Synthesis and in vitro evaluation of analogues of avocado-produced toxin (+)-(R)-persin in human breast cancer cells

Article abstract of DOI:10.1016/j.bmc.2011.10.006

A structure-activity study of several new synthetic analogues of the avocado-produced toxin persin has been conducted, with compounds being evaluated for their cytostatic and pro-apoptotic effects in human breast cancer cells. A 4-pyridinyl derivative demonstrated activity comparable to that of the natural product, suggesting future directions for exploration of structure-activity relationships.

Full text of DOI:10.1016/j.bmc.2011.10.006

Bioorganic & Medicinal Chemistry 19 (2011) 7033–7043
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and in vitro evaluation of analogues of avocado-produced toxin
(+)-(R)-persin in human breast cancer cells
Darby G. Brooke a, , Elizabeth J. Shelley b, Caroline G. Roberts b, William A. Denny a,
⇑
Robert L. Sutherland b,c, Alison J. Butt b,c,
a Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
b Cancer Research Program, Garvan Institute of Medical Research, 384 Victoria St., Darlinghurst, Sydney 2010, New South Wales, Australia
c St. Vincent’s Clinical School, Faculty of Medicine, University of New South Wales, Sydney 2052, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2011
Revised 28 September 2011
Accepted 5 October 2011
Available online 13 October 2011
A structure–activity study of several new synthetic analogues of the avocado-produced toxin persin has
been conducted, with compounds being evaluated for their cytostatic and pro-apoptotic effects in human
breast cancer cells. A 4-pyridinyl derivative demonstrated activity comparable to that of the natural prod-
uct, suggesting future directions for exploration of structure–activity relationships.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Avocado
Persin
b-Hydroxyketone
Anti-cancer agent
Breast cancer
Estrogen receptor
1. Introduction
marine sponge natural product halichondrin B,13 whose isolation
and potent anti-cancer activity was reported 25 years ago,10 serves
Breast cancer is the most common cancer in women in both
developed and undeveloped countries, and the second most fre-
quent cause of cancer deaths, despite a major decline in breast
cancer mortality in the past decade.1 Current chemotherapy, pre-
dominantly for estrogen receptor-negative (ERꢀ) cancers, includes
the use of microtubule-interacting molecules such as paclitaxel and
related taxanes, plant-derived compounds whose apoptosis-pro-
moting abilities fuel much of the continuing interest in natural
products for treatment of human cancers.2,3 The susceptibility of
cancer cells to such disruptors of intracellular cytoskeletal integrity
is further emphasized by the varied structural classes of microtu-
bule-targeting agents currently in clinical4,5 and pre-clinical devel-
opment,6 and exemplified by the recent US and European approval
of eribulin (E7389,7 HalavenÒ) for the treatment of advanced met-
astatic breast cancer in women for whom anthracycline- and tax-
ane-based therapies have not been successful, or suitable.8
Eribulin affects microtubule dynamics in a unique fashion.9 This
property, coupled with the fact that it is a fully synthetic, structur-
ally simplified yet more potent macrocyclic ketone analogue of the
to underline the importance of continued investigations of natural
products to inspire and inform the development of new
pharmaceuticals.
(+)-(R)-(12Z,15Z)-2-Hydroxy-4-oxohenicosa-12,15-dien-1-yl
acetate (1) (Fig. 1), commonly called (+)-(R)-persin, is a novel poly-
ketide (‘acetogenin’), comprised of a b-hydroxy ketone system,
flanked on one side by an acetate group, and on the other by a long,
partially unsaturated hydrocarbon chain. It was originally isolated
from the leaves of the avocado Persea americana Mill. (Lauraceae)
by Japanese workers, who described its inhibition of the growth
of Bombyx mori (silkworm) larvae, and deduced its chemical struc-
ture.11 However, the absolute configuration about C-2 of 1 was not
confirmed until a stereoselective synthesis two decades later.12
Bioassay-driven fractionation analysis by Rodriguez-Saona et al.
located 1 and the structurally related 2-alkylfurans (‘avocadofurans’:
exemplified by 2 and originally reported by Kashman et al.13 and
Chang et al.11) in the idioblast oil cells of avocado fruit, and found
1 to deter feeding by the beet armyworm [Spodoptera exigua
Hübner (Noctuidae)], a major phytophagous insect pest in agricul-
ture.14 These workers also reported the isolation and characteriza-
tion from avocado idioblast oil cells of a compound they called
‘isopersin’ (3), in which the C-1 acetate and C-2 hydroxyl moieties
are in opposite positions relative to their location in 1, and which
had no deterrent effect to feeding by S. exigua.15 A solution of 3
⇑
Corresponding author. Tel.: +64 9 923 2233; fax: +64 9 373 7502.
E-mail address: d.brooke@auckland.ac.nz (D.G. Brooke).
Present address: Research Investment, National Breast Cancer Foundation, Level
9, 50 Pitt St., Sydney 2000, Australia.
0968-0896/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2011.10.006

7034
D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
sensitivity to circulatingsteroid hormone levels.19,20 In addition, sig-
OH
O
nificant positive effects have been observed in the dual treatment of
primary ER+ breast cancers with 5 and the anti-estrogen, tamoxi-
fen.21 5 has also been reported to synergize with the microtubule
inhibitor vinorelbine, an alkaloid derived by semi-synthesis from
alkaloids extracted from the rosy periwinkle (Catharanthus roseus),
in the inhibition of breast cancer cell proliferation.22 6 and 7 are po-
tent anti-cancer agents, particularly against breast cancer,23,24 how-
ever the pro-carcinogenicity of 7 in mouse models25 suggests its use
in cancer chemopreventative strategies should be avoided.
Me
O
2
Me
3
1
O
1
2
O
Me
Me
It has been proposed26 that the similarity of 1 to a monoglycer-
ide of linoleic acid (8) may indicate it interferes with fundamental
lipid metabolism processes within cells, thus accounting for its
wide range of biological activities. The precise biosynthetic origins
of 1 are unclear; whilst one might imagine its derivation from 2,
Carman and co-workers note27,28 that there are as-yet no known
enzymatic or natural chemical processes whereby the necessary
extrusion of an oxygen atom (a ‘reverse’ of the Baeyer–Villiger oxi-
dation) can be effected.§
We have previously described biological studies of 1, demon-
strating its selective induction of G2-M cell-cycle arrest, concomi-
tant with caspase-dependent apoptosis, in human breast cancer
cells.29 Observation of the intracellular morphological changes
resulting from this G2-M arrest, and other data, led us to hypothe-
size that 1 may interact with microtubules in a similar manner to
paclitaxel, although this has yet to be conclusively established,
and may be distinct from its activity in breast tissue. Further inves-
tigations revealed marked synergistic, pro-apoptotic cytotoxicity
between 1 and the active metabolite of tamoxifen, 4-hydroxytam-
oxifen, in human breast cancer cells, which we found to depend
on expression of the pro-apoptotic protein, Bim, and to be associ-
ated with an increase in de novo ceramide synthesis.30 Crucially,
1 had no effect on normal breast epithelial cells and, in contrast
with 4 and 5, its anti-cancer effects are independent of the ER status
of cells.– Although sensitization to the effects of tamoxifen has been
O
HO
O
O
Me
2
1
3
3
4
5
O
Me
HO
HO
O
Me
O
Me
Me
HO
HO
6
7
O
O
Me
HO
O
observed in ERꢀ MDA-MB-231 cells treated with
a celecoxib
OH
analogue,31 and in ER+ MCF-7 cells treated with extracts of Coptis
japonica (or the purified major alkaloid from the plant),32 the ER-
independent mode of action of 1 appears unique. These observations,
and the specificity of 1 for the malignant phenotype, spurred our
interest in synthesizing and examining the structure–activity rela-
tionships of a set of new analogues of 1.
