Nuapapuin A and sigmosceptrellins D and E: New norterpene cyclic peroxides from a southern Australian marine sponge, Sigmoseeptrella sp.

Article abstract of DOI:10.1021/np980223r

A Sigmosceptrella sp. from the Great Australian Bight, Australia, has yielded the new norditerpene cyclic peroxide, nuapapuin A (2a), and the norsesterterpene cyclic peroxide sigmosceptrellin D (3a), characterized as the corresponding methyl esters 2b and 3b. The crude methylated sponge extract also yielded the new norsesterterpene cyclic peroxide sigmosceptrellin E methyl ester (4). Relative stereochemistry about C2, C3, and C6 was assigned by established empirical rules and absolute stereochemistry by the advanced Mosher procedure. A plausible biosynthetic pathway has been proposed that rationalizes key transformations in the biosynthesis of all known norterpene cyclic peroxides and related norterpene ketones, dienes and sigmosceptrins.

Full text of DOI:10.1021/np980223r

214
J . Nat. Prod. 1999, 62, 214-218
Nu a p a p u in A a n d Sigm oscep tr ellin s D a n d E: New Nor ter p en e Cyclic P er oxid es
fr om a Sou th er n Au str a lia n Ma r in e Sp on ge, Sigm osceptr ella sp .
Simon P. B. Ovenden and Robert J . Capon*
School of Chemistry, University of Melbourne, Parkville, Victoria, 3052, Australia
Received May 29, 1998
A Sigmosceptrella sp. from the Great Australian Bight, Australia, has yielded the new norditerpene cyclic
peroxide, nuapapuin A (2a ), and the norsesterterpene cyclic peroxide sigmosceptrellin D (3a ), characterized
as the corresponding methyl esters 2b and 3b. The crude methylated sponge extract also yielded the
new norsesterterpene cyclic peroxide sigmosceptrellin E methyl ester (4). Relative stereochemistry about
C2, C3, and C6 was assigned by established empirical rules and absolute stereochemistry by the advanced
Mosher procedure. A plausible biosynthetic pathway has been proposed that rationalizes key transforma-
tions in the biosynthesis of all known norterpene cyclic peroxides and related norterpene ketones, dienes
and sigmosceptrins.
Over the last two decades, numerous norterpene cyclic
peroxides have been reported from marine sponges.1-13
Southern Australian sponges have been particularly pro-
ductive in this regard, with specimens of the genera
Latrunculia,5,7,8,12 Mycale,4,6,9-11 and Sigmosceptrella2 fea-
turing prominently in the discovery of new norterpene
cyclic peroxides. In addition to novel structures, we have
come to recognize, through screening by the National
Cancer Institute, that selected norterpene cyclic peroxides
such as trunculin A (1)5 possess noteworthy antitumor
properties. In continuing our investigations into the chem-
istry of southern Australian marine sponges, we antici-
pated that discovery of new norterpene cyclic peroxides
would provide evidence supporting a biosynthetic origin for
this unique class of marine metabolite. Such compounds
would also prove useful in defining structure-activity
relationships.
Resu lts a n d Discu ssion
The crude EtOH extract of a Sigmosceptrella sp. obtained
during trawling operations in the Great Australian Bight,
Australia, displayed growth inhibitory properties against
Micrococcus luteus, Serratia marcescens, and Staphylococ-
cus aureus. TLC and 1H NMR analysis suggested the
presence of cyclic peroxide carboxylic acids accompanied
by minor amounts of related methyl esters. Following
established procedures,4-8,10-12 the crude extract was ex-
haustively methylated with ethereal CH2N2 and subjected
to chromatographic fractionation to yield the norditerpene
cyclic peroxide methyl ester 2b and the norsesterterpene
cyclic peroxide methyl esters 3b and 4.
Compound 2b was isolated as a stable oil with a
molecular formula (M + Na, C20H34O4Na, ∆ mmu -1.7)
isomeric to the known sponge metabolite nuapapuin A
methyl ester3 (formerly known as methyl nuapauanoate).13
Comparison of NMR and [R]D data for 2b with that
provide experimental evidence to resolve assignment of
either relative or absolute stereochemistry. Our reisolation
of 2b permitted the relative stereochemistry to be deter-
mined using established empirical rules.4 The 1H NMR
reported in the literature3 revealed 2b to be identical with
nuapapuin A methyl ester. Although nuapapuin A methyl
ester has been known since 1984,3 doubt has been raised
about the assigned relative stereochemistry,14 and the
chemical shift for the 2-CH3 (δ 1.13), a large J 3,4ax (8 Hz),
absolute stereochemistry has yet to be assigned. A recent
report of 2b in the chemical literature13 acknowledged
earlier concerns about relative stereochemistry, but did not
and the 13C NMR chemical shift for the 6-CH3 (23.4 ppm)
were consistent with the 2R*,3R*,6R* stereochemistry as
shown. The absolute stereochemistry for 2b was deter-
mined using the advanced Mosher procedure.15,16 Hydro-
* To whom correspondence should be addressed. Tel: +61 3 9344 6468.
