); 13C NMR
(CDCl3, 75 MHz) δ 38.0 (d, C-1), 27.7 (t, C-2), 73.5 (d, C-3),
74.6 (s, C-4), 39.2 (t, C-5), 21.5 (t, C-6), 128.6 (d, C-7), 134.2
(s, C-8), 35.8 (t, C-9), 20.4 (t, C-10), 30.9 (t, C-11), 28.3 (d, C-12),
74.4 (d, C-13), 82.1 (d, C-14), 138.6 (s, C-15), 169.8 (s, C-16),
123.5 (t, C-17), 28.7 (q, C-18), 14.1 (q, C-19), 10.1 (q, C-20);
HREI-MS m/z [M - H2O]+ calcd for C20H30O4 334.2144, found
334.2134, 334 (12), 316 (7), 248 (6), 181 (10), 107 (42), 95 (77),
81 (96), 55 (100).
D
(neat) 3443, 1720, 1638, 1214, 1135, 1091 cm-1; UV (MeOH)
1
λmax 220 nm (ꢀ 6200); H NMR (CDCl3, 300 MHz) δ 2.52 (m,
1H, H-1), 3.99 (dd, 1H, J ) 4.5, 9.3 Hz, H-3), 5.25 (br t, 1H, J
) 7.5 Hz, H-7), 3.94 (dd, 1H, J ) 9.6, 9.9 Hz, H-13), 3.17 (dd,
1H, J ) 9.3, 9.6 Hz, H-14), 6.10 (dq, 1H, J ) 2.7, 7.5 Hz, H-17),
1.13 (s, 3H, Me-18), 1.58 (s, 3H, Me-19), 1.11 (d, 3H, J ) 6.6
Hz, Me-20), 2.17 (dd, 3H, J ) 2.7, 7.5 Hz, Me-21); 13C NMR
(CDCl3, 75 MHz) δ 47.2 (d, C-1), 28.1 (t, C-2), 84.0 (d, C-3),
73.3 (s, C-4), 41.2 (t, C-5), 21.4 (t, C-6), 126.8 (d, C-7), 133.2
(s, C-8), 36.9 (t, C-9), 25.2 (t, C-10), 28.6 (t, C-11), 39.0 (d, C-12),
85.8 (d, C-13), 81.4 (d, C-14), 127.9 (s, C-15), 163.9 (s, C-16),
140.0 (d, C-17), 23.2 (q, C-18), 16.9 (q, C-19), 17.8 (q, C-20),
15.7 (q, C-21); HREI-MS m/z [M]+ calcd for C21H32O4 348.2300,
found 348.2294, 348 (56), 330 (43), 256 (18), 178 (46), 109 (76),
81 (88), 55 (100).
P a th B. A suspension of 3 (3.50 g, 9.31 mmol) in 3% aqueous
KOH (100 mL) was stirred vigorously at 70 °C for 2 h and
then cooled, quenched with 5 N HCl, and extracted with
chloroform (3 × 150 mL). The combined organic extracts were
washed with saturated NaCl, dried, and concentrated to leave
a white solid residue (3.54 g) that was used without further
purification. Chloroform (50 mL) and a solution of diazo-
methane in ether (50 mL) were added. The solution was stirred
at room temperature for 15 min prior to being concentrated
and stored under high vacuum. Silica gel chromatography (95
g) eluting with 20% ethyl acetate in hexane followed by
normal-phase HPLC (Partisil-10, elution with 1:1 (v/v) 2-pro-
panol in hexane) provided 956 mg (27%) of 21, 570 mg (16%)
of 22, 393 mg (10%) of 23, 268 mg (8%) of 24, and 893 mg
(24%) of 25.
Sa p on ifica tion of Eu p a lm er in Aceta te (3) w ith Aqu e-
ou s KOH. P a th A. A suspension of 3 (2.03 g, 5.41 mmol) in
3% aqueous KOH (40 mL) was stirred vigorously at 70 °C for
18 h and then cooled, diluted with water (125 mL), quenched
with 5 N HCl, and extracted with CHCl3 (3 × 125 mL). The
combined organic extracts were washed with saturated NaCl,
dried, and concentrated. The foam obtained (1.67 g) was
chromatographed on a silica gel column (70 g) eluted with a
97:3:0.5 mixture of chloroform/MeOH/acetic acid to yield
390 mg (21%) of 3,14-eupalmeroic acid (17), 308 mg (16%) of
4,14-eupalmeroic acid (18), 91 mg (5%) of eucrassin alcohol
(19), and 28 mg (2%) of isoeucrassin alcohol (20).
Da ta for 17: colorless oil; [R]21 -36.3° (c 1.3, CHCl3); IR
D
(neat) 3630-3075 (broad), 1767, 1208, 1165, 1093 cm-1; UV
1
(MeOH) λmax 210 nm; H NMR (CDCl3, 300 MHz) δ 3.14 (m,
Da ta for 21: light yellow oil; [R]21 -160.1° (c 6.0, CHCl3);
D
1H, H-1), 3.86 (t, 1H, J ) 7.5 Hz, H-3), 5.19 (br s, 1H, H-7),
3.03 (d, 1H, J ) 9.3 Hz, H-13), 3.70 (d, 1H, J ) 9.3 Hz, H-14),
5.76 (br s, 1H, H-17), 6.38 (br s, 1H, H-17′), 1.16 (s, 3H, Me-
18), 1.53 (s, 3H, Me-19), 0.98 (d, 3H, J ) 6.3 Hz, Me-20), 4.53
(br s, exchangeable, OH); 13C NMR (CDCl3, 75 MHz) δ 39.9
(d, C-1), 33.2 (t, C-2), 80.7 (d, C-3), 74.1 (s, C-4), 39.4 (t, C-5),
21.9 (t, C-6), 131.7 (d, C-7), 127.3 (s, C-8), 42.7 (t, C-9), 22.4 (t,
C-10), 30.0 (t, C-11), 37.0 (d, C-12), 73.8 (d, C-13), 83.4 (d,
C-14), 139.4 (s, C-15), 170.9 (s, C-16), 128.6 (t, C-17), 21.7 (q,
C-18), 15.6 (q, C-19), 16.7 (q, C-20); HREI-MS m/z [M]+ calcd
for C20H32O5 352.2250, found 352.2235, 352 (5), 334 (21), 316
(9), 193 (22), 141 (45), 109 (40), 95 (82), 81 (100).
