Synthesis and biological evaluation of prodigiosene conjugates of porphyrin, estrone and 4-hydroxytamoxifen

Article abstract of DOI:10.1016/j.bmc.2013.07.042

To generate the first series of prodigiosene conjugates, the tripyrrolic skeleton was appended to estrone, tamoxifen and porphyrin frameworks by way of ester linkers and various hydrocarbon chain lengths. The ability of the conjugates to inhibit various types of cancer cells was evaluated in vitro. The porphyrin conjugates did not exhibit significant activity. The estrone conjugates exhibited modest activity, for the most part. However, significantly greater growth inhibition activity against certain breast, colon, lung, leukemia, melanoma and prostate cell lines was noted. This unusual effect for this first generation model class of compound warrants further investigation and comparison to cases where estrogens are linked to prodigiosenes via connection points that do not feature in estrogen receptor binding. The 4-hydroxytamoxifen conjugates exhibit nanomolar range activity against the MCF-7 breast cancer cell line, paving the way to expand the scope and connectivity of prodigiosene-tamoxifen conjugates.

Full text of DOI:10.1016/j.bmc.2013.07.042

Bioorganic & Medicinal Chemistry 21 (2013) 5995–6002
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and biological evaluation of prodigiosene conjugates
of porphyrin, estrone and 4-hydroxytamoxifen
Cassandra L. A. Hawco a, Estelle Marchal a, Md. Imam Uddin a, Alexander E. G. Baker a, Dale P. Corkery b,
Graham Dellaire b, , Alison Thompson a,
⇑
⇑
a Department of Chemistry, Dalhousie University, PO Box 15000, Halifax, Nova Scotia B3H 4R2, Canada
b Departments of Pathology and Biochemistry & Molecular Biology, Dalhousie University, PO Box 15000, Halifax, Nova Scotia B3H 4R2, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
To generate the first series of prodigiosene conjugates, the tripyrrolic skeleton was appended to estrone,
tamoxifen and porphyrin frameworks by way of ester linkers and various hydrocarbon chain lengths. The
ability of the conjugates to inhibit various types of cancer cells was evaluated in vitro. The porphyrin con-
jugates did not exhibit significant activity. The estrone conjugates exhibited modest activity, for the most
part. However, significantly greater growth inhibition activity against certain breast, colon, lung, leuke-
mia, melanoma and prostate cell lines was noted. This unusual effect for this first generation model class
of compound warrants further investigation and comparison to cases where estrogens are linked to prod-
igiosenes via connection points that do not feature in estrogen receptor binding. The 4-hydroxytamoxifen
conjugates exhibit nanomolar range activity against the MCF-7 breast cancer cell line, paving the way to
expand the scope and connectivity of prodigiosene–tamoxifen conjugates.
Received 14 June 2013
Revised 15 July 2013
Accepted 21 July 2013
Available online 31 July 2013
Keywords:
Drug-targeting
Prodigiosenes
Estrone
Tamoxifen
Ó 2013 Elsevier Ltd. All rights reserved.
Porphyrin
Natural product
Anticancer
1. Introduction
ing a compound known to accumulate in cancer cells to an anti-
cancer compound, is a strategy that could be used to overcome
Prodigiosenes constitute a class of tripyrrolic compounds based
on the natural product prodigiosin (a, Fig. 1) that share a common
4-methoxypyrrolyldipyrrin core unit. They have demonstrated sig-
nificant immunosuppressive, antimicrobial, antifungal, antiproto-
MDR by increasing uptake into the cancerous cell compared to
healthy cells.11–28
Conjugating prodigiosenes to a molecule that already possesses
selectivity toward the tumor should help to deliver the drug at a
specific site. Thus, it should be possible to target estrogen receptor
(ER) positive breast cancers by using a ligand of the estrogen recep-
tor.11–16,20,24–26 Several ligands of the ER are used as a treatment in
breast cancer therapy.29,30 For example the pure antagonist fulve-
strant (b, Fig. 1)31,32 is used to treat post-menopausal women with
a progressive or metastatic disease. Another example is tamoxifen
(c, Fig. 1), a selective estrogen receptor modulator (SERM) that has
agonist or antagonist activity depending on the tissue.33 It has been
shown that after treatment with tamoxifen therapy 46% of the
resistant tumors retain ER expression.34 This means that the ER
is a potential target in resistant tumors. Furthermore, porphyrins
are aromatic macrocyclic analogues of the natural hematoporphy-
rin (d, Fig. 1), and have demonstrated an ability to accumulate in
cancer cells as compared to normal cells.35 They are known to
localize in subcellular structures such as lysosomes, endoplasmic
reticulum, mitochondria and Golgi apparatus.36 Thus, conjugation
of a therapeutic drug to a porphyrin also seems to be an applicable
strategy for drug delivery into tumor cells.28
zoal, antimalarial and anticancer activities.1–3
A
singular
mechanism of action by which prodigiosenes induce apoptosis
has not been identified, rather a diverse range of activities have
been noted which are thought to collectively account for the cyto-
toxic effects. For example, prodigiosenes have demonstrated the
ability to induce copper-mediated double strand DNA (dsDNA)
breakage, inhibit Bcl-2, intercalate DNA and uncouple V-ATPase
through promotion of H+/Clꢀ symport.1,2,4–9
Multidrug resistance (MDR), a resistance to a range of structur-
ally unrelated compounds, may develop in tumor cells following
drug exposure.10 This may significantly limit the effectiveness of
chemotherapeutic treatments. Prodigiosenes are of interest due
to their potential to combat MDR for two principal reasons; the
number of potential targets affected and their inability to be trans-
ported by the MDR transporter.2 Targeted drug design, i.e. attach-
⇑
Corresponding authors. Tel.: +1 902 494 3305; fax: +1 902 494 1310 (A.T.).
E-mail addresses: Dellaire@dal.ca (G. Dellaire), Alison.Thompson@dal.ca (A.
Thompson).
0968-0896/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2013.07.042

5996
C. L. A. Hawco et al. / Bioorg. Med. Chem. 21 (2013) 5995–6002
O
OH
N
HN
HN
O
S
F
F
a, prodigiosin
O
F
F
HO
b, fulvestrant
F
N
OH
HN
N
MeO2C
MeO2C
c, tamoxifen
O
N
NH
O
OH
d, hematoporphyrin
O
HN
N
n
O
HN
porphyrin,
ER ligand, etc
e, conjugated prodigiosene
Figure 1. Prodigiosin, estrogen receptor ligands, hematoporphyrin and proposed prodigiosene conjugates.
concentration of 1 lM. The viability of the cells was measured
2. Results and discussion
using MTT assays and the results are summarized in Figure 2.