Fax: +61 3 9347 5180. E-mail: r.capon@chemistry.unimelb.edu.au.
genation of 2b yielded the diol 5, which was subsequently
10.1021/np980223r CCC: $18.00
© 1999 American Chemical Society and American Society of Pharmacognosy
Published on Web 12/05/1998

Nuapapuin A and Sigmosceptrellins D and E
J ournal of Natural Products, 1999, Vol. 62, No. 2 215
Sch em e 1a
- δR; 2-CH3 (+13.7 Hz), H-2 (+4.4 Hz), -CO2CH3 (+12.2
Hz), 6-CH3 (-18.1 Hz)) were consistent with a 3S and hence
2R,3S,6R absolute stereochemistry. Stereochemical deter-
minations about C10 and C14 remain unassigned. As with
1
nuapapuin A methyl ester (2b), careful analysis of the H
NMR (relative integration between H-17 and CO2CH3) and
TLC data for the crude unmethylated sponge extract
confirmed that sigmosceptrellin D occurred naturally as
its carboxylic acid 3a . It was not possible to unambiguously
determine whether the corresponding methyl ester 3b
occurred naturally, although as noted earlier methyl esters
were present in minor amounts in the initial ethanol
extract.
a
Key: (i) H2SO4, aq HBr, ∆; (ii) Mg, Et2O, ∆; (iii) 6-methyl-5-hepten-2-
one, Et2O, ∆.
esterified to yield the R and S MTPA esters 6 and 7,
respectively. Diagnostic 1H NMR chemical shift differences
between the diastereomeric MTPA esters (∆ δS - δR;
2-CH3 (-21.7 Hz), H-2 (-3.2 Hz), -CO2CH3 (-17.1 Hz),
6-CH3 (+22.7 Hz)) confirmed a 3R and hence 2R,3R,6R
Sigmosceptrellin E methyl ester (4) was isolated as a
stable oil with a molecular formula (C25H42O4Na, ∆mmu
0.7) consistent with five degrees of unsaturation. Examina-
tion of the NMR and IR data for 4 revealed a cyclic peroxide
methyl ester moiety common with that for 3b (1H NMR
chemical shift for the 2-CH3 (δ 1.25), a large J 3,4ax (7.6 Hz),
and 13C NMR chemical shift for the 6-CH3 (20.6 ppm)).
Further examination of the NMR data revealed the pres-
ence of three trisubstituted double bonds (1H: δ 5.09; 13C:
135.5, 135.0, 131.3, 124.4, 124.1, 123.9), which, in the
absence of additional sp or sp2 hybridized carbons, required
that the remaining structural unit in 4 be acyclic. COSY
NMR analysis confirmed the gross structure for 4 as shown,
while 13C NMR chemical shifts for C10-CH3 and C14-CH3
(16.0 and 16.0 ppm) were consistent with E geometries
about ∆10,11 and ∆14,15. The limited supply of 4 isolated
during this investigation precluded an independent experi-
mental determination of absolute stereochemistry; how-
ever, a 2R,3S,6R absolute stereochemistry was tentatively
assigned on biosynthetic considerations (given the co-
occurrence of the closely related 3b). The low yield of
“sigmosceptrellin E” in the crude extract made it impossible
to establish whether it occurred naturally as either the
carboxylic acid, the methyl ester, or both.
1
absolute stereochemistry. Careful analysis of the H NMR
spectrum of the crude unmethylated sponge extract (rela-
tive integration between the gem-dimethyls at C-10 and
CO2CH3) confirmed that 2b occurred naturally as the free
carboxylic acid, nuapapuin A (2a ). It was not possible to
confirm whether nuapapuin A methyl ester (2b) occurred
naturally in the crude extractseven though trace amounts
of norterpene cyclic peroxide methyl esters were clearly
present by TLC and 1H NMR (CO2CH3 resonance) analysis.
This is the first account of nuapapuin A as a natural
product.