8
Figure 1. Structures of (+)-(R)-persin (1),
(R)-isopersin (3), linoleic acid (4), -linolenic acid (5), 9-cis-11-trans-linoleic acid
(6), 10-trans-12-cis-linoleic acid (7), and a monoglyceride of linoleic acid (8).
a 2-alkyl furan derived from 1 (2),
c
in acetone at ꢀ20 °C was found to equilibrate to a mixture of 3 and
1 over several weeks, with the lack of prior reports of 3 being
attributed to this instability. Analogous to 1, compound 3 under-
went dehydration to 2 in the presence of trace acid.à The chemistry
and biology of these molecules, and around forty others isolated
from various parts of the avocado plant, have been reviewed.16
An Australian team reported in 199517 that the agalactia and
non-infectious mastitis observed in lactating animals fed avocado
leaves was due to 1 causing coagulative necrosis of the secretory epi-
thelium. High doses were shown to cause myocardial fibrosis and
necrosis in mice, accounting for the reported cardiotoxicity of in-
gested avocado leaves to animals. These researchers claimed the
utilization of 1 (and side-chain analogues thereof) for the treatment
of cancer (in particular breast cancer) in mammals, as well for the
inhibition of lactation, in a patent of the same year.18 The structure
of 1 suggests it shares a commonbiosyntheticorigin with polyunsat-
2. Chemistry
Synthesisof 1usedthemethodologyof MacLeodandSchäffeler,12
whereby treatment of ketone 9 with a commercially available
solution of (ꢀ)-B-chlorodiisopinocampheylborane [(ꢀ)-DIP-Cl]33
formed enol borinate 10, which then underwent an enantioselec-
tive aldol reaction with volatile aldehyde 11 (obtained by ozonol-
ysis of allyl acetate) to afford a reasonable yield of the natural
product (Scheme 1). Comparison of the measured optical rotation
value of the product (½a D25
ꢁ
= +10.78° (c 1.02, CHCl3)) with that ob-
tained by MacLeod and Schäffeler (½a D20
ꢁ
= +10.20° (c 1.00, CHCl3))12
confirmed the desired (R)-isomer had been formed. The close
agreement between these values (despite their being measured
at slightly different temperatures) suggests that the enantiomeric
urated fatty acids linoleic acid (4) and c-linolenic acid (5), and the
conjugated linoleic acids (CLAs) exemplified by cis-9-trans-11-lino-
leic acid (6) and trans-10-cis-12-linoleic acid (7) (Fig. 1). Biologically,
4 and 5 directly affect ER levels in cells, thereby modifying cellular
§
The only literature example comprises a formal ‘reverse Baeyer–Villiger’, induced
via a 3-step process, in a fully synthetic environment (Smith, III, A. B.; Foster, A. M.;
Agosta, W. C. J. Am. Chem. Soc. 1972, 94, 5100).
–
It has been suggested (Ref. 29) that the apparent in vivo specificity shown by 1 for
lactating mammarian tissue described in previous reports (Ref. 18) may be due to the
lactation process itself i.e. the dynamic changes in lipid composition known to occur
in lactating mammary epithelium could effect increased absorption/incorporation of
1 and its metabolites, generating the observed toxicity.
à
This acid-lability of 1 and 3, and the facility of acyl migration from C-2 to C-1 in 3,
illustrates the restrictions incumbent on any synthetic approaches to analogues of
these compounds.

D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
7035
excess (e.e.) of the quantity of 1 obtained by us was approximately
equal to the >90% e.e. of the literature material, which was calcu-
lated by chiral shift 1H NMR analysis of 1 with Eu(hfc)3.12 Under
the same conditions, reaction of 11 and 2-octanone (12) afforded
the truncated-chain analogue (+)-(R)-hexylpersin (13).
O
B
a
b
4
O
R
c
Me
9
Subsequent reduction of 1 gave its fully saturated analogue
(+)-(R)-tetrahydropersin (14). The isolation, from the avocado
plant,28 synthesis34,27 and the equipotency17,18 of 14 with 1 in
anti-cancer and anti-lactation screens have been previously
described. These workers also synthesized the enantiomeric
(ꢀ)-(S)-persin, and, interestingly, found it to be devoid of the bio-
logical activity shown by 1. A recent computational chemistry
study suggests that this may be due to: (a) the enantiomers pos-
sessing different torsion angles in the (Z,Z)-1,4-pentadiene system;
and (b) a possible anionic reaction intermediate of the (S)-enantio-
mer being incapable of favorable molecular orbital interactions
with any electrophilic reactant.35
R
10
CHO
Me
O
Me
O
d
O
O
11
1
e
OH
O
Me
O
Me
O
14
Attempts to access a more soluble analogue by transformation
of 14 to a C-2 phosphate ester via standard procedures (e.g.,36,37
)
R =
Me
were fruitless, with only unreacted and/or degraded 14 being
recovered in each case. This may be due to intramolecular hydro-
gen-bonding between the secondary b-hydroxyl group of 14 and
the adjacent carbonyl oxygen rendering the former moiety unreac-
tive (the presence of such an H-bond is supported by computa-
tional studies||) and/or inherent instability of 14 to the
phosphorylation conditions themselves.
OH
O
O
f
Me
O
Me
Me
Me
O
12
13
Subsequently, following information [MacLeod, J. K., personal
communication] that replacement of the acetate group of 1 with a
benzoate group afforded a compound with only slightly less activity
than 1, we turned to accessing an alternative set of (R)-aryl persin
analogues. Variation of the above route to 1, utilizing appropriate ar-
oyl aldehydes, was initially investigated as an approach to these.
Unfortunately, although the enantioselective aldol reaction be-
tween 9 and 2-oxoethyl benzoate38 afforded some of the desired
phenyl analogue (15), it was inseparable (via column or preparative
TLC chromatography) from large quantities of aldehyde-derived
impurities, and/or most of 9 was recovered unreacted. Other substi-
tuted aryl aldehydes yielded similar results, so this approach was
abandoned.
An alternative route to 15 was then devised, based upon the
route to 1 described by Li and co-workers.39 Thus, Horner–
Wadsworth–Emmons olefination of methyl linoleate (16) with
dimethyl methyl phosphonate, followed by condensation of the
resulting adduct with glycoaldehyde dimer, yielded enone alcohol
17. Treatment of 17 with phenylboronic acid and the quinine-thio-
urea catalyst 18 (obtained in a two-step process from quinine, as
per Vakulya et al.40), followed by hydrogen peroxide, effected a
stereospecific Michael addition of hydroxide to the b-carbon of
Scheme 1. Synthesis of (+)-(R)-persin (1) (+)-(R)-hexylpersin (13) and (+)-(R)-
tetrahydropersin (14). Reagents and conditions: (a) MeLi, THF, 0 °C, 2 h (76%); (b)
(ꢀ)-DIP-Cl (50–65 wt% in hexane), (i-Pr)2NEt, CH2Cl2, ꢀ78 °C, 5 h; (c) (i) O3, CH2Cl2,
ꢀ78 °C; (ii) PPh3, CH2Cl2, ꢀ78 °C, 3 h then ꢀ78 °C to rt, 12 h; (iii) Et2O, ꢀ15 °C, 12 h;
(d) (i) 11 (6.32 equiv), CH2Cl2, ꢀ78 °C, 1 h; then ꢀ15 °C, 19 h; (ii) 30% aq H2O2,
MeOH: pH 7 buffer, 2 h (33% from 9); (e) Pd/C, H2, EtOAc, rt, 12–24 h (quant.). (f) (i)
(ꢀ)-DIP-Cl (50–65 wt% in hexane), (i-Pr)2NEt, CH2Cl2, ꢀ78 °C, 2.5 h; (ii) 11
(6.04 equiv), CH2Cl2, ꢀ78 °C, 68 h; (iii) 30% aq H2O2, MeOH: pH 7 buffer, 3.3 h
(quant.).
(25 °C) = ꢀ127.9° (c 0.50, CHCl3)) showed it had the correct stereo-
chemistry to afford the desired (+)-(R)-enantiomers, and this was
supported by the measurement of the optical rotation of 15, which
was both positive and similar in magnitude to the literature value
([a] [a] (20 °C) = +10.70° (c
(28 °C) = +9.35° (c 1.03, CHCl3); lit.39
D
D
0.43, CHCl3)). Formation of deshydroxy compound 23 was unex-
pected (only a trace amount of the desired 4-nitrophenyl product
was isolated), but seems to be related to the presence of the 4-nitro
substituent on the phenyl ring. It is possible that re-exposure of 23
to the stereoselective hydroxide addition conditions described
above might yield the desired product, but this was not explored.
The fully saturated analogue 14 had proven similarly potent to 1
in our own and reported screens,17 and Kashman et al.13 and Carman
et al.26 have both suggested possible acid-catalyzed mechanisms by
which avocado-derived b-hydroxy ketones such as (or similar to) 1
and 14 might cyclize to 2-alkylfurans (e.g., 2, Fig. 1) which have also
been isolated from the plant,14,16 by a process involving loss of an
the olefin to give key b,c-diol 19 (Scheme 2). As expected, reaction
of 19 with benzoyl chloride and pyridine furnished 15, together
with a significant quantity of bis-addition adduct 20. Reaction of
19 with various appropriately functionalized aroyl chlorides suc-
cessfully produced several other persin analogues (21–25). In these
experiments, use of the more hindered 2,4,6-trimethylpyridine as a
base, as prescribed by Li et al.39 afforded a greater ratio of the
desired mono-aroylated product 21 than bis-isomer 22 (c.f. yields
of 15 vs 20), but it is not known whether this is a general effect.
