Design, synthesis, and evaluation of curcumin-derived arylheptanoids for glioblastoma and neuroblastoma cytotoxicity

Article abstract of DOI:10.1016/j.bmcl.2013.09.095

Using an innovative approach toward multiple carbon-carbon bond-formations that relies on the multifaceted catalytic properties of titanocene complexes we constructed a series of C1-C7 analogs of curcumin for evaluation as brain and peripheral nervous system anti-cancer agents. C2-Arylated analogs proved efficacious against neuroblastoma (SK-N-SH & SK-N-FI) and glioblastoma multiforme (U87MG) cell lines. Similar inhibitory activity was also evident in p53 knockdown U87MG GBM cells. Furthermore, lead compounds showed limited growth inhibition in vitro against normal primary human CD34+hematopoietic progenitor cells. Taken together, the present findings indicate that these curcumin analogs are viable lead compounds for the development of new central and peripheral nervous system cancer chemotherapeutics with the potential for little effects on normal hematopoietic progenitor cells.

Full text of DOI:10.1016/j.bmcl.2013.09.095

Bioorganic & Medicinal Chemistry Letters 23 (2013) 6874–6878
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis, and evaluation of curcumin-derived
arylheptanoids for glioblastoma and neuroblastoma cytotoxicity
Catherine A. Campos a, Joseph B. Gianino a, Barbara J. Bailey b, Mary E. Baluyut b, Constanze Wiek d,
Helmut Hanenberg c,d,e,f, Harlan E. Shannon b, Karen E. Pollok b, , Brandon L. Ashfeld a,
⇑
⇑
a Department of Chemistry and Biochemistry, Mike and Josie Harper Cancer Research Institute, University of Notre Dame, Notre Dame, IN 46556, United States
b Herman B Wells Center for Pediatric Research, Department of Pediatrics, Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, IN 46202, United States
c Indiana University Simon Cancer Center, Indiana University School of Medicine (IUSM), Indianapolis, IN 46202, United States
d Department of Otorhinolaryngology (ENT), Heinrich Heine University School of Medicine, Düsseldorf 40225, Germany
e Department of Pediatrics, Herman B Wells Center for Pediatric Research, Indiana University School of Medicine, Indianapolis, IN 46202, United States
f Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN 46202, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 July 2013
Revised 26 September 2013
Accepted 30 September 2013
Available online 11 October 2013
Using an innovative approach toward multiple carbon–carbon bond-formations that relies on the multi-
faceted catalytic properties of titanocene complexes we constructed a series of C1–C7 analogs of curcu-
min for evaluation as brain and peripheral nervous system anti-cancer agents. C2-Arylated analogs
proved efficacious against neuroblastoma (SK-N-SH & SK-N-FI) and glioblastoma multiforme (U87MG)
cell lines. Similar inhibitory activity was also evident in p53 knockdown U87MG GBM cells. Furthermore,
lead compounds showed limited growth inhibition in vitro against normal primary human CD34+hema-
topoietic progenitor cells. Taken together, the present findings indicate that these curcumin analogs are
viable lead compounds for the development of new central and peripheral nervous system cancer chemo-
therapeutics with the potential for little effects on normal hematopoietic progenitor cells.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Curcumin
Relay catalysis
Arylheptanoids
Glioblastoma
Neuroblastoma
Despite remarkable advances in pharmaceutical drug design,
effective chemotherapy options for brain and nervous system can-
cers that demonstrate selective cytotoxicity remain a challenge in
medicinal chemistry. A recent National Cancer Institute report sta-
ted, ‘over the last 30–40 years, the mortality rate for brain and
other CNS cancers has remained largely unchanged.’1 Current che-
motherapeutic options are limited, and typically only provide 6–
24 month survival rates.2 Recently, curcumin has become a phar-
maceutical target of interest based on its diverse range of biological
activity. A bioactive metabolite of the rhizome of Curcuma longa
and the major component of the traditional Indian folk medicine
turmeric, this diarylheptanoid exhibits anti-cancer, anti-inflamma-
tory, anti-oxidant, and chemopreventative properties.3 This natu-
rally occurring metabolite demonstrated apoptotic induction and
cytotoxicity toward a variety of cancer cell lines, while exhibiting