Sigmosceptrellin D methyl ester (3b) was isolated as a
stable oil with a molecular formula (M + Na - H2O,
25H44O5Na, ∆ mmu -0.3) consistent with three degrees
C
of unsaturation. Examination of the NMR and IR data for
3b revealed the presence of a cyclic peroxide methyl ester
moiety. Application of empirical rules (1H NMR chemical
shift for 2-CH3 (δ 1.24), a large J 3,4ax (8.2 Hz), and 13C NMR
chemical shift for the 6-CH3 (20.2 ppm)) confirmed a
2R*,3S*,6R* relative stereochemistry. Further examination
of the NMR data revealed resonances consistent with a
single trisubstituted double bond (1H: δ 5.14; 13C: 124.7,
131.7 ppm), which, in the absence of additional sp or sp2
hybridized carbons, required that the remaining structural
unit in 3b be acyclic. The 13C NMR data for 3b also
revealed a single deshielded quaternary carbon (77.2 ppm),
which, given the need to accommodate two remaining
oxygen atoms, pointed to the presence of a hydroperoxide
moiety. COSY and HMBC NMR experiments established
the gross structure for 3b as shown (or the regioisomer with
a C 10-hydroperoxide). The position of the hydroperoxide
moiety was confirmed by reduction of 3b to a mixture of
diene regioisomers (8). Most significantly, the COSY NMR
spectra for the mixed dienes (8) displayed a correlation
from H15 and H17 to a common bisallylic methylene (δ
2.70), requiring that the hydroperoxide in the natural
product 3b be positioned at C14. Since a hydroperoxide is
a rare functional group in the marine natural products
literature,17,18 we undertook to support the assigned struc-
ture by preparing the model alcohol 9 (see Scheme 1).
Spectroscopic comparisons revealed significant differences
between 3b (1H: 14 H3, δ 0.87; 13C: C 14, 77.2 ppm) and 9
(1H: 14 H3, δ 1.16; 13C: C 14, 72.7 ppm), consistent with
literature precedence between a tertiary hydroperoxide and
Although a large number of norterpene cyclic peroxides
and related co-metabolites have been reported from marine
sponges, no attempt has been made to propose a biosyn-
thetic pathway that satisfactorily accounts for all stereo-
isomeric forms of the terminal cyclic peroxide moiety and
related analogues. In an earlier report we isolated, char-
acterized, identified, and speculated on the possible bio-
synthetic role of norterpene dienes.19 More recently,20 we
proposed that norterpene dienes were biosynthetic precur-
sors to the sigmosceptrins. The norterpene cyclic peroxides
encountered in this paper have prompted us to review the
array of known norterpene cyclic peroxides and propose a
common biosynthetic pathway that accounts for key struc-
tural and stereochemical features. This proposal is outlined
in Scheme 2.
Key to proposing this biosynthetic pathway was the
discovery of sigmosceptrellin D (3a ), with a hydroperoxide
moiety strategically positioned in such a way as to mimic
the cyclic peroxide moiety at the opposite end of the
molecule. This observation encouraged a belief that the
biosynthetic origin of some or all marine norterpene cyclic
peroxides involved a common intermediate C6 hydroper-
oxide (Scheme 2, step 1), undergoing a “Michael addition”
to an adjacent R,â-unsaturated carboxylic acid or ester
moiety (Scheme 2, step 2). Initial formation of the C6
hydroperoxide could occur on either the Re or Si face of a
17,18
a tertiary hydroxide.
The absolute stereochemistry of 3b was determined
using the advanced Mosher procedure.15,16 Hydrogenation
of 3b yielded the eriol 10, which was esterified with R and
S MTPA acid to yield the corresponding MTPA esters 11
and 12, respectively. Diagnostic 1H NMR chemical shift
differences between the diastereomeric MTPA esters (∆ δS
∆
5,6 precursor, thereby defining the absolute stereochemical
outcome of the biosynthetic process. Scheme 2 arbitrarily
illustrates this process occurring via oxidation of the Re
face of a ∆5,6 precursor, although the antipodal pathway

216 J ournal of Natural Products, 1999, Vol. 62, No. 2
Sch em e 2. Proposed Biosynthetic Pathway
Ovenden and Capon
could be evidenced by known norterpene cyclic peroxides.
