Synthesis and cytotoxic evaluation of novel platinum(II) complexes with C2-asymmetric and C2-symmetric chiral vicinal diamines

Article abstract of DOI:10.1002/cjoc.201201168

A series of new platinum(II) complexes with C₂-asymmetric and C₂-symmetric 1,2-diamines were designed and synthesized by convenient methods, involving samarium diiodide induced reductive coupling as the key step. The results of cytotoxicity showed that compounds (R,R)-11a and (S,S)-11a, two novel platinum(II) complexes with asymmetric 1,2-diamines, exhibited more potent cytotoxicity than that of oxaliplatin against all leukemia cell lines. Interestingly, (R,R)-11a and (S,S)-11a demonstrated less potent activity against three solid cancer cell lines than that of oxaliplatin, which indicated that these two compounds may only selectively inhibit the leukemia cell lines. In contrast, (R,R)-15a and (S,S)-15a, two platinum(II) complexes with symmetric 1,2-diamines, showed similar cytotoxicity to that of oxaliplatin against all leukemia cell lines and more potent activity against solid cancer cell lines. Further flow cytometry data indicated that (R,R)-11a could obviously arrest leukemia K562 cells in G2/M phases. A series of new platinum(II) complexes with C₂-asymmetric and C₂-symmetric 1,2-diamines were designed and synthesized by convenient methods, involving samarium diiodide induced reductive coupling as the key step. The cytotoxicity of these analogs against four leukemia and three solid cancer cell lines was evaluated and the preliminary structure-activity relationship is also discussed. Flow cytometry data indicated that (R,R)-11a could obviously arrest leukemia K562 cells in G2/M phases. Copyright

Full text of DOI:10.1002/cjoc.201201168

NOTE
DOI: 10.1002/cjoc.201201168
Synthesis and Cytotoxic Evaluation of Novel Platinum(II)
Complexes with C2-Asymmetric and C2-Symmetric Chiral
Vicinal Diamines†
Chen Zhang,#,a Hongrui Liu,b,# Qing Yang,a Jun Chang,*,a and Xun Sun*,a,c
a Department of Natural Products Chemistry, School of Pharmacy, Fudan University, Shanghai 201203, China
b Department of Pharmacology, School of Pharmacy, Fudan University, Shanghai 201203, China
c Key Lab of Smart Drug Delivery, Ministry of Education & PLA, Fudan University, Shanghai 201203, China
A series of new platinum(II) complexes with C2-asymmetric and C2-symmetric 1,2-diamines were designed and
synthesized by convenient methods, involving samarium diiodide induced reductive coupling as the key step. The
results of cytotoxicity showed that compounds (R,R)-11a and (S,S)-11a, two novel platinum(II) complexes with
asymmetric 1,2-diamines, exhibited more potent cytotoxicity than that of oxaliplatin against all leukemia cell lines.
Interestingly, (R,R)-11a and (S,S)-11a demonstrated less potent activity against three solid cancer cell lines than that
of oxaliplatin, which indicated that these two compounds may only selectively inhibit the leukemia cell lines. In
contrast, (R,R)-15a and (S,S)-15a, two platinum(II) complexes with symmetric 1,2-diamines, showed similar cyto-
toxicity to that of oxaliplatin against all leukemia cell lines and more potent activity against solid cancer cell lines.
Further flow cytometry data indicated that (R,R)-11a could obviously arrest leukemia K562 cells in G2/M phases.
Keywords platinum(II) complexes, chiral vicinal diamines, cytotoxicity, leukemia cell
Cl
Cl
H2
N
Pt
O
Introduction
H3N
N
O
O
Cl
Cl
H3N
H3N
H3N
H3N
O
O
Pt
O
O
Pt
Pt
Cisplatin (Figure 1) is a widely used chemo-thera-
peutic agent for the treatment of testicular cancer, and is
also used in combination regimens for a variety of other
tumors, including ovarian, cervical, bladder, lung, and
those of the head and neck.[1-3] However, the significant
side effects, such as cumulative toxicities of nephrotox-
icity, ototoxicity, and peripheral neuropathy, restrict the
clinical success of cisplatin.[4,5] Moreover, the therapeu-
tic efficacy of cisplatin is limited by inherent or treat-
ment-induced resistant tumor cell sub-populations.
Therefore, much more attention has been focused on
designing new platinum compounds with improved
pharmacological properties and a broader range of anti-
tumor activity. Among the over 30 platinum agents,
which have entered clinical trials, only carboplatin and
oxaliplatin have received worldwide approval so far.
Others, such as nedaplatin, lobaplatin and heptaplatin,
only have gained regionally limited approval. Although
several new candidates were abandoned during the
clinical trials due to the low efficacy, high toxicity and
no advantage over cisplatin and carboplatin, the steri-
cally hindered complex cis-aminedichloro (2-methyl-
pyridine)-platinum(II) (ZD0473)[6,7] and multinuclear
N
O
H2
Oxaliplatin
Cisplatin
Carboplatin
ZD0473
4+
NH(CH2)5H2N
NH3
H3N
Pt
NH3
H3N
Cl
Pt
Pt
NH3
H3N
Cl
NH(CH2)5H2N
BBR-3464
Figure 1 Reported platinum complexes.
complexes BBR-3464[8] have been still continued for
evaluation. To our best knowledge, chiral ligands are
important for the cytotoxicity of oxaliplatin.[9] Further,
Noji reported that trans isomers of 1,2-cyclohexane-
diamine platinum(II) complexes were more efficacious
than corresponding cis isomers against leukemia
P388.[10] Gust also reported the synthesis of platinum(II)
complexes with chiral diamines and their cytotoxicities
against breast cancer.[11] During the course of our re-
search, we have developed an efficient method for the
preparation of optically pure C2-asymmetrical and
C2-symmetrical vicinal diamines by samarium diiodide
(SmI2) induced reductive coupling for the synthesis of
*
E-mail: sunxunf@shmu.edu.cn, jchang@fudan.edu.cn. # Both authors contributed equally to this work.
Received November 28, 2012; accepted December 10, 2012; published online January 8, 2013.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201201168 or from the author.
Dedicated to the Memory of Professor Weishan Zhou.
†
154
© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 154—158