a remarkable lack of adverse side effects and no systemic toxicity.4
Recent work has shown that curcumin possesses impressive
growth inhibition and induction of apoptosis of glioblastoma and
neuroblastoma cells in vitro, and decreased tumorigenesis in vivo.5
Unfortunately, its affinity for a wide range of targets, low potency,
and unsatisfactory pharmacokinetics limits the clinical viability of
this biologically versatile natural product.6
As a result, a number of groups have focused on the design of
curcumin structural analogs to optimize specific chemotherapeutic
properties. Analog evaluation has primarily fixated on the aryl and
b-diketone regions, which are considered crucial for activity.6 In
contrast, the olefins at C1 and C6 are commonly believed to serve
as linkers for the aromatic and ketone regions, and therefore, sig-
nificant structural modification of this region has not been studied
in detail. We chose to target analogs possessing an aryl-substituted
tertiary center at C1 or C3 and evaluate them for brain and nervous
system anticancer activity to glean insight into the biological activ-
ity of curcumin (Fig. 1). Our recently developed titanocene-cata-
lyzed multicomponent coupling reactions7 enables rapid access
to C1 and C3 aryl-substituted analogs 2 and 3 of curcumin, thereby
allowing us to strategically design, synthesize, and evaluate a di-
verse array of curcumin-derived arylheptanoid analogs.8
We envisioned that our titanocene-catalyzed multicomponent
coupling9 would provide a direct route to C1-arylated curcumin
analogs through the union of an electron rich arene, benzaldehyde
derivative, and an iodoalkyne comprised of the C1–C7 carbon chain
oxidized at C5. In an effort to maintain the enol–OH functionality
present in curcumin, we targeted secondary alcohol 9 as a mixture
of C1 epimers (Scheme 1).
⇑
Corresponding authors. Tel.: +1 317 274 8891 (K.E.Pollok); Tel.: +1 574 631
1727; fax: +1 574 631 6652 (B.L.Ashfeld).
E-mail addresses: kpollok@iu.edu (K.E. Pollok), bashfeld@nd.edu (B.L. Ashfeld).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.09.095

C. A. Campos et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6874–6878
6875
120
100
80
*
*
16a
*
16b
*
60
16c
17
40
20
0
9
10
*
* * *
Curcumin
0.1
1
10
100
1000
Concentration (µM)
Figure 2. Dose-related decreases in cell survival of U87 MG GBM cells by curcumin
analogs. Cells were exposed in triplicate to vehicle or increasing concentrations of
compounds 9, 10, 16a–c, 17, or curcumin and survival was measured at 5 days post-
exposure.16 ⁄p <0.05 versus media control, Dunnett’s multiple comparisons test.
yield. With alcohol 9 in hand, we sought to reduce the alkyne func-
tionality to the corresponding trans olefin in an effort to provide a
comparison to the curcumin carbon backbone. Thus, treatment of 9
with Me2SiHCl followed by a ruthenium-catalyzed alkyne hydrosi-
lylation gave the trans-alkene 10.12 This highly convergent strategy
toward constructing the triarylated curcumin C1–C7 carbon frame-
work ultimately permits modular flexibility required for a com-
plete SAR study based on the general structure of 2.
Our synthesis of the C3-arylated curcumin analogs began with
construction of the C4–C7 fragment for the titanocene-catalyzed
multicomponent coupling (Scheme 2). Esterification of commer-
cially available acid 11 followed by silylation of the phenol and
treatment with DIBAL-H gave aldehyde 12 in 64% yield over three
Figure 1. Design and synthesis of curcumin analogs.
Enantioenriched iodoalkyne 5 was obtained in three steps from
known aldehyde 410 using a titanium-catalyzed asymmetric prop-
argylation.11 Treatment of 5, arene 6, and aldehyde 7 with Cp2TiCl2
(5 mol %), PtBu3, Zn, Cs2CO3, and Ac2O provided diarylethynyl
methane 8 in 99% yield.7b Treatment with TBAF liberated the sec-
ondary hydroxyl group at C5 to give the target alcohol 9 in 83%
Scheme 1. Synthesis of the C2-arylated curcumin derivatives.
Scheme 2. Synthesis of iodoalkyne 13.
Scheme 3. Synthesis of C3-arylated curcumin analogs.

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Table 1
C. A. Campos et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6874–6878
steps.13 A Corey–Fuchs alkynylation14 in which the lithium acety-
lide was quenched with I2 yielded iodoalkyne 13 in 69% yield.15
This establishes a simple and reliable route toward this curcumi-
noid fragment.