Depending on the conformation of the hydroperoxy car-
boxylic acid precursor, the electrophilic ∆2,3 addition can
proceed via the Si face (Scheme 2, step 2a) or the Re face
(Scheme 2, step 2b), leading to epimers about C3. Quench-
ing of the resulting ∆1,2 “enolate” can proceed via both Re
and/or Si facial addition of H+ to yield the full suite of C2
and C3 stereoisomers. Those isomers originating via the
process step 2b-3b-4b also experience inversion of the
cyclic peroxide chair conformation to attain the more stable
conformer bearing an equatorial C 3 substituent. This
inversion has the effect of repositioning the C 6 “terpene”
side chain from an equatorial to axial conformation. That
the C 14 hydroperoxide in sigmosceptrellin D (3a ) did not
yield a cyclic peroxide is readily explained in that, lacking
a C19 carboxylic acid, ∆17,18 is not sufficiently activated
toward electrophilic attack by the C 14 hydroperoxide. This
proposed biosynthetic pathway not only provides an ef-
ficient route to the key structural feature in norterpene
cyclic peroxides but also provides ready access to known
cometabolites. Oxidative degradation through loss of water
from the hydroperoxide carboxylic acid precursor, with
accompanying intramolecular abstraction of an allylic C 4
proton and cleavage of C5-C6 (see Scheme 2), can yield
norterpene ketones. Such ketones are increasingly being
identified10,11 as minor cometabolites with norterpene cyclic
peroxides. Likewise, a pro-R 1,3 hydride shift from C4 to
C2 can yield norterpene dienes, which are known co-
metabolites19 and have been proposed as biosynthetic
precursors for the closely related sigmosceptrins.20 It should
be emphasized that in the proposed biosynthetic scheme
the conjugated norterpene dienes described above are not
biosynthetic precursors to the cyclic peroxides, but are
rather an offshoot of the biosynthetic pathway. This
proposal differs from an earlier hypothesis19 that required
the 2+4 cycloaddition of oxygen to conjugated norterpene
dienes. Although no experimental evidence is presented to
support the biosynthetic pathway outlined in Scheme 2, it
is an attractive proposal in that it goes a long way toward
explaining the stereochemical versatility encountered among
known marine norterpene cyclic peroxides, and accounts
for the occurrence of related metabolites.
Exp er im en ta l Section
Gen er a l Meth od s. For general experimental details see
ref 12.
Collection , Extr a ction , a n d Isola tion . A specimen of
Sigmosceptrellin sp. (154 g dry weight, Museum of Victoria
registry no. F79981) collected by epibenthic sled at a depth of
150 m from the Great Australian Bight, Australia, was frozen
and transported to the laboratory where it was diced, steeped
in EtOH, and stored at -18 °C [growth form: macrobenthic,
fixed directly to the substrate, massive-lobate; color: pink-beige
on deck, beige-white in ethanol; texture: compressible, tough,
leathery; surface: opaque, optically smooth, irregular with long
papillose-fistulose projections flattened apically; oscules: raised
on small fistules; megascleres: styles (slight constriction,
occasionally deformed, 360-430 µm) microscleres: sanidastoid
discorhabds (four symmetrical whorls of spines 30-100 µm);

Nuapapuin A and Sigmosceptrellins D and E
J ournal of Natural Products, 1999, Vol. 62, No. 2 217
Ta ble 1. NMR Data (CDCl3, 400 MHz) for Sigmosceptrellin D
Methyl Ester (3b)b
18-CH3), 16.0 (q, 14-CH3), 16.0 (q, 10-CH3), 13.6 (q, 2-CH3);
EIMS (30 eV) m/z 406 (M+, 1), 371 (3), 315 (4), 253 (7), 185
(9), 147 (32); HRESIMS (M + Na) 429.2988 (C25H42O4Na
requires 429.2981).
13C
δ
1H
δ
gHMBC
1H to 13
C
no.
m
COSY
Hyd r ogen a tion of 2b. A sample of 2b (58.7 mg, 0.17 mmol)
in ether (10 mL) was treated with 10% palladium on carbon
(20 mg) and stirred under an atmosphere of H2 for 16 h. The
reaction mixture was then filtered through Celite and con-
centrated in vacuo to yield the saturated diol 5 (49.8 mg,
88%): [R]D -1.8° (c 1.42, CHCl3); IR (CHCl3) νmax 3610, 1720
cm-1; 1H NMR (CDCl3, 400 MHz) δ 3.71 (s, CO2CH3), 3.68 (m,
H3), 2.55 (m, H2), 0.80-1.90 (br envelope, H24, H25, H27, H28,
H9, H211, H212, H213, H14, 10-CH3, 10-CH3, 14-CH3), 1.20 (d,
J ) 7.2 Hz, 2-CH3), 1.18 (s, 6-CH3); ESIMS (25 kV) m/z 381
(M + K, 40), 365 (M + Na, 55), 343 (M + H, 55). EIMS (70 eV)
m/z 324 (M - H2O, 4), 322 (26), 281 (29), 215 (49), 183 (30);
HRESIMS (M + Na) 366.2683 (C20H38O4Na requires 366.2667)
Red u ction of Sigm oscep tr ellin D Meth yl Ester (3b).