IR (neat) 3477, 1764, 1284, 1216, 1143, 1074, 1005 cm-1; UV
(MeOH) λmax 206 and 320 (sh) nm; 1H NMR (CDCl3, 300 MHz)
δ 3.25 (m, 1H, H-1), 2.85 (dd, 1H, J ) 5.4, 8.1 Hz, H-3), 5.05
(br t, 1H, J ) 5.8 Hz, H-7), 3.61 (br d, 1H, J ) 7.5 Hz, H-13),
4.99 (dd, 1H, J ) 2.1, 7.5 Hz, H-14), 1.24 (s, 3H, Me-18), 1.64
(s, 3H, Me-19), 1.03 (d, 3H, J ) 6.9 Hz, Me-20), 4.65 (br t, 2H,
J ) 7.6 Hz, H-21); 13C NMR (CDCl3, 75 MHz) δ 41.9 (d, C-1),
25.4 (t, C-2), 58.8 (d, C-3), 60.2 (s, C-4), 38.3 (t, C-5), 23.2 (t,
C-6), 126.0 (d, C-7), 135.3 (s, C-8), 38.0 (t, C-9), 23.7 (t, C-10),
31.6 (t, C-11), 34.9 (d, C-12), 73.0 (d, C-13), 80.1 (d, C-14), 97.6
(s, C-15), 174.0 (s, C-16), 23.2 (t, C-17), 16.3 (q, C-18), 16.2 (q,
C-19), 16.5 (q, C-20), 78.4 (t, C-21); HREI-MS m/z [M]+ calcd
for C21H32N2O4 376.2362, found 376.2414, 376 (1), 348 (7), 330
(11), 121 (45), 107 (49), 95 (57), 55 (100).
Da ta for 18: colorless oil; IR (neat) 3620-3045 (broad),
1763, 1448, 1158, 1066, 1037 cm-1; UV (MeOH) λmax 210 nm;
1H NMR (CDCl3, 300 MHz) δ 3.17 (m, 1H, H-1), 3.37 (br s,
1H, H-3), 5.49 (br t, 1H, J ) 9.3 Hz, H-7), 2.87 (d, 1H, J )
10.5 Hz, H-13), 4.02 (br d, 1H, J ) 10.5 Hz, H-14), 5.63 (br s,
1H, H-17), 6.33 (br s, 1H, H-17′), 1.32 (s, 3H, Me-18), 1.56 (s,
3H, Me-19), 0.87 (d, 3H, J ) 6.3 Hz, Me-20), 4.79 (br s,
exchangeable, OH); 13C NMR (CDCl3, 75 MHz) δ 32.9 (d, C-1),
33.3 (t, C-2), 71.5 (d, C-3), 77.6 (s, C-4), 31.0 (t, C-5), 23.1 (t,
C-6), 126.3 (d, C-7), 131.6 (s, C-8), 36.4 (t, C-9), 20.6 (t, C-10),
29.0 (t, C-11), 29.5 (d, C-12), 75.1 (d, C-13), 70.0 (d, C-14), 141.6
(s, C-15), 170.0 (s, C-16), 127.8 (t, C-17), 20.9 (q, C-18), 13.7
(q, C-19), 15.1 (q, C-20); HREI-MS m/z [M]+ calcd for C20H32O5
352.2250, found 352.2245, 352 (60), 334 (25), 316 (9), 184 (11),
181 (12), 121 (28), 95 (81), 81 (100).
Da ta for 22: light yellow oil; [R]21 +50.7° (c 32.4, CHCl3);
D
IR (neat) 3421, 1777, 1338, 1218, 1143, 1072 cm-1; UV (CHCl3)
λ
max 244 (ꢀ 700) and 326 nm (ꢀ 300); 1H NMR (CDCl3, 300 MHz)
δ 2.65 (m, 1H, H-1), 2.86 (dd, 1H, J ) 5.1, 8.8 Hz, H-3), 5.04
(br t, 1H, J ) 6.4 Hz, H-7), 3.70 (d, 1H, J ) 8.7 Hz, H-13),
4.86 (d, 1H, J ) 8.7 Hz, H-14), 1.24 (s, 3H, Me-18), 1.58 (s,
3H, Me-19), 1.07 (d, 3H, J ) 6.9 Hz, Me-20), 4.67 (m, 1H,
H-21), 4.83 (m, 1H, H-21′), 4.36 (br s, 1H, exchangeable, OH);
13C NMR (CDCl3, 75 MHz) δ 45.9 (d, C-1), 23.9 (t, C-2), 58.1
(d, C-3), 59.7 (s, C-4), 37.7 (t, C-5), 22.7 (t, C-6), 125.9 (d, C-7),
134.6 (s, C-8), 37.3 (t, C-9), 23.1 (t, C-10), 31.3 (t, C-11), 35.0
(d, C-12), 71.6 (d, C-13), 80.4 (d, C-14), 95.3 (s, C-15), 172.0 (s,
C-16), 25.0 (t, C-17), 16.2 (q, C-18), 15.6 (q, C-19), 16.5 (q, C-20),
77.9 (t, C-21); HREI-MS m/z [M]+ calcd for C21H32N2O4
376.2362, found 376.2359, 376 (6), 348 (3), 330 (3), 195 (9),
177 (16), 95 (62), 81 (100).
Da ta for 19: colorless oil; [R]21 +49.4° (c 3.4, CHCl3); IR
D
(neat) 3411, 1708, 1620, 1262, 1179, 1101, 1028 cm-1; UV
1
(MeOH) λmax 210 nm; H NMR (CDCl3, 300 MHz) δ 2.71 (m,
1H, H-1), 4.11 (d, 1H, J ) 10.5 Hz, H-3), 5.13 (br t, 1H, J )
7.5 Hz, H-7), 3.43 (d, 1H, J ) 8.7 Hz, H-13), 3.97 (br d, 1H, J
) 8.7 Hz, H-14), 5.81 (br s, 1H, H-17), 6.71 (br d, 1H, J ) 2.1
Da ta for 23: light yellow oil; [R]25 -55.4° (c 7.4, CHCl3);
D
IR (neat) 3396, 1730, 1554, 1228, 1071 cm-1; UV (CHCl3) λmax
1
244 and 330 nm; H NMR (CDCl3, 300 MHz) δ 2.95 (m, 1H,

656 J . Org. Chem., Vol. 66, No. 3, 2001
Rodr´ıguez et al.