Potency of curcumin derivatives in decreasing glioblastoma cell and neuroblastoma
cell survivala
Entry
Tested compounds
IC50 (lM)
With our C4–C7 fragment in hand, we turned our attention to-
ward the crucial titanocene-catalyzed multicomponent coupling.
Thus, treatment of iodoalkyne 13, aldehyde 14, and silyl enol ether
1517 with Cp2TiCl2 (2 mol %), (4-MeOC6H4)3P, Zn(0), and Ac2O gave
a mixture of b-aryl ketones 16a and 16b in which the TMS-phenol
protodesilylation proved remarkably facile (Scheme 3). Silylation
of the resulting free phenol in 16a gave ketone 16c in 91% yield.
Diastereoselective ketone reduction using Corey’s CBS reagent pro-
vided alcohol 17 in 77% yield as a 1:1 mixture of diastereomers in
92% ee each.18
Structure–activity relationships of compounds were evaluated
in human U87 MG GBM and neuroblastoma (NB) SK-N-SH and
SK-N-FI cells. Cells were exposed to increasing concentrations of
compounds 9, 10, 16a–c, or 17. Cell growth was determined using
a methylene blue staining assay that measures cell mass and cor-
relates with cell number (Fig. 2).19 Both 16a and 16b significantly
Glioblastoma cell lines
1
2
3
4
5
6
7
8
U87-MG
16a
16b
16c
Curcumin
16a
16b
16a
16b
7.5
8.0
19.1
8.1
7.0
6.9
7.0
7.0
U87-MG sh-gfp
U87-MG sh-p53
Neuroblastoma cells
9
10
11
12
13
14
15
16
SK-N-SH
16a
16b
16c
Curcumin
16a
16b
16c
Curcumin
18.1
11.7
48.8
6.4
31.1
22.1
SK-N-FI
>100
11.3
a
IC50 values for each compound were determined using CalcuSyn Software
(Biosoft, Cambridge, UK).
affected growth in the low
lM range in U87 GBM cells as
Figure 3. Dose-related decreases in cell survival of glioblastoma and neuroblastoma cells irrespective of p53 status. Cells were exposed in triplicate to vehicle or increasing
concentrations of compound and survival was measured at 5 days post-exposure.16 ⁄p <0.05, 16a and 16b versus vehicle control. (A) Effect of 16a and (B) 16b on U87 parental
wild type p53, U87 vector control (U87gfpcontrol), and cells with knock down of p53 (U87 shp53) were determined as described above. (C and D) Dose response curves of
wild type 53 NB (SK-N-SH) and mutant p53 NB (SK-N-FI) cells to 16a and 16b. ⁄p <0.05 versus media control, Dunnett’s multiple comparisons test.

C. A. Campos et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6874–6878
6877
400
350
300
250
200
150
100
50
collection of umbilical cord blood products and Christophe Mar-
chal for his expert assistance with production of lentiviral vector
supernatants. We also acknowledge financial support of this re-
search from the University of Notre Dame, the Walther Cancer
Foundation, Riley Children’s Foundation, the Indiana University Si-
mon Cancer Center, the Jeff Gordon Research Foundation (B.B. and
K.P.), and RO1 CA138798 (B.B. and K.P.). This work was also sup-
ported by the NIH R01s CA138237 and CA155294 and by the BMBF
grant ‘FoneFA’ and the DFG SPP1230 to HH. Indiana University is a
Center for Excellence in Molecular Hematology (P30).
*
0
Supplementary data
Control
DMSO
0.3
3
30
0.3
3
30
0.3
3
30
Control
16a (uM)
16b (uM)
10 (uM)
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.09.
095.
Figure 4. Effect of select compounds on human progenitor cell growth. Human
CD34+ cells were exposed in triplicate to 0.3–30 M of compounds 16a, 16b, or 10.