To a sample of 3b (12.3 mg, 0.021 mmol) in dry benzene (10
mL) was added 25 mg (0.22 mmol) of freshly sublimed oxalic
acid and the mixture refluxed for 24 h, during which time the
reaction mixture was allowed to evaporate to dryness. The
crude product was then extracted with ether (2 × 20 mL), and
the organic phase was washed with saturated Na2CO3 (2 ×
40 mL) and brine (1 × 40 mL) and then dried with anhydrous
MgSO4 to yield 8 (8.3 mg, 95%) as a stable oil: [R]D -12.5° (c
0.35, CHCl3); IR (CHCl3) νmax 1730 cm-1; 1H NMR (CDCl3, 400
MHz) δ 5.14 (m, H13, ∆13,14), 5.07 (m, H17), 5.01 (t, J ) 6.4
Hz, H15, ∆14,15), 4.10 (ddd, J ) 8.2, 8.2, 3.4 Hz, H3), 3.69 (s,
CO2CH3), 2.70 (br t, J ) 6.7 Hz, H216, ∆14,15), 2.63 (m, H2),
2.10-0.80 (br envelope, H24, H25, H27, H28, H29, H10, H211,
H212), 1.69 (s, 18-CH3), 1.67 (s, 14-CH3, ∆14,15), 1.62 (s, 18-
CH3), 1.60 (s, 14-CH3, ∆13,14), 1.25 (s, 6-CH3), 1.25 (d, J ) 6.9
Hz, 2-CH3), 0.81 (d, J ) 6.8 Hz, 10-CH3); 13C NMR (CDCl3,
100 MHz), δ 174.3 (s, C1), 142.8, 140.8 (2s, C14∆13,14, C14∆14,15),
131.1 (s, C18), 124.9, 124.0 (2d, C17∆13,14, C17∆14,15), 121.9,
121.8 (2d, C13∆,13,14 C14∆14,15), 81.4 (s, C6), 80.4 (d, C3), 51.8
(q, CO2CH3), 42.4 (d, C2), 43.0, 40.4, 33.9, 33.5, 32.1, 30.1, 29.3,
1
2
3
4
5
6
7
8
174.2
42.9
2.63 dq
4.11 ddd H-2
H-3, 2-CH3 C-1, C-3, CH3-2
C-1, C-2, CH3-2
80.5
23.5a
32.3a
81.3
*
*
m
m
35.6a
22.3a
43.2a
37.8
*
*
*
*
*
*
*
m
m
m
m
m
m
m
9
10
11
12
13
14
15
16
17
29.3a
32.8a
30.4a
77.2
32.6
21.8
*
1.99
m
m
H-16
H-15, H-17 C-15, C-17, C-18
124.7 5.14 br t H-16, H-19, C-15, C-16, C-19,
CH3-18
CH3-18
18
19
131.7
25.7
1.69
3.69
1.24
1.27
0.84
0.87
1.62
s
s
d
s
d
s
s
H-17
C-17, C-18, CH3-18
C-1, C-2
CO2CH3 51.8
2-CH3
6-CH3
10-CH3
14-CH3
18-CH3
13.5
20.2
12.7
16.9
17.6
H-2
C-1, C-2, C-3
C-5, C-6, C-7
C-9, C-10, C-11
C-14
H-17
C-17, C-18, C-19
a
Indicates that assignments may be interchanged. *Refers to
b
an overlapping envelope. J 2,2-Me ) 7.0 Hz, J 2,3ax ) 8.2 Hz, J 3,4ax
) 8.2 Hz, J 3,4eq ) 3.4 Hz.
ectosome: a continuous palisade of megascleres just protruding
the surface obscured by a dense layer of discorhabd micro-
scleres (approx 1 mm thick); choanosome: dense and disorga-
nized styles centrally becoming more organized into multi-
spicular almost radial tracts subectosomally with discorhabd
microscleres scattered throughout the light interstitial col-
lagen].
23.6, 21.4 (10t, C 4, C 5, C 7, C 8, C 9, C 11, C 12, C 13∆14-15
,
C 15∆13,14, C 16), 38.8 (d, C 10), 25.7 (q, C 19), 20.7 (q, 6-CH3),
17.7 (q, 18-CH3), 15.9, 15.7 (2q, 10-CH3, 14-CH3), 13.6 (q,
2-CH3); ESIMS (25 kV) m/z 409 (M + H, 70); EIMS (30 eV)
m/z 408 (M, 1), 388 (8), 331 (4), 301 (15), 245 (16).
The decanted crude EtOH extract was concentrated in vacuo
and partitioned into CH2Cl2-soluble and -insoluble fractions.
The CH2Cl2-soluble fraction was methylated with ethereal
CH2N2 and subjected to rapid filtration through silica (20%
stepwise gradient from petroleum ether to CH2Cl2 to EtOAc).
Interesting fractions identified by TLC and 1H NMR were
subjected to further purification by HPLC (2 mL/min, 10%
EtOAc/petroleum ether through a Phenomenex 5 µm silica 250
mm × 10 mm column) to yield nuapapuin A methyl ester (2b)
(270 mg, 0.18%), sigmosceptrellin D methyl ester (3b) (130 mg,
0.08%), and sigmosceptrellin E methyl ester (4) (3 mg, 0.002%).