H-1), 3.35 (br t, 1H, J ) 2.7 Hz, H-3), 5.48 (m, 1H, H-7), 3.41
(d, 1H, J ) 10.2 Hz, H-13), 3.89 (d, 1H, J ) 10.5 Hz, H-14),
1.31 (s, 3H, Me-18), 1.55 (s, 3H, Me-19), 0.91 (d, 3H, J ) 6.6
Hz, Me-20), 4.16 (m, 1H, H-21), 4.79 (ddd, 1H, J ) 2.1, 9.3,
17.7 Hz, H-21′), 3.70 (s, 3H, CO2CH3); 13C NMR (CDCl3, 75
MHz) δ 35.0 (d, C-1), 28.2 (t, C-2), 71.5 (d, C-3), 77.0 (s, C-4),
31.1 (t, C-5), 23.1 (t, C-6), 126.2 (d, C-7), 131.6 (s, C-8), 36.4 (t,
C-9), 20.6 (t, C-10), 29.2 (t, C-11), 29.6 (d, C-12), 75.5 (d, C-13),
69.3 (d, C-14), 100.0 (s, C-15), 170.2 (s, C-16), 24.7 (t, C-17),
20.7 (q, C-18), 13.8 (q, C-19), 15.1 (q, C-20), 76.4 (t, C-21), 52.7
(q, C-22); HREI-MS m/z [M]+ calcd for C22H36N2O5 408.2624,
found 408.2637, 408 (1), 380 (58), 362 (29), 344 (9), 330 (8),
196 (38), 81 (100).
Da ta for 27: colorless oil; IR (neat) 3650-3039 (broad),
1721, 1712, 1240, 1073, 1025 cm-1; UV (MeOH) λmax 208 nm;
1H NMR (CDCl3, 300 MHz) δ 2.79 (m, 1H, H-1), 3.86 (br t,
1H, J ) 7.6 Hz, H-3), 5.27 (br t, 1H, J ) 5.7 Hz, H-7), 4.64
(dd, 1H, J ) 1.8, 9.6 Hz, H-13), 3.98 (dd, 1H, J ) 2.1, 9.0 Hz,
H-14), 5.68 (br s, 1H, H-17), 6.37 (br s, 1H, H-17′), 1.18 (s, 3H,
Me-18), 1.55 (s, 3H, Me-19), 0.82 (d, 3H, J ) 6.6 Hz, Me-20),
2.09 (s, 3H, OCOCH3), 3.20 (br s, exchangeable, OH); 13C NMR
(CDCl3, 75 MHz) δ 40.6 (d, C-1), 34.2 (t, C-2), 81.4 (d, C-3),
74.0 (s, C-4), 39.4 (t, C-5), 22.4 (t, C-6), 128.4 (d, C-7), 131.8
(s, C-8), 42.1 (t, C-9), 25.3 (t, C-10), 30.3 (t, C-11), 34.8 (d, C-12),
75.4 (d, C-13), 81.3 (d, C-14), 139.3 (s, C-15), 170.1 (s, C-16),
127.5 (t, C-17), 22.1 (q, C-18), 15.7 (q, C-19), 16.2 (q, C-20),
171.0 (s, C-21), 20.9 (q, C-22); HREI-MS m/z [M]+ calcd for
C22H34O6 394.2355, found 394.2355, 394 (4), 376 (25), 335 (12),
334 (51), 316 (30), 81 (100).
Da ta for 24: light yellow oil; [R]25 +60.8° (c 7.4, CHCl3);
D
IR (neat) 3396, 1732, 1558, 1223, 1070, 1051 cm-1; UV (CHCl3)
1
λmax 244 and 330 nm; H NMR (CDCl3, 300 MHz) δ 2.72 (m,
1H, H-1), 3.39 (br t, 1H, J ) 3.0 Hz, H-3), 5.44 (m, 1H, H-7),
2.94 (d, 1H, J ) 10.2 Hz, H-13), 3.95 (d, 1H, J ) 10.5 Hz, H-14),
1.28 (s, 3H, Me-18), 1.57 (s, 3H, Me-19), 0.90 (d, 3H, J ) 6.6
Hz, Me-20), 4.50 (ddd, 1H, J ) 6.6, 9.3, 18.3 Hz, H-21), 4.63
(ddd, 1H, J ) 5.4, 9.6, 18.3 Hz, H-21′), 3.77 (s, 3H, -CO2CH3);
13C NMR (CDCl3, 75 MHz) δ 37.3 (d, C-1), 29.1 (t, C-2), 71.5
(d, C-3), 78.0 (s, C-4), 31.2 (t, C-5), 23.1 (t, C-6), 126.1 (d, C-7),
131.8 (s, C-8), 36.4 (t, C-9), 20.5 (t, C-10), 29.0 (t, C-11), 29.8
(d, C-12), 75.2 (d, C-13), 68.6 (d, C-14), 100.1 (s, C-15), 169.8
(s, C-16), 26.3 (t, C-17), 20.7 (q, C-18), 13.8 (q, C-19), 15.0 (q,
C-20), 77.2 (t, C-21), 52.7 (q, C-22); HREI-MS m/z [M]+ calcd
for C22H36N2O5 408.2624, found 408.2558, 408 (1), 380 (53),
362 (24), 344 (6), 196 (33), 152 (27), 95 (68), 55 (100).