The three prodigiosenes conjugated to estrone by means of three
different linker lengths (3a, n = 2; 3b, n = 4; 3c, n = 8) all demon-
strated rather poor activity at this concentration against the
MCF-7 cell line (Fig. 2), and this is not surprising given that the
important phenolic binding site42 of estrone is essentially blocked
by the appended prodigiosene. However, it is interesting to note
that the estrone conjugates 3 did not exhibit an estrogenic prolif-
erative effect, as would be expected for estrone alone such as might
be the case if hydrolysis were immediate to reveal estrone and the
parent prodigiosene carboxylic acid. Rather, the compounds re-
duced the cell viability of the MCF-7 cells. For each of the conju-
gates, the longer chain linker (n = 8 carbon-chain, 3c and 4c)
performed relatively poorly as compared to the other two chain
lengths within each series.
To determine the effects caused by the presence/absence of
estrogen receptors, the activity of conjugates bearing a two-carbon
linker (3a and 4a) and the ethyl ester conjugate 1a, as a control for
the parent ‘naked’ prodigisene versus conjugated analogues, were
investigated using the MDA-MB-231 cell line. As this cell line lacks
the presence of estrogen receptors we hoped to see a difference in
activity for our conjugates against MDA-MB-231 and MCF-7 cell
lines. The biological activity of each compound was again deter-
We herein report, as part of our efforts to synthesize and iden-
tify useful anti-cancer compounds based on the prodigiosene
skeleton,37–41 first steps towards probing the conjugation of prod-
igiosenes with ER ligands and porphyrins using linkers of various
chain lengths as shown in Figure 1, e.
We first sought a model set of compounds by which targeting
moieties could be appended to prodigiosenes. Towards this goal,
the prodigiosene-linker core 1 (Scheme 1) was prepared using a re-
ported procedure.37,38 The corresponding acids (2) were obtained in
good yields via saponification using a large excess of potassium
hydroxide at 70 °C. We then studied the feasibility of esterification
with the commercially available estrone as a model, cognizant that
ultimately the phenolic position would need to be available for
binding.42 The use of EDCI as a coupling reagent in the presence
of DMAP in CH2Cl2 emerged as optimal, giving the conjugates 3 in
moderate to good yield. This lead us to perform the reaction with
the more valuable (Z)-4-hydroxytamoxifen (Afimoxifene, 4-OHT),
the active metabolite of tamoxifen, that was prepared using a liter-
ature process.43 The corresponding conjugates 4 were obtained in
good yields after purification using column chromatography.
To conjugate prodigiosenes with amino-tetraphenylporphyrin
(NH2–TPP, 5, Scheme 2)44–46 via an amide linkage, two procedures
were used: the coupling reagent COMU in the presence of DBU,47
and a polystyrene supported carbodiimide coupling reagent in
the presence of DMAP. Both sets of reaction conditions provided
conjugates 6 in moderate yield (Scheme 2).
mined using MTT assays, again at 1 lM concentration. Results from
these studies were compared to results from the MCF-7 cell line
and are shown in Figure 3.
At 1 lM there was no notable difference in activity between cell
lines for compounds 1a (ethyl ester prodigiosene) and 4a ((Z)-4-
hydroxytamoxifen conjugated at the phenolic position). A lack of
selectivity between the MCF-7 and MDA-MB-231 cell lines was
similarly reported for the natural product prodigiosin.49 These re-
sults suggest that the conjugates do not exhibit significant ER-
mediated selectivity against breast cancer cell lines, as anticipated
for this model set of conjugates. However, the estrone–prodigio-
sene conjugate 3a exhibited differential activity across the two cell
lines used. Indeed, there was a significant difference in cell viability
The porphyrin conjugates were screened at 10 lM by the Na-
tional Cancer Institute (NCI) against their standard panel of 60 hu-
man cell lines, derived from nine cancer cell types. At this
concentration significant cytotoxicity was not observed, and the
conjugates were not pursued further. Nevertheless, the synthetic
methodology could be applied to the coupling of more elaborate
porphyrins (i.e., porphyrins substituted with functional groups),
including those with structures that match tetrapyrrolic macrocy-
cles used in photodynamic therapy.48
following treatment with 1 lM 3a (MCF-7: 0.90; MDA-MB-231:
0.25), that is, 3a was more effective against the ER-negative cell
A preliminary evaluation of the activity of our first-generation
model ER-targeted conjugates was accomplished by treating an
line than against the ER-positive cell line.
ER-positive cell line, MCF-7, with conjugates
3 and 4 at a

C. L. A. Hawco et al. / Bioorg. Med. Chem. 21 (2013) 5995–6002
5997
O
O
O
O
O
O
O
EtO
HO
O
n
n
O
1. KOH, THF,
H2O, 70
O
estrone
n
N
EDCI, DMAP
N
N
HN
HN
HN
HN
HN
HN
DCM, r.t.
2. HCl
HCl
1a, n = 2
1b, n = 4
1c, n = 8
2a, n = 2, 73%
2b, n = 4, 81%
2c, n = 8, 99%
H
3a, n = 2, 44%
3b, n = 4, 49%
3c, n = 8, 59%
O
4-hydroxytamoxifen
EDCI, DMAP
DCM, r.t.
O
O
O
O
n
N
HN
HN
N
O
4a, n = 2, 76%
4b, n = 4, 83%
4c, n = 8, 45%
Scheme 1. Synthesis of estrone and tamoxifen prodigiosene conjugates.
Ph
O
O
Procedure A:
COMU, DBU
DMF, r.t.
HN
TPP
O
n
N
HN
N
2a, n = 2
2b, n = 4
2c, n = 8
N
Ph
NH2
HN
HN
Procedure B:
PS-carbodiimide,
DMAP,
NH
DCM, DMF, r.t.
Ph
6a, n = 2, 34% (procedure B)
6b, n = 4, 50% (procedure A)
6c, n = 8, 40% (procedure A)
42% (procedure B)
5
Scheme 2. Synthesis of prodigiosene porphyrin conjugates.
