Synthetic studies on natural diterpenoid glyceryl esters

Article abstract of DOI:10.1016/S0040-4020(00)00097-1

Synthesis of natural bicyclic and tricyclic diterpenoid diacylglycerols has been performed by regioselective coupling of terpenoid acid with glycerol at 1'-sn position. This method may be considered a general approach to obtain optically active acylglycerols. The preparation of ¹³C-labelled geranylgeranoic acid glyceryl esters is also described here. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4020(00)00097-1

TETRAHEDRON
Pergamon
Tetrahedron 56 (2000) 2503–2512
Synthetic Studies on Natural Diterpenoid Glyceryl Esters
†
*
Nicon Ungur, Margherita Gavagnin, Angelo Fontana and Guido Cimino
Istituto per la Chimica di Molecole di Interesse Biologico, CNR, Via Toiano 6, I 80072 Arco Felice (Na), Italy
Received 9 November 1999; revised 5 January 2000; accepted 27 January 2000
Abstract—Synthesis of natural bicyclic and tricyclic diterpenoid diacylglycerols has been performed by regioselective coupling of terpe-
noid acid with glycerol at 10-sn position. This method may be considered a general approach to obtain optically active acylglycerols. The
preparation of 13C-labelled geranylgeranoic acid glyceryl esters is also described here. ᭧ 2000 Elsevier Science Ltd. All rights reserved.
Introduction
tricyclic isocopalane5,6,9 and ent-isocopalane7,9,14,15,17 skele-
tons, including rearranged and functionalized structures.
Terpenoid acylglycerols represent an interesting group of
natural bioactive molecules, which could be considered
the chemical marker of marine dorid nudibranchs belonging
to the related genera Anisodoris, Archidoris, Austrodoris,
Doris and Sclerodoris.1–3 After the first report of farnesyl
glyceryl esters from the skin of Archidoris odhneri,4 an
increasing number of terpenoid diacylglycerols have been
isolated from the mantle of several dorid species in the last
years.5–15 These molecules, which are supposed to be
involved in the chemical defense of nudibranchs, shell-
less molluscs apparently unprotected from predation,
display deterrent and ichthyotoxic properties.6,7 Promising
physiological activities, such as the activation of protein
kinase C in vitro and morphogenetic effects in the
regenerative test in vivo with the fresh water hydrozoan
Hydra vulgaris, have been also reported.16 The majority
of natural terpenoid acylglycerols are structurally character-
ized by the presence of a terpenoid acid residue esterified at
C-10 of glycerol, which is further linked to an acetyl group at
C-20 or C-30. However, a few glyceryl esters with the
terpene moiety linked to the secondary carbon of glycerol
have been also isolated.10,12,17 The S absolute configuration
at C-20 of glycerol has been determined for several 1,3-
diacylglycerols by using different chemical methods18,19 as
well as by synthesis.14,15 Surprisingly, the opposite R stereo-
chemistry at C-20 has been recently reported for two 1,3-
diacylglycerols occurring in an Antarctic nudibranch.19
Terpenoid acylglycerols are likely biosynthesized de novo
by the nudibranch, as has been recently demonstrated in
some Pacific dorid species.20
In the course of our research on marine molluscs, in the last
few years we have directed our interest towards dorid
nudibranchs containing terpenoid acylglycerols. Several
new bicyclic and tricyclic molecules have been isolated
from different dorid species. Among these, an interesting
pair of diastereoisomeric diacylglycerols, exhibiting
enantiomeric terpenoid skeletons (isocopalane and ent-
isocopalane structure), has been also reported.9 The promis-
ing biological activities of terpenoid diacylglycerols have
also prompted synthetic studies with the aim of either
confirming the proposed structures or obtaining larger
quantities of compounds for pharmacological studies. A
series of linear and cyclic optically active terpenoid glyceryl
esters have been prepared. Accounts of this synthetic work,
including the assignment of the absolute stereochemistry of
some natural sesquiterpenoid diacylglycerols, have already
been published.14,15,21–23
Herein, we report the full experimental data on the synthesis
of the natural glyceryl ester derivatives of bicyclic and
tricyclic diterpenoid acids, with the aim at presenting a
survey on our recent studies in this field. In particular, the
preparation of the natural diacylglycerols 1e, 2e, 2i, 3e and
3i, previously isolated from some dorid species, as indicated
in Fig. 1, is described here.
The terpenoid structure is quite variable. However, so far,
the majority of diacylglycerols display either bicyclic
labdane,8,19 halimane,13,19 and copalane14 skeletons, or
Furthermore, the synthesis of the mixture of diastereo-
isomeric glyceryl derivatives of rac-isocopalic acid (2a/
3a), obtained by superacidic cyclization of geranylgeranoic
acid, is reported. Finally, this synthetic method has been
also applied to prepare glyceryl derivatives of geranyl-
geranoic acid labelled with 13C isotope, in order to achieve
Keywords: terpenes and terpenoids; glycerol; marine metabolites; labelling.
* Corresponding author. Tel.: ϩ39-081-8534247; fax: ϩ39-081-8041770;
e-mail: mgavagnin@icmib.na.cnr.it
On leave from Institute of Chemistry, Academy of Sciences, MD-2028
Chisinau, Republic of Moldova.
†
0040–4020/00/$ - see front matter ᭧ 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00097-1

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N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
Figure 1.
suitable precursors for biosynthetic studies of diacyl-
glycerols in dorid nudibranchs. The synthesis of the mono-
glyceryl and the 1,3-diacylglyceryl esters of 3,20-13C2-(all
E)-geranylgeranoic acid (4a) is also described here.
a) preparation of the starting diterpenoid acid;
b) regioselective coupling of the diterpenoid acid
chloride with glycerol at 10-sn position;21
c) regioselective acetylation at C-20 or C-30.22
Steps b and c, which are common for all compounds synthe-
sized, are illustrated in Scheme 1, whereas the preparation
of the starting acids is described below. Overall yields
obtained in the synthesis of natural acylglycerols are
reported in Table 1.
Results and Discussion
Synthetic strategy
The starting diterpenoid acids (1a–4a) were first
transformed into the corresponding chlorides (1b–4b) by
All diterpenoid acylglycerols were synthesized using a
general strategy, which was based on three sequential steps:
Scheme 1. Reagents and conditions: (i) (COCl)2, C6H6, room temperature (2 h), 45ЊC (0.5 h); (ii) (Ϫ)-2,3-O-isopropylidene-sn-glycerol, NaH, dry CH2Cl2, 0ЊC
(20 min), room temperature (10 min); (iii) H2SO4, MeOH, room temperature (4 h); (iv) N-acetylimidazole, DBU, C6H6, room temperature (1 h); (v) 1.1 equiv.
TBDMSCl, dry Pyr, room temperature (12 h); (vi) Ac2O, dry Pyr, room temperature (12 h); (vii) ca. 1.1 equiv. PdCl2(MeCN)2, Me2CO, room temperature
(1 h).

N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
2505
Table 1. Coupling scheme of terpenoid acylglycerols. Overall yields (from starting acids 1a–3a) are reported in brackets
1d (85%)
1e (55%)
1i (56%)
2d (66%)
2e (44%)
2i (40%)
3d (70%)
3e (47%)
3i (49%)
treatment with (COCl)2 in dry C6H6, at room temperature
for 2 h and at 45ЊC for 30 min. The crude chlorides, without
purification, were immediately coupled with (Ϫ)-2,3-O-
isopropylidene-sn-glycerol, by NaH in CH2Cl2, to give
the acetonides 1c–4c. These latter compounds were
subsequently deprotected by 0.006 M H2SO4 in CH3OH to
afford the corresponding monoacylglycerols 1d–4d.21
Acetylation of 1d–4d by N-acetylimidazole (DBU, C6H6)
yielded the 1,3-diacyl glycerols 1e–4e, as main products,
along with the diacetyl derivatives 1f–4f (ratio ca. 3:1).
The 1,2-diacyl glyceryl esters 1i–3i were also synthe-
sized by selective protection with TBDMSCl of the
primary hydroxyl group (compounds 1g–3g), followed
by acetylation of the secondary –OH (compounds 1h–
3h) and subsequent removal of TBDMS group by
PdCl2(CH3CN)2.22
Preparation of starting diterpenoid acids
Bicyclic acylglycerols. Copalic acid (1a) was easily
obtained by hydrolysis of the corresponding methyl ester,
which was isolated from commercial ‘Copaiva Balsam’, as
already reported.14
Tricyclic acylglycerols. The synthetic procedure in Scheme
1 was first carried out using as substrate (rac)-isocopalic
acid (2a/3a) (Scheme 2), which was prepared by superacidic
cyclization of geranylgeranoic acid (5), according to the
literature.24 In order to get the diastereoisomeric pairs
2e–3e and 2i–3i, the mixture of epimeric monoacylgly-
cerols 2d and 3d obtained, was submitted to different
chromatographic techniques. Every attempt to separate the
two compounds failed, so it was decided to perform the
Scheme 2. Reagents and conditions: (i) FSO3H (5 equiv.), i-PrNO2, Ϫ78ЊC, 40 min, then Et3N; (ii) (COCl)2, C6H6, room temperature (2 h), 45ЊC (0.5 h);
(iii) (Ϫ)-2,3-O-isopropylidene-sn-glycerol, NaH, dry CH2Cl2, 0ЊC (20 min), room temperature (10 min); (iv) H2SO4, MeOH, room temperature (4 h).