Nu a p a p u in A m eth yl ester (2b): a stable oil; [R]D +61.7°
H yd r ogen a t ion of Sigm oscep t r ellin D Met h yl E st er
(3b). Treatment of a sample of 3b (32.4 mg, 0.073 mmol) as
described above for 2b yielded the saturated diol 10 (28 mg,
86%): [R]D -4.4° (c 0.98, CHCl3); IR (CHCl3) νmax 3610, 1730
cm-1; 1H NMR (CDCl3, 400 MHz) δ 3.88 (m, H3), 3.71 (s, CO2-
CH3), 2.56 (m, H2), 1.00-2.00 (br envelope, H24, H25, H27, H28,
H29, H10, H211, H212, H213, H215, H216, H217, H18), 1.25 (s,
6-CH3), 1.21 (d, J ) 7.1 Hz, 2-CH3), 0.88 (m, 10-CH3, 14-CH3,
18-CH3, 18-CH3); ESIMS (25 kV) m/z 431 (M + H, 10), 453 (M
+ Na, 10); HRESIMS (M + Na - 2H) 451.3391 (C25H48O5Na
requires 451.3399).
(c 0.78, CHCl3); IR (film) νmax 1740 cm-1 1H and 13C NMR
;
(CDCl3) identical in all respects to published results3; EIMS
(70 eV) m/z 338 (0.4, M+), 282 (1), 251 (1), 193 (1), 175 (2), 95
(9), 83 (100); HRESIMS (M+Na) 361.2355 (C20H34O4Na re-
quires 361.2355).
Rea ction of Diol 5 w ith (R)-MTP A Acid . To a solution
of 5 (24 mg) in 5 mL of dry CH2Cl2 were added DCC (82.7
mg), DMAP (28 mg), and (R)-MTPA acid (82.7 mg) and the
solution stirred for 16 h. The reaction mixture was concen-
trated, prepurified on a silica Sep-Pak (20% gradient elution
from petrol to EtOAc), and subjected to HPLC chromatography
(2 mL/min 20% EtOAc/petroleum ether, Phenomenex 5 µm
silica 250 × 10 mm column) to yield the (R)-MTPA ester 6 (13
mg, 33%): [R]D -71.2° (c 0.17, CHCl3); IR (CHCl3) νmax 3600,
Sigm oscep tr ellin D m eth yl ester (3b): a stable oil; [R]D
-57.8° (c 5.9, CHCl3); IR (film) νmax 1734 cm-1 1H and 13C
;
NMR (CDCl3) see Table 1; ESIMS (40 kV) m/z 443 (M + H,
31); HRESIMS (M + Na - H2O) 447.3089 (C25H44O5Na
requires 447.3086).
1
Sigm oscep tr ellin E m eth yl ester (4): a stable oil; [R]D
1740 cm-1; H NMR (CDCl3, 300 MHz) δ 7.54 (m, H3′, H5′),
-16.7° (c 0.23, CHCl3); IR (CHCl3) νmax 1730 cm-1; H NMR
7.40 (m, H2′, H4′, H6′), 5.38 (m, H3), 3.64 (s, CO2CH3), 3.54
(s, MTPA-OCH3), 2.86 (s, H2), 0.80-1.90 (br envelope, H24,
H25, H27, H28, H211, H212, H213, 10-CH3, 10-CH3, 14-CH3),
1.18 (d, J ) 7.3 Hz, 2-CH3), 1.04 (s, 6-CH3); EIMS (70 eV) m/z
541 (M - OH, 1), 405 (2), 307 (17), 237 (4), 197 (7), 189 (40).