Figure 2. Cell viability following treatment of MCF-7 cell line with conjugates 3 and
4 at 1 M. MCF-7 cell lines were treated with prodigiosene conjugates for 72 h
followed by the MTT dye reduction assay to determine relative viability compared
to cells treated with vehicle alone. Average of four replicates. Error bars = SE, ⁄p
<0.05.
l
Figure 3. Cell viability following treatment of MCF-7 and MDA-MB-231 breast
cancer cell lines with prodigiosene conjugates 1a, 3a and 4a at 1 M. MCF-7 and
MDA-MB-231 cell lines were treated with prodigiosene conjugates for 72 h
followed by the MTT dye reduction assay to determine relative viability compared
to cells treated with vehicle alone. Average of four replicates. Error bars = SE, ⁄p
<0.05.
l
Intrigued by the interesting cell viability activity against the ER-
negative MDA-MB-231 cell line,50 3a was screened against the
NCI60 panel using five different concentration doses. The GI50 val-
ues thus obtained for estrone conjugate 3a against six breast can-
ER-positive and 3a exhibited more modest activity against that line
(GI50 = 15.4
factor to the activity of 3a, as we had suspected using our 1
viability MTT assays and given that the estrone derivatives are first
l
M), suggesting that ER
a
status is not a contributing
lM cell
cer cell lines are displayed in Figure 4. A GI50 of 1.9
lM was
observed against ER-positive MCF-7. However, T-47D is also

5998
C. L. A. Hawco et al. / Bioorg. Med. Chem. 21 (2013) 5995–6002
Previous studies have noted that the natural product prodigi-
osin triggers apoptosis in hematopoietic cancer cell lines, as well
as colon and gastric cell lines.51 In the NCI screen, compound 3a
was shown to be particularly active against several cell lines, most
notably colon cancer (HCT-116, HCT-15, HT29, SW-620) but also
leukemia (CCRF-CEM, MOLT-4, SR), melanoma (LOXIMVI), lung
cancer (A459/ATCC, HOP92) and prostate cancer (DU-145) cell
lines (Fig. 5). This data suggests a unifying feature across these cell
lines, a feature that results in 3a inhibiting their growth more dra-
matically than other cell lines. Prodigiosenes appended with ER li-
gands via positions not involved in binding to the ER will be used
to investigate this hypothesis.
GI50 values of the tamoxifen–prodigiosene conjugates 4 against
cancer cell lines in the NCI-60 panel were also measured and com-
pared to values obtained for tamoxifen (Figs. 5 and 6). Again, the
conjugate possessing a linker of 8 carbon atoms (4c) is the least ac-
tive. In general, 4a is more active than 3a, with excellent activity
particularly observed against the MCF-7 cell line (GI50 = 30 nM
for 4a, see Supplementary data). Again, particularly high activity
was demonstrated against several cell lines, including breast
cancer (MCF-7, MDA-MB-231), colon cancer (HCT-116, HCT-15,
Figure 4. GI50 (half minimal growth inhibition concentration) of estrone conjugate
3a against the NCI panel of breast cancer cells; average of two replicates. http://
dtp.cancer.gov.
generation models whereby a crucial binding position is blocked.
As reported above, 3a is also highly active against the ER-negative
MDA-MDAB-231/ATCC cell line (GI50 value of 0.3 lM).
Figure 5. GI50 (half minimal growth inhibition concentration) of estrone conjugate 3a and 4a against the NCI panel of cancer cells; http://dtp.cancer.gov. Average of two
replicates. Darker-coloured bars represents GI50 <3 M for 3a and GI50 <1 M for 4a.
l
l
Figure 6. GI50 (half minimal growth inhibition concentration) of tamoxifen conjugates 4 and tamoxifen (NSC 180973, average of three replicates) against the NCI panel of
breast cancer cells. http://dtp.cancer.gov.

C. L. A. Hawco et al. / Bioorg. Med. Chem. 21 (2013) 5995–6002
5999
HT29, KM12, SW-620), leukemia (CCRF-CEM, MOLT-4, SR), mela-
4.2. MTT testing
noma (LOXIMVI), lung cancer (A459/ATCC, HOP92) and prostate
cancer (DU-145) cell lines, as shown in Figure 5. This substantial
growth inhibition paves the way for investigations regarding other
conjugate models for prodigiosenes and targeting moieties de-
signed so as to maximise binding to receptors.
The NCI COMPARE software calculates correlation coefficients
that can be interpreted as an indication of similarities in differen-
tial cellular sensitivities, courtesy of characteristic NCI60 activity
fingerprints for each compound.52 Given the nanomolar activity
of 4a against MCF-7, we used the COMPARE software to compare
the GI50 values of the tamoxifen conjugate 4a versus the NCI stan-
dard-agent database. The best match for the activity fingerprint
profile of 4a compared to those of the 171 standard agents was
found to be tamoxifen, with a correlation coefficient of 0.54. A cor-
relation coefficient of only 0.35 was obtained when comparing 4a
and the natural product prodigiosin. This suggests that the mode of
activity of compound 4a most closely parallels tamoxifen.
Human breast cancer cell lines MCF-7 and MDA-MB-231 were
maintained in DMEM (Sigma Aldrich) medium supplemented with
10% fetal bovine serum (Sigma Aldrich) as well as 1% penicillin and
streptomycin (Sigma Aldich). The cells were incubated at 37 °C and
5% CO2. MTT analyses followed standard protocol,17 using a treat-
ment time of 72 h. Viability was then expressed as a mean percent-
age of MTT reduced to purple formazan by treated versus mock
treated (0.1% DMSO) cells. All (non-NCI) experiments were per-
formed in quadruplicate with error analysis representing the stan-
dard error and significance determined by the ‘Student’s’ t-test.
4.3. NCI testing
The Developmental Therapeutics Program (DTP) of the National
Cancer Institute (NCI) employs the NCI60 cell line screen as an
early stage of drug discovery and development. The NCI60 cell line
screen consists of 60 human tumor cell lines, each chosen for their
ability to perform consistently and provided appropriate represen-
tation of a variety of tumor types: 59 cell lines were available for
screening when this work was performed.53 Each cell line used
has been extensively characterized.53 The multi-dose drug screen
involves treatment of each cell line with compounds over a
5-log mol/L concentration range for 2 days.53,54 The cells are then
fixed and stained with sulphorhodamine B and optical densities
are measured.53,54 Growth inhibition is calculated relative to cells
at the time zero control and those without drug treatment.53,54
http://dtp.cancer.gov.
3. Conclusions
To summarize, although the porphyrin–prodigiosene conju-
gates showed no activity against the NCI cancer cell panel, the
estrone conjugate 3a demonstrated growth inhibition against
the ER-negative cell line MDA-MB-231/ATCC (GI50 = 0.3
lM) cf.
the ER-positive cell line MCF-7 (GI50 = 1.9 M). The tamoxifen con-
l
jugates 4a and 4b showed excellent growth inhibition against
MCF-7 (GI50 = 30 nM for 4a; GI50 = 50 nM for 4b), with better activ-
ity than tamoxifen itself against this cell line. These results bode
well as we delve into prodigiosene–ER conjugates featuring opti-
mum binding characteristics. Furthermore, from these experi-
ments it transpires that conjugates with shorter chain length
(linker with 2 and 4 carbon atoms) are more active than conjugates
with longer chain length (linker with 8 carbon atoms). The peculiar
observations as regards the growth inhibition effects of 3a and 4a
against certain cell lines warrant further study. Indeed, these ef-
fects will be investigated using prodigiosene–estrogen conjugates
linked via other positions on the estrogen, thereby maximizing
binding to the ER.