P a th D. A suspension of 3 (1.05 g, 2.79 mmol) in 3%
aqueous KOH (26 mL) was stirred vigorously at 45 °C for 18
h and then cooled, diluted with water (50 mL), quenched with
5 N HCl, and extracted with ether (3 × 75 mL). The combined
organic extracts were washed with saturated NaCl, dried, and
concentrated. A cooled solution (-78 °C) of the foam obtained
(843 mg) in ethyl acetate (40 mL) was treated with O3 until
the solution turned light blue. The reaction was warmed to
20 °C, concentrated, diluted with water (40 mL), and treated
with 30% hydrogen peroxide (5 drops). The solution was
refluxed for 18 h and then cooled and concentrated to afford
the crude product as a viscous oil that was purified by normal-
phase HPLC (Ultrasphere-CN, elution with 15% 2-propanol
in hexane) to provide 288 mg (30%) of carboxylic acid 28 and
552 mg (54%) of dicarboxylic acid 29. Since 29 was sparingly
soluble in CDCl3 it was dissolved in a 1:1 mixture of chloroform
and MeOH (10 mL), treated with 20 mL of diazomethane
solution in ether, and concentrated to give 564 mg (96%) of
diester 31 as an oil that was analyzed without further
purification. After being treated with 10 mL of diazomethane
solution in ether and stirred at room temperature for 30 min,
carboxylic acid 28 (90 mg, 0.25 mmol) was layered on top of a
10 × 10 cm plug of silica gel (12 g) in a sintered glass frit, and
100 mL of 30% ethyl acetate in hexane was poured through
under aspirator vacuum. Concentration of the filtrate afforded
pure 30 (84 mg, 90%).
Da ta for 25: light yellow oil; [R]25 -94.5° (c 30.3, CHCl3);
D
IR (neat) 3400, 1733, 1558, 1249, 1123, 1070 cm-1; UV (CHCl3)
λ
max 244 (ꢀ 350) and 326 nm (ꢀ 300); 1H NMR (CDCl3, 300 MHz)
δ 3.01 (m, 1H, H-1), 3.64 (t, 1H, J ) 8.1 Hz, H-3), 5.11 (t, 1H,
J ) 5.4 Hz, H-7), 3.07 (m, 1H, H-13), 3.73 (d, 1H, J ) 8.4 Hz,
H-14), 1.09 (s, 3H, Me-18), 1.47 (s, 3H, Me-19), 0.94 (d, 3H, J
) 6.3 Hz, Me-20), 4.46 (m, 1H, H-21), 4.67 (ddd, 1H, J ) 4.8,
10.2, 18.0 Hz, H-21′), 3.72 (s, 3H, -CO2CH3); 13C NMR (CDCl3,
75 MHz) δ 42.6 (d, C-1), 29.7 (t, C-2), 81.1 (d, C-3), 73.1 (s,
C-4), 39.5 (t, C-5), 22.0 (t, C-6), 128.2 (d, C-7), 131.3 (s, C-8),
42.8 (t, C-9), 21.9 (t, C-10), 30.3 (t, C-11), 36.8 (d, C-12), 74.9
(d, C-13), 79.7 (d, C-14), 99.9 (s, C-15), 170.2 (s, C-16), 24.4 (t,
C-17), 21.0 (q, C-18), 15.2 (q, C-19), 16.5 (q, C-20), 77.2 (t, C-21),
52.4 (q, C-22); HREI-MS m/z [M]+ calcd for C22H36N2O5
408.2624, found 408.2609, 408 (1), 390 (1), 380 (1), 362 (5), 85
(66), 83 (100).
Da ta for 28: colorless oil; [R]21 -26.9° (c 7.2, CHCl3); IR
D
(neat) 3790-3050 (broad), 1770, 1734, 1713, 1261, 1171 cm-1
;
1
UV (MeOH) λmax 210 nm; H NMR (CDCl3, 300 MHz) δ 3.08
(m, 1H, H-1), 1.89 (m, 1H, H-2), 2.25 (m, 1H, H-2′), 4.05 (dd,
1H, J ) 7.0, 8.8 Hz, H-3), 1.89 (m, 1H, H-5), 2.25 (m, 1H, H-5′),
2.61 (m, 2H, H-6), 2.41 (br t, 2H, J ) 7.2 Hz, H-9), 3.45 (m,
1H, H-13), 4.14 (dd, 1H, J ) 3.1, 6.1 Hz, H-14), 1.38 (s, 3H,
Me-18), 2.12 (s, 3H, Me-19), 0.93 (d, 3H, J ) 6.6 Hz, Me-20);
13C NMR (CDCl3, 75 MHz) δ 45.4 (d, C-1), 28.8 (t, C-2), 83.4
(d, C-3), 86.7 (s, C-4), 30.2 (t, C-5), 29.0 (t, C-6), 176.9 (s, C-7),
210.1 (s, C-8), 43.6 (t, C-9), 21.0 (t, C-10), 32.7 (t, C-11), 36.3
(d, C-12), 75.4 (d, C-13), 82.6 (d, C-14), 176.9 (s, C-15), 23.6
(q, C-18), 29.9 (q, C-19), 14.6 (q, C-20); HRFAB-MS m/z [M +
Na]+ calcd for C18H28O7Na 379.1733, found 379.1724; HREI-
MS m/z [M-H2O]+ calcd for C18H26O6 338.1729, found 338.1738,
338 (8), 320 (3), 221 (25), 143 (34), 126 (43), 99 (100).
P a th C. A suspension of 3 (106 mg, 0.28 mmol) in 3%
aqueous KOH (28 mL) was stirred vigorously at 45 °C for 12
h and then cooled, quenched with 5 N HCl, and extracted with
ether (3 × 30 mL). The combined organic extracts were washed
with saturated NaCl, dried, and concentrated to leave a
residue that was used without further purification. Pyridine
(25 mL) and acetic anhydride (25 mL) were added, and the
solution was stirred at room temperature for 1.5 h prior to
being concentrated. Purification by silica gel chromatography
(13 g) eluting with 40% ethyl acetate in hexane followed by
normal-phase HPLC (Partisil-10, elution with 1:4 (v/v) 2-pro-
panol in hexane) provided 18 mg (20%) of eupalmerolide (26)
and 22 mg (20%) of acetate 27. An undetermined amount of
starting material 3 was also recovered.