Progenitor cell frequency was determined after 14 days. ⁄p <0.05 versus media
control, Dunnett’s multiple comparisons test (16b at 30 M).
l
l
References and notes
illustrated by the IC50 values of 16a, 16b and curcumin20 (Table 1,
entries 1–8). Since p53 mutations can be found in a variety of can-
cers, including GBM and NB, we evaluated the dependency of com-
pound efficacy on p53 status.21 U87MG cells (parental p53 wild
type, vector control, and p53 knockdown) had identical sensitivity
profiles, indicating that 16a and 16b can block growth independent
of p53 expression (Fig. 3, A and B). Additionally, effect on cell
growth was not dependent on functional p53 in either SK-N-SH
(wild type p53) or SK-N-FI (mutant p53) neuroblastoma cells, as
both were sensitive to 16a and 16b (Figure 3, C and D; Table 1, en-
tries 9–16). Given that normal tissue toxicity can be a limiting fac-
tor in many anticancer therapies, we screened for compound effect
on normal hematopoietic progenitor cells using colony-forming
unit assays.22 Human CD34+ cells isolated from umbilical cord
blood served as a fresh source of human progenitor cells and were
treated with doses of the most active compounds, 16a and 16b and
10, for purposes of comparison. The assay was performed at con-
centrations of these compounds that had minimal effect on U87
1. (a) Surveillance, Epidemiology, and End Results (SEER) Program and the
National Center for Health Statistics. http://seer.cancer.gov/statfacts/html/
brain.html.; (b) Ries, L. A. G.; Melbert, D.; Krapcho, M.; Mariotto, A.; Miller, B.
A.; Feuer, E. J.; Clegg, L.; Horner, M. J.; Howlader, N.; Eisner, M. P.; Reichman,
M.; Edwards, B. K. SEER Cancer Statistics Review 1975–2004; National Institutes of
Health; Bethesda, MD: National Cancer Institute, 2007.
2. (a) Balmaceda, C.; Peereboom, D.; Pannullo, S.; Cheung, Y. K. K.; Fisher, P. G.;
Alavi, J.; Sisti, M.; Chen, J.; Fine, R. L. Cancer 2008, 112, 1139; (b) Galanis, E.;
Jaeckle, K. A.; Maurer, M. J.; Reid, J. M.; Ames, M. M.; Hardwick, J. S.; Reilly, J. F.;
Loboda, A.; Nebozhyn, M.; Fantin, V. R.; Richon, V. M.; Scheithauer, B.; Giannini,
C.; Flynn, P. J.; Moore, D. F., Jr.; Zwiebel, J.; Buckner, J. C. J. Clin. Oncol. 2009, 27,
2052.
3. (a) Agrawal, D. K.; Mishra, P. K. Med. Res. Rev. 2010, 30, 818; (b) Anand, P.;
Thomas, S. G.; Kunnumakkara, A. B.; Sundaram, C.; Harikumar, K. B.; Sung, B.;
Tharakan, S. T.; Misra, K.; Priyadarsini, I. K.; Rajasekharan, K. N.; Aggarwal, B. B.
Biochem. Pharmacol. 2008, 76, 1590; (c) Goel, A.; Kunnumakkara, A. B.;
Aggarwal, B. B. Biochem. Pharmacol. 2008, 75, 787; (d) Ruby, A. J.; Kuttan, G.;
Dinesh Babu, K.; Rajasekharan, K. N.; Kuttan, R. Cancer Lett. 1995, 94, 79.
4. (a) Bush, J. A.; Cheung, K. J. J., Jr; Li, G. Exp. Cell. Res. 2001, 271, 305; (b) Jiang, M.
C. M.; Yang-Yen, H. F. H.; Yen, J. J. J.; Lin, J. K. J. Nutr. Cancer 1996, 26, 111; (c)
Nakamura, K.; Yasunaga, Y.; Segawa, T.; Ko, D.; Moul, J. W.; Srivastava, S.; Rhim,
J. S. Int. J. Oncol. 2002, 21, 825; (d) Ramachandran, C.; Rodriguez, S.;
Ramachandran, R.; Raveendran Nair, P. K.; Fonseca, H.; Khatib, Z.; Escalon, E.;
Melnick, S. J. Anticancer Res. 2005, 25, 3293; (d) Sharma, R. A.; Gescher, A. J.;
Steward, W. P. Eur. J. Cancer 1955, 2005, 41.
5. (a) Dhandapani, K. M.; Mahesh, V. B.; Brann, D. W. J. Neurochem. 2007, 102, 522;
(b) Freudlsperger, C.; Greten, J.; Schumacker, U. Anticancer Res. 2008, 28, 209;
(c) Liontas, A.; Yeger, H. Anticancer Res. 2009, 24, 987; (d) Perry, M.-C.;
Demeule, M.; Régina, A.; Moumdjian, R.; Béliveau, R. Mol. Nutr. Food Res. 2010,
54, 1192; (e) Purkayastha, S.; Berliner, A.; Fernando, S. S.; Ranasinghe, B.; Ray,
I.; Tariq, H.; Banerjee, P. Brain Res. 2009, 1266, 130; (f) Senft, C.; Polacin, M.;
Priester, M.; Seifert, V.; Kögel, D.; Weissenberger, J. BMC Cancer 2010, 10, 491.