4.4. (Z)-10-(2-((4-Methoxy-1H,10H-2,20-bipyrrol-5-
yl)methylene)-3,5-dimethyl-2H-pyrrol-4-yl)-10-oxodecanoic
acid hydrochloride (2cꢁHCl)
A solution of prodigiosene 1c (100 mg, 0.21 mmol) in THF
(21 mL) under N2 was treated with aq KOH (21 mL, 5 M) and stirred
at 70 °C under N2 for 24 h. The reaction mixture was then cooled to
room temperature. THF was removed in vacuo and the aqueous
solution was adjusted to pH 2 with concd HCl. The resulting precip-
itate was isolated via filtration, washed with H2O (3 ꢂ 3 mL) and
acetone (3 ꢂ 3 mL) and then dried in vacuo to give the desired pro-
digiosene 2cꢁHCl (84 mg, 99%) as a dark red solid. 1H NMR (CDCl3,
500 MHz) 1.31–1.37 (m, 8H), 1.59–1.69 (m, 4H), 2.34 (t, J = 7.5 Hz,
2H), 2.50 (s, 3H), 2.73 (t, J = 7.5 Hz, 2H), 2.83 (s, 3H), 4.01 (s, 3H),
6.11 (s, 1H), 6.39–6.40 (1H, m), 7.01–7.02 (m, 1H), 7.12 (s, 1H),
7.30 (s, 1H), 12.66 (br s, 2H), 12.94 (br s, 1H). HR-MS (ESI): [MꢀCl]+
calcd for C26H34N3O4: 452.2544; found 452.2547.
4. Experimental
4.1. Synthesis general procedures
All chemicals were purchased and used as received unless other-
wise indicated. Moisture sensitive reactions were performed in
flame-dried glassware under a positive pressure of nitrogen or ar-
gon. Air- and moisture-sensitive compounds were introduced via
syringe or cannula through a rubber septum. Flash chromatography
was performed using ultra pure silica (230–400 mm) or 150 mesh
Brockmann III activated neutral alumina oxide as indicated. The
NMR spectra were recorded using a 500 MHz spectrometer instru-
ment using CDCl3, DMSO-d6 or MeOD as solvent and are reported in
parts per million (d) using the solvent signals at 7.26 ppm for 1H and
at 71.16 ppm for 13C when CDCl3 was used, at 2.50 ppm for 1H and
at 39.52 ppm for 13C when DMSO-d6 was used and at 3.31 ppm for
1H and at 49.00 ppm for 13C when MeOD was used, as internal ref-
erence with J values given in Hertz. Mass spectra were obtained
using TOF and LCQ Duo ion trap instruments operating in ESI+
mode. UV–visible spectra were recorded using a Varian CARY 100
bio spectrophotometer. Analytical HPLC was carried out using a
Varian Prostar instrument. The purity of all tested compounds
was P95%, as determined by analytical HPLC. Melting points are
uncorrected. Compounds 2a–c,37,38 (Z)-4-hydroxytamoxifen43 and
NH2–TPP44–46 were prepared according to literature procedures.
4.5. General procedure for ester coupling
Prodigiosene
2 (1.0 equiv), the alcohol (1.0 equiv), EDC
(1.1 equiv) and DMAP (1.1 equiv) were dissolved in DCM under
N2. After stirring at room temperature water was added and the
crude mixture was extracted with DCM three times. The combined
organic layers were washed with brine, and then dried (Na2SO4).
After evaporation of the solvent under vacuum the crude solid
was purified using column chromatography.
4.6. (13S,14S)-13-Methyl-17-oxo-7,8,9,11,12,13,14,15,16,17-
decahydro-6H-cyclopenta[a]phenanthren-3-yl 4-((Z)-2-((4-
methoxy-1H,10H-[2,20-bipyrrol]-5-yl)methylene)-3,5-dimethyl-
2H-pyrrol-4-yl)-4-oxobutanoate (3a)
Using the general ester coupling procedure, prodigiosene 2a
(100 mg, 0.25 mmol) and estrone (100 mg, 0.38 mmol) were re-
acted for 3 days in DCM (25 mL). The crude solid was purified using

6000
C. L. A. Hawco et al. / Bioorg. Med. Chem. 21 (2013) 5995–6002
column chromatography (Al2O3 neutral type III, EtOAc/hexane 5/5)
to give the title compound as a red solid (35 mg, 49%). Mp 157 °C.
1H NMR (CDCl3, 500 MHz) 0.90 (s, 3H), 1.41–1.64 (m, 7H), 1.94–
2.08 (m, 4H), 2.10–2.16 (m, 1H), 2.25–2.30 (m, 1H), 2.32–2.41 (m,
4H), 2.45 (s, 3H), 2.47–2.53 (m, 1H), 2.88–2.89 (m, 4H), 3.12 (t,
J = 6.5 Hz, 2H), 3.96 (s, 3H), 6.01 (s, 1H), 6.26 (s, 1H), 6.74 (d,
J = 3.0 Hz, 1H), 6.83–6.88 (m, 3H), 6.87–6.88 (m, 1H), 6.90 (s, 1H),
7.25–7.27 (m, 1H). 13C NMR (CDCl3, 125 MHz) 12.6, 14.0, 15.1,
21.7, 25.9, 26.5, 28.7, 29.5, 31.7, 36.0, 37.5, 38.1, 44.3, 48.1, 50.6,
58.7, 95.9, 111.0, 112.0, 113.8, 118.9, 121.7, 122.8, 126.4, 126.6,
137.3, 138.0, 148.8, 168.8, 172.4, 194.8, 7 13C signals missing. HR-
MS (ESI): [M+H]+ calcd for C38H42N3O5: 620.3124; found 620.3119.
0.08 mmol) were reacted for two days in DCM (10 mL). The crude
solid was purified using column chromatography (Al2O3 neutral
type III, DCM/MeOH 9.5/0.5) to give the title compound as an or-
ange-red solid (45 mg, 76%): 1H NMR (CD2Cl2, 500 MHz) 0.88–0.91
(m, 3H), 1.25 (s, 4H), 2.22 (s, 6H), 2.44 (t, J = 3.7 Hz, 4H), 2.58 (t,
J = 5.8 Hz, 2H), 2.87 (t, J = 6.4 Hz, 2H), 3.13 (t, J = 6.4 Hz, 2H), 3.89
(t, J = 4.8 Hz, 2H), 3.95 (s, 3H), 6.05 (s, 1H), 6.26 (dd, J = 4.8,
2.6 Hz, 2H), 6.53–6.56 (m, 2H), 6.75–6.77 (m, 2H), 6.78 (t,
J = 2.6 Hz, 1H), 6.87 (s, 1H), 6.93 (s, 1H), 7.06–7.09 (m, 2H),
7.11–7.13 (m, 3H), 7.16–7.19 (m, 2H), 7.21–7.24 (m, 2H). 13C
NMR (CD2Cl2, 125 MHz) 12.6, 13.6, 29.0, 29.3, 37.8, 45.9, 58.5,
58.9, 66.2, 66.3, 66.4, 96.0, 111.1, 112.1, 113.6, 113.9, 116.6,
121.6, 123.2, 126.4, 128.1, 130.0, 130.6, 132.1, 135.7, 137.8,
141.6, 142.2, 142.7, 149.9, 157.3, 172.2, 194.8, 6 13C signals miss-
ing. HR-MS (ESI): [M+H]+ calcd for C46H49N4O5: 737.3703; found
737.3697.