Synthesis and Cytotoxic Evaluation of Novel Platinum(II) Complexes
platinum(II) complexes.[12] The advantages of this
method could provide chiral 1,2-diamines with high ee
values and high yields. With these amines in hand, we
prepared two types of new platinum(II) complexes with
C2-asymmetric and C2-symmetric 1,2-diamines. Herein,
we report the synthesis and cytotoxic evaluation of these
analogs against four leukemia cell lines and three solid
cancer cell lines. The preliminary study of structure-
activity relationship was also discussed.
With 4a and 4b in hand, the synthesis of desired
targets (R,R)-11a－11e was accomplished by the route
shown in Scheme 2.[12] (R)-(＋)-2-Methyl-2-propanesul-
finamide 5 reacted with aromatic aldehydes to obtain
(R)-N-tert-butylsulfinyl imine 6a－6c in 60%－70%
yields. After applying the SmI2 induced reductive cou-
pling reaction, a series of optically pure C2-asymme-
trical vicinal diamine precursors (R,R)-7a－7e were
efficiently obtained by reacting nitrone with (R)-N-tert-
butanesulfinyl imine in THF at −78 ℃ in the presence
of SmI2 and tert-butyl alcohol. After removing the hy-
droxy group on nitrogen in (R,R)-7a－7e with acetic
acid, Cu(OAc)2 and zinc powder at room temperature,
the corresponding intermediates (R,R)-8a － 8e were
achieved in 80%－85% yields. The sulfinyl groups in
(R,R)-8a－8e were further removed by using 4 mol/L
HCl in 1,4-dioxane at room temperature in the presence
of MeOH. Then, optically pure asymmetric (R,R)-1,2-
diamines 10a－10e were prepared by catalytic deben-
zylation with 10% Pd(OH)2 under hydrogen. Finally,
the corresponding (R,R)-1,2-diamine platinum(II) com-
plexes 11a－11e were obtained by reacting 10a－10e
with potassium tetrachloroplatinate in 65% － 75%
yields. By adopting the similar methods for (R,R)-11a－
11e, the synthesis of (S,S)-11a－11e was accomplished
from (S)-(−)-2-methyl-2-propanesulfinamide 5 in six
steps.
Results and Discussion
The important intermediates nitrones (4a and 4b)
were synthesized by using benzaldehyde (1) as the
starting material, as illustrated in Scheme 1. Benzalde-
hyde (1) was first transformed into oxime (2) by using
hydroxylamine hydrochloride. The obtained oxime (2)
was then reduced by adding sodium cyanoborohydride
and stirred at room temperature overnight to afford
N-benzyl hydroxylamine (3) in 80% yield. Compound 3
was reacted with aldehydes to obtain their correspond-
ing nitrones (4a and 4b) in 85% and 90% yields, respec-
tively.
Scheme 1 Synthesis of compounds 4a－4b
OH
N
a
b
The reductive homocouplings of (R)-N-tert-butyl-
sulfinyl imine 12a－12c were successfully proceeded in
the presence of SmI2 and HMPA in THF at −78 ℃ to
produce (S,S)-13a－13c.[13] The sulfinyl groups in
(S,S)-13a－13c were further removed by using 4 mol/L
HCl in 1,4-dioxane at room temperature in the presence
of MeOH to yield C2-symmetric (S,S)-1,2-diamines 14a
－14c. With 14a－14c in hand, (S,S)-1,2-diamine plati-
num(II) complexes 15a－15c were synthesized simply
by reacting with potassium tetrachloroplatinate at room
BnNHOH
PhCHO
Ph
3
1
2
Bn
O
c
N
R1
4a R1 = CH(CH3)2
4b R1 = C6H11
Reagents and conditions: (a) NH2OH•HCl, r.t., 30 min; (b)
NaBH3CN, r.t., overnight; (c) R1CHO, MgSO4, r.t., 5 h
Scheme 2 Synthesis of the title compounds (R,R)-11a－11e
O
S
O
S
O
OH
N
O
S
S
Bn
NH
Bn NH
R1
NH
N
c
a
b
R1
H2N
H
R2
(R,R)-7a R1 = CH(CH3)2, R2 = H
R2
R2
(R)-5
(R,R)-8a - 8e
(R)-6a R2 = H
(R)-6b R2 = OCH3
(R)-6c R2 = CH3
(R,R)-7b R1 = CH(CH3)2, R2 = OCH3
(R,R)-7c R1 = c-C6H11
(R,R)-7d R1 = c-C6H11
,
R2 = H
R2 = OCH3
,
(R,R)-7e R1 = CH(CH3)2, R2 = CH3
H2
R1
Cl
N
H
N
H2N
R1
NH2
Bn
NH2
Pt
e
d
f
R1
N
Cl
H2
R2
R2
R2
(R,R)-10a - 10e
(R,R)-9a - 9e
(R,R)-11a - 11e
Reagents and conditions: (a) KHSO4, R2PhCHO, toluene, 45 ℃; (b) 4a/4b, 2 equiv. SmI2, t-BuOH, THF, -78 ℃; (c) Zn, Cu(OAc)2, AcOH,
EDTA-2Na, r.t.; (d) HCl, MeOH, r.t.; (e) H2, Pd(OH)2/C, r.t.; (f) K2PtCl4, r.t., overnight
Chin. J. Chem. 2013, 31, 154—158
© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
155