6. For selected references describing modification of the 1,3-dicarbonyl region of
curcumin, see: (a) Lin, L.; Shi, Q.; Nyarko, A. K.; Bastow, K. F.; Wu, C.-C.; Su, C.-
Y.; Shih, C. C. Y.; Lee, K.-H. J. Med. Chem. 2006, 49, 3963; (b) Tan, K.-L.; Koh, S.-B.;
Ee, R. P.-L.; Khan, M.; Go, M.-L. ChemMedChem 2012, 7, 1567; (c) Yamaguchi,
M.; Moore, T. W.; Sun, A.; Snyder, J. P.; Shoji, M. Integr. Biol. 2012, 4, 905; (d)
Zuo, Y.; Huang, J.; Zhou, B.; Wang, S.; Shao, W.; Zhu, C.; Lin, L.; Wen, G.; Wang,
H.; Du, J.; Bu, X. Eur. J. Med. Chem. 2012, 55, 346; (e) Ohori, H.; Yamakoshi, H.;
Tomizawa, M.; Shibuya, M.; Kakudo, Y.; Takahashi, A.; Takahashi, S.; Kato, S.;
Suzuki, T.; Ishioka, C.; Iwabuchi, Y.; Shibata, H. Mol. Cancer Ther. 2006, 5, 2563;
(f) Zhang, Q.; Zhong, Y.; Yan, L.-N.; Sun, X.; Gong, T.; Zhang, Z.-R. Biorg. Med
Chem. Lett. 2011, 21, 1010; (g) Batie, S.; Lee, J. H.; Jama, R. A.; Browder, D. O.;
Montano, L. A.; Huynh, C. C.; Marcus, L. M.; Tsosie, D. G.; Mohammed, Z.; Trang,
V.; Marshall, P. A.; Jurutka, P. W.; Wagner, C. E. Bioorg. Med. Chem. 2013, 21,
693.
7. (a) Campos, C. A.; Gianino, J. B.; Pinkerton, D. M.; Ashfeld, B. L. Org. Lett. 2011,
13, 5680; (b) Gianino, J. B.; Ashfeld, B. L. J. Am. Chem. Soc. 2012, 134, 18217; (c)
Campos, C. A.; Gianino, J. B.; Ashfeld, B. L. Org. Lett. 2013, 15, 2656; (d) Lepore,
A. J.; Pinkerton, D. M.; Ashfeld, B. L. Adv. Synth. Catal. 2013, 355, 1500.
8. (a) Anastas, P.; Kirchhoff, M. Acc. Chem. Res. 2002, 35, 686; (b) Felpin, F.-X.;
Fouquet, E. ChemSusChem 2008, 1, 718; Nicolaou, K. C.; Edmonds, D. J.; Bulger,
P. G. Angew. Chem., Int. Ed. 2006, 45, 7134; (c) Tietze, L. F. Chem. Rev. 1996, 96,
115; Tietze, L. F.; Beifuss, U. Angew. Chem., Int. Ed. 1993, 32, 131.
9. For recent work on titanocene-catalyzed metallations and related processes,
see: (a) Fleury, L. M.; Ashfeld, B. L. Org. Lett. 2009, 11, 5670; (a) Fleury, L. M.;
Ashfeld, B. L. Tetrahedron Lett. 2010, 51, 2427; (b) Fleury, L. M.; Gianino, J. B.;
Ashfeld, B. L. Tetrahedron Lett. 2012, 53, 5376; (c) Fleury, L. M.; Kosal, A. D.;
Masters, J. T.; Ashfeld, B. L. J. Org. Chem. 2012. ASAP Article; (d) Kosal, A. D.;
Ashfeld, B. L. Org. Lett. 2010, 12, 44; (e) Wilson, E. E.; Oliver, A. G.; Hughes, R. P.;
Ashfeld, B. L. Organometallics 2011, 30, 5214.