Rea ction of Diol 5 w ith (S)-MTP A Acid . To a solution
of 5 (24 mg) in 5 mL of dry CH2Cl2 were added DCC (82.7
mg), DMAP (28 mg), and (S)-MTPA acid (82.7 mg), and the
solution was stirred for 16 h. The reaction mixture was
concentrated and purified as described above for 5 to yield the
(S)-MTPA ester 7 (24 mg, 61%): [R]D -37.8° (c 0.79, CHCl3);
1
(CDCl3, 400 MHz) δ 5.09 (br s, H9, H13, H17), 4.13 (ddd, J )
7.6, 7.6, 3.5 Hz, H3), 3.70 (s, CO2CH3), 2.65 (dq, J ) 7.6, 6.9
Hz, H2), 1.68 (s, H319), 1.60 (s, 10-CH3, 14-CH3, 18-CH3), 1.40-
2.05 (br envelope, H24, H25, H27, H28, H211, H212, H215, H2-
16), 1.29 (s, 6-CH3), 1.25 (d, J ) 6.9 Hz, 2-CH3); 13C NMR
(CDCl3, 100 MHz) δ 174.3 (s, C1), 135.5, 135.0, 131.3 (3s, C10,
C14, C18), 124.4, 124.1, 123.9 (3d, C9, C13, C17), 81.2 (d, C3),
80.1 (s, C6), 51.9 (q, CO2CH3), 43.0 (d, C2), 39.9, 39.7, 39.6
(3t, C7, C11, C15), 32.0 (t, C8), 26.7, 26.5 (2t, C12, C16), 25.7
(q, C19), 23.5 (t, C4), 21.7 (t, C16), 20.6 (q, 6-CH3), 17.7 (q,

218 J ournal of Natural Products, 1999, Vol. 62, No. 2
Ovenden and Capon
1
IR (CHCl3) νmax 3600, 1740 cm-1; H NMR (CDCl3, 300 MHz)
22%): IR (CHCl3) νmax 3610 cm-1; 1H NMR (CDCl3, 300 MHz)
δ 5.13 (br t, J ) 7.1 Hz, H 3), 2.04 (m, H2 4), 1.69 (s, 2 CH3),
1.62 (s, 1-CH3), 1.10-1.70 (br envelope, H2 5, H2 7, H2 8, H2 9,
H 10), 1.16 (s, 6-CH3), 0.88 (m, 10-CH3, 11-CH3); 13C NMR
(CDCl3, 75 MHz), 131.4 (s, C 2), 124.5 (d, C 3), 72.7 (s, C 6),
42.1, 41.5, 39.5 (3t, C 4, C 5, C 7), 27.9, 26.8, 25.6, 22.6 (4q, C
1, C 11, 6-CH3, 10-CH3), 22.6 (t, C 9), 22.5 (d, C 10), 21.6 (t, C
8), 17.5 (q, 2-CH3); ESIMS (25 kV) m/z 213 (M + H, 20), 235
(M + Na, 5); HRESIMS (M + Na) 235.2046 (C14H28ONa
requires 235.2038).
δ 7.54 (m, H3′, H5′), 7.40 (m, H2′, H4′, H6′), 5.38 (m, H5), 3.58
(s, CO2CH3), 3.51 (s, MTPA-OCH3), 2.85 (m, H2), 0.80-1.90
(br envelope, H24, H25, H27, H28, H211, H212, H213, 10-CH3,
10-CH3, 14-CH3), 1.12 (m, 2-CH3, 6-CH3); EIMS (70 eV) m/z
540 (M - H2O, 0.4), 525 (0.4), 385 (2), 359 (4), 251 (12).
Rea ction of Diol 10 w ith (R)-MTP A Acid . A solution of
10 (15 mg) in 5 mL of dry CH2Cl2 was treated as above for the
conversion of 5 into 6 to yield the (R)-MTPA ester 11 (5.3 mg,
24%): [R]D -90.7° (c 0.10, CHCl3); IR (CHCl3) νmax 3610, 1740
cm-1 1H NMR (CDCl3, 300 MHz) δ 7.54 (m, H3′, H5′), 7.40
;
Ack n ow led gm en t. We acknowledge L. Goudie and the
CSIRO Division of Oceanography, along with the crew and
scientific personnel aboard the O. R. V. Franklin, for the
collection of sponge specimens. We also acknowledge taxonomic
classification by L. Goudie, technical support by P. Niclasen,
and financial assistance from the Australian Research Council.
(m, H2′, H4′, H6′), 5.41 (m, H3), 3.62 (s, CO2CH3), 3.52 (s,
MTPA-OCH3), 2.77 (m, H2), 1.10-1.98 (br envelope, H24, H25,
H27, H28, H29, H10, H211, H212, H213, H215, H216, H217, H18),
1.14 (d, J ) 5.3 Hz, 2-CH3), 1.13 (s, 6-CH3), 0.87 (m, 10-CH3,
14-CH3, 18-CH3, H319); ESIMS (25 kV) m/z 631 (M + H, 5),
653 (M + Na, 1), 669 (M + K, 10).
Rea ction of Diol 10 w ith (S)-MTP A Acid . A solution of
10 (10 mg) in 5 mL of dry CH2Cl2 was treated as above for
conversion of 5 into 7 to yield the (S)-MTPA ester 12 (13.6
mg, 94%): [R]D -99.1° (c 0.13, CHCl3); IR (CHCl3) νmax 3610,
Refer en ces a n d Notes
(1) Kashman, Y.; Rotem, M. Tetrahedron Lett. 1979, 1707-1708.
(2) Albericci, M.; Braekman, J . C.; Daloze, D.; Tursch, B. Tetrahedron
1982, 38, 1881-1890.
(3) Manes, L.; Bakus, G.; Crews, P. Tetrahedron Lett. 1984, 25, 931-
934.
(4) Capon, R. J .; Macleod, J . K. Tetrahedron 1985, 41, 3391-3404.