Comparison of the optical rotation of the catalyst 18 with the
a
-hydrogen from C-3. We therefore reasoned that an analogue with
a quaternary centre at C-3 might possess greater stability, and hence
improved biological activity.41 Thus, we devised a synthetic ap-
proach to 26, the -diol analogue of 19, which we
envisaged could be elaborated to a-dimethyl-tetrahydropersin (27).
Octadecanol (28) was oxidized via the conditions of Easton et
al.42 to the corresponding aldehyde 29, which was in turn reacted
with an in situ-generated prenyl-indium species43,44 to yield the
a
-dimethyl-b,
c
literature value ([
a]
(29 °C) = ꢀ125.6° (c 1.06, CHCl3); lit.40
[
a]
D
D
||
As delineated by Mendoza-Wilson et al. (Ref. 35), the presence of a hydrogen
bond in 1 is supported by: (a) the relatively downfield chemical shift for the 2-OH
proton in the 1H NMR spectrum of 1 (3.24 ppm); and (b) by the calculated distance
between the 2-OH proton and the oxygen of the C-4 carbonyl group in the optimized
aqueous phase structures (of both enantiomers) being 2.00 Å (correlating with the
existence of a medium-to-weak-strength hydrogen bond).
key
Goldman oxidation44,45 of 30 to ketone 31, followed by epoxidation
of the terminal olefin of 31,46 afforded
-dimethyl-b, -epoxide 32.
Crucially, by utilization of hydrolytic kinetic resolution (HKR)
a-dimethyl-b,c-unsaturated alcohol 30 (Scheme 3). Albright-
a
c

7036
D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
O
O
OH
OH
O
O
O
O
O
+
+
O
O
R
R
R
R
O
O
15
20
c
Br
Br
O
O
O
O
c
O
O
O
O
OH
b
21
22
a
HO
HO
R
R
MeO
R
19
17
c
16
O2N
O2N
O
O
O
O
O
O
R =
Me
c
+
O
R
R
R
O
O
O
23
24
OMe
H
N
CF3
N
OH
NH
N
O
S
18
N
CF3
H
25
Scheme 2. Synthesis of (R)-aryl-substituted persin analogues. Reagents and conditions: (a) (i) MeP(O)(OMe)2, LDA, THF, ꢀ78 °C, 2 h; (ii) [HC(O)CH2OH]2, LiCl, (i-Pr)2NEt,
CH3CN, rt, 2 h; (b) PhB(OH)2, 18 (10 mol %), 4Å MS, CH2Cl2, rt, 56 h then H2O2, Na2CO3, rt, 15 min (71%); (c) benzoyl chlorides, pyridine, CH2Cl2, rt, 12–23 h.
OH
O
O
our surprise, the optical rotation for 27 was negative
a
b
(½a 2D8
ꢁ
= ꢀ13.66° (c 1.03, CHCl3)), the significance of which will be
c
HO
R
R
R
H
R
discussed later.
Me Me
30
Me Me
28
29
31
3. Biological results and discussion
O
O
OH
O
O
O
d
e
HO
+
Of the many biologically active compounds isolated from avoca-
dos,14,16 (+)-(R)-persin (1) and, additionally, (+)-(R)-tetrahydroper-
sin (14), have been determined as responsible for the toxicity
observed in mammary and heart tissues of animals.17 Having noted
the structural similarities between 1 and the naturally occurring
R
R
R
Me Me
Me Me
Me Me
34
32
26
f
compounds linoleic acid (4), c-linolenic acid (5), and CLAs 6 and
OH
O
H
N
H
7 (Fig. 1), some of which are known to possess anti-cancer proper-
ties of their own,21–24 we conducted and have previously reported
investigations which revealed its ability to selectively induce G2-M
cell cycle arrest in human breast cancer cells.29 Moreover, we
found that 1 demonstrated synergistic pro-apoptotic cytotoxicity
with the anti-estrogen, tamoxifen, in human breast cancer cells,
which depended on expression of the pro-apoptotic protein BIM,
and was associated with increased de novo ceramide synthesis.30
Given these observations, and the fact that 1 had no effect on
normal breast cancer cells, nor any requirement for cells possess-
ing a particular ER status,30 we instigated the research project
described herein, with the aim of finding a more potent analogue
of 1. The results of this work are collated in Tables 1 and 2.
All compounds were tested for efficacy over a 24 h period, and
cell viability was determined by MTS assay. As can be seen in Table
1, the fully saturated natural product (+)-(R)-tetrahydropersin (14),
which has been reported as being as active as 1 in anti-lactation
screens,17 indeed proved similarly potent, whilst the truncated-
chain analogue 13 was devoid of activity within the studied concen-
tration range. These data indicate that side-chain length is crucial to
N
Me
O
R
Co
Me Me
27
O
tBu
O
O
tBu
OAc
33
tBu
tBu
R = (CH2)16Me
Scheme 3. Route to (ꢀ)-(R)-
a
-dimethyl tetrahydropersin (27). Reagents and
conditions: (a) PCC, CH2Cl2, rt (82%); (b) 1-bromo-3-methylbut-2-ene, In (powder),
DMF, rt (22%); (c) Ac2O, DMSO, rt, 46 h (96%); (d) OxoneÒ, NaHCO3, acetone:H2O
(4:1), rt (75%); (e) 33 (2.7 mol %), H2O, rt, 36 h [53%(34), 34%(26)]; (f) acetyl
chloride, 2,4,6-trimethylpyridine, CH2Cl2, ꢀ78 °C to rt (40%).
methodology developed by Schaus et al.47 as employed in a struc-
turally analogous system by Liu et al.46 and also by reference to the
HKR conditions of others,48–50 (S,S)-cobalt(III)-salen complex 3351
effected the transformation of racemic epoxide 32 into a ꢂ1.7:1.0
mixture of epoxide 34 and desired a-dimethyl-b, c-diol 26. Treat-
ment of 26 with acetyl chloride, under basic conditions analogous
to those used for formation of 21–25, provided 27 in fair yield. To

D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
7037
Table 1
Inhibition of growth of ER+ human breast cancer cell line MCF-7 by 24 h treatment with (+)-(R)-persin (1) and analogues
Structure
No.
clogPa
tPSAa
63.6
IC50 (lM)
O
OH
Me
Me
O
1
6.8
15.1b 1.3c
Me
O
OH
O
O
14
13
15
7.8
2.0
8.5
63.6
63.6
63.6
17.1 1.7
Me
O
OH
O
Me
Me
O
Inactive (>65)d
27.0 5.5
O
O
OH
O
Me
Me
O
O
20
21
10.9
9.37
69.7
63.6
Inactive (>27)c
O
O
O
O
Br
OH
O
O
23.8 2.2
Me
O
Br
22
23
24
12.7
69.7
95.2
173.3
Inactive (>21)c
Inactive (>32)c
Inactive (>24)c
Br
O
O
O
O
Me
O
O2N
O
O
9.1
Me
O
NO2
10.4
O2N
N
O
O
O
O
Me
O
O
OH
OH
O
25
27
7.1
8.7
76.0
63.6
20.1 3.6
29.0 4.2
Me
O
O
Me
O
Me
Me Me
O
a
b
c
clogP = calculated logarithm of the octanol/water partition coefficient, tPSA = topological polar surface area (calculated by ChemBioDraw Ultra v.12.0).
c.f. IC50 = 21.5 1.9 for 1 extracted from avocado leaves: this demonstrates the efficacy of a synthetic approach to 1.
Standard deviation.
d
IC50 lies above the stated (highest tested) concentration (= 15
lg/mL): 1 is highly toxic to the majority of breast cancer cell lines studied at 10 lg/mL, thus, in order to
identify any more analogues, 15
l
g/mL was the maximum tested concentration.

7038
D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
Table 2
Inhibition of growth of human cancer cell lines by 24 h treatment with (+)-(R)-persin (1) and (+)-(R)-tetrahydropersin (14)f
a
Tissue
Breast
Cell line
SHR statusb
p53 status
Bim statusc
IC50 (lM)
1
14
MCF-7
T-47D
MDA-MB-468
MDA-MB-157
SkBr3
ER+
ER+
ERꢀ
ERꢀ
ERꢀ
ERꢀ
ERꢀ
ERꢀ
n/a
wt
+++
15.1 1.3
30.3 2.3
25.0 2.8
12.8 1.25
19.7 1.3
32.1 2.3
>39
18.2 2.3
20.7 3.2
>39d
>39
>39
>39
>39
>39
>39
>39
mut
mut
mut
mut
mut
mut
wt
mut
mut
mut
wt
+ꢀꢀ
+++
+ꢀꢀ
+++
Hs578T
ꢀꢀꢀ
ꢀꢀꢀ
+ꢀꢀ
ꢀꢀꢀ
+++
MDA-MB-231
MCF-10A (n)e
OVCAR3
IGROV-1
PC-3
>39
Ovarian
27.9 4.5
15.6 3.6
30.0 3.0
22.0 1.8
n/a
Prostrate
ARꢀ
++ꢀ
>39
>39
LNCaP
AR+
+++
a
b
c
d
e
f
Mean standard error of triplicate wells from at least three independent experiments.