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N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
Scheme 3. Reagents and conditions: (i) FSO3H (5 equiv.), i-PrNO2, Ϫ78ЊC, 40 min, then Et3N.
synthesis starting from both optically active isocopalic acid
(2a) and ent-isocopalic acid (3a). Compound 2a was
prepared in high yields by superacidic cyclization of natural
copalic acid (1a), whereas 3a was obtained in high yields21
by superacidic cyclization of the bicyclic diterpene acid 6,
previously synthesized from sclareol (7) in five steps24
(Scheme 3).
[1,2-13C2]-(E,E)-farnesylacetone (11). This compound was
submitted to Wittig reaction with trimethylphosphono-
acetate/MeONa, in C6H6, to afford a mixture of the two
isomeric esters 12 (D2 Z) and 13 (D2 E). Finally, the ester
mixture was hydrolyzed by KOH/EtOH to give, after
chromatographic purification on Si-gel, pure (all E) isomer
4a.
Synthesis of 3,20-13C2-(all E)-geranylgeranoic acid (4a).
The 1,3-diacylglyceryl derivative of (all E)-geranylgeranoic
acid (5) was found in the Mediterranean Doris verrucosa
along with a series of bicyclic and tricyclic acylglycerols,
which were suggested to be biogenetically correlated.14
Unfortunately, preliminary incorporation in vivo of labelled
mevalonate25 gave ambiguous results. Therefore, in order to
get suitable precursors for further biosynthetic studies in
vivo in D. verrucosa, the synthesis of the monoglyceryl
and the 1,3-acetylglyceryl derivatives of 3,20-13C2-(all E)-
geranylgeranoic acid (4a), obtained as reported in Scheme
4, has been also planned.
Labelled compounds 10, 11, 4a–4f were characterized by
MS and NMR data. In particular, H NMR spectra were
1
identical with those of the corresponding natural abundance
molecules, except for the signal of the labelled methyl
which resonates as a double doublet (J1ϳ100–140 Hz and
J2ϳ6.0–7.0 Hz) for heteronuclear geminal and vicinal
couplings (see Experimental). On the other side, 13C NMR
spectra were characterized by the presence of two very
intense apparent doublet signals attributed to the geminal
labeled carbons, each other coupled. In addition, expected
13C–13C couplings through two or three bonds27 were also
detected (see Experimental).
According to the literature24,26 for (all E)-geranylgeranoic
acid (5), (E,E)-farnesylbromide (8) was coupled with
[3,4-13C2]-ethyl acetoacetate (9), by Na metal in toluene,
to give [1,2-13C2]-3-ethylcarboxy-(E,E)-farnesylacetone
(10), which was decarboxylated by KOH/EtOH to obtain
Conclusions
In conclusion, we have described a general synthetic
method to prepare in good yield optically active diterpenoid
Scheme 4. Reagents and conditions: (i) 9, Na metal, toluene, reflux 2 h; (ii) KOH, aq. EtOH, reflux 2 h; (iii) (MeO)2P(O)CH2CO2Me, MeONa, C6H6, reflux
1.5 h.

N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
2507
acylglycerols. It has been reported that many of these
natural compounds show potent PKC stimulatory effects
in vitro and PKC morphogenetic properties in vivo in the
Hydra test, suggesting their use as molecular probes for cell
development studies.16 The synthetic approach here
described opens a very easily accessible way to better
investigate such interesting pharmacological activities.
(from petr. ether); [a]Dˆϩ7.2Њ (c 0.11, CHCl3); IR: nmax
(liquid film) 3500, 1715 cmϪ1; 1H NMR (400 MHz, selected
values) dH: 0.81 (3H, s, H3-18), 0.86 (3H, s, H3-19), 0.91
(3H, s, H3-20), 0.97 (3H, s, H3-17), 1.67 (3H, bs, H3-16),
2.93 (1H, bs, H-14), 5.54 (1H, bs, H-12); 13C NMR
(100 MHz) dC: 177.1 (C-15), 128.4 (C-13), 124.4 (C-12),
62.1 (C-14), 56.4 (C-5), 54.2 (C-9), 41.8 (2C, C-3 and C-7),
39.9 (C-1), 37.4 (C-8), 36.4 (C-10), 33.4 (C-19), 33.1 (C-4),
22.6 (C-11), 21.6 (C-18), 21.2 (C-16), 18.6 (C-2 or C-6),
18.5 (C-6 or C-2), 15.8 (C-20), 15.5 (C-17); HRMS calcd
for C20H32O2 (Mϩ) m/z 304.2402, found 304.2410.
Experimental
General procedures
(Ϫ)-ent-Isocopalic acid 3a. Using the procedure above
described and as already reported in Ref. 21, acid 6
(152 mg, 0.50 mmol) was dissolved in i-PrNO2 (3 ml),
cooled at Ϫ78ЊC and treated with FSO3H (260 mg,
2.60 mmol) in i-PrNO2 (1.5 ml), under stirring. After
40 min, a solution of Et3N (3 ml) in petroleum ether
(1.5 ml) was added. The reaction mixture was extracted
and after removing of the solvent, the residue was chroma-
tographed on a silica gel column (2.5 g, petr. ether–Et2O,
97:3) to give 140 mg (92%) of (Ϫ)-ent-isocopalic acid 3a:
colorless crystals, mp 177–178ЊC (from petr. ether);
Melting points were measured on a Kofler apparatus and are
uncorrected. The IR spectra were taken on a Bio-Rad FTS 7
spectrophotometer. 1H and 13C NMR spectra were recorded
in CDCl3 on Bruker WM 500, Bruker AM 400 and Bruker
WM 300 spectrometers; chemical shifts are reported in ppm
and are referred to CHCl3 as internal standard (d 7.26 for
proton and d 77.0 for carbon). Optical rotations were
measured in CHCl3 on a Jasco DIP 370 polarimeter, using
a 10-cm cell. EIMS spectra were recorded on a Carlo Erba
TRIO 2000 spectrometer, coupled with an INTEL com-
puter. HREIMS spectra of labelled compounds were
obtained on a VG 70–70 EQ-HF instrument with manual
peak-matching technique, using the appropriate PKF
peaks as internal reference. Commercial Merck Si gel 60
(70–230 mesh ASTM) was used for column chromato-
graphy, and Merck precoated Si gel plates were used for
TLC. The chromatograms were sprayed with 0.1%
Ce(SO4)2 in 2N H2SO4 and heated at 80ЊC for 5 min to
detect the spots. The work-up of the reaction mixtures in
organic solvents included exhaustive extraction with diethyl
ether and washing with water, up to neutral reaction, drying
over anhydrous Na2SO4, filtration, and removal of the
solvent in vacuo. Acid solutions were also washed with
saturated NaHCO3 water solutions and water, up to neutral
reaction, and dried over anhydrous Na2SO4. [3,4-13C2]-ethyl
acetoacetate (13C 99%) was purchased by Trimital s.r.l. Co.
(Milan, Italy).
1
[a]DˆϪ9.1Њ (c 0.30, CHCl3); IR, H and 13C NMR data
were identical with those of 2a.
(rac)-Isocopalic acid 2a/3a. A solution of FSO3H (330 mg,
3.30 mmol) in i-PrNO2 (1.9 ml) was added at Ϫ78ЊC, under
stirring, to 200 mg (0.66 mmol) of E,E,E-geranylgeranoic
acid 5 in i-PrNO2 (4 ml), according to the above procedure.
The usual work up yielded 199 mg of a crude residue, which
was purified on a silica gel column (4.5 g, petr. ether–Et2O,
97:3) to give 171 mg (85%) of (rac)-isocopalic acid 2a/3a:
colorless crystals, mp 174–176ЊC (from petr. ether); IR, 1H
and 13C NMR data were identical with those of isocopalic
acid 2a and ent-isocopalic acid 3a.