(5) Capon, R. J .; MacLeod, J . K.; Willis, A. C. J . Org. Chem. 1987, 52,
339-342.
(6) Capon, R. J . J . Nat. Prod. 1991, 54, 190-195.
(7) He, H. Y.; Faulkner, D. J .; Lu, H. S. M.; Clardy, J . J . Org. Chem.
1991, 56, 2112-15.
1
1740 cm-1; H NMR (CDCl3, 300 MHz) δ 7.54 (m, H3′, H5′),
7.40 (m, H2′, H4′, H6′), 5.41 (m, H3), 3.66 (s, CO2CH3), 3.55
(s, MTPA-OCH3), 2.79 (m, H2), 1.10-1.98 (br envelope, H24,
H25, H27, H28, H29, H10, H211, H212, H213, H215, H216, H217,
H18), 1.18 (d, J ) 7.3 Hz, 2-CH3), 1.07 (s, 6-CH3), 0.87 (12H,
m, 10-CH3, 14-CH3, 18-CH3, H319); ESIMS (25 kV) m/z 631
(M + H, 5), 653 (M + Na, 1), 669 (M + K, 10).
Syn th esis of Alcoh ol 9. Concentrated H2SO4 (0.48 g, 4.9
mmol) was slowly added to 4-methyl-1-pentanol (1 g, 9.8
mmol), followed by slow addition of 48% hydrobromic acid (2.48
g, 0.015 mol), and the resulting mixture was refluxed for 5 h.
The reaction mixture was then diluted with H2O (100 mL) and
extracted into Et2O (3 × 50 mL). The combined ether extract
was washed with NaHCO3 (3 × 50 mL) and then brine (100
mL) and finally dried over anhydrous MgSO4 to yield 4-methyl-
1-bromopentane (740 mg, 46%). The crude bromide was
dissolved in Et2O (20 mL) and added dropwise to Mg turnings
(0.108 g, 4.5 mmol) in Et2O (10 mL) and refluxed for 2 h. After
this time, 6-methyl-5-hepten-2-one (0.57 g, 4.5 mmol) in Et2O
(20 mL) was added dropwise and the reaction mixture refluxed
for 30 min. The reaction mixture was diluted with H2O (50
mL) and 5 mL of 10% HCl added to dissolve the precipitate.
This mixture was then extracted into Et2O (3 × 50 mL),
washed with NaHCO3 (2 × 50 mL) and brine (100 mL), and
subjected to normal-phase HPLC (2.0 mL/min 10% EtOAc/
petroleum ether, Phenomenex 5 µm silica 250 × 10 mm
column) to yield 2,6,10-trimethyl-2-undecen-6-ol (9) (210 mg,
(8) Butler, M. S.; Capon, R. J . Aust. J . Chem. 1993, 46, 1363-1374.
(9) Tanaka, J .; Higa, T.; Suwanborirux, K.; Kokpol, U.; Bernardinelli,
G.; J efford, C. W. J . Org. Chem. 1993, 58, 2999-3002.
(10) Capon, R. J .; Rochfort, S. J .; Ovenden, S. P. B. J . Nat. Prod. 1997,
60, 1261-1264.
(11) Capon, R. J .; Rochfort, S. J .; Ovenden, S. P. B.; Metger, R. P. J . Nat.
Prod. 1998, 61, 525-528.
(12) Ovenden, S. P. B.; Capon. R. J . Aust. J . Chem. 1998, 51, 573-579.
(13) Sperry, S.; Valeriotre, F. A.; Corbett, T. H.; Crews, P. J . Nat. Prod.
1998, 61, 241-247.
(14) Capon, R. J . Marine norterpene cyclic peroxides: A stereochemical
paper chase. In Studies in Natural Products Chemistry; Atta-ur-
Rahman, Ed.; Elsevier: The Netherlands, 1991; Vol. 9, pp 15-34.
(15) Dale, J . A.; Mosher, H. S. J . Am. Chem. Soc. 1973, 95, 512.
(16) Kusumi, T.; Ohtani, I.; Inouye, Y.; Kakisawa, H. Tetrahedron Lett.
1988, 29, 4731-4734.
(17) Zheng, G.-C.; Ichikawa, A.; Ishitsuka, M. O.; Kusumi, T.; Yamamoto,
H.; Kakisawa, H. J . Org. Chem. 1990, 55, 3677-3679.
(18) Kitagawa, I.; Cui, Z.; Son, B. W.; Kobayashi, M.; Kyogoku, Y. Chem.
Pharm. Bull. 1987, 35, 124-135.
(19) Butler, M. S.; Capon, R. J . Aust. J . Chem. 1991, 44, 77-85.
(20) Bassett, S.; Gable, R. W.; Ovenden, S. P. B.; Capon, R. J . Aust. J .
Chem. 1997, 50, 1137-1143.
NP980223R