SHR = steroid hormone receptor.
‘+++’ indicates expression of BimEL, BimL, and BimS isoforms, respectively.
IC50 lies above the stated (highest tested) concentration (= 15
(n) = normal.
lg/mL: see Table 1 footnote).
The experiments summarised in Table 1 (a comparison of the effect of several different analogues on MCF-7 cells) and Table 2 (a comparison of the effect of two analogues
on a panel of cell-lines, including MCF-7 cells) were performed independently, and the differing values for MCF-7 cells (although not actually statistically different from each
other) may reflect small differences in batches of cell lines, sera or other biological variables.
the anti-breast cancer activity of 1, whilst the presence of unsatura-
tion is not. It is interesting to note, however, that short-chain ,b-
27 did display activity suggests the hydrolytic kinetic resolution
of epoxide 32 catalyzed by 33 did afford the desired (R)-diol 26,
with the absolute configuration about C-2 being preserved in 27.
(The activity of (ꢀ)-(S)-persin against breast cancer cells has yet
to be investigated, although it seems reasonable to propose that
this unnatural isomer will be as inactive therein as it is in lactating
mammary tissue).
a
unsaturated b0-hydroxy-, -acetoxy-, and -phenoxy-ketones have
potency against malignant pleural mesothelioma cell lines, have
been shown to potentiate the effects of paclitaxel in pancreatic duc-
tal adenocarcinoma cells,52,53 and, in addition, are efficacious
against colon carcinoma, ovarian, breast and non small-cell lung
cancer cell lines.54
Accordingly, we hypothesize that the presence of the two methyl
groups on C-3, adjacent to the chiral carbon, has profound effects on
the configuration adopted by 27 in solution, leading to the observed
optical rotation. This novel finding needs further investigation, but
may be analogous to the large variability in optical rotation values
observed in a set of tubulin-binding thiocolchicines, which is attrib-
uted to changes in biaryl dihedral angle resulting from different sub-
stituents on a position beta to a chiral carbon.57 An even more
striking example of substituent effects upon the optical rotation of
otherwise identical molecules is seen in calyculins A and B, members
of a family of natural products with significant anti-protein phos-
phatase and both anti- and pro-carcinogenic activities isolated from
the sponge Discodermia calyx.58 In this instance, a 70-unit difference
in the optical rotation of the two compounds is observed, with the
only structural difference between the molecules being the position
of a –CN substituent on a double bond separated by nine carbons
from the nearest asymmetric centre (of which there are 15). A com-
putational analysis concluded that this remarkable variation is due
to the differing degree of polarizability of the –CN group in each iso-
mer, which influences the electronic character of the adjoining car-
bon–carbon double bond, and which may be amplified through the
molecules’ extended conjugated system.59
The activity of 15 and 21, whilst less than that of 1, indicates
there is a significant degree of lipophilic bulk-tolerance at the
left-hand end of the molecule, with the more lipophilic and more
electron-deficient bromophenyl compound 21 being slightly more
potent. This may suggest an electronic-deficient aromatic system is
more favored at this position. In contrast, bis-aroylated compounds
20, 22 and 24, and the enone 23, were inactive, underscoring the
importance of the b-hydroxyl moiety [and echoing the inactivity
of 3 (Fig. 1), albeit in a different context15].
The comparable activity of pyridinyl compound 25 with that of
1 is noteworthy, and may be partly attributable to these com-
pounds’ similar lipophilicity. In addition, the greater polarity im-
parted by the presence of the N atom in the aromatic ring, as
evidenced by its higher tPSA value (Table 1), presumably enhances
the solubility of 25. This suggests that future exploration of similar
heteroaryl analogues of 1 could prove fruitful.
Finally, it can be seen that the dimethyl moiety on C-3 of 27 does
not enhance its biological activity relative to 14, as had been hoped.
This may be due to steric constraints imposed on the b-hydroxy ke-
tone system by the presence of an
a-dimethyl group, and indicative
of a role played by the -CH2 moiety in the in vitro mode of action of
a
these compounds. However, as no data have been reported on the
anti-cancer activity of alkyl furan 2 (Fig. 1) or its analogues
(although one publication describes the inhibition of chemically in-
duced carcinogenesis by 2-n-heptyl furan and a related alkyl thio-
phene55), this is not necessarily evidence of a 2-alkyl furan
derived from 14 possessing biologically activity. It is nevertheless
interesting to note that the activity of 27 is comparable to that of
We have previously reported that the activity of 1 in breast can-
cer cells is not dependent on their ER status, and is specific for the
malignant phenotype,30 and this is supported by further data in
Table 2. Firstly, the phenotypically normal mammary cell-line
MCF-10A was non-responsive to both 1 and 14, in keeping with
prior observations.30 Moreover, it can be seen that the presence
of neither ER nor androgen receptor (AR) is necessary for the
cytostatic effects of 1 to be observed, which suggests 1 and its
15 and 21, which shows that a-substitution of the b-hydroxyketone
system is not wholly deleterious.
The negative optical rotation exhibited by 27 is intriguing, being
in contrast to the positive optical rotations displayed by the other
isomers of 1 described here.56 However, given the reported inactiv-
ity of (ꢀ)-(S)-persin in lactating mammary glands,17 the fact that
In contrast to this inactivity of (S)-1, the orientation of the C-2 hydroxyl group in
persenones A & B, a0,b0-unsaturated analogues of 1, is reportedly not critical to their
activity (Kim, O. K.; Murakami, A.; Nakamura, Y.; Kim, H. W. Biosci. Biotechnol.
Biochem. 2000, 64, 2500).

D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
7039
analogues may have efficacy in other cancers.àà The same trend
cannot be said to hold for 14, however, whose fully saturated side-
chain appears to render it inactive in all but ER+ cells. The toxicity
of 1 in Hs578 cells indicates Bim-independent cytostatic pathways
may also be activated by this compound.
VG-70SE mass spectrometer at nominal 5000 resolution. High-
resolution electrospray ionization (HRESIMS) and atmospheric
pressure chemical ionization (HRAPCIMS) mass spectra were
determined on a Bruker micrOTOF-Q II mass spectrometer. Low-
resolution atmospheric pressure chemical ionization (APCI) mass
spectra were measured for organic solutions on a ThermoFinnigan
Surveyor MSQ mass spectrometer, connected to a Gilson autosam-
pler. Thin-layer chromatography was carried out on aluminium-
backed silica gel plates (Merck 60 F254), with visualization of
components by UV light (254 and 365 nm), and by staining in basic
aqueous permanganate and ethanolic phosphomolybdic acid solu-
tions. Column chromatography was carried out on silica gel (Merck
230–400 mesh). Tested compounds were unanalyzable by stan-
dard HPLC techniques due to their lack of a suitable chromophore
and/or instability, but were estimated as being >90–95% pure by 1H
NMR and TLC analysis. Optical rotation measurements were per-
formed on a Schmidt and Haensch Polartronic NH8 polarimeter
at 589.44 nm, and are referenced to a certified quartz cell. The
absolute configurations of 1,12 1428 and 1539 were established by
comparison of their optical rotations with literature values. All
other absolute configurations (20, 22, 24 and 25) were assigned
by analogy, although a similar assumption cannot be made as to
the polarity of optical rotation of these compounds. A slight mod-
ification of the literature method12 was used for the synthesis of
(+)-(R)-persin, as outlined below. Other known compounds were
synthesized by reported methods, as indicated.