Da ta for 30: colorless oil; [R]21 -36.0° (c 1.2, CHCl3); IR
D
Da ta for 26: colorless oil; IR (neat) 3450, 1722, 1642, 1260,
(neat) 3340, 1774, 1737, 1261, 1159, 1118, 1069 cm-1; UV
1
1
1130, 1094 cm-1; UV (MeOH) λmax 210 nm; H NMR (CDCl3,
(MeOH) λmax 206 nm (ꢀ 1700); H NMR (CDCl3, 300 MHz) δ
300 MHz) δ 2.86 (m, 1H, H-1), 4.03 (dd, 1H, J ) 4.6, 9.7 Hz,
H-3), 5.19 (br t, 1H, J ) 7.2 Hz, H-7), 4.37 (dd, 1H, J ) 5.7,
10.5 Hz, H-13), 3.85 (dd, 1H, J ) 5.4, 12.0 Hz, H-14), 5.49 (d,
1H, J ) 2.1 Hz, H-17), 6.43 (d, 1H, J ) 2.4 Hz, H-17′), 1.16 (s,
3H, Me-18), 1.59 (s, 3H, Me-19), 1.10 (d, 3H, J ) 6.3 Hz, Me-
20); 13C NMR (CDCl3, 75 MHz) δ 40.7 (d, C-1), 29.4 (t, C-2),
88.4 (d, C-3), 72.9 (s, C-4), 36.6 (t, C-5), 22.3 (t, C-6), 128.4 (d,
C-7), 133.3 (s, C-8), 37.6 (t, C-9), 23.3 (t, C-10), 29.2 (t, C-11),
35.9 (d, C-12), 84.1 (d, C-13), 78.7 (d, C-14), 136.9 (s, C-15),
163.8 (s, C-16), 126.0 (t, C-17), 25.8 (q, C-18), 16.5 (q, C-19),
15.7 (q, C-20); HRFAB-MS m/z [M + Na]+ calcd for C20H30O4-
Na 357.2042, found 357.2039; HREI-MS m/z [M-H2O]+ calcd
for C20H28O3 316.2038, found 316.2045, 316 (21), 167 (24), 95
(76), 81 (100).
2.74 (m, 1H, H-1), 4.19 (t, 1H, J ) 7.6 Hz, H-3), 2.64 (br t, 2H,
J ) 9.6 Hz, H-6), 1.85 (m, 1H, H-12), 3.76 (br d, 1H, J ) 9.9
Hz, H-13), 4.29 (t, 1H, J ) 8.4 Hz, H-14), 1.40 (s, 3H, Me-18),
1.46 (s, 3H, Me-19), 0.88 (d, 3H, J ) 6.9 Hz, Me-20), 3.73 (s,
3H, CO2CH3), 9.92 (br s, 1H, exchangeable, OH); 13C NMR
(CDCl3, 75 MHz) δ 45.8 (d, C-1), 32.3 (t, C-2), 82.5 (d, C-3),
84.4 (s, C-4), 29.7 (t, C-5), 28.2 (t, C-6), 175.9 (s, C-7), 107.6 (s,
C-8), 36.5 (t, C-9), 18.3 (t, C-10), 37.4 (t, C-11), 31.9 (d, C-12),
76.3 (d, C-13), 85.6 (d, C-14), 173.3 (s, C-15), 21.8 (q, C-18),
23.1 (q, C-19), 12.4 (q, C-20), 52.4 (q, CO2CH3); HREI-MS m/z
[M - OH]+ calcd for C19H29O6 353.1964, found 353.1951, 353
(9), 321 (45), 267 (14), 195 (58), 125 (69), 99 (100).
Da ta for 31: colorless oil; IR (neat) 3440, 1773, 1732, 1716,
1260, 1197, 1082, 1035 cm-1; UV (MeOH) λmax 210 nm; 1H

Synthesis of Analogues of Eunicea γ-Cembranolides
J . Org. Chem., Vol. 66, No. 3, 2001 657
NMR (CDCl3, 300 MHz) δ 3.10 (m, 1H, H-1), 1.61 (m, 1H, H-2),
2.10 (m, 1H, H-2′), 3.45 (m, 1H, H-3), 2.05 (m, 2H, H-5), 2.37
(m, 2H, H-6), 3.08 (m, 1H, H-13), 3.83 (br d, 1H, J ) 10.5 Hz,
H-14), 1.13 (s, 3H, Me-18), 2.09 (s, 3H, Me-19), 0.94 (d, 3H, J
) 6.6 Hz, Me-20), 3.65 (s, 3H, CO2CH3), 3.63 (s, 3H, CO2CH3);
13C NMR (CDCl3, 75 MHz) δ 36.9 (d, C-1), 28.4 (t, C-2), 68.1
(d, C-3), 76.0 (s, C-4), 30.5 (t, C-5), 28.1 (t, C-6), 174.5 (s, C-7),
208.9 (s, C-8), 43.8 (t, C-9), 21.0 (t, C-10), 32.8 (t, C-11), 35.6
(d, C-12), 75.0 (d, C-13), 69.9 (d, C-14), 173.7 (s, C-15), 21.5
(q, C-18), 29.7 (q, C-19), 15.2 (q, C-20), 51.7 (q, CO2CH3), 51.6
(q, CO2CH3); HREI-MS m/z [M - CH3OH - OH]+ calcd for
C19H29O6 353.1964, found 353.1975, 353 (3), 321 (17), 309 (8),
209 (32), 195 (73), 125 (53), 99 (100).
MS m/z [M]+ calcd for C22H36O5 380.2563, found 380.2568, 380
(2), 378 (4), 376 (4), 362 (10), 169 (46), 83 (79), 55 (100).
Da ta for 36: colorless oil; 1H NMR (CDCl3, 300 MHz) δ 6.09
(q, 1H, J ) 7.2 Hz, H-17), 1.92 (d, 3H, J ) 7.2 Hz, Me-21),
3.64 (s, 3H, CO2CH3); 13C NMR (CDCl3, 125 MHz) δ 82.9 (d,
C-3), 73.6 (s, C-4), 73.8 (d, C-13), 81.1 (d, C-14), 136.2 (s, C-15),
148.1 (d, C-17), 14.1 (q, C-21), 51.4 (q, C-22); HREI-MS m/z
[M]+ calcd for C22H36O5 380.2563, found 380.2592, 380 (3).