4.7. (13S,14S)-13-Methyl-17-oxo-7,8,9,11,12,13,14,15,16,17-
decahydro-6H-cyclopenta[a]phenanthren-3-yl 6-((Z)-2-((4-
methoxy-1H,10H-[2,20-bipyrrol]-5-yl)methylene)-3,5-dimethyl-
2H-pyrrol-4-yl)-6-oxohexanoate (3b)
4.10. 4-((Z)-1-(4-(2-(Dimethylamino)ethoxy)phenyl)-2-
phenylbut-1-en-1-yl)phenyl 6-((Z)-2-((4-methoxy-1H,10H-[2,20-
bipyrrol]-5-yl)methylene)-3,5-dimethyl-2H-pyrrol-4-yl)-6-
oxohexanoate (4b)
Using the general ester coupling procedure, prodigiosene 2b
(50 mg, 0.11 mmol) and estrone (30 mg, 0.11 mmol) were reacted
for 2 days in DCM (12 mL). The crude solid was purified using col-
umn chromatography (Al2O3 neutral type III, EtOAc/hexane 5/5) to
give the title compound as a red solid (35 mg, 49%). Rf = 0.28
(EtOAc/hexane 5/5). Mp 146 °C. 1H NMR (CDCl3, 500 MHz) 0.90
(s, 3H), 1.39–1.64 (m, 6H), 1.78–1.79 (m, 4H), 1.94–2.07 (m, 3H),
2.10–2.18 (m, 1H), 2.24–2.26 (m, 1H), 2.30 (s, 3H), 2.37–2.40 (m,
1H), 2.42 (s, 3H), 2.50 (dd, J = 9.0, 19.5 Hz, 1H), 2.26–2.59 (m,
2H), 2.73–2.75 (m, 2H), 2.87–2.90 (m, 2H), 3.98 (s, 3H), 6.05 (s,
1H), 6.24–625 (m, 1H), 6.75–6.85 (m, 4H), 6.93 (s, 1H), 7.26 (d,
J = 8.0 Hz, 1H). 13C NMR (CDCl3, 125 MHz) 12.5, 13.9, 14.5, 21.7,
23.7, 24.8, 25.8, 26.4, 29.5, 31.6, 34.4, 36.0, 38.1, 42.4, 44.2, 48.1,
50.5, 58.7, 95.9, 110.9, 112.1, 114.5, 118.9, 121.7, 123.5, 124.0,
126.1, 126.5, 127.6, 130.4, 137.4, 138.1, 142.7, 148.7, 168.9,
Using the general ester coupling procedure, prodigiosene 2b
(50 mg,
0.11 mmol)
and
(Z)-4-hydroxtamoxifen
(43 mg,
0.11 mmol) were reacted for one day in DCM (12 mL). The crude
solid was purified using column chromatography (Al2O3 neutral
type III, DCM/MeOH 9.5/0.5) to give the title compound as an or-
ange-red solid (51 mg, 85%). Rf = 0.39 (CH2Cl2/MeOH 19/1). 1H
NMR (MeOD, 500 MHz) 0.88 (t, J = 7.5 Hz, 3H), 1.82–1.85 (m, 4H),
2.30 (s, 6H), 2.42 (s, 3H), 2.43–2.45 (m, 2H), 2.64–2.65 (m, 2H),
2.68 (s, 3H), 2.68–2.71 (m, 2H), 2.88–2.89 (m, 2H), 3.92 (s, 3H),
3.95 (t, J = 5.5 Hz, 2H), 6.1 (s, 1H), 6.27 (dd, J = 3.0, 2.5 Hz, 1H),
6.55 (d, J = 9.0 Hz, 2H), 6.74 (d, J = 9.0, 1.0 Hz, 2H), 6.77–6.78 (m,
1H), 6.79 (s, 1H), 6.99 (d, J = 8.0 Hz, 2H), 7.03 (br s, 1H), 7.08–
7.10 (m, 3H), 7.14–7.20 (m, 4H). 13C NMR (MeOD, 125 MHz) 11.8,
13.2, 15.4, 23.1, 24.1, 28.5, 33.5, 41.4, 45.4, 57.6, 58.4, 65.4, 96.3,
110.2, 121.6, 122.3, 122.9, 126.4, 127.5, 127.9, 128.2, 129.3,
129.9, 131.3, 134.7, 137.1, 140.6, 140.8, 141.1, 141.7, 142.2,
149.1, 156.4, 159.4, 167.3, 171.7, 196.3, 4 13C signals missing. UV
172.4, 197.2, 221.0, 2 13C signals missing. UV (DMSO) kmax
(e):
460 (41,000). HR-MS (ESI): [M+H]+ calcd for C40H46N3O5:
648.3432; found 648.3410.
4.8. (8R,9S,13S,14S)-13-Methyl-17-oxo-7,8,9,11,12,
13,14,15,16,17-decahydro-6H-cyclopenta[a]phenanthren-3-yl-
10-((Z)-2-((4-methoxy-1H,10H-2,20-bipyrrol-5-yl)methylene)-
3,5-dimethyl-2H-pyrrol-4-yl)-10-oxodecanoate (3c)
(DMSO) kmax (e
): 460 (48 000). HR-MS (ESI): [M+H]+ calcd. for
C48H53N4O5: 765.4035; found 765.4010.