A recent study demonstrated that in a cell-line model of
ERꢀ/AR+ molecular apocrine breast cancer, MDA-MB-453, AR emu-
lates the pro-proliferative DNA-binding and transcriptional regula-
tion capabilities of ER.60 The authors suggest that these findings add
further weight to the concept of utilizing anti-androgens for the
treatment of apocrine breast cancers, which do not respond well
to therapy with ER antagonists (e.g., tamoxifen, aromatase inhibi-
tors).61 This thesis is supported by other new research, showing
that the anti-androgen bicalutamide inhibits the growth of ERꢀ/
AR+/HER2+ tumors (derived from MDA-MB-453 xenografts) in
mice, via inhibition of the androgen-stimulated HER2/HER3 signal-
ing cascade.62 Bicalutamide is currently under investigation for the
treatment of metastatic ERꢀ/AR+ breast cancer (NCT00468715),
and these researchers note that the androgen-signaling- and
HER2-dependence of the growth inhibition they observed may be
critical to its efficacy in this setting. It would be interesting to exam-
ine the role 1 might play in this milieu, given the known ability of 1
to potentiate the pro-apoptotic effects of tamoxifen in both ERꢀ
and ER+ cells.30
4. Conclusion
5.2. Synthesis
Several analogues of the avocado-produced toxins (+)-(R)-persin
(1) and (+)-(R)-tetrahydropersin (14) have been synthesized, and
analyzed for their cytostatic and pro-apoptotic effects in human
breast cancer cell lines. A number of structural features important
and/or critical to the biological activity of such compounds have
been revealed. Truncated-chain analogue 13 was inactive within
the concentration range of interest, showing that the length of the
side-chain was crucial for activity. Enone 23 and bis-aroylated com-
pounds 20, 22 and 24 were similarly inactive, indicating that a free
b-hydroxyl group is essential. Phenyl (15) and 4-bromophenyl (21)
analogues were less active than the natural products, but 4-pyridi-
nyl derivative 25 demonstrated potency comparable to that of 1,
indicating heterocyclic analogues may be a fruitful area for future
5.2.1. 2-Acetoxyacetaldehyde (11)
Two batches of allyl acetate (each of 13.00 mL, 119.46 mmol;
total of 238.92 mmol) were ozonolysed according to the procedure
of MacLeod & Schäffeler12 and the resulting crude product mix-
tures combined. Column chromatography of this material on silica
gel, eluting with 0–50% Et2O:CH2Cl2, afforded 11 as a pale yellow
oil (15.62 g, 64%), which was estimated as ꢂ60% clean by 1H
NMR analysis, and whose primary 1H NMR signals were consistent
with the literature.12 This was used immediately, without further
purification: TLC Rf = 0.29 in 10% Et2O:CH2Cl2.
5.2.2. (+)-(R)-(12Z,15Z)-2-Hydroxy-4-oxohenicosa-12,15-dien-1-
yl acetate [(+)-(R)-persin] (1)
exploration. In contrast, the lower activity of a-dimethyl analogue
27 suggests the natural b-hydroxyketone system is important for
A solution of (ꢀ)-B-chlorodiisopinocampheylborane [(ꢀ)-DIP-Cl]
(50–65 wt.% in hexanes—assumed to be 50 wt.%, 7.35 mL,
10.64 mmol, 2.00 equiv) was added to CH2Cl2 (5 mL), and the result-
ing solution cooled to ꢀ78 °C. To this solution (i-Pr)2NEt (2.78 mL,
15.96 mmol, 3.00 equiv) was added dropwise, followed by a solu-
tion of linoleic ketone 912 (1.48 g, 5.32 mmol, 1.00 equiv) in CH2Cl2
(10 mL), and the resulting mixture stirred in the dark at ꢀ78 °C for
195 min. At this point, further quantities of (ꢀ)-DIP-Cl (7.35 mL,
10.64 mmol, 2.00 equiv) and (i-Pr)2NEt (2.78 mL, 15.96 mmol,
3.00 equiv) were added, and stirring was continued in the dark at
ꢀ78 °C for 325 min. After this time, a solution of freshly columned
aldehyde 11 (ꢂ60% clean, 5.72 g, 33.59 mmol, 6.32 equiv) in CH2Cl2
(19 mL) was added, and the resulting mixture stirred in the dark at
ꢀ78 °C for 65 min, and then left sitting between ꢀ30 and ꢀ20 °C
in a freezer in the dark for 19 h. The reaction mixture, held at
ꢀ20 °C in a cooling-bath, was then quenchedby addition ofpH 7 buf-
fer (50 mL), and the resulting mixture extracted with Et2O (ꢃ4). The
combined organic extracts were dried (MgSO4), and then concen-
trated to dryness in vacuo. The residue was re-dissolved in MeOH
(100 mL) and pH 7 buffer (30 mL), and cooled to 0 °C. 30% aq H2O2
(30 mL) was added, and resulting mixture stirred at rt in the dark
for 2 h. The mixture was then poured into H2O, and extracted with
CH2Cl2 (ꢃ3). The combined organic extracts were washed sequen-
tially with saturated aqueous NaHCO3 and brine, and then dried
the optimal anti-cancer activity of these compounds.
5. Experimental section
5.1. General procedures
All non-aqueous reactions were conducted in oven- or heat-
gun-dried glassware under a positive pressure of dry nitrogen,
and utilizing commercially available dry solvents, unless otherwise
noted. 2,4,6-Trimethyl pyridine was distilled from CaH2, and stored
over 4 Å molecular sieves. pH 7 buffer was prepared from aqueous
mixtures of NaH2PO4 and Na2HPO4. Melting points were deter-
mined on an Electrothermal IA9100 melting point apparatus, and
are as read. 1H NMR spectra were measured on a Bruker Avance
400 spectrometer at 400 MHz and are referenced to Me4Si. Chem-
ical shifts and coupling constants are recorded in units of parts per
million (ppm) and hertz (Hz), respectively. High-resolution
electron impact (HREIMS) mass spectra were determined on a
àà
This finding illustrates that the cytostatic effects of 1 cannot be ascribed solely to
dynamic changes in lipid composition occurring during lactation. It is interesting to
speculate that 1 may behave as a less lipophilic analogue of linoleic acid (4), and thus
deleteriously perturb levels of arachidonic acid and derived eicosanoids in rapidly
replicating cancer cells.

7040
D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
(MgSO4), and finally concentrated to dryness in vacuo. The resulting
colorless oil was purified by column chromatography on silica gel,
eluting with 0–40% EtOAc/hexanes, to afford 1 (658 mg, 33%) as a
colorless oil: 1H NMR (CDCl3): 5.48–5.24 (m, 4H), 4.38–4.24 (m,
1H), 4.11 (dd, J = 11.5, 4.0 Hz, 1H), 4.05 (dd, J = 11.5, 6.2 Hz, 1H),
3.11 (d, J = 3.9 Hz, 1H), 2.77 (distorted t, 2H), 2.65–2.60 (m, 2H),
2.44 (t, J = 7.4 Hz, 2H), 2.10 (s, 3H), 2.05 (app q, J = 13.6, 6.7 Hz,
4H), 1.65–1.50(moverlapping water peak, 2H), 1.43–1.22 (m, 14H), 0.89
(t, J = 6.9 Hz, 3H); HRESIMS calc. for C23H40NaO4 (M+Na)+ m/z
C
23H44NaO4 m/z (M+Na)+ 407.3132, found 407.3160; ½a 3D0
ꢁ
= +6.94°
(c 0.87, CHCl3; lit.28
½
a 3D0
= +13.8° (c 3.90, CHCl3)); TLC Rf = 0.20–
ꢁ
0.40 (30% EtOAc/hexanes).
5.2.5. (+)-(R)-(12Z,15Z)-2-hydroxy-4-oxohenicosa-12,15-dien-1-
yl benzoate (15) and (R)-(12Z,15Z)-4-oxohenicosa-12,15-diene-
1,2-diyl dibenzoate (20)
To a solution of b,c
-diol 1939 (381 mg, 1.13 mmol, 1.00 equiv) in
CH2Cl2 (20 mL) was added pyridine (0.45 mL, 5.63 mmol,
5.00 equiv), and the resulting solution cooled to 0 °C. Benzoyl chlo-
ride (0.33 mL, 2.81 mmol, 2.50 equiv) was added slowly to this
solution, and the resulting mixture allowed to stir for a further
5 min at 0 °C, and then allowed to warm to rt overnight, in the
dark. After this time, the reaction mixture was cooled to 0 °C,
quenched with saturated aqueous NaHCO3, and allowed to warm
to rt The mixture was extracted with CH2Cl2 (ꢃ5), and the com-
bined extracts were washed with brine, dried (MgSO4), and con-
centrated to dryness in vacuo. The resulting oil was purified by
column chromatography on silica gel, eluting with 0–25% EtOAc/
hexanes, to afford 20 (431 mg, 70%) as a colorless oil: 1H NMR
(CDCl3): 8.06–7.96 (m, 4H), 7.60–7.51 (m, 2H), 7.46–7.38 (m, 4H),
5.89–5.79 (m, 1H), 5.44–5.28 (m, 4H), 4.64 (dd, J = 12.0, 3.7 Hz,
1H), 4.58 (dd, J = 12.0, 5.4 Hz, 1H), 3.20 (dd, J = 17.0, 6.5 Hz, 1H),
2.90 (dd, J = 17.0, 6.5 Hz, 1H), 2.76 (t, J = 6.2 Hz, 2H), 2.46 (t,
403.2819, found 403.2832; ½a D25
ꢁ
= +10.78° (c 1.02, CHCl3; lit.