3,20-13C2-E,E,E-geranylgeranoic acid 4a. (a) 1,2-13C2-3-
ethylcarboxy-E,E-farnesylacetone 10: To a solution of
3,4-13C2-ethyl acetoacetate (9, 1.0 g, 7.58 mmol) in dry
toluene (15 ml), 176 mg (7.65 equiv.) of sodium were
added, under Ar atmosphere. After complete dissolving of
sodium, the solution was treated with E,E-farnesylbromide
(8, 1.9 g, 6.67 mmol) in dry toluene (9.3 ml). The reaction
mixture was refluxed for 2 h and then stopped. The usual
work-up yielded 2.1 g of a crude residue, which was purified
on a silica gel column (45 g) (petr. ether–Et2O, 97:3) to give
1.45 g (65%) of 1,2-13C2-3-ethylcarboxy-E,E-farnesylace-
tone (10): colorless oil; IR: nmax (liquid film) 1730,
Preparation of starting acids
Copalic acid 1a. Copalic acid methyl ester (220 mg,
0.692 mmol) was isolated from commercial ‘Copaiva
Balsam’ as reported in Ref. 14. The ester was treated with
5% ethanolic solution of NaOH (5.5 ml), and the mixture
was heated under reflux for 1.5 h. The crude product
(256 mg), obtained after the usual work up, was purified
on a silica gel column (5.5 g, petr. ether–Et2O, 93:7) to
give 152 mg (72%) of pure copalic acid 1a: colorless oil;
[a]Dˆϩ7.2Њ (c 0.31, CHCl3), lit.28 [a]Dˆϩ6.9Њ (c 1.15,
CHCl3).
1
1684 cmϪ1; H NMR (400 MHz, selected values) dH: 1.26
(3H, t, Jˆ7.1 Hz, CH2CH3), 1.58 (3H, s, H3-17 or H3-18),
1.59 (3H, s, H3-18 or H3-17), 1.62 (3H, s, H3-16), 1.67 (3H,
s, H3-15), 2.21 (3H, dd, JCHˆ128 and 6 Hz, H3-1ء), 4.17
(2H, q, Jˆ7.1 Hz, CH2–CH3), 5.05 (3H, m, H-5, H-9 and
H-13); 13C NMR (100 MHz) dC: 203.1 (apparent d,
Jˆ42 Hz, Cء-2), 172.0 (C-19), 138.4 (C-6), 135.2 (C-10),
131.3 (C-14), 124.3 (C-13 or C-9), 123.8 (C-9 or C-13),
119.6 (C-5), 61.2 (CH2CH3), 59.6 (dd, Jˆ38 and 13 Hz,
C-3), 39.7 (2C, C-7 and C-11), 29.1 (apparent d,
Jˆ42 Hz, Cء-1), 26.9 (C-12 or C-8 or C-4), 26.7 (C-8 or
C-4 or C-12), 26.5 (C-4 or C-8 or C-12), 25.7 (C-15), 18.4
(C-17), 17.6 (C-16), 16.0 (C-18, d, Jˆ3.8 Hz), 14.1
(CH2CH3); MS, m/z (%): 336 (Mϩ, 14), 291 (9), 275 (8),
(ϩ)-Isocopalic acid 2a. A solution of copalic acid 1a
(35 mg, 0.115 mmol) in i-PrNO2 (0.7 ml) was cooled at
Ϫ78ЊC and treated with FSO3H (58 mg, 0.58 mmol) in
i-PrNO2 (0.3 ml), under stirring. After 40 min, the reaction
was stopped by adding a solution of Et3N (1 ml) in petro-
leum ether (1 ml). The usual work up gave 35 mg of a crude
residue, which was purified on a silica gel column (0.6 g)
(petr. ether–Et2O, 97:3) to give 28.4 mg (81%) of (ϩ)-
isocopalic acid 2a: colorless crystals, mp 176–177.5ЊC

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N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
249 (10), 212 (15), 199 (42), 175 (30), 161 (63), 155 (100),
137 (78); HRMS calcd for C1913C2H34O3 (Mϩ) m/z
336.2575, found 336.2561. (b) 1,2-13C2-E,E-farnesyl-
acetone 11: 1,2-13C2-3-Ethylcarboxy-E,E-farnesylacetone
(10, 1.44 g, 4.29 mmol) was dissolved in 5.5 ml of EtOH
and 8.5 ml of 10% KOH/EtOH solution were added. The
reaction mixture was refluxed for 2 h. After the usual work-
up, 1.11 g of a crude residue was obtained and purified on a
silica gel column (23 g) (petr. ether–Et2O, 7:3) to give
952 mg (84%) of 1,2-13C2-E,E-farnesylacetone (11): color-
and the solution was added to 0.11 ml (1.26 mmol) of
(COCl)2 in 0.8 ml of dry C6H6, under Ar atmosphere. The
reaction mixture was stirred at room temperature, for 2 h
and at 45ЊC, for 30 min. Both the solvent and the unreacted
oxalyl chloride were removed in vacuo to give 80.4 mg of
crude chloride 1b, which was used in the next step without
any purification. A suspension of NaH (27 mg, 0.92 mmol,
80% dispersed in mineral oil) and 0.1 ml of dry pyridine
were added to a solution of (Ϫ)-2,3-O-isopropylidene-sn-
glycerol (120 mg, 0.91 mmol) in 3.3 ml of anhydrous
CH2Cl2, at 0ЊC, under an Ar atmosphere. The mixture was
stirred for 10 min and then crude 1c (80.4 mg, 0.25 mmol)
in 1.6 ml of anhydrous CH2Cl2 was added. The reaction
mixture was stirred at 0ЊC for 20 min and at room tempera-
ture for 10 min. After the usual work-up, the crude residue
(101.4 mg) was purified on a silica gel column (petr. ether–
Et2O, 93:7) to give 96.2 mg (92%) of acetonide 1c: colorless
oil; [a]DˆϪ10.8Њ (c 0.65, CHCl3); IR: nmax (liquid film)
less oil; IR: nmax (liquid film) 1675 cmϪ1 1H NMR
;
(400 MHz, selected values) dH: 1.58 (3H, s, H3-17 or
H3-18), 1.59 (3H, s, H3-18 or H3-17), 1.62 (3H, s, H3-16),
1.67 (3H, s, H3-15), 2.13 (3H, dd, JCHˆ127 and 6 Hz,
H3-1ء), 5.08 (3H, m, H-5, H-9 and H-13); 13C NMR
(100 MHz) dC: 208.9 (apparent d, Jˆ40 Hz, Cء-2), 136.4
(C-6 or C-10), 133.0 (C-10 or C-6), 131.2 (C-14), 124.3
(C-13), 124.0 (C-9), 122.5 (C-5), 43.7 (dd, Jˆ39 and
13 Hz, C-3), 39.7 (C-11 or C-7), 39.6 (C-7 or C-11), 29.9
(apparent d, Jˆ40 Hz, Cء-1), 26.7 (C-12 or C-7 or C-4), 26.6
(C-8 or C-12 or C-4), 26.5 (C-4 or C-8 or C-12), 25.7
(C-15), 17.7 (C-16), 16.0 (2C, C-17 and C-18); MS, m/z
(%): 264 (Mϩ, 5), 225 (40), 209 (41), 207 (88), 169 (8),
142 (42), 97 (100), 83 (26), 69 (22), 57 (68); HRMS calcd
for C1613C2H30O (Mϩ) m/z 264.2364, found 264.2369. (c)
3,20-13C2-E,E,E-geranylgeranoic acid 4a: A solution of
sodium methoxide in methanol [248 mg (10.78 equiv.) of
sodium metal in 6.1 ml of methanol] was slowly added to
a stirred solution of ketone 11 (940 mg, 3.56 mmol) and
trimethylphosphonoacetate (1.97 g, 10.82 mmol) in
benzene (80 ml). After refluxing 1.5 h, the mixture was
cooled, treated with ice-water and extracted with Et2O.
The residue (1.11 g), obtained after the usual work-up,
contained a mixture of the isomeric esters 12 and 13 and
was used in the next step without any purification. The
mixture of the esters 12 and 13 (1.11 g) was dissolved in
4 ml of EtOH and 7 ml of 10% KOH/EtOH solution (7.0 ml)
were added. The reaction mixture was refluxed for 2 h. The
usual work-up yielded 1.01 g of crude reaction product,
which was purified by SiO2 chromatography (petr. ether–
Et2O gradient as eluent) to give 470 mg of a mixture
containing the E,E,E-isomer acid 4a and the Z,E,E-isomer
acid 14, along with 280 mg of pure 4a: colorless oil; IR:
1
1723, 1382, 1228, 1145, 1066, 890, 850 cmϪ1; H NMR
(300 MHz, selected values) dH: 0.67 (3H, s, H3-20), 0.80
(3H, s, H3-18), 0.87 (3H, s, H3-19), 1.37 (3H, s, H3-aceto-
nide), 1.43 (3H, s, H3-acetonide), 2.16 (3H, bs, H3-16), 3.75
(1H, m, H-30a), 4.09 (1H, m, H-30b), 4.06–4.22 (2H, m,
H2-10), 4.33 (1H, m, H-20), 4.47 (1H, bs, H-17a), 4.83
(1H, bs, H-17b), 5.69 (1H, bs, H-14); 13C NMR
(100 MHz) dC: 166.5 (C-15), 162.3 (C-13), 148.3 (C-8),
114.6 (C-14), 109.9 [(O)2C(CH3)2], 106.3 (C-17), 73.8
(C-20), 66.5 (C-10), 63.9 (C-30), 56.2 (C-9), 55.5 (C-5),
42.1 (C-3), 39.9 (C-12), 39.7 (C-10), 39.0 (C-1), 38.3
(C-7), 33.6 (2C, C-4 and C-19), 26.7 (Me-acetonide), 25.4
(Me-acetonide), 24.4 (C-6), 21.7 (C-18), 21.5 (C-11), 19.4
(C-2), 19.1 (C-16), 14.5 (C-20); MS, m/z (%): 418 (Mϩ, 5),
403 (25), 360 (29), 345 (48), 286 (16), 271 (19), 244 (63),
169 (83), 156 (100); HRMS calcd for C26H42O4 (Mϩ) m/z
418.3083, found 418.3075.