Zhang et al.
NOTE
temperature overnight. Compounds (R,R)-15a － 15c
were also synthesized from (S)-N-tert-butylsulfinyl
imine 12a－12c in a same manner as that for (S,S)-15a
－15c (Scheme 3).
The in vitro cytotoxicities of platinum(II) complexes
were evaluated against four leukemia cell lines (THP-1,
K562, KASUMI-1 and NB4) and three solid cancer cell
lines ( MDA-MB-231, OMC685, A-549) by MTT or
SRB assay (Table 1).
Scheme 3 Synthesis of the title compounds (S,S)-15a－15c
For the first series of analogs [(R,R)-11a－11e and
(S,S)-11a － 11e], (R,R)-11a and (S,S)-11a exhibited
more potent activity than that of oxaliplatin against all
leukemia cell lines. Interestingly, when the isopropyl
was substituted by cyclohexyl group, analogs, such as
(R,R)-11c and (S,S)-11c, abolished their potencies,
which indicated that increased steric bulky groups could
be unfavorable to their cytotoxicity. Furthermore, when
the p–position of phenyl group was substituted by elec-
tron-donating group, i.e. methoxyl, (R,R)-11b lost its
cytotoxicity against K562 and NB4 cell lines, though
still maintained moderate activity against THP-1 and
KASUMI-1 cell lines. However, for its (SS) analog,
(S,S)-11b only slightly decreased its potency. For three
solid cancer cell lines, all novel platinum(II) complexes
with C2-asymmetric 1,2-diamines exhibited weaker ac-
tivity than that of oxaliplatin, indicating that this type of
compounds may only inhibit leukemia cell lines selec-
tively, and not inhibit solid cancer cell lines. It was
found that the cytotoxicities of (S,S)-11a, 11b, 11e
against K562 and NB4 were more active than those of
(R,R)-11a, 11b, 11e.
O
S
N
O
a
b
H
S
R
H2N
R
(R)-5
(R)-12a R = F
(R)-12b R = Cl
(R)-12c R = Br
O
O
S
S
NH
HN
H2N
NH2
c
R
R
R
R
(S,S)-14a - 14c
(S,S)-13a - 13c
R
H2
N
Cl
Cl
d
Pt
N
H2
R
For the second series of novel platinum(II) com-
plexes with C2-symmetric 1,2-diamines, (R,R)-15a and
(S,S)-15a showed slightly decreased activity compared
with that of oxaliplatin against all leukemia cell lines,
while both (R,R)-15b and (S,S)-15c diminished their
cytotoxicity against all leukemia cell lines. In contrast to
platinum(II) complexes with C2-asymmetric 1,2-di-
(S,S)-15a R = F
(S,S)-15b R = Cl
(S,S)-15c R = Br
Reagents and conditions: (a) KHSO4, RPhCHO, toluene, 45 ℃;
(b) SmI2, HMPA, THF, −78 ℃; (c) HCl, MeOH, r.t.; (d) K2PtCl4, r.t.,
overnight
－
Table 1 Cytotoxicities (IC50, μmol•L ) of platinum(II) complexes with chiral 1,2-diamines
1
Compound
(R,R)-11a
(S,S)-11a
(R,R)-11b
(S,S)-11b
(R,R)-11c
(S,S)-11c
(R,R)-11d
(S,S)-11d
(R,R)-11e
(S,S)-11e
(R,R)-15a
(S,S)-15a
(R,R)-15b
(S,S)-15b
(R,R)-15c
(S,S)-15c
Oxaliplatin
THP-1
0.23
0.34
2.87
1.70
＞10
＞10
＞10
14.88
2.84
0.63
3.21
1.27
＞10
4.79
1.08
＞10
0.49
K562 KASUMI-1
NB4
1.15
0.24
＞10
3.88
5.22
＞10
＞10
11.32
＞10
1.58
2.99
1.59
＞10
＞10
3.51
＞10
1.81
MDA-MB-231
168.55
354.39
182.11
384.98
126.61
427.28
149.66
178.46
98.02
OMC685
88.73
A-549
237.92
358.89
167.35
249.39
＞600
526.33
166.83
172.68
284.85
281.51
75.43
0.99
0.32
0.27
0.41
107.44
278.44
207.22
114.35
＞600
234.82
107.75
86.21
＞10 5.28
2.46 9.09
＞10 ＞10
＞10 ＞10
＞10 ＞10
＞10 6.00
＞10 3.45
1.63
2.17
1.58
1.03
0.61
1.21
332.22
47.66
169.15
95.09
23.53
100.94
157.58
87.09
85.03
＞10 ＞10
＞10 1.42
＞10 ＞10
＞10 ＞10
52.16
68.70
110.52
56.83
77.03
106.09
153.11
59.20
50.91
116.54
61.31
95.15
1.46
0.53
76.67
156
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Chin. J. Chem. 2013, 31, 154—158