½
½
½
a 2D0
a 2D2
a 2D3
ꢁ
= +10.20° (c 1.00, CHCl3),12
½
½
a 2D2
a 2D4
ꢁ
= +10.70° (c 1.00, CHCl3),17
= +11.30° (c 0.45, CHCl3),11
ꢁ
= +11.98° (c 1.00, CHCl3),17
+11.20° (c 1.00, CHCl3),63
ꢁ
ꢁ
½
a 2D2
ꢁ
+10.50° (c 0.26, CHCl3)64); TLC
Rf = 0.20–0.30 (30% EtOAc/hexanes).
5.2.3. (R)-2-Hydroxy-4-oxodecyl acetate (13)
A solution of (ꢀ)-B-chlorodiisopinocampheylborane [(ꢀ)-DIP-Cl]
(50–65 wt.% in hexanes—assumed to be 50 wt.%, 1.50 mL,
2.04 mmol, 2.00 equiv) was added toCH2Cl2 (1.5 mL), and the result-
ing solution cooled to ꢀ78 °C. To this solution (i-Pr)2NEt (0.53 mL,
3.07 mmol, 3.00 equiv) was added dropwise, followed by a solution
of 2-octanone (12) (0.16 mL, 1.02 mmol, 1.00 equiv) in CH2Cl2
(1.5 mL), and the resulting mixture stirred in the dark at ꢀ78 °C
for 80 min. At this point, further quantities of (ꢀ)-DIP-Cl (1.50 mL,
2.04 mmol, 2.00 equiv) and (i-Pr)2NEt (0.53 mL, 3.07 mmol,
3.00 equiv) were added, and stirring was continued in the dark at
ꢀ78 °C for 85 min. After this time, a solution of freshly columned
aldehyde 1112 (ꢂ50% clean, 1.261 g, 6.17 mmol, 6.04 equiv) in
CH2Cl2 (10 mL) was added, and the resulting mixture stirred in the
dark at ꢀ78 °C for 70 min, and then left sitting between ꢀ30 and
ꢀ20 °C in a freezer in the dark for 68 h. The reaction mixture, held
at ꢀ20 °C in a cooling-bath, was then quenched by addition of pH
7 buffer (10 mL), and the resulting mixture extracted with Et2O
(ꢃ4). The combined organic extracts were dried (MgSO4), and then
concentrated to dryness in vacuo. The residue was re-dissolved in
MeOH (40 mL) and pH 7 buffer (15 mL), and cooled to 0 °C. 30% aq
H2O2 (40 mL) was added, and resulting mixture stirred at rt in the
dark for 2 h. The mixture was then poured into H2O, and extracted
with CH2Cl2 (ꢃ3). The combined organic extracts were washed
sequentially with saturated aqueous NaHCO3 and brine, and then
dried (MgSO4), and finally concentrated to dryness in vacuo. The
resulting colorless oil was purified by column chromatography on
silica gel, eluting with 0–40% EtOAc/hexanes, to afford 13 (303 mg,
quantitative) as a colorless oil: 1H NMR (CDCl3): 4.35–4.25 (m,
1H), 4.11 (dd, J = 11.5, 4.1 Hz, 1H), 4.06 (dd, J = 11.5, 6.2 Hz, 1H),
3.12 (d, J = 3.9 Hz, 1H), 2.67–2.59 (m, 2H), 2.44 (t, J = 7.4 Hz, 2H),
J = 7.4 Hz, 2H), 2.10–1.96 (m, 2H), 1.67–1.51 (moverlapping water peak
,
4H), 1.41–1.18 (m, 14H), 0.88 (t, J = 6.9 Hz, 3H); HRESIMS calcd
for m/z C35H46NaO5 m/z (M+Na)+ 569.3237; found 569.3253; TLC
Rf = 0.41 (20% EtOAc/hexanes); and 15 (91 mg, 18%) as a low-melt-
ing crystalline solid: mp <37 °C; 1H NMR (CDCl3): 8.09–8.01 (m,
2H), 7.62–7.54 (m, 1H), 7.50–7.41 (m, 2H), 5.44–5.27 (m, 4H),
4.49–4.40 (m, 1H), 4.40–4.30 (m, 2H), 3.20 (br s, 1H), 2.77 (dis-
torted t, 2H), 2.71 (d, J = 6.0 Hz, 2H), 2.46 (t, J = 7.4 Hz, 2H),
2.11–1.98 (m, 4H), 1.68–1.44 (moverlapping
peak, 2H), 1.41–
water
1.22 (m, 14H), 0.89 (t, J = 6.9 Hz, 3H); HRESIMS calcd for
28H42NaO4 m/z 465.2975, found 465.2987;
(M+Na)+
= +8.74° (c 1.03, CHCl3; lit.39
= +10.70 (c 0.43, CHCl3));
TLC Rf = 0.29 (20% EtOAc/hexanes).
C
½
a 2D8
ꢁ
½ ꢁ
a 2D0
5.2.6. (+)-(R)-(12Z,15Z)-2-hydroxy-4-oxohenicosa-12,15-dien-1-
yl 4-bromobenzoate (21) and (R)-(12Z,15Z)-4-oxohenicosa-
12,15-diene-1,2-diyl bis(4-bromobenzoate) (22)
A solution of b,c
-diol 1939 (412 mg, 1.22 mmol, 1.00 equiv) in
CH2Cl2 (35 mL) was allowed to react with 2,4,6-trimethyl pyridine
(0.80 mL, 6.09 mmol, 5.00 equiv) and 4-bromobenzoyl chloride
(724 mg, 3.30 mmol, 2.71 equiv) for 23 h under the conditions out-
lined in Section 5.2.5. The resulting solid was purified by column
chromatography on silica gel, eluting with 0–20% EtOAc/hexanes,
to afford 22 (195 mg, 23%) as a colorless oil: 1H NMR (CDCl3):
7.95–7.77 (m, 4H), 7.67–7.49 (m, 4H), 5.86–5.77 (m, 1H),
5.43–5.27 (m, 4H), 4.62 (dd, J = 12.0, 3.5 Hz, 1H), 4.55 (dd,
J = 12.0, 5.8 Hz, 1H), 2.99 (dd, J = 17.1, 6.5 Hz, 1H), 2.87 (dd,
J = 17.1, 6.5 Hz, 1H), 2.76 (t, J = 6.0 Hz, 2H), 2.45 (t, J = 7.4 Hz, 2H),
2.10 (s, 3H), 1.65–1.51 (moverlapping
peak, 2H), 1.37–1.22
water
(m, 6H), 0.96–0.82 (m, 3H); HRESIMS calcd for
C12H22NaO4
(M+Na)+ m/z 253.1410, found 253.1423; TLC Rf = 0.20–0.30 (30%
EtOAc/hexanes).
5.2.4. (+)-(R)-2-Hydroxy-4-oxohenicosyl acetate [(+)-(R)-
tetrahydropersin] (14)
2.10–1.80 (m, 4H), 1.65–1.52 (moverlapping
peak, 2H), 1.44–
water
To a solution of 1 (160 mg, 0.42 mol) in EtOAc (150 mL) was
added 10% Pd/C (ꢂ100 mg), and the resulting suspension was
hydrogenated at 15 psi overnight. After this time, the mixture
was filtered through a pad of CeliteÒ, and concentrated to dryness
in vacuo. Purification of the resulting white solid residue by column
chromatography, eluting with 0–40% EtOAc/hexanes, and re-
precipitation from acetone, afforded 14 (81 mg, 50%) as an
amorphous white waxy solid: mp 71–72 °C (lit.28 68.5–70 °C); 1H
NMR (CDCl3): 4.35–4.25 (m, 1H), 4.11 (dd, J = 11.5, 4.0 Hz, 1H),
4.05 (dd, J = 11.5, 6.2 Hz, 1H), 3.12 (d, J = 4.0 Hz, 1H), 2.62 (m, 2H),
1.17 (m, 14H), 0.89 (t, J = 6.9 Hz, 3H); HRESIMS calcd for
C
35H44Br2NaO5 (M+Na)+ m/z 727.1431, 725.1448, found 727.1432,
725.1456; TLC Rf = 0.51 (20% EtOAc/hexanes); and 21 (386 mg,
61%) as a white feathery crystalline solid: mp 50–52 °C; 1H NMR
(CDCl3): 7.91 (dt, J = 9.0, 2.1 Hz, 2H), 7.59 (dt, J = 9.0, 2.1 Hz, 2H),
5.44–5.27 (m, 4H), 4.49–4.38 (m, 1H), 4.38–4.28 (m, 2H), 3.20 (d,
J = 4.0 Hz, 1H), 2.77 (t, J = 6.4 Hz, 2H), 2.69 (d, J = 6.0 Hz, 2H), 2.45
(t, J = 7.4 Hz, 2H), 2.05 (app q, J = 13.5, 6.7 Hz, 4H), 1.66–1.52 (m,
2H), 1.41–1.21 (m, 14H), 0.89 (t, J = 6.9 Hz, 3H); HRESIMS calcd
for C28H42BrO4 (M+H)+ m/z 523.2242, 521.2261, found 523.2236,
2.44 (t, J = 7.4 Hz, 2H), 2.10 (s, 3H), 1.63–1.51 (moverlapping water peak
,
521.2257;
EtOAc/hexanes).