Compound 2c. Following the procedure above reported for
1c, 27.4 mg (0.09 mmol) of isocopalic acid 2a were treated
with 43.6 mg (0.33 mmol) of (Ϫ)-2,3-O-isopropylidene-sn-
glycerol to give, after purification, 30.4 mg (81%) of
acetonide 2c: colorless oil; [a]DˆϪ4.5Њ (c 0.07, CHCl3);
IR: nmax (liquid film) 1735, 1636, 1236, 1050, 841 cmϪ1
;
1H NMR (400 MHz, selected values) dH: 0.81 (3H, s,
H3-18), 0.86 (3H, s, H3-19), 0.90 (3H, s, H3-20), 0.94 (3H,
s, H3-17), 1.37 (3H, s, H3-acetonide), 1.43 (3H, s, H3-
acetonide), 1.60 (3H, d, Jˆ1.4 Hz, H3-16), 2.94 (1H, bs,
H-14), 3.77 (1H, dd, Jˆ6.3 and 8.5 Hz, H-30a), 4.08 (1H,
m, H-30b), 4.10–4.18 (2H, m, H2-10), 4.31 (1H, m, H-20),
5.51 (1H, bs, H-7); 13C NMR (100 MHz) dC: 124.1 (C-12),
106.3 [(O)2C(CH3)2], 73.8 (C-20), 66.7 (C-10), 64.2 (C-30),
62.5 (C-14), 56.4 (C-5), 54.3 (C-9), 41.8 (C-3), 41.7 (C-7),
39.9 (C-1), 38.3 (C-10), 37.4 (C-8), 33.4 (C-19), 33.2 (C-4),
26.8 (Me-acetonide), 25.4 (Me-acetonide), 22.7 (C-11), 21.7
(C-18), 21.2 (C-16), 18.6 (C-2), 18.4 (C-6), 15.6 (C-20), 15.5
(C-17), (C-13 and C-15 were not detected); MS, m/z (%): 418
(Mϩ, 10), 403 (61), 360 (100), 345 (30), 286 (51), 271 (33),
258 (35), 192 (90), 177 (95), 156 (99); HRMS calcd for
C26H42O4 (Mϩ) m/z 418.3083, found 418.3077.
;
nmax (liquid film) 1683, 1614, 1236 cmϪ1 1H NMR
(400 MHz, selected values) dH: 1.60 (6H, bs, H3-16 and
H3-18), 1.61 (3H, bs, H3-19), 1.68 (3H, bs, H3-17), 2.20
(3H, dd, JCHˆ108 and 7 Hz, H3-20), 5.09 (3H, m, H-6,
H-10 and H-14), 5.69 (1H, d, JCHˆ8 Hz, H-2); 13C NMR
(100 MHz) dC: 171.7 (C-1), 162.9 (apparent d, Jˆ40 Hz,
Cء-3), 136.3 (C-7), 135.1 (C-11), 131.2 (C-15), 124.4
(C-14), 124.1 (C-10), 122.7 (C-6), 115.1 (d, Jˆ72 Hz,
C-2), 41.2 (d, Jˆ39 Hz, C-4), 39.7 (2C, C-8 and C-12),
26.8 (C-13 or C-9), 26.6 (C-9 or C-13), 25.7 (2C, C-5 and
C-17), 19.1 (apparent d, Jˆ40 Hz, Cء-20), 17.7 (C-16), 16.0
(2C, C-18 and C-19). MS, m/z (%): 306 (Mϩ, 6), 263 (5),
220 (5), 205 (18), 191 (12), 177 (11), 149 (21), 136 (100),
123 (95), 109 (52); HRMS calcd for C1813C2H32O2 (Mϩ) m/z
306.2469, found 306.2447.
Compound 3c. See Ref. 21.
Preparation of acetonides 1c–4c
Mixture of compounds 2cϩ3c. Following the procedure
above described for 1c, 150 mg (0.49 mmol) of (rac)-iso-
Compound 1c. In a typical procedure, copalic acid (1a,
76 mg, 0.25 mmol) was dissolved in 0.8 ml of dry C6H6

N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
2509
copalic acid (2a/3a) reacted with 225 mg (1.70 mmol) of
(Ϫ)-2,3-O-isopropylidene-sn-glycerol to give 172 mg
(83%) of an unseparable diastereoisomeric mixture of
acetonides 2cϩ3c.
Et2O–petr. ether); [a]Dˆϩ7.6Њ (c 0.36, CHCl3);‡ IR: nmax
1
(liquid film) 3421, 1730, 1636, 1390, 1166, 1050 cmϪ1; H
NMR (400 MHz, selected values) dH: 0.81 (s, 3H, H3-18),
0.86 (s, 3H, H3-19), 0.90 (s, 3H, H3-20), 0.94 (s, 3H, H3-17),
1.60 (s, 3H, H3-16), 2.95 (1H, bs, H-14), 3.60–3.72 (2H, m,
H2-30), 3.94 (1H, bs, H-20), 4.13-4.26 (2H, m, H2-10), 5.53
(1H, bs, H-12); 13C NMR (100 MHz) dC: 173.5 (C-15),
128.4 (C-13), 124.4 (C-12), 70.3 (C-20), 65.1 (C-30), 63.5
(C-10), 62.5 (C-14), 56.4 (C-5), 54.2 (C-9), 41.8 (2C, C-3
and C-7), 39.8 (C-1), 37.4 (C-8), 36.6 (C-10), 33.4 (C-19),
33.1 (C-4), 22.6 (C-11), 21.6 (C-18), 21.2 (C-16), 18.6 (C-2
or C-6), 18.5 (C-6 or C-2), 15.7 (C-20), 15.6 (C-17); MS,
m/z (%): 378 (Mϩ, 5), 360 (10), 345 (5), 286 (27), 258 (18),
192 (85), 177 (100), 149 (63), 12; HRMS calcd for C23H38O4
(Mϩ) m/z 378.2770, found 378.2761.
Compound 4c. According to the procedure above reported
for 1c, 160 mg (0.52 mmol) of 3,20-13C2-E,E,E-geranyl-
geranoic acid (4a) were treated with 248.5 mg
(1.88 mmol) of (Ϫ)-2,3-O-isopropylidene-sn-glycerol to
give 190.7 mg (87%) of acetonide 4c: colorless oil; IR:
1
nmax (liquid film) 1714, 1197 cmϪ1; H NMR (400 MHz,
selected values) dH: 1.37 (3H, s, H3-acetonide), 1.43 (3H,
s, H3-acetonide), 1.59 (9H, bs, H3-16, H3-18 and H3-19),
1.67 (3H, bs, H3-17), 2.16 (3H, dd, JCHˆ134 and 6 Hz,
H3-20), 3.75 (1H, dd, Jˆ8.2 and 6.3 Hz, H-30a), 4.11–
4.07 (2H, m, H-10a and H-30b), 4.18 (1H, dd, Jˆ11.5 and
4.7 Hz, H-10b), 4.33 (1H, m, H-20), 5.09 (3H, m, H-6, H-10
and H-14), 5.71 (1H, d, JCHˆ8 Hz, H-2); 13C NMR
(100 MHz) dC: 166.4 (C-1), 161.2 (apparent d, Jˆ40 Hz,
Cء-3), 136.2 (C-7), 135.0 (C-11), 131.2 (C-15), 124.3
(C-14), 124.0 (C-10), 122.8 (C-6), 114.4 (dd, Jˆ109 and
72 Hz, C-2), 109.7 [(O)2C(CH3)2], 73.8 (C-20), 66.5
(C-10), 63.9 (C-30), 41.0 (d, Jˆ39 Hz, C-4), 39.7 (2C,
C-8 and C-12), 26.7 (C-13 or C-9), 26.6 (C-9 or C-13),
25.9 (C-5), 25.6 (C-17), 25.4 (Me-acetonide), 25.2
(Me-acetonide), 18.9 (apparent d, Jˆ40 Hz, Cء-20),
17.7 (C-16), 16.0 (2C, C-18 and C-19); MS, m/z (%):
420 (Mϩ, 7), 405 (78), 362 (27), 293 (38), 239 (12),
225 (43), 200 (40), 171 (35), 158 (100), 136 (91);
HRMS calcd for C2413C2H42O4 (Mϩ) m/z 420.3150,
found 420.3113.