Th er m olysis of P yr a zolin e 25. A solution of pyrazoline
25 (15 mg, 0.035 mmol) in benzene (10 mL) was treated with
glacial acetic acid (3 drops), warmed to 90-100 °C for 5 days,
cooled, and concentrated to leave a crude residue (20 mg) that
was purified by means of silica gel chromatography (1 g,
elution with 20% ethyl acetate in hexane) to give 10 mg (75%)
of a 3:1 mixture of compounds 34 and 36, respectively.
Tr ea tm en t of 4,14-Eu p a lm er oic a cid (18) w ith Dia zo-
m eth a n e a n d Th er m olysis of th e Mixtu r e of P yr a zolin es
23 a n d 24. A solution of diazomethane in ether (25 mL) was
added to a solution of 18 (271 mg, 0.77 mmol) in CH2Cl2 (15
mL). The reaction mixture was stirred at room temperature
for 30 min prior to being concentrated and stored under high
vacuum. The resulting oil (238 mg, 76%), which consisted of a
1:1 mixture of pyrazolines, was used in the next step without
further purification. A solution of 23 and 24 (73 mg, 0.18 mmol)
in toluene (4 mL) was treated with glacial acetic acid (1 mL),
warmed to 115 °C for 4.5 h, cooled, and concentrated to leave
an oil that was purified by means of silica gel chromatography
(2.4 g, elution with chloroform), giving 15 mg (22%) of
derivative 32, 13 mg (18%) of 38, and ca. 1-2 mg (2%) of 39.
P h otolysis of P yr a zolin e 23. A magnetically stirred
solution of 23 (50 mg, 0.12 mmol) in 10% ethyl acetate in
hexane (5 mL) placed in a small Pyrex test tube was irradiated
for 2.5 h at 25 °C. After concentration, the resulting oil was
chromatographed on silica gel (2 g, 30% ethyl acetate in
hexane) to provide 47 mg (100%) of 32.
Da ta for 32: colorless oil; [R]25 +13.4° (c 9.3, CHCl3); IR
D
(neat) 3401, 1718, 1226, 1193, 1152, 1068 cm-1; UV (CHCl3)
λmax 246 nm (ꢀ 450); 1H NMR (CDCl3, 300 MHz) δ 1.28 (m,
1H, H-1), 3.36 (br t, 1H, J ) 3.0 Hz, H-3), 5.48 (dd, 1H, J )
6.0, 10.5 Hz, H-7), 3.16 (d, 1H, J ) 10.5 Hz, H-13), 4.54 (d,
1H, J ) 10.8 Hz, H-14), 1.27 (s, 3H, Me-18), 1.61 (s, 3H, Me-
19), 0.93 (d, 3H, J ) 6.6 Hz, Me-20), 3.61 (s, 3H, -CO2CH3);
13C NMR (CDCl3, 75 MHz) δ 36.2 (d, C-1), 30.5 (t, C-2), 72.4
(d, C-3), 77.4 (s, C-4), 31.4 (t, C-5), 23.2 (t, C-6), 126.4 (d, C-7),
131.8 (s, C-8), 36.6 (t, C-9), 20.7 (t, C-10), 28.9 (t, C-11), 30.0
(d, C-12), 74.8 (d, C-13), 68.9 (d, C-14), 23.9 (s, C-15), 174.4 (s,
C-16), 18.1 (t, C-17), 21.0 (q, C-18), 13.8 (q, C-19), 15.3 (q, C-20),
15.4 (t, C-21), 51.4 (q, C-22); HREI-MS m/z [M]+ calcd for
C22H36O5 380.2563, found 380.2567, 380 (93), 363 (51), 362 (48),
344 (17), 207 (34), 196 (61), 95 (66) 55 (100).
Da ta for 38: colorless oil; [R]25 +21.9° (c 2.1, CHCl3); IR
D
(neat) 3396, 1715, 1231, 1148, 1068, 1036 cm-1; UV (MeOH)
1
λmax 225 nm (ꢀ 3100); H NMR (CDCl3, 300 MHz) δ 2.90 (m,
1H, H-1), 3.33 (br t, 1H, J ) 2.9 Hz, H-3), 5.47 (m, 1H, H-7),
2.88 (d, 1H, J ) 10.6 Hz, H-13), 4.06 (d, 1H, J ) 11.0 Hz, H-14),
6.05 (q, 1H, J ) 7.1 Hz, H-17), 1.29 (s, 3H, Me-18), 1.59 (s,
3H, Me-19), 0.91 (d, 3H, J ) 6.5 Hz, Me-20), 1.86 (d, 3H, J )
7.1 Hz, Me-21), 3.74 (s, 3H, -CO2CH3); 13C NMR (CDCl3, 75
MHz) δ 37.4 (d, C-1), 32.5 (t, C-2), 71.6 (d, C-3), 77.7 (s, C-4),
31.1 (t, C-5), 23.1 (t, C-6), 126.2 (d, C-7), 131.9 (s, C-8), 36.5 (t,
C-9), 20.6 (t, C-10), 28.8 (t, C-11), 30.0 (d, C-12), 75.0 (d, C-13),
68.9 (d, C-14), 133.5 (s, C-15), 168.6 (s, C-16), 137.5 (d, C-17),
21.0 (q, C-18), 13.7 (q, C-19), 15.2 (q, C-20), 15.8 (q, C-21), 51.2
(q, C-22); HREI-MS m/z [M]+ calcd for C22H36O5 380.2563,
found 380.2572, 380 (100), 362 (34), 349 (17), 196 (40), 180
(18), 152 (41).
P h otolysis of P yr a zolin e 25. Compound 25 (22 mg, 0.05
mmol) was dissolved in 5 mL of a mixture of 10% ethyl acetate
in hexane, and the resulting solution was irradiated with
stirring for 1 h at 25 °C. After concentration, the oil was
chromatographed on silica gel (1 g, 20% ethyl acetate in
hexane) to provide 20 mg (100%) of 34. When a solution of 25
(35 mg, 0.086 mmol) in 10% ethyl acetate in hexane was
irradiated at 25 °C for 13 h using a 7-59 Corning filter,
compound 34 (88%) and a 1:1 mixture of 35 and 36 were
obtained. The mixture was flash chromatographed on a short
silica gel (3.0 g) column and eluted with 25% ethyl acetate in
hexane to furnish 2 mg (6%) of 35 and 2 mg (6%) of 36.