½
a 2D8
= +3.77° (c 1.06, CHCl3); TLC Rf = 0.25 (20%
ꢁ
2H), 1.37–1.17 (m, 28H), 0.88 (t, J = 6.8 Hz, 3H); HRESIMS calcd for

D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
7041
5.2.7. (2E,12Z,15Z)-4-oxohenicosa-2,12,15-trien-1-yl 4-nitro
benzoate (23) and (R)-(12Z,15Z)-4-oxohenicosa-12,15-diene-
1,2-diyl bis(4-nitrobenzoate) (24)
1.36–1.16 (m, 30H), 1.00 (app d, J = 1.8 Hz, 6H), 0.88 (t, J = 6.8 Hz,
3H); HRESIMS calcd for C23H46ONa (M+Na)+ m/z 361.3441, found
361.3435; TLC Rf = 0.34 (10% Et2O/hexanes).
A solution of b,c
-diol 1939 (402 mg, 1.19 mmol, 1.00 equiv) in
5.2.10. 3,3-Dimethylhenicos-1-en-4-one (31)
CH2Cl2 (40 mL) was allowed to react with 2,4,6-trimethyl pyridine
(0.80 mL, 6.05 mmol, 5.00 equiv) and 4-nitrobenzoyl chloride
(741 mg, 3.85 mmol, 3.24 equiv) for 16 h under the conditions out-
lined in Section 5.2.5. The resulting solid was purified by column
chromatography on silica gel, eluting with 0–20% EtOAc/hexanes,
to afford 23 (156 mg, 28%) as yellow semi-solid oil: 1H NMR
(CDCl3): 8.32 (dt, J = 8.9, 2.1 Hz, 2H), 8.25 (dt, J = 8.9, 2.1 Hz, 2H),
6.89 (dt, J = 16.0, 4.9 Hz, 1H), 6.36 (dt, J = 16.0, 4.9 Hz, 1H),
5.43–5.28 (m, 4H), 5.05 (dd, J = 4.9, 1.8 Hz, 2H), 2.77 (t, J = 6.4 Hz,
2H), 2.58 (t, J = 7.4 Hz, 2H), 2.05 (app q, J = 13.6, 6.7 Hz, 4H),
1.68–1.58 (m, 2H), 1.42–1.23 (m, 14H), 0.89 (t, J = 6.9 Hz, 3H); HRE-
A solution of alcohol 30 (1.25 g, 3.70 mmol, 1.00 equiv) in DMSO
(70 mL) was treated with acetic anhydride (14.00 mL, 14.72 mL,
39.00 equiv), and the resulting mixture stirred at rt for 10 min. After
this time, NEt3 (14.00 mL, 99.84 mmol, 27.00 equiv) was added, and
the resulting mixture was stirred at rt in the dark for 46 h. At this
point, the reaction mixture was diluted first with EtOAc, and then
with 30% EtOAc/hexanes, and the resulting solution washed
sequentially with H2O (ꢃ2) and brine, and then dried (MgSO4). Sol-
vent was removed in vacuo to give an odoriferous dark brown amor-
phous solid, which was purified by column chromatography on
silica gel, eluting with 0–1% Et2O/hexanes, to give 31 (1.20 g, 96%)
as a semi-crystalline off-white solid. This material was estimated
by 1H NMR analysis to contain ꢂ4% unreacted 30, and was used
without further purification: 1H NMR (CDCl3): 5.91 (dd, J = 17.5,
10.5 Hz, 1H), 5.15 (dd, J = 3.9, 0.8 Hz, 1H), 5.11 (dd, J = 2.9, 0.8 Hz,
1H), 2.43 (t, J = 7.4 Hz, 2H), 1.52 (moverlapping water peak, 2H), 1.35–
1.15 (m, 34H), 0.88 (t, J = 7.4 Hz, 3H); HRESIMS calcd for C23H44NaO
(M+Na)+ m/z 359.3284, found 359.3293; TLC Rf = 0.75 (10%
Et2O:hexanes).
SIMS calcd for
C
28H39NNaO5 (M+Na)+ m/z 492.2720, found
492.2712; TLC Rf = 0.45 (20% EtOAc/hexanes); and 24 (277 mg,
37%) as an amorphous greasy solid: 1H NMR (CDCl3): 8.31–8.24
(m, 4H), 8.20–8.12 (m, 4H), 5.94–5.87 (m, 1H), 5.43–5.28 (m,
4H), 4.72 (dd, J = 12.1, 3.2 Hz, 1H), 4.63 (dd, J = 12.1, 6.2 Hz, 1H),
3.05 (dd, J = 17.4, 6.6 Hz, 1H), 2.92 (dd, J = 17.4, 6.3 Hz, 1H), 2.76
(t, J = 6.1 Hz, 2H), 2.48 (t, J = 7.4 Hz, 2H), 2.11–1.98 (m, 4H),
1.66–1.52 (moverlapping
peak, 2H), 1.41–1.22 (m, 14H), 0.88 (t,
water
J = 6.8 Hz, 3H); HRESIMS calcd for C35H44N2NaO9 (M+Na)+ m/z
659.2939, found 659.2936; TLC Rf = 0.30 (20% EtOAc/hexanes).
5.2.11. 2-Methyl-2-(oxiran-2-yl)icosan-3-one (32)
To a mixture of ketone 31 (1.19 g, 3.54 mmol, 1.00 equiv) and
EDTA (5 mg) in acetone (71.6 mL) and H2O (2.4 mL) at 0 °C was
added, portionwise, a mixture of NaHCO3 (1.67 g) and OxoneÒ
(1.67 g, 5.31 mmol, 1.54 equiv), and the resulting suspension stirred
at rt for 40 h. At this point, TLC analysis indicated that the reaction
mixture was only partially complete, and so the reaction mixture
was re-cooled to 0 °C, and a further, larger excess of OxoneÒ
(25.89 g, 84.23 mmol, 23.82 equiv) and NaHCO3 (25.89 g) was
added, portionwise, together with proportional quantities of EDTA
(62 mg) and acetone (50 mL). The resulting mixture was stirred vig-
orously at rt for another 24 h. After this time, TLC analysis of the
reaction mixture indicated a significant amount of 31 remained
unreacted, and so the reaction mixture was re-cooled to 0 °C, and
more OxoneÒ (31.31 g, 101.867 mmol, 28.81 equiv) and NaHCO3
(31.31 g) was added, portionwise, together with proportional quan-
tities of EDTA (105 mg) and acetone (50 mL). The resulting mixture
was stirred vigorously at rt for another 23 h and then, with only a
trace of 31 being visible by TLC analysis of the reaction mixture, fil-
tered through a pad of CeliteÒ. The filtrate was extracted with CH2Cl2
(ꢃ5), and the combined organic extracts were dried (MgSO4) and
concentrated to dryness in vacuo. The resulting pale yellow amor-
phous solid was purified by column chromatography on silica gel,
eluting with 0–5% Et2O:hexanes, to furnish 32 (941 mg, 75%) as an
amorphous white solid: 1H NMR (CDCl3): 3.04 (dd, J = 4.0, 2.8 Hz,
1H), 2.74 (t, J = 4.3 Hz, 1H), 2.64 (dd, J = 4.6, 2.8 Hz, 1H), 2.60–2.50
(m, 2H), 1.62–1.52 (moverlapping water peak, 2H), 1.27 (br s, 28H), 1.10
(s, 6H), 0.90 (t, J = 6.8 Hz, 3H); HRESIMS calcd for C23H44NaO2
(M+Na)+ m/z 375.3234, found 375.3231; TLC Rf = 0.16 (5%
Et2O:hexanes).