Using the general ester coupling procedure, prodigiosene 2c
(35 mg, 0.072 mmol) and estrone (20 mg, 0.072 mmol) were reacted
for 2 days in DCM (7 mL). The crude solid was purified using column
chromatography (SiO2, EtOAc/hexane 10/90 to 40/60) to give the ti-
tle compound as a red film (30 mg, 50%). Rf = 0.15 (EtOAc/hexane 2/
1). 1H NMR (CDCl3, 500 MHz) 0.90 (s, 3H), 1.36–1.74 (m, 18H), 1.93–
2.18 (m, 6H), 2.24–2.30 (m, 1H), 2.44–2.46 (m, 6H), 2.52 (t, J = 7.5 Hz,
2H), 2.70 (t, J = 7.5 Hz, 2H), 2.88–2.91 (m, 2H), 3.99 (s, 3H), 6.04 (br s,
1H), 6.30 (br s, 1H), 6.79–6.85 (m, 3H), 6.96 (br s, 1H), 7.02 (br s, 1H),
7.28 (d, J = 8.5 Hz, 1H). 13C NMR (CDCl3, 125 MHz) 12.6, 13.9, 21.7,
24.2, 25.0, 25.1, 25.9, 26.4, 29.1, 29.2, 29.5, 31.6, 34.5, 35.9, 38.1,
41.4, 42.9, 44.2, 48.1, 50.5, 58.8, 60.5, 95.2, 111.4, 112.1, 115.9,
118.9, 121.7, 123.9, 124.0, 125.5, 125.6, 126.5, 137.3, 138.1, 143.7,
143.8, 148.7, 168.1, 171.3, 172.7, 179.3, 197.9, 220.9. HR-MS (ESI):
[M+H]+ calcd for C44H54N3O5: 704.4058; found 704.4056. UV
4.11. 4-((E)-1-(4-(2-(Dimethylamino)ethoxy)phenyl)-2-
phenylbut-1-enyl)phenyl-10-((Z)-2-((4-methoxy-1H,1’H-2,2’-
bipyrrol-5-yl)methylene)-3,5-dimethyl-2H-pyrrol-4-yl)-10-
oxodecanoate (4c)
Using the general ester coupling procedure, prodigiosene2c
(44 mg,
0.09 mmol)
and
(Z)-4-hydroxtamoxifen
(35 mg,
0.09 mmol) were reacted for one day in DCM (9 mL). The crude so-
lid was purified using column chromatography (Al2O3 neutral type
III, DCM/MeOH 99/1 to 90/10) to give the title compound as a deep
red solid (33 mg, 45%). Rf = 0.40 (DCM/MeOH 9/1). 1H NMR (CD2Cl2,
500 MHz) 0.90 (t, J = 7.5 Hz, 3H), 1.33–1.43 (m, 8H), 1.62–1.66 (m,
2H), 1.71–1.77 (m, 2H), 2.23 (s, 6H), 2.42 (s, 3H), 2.43–2.47 (m, 2H),
2.55 (t, J = 7.5 Hz, 2H), 2.59–2.61 (m, 5H), 2.69 (t, J = 7.5 Hz, 2H),
3.90 (t, J = 7.5 Hz, 2H), 3.98 (s, 3H), 6.10 (s, 1H), 6.34 (q, J = 4.0,
2.5 Hz, 1H), 6.55 (dt, J = 9.0, 2.5 Hz, 2H), 6.78 (dt, J = 9.0, 2.5 Hz,
2H), 6.91 (dd, J = 4.0, 1.0 Hz, 1H), 7.01 (s, 1H), 7.06 (dt, J = 8.5,
2.5 Hz, 2H), 7.11–7.14 (m, 4H), 7.15–7.19 (m, 2H), 7.23 (dt,
J = 8.5, 2.5 Hz, 2H), 11.93 (br s, 1H) ppm. 13C NMR (CD2Cl2,
125 MHz) 12.5, 13.6, 15.4, 24.4, 25.3, 29.3, 29.4, 29.5, 29.7, 29.8,
34.6, 43.3, 45.9, 58.5, 59.2, 66.1, 94.4, 112.2, 112.7, 113.6, 117.4,
121.6, 124.7, 124.8, 126.4, 126.7, 128.1, 130.0, 130.6, 132.1,
135.8, 137.7, 141.6, 142.2, 142.7, 146.4, 149.8, 153.6, 157.3,
167.7, 172.6, 197.5, 3 13C signals missing. HR-MS (ESI): [M+H]+
(DMSO) kmax (e): 461 (30,000).
4.9. 4-((E)-1-(4-(2-(Dimethylamino)ethoxy)phenyl)-2-
phenylbut-1-en-1-yl)phenyl 4-((Z)-2-((4-methoxy-1H,10H-[2,20-
bipyrrol]-5-yl)methylene)-3,5-dimethyl-2H-pyrrol-4-yl)-4-
oxobutanoate (4a)
Using the general ester coupling procedure, prodigiosene 2a
(34 mg,
0.08 mmol)
and
(Z)-4-hydroxtamoxifen
(34 mg,

C. L. A. Hawco et al. / Bioorg. Med. Chem. 21 (2013) 5995–6002
6001
calcd for C52H61N4O5: 821.4636; found: 821.4649. UV (in DMSO)
kmax ): 460 (30,000).
4.16. Prodigiosene–NH–TPP conjugate 6c
(e
This compound was obtained according to both procedure A
(41 mg, 40% yield) and procedure B (43 mg, 42% yield). 1H NMR
(DMSO, 500 MHz) ꢀ2.92 (s, 2H), 1.35 (m, 8H), 1.59 (m, 2H), 1.73
(m, 2H), 2.31 (s, 3H), 2.48 (t, J = 7.5 Hz, 2H), 2.67 (s, 3H), 2.71 (t,
2H), 3.82 (s, 3H), 6.18 (s, 1H), 6.24 (s, 1H), 6.67 (s, 1H) 6.79 (s.
1H), 7.13 (s, 1H), 7.81–7.82 (m, 7H), 8.08 (d, J = 8.0 Hz, 2H), 8.15
(d, J = 8.5 Hz, 2H), 8.21–8.22 (m, 5H), 8.82–8.89 (m, 9H), 10.34 (s,
1H), 11.84 (s, 1H). 13C NMR (DMSO, 125 MHz) 11.8, 15.4, 23.8,
24.5, 25.3, 28.7, 28.8, 28.9, 29.0, 36.7, 41.9, 58.4, 96.3, 110.0,
113.2, 117.4, 119.9, 120.0, 120.1, 122.4, 126.3, 127.0, 128.1,
131.6, 132.7, 134.2, 134.7, 135.6, 139.4, 141.2, 159.4, 167.3,
171.8, 196.6. HR-MS (ESI): [M+H]+ calcd for C70H63N8O3:
1063.5018; found 1063.5013.
4.12. Procedure A
To a solution of prodigiosene 2 (50 mg) in DMF (6 mL) was
added COMU (1.5 equiv) and DBU (3 equiv) at room temperature
under N2. After 30 min, TPP–NH2 (1.2 equiv) was added and the
reaction mixture was stirred for 14 h. Water (20 mL) was added
and the mixture was extracted with ethyl acetate (3 ꢂ 20 mL).
The combined organic layers were washed with water
(2 ꢂ 40 mL) and brine (50 mL) and then dried (Na2SO4). After re-
moval of the solvent under reduced pressure the crude product
was purified using column chromatography (Al2O3 type III basic,
DCM 100% then EtOAc/hexane 5/5). After removal of the solvent
under reduced pressure, the purple solid was triturated with meth-
anol then filtered using MilliporeÒ apparatus and then washed
with methanol to give a purple solid.