Compound 3d. See Ref. 21.
Mixture of compounds 2dϩ3d. Following the procedure
reported for 1d, 100 mg (0.24 mmol) of the mixture of
acetonides 2cϩ3c afforded, after deprotection by 0.006 M
H2SO4/MeOH (4.3 ml), 74 mg (83%) of an unseparable
diastereoisomeric mixture of diols 2dϩ3d.
Compound 4d. According to the procedure above reported
for 1d, 140 mg (0.33 mmol) of acetonide 4c afforded, after
deprotection by 0.006 M H2SO4/MeOH (6.0 ml), 102 mg
(81%) of diol 4d: colorless oil; IR: nmax (liquid film)
1707, 1197 cmϪ1 1H NMR (400 MHz, selected values)
;
dH: 1.59 (6H, bs, H3-16 and H3-18), 1.60 (3H, bs, H3-19),
1.67 (3H, bs, H3-17), 2.16 (3H, dd, JCHˆ133 and 6 Hz, H3-
20), 3.59–3.71 (2H, m, H2-30), 3.94 (1H, m, H-20), 4.17 (1H,
dd, Jˆ6.1 and 11.7 Hz, H-10a), 4.22 (1H, dd, Jˆ4.8 and
11.7 Hz, H-10b), 5.09 (3H, m, H-6, H-10 and H-14), 5.70
(1H, d, JCHˆ7.9 Hz, H-2); 13C NMR (100 MHz) dC: 167.1
(C-1), 162.0 (apparent d, Jˆ40 Hz, Cء-3), 136.3 (C-7),
135.1 (C-11), 131.3 (C-15), 124.3 (C-14), 124.0 (C-10),
122.7 (C-6), 114.1 (dd, Jˆ100 and 72 Hz, C-2), 70.4
(C-20), 64.5 (C-10or C-30), 63.3 (C-30or C-10), 41.0 (d,
Jˆ39 Hz, C-4), 39.7 (2C, C-8 and C-12), 26.7 (C-13 or
C-9), 26.6 (C-9 or C-13), 25.9 (C-5), 25.7 (C-17), 19.0
(apparent d, Jˆ40 Hz, Cء-20), 17.6 (C-16), 16.0 (2C, C-18
and C-19); MS, m/z (%): 380 (Mϩ, 5), 288 (10), 245 (8), 219
(11), 205 (18), 191 (21), 176 (38), 136 (90), 123 (92), 81
(100); HRMS calcd for C2113C2H38O4 (Mϩ) m/z 380.2837,
found 380.2847.
Preparation of diols 1d–4d
Compound 1d. In a typical procedure, compound 1c
(83.7 mg, 0.20 mmol) was dissolved in 0.4 ml of MeOH
and 0.006 M H2SO4/MeOH (3.7 ml) was added at room
temperature in Ar atmosphere. The mixture was stirred at
room temperature for 4 h. The usual work up gave 77.2 mg
of a crude residue, which was purified on a silica gel
column (petr. ether–Et2O, 1:2) to give 70.8 mg (94%)
of diol 1d: colorless oil; [a]DˆϪ9.1Њ (c 0.91, CHCl3);
IR: nmax 3410, 1711, 1390, 1224, 1150, 1050, 890,
850 cmϪ1 1H NMR (300 MHz, selected values) dH:
;
0.68 (3H, s, H3-20), 0.80 (3H, s, H3-18), 0.87 (3H, s,
H3-19), 2.16 (3H, bs, H3-16), 3.66 (2H, m, H2-30), 3.94
(1H, m, H-20), 4.20 (2H, m, H2-10), 4.48 (1H, bs, H-
17a) and 4.84 (1H, bs, H-17b), 5.68 (1H, bs, 1H, H-14);
13C NMR (75 MHz) dC: 167.2 (C-15), 163.2 (C-13),
148.3 (C-8), 114.3 (C-14), 106.3 (C-17), 70.4 (C-20),
64.5 (C-10), 63.4 (C-30), 56.2 (C-9), 55.5 (C-5), 42.1
(C-3), 40.0 (C-12), 39.7 (C-10), 39.1 (C-1), 38.3 (C-7),
33.6 (2C, C-4 and C-19), 24.4 (C-6), 21.7 (C-18),
21.5 (C-11), 19.4 (C-2), 19.2 (C-16), 14.5 (C-20); MS,
m/z (%): 378 (Mϩ, 5), 363 (36), 347 (7), 305 (12), 286
(21), 271 (53), 258 (54), 244 (92), 174 (87), 137 (100);
HRMS calcd for C23H38O4 (Mϩ) m/z 378.2770, found
378.2778.
Preparation of 1,3 diacyl derivatives 1e–4e
Selective acetylation of diol 1d. In a typical procedure
1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU, 3.1 mg, 0.02
mmol) and N-acetylimidazole (9.6 mg, 0.09 mmol) were
added to a solution of diol 1d (30.3 mg, 0.08 mmol) in dry
C6H6 (0.5 ml). The mixture was stirred under Ar atmosphere
at room temperature for 1 h, then the reaction was stopped
by adding 1 ml of H2O. After usual work-up the solvent
was removed in vacuo and the residue (30.1 mg) was
‡
[a]D of compound 2d was obviously opposite in sign to that of compound
Compound 2d. According to the procedure above described
for 1d, 21 mg (0.05 mmol) of acetonide 2c afforded, after
deprotection by 0.006 M H2SO4/MeOH (0.9 ml), 15.5 mg
(82%) of diol 2d: colorless crystals, mp 132–134ЊC (from
ent-2d (Ref. 21), but surprisingly differed also in its absolute value. This
apparent conflictual result is due to the wrong report in Ref. 21 of the [a]D
of compound ent-2d: [a]DˆϪ5.2 (c 0.25, CHCl3), reported value
Ϫ51.8 (c 0.25, CHCl3).

2510
N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
chromatographed on SiO2 column by elution with petr.
ether/Et2O gradient giving, in order of increasing polarity,
6.9 mg (22%) of diacetate 1f, 18.7 mg (64%) of 1,3-diacyl-
glycerol 1e, which showed spectral data identical with those of
natural verrucosin-5,14 and 4.2 mg (14%) of starting diol 1d.
DBU, and 11.0 mg (0.10 mmol) of N-acetylimidazole,
35.5 mg of crude reaction product, which was purified by
SiO2 chromatography (petr. ether–Et2O gradient as eluent)
to give, in order of increasing polarity, diacetate 3f (8.1 mg,
21%), 1,3-diacylglycerol 3e (22.8 mg, 67%), which showed
spectral data identical with those of natural 3e,6 and starting
diol 3d (4.1 mg, 12%).
1f. Colorless oil; [a]DˆϪ15.2Њ (c 0.41, CHCl3); IR: nmax
(liquid film) 1750, 1710, 1646, 1373, 1223, 1142, 1058,
1
888 cmϪ1; H NMR (300 MHz) dH: 0.69 (3H, s, H3-20),
3f. Colorless oil; [a]DˆϪ42.0Њ (c 0.13, CHCl3); IR: nmax
1
0.80 (3H, s, H3-18), 0.87 (3H, s, H3-19), 2.07 (3H, s,
OAc), 2.09 (3H, s, OAc), 2.15 (3H, s, H3-16), 4.10-4.35
(4H, m, H2-30 and H2-10), 4.49 (1H, bs,H-17a), 4.85 (1H,
bs,H-17b), 5.28 (1H, m, H-20), 5.64 (1H, bs, H-14); MS, m/z
(%): 462 (Mϩ, 2), 447 (4), 387 (3), 305 (3), 286 (35), 271
(49), 258 (62), 198 (92), 159 (100), 137 (98).
(liquid film) 1749, 1375, 1224 cmϪ1; H NMR (400 MHz,
selected values) dH: 0.81 (3H, s, H3-18), 0.87 (3H, s, H3-19),
0.90 (3H, s, H3-20), 0.93 (3H, s, H3-17), 1.58 (3H, bs, H3-
16), 2.08 (6H, s, 2OAc), 2.93 (1H, bs, H-14), 4.16–4.34
(4H, m, H2-10 and H2-30), 5.26 (1H, m, H-20), 5.53 (1H,
m, H-12); MS, m/z (%): 286 (MϩϪC7H12O5, 83), 271
(23), 258 (25), 243 (9), 192 (79), 177 (89), 159 (100), 149
(39), 123 (76); HRMS calcd for C20H30O (MϩϪC7H12O5)
m/z 286.2297, found 286.2306.