5.2.8. (R)-(12Z,15Z)-2-hydroxy-4-oxohenicosa-12,15-dien-1-yl
isonicotinate (25)
A solution of b,c
-diol 1939 (666 mg, 1.97 mmol, 1.00 equiv) in
CH2Cl2 (60 mL) and DMF (25 mL) was allowed to react with
2,4,6-trimethyl pyridine (1.95 mL, 14.76 mmol, 7.50 equiv) and
isonicotinoyl chloride hydrochloride (876 mg, 4.92 mmol,
2.50 equiv) for 16 h under the conditions outlined in Section
5.2.5. After this time, the reaction mixture was cooled to 0 °C,
quenched with saturated aqueous NaHCO3, and allowed to warm
to rt The mixture was extracted with CH2Cl2 (ꢃ5), and the com-
bined extracts were washed with H2O (ꢃ3), and the aqueous layer
back-extracted with CH2Cl2 (ꢃ1). The combined organic extracts
were washed with brine, dried (MgSO4), and concentrated to dry-
ness in vacuo. The resulting solid was purified by column chroma-
tography on silica gel, eluting with 0–50% EtOAc/hexanes, to afford
25 (98 mg, 11%) as an off-white semi-solid oil: 1H NMR (CDCl3):
8.79 (app dd, J = 4.5, 1.5 Hz, 2H), 7.86 (app dd, J = 4.4, 1.7 Hz, 2H),
5.45–5.26 (m, 4H), 4.51–4.41 (m, 1H), 4.41–4.31 (m, 2H), 3.23 (d,
J = 4.0 Hz, 1H), 2.77 (t, J = 6.3 Hz, 2H), 2.70 (d, J = 5.9 Hz, 2H), 2.46
(t, J = 7.4 Hz, 2H), 2.05 (app q, J = 13.6, 6.8 Hz, 4H), 1.66–1.50
(moverlapping
peak, 2H), 1.42–1.22 (m, 14H), 0.89 (t, J = 6.9 Hz,
water
3H); HRESIMS calcd for C27H42NO4 (M+H)+ m/z 444.3108, found
444.3109; TLC Rf = 0.32 (50% EtOAc/hexanes).
5.2.9. 3,3-Dimethylhenicos-1-en-4-ol (30)
To a suspension of In powder (3.09 g, 26.91 mmol, 1.51 equiv)
in DMF (80 mL) was added
a mixture of prenyl bromide
(3.11 mL, 26.67 mmol, 1.50 equiv) and aldehyde 2942 (4.77 g,
17.78 mmol, 1.00 equiv) in DMF (30 mL), resulting in bubbling
and a slightly exothermic reaction. This mixture was stirred at rt
for 19 h, and then diluted with EtOAc. The resulting suspension
was filtered through a pad of Celite,Ò and the filtrate was diluted
with 30% EtOAc/hexanes. This mixture was washed sequentially
with 1 M HCl, saturated aqueous NaHCO3, and brine, and then
dried (MgSO4). Removal of solvent in vacuo afforded an amorphous
off-white solid, which was purified by column chromatography on
silica gel, eluting with 0–10% Et2O:hexanes, to give 30 (1.33 g, 22%,
unoptimized): mp 34–36 °C; 1H NMR (CDCl3): 5.86 (dd, J = 17.5,
10.9 Hz, 1H), 5.13–5.00 (m, 2H), 3.24 (ddd, J = 10.0, 4.9, 1.5 Hz,
5.2.12. (+)-(R)-1,2-Dihydroxy-3,3-dimethylhenicosan-4-one (26)
Catalyst formation:47,48,50 To a solution of (S,S)-N,N0-bis(3,5-
di-tert-butylsalicylidene)-1,2-cyclohexanediaminato(2ꢀ)]cobalt(II)
[(S,S)-t-Bu cobalt(II) salen] (42 mg, 0.07 mmol, 0.027 equiv) in
CH2Cl2 (2 mL) exposed to air was added acetic acid (0.036 mL,
0.620 mmol, 0.238 equiv), generating an immediate color change
of the solution from vermilion to dark brown. The solution was
stirred at rt for 72 min, after which time solvent was removed in
vacuo to give the desired (S,S)-N,N’-bis(3,5-di-tert-butylsalicylid-
ene)-1,2-cyclohexanediaminato(2ꢀ)]cobalt(III) acetate [(S,S)-t-Bu
cobalt(II) salen acetate] catalyst 33 as an amorphous brown solid.
1H), 1.62–1.45 (moverlapping
peak, 2H), 1.39 (d, J = 5.0 z, 1H),
water

7042
D. G. Brooke et al. / Bioorg. Med. Chem. 19 (2011) 7033–7043
Hydrolytic kinetic resolution:47–50 Epoxide 32 (921 mg, 2.61 mmol,
1.00 equiv) was dissolved in THF (2.5 mL), and the resulting solu-
tion added to catalyst 33 (as prepared above). This mixture was
cooled to 0 °C, and then treated dropwise with distilled H2O
(0.038 mL, 2.09 mmol, 0.80 equiv) over 1 min. The resulting solu-
tion was allowed to warm to rt and stirred thus for 100 h. After this
time, the reaction mixture was diluted with THF and MeOH, and
then concentrated to dryness in vacuo. The brown semi-solid res-
idue was purified by column chromatography on silica gel, eluting
with 0–30% EtOAc/hexanes, to afford recovered epoxide 34
(484 mg) and diol 26 (331 mg) as an amorphous white solid
(APCI + MS [MꢀH2O] + m/z 354.0). The presence of the desired
Ms. Stefanie Maurer, Dr. Cary Lam, Dr. Maruta Boyd and
Dr. Shannon Black for 1H NMR analyses, Ms. Karin Tan and Mr.
Sisira Kumara for HPLC analyses, and Ms. Raisa Imatdieva and
Mr. Ian Stewart for HRMS analysis. This study was supported by
a
Cancer Institute NSW Postgraduate Scholarship (EJS), an
Australian Postgraduate Award (EJS), National Health and
a
Medical Research Council (Australia) Program Grant 535903
(AJB), and a Breast Cancer Australia Project Grant (AJB).
References and notes
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1H NMR data of this material with that reported for an analogous
system by Liu et al.,46 and 26 was then used without further puri-
fication. HRESIMS calcd for C23H46NaO3 (M+Na)+ m/z 393.3339,
found 393.3338; TLC Rf = 0.30 (30% EtOAc/hexanes).
5.2.13. (ꢀ)-(R)-2-hydroxy-3,3-dimethyl-4-oxohenicosyl acetate
(27)
To a solution of
a-dimethyl-b,c-diol 26 (324 mg) in CH2Cl2
(35 mL) cooled to ꢀ78 °C were sequentially added 2,4,6-trimethyl
pyridine (0.250 mL, 1.89 mmol, 2.16 equiv) and acetyl chloride
(0.075 mL, 1.049 mmol, 1.20 equiv), and the resulting solution
was stirred at rt for 60 h. After this time, the reaction mixture
was quenched by addition of saturated aqueous NaHCO3, and then
extracted with CH2Cl2 (ꢃ5). The combined organic extracts were
washed with brine, dried (MgSO4), and then concentrated to dry-
ness in vacuo. The residue was purified by column chromatogra-
phy on silica gel, eluting with 0–20% EtOAc/hexanes, to afford 27
(144 mg, 40%) as a white waxy solid: mp 41–44 °C; 1H NMR
(CDCl3): 4.23 (dd, J = 11.2, 2.2 Hz, 1H), 4.02 (dd, J = 11.2, 8.0 Hz,
1H), 3.98–3.92 (m, 1H), 2.90 (d, J = 5.2 Hz, 1H), 2.57–2.43 (m,
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2H), 2.08 (s, 3H), 1.60–1.50 (moverlapping
peak, 2H), 1.26 (br s,
water
28H), 1.21 (s, 3H), 1.19 (s, 3H), 0.88 (t, J = 6.8 Hz, 3H); HRESIMS
calcd for C25H48NaO4 (M+Na)+ m/z 435.3445, found 435.3439;
½
a 2D8
ꢁ
= ꢀ13.66° (c 1.03, CHCl3); TLC Rf 0.33 (20% EtOAc/hexanes).
5.3. Biological methods
The panel of normal and breast cancer cell lines were all ob-
tained from ATCC (American Type Culture Collection, Manassas,
VA, USA). Characteristics of these cell lines have been described
previously.65 Human breast cancer cell lines were routinely main-
tained in RPMI-1640 supplemented with 5% fetal calf serum (FCS),
10
l
g/mL insulin and 2.92 mg/mL glutamine under standard con-
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lg/mL
l
50 units/mL penicillin G, and 50
standard conditions.
l
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Acknowledgements
The authors thank Professors Marie Dziadek and John MacLeod
for useful discussions and advice. We are also grateful to

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