Acknowledgements
E.M. and D.P.C. are supported by trainee awards from The Bea-
trice Hunter Cancer Research Institute (BHCRI) with funds pro-
vided by Cancer Care Nova Scotia as part of The Terry Fox
Foundation Strategic Health Research Training Program in Cancer
Research at CIHR; A.E.G.B. was funded by the Canadian Breast Can-
cer Foundation (CBCF), Atlantic Region by way of a CBCF Student-
ship awarded through the BHCRI; G.D. and A.T. are Senior Scientists
of the BHCRI, and G.D. is a CIHR New Investigator. This work was
funded by research grants to: A.T. from the Nova Scotia Health Re-
search Foundation; and G.D. from the CBCF-Atlantic and the Dal-
housie Medical Research Foundation. Human cell-line screening
and in vivo toxicity evaluations were performed by the Develop-
mental Therapeutics Program, Division of Cancer Treatment and
Diagnosis, National Cancer Institute (http://dtp.cancer.gov).
4.13. Procedure B
To a suspension of the PS-carbodiimide resin (2 equiv) in DMF
(0.30 mL) was added prodigiosene 2 (50 mg) under N2. The mixture
was stirred for 10 min, then TPP–NH2 (1 equiv) and DMAP
(3 equiv) were added and the reaction mixture was stirred for
24 h. Analysis of the reaction mixture using TLC showed incomple-
tion so DMF (0.25 mL) was added. After 24 h further stirring, the
reaction mixture was filtered and the polymer was washed with
DCM. Water (20 mL) was added to the filtrate and the mixture
was extracted with ethyl acetate (3 ꢂ 20 mL). The combined or-
ganic layers were washed with water (3 ꢂ 40 mL) and brine
(50 mL) and then dried (Na2SO4). The crude solid was purified
using column chromatography (Al2O3 type III basic, DCM/hexanes
5/5, then MeOH/DCM/hexane 5/47.5/47.5). After removal of the
solvent under reduced pressure, the purple solid was triturated
with methanol then filtered using MilliporeÒ apparatus and then
washed with methanol to give a purple solid.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2013.07.042.
4.14. Prodigiosene–NH–TPP conjugate 6a
References and notes
1. Fuerstner, A. Angew. Chem., Int. Ed. 2003, 42, 3582.
According to procedure B and using 2a (40 mg, 0.099) the title
compound was obtained as a purple solid (30 mg, 34% yield). 1H
NMR (DMSO, 500 MHz) ꢀ2.92 (s, 2H), 2.36 (s, 3H), 2.45 (t,
J = 6.0 Hz, 2H), 2.64 (t, J = 6.0 Hz, 2H), 2.80 (s, 3H), 3.89 (s, 3H),
6.21 (s, 1H), 6.26 (s, 1H), 6.75 (s, 1H), 6.81 (s, 1H), 7.16 (s, 1H),
7.82–7.85 (br s, 7H), 8.10 (d, J = 8.7 Hz, 2H), 8.16 (d, J = 8.7 Hz,
2H), 8.22–8.24 (br s, 5H), 8.83–8.91 (m, 9H), 10.49 (s, 1H), 11.87
(s, 1H). Considering the poor solubilty of this compound 13C NMR
data is not provided. HR-MS (ESI): [M+H]+ calcd for C64H51N8O3:
979.4079; found 979.4043.
2. Pandey, R.; Chander, R.; Sainis, K. B. Curr. Pharm. Des. 2009, 15, 732.
3. Williamson, N. R.; Fineran, P. C.; Gristwood, T.; Chawrai, S. R.; Leeper, F. J.;
Salmond, G. P. C. Future Microbiol. 2007, 2, 605.
4. Perez-Tomas, R.; Montaner, B.; Llagostera, E.; Soto-Cerrato, V. Biochem.
Pharmacol. 2003, 66, 1447.
5. Montaner, B.; Perez-Tomas, R. Life Sci. 2001, 68, 2025.
6. Manderville, R. A. Curr. Med. Chem.: Anticancer Agents 2001, 1, 195.
7. Francisco, R.; Perez-Tomas, R.; Gimenez-Bonafe, P.; Soto-Cerrato, V.; Gimenez-
Xavier, P.; Ambrosio, S. Eur. J. Pharmacol. 2007, 572, 111.
8. Melvin, M. S.; Tomlinson, J. T.; Saluta, G. R.; Kucera, G. L.; Lindquist, N.;
Manderville, R. A. J. Am. Chem. Soc. 2000, 122, 6333.
9. Konopleva, M.; Watt, J.; Contractor, R.; Tsao, T.; Harris, D.; Estrov, Z.;
Bornmann, W.; Kantarjian, H.; Viallet, J.; Samudio, I.; Andreeff, M. Cancer Res.
2008, 68, 3413.
4.15. Prodigiosene–NH–TPP conjugate 6b
10. Ullah, M. F. Asian Pac. J. Cancer Prev. 2008, 9, 1.
11. Mazza, M.; Uchegbu, I. F.; Schaetzlein, A. G. Br. J. Pharmacol. 2008, 155, 149.
12. Spradau, T. W.; Katzenellenbogen, J. A. Bioorg. Med. Chem. Lett. 1998, 8, 3235.
13. Perron, V.; Rabouin, D.; Asselin, É.; Parent, S.; C.-Gaudreault, R.; Bérubé, G.
Bioorg. Chem. 2005, 33, 1.
14. Van Themsche, C.; Parent, S.; Leblanc, V.; Descôteaux, C.; Simard, A.-M.;
Bérubé, G.; Asselin, E. Endocr. Relat. Cancer 2009, 16, 1185.
15. Provencher-Mandeville, J.; Debnath, C.; Mandal, S. K.; Leblanc, V.; Parent, S.;
Asselin, É.; Bérubé, G. Steroids 2011, 76, 94.
16. Cyrus, K.; Wehenkel, M.; Choi, E.-Y.; Lee, H.; Swanson, H.; Kim, K.-B.
ChemMedChem 2010, 5, 979.
17. Kuduk, S. D.; Zheng, F. F.; Sepp-Lorenzino, L.; Rosen, N.; Danishefsky, S. J.
Bioorg. Med. Chem. Lett. 1999, 9, 1233.
18. Kuduk, S. D.; Harris, C. R.; Zheng, F. F.; Sepp-Lorenzino, L.; Ouerfelli, Q.; Rosen,
N.; Danishefsky, S. J. Bioorg. Med. Chem. Lett. 2000, 10, 1303.
19. Zhang, D.; Baek, S.-H.; Ho, A.; Kim, K. Bioorg. Med. Chem. Lett. 2004, 14, 645.
20. Gacio, A. F.; Fernandez-Marcos, C.; Swamy, N.; Dunn, D.; Ray, R. J. Cell. Biochem.
2006, 99, 665.