1e. Colorless oil; [a]DˆϪ15.9Њ (c 0.27, CHCl3); {[a]D
natural 1e Ϫ12.6Њ (c 0.26; CHCl3)}14; IR: nmax (liquid
1
film) 3421, 1733, 1722, 1637, 1228, 1150, 888 cmϪ1; H
NMR (400 MHz, selected values) dH: 0.68 (3H, s, H3-20),
0.80 (3H, s, H3-18), 0.87 (3H, s, H3-19), 2.11 (3H, s, OAc),
2.17 (3H, d, Jˆ0.8 Hz, H3-16), 2.51 (1H, d, Jˆ5.0 Hz,
–OH), 4.12–4.22 (5H, m, H2-10, H-20 and H2-30), 4.48
(1H, bs, H-17a), 4.84 (1H, bs, H-17b), 5.68 (1H, bs,
H-14); 13C NMR (100 MHz) dC: 166.8 (C-15), 163.0
(C-13), 148.3 (C-8), 114.3 (C-14), 68.5 (C-20), 65.4
(C-30), 64.5 (C-10), 56.3 (C-9), 55.5 (C-5), 42.1 (C-3),
40.0 (C-12), 39.7 (C-10), 39.1 (C-1), 38.3 (C-7), 33.6
(C-4), 24.4 (C-6), 21.5 (C-11), 20.8 (OAc), 19.4 (C-2).
3e. Colorless crystals, mp 116.5–119ЊC (from Et2O–petr.
ether) lit.6 mp 117–119ЊC (hexane–Et2O); [a]DˆϪ47.7Њ (c
0.21; CHCl3) {[a]D natural 3e Ϫ53.7Њ (c 0.13, CHCl3)};6 IR:
nmax (liquid film) 1738, 1266, 1158 cmϪ1
;
1H NMR
(300 MHz, selected values) dH: 0.82 (3H, s, H3-18), 0.87
(3H, s, H3-19), 0.91 (3H, s, H3-20), 0.95 (3H, s, H3-17), 1.57
(3H, s, H3-16), 2.11 (3H, s, OAc), 2.96 (1H, bs, H-14),
4.09–4.19 (5H, m, H2-10, H-20 and H2-30), 5.53 (1H, m,
H-12).
Selective acetylation of diol 4d. Following the procedure
described for 1d, 70 mg (0.18 mmol) of diol 4d afforded,
after treatment with 7.0 mg (0.05 mmol) of DBU, and
21.9 mg (0.20 mmol) of N-acetylimidazole, 68.5 mg of
crude reaction product, which was purified by SiO2 chroma-
tography (petr. ether–Et2O gradient as eluent) to give, in
order of increasing polarity, diacetate 4f (12 mg, 16%),
1,3-diacylglycerol 4e (43.4 mg, 65%), and starting diol 4d
(10.1 mg, 14%).
Selective acetylation of diol 2d. According to the proce-
dure above reported for 1d, 16 mg (0.04 mmol) of diol 2d
afforded, after treatment with 1.6 mg (0.01 mmol) of DBU
and 5.0 mg (0.05 mmol) of N-acetylimidazole, 15.7 mg of
crude reaction product, which was purified by SiO2 chroma-
tography (petr. ether–Et2O gradient as eluent) to give, in
order of increasing polarity, diacetate 2f (3.3 mg, 20%),
1,3-diacylglycerol 2e (9.9 mg, 65%), which showed spectral
data identical with those of natural 2e,9 and starting diol 2d
(2.3 mg, 14%).
4f. Colorless oil; IR: nmax (liquid film) 1745 (broad),
1
1220 cmϪ1; H NMR (400 MHz, selected values) dH: 1.59
2f. Colorless oil; [a]Dˆϩ54.5Њ (c 0.07, CHCl3); IR: nmax
(6H, bs, H3-16 and H3-18), 1.60 (3H, bs, H3-19), 1.67 (3H,
bs, H3-17), 2.07 (3H, s, OAc), 2.09 (3H, s, OAc), 2.15 (3H,
dd, JCHˆ118 and 6 Hz, H3-20), 4.14–4.21 (2H, m, H-10a
and H-30a), 4.27–4.33 (2H, m, H-10b and H-30b), 5.09
(3H, m, H-6, H-10 and H-14), 5.27 (1H, m, H-20), 5.68
(1H, d, JCHˆ7.5 Hz, H-2); 13C NMR (100 MHz) dC: 170.5
(CH3CO), 170.1 (CH3CO), 166.0 (C-1), 161.6 (apparent d,
Jˆ40 Hz, Cء-3), 136.3 (C-7), 135.0 (C-11), 131.2 (C-15),
124.3 (C-14), 124.0 (C-10), 122.7 (C-6), 114.3 (dd, Jˆ73.5
and 73.9 Hz, C-2), 69.3 (C-20), 62.4 (C-30 or C-10), 61.3
(C-10 or C-30), 41.0 (d, Jˆ39 Hz, C-4), 39.7 (2C, C-8 and
C-12), 26.7 (C-13 or C-9), 26.6 (C-9 or C-13), 26.0 (C-5),
25.7 (C-17), 20.9 (CH3CO), 20.7 (CH3CO), 19.0 (apparent
d, Jˆ40 Hz, Cء-20), 17.6 (C-16), 16.0 (2C, C-18 and C-19);
MS, m/z (%): 464 (Mϩ, 8), 288 (16), 245 (10), 219 (15), 200
(28), 177 (32), 159 (100), 149 (45), 136 (98), 95 (92);
HRMS calcd for C2513C2H42O6 (Mϩ) m/z 464.3048, found
464.3067.
1
(liquid film) 1749, 1375, 1223 cmϪ1; H NMR (400 MHz,
selected values) dH: 0.81 (3H, s, H3-18), 0.86 (3H, s, H3-19),
0.90 (3H, s, H3-20), 0.93 (3H, s, H3-17), 1.58 (3H, s, H3-16),
2.08 (6H, s, 2OAc), 2.93 (1H, bs, H-14), 4.16–4.32 (4H, m,
H2-10 and H2-30), 5.26 (1H, m, H-20), 5.53 (1H, m, H-12);
MS, m/z (%): 286 (MϩϪC7H12O5, 77), 271 (14), 258 (15),
243 (8), 192 (85), 177 (90), 159 (100), 123 (65), 109 (48);
HRMS calcd for C20H30O (MϩϪC7H12O5) m/z 286.2297,
found 286.2289.
2e. Colorless oil; [a]Dˆϩ13.9Њ (c 0.30, CHCl3) {[a]D
natural 2e ϩ21.9Њ (c 0.22, CHCl3)}9; IR: nmax (liquid film)
3444, 1738, 1266, 1158 cmϪ1; 1H NMR (400 MHz, selected
values) dH: 0.81 (3H, s, H3-18), 0.86 (3H, s, H3-19), 0.90
(3H, s, H3-20), 0.96 (3H, s, H3-17), 2.11 (3H, s, OAc), 2.96
(1H, bs, H-14), 4.12–4.24 (5H, m, H2-10, H-20 and H2-30),
5.53 (1H, m, H-12).
Selective acetylation of diol 3d. According to the proce-
dure above reported for 1d, 34.8 mg (0.09 mmol) of diol
3d21 afforded after treatment with 3.6 mg (0.02 mmol) of
4e. Colorless oil; IR: nmax (liquid film) 1738, 1714, 1259,
1
1197 cmϪ1; H NMR (300 MHz, selected values) dH: 1.59
(6H, bs, H3-16 and H3-18), 1.60 (3H, bs, H3-19), 1.67 (3H,

N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
2511
bs, H3-17), 2.09 (3H, s, OAc), 2.17 (3H, dd, overlapped, H3-
20), 4.10 (1H, m, H-20), 4.10–4.20 (4H, m, H2-10 and H2-30),
5.09 (3H, m, H-6, H-10 and H-14), 5.70 (1H, d, JCHˆ7.9 Hz,
H-2); 13C NMR (75 MHz) dC: 171.0 (CH3CO), 166.7 (C-1),
161.9 (apparent d, Jˆ40 Hz, Cء-3), 136.3 (C-7 or C-11),
135.0 (C-11 or C-7), 131.2 (C-15), 124.3 (C-14), 124.0
(C-10), 122.69 (C-6), 114.6 (d, Jˆ73 Hz, C-2), 68.4
(C-20), 65.3 (C-30), 64.5 (C-10), 41.9 (d, Jˆ39 Hz, C-4),
39.7 (C-12 or C-8), 39.6 (C-8 or C-12), 26.7 (C-9 or
C-13), 26.6 (C-13 or C-9), 25.9 (C-5), 25.7 (C-16), 20.8
(CH3CO), 19.0 (apparent d, Jˆ40 Hz, Cء-20), 17.6 (C-17),
16.0 (2C, C-18 and C-19); MS, m/z (%): 422 (Mϩ, 6), 288
(12), 245 (8), 219 (12), 205 (32), 200 (21), 177 (23), 149
(48), 136 (85), 117 (100); HRMS calcd for C2313C2H40O5
(Mϩ) m/z 422.2943, found 422.2958.