Da ta for 39: colorless oil; 1H NMR (CDCl3, 300 MHz) δ 6.94
(q, 1H, J ) 7.2 Hz, H-17), 1.87 (d, 3H, J ) 7.2 Hz, Me-21),
3.71 (s, 3H, -CO2CH3); 13C NMR (CDCl3, 75 MHz) δ 71.7 (d,
C-3), 75.6 (d, C-13), 67.9 (d, C-14).
Da ta for 34: colorless oil; [R]25 -33.1° (c 4.2, CHCl3); IR
D
(neat) 3446, 1716, 1252, 1195, 1151, 1076 cm-1; UV (CHCl3)
λmax 244 nm (ꢀ 400); 1H NMR (CDCl3, 300 MHz) δ 2.14 (m,
1H, H-1), 3.77 (m, 1H, H-3), 5.19 (br t, 1H, J ) 5.1 Hz, H-7),
3.01 (br t, 1H, J ) 9.1 Hz, H-13), 3.80 (m, 1H, H-14), 1.11 (s,
3H, Me-18), 1.52 (s, 3H, Me-19), 0.99 (d, 3H, J ) 6.6 Hz, Me-
20), 3.64 (s, 3H, -CO2CH3); 13C NMR (CDCl3, 75 MHz) δ 40.9
(d, C-1), 30.5 (t, C-2), 80.6 (d, C-3), 73.8 (s, C-4), 42.9 (t, C-5),
22.0 (t, C-6), 128.6 (d, C-7), 131.6 (s, C-8), 39.7 (t, C-9), 22.4 (t,
C-10), 30.3 (t, C-11), 37.4 (d, C-12), 74.5 (d, C-13), 80.6 (d,
C-14), 22.1 (s, C-15), 175.3 (s, C-16), 15.0 (t, C-17), 21.7 (q,
C-18), 15.6 (q, C-19), 16.9 (q, C-20), 13.2 (t, C-21), 51.7 (q, C-22);
HREI-MS m/z [M - H2O]+ calcd for C22H34O4 362.2457, found
362.2469, 362 (6), 344 (14), 167 (31), 149 (90), 93 (53), 83 (100).
Deh yd r a tion of 3,14-Eu p a lm er oic Acid (17) w ith p-
Tolu en esu lfon ic Acid Hyd r a te. To a solution of 17 (99 mg,
0.28 mmol) in dry benzene (15 mL) was added PTSA‚H2O (a
few crystals). The solution was heated to 75 °C for 2 h and
then cooled, quenched with saturated NaHCO3, and extracted
with benzene (3 × 30 mL). The combined organic layers were
washed with brine and concentrated, and the residue was
purified by normal-phase HPLC (Partisil-10, 15% 2-propanol
in hexane) to give 56 mg (60%) of 40 and 19 mg (20%) of 41.
An attempt to prepare δ-lactone 42 by dehydration of 4,14-
eupalmeroic acid (18) under similar reaction conditions fur-
nished unchanged starting material.
Da ta for 35: colorless oil; [R]31 +9.0° (c 0.7, CHCl3); IR
Da ta for 40: colorless oil; [R]25 -1.5° (c 3.4, CHCl3); IR
D
D
(neat) 3439, 1710, 1637, 1273, 1195, 1137 cm-1; UV (MeOH)
(neat) 3568 (sharp), 1709, 1641, 1272, 1234, 1155, 1135, 1093
cm-1; UV (CH3OH) λmax 212 nm (ꢀ 9900); 1H NMR (CDCl3, 300
MHz) δ 2.86 (m, 1H, H-1), 4.15 (dd, 1H, J ) 4.1, 9.4 Hz, H-3),
1.88 (m, 1H, H-7), 2.33 (m, 1H, H-7′), 5.14 (br t, 1H, J ) 8.3
Hz, H-9), 4.43 (dd, 1H, J ) 5.7, 9.5 Hz, H-13), 3.91 (dd, 1H, J
) 5.5, 12.0 Hz, H-14), 5.44 (d, 1H, J ) 2.6 Hz, H-17), 6.37 (d,
1H, J ) 2.8 Hz, H-17′), 1.11 (s, 3H, Me-18), 1.55 (s, 3H, Me-
19), 1.10 (d, 3H, J ) 6.2 Hz, Me-20); 13C NMR (CDCl3, 75 MHz)
δ 40.3 (d, C-1), 29.0 (t, C-2), 88.8 (d, C-3), 74.2 (s, C-4), 27.4 (t,
C-5), 17.7 (t, C-6), 38.7 (t, C-7), 134.4 (s, C-8), 126.9 (d, C-9),
23.6 (t, C-10), 35.9 (t, C-11), 30.4 (d, C-12), 83.7 (d, C-13), 78.8
(d, C-14), 136.7 (s, C-15), 163.8 (s, C-16), 125.1 (t, C-17), 22.6
(q, C-18), 15.1 (q, C-19), 15.2 (q, C-20); HREI-MS m/z [M]+
λ
max 220 nm (ꢀ 35000); 1H NMR (CDCl3, 500 MHz) δ 3.39 (ddd,
1H, J ) 6.9, 9.9, 11.7 Hz, H-1), 4.01 (t, 1H, J ) 8.0 Hz, H-3),
5.21 (br t, 1H, J ) 5.1 Hz, H-7), 2.83 (dd, 1H, J ) 1.2, 9.6 Hz,
H-13), 4.13 (dd, 1H, J ) 1.2, 9.9 Hz, H-14), 6.93 (q, 1H, J )
7.2 Hz, H-17), 1.16 (s, 3H, Me-18), 1.53 (s, 3H, Me-19), 0.98
(d, 3H, J ) 6.6 Hz, Me-20), 1.88 (d, 3H, J ) 7.2 Hz, Me-21),
3.74 (s, 3H, -CO2CH3); 13C NMR (CDCl3, 125 MHz) δ 36.5 (d,
C-1), 31.6 (t, C-2), 82.3 (d, C-3), 73.8 (s, C-4), 43.3 (t, C-5), 22.4
(t, C-6), 128.7 (d, C-7), 131.6 (s, C-8), 39.8 (t, C-9), 22.3 (t, C-10),
30.5 (t, C-11), 37.7 (d, C-12), 74.0 (d, C-13), 80.8 (d, C-14), 131.4
(s, C-15), 167.4 (s, C-16), 140.8 (d, C-17), 21.4 (q, C-18), 15.6
(q, C-19), 16.9 (q, C-20), 14.3 (q, C-21), 51.5 (q, C-22); HREI-

658 J . Org. Chem., Vol. 66, No. 3, 2001
Rodr´ıguez et al.