According to procedure A, the title compound was obtained as a
purple solid (55 mg, 50%). Mp 206 °C. 1H NMR (CD2Cl2, 500 MHz)
ꢀ2.85 (s, 2H), 1.89–1.90 (m, 4H), 2.48 (s, 3H), 2.57–2.60 (m, 5H),
2.91 (t, J = 6.0 Hz, 2H), 3.89 (s, 3H), 5.97 (s, 1H), 6.29 (dd, J = 3.5,
2.7 Hz, 1H), 6.73 (dd, J = 3.5, 1.5 Hz, 1H), 6.89 (s, 1H), 6.96 (br s,
1H), 7.74–7.81 (m, 9H), 8.08 (d, J = 6.5 Hz, 2H), 8.17 (d, J = 6.5 Hz,
2H), 8.20–8.22 (m, 6H), 8.51 (br s, 1H), 8.85 (m, 5H), 8.91 (d,
J = 5.0 Hz, 2H). 13C NMR (CD2Cl2, 125 MHz) 12.6, 12.4, 23.6, 25.4,
37.9, 42.5, 58.9, 95.9, 111.1, 112.0, 113.8, 118.2, 120.2, 120.5,
123.1, 123.4, 125.2, 126.9, 127.0, 128.0, 128.4, 131.5, 134.9,
135.3, 137.7, 138.9, 142.2, 142.4, 169.0, 171.8, 197.9. HR-Ms
(ESI): [M+H]+ calcd for C66H55N8O3: 1007.4392; found: 1007.4424.

6002
C. L. A. Hawco et al. / Bioorg. Med. Chem. 21 (2013) 5995–6002
21. Devraj, R.; Barrett, J. F.; Fernandez, J. A.; Katzenellenbogen, J. A.; Cushman, M. J.
Med. Chem. 1996, 39, 3367.
22. Schobert, R.; Bernhardt, G.; Biersack, B.; Bollwein, S.; Fallahi, M.; Grotemeier,
A.; Hammond, G. L. ChemMedChem 2007, 2, 333.
37. Regourd, J.; Ali, A. A.-S.; Thompson, A. J. Med. Chem. 2007, 50, 1528.
38. Saez, D. R. I.; Bennett, S. M.; Thompson, A. ChemMedChem 2009, 4, 742.
39. Saez, D. R. I.; Regourd, J.; Santacroce, P. V.; Davis, J. T.; Jakeman, D. L.;
Thompson, A. Chem. Commun. 2007, 2701.
23. Burke, P. J.; Koch, T. H. J. Med. Chem. 2004, 47, 1193.
24. El Amouri, H.; Vessieres, A.; Vichard, D.; Top, S.; Gruselle, M.; Jaouen, G. J. Med.
Chem. 1992, 35, 3130.
25. Top, S.; El Hafa, H.; Vessieres, A.; Quivy, J.; Vaissermann, J.; Hughes, D. W.;
McGlinchey, M. J.; Mornon, J.-P.; Thoreau, E.; Jaouen, G. J. Am. Chem. Soc. 1995,
117, 8372.
40. Smithen, D. A.; Forrester, A. M.; Corkery, D. P.; Dellaire, G.; Colpitts, J.;
McFarland, S. A.; Berman, J. N.; Thompson, A. Org. Biomol. Chem. 2013, 11, 62.
41. Uddin, M. I.; Thirumalairajan, S.; Crawford, S. M.; Cameron, T. S.; Thompson, A.
Synlett 2010, 2561.
42. Dao, K.-L.; Hanson, R. N. Bioconjugate Chem. 2012, 23, 2139.
43. Yu, D. D.; Forman, B. M. J. Org. Chem. 2003, 68, 9489.
26. Tang, J.; Top, S.; Vessières, A.; Sellier, N.; Vaissermann, J.; Jaouen, G. Appl.
Organomet. Chem. 1997, 11, 771.
44. Ajit, S.; Palaniappan, S.; Kumar, P. U.; Madhusudhanachary, P. J. Polym. Sci., Part
A: Polym. Chem. 2012, 50, 884.
27. Morel, P.; Top, S.; Vessieres, A.; Stephan, E.; Laios, I.; Leclercq, G.; Jaouen, G. C. R.
Acad. Sci., Ser. IIc: Chim. 2001, 4, 201.
28. Trivedi, E. R.; Blumenfeld, C. M.; Wielgos, T.; Pokropinski, S.; Dande, P.; Hai, T.
T.; Barrett, A. G. M.; Hoffman, B. M. Tetrahedron Lett. 2012, 53, 5475.
29. Jordan, V. C. J. Med. Chem. 2003, 46, 883.
45. Bhatt, R. K.; Sharma, S.; Nath, M. Monatsh. Chem. 2012, 143, 309.
46. Luguya, R.; Jaquinod, L.; Fronczek, F. R.; Vicente, M. G. H.; Smith, K. M.
Tetrahedron 2004, 60, 2757.
47. Twibanire, J.-d. A. K.; Grindley, T. B. Org. Lett. 2011, 13, 2988.
48. Sternberg, E. D.; Dolphin, D.; Brückner, C. Tetrahedron 1998, 54, 4151.
49. Soto-Cerrato, V.; Llagostera, E.; Montaner, B.; Scheffer, G. L.; Peren-Tomas, R.
Biochem. Pharmacol. 2004, 1345.
50. Al-Bader, M.; Ford, C.; Al-Ayadhy, B.; Francis, I. Exp. Ther. Med. 2011, 2, 537.
51. Montaner, B.; Perez-Tomas, R. Curr. Cancer Drug Tar. 2003, 3, 57.
52. Paull, K. D.; Shoemaker, R. H.; Hodes, L.; Monks, A.; Scudiero, D. A.; Rubinstein,
L.; Plowman, J.; Boyd, M. R. J. Natl Cancer Inst. 1989, 81, 1088.
53. Holbeck, S. L.; Collins, J. M.; Doroshow, J. H. Mol. Cancer Ther. 2010, 1451.
54. Boyd, M. R.; Paull, K. D. Drug Dev. Res. 1995, 91.
30. Jordan, V. C. J. Med. Chem. 2003, 46, 1081.
31. Dowsett, M.; Nicholson, R.; Pietras, R. Breast Cancer Res. Treat. 2005, 93, 11.
32. Wakeling, A. E.; Bowler, J. Biochem. Soc. Trans. 1991, 19, 899.
33. Peng, J.; Sengupta, S.; Jordan, V. C. Anticancer Agents Med. 2009, 9, 481.
34. Kuukasjärvi, T.; Kononen, J.; Helin, H.; Holli, K.; Isola, J. J. Clin. Oncol. 1996, 14,
2584.
35. Ishikawa, T.; Nakagawa, H.; Hagiya, Y.; Nonoguchi, N.; Miyatake, S.-i.; Kuroiwa,
T. Adv. Pharmacol. Sci. 2010. Article ID 587306.
36. Vicente, M. G. H. Curr. Med. Chem.: Anticancer Agents 2001, 1, 175.