170.4 (CH3CO), 166.4 (C-15), 161.8 (C-13), 148.3 (C-8),
114.8 (C-14), 106.3 (C-17), 72.2 (C-20), 61.8 (C-10), 61.5
(C-30), 56.2 (C-9), 55.5 (C-5), 42.1 (C-3), 39.9 (C-12), 39.7
(C-10), 39.1 (C-1), 38.3 (C-7), 33.6 (2C, C-4 and C-19),
25.9 [C(CH3)3], 24.4 (C-6), 21.7 (C-18), 21.5 (C-11), 21.1
(CH3CO), 19.4 (C-2), 19.0 (C-16), 18.2 [C(CH3)3], 14.5
(C-20), Ϫ5.5 [Si(CH3)2]; MS, m/z (%): 477 (MϩϪC4H9,
45), 361 (23), 287 (43), 271 (62), 231 (92), 191 (35), 177
(76), 117 (100), 95 (88).
Compound 1i. See Ref. 22.
Compound 2g. Following the procedure above reported for
1g, diol 2d (37.1 mg, 0.10 mmol) reacted with TBDMSCl
(17 mg, 0.11 mmol) to afford 42.0 mg of crude reaction
product, which, after chromatographic purification (SiO2,
petr. ether/Et2O, 97:3), gave 39.4 mg (82%) of 1-acyl-3-(t-
butyldimethylsilyl)-glycerol 2g: colorless oil; [a]Dˆϩ56.3Њ
(c 0.05, CHCl3); IR: nmax (liquid film) 3460, 1745, 1251,
1166, 1112 cmϪ1; 1H NMR (300 MHz, selected values) dH:
0.08 [6H, s, (CH3)2Si], 0.81 (3H, s, H3-18), 0.86 (3H, s, H3-
19), 0.90 [12H, s, C(CH3)3 and H3-20], 0.95 (3H, s, H3-17),
1.61 (3H, bs, H3-16), 2.96 (1H, bs, H-14), 3.60–3.71 (2H, m,
H2-30), 3.90 (1H, m, H-20), 4.10–4.21 (2H, m, H2-10), 5.52
(1H, m, H-12); 13C NMR (75 MHz) dC: 173.1 (C-15), 128.8
(C-13), 124.1 (C-12), 70.1 (C-20), 64.7 (C-30), 63.9 (C-10),
62.6 (C-14), 56.4 (C-5), 54.3 (C-9), 41.8 (2C, C-3 and C-7),
39.9 (C-1), 37.4 (C-8), 36.6 (C-10), 33.4 (C-19), 33.2 (C-4),
25.8 [C(CH3)3], 22.7 (C-11), 21.4 (C-18), 21.2 (C-16), 18.6
(C-2), 18.5 (2C, C-6 and [C(CH3)3], 15.7 (C-17), 15.5
(C-20), -5.45 [Si(CH3)2]; MS, m/z (%): 435 (MϩϪC4H9,
8), 361 (6), 287 (83), 260 (77), 259 (99), 243 (21), 191
(76), 177 (97), 135 (98), 109 (100).
Preparation of 1,2 diacyl derivatives 1i–3i
Compound 1g. In a typical procedure, t-butyl-dimethylsilyl
chloride (TBDMSCl, 16.0 mg, 0.11 mmol) was added to a
solution of diol 1d (35 mg, 0.09 mmol) in dry pyridine
(1.5 ml), under Ar atmosphere. The reaction mixture was
stirred at room temperature for 12 h. Then 15 ml of 10%
aqueous solution of H2SO4 was added. Usual work-up gave
a crude reaction product (39.6 mg), which was purified on
SiO2 column (petr. ether/Et2O, 97:3 as eluent) to afford
37.5 mg (82%) of 1-acyl-3-(t-butyldimethylsilyl)-glycerol
1g: colorless oil; [a]DˆϪ24.3Њ (c 0.07, CHCl3); IR: nmax
1
(liquid film) 3460, 1722, 1645, 1212, 1142, 890 cmϪ1; H
NMR (400 MHz, selected values) dH: 0.07 [6H, s,
(CH3)2Si], 0.67 (3H, s, H3-20), 0.79 (3H, s, H3-18), 0.86
(3H, s, H3-19), 0.90 [9H, s, C(CH3)3], 2.16 (3H, bs, H3-
16), 3.63 (1H, dd, Jˆ5.6 and 10.1 Hz, H-30a), 3.68 (1H,
dd, Jˆ4.7 and 10.1 Hz, H-30b), 3.90 (1H, m, H-20), 4.12
(1H, dd, Jˆ6.1 and 11.5 Hz, H-10a), 4.17 (1H, dd, Jˆ4.7
and 11.5 Hz, H-10b), 4.48 (1H, bs, H-17a), 4.84 (1H, d,
Jˆ0.6 Hz, H-17b), 5.68 (1H, bs, H-14); 13C NMR
(100 MHz) dC: 166.9 (C-15), 162.0 (C-13), 148.3 (C-8),
114.7 (C-14), 106.3 (C-17), 70.2 (C-20), 64.5 (C-10), 63.8
(C-30), 56.2 (C-9), 55.5 (C-5), 42.1 (C-3), 39.9 (C-12), 39.7
(C-10), 39.1 (C-1), 38.3 (C-7), 33.6 (2C, C-4 and C-19), 25.9
[C(CH3)3], 24.4 (C-6), 21.7 (C-18), 21.5 (C-11), 19.4 (C-2),
19.0 (C-16), 18.3 [C(CH3)3], 14.5 (C-20), Ϫ5.5 [Si(CH3)2];
MS, m/z (%): 435 (MϩϪC4H9, 12), 361 (7), 347 (7), 288 (30),
287 (98), 271 (62), 259 (90), 177 (61), 69 (100).
Compound 2h. A solution of 26 mg (0.05 mmol) of t-butyl-
dimethylsilylglyceryl ester 2g in 1.5 ml of dry pyridine was
treated with 0.05 ml of Ac2O. The reaction mixture was
stirred at room temperature for 12 h. After usual work-up,
the crude reaction product (28.3 mg) was chromatographed
by SiO2 column (petr. ether/Et2O, 99:1) to give 25.8 mg
(91%) of 1,2-diacyl-3-(t-butyldimethylsilyl)-glycerol 2h:
colorless oil; [a]Dˆϩ1.1Њ (c 0.13, CHCl3); IR: nmax (liquid
1
film) 1745, 1637, 1390, 1236 cmϪ1; H NMR (400 MHz,
selected values) dH: 0.05 [6H, s, (CH3)2Si], 0.81 (3H, s,
H3-18), 0.86 (3H, s, H3-19), 0.88 [9H, s, C(CH3)3], 0.91
(3H, s, H3-20), 0.93 (3H, s, H3-17), 1.59 (3H, bs, H3-16),
2.03 (3H, s, OAc), 2.94 (1H, bs, H-14), 3.71–3.74 (2H, m,
H2-30), 4.11–4.35 (2H, m, H2-10), 5.10 (1H, m, H-20), 5.51
(1H, m, H-12); MS, m/z (%): 477 (MϩϪC4H9, 70), 361 (23),
287 (25), 259 (30), 243 (12), 231 (21), 191 (30), 177 (30),
131 (42), 117 (100).
Compound 1h. A solution of 28.1 mg (0.06 mmol) of
t-butyldimethylsilylglyceryl ester 1g in 1.5 ml of dry
pyridine was treated with 0.06 ml of Ac2O. The reaction
mixture was stirred at room temperature for 12 h. After
usual work-up, the crude reaction product (31.2 mg) was
chromatographed by SiO2 column (petr. ether/Et2O, 99:1)
to give 28.1 mg (92%) of 1,2-diacyl-3-(t-butyldimethyl-
silyl)-glycerol 1h: colorless oil; [a]DˆϪ8.5Њ (c 0.07,
CHCl3); IR: nma1x (liquid film) 1745, 1722, 1637, 1235,
890, 842 cmϪ1; H NMR (400 MHz, selected values) dH:
0.05 [6H, s, (CH3)2Si], 0.68 (3H, s, H3-20), 0.79 (3H, s,
H3-18), 0.86 (3H, s, H3-19), 0.88 [9H, s, C(CH3)3], 2.07
(3H, s, OAc), 2.14 (3H, d, Jˆ1.2 Hz, H3-16), 3.74 (1H, d,
Jˆ5.2 Hz, H2-30), 4.20 (1H, dd, Jˆ6.0 and 12.0 Hz, H-10a),
4.32 (1H, dd, Jˆ3.9 and 12.0 Hz, H-10b), 4.48 (1H, bs,
H-17a), 4.84 (1H, d, Jˆ1.2 Hz, H-17b), 5.08 (1H, m,
H-20), 5.64 (1H, bs, H-14); 13C NMR (100 MHz) dC:
Compound 2i. See Ref. 22.