MG cell growth (0.3 & 3.0
the growth of U87 MG cells (30
compound-mediated toxicity was minimal over a 0.3–30
dose-range of 16a and 16b. At 30 M, treatment with 16b led to
l
M) and doses that significantly affected
l
M). As illustrated in Figure 4,
lM
l
a 20–25% decrease in the number of colonies. These data indicate
that, at least in vitro, compound-mediated toxicity to hematopoi-
etic cells was not pronounced.
In summary, we have established a universal and direct strategy
for the assembly of curcumin analogs using a transition metal-cat-
alyzed multicomponent coupling strategy. This highly convergent
approach enables the rapid evaluation of structural analogs based
on this biologically active natural product. A series of curcumin-
based diarylheptanoid analogs were synthesized and evaluated
for anti-glioblastoma and anti-neuroblastoma properties. The po-
tency of the 16a and 16b was only slightly less than that of curcu-
min and was still in the low micromolar range, These results
enabled us to identify a number of lead compounds that provides
a foundation toward identifying diarylheptanoid analogs which
are cytotoxic against brain and peripheral nervous system cancers
and have improved metabolic and pharmacokinetic profiles
in vivo. Further investigation of individual diastereomers, the
application of our design strategy and subsequent evaluation of
curcumin-based analogs is currently underway and will be re-
ported in due course.
Acknowledgments
The authors thank the nursing staff and Dr. Arthur Baluyut at
the St. Vincent Women’s Hospital for donation of their time for

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C. A. Campos et al. / Bioorg. Med. Chem. Lett. 23 (2013) 6874–6878
10. Boulard, L.; BouzBouz, S.; Cossy, J.; Franck, X.; Figadère, B. Tetrahedron Lett.
2004, 45, 6603.
17. Saitoh, T.; Oyama, T.; Sakurai, K.; Niimura, Y.; Hinata, M.; Horiguchi, Y.; Toda, J.;
Sano, T. Chem. Pharm. Bull. 1996, 44, 956.
11. (a) Hanawa, H.; Uraguchi, D.; Konishi, S.; Hashimoto, T.; Maruoka, K. Chem. Eur.
J. 2003, 9, 4405; (b) Usanov, D. L.; Yamamoto, H. J. Am. Chem. Soc. 2011, 133,
1286.
18. (a) Corey, E. J.; Bakshi, R. K.; Shibata, S.; Chen, C. P.; Singh, V. K. J. Am. Chem. Soc.
1987, 109, 7925; (b) Helal, C. J.; Magriotis, P. A.; Corey, E. J. J. Am. Chem. Soc.
1996, 118, 10938.
12. (a) Fürstner, A.; Radkowski, K. Chem. Commun. 2002, 2182; (b) Micoine, K.;
Fürstner, A. J. Am. Chem. Soc. 2010, 132, 14064; (c) Trost, B. M.; Ball, Z. T. J. Am.
Chem. Soc. 2003, 125, 30; (d) Trost, B. M.; Ball, Z. T.; Jöge, T. J. Am. Chem. Soc.
2002, 124, 7922.
13. Rauniyar, V.; Hall, D. G. J. Org. Chem. 2009, 74, 4236.
14. Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 13, 3769.
15. Chen, H.-B.; Yin, J.; Wang, Y.; Pei, J. Org. Lett. 2008, 10, 3113.
16. To quantify cell mass, cells were stained with methylene blue, solubilized in
0.1 N HCl, and absorbance determined at 610 nm. Mean and standard
deviation were determined.
19. Oliver, M. H.; Harrison, N. K.; Bishop, J. E.; Cole, P. J.; Laurent, G. J. J. Cell Sci.
1989, 92, 513.
20. Curcumin was purchased from a commercial source as a mixture of curcumin,
demethoxycurcumin and bisdemthoxycurcumin. Purification via flash column
chromatography (1:1 hexanes/ethyl acetate) provided curcumin in P97%
purity that was used for analysis. In.
21. Petitjean, A.; Mathe, E.; Kato, S.; Ishioka, C.; Tavtigian, S. V.; Hainaut, P.; Olivier,
M. Hum. Mutat. 2007, 28, 622.
22. Cai, S.; Wang, H.; Baluyut, A. R.; Ernstberger, A.; Juliar, B.; Sinn, A. L.; Mayo, L.
D.; Goebel, W. S.; Pollok, K. E. Clin. Cancer Res. 2011, 8, 2195.