calcd for C20H30O4 334.2144, found 334.2176, 334 (3), 316 (73),
277 (11), 164 (28), 121 (62), 93 (57), 81 (100).
(d, C-3), 76.0 (s, C-4), 29.7 (t, C-5), 22.7 (t, C-6), 125.8 (d, C-7),
132.1 (s, C-8), 36.4 (t, C-9), 20.3 (t, C-10), 28.8 (t, C-11), 27.8
(d, C-12), 81.0 (d, C-13), 68.3 (d, C-14), 138.6 (s, C-15), 170.0
(s, C-16), 131.5 (t, C-17), 20.6 (q, C-18), 13.7 (q, C-19), 13.9 (q,
C-20), 157.8 (q, C-21), 114.7 (q, C-22), 157.0 (q, C-23), 114.5
(q, C-24). The resonance lines due to C-1 and C-15 were broad
signals of very low intensity. Unfortunately, this compound
decomposed before the HREI mass spectrum could be recorded.
Da ta for 41: colorless oil; 1H NMR (CDCl3, 300 MHz) δ 2.96
(m, 1H, H-1), 4.19 (dd, 1H, J ) 3.5, 9.9 Hz, H-3), 5.28 (dd, 1H,
J ) 5.4, 11.3 Hz, H-9), 4.41 (dd, 1H, J ) 4.8, 11.1 Hz, H-13),
3.97 (dd, 1H, J ) 4.9, 12.3 Hz, H-14), 5.48 (d, 1H, J ) 2.3 Hz,
H-17), 6.42 (d, 1H, J ) 2.8 Hz, H-17′), 1.10 (s, 3H, Me-18),
1.69 (s, 3H, Me-19), 1.16 (d, 3H, J ) 6.5 Hz, Me-20); 13C NMR
(CDCl3, 75 MHz) δ 39.7 (d, C-1), 29.9 (t, C-2), 89.1 (d, C-3),
74.3 (s, C-4), 32.6 (t, C-5), 19.2 (t, C-6), 31.4 (t, C-7), 135.1 (s,
C-8), 125.6 (d, C-9), 27.2 (t, C-10), 32.9 (t, C-11), 36.3 (d, C-12),
83.0 (d, C-13), 79.9 (d, C-14), 137.0 (s, C-15), 163.8 (s, C-16),
125.8 (t, C-17), 21.9 (q, C-18), 23.7 (q, C-19), 17.1 (q, C-20);
HREI-MS m/z [M - H2O]+ calcd for C20H28O3 316.2038, found
316.2056, 316 (25), 277 (16), 111 (48), 97 (46), 81 (60), 57 (100).
Tr iflu or oa cetyla tion of 4,14-Eu p a lm er oic Acid (18).
Trifluoroacetic anhydride (0.6 mL, 4.46 mmol) was added to a
solution of 18 (26 mg, 0.075 mmol) in benzene-d6 (1 mL). After
22 h at 25 °C, the mixture was concentrated. Purification of
the residue by chromatography on silica gel (elution with a
95:5:0.5 mixture of chloroform/MeOH/acetic acid) provided
ditrifluoroacetate 43 as a colorless oil (18 mg, 44%).
Ack n ow led gm en t. This work was supported by
grants from the NSF-EPSCoR, NSF-MRCE, and NIH-
MBRS Programs of the University of Puerto Rico. We
thank Anthony Sostre for assistance during the collec-
tion of Eunicea species and the crew of the R/V Isla
Magueyes for logistic support. We extend our sincere
appreciation to Drs. V. L. Narayanan and Edward
Sausville (NCI) for the cytotoxicity assays on human
cells, and Dr. M. Hollingshead for the in vivo Hollow
Fiber Assay of compound 3. The authors also thank Mr.
Samuel E. Suleiman at U.P.R. for the design of the cover
graphic. The cover photo of Eunicea succinea was taken
by J uan A. Sa´nchez.
Da ta for 43: colorless oil; [R]30 -12.8° (c 3.7, MeOH); IR
D
(neat) 3600-3100 (broad), 1710 (broad), 1621, 1204, 1139, 1069
cm-1; UV (MeOH) λmax 210 nm (ꢀ 5000); 1H NMR (CDCl3, 300
MHz) δ 2.76 (m, 1H, H-1), 4.83 (br t, 1H, J ) 2.6 Hz, H-3),
5.53 (br t, 1H, J ) 9.5 Hz, H-7), 4.57 (d, 1H, J ) 11.0 Hz,
H-13), 4.44 (br d, 1H, J ) 11.0 Hz, H-14), 5.68 (br s, 1H, H-17),
6.48 (br s, 1H, H-17′), 1.30 (s, 3H, Me-18), 1.60 (s, 3H, Me-19),
0.78 (d, 3H, J ) 6.6 Hz, Me-20), 3.30 (br s, exchangeable, OH);
13C NMR (CDCl3, 75 MHz) δ 34.6 (d, C-1), 30.1 (t, C-2), 77.2
Su p p or tin g In for m a tion Ava ila ble: Proposed mecha-
1
nism for the formation of diepoxide 5 and copies of the H and
13C NMR spectra for analogues 4-6, 8-10, 12, 13, 15-18, 20,
21, 23-25, 27, 28, 30, 32, 34, 35, 38, and 40. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O001025J