Compound 3g. According to the procedure described for
1g, diol 3d (46.9 mg, 0.12 mmol) reacted with TBDMSCl
(21.4 mg, 0.14 mmol) to obtain 55.6 mg of crude reaction
product, which was purified (SiO2, petr. ether/Et2O, 97:3),
giving 52.3 mg (86%) of 1-acyl-3-(t-butyldimethylsilyl)-
glycerol 3g: oil; [a]DˆϪ31.7Њ (c 0.25, CHCl3); IR: nmax
(liquid film) 3475, 1735, 1251, 1112, 1019 cmϪ1 1H
;
NMR (400 MHz, selected values) dH: 0.08 [6H, s,
(CH3)2Si], 0.81 (3H, s, H3-18), 0.86 (3H, s, H3-19), 0.90

2512
N. Ungur et al. / Tetrahedron 56 (2000) 2503–2512
`
[12H, s, C(CH3)3 and H3-20], 0.94 (3H, s, H3-17), 1.61 (3H,
bs, H3-16), 2.95 (1H, bs, H-14), 3.62–3.71 (2H, m, H2-30),
3.87 (1H, m, H-20), 4.12–4.19 (2H, m, H2-10), 5.52 (1H, m,
H-12); 13C NMR (100 MHz) dC: 174.0 (C-15), 128.8 (C-
13), 124.1 (C-12), 70.1 (C-20), 64.7 (C-30), 63.9 (C-10), 62.6
(C-14), 56.5 (C-5), 54.3 (C-9), 42.1 (C-7), 41.8 (C-3), 39.9
(C-1), 37.4 (C-8), 36.6 (C-10), 33.4 (C-19), 33.2 (C-4), 25.8
[C(CH3)3], 22.7 (C-11), 21.7 (C-18), 21.2 (C-16), 18.6 (C-
2), 18.5 (C-6), 18.3 [C(CH3)3], 15.7 (C-17), 15.5 (C-20),
Ϫ5.5 [Si(CH3)2]; MS, m/z (%): 435 (MϩϪC4H9, 7), 361
(4), 287 (91), 259 (100), 243 (15), 191 (29), 177 (68), 163
(70), 135 (75), 109 (95).
Spettrometria di Massa del CNR e dell’Universita di
Napoli’ and at ‘Servizio di Spettrometria di Massa, Diparti-
mento di Chimica Organica e Industriale dell’Universita di
Milano’. N. U. acknowledges Italian National Programme
for Antarctic Research for financial support.
`
References
1. Karuso, P. In Bioorganic Marine Chemistry, Scheuer, P. J., Ed.;
Springer: Berlin, 1987; Vol. 1, pp 31–60.
2. Faulkner, D. J. Ecological Roles of Marine Natural Products;
Paul, V. J., Ed.; Comstock Publishing Associates: Ithaca, NY,
1992, pp 119–163.
Compound 3h. A solution of 35.0 mg (0.07 mmol) of
t-butyldimethylsilylglyceryl ester 3g in 1.5 ml of dry
pyridine was treated with 0.04 ml of Ac2O. The reaction
mixture was stirred at room temperature for 12 h. After
usual work-up, the crude reaction product (37.5 mg) was
chromatographed by SiO2 column (petr. ether/Et2O, 99:1)
to give 35.1 mg (92%) of 1,2-diacyl-3-(t-butyldimethyl-
silyl)-glycerol 3h: colorless oil; [a]DˆϪ27.0Њ (c 0.12,
3. Cimino, G.; Fontana, A.; Gavagnin, M. Curr. Org. Chem. 1999,
3, 327–372.
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1
CHCl3); IR: nmax (liquid film) 1745, 1382, 1236 cmϪ1; H
NMR (400 MHz, selected values) dH: 0.05 [6H, s,
(CH3)2Si], 0.81 (3H, s, H3-18), 0.86 (3H, s, H3-19), 0.88
[9H, s, C(CH3)3], 0.90 (3H, s, H3-20), 0.93 (3H, s, H3-17),
1.59 (3H, bs, H3-16), 2.03 (3H, s, OAc), 2.92 (1H, bs, H-14),
3.74 (2H, d, Jˆ5.4 Hz, H2-30), 4.17 (1H, dd, Jˆ5.5 and
11.9 Hz, H-10), 4.37 (1H, dd, Jˆ3.7 and 11.9 Hz, H-10),
5.05 (1H, m, H-20), 5.51 (1H, m, H-12); MS, m/z (%): 478
(MϩϪC4H8, 100), 435 (6), 361 (43), 287 (68), 259 (51), 231
(22), 191 (31), 177 (52), 117 (99), 109 (62).
´
9. Zubia, E.; Gavagnin, M.; Crispino, A.; Martınez, E.; Ortea, J.;
Cimino, G. Experientia 1993, 49, 268–271.
10. Cimino, G.; Crispino, A.; Gavagnin, M.; Zubia, E.; Trivellone,
E. J. Nat. Prod. 1993, 56, 1642–1646.
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Lett. 1993, 3, 31–35.
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11063–11074.
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Tetrahedron 1997, 53, 1491–1504.
Compound 3i. Using a procedure already reported in the
literature for synthesis of 1i and 2i,22 1,2-diacyl-sn-t-butyl-
dimethylsilylglyceryl ester 3h (21 mg, 0.04 mmol) in dry
acetone (4.5 ml) was treated with 11.1 mg (0.04 mmol) of
PdCl2(CH3CN)2. The reaction mixture was stirred at room
temperature for 1 h and then 7 ml of H2O were added. The
usual work up gave a residue (16.7 mg) which was purified
by SiO2 column chromatography (petr. ether/Et2O gradient)
affording, in order of increasing polarity, starting ester 3h
(1.1 mg, 5%), and 1,2-diacylglycerol 3i (13.5 mg, 86%),
´
15. Gavagnin, M.; Ungur, N.; Castelluccio, F.; Muniaın, C.;
Cimino, G. J. Nat. Prod. 1999, 62, 269–274.
16. De Petrocellis, L.; Orlando, P.; Gavagnin, M.; Ventriglia, M.;
Cimino, G.; Di Marzo, V. Experientia 1996, 52, 874–877.
17. Gavagnin, M.; De Napoli, A.; Castelluccio, F.; Cimino, G.
Tetrahedron Lett. 1999, 40, 8471–8475.
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Lett. 1990, 31, 6093–6094.
19. Gavagnin, M.; De Napoli, A.; Cimino, G.; Iken, K.; Avila, C.;
Garcia, F. J. Tetrahedron: Asymmetry 1999, 10, 2647–2650.
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Asymmetry 1999, 10, 1263–1273.
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1
which showed spectral data (MS, IR, H and 13C NMR)
identical with those of natural 3i.6
3i. Colorless crystals, mp 75–76ЊC (from petr. ether);
[a]DˆϪ41.8Њ (c 0.57, CHCl3) {[a]D natural 3i Ϫ33.0Њ (c
0.83; CHCl3)};6 IR: nmax (liquid film) 3482, 1740, 1238,
1
1161, 1050 cmϪ1; H NMR (500 MHz) dH: 0.82 (3H, s,
H3-18), 0.86 (3H, s, H3-19), 0.91 (s, 3H, H3-20), 0.94 (3H,
s, H3-17), 1.60 (3H, s, H3-16), 2.10 (3H, s, OAc), 2.94 (1H,
bs, H-14), 3.76 (d, Jˆ5.5 Hz, 2H, H2-30), 4.27 (1H, dd,
Jˆ5.1 and 12.1 Hz, H-10a) and 4.34 (1H, dd, Jˆ4.4 and
12.1 Hz, H-10b), 5.07 (1H, m, H-20), 5.53 (1H, m, H-12).
Acknowledgements
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1976, 72, 1004–1014; Chem. Abstr. 1978, 88. 23 188
27. Kalinowski, H.-O.; Berger, S.; Braun, S. Carbon-13 NMR
Spectroscopy; Wiley: New York, 1988, pp 546–567.
28. Nakano, T.; Djerassi, C. J. Org. Chem. 1961, 26, 167–173.
We thank Mr F. Castelluccio for his valuable technical help,
Mr G. Scognamiglio for spectrophotometric measurements
and Mr R. Turco for artwork. The NMR spectra were
recorded at the ‘Servizio NMR dell’ICMIB e dell’Area di
Ricerca di Napoli’ and mass spectra at the ‘Servizio di