Synthesis and Cytotoxic Evaluation of Novel Platinum(II) Complexes
amines, (R,R)-15a－15c and (S,S)-15a showed more
potent activity than that of oxaliplatin against MDA-
MB-231, and (R,R)-15a－15c showed more potent ac-
tivity than that of oxaliplatin against A549. All these
platinum(II) complexes with C2-symmetric 1,2-di-
amines exhibited weaker activity against OMC685 than
that of oxaliplatin. On the four leukemia and three solid
cancer cell lines, platinum(II) complexes with C2-sym-
metric 1,2-diamines showed no enantioselectivity, con-
sistent with the result of Gust.[11]
Flow cytometry was used to quantitatively detect the
apoptotic rate. Cells (5×103/well) were seeded into
6-well plates and exposed to (R,R)-11a at various con-
－
1
centrations (0, 1, 2 and 4 μmol•L ) for 48 h, and then
harvested and washed with phosphate buffered saline
(PBS). Staining went along with 195 µL bonding buffer
containing 5 µL Annexin V-FITC in the dark at room
temperature for 10 min, and then added 10 µL PI in the
dark at 4 ℃ for 10 min. The apoptotic cells were ana-
lyzed with FACScan flow cytometry (BD FACSCalibur)
(Figure 3).
The ability of compound (R,R)-11a to inhibit the cell
cycle was also investigated. After administration of
various concentrations of (R,R)-11a for 48 h, K562 cell
cycle was measured by flow cytometry. The results of
(R,R)-11a on K562 cell cycle progression were shown
in Figure 2. As compared to the control, G2/M phases of
K562 cells administrated with (R,R)-11a (0, 1, 2 and 4
－
1
μmol•L ) for 48 h were increased from (23.57±2.6)%
to (34.92±8.2)%, whilst S phase cells were decreased
from (51.75±5.4)% to (35.48±0.28)%. Almost all
cells treated with 4 μmol•L－1 of (R,R)-11a for 48 h died.
The results showed that (R,R)-11a could arrest K562
cells in G2/M phases (p＜0.05).
Figure 3 (R,R)-11a induced the apoptosis of K562 cells.
Apoptotic cells were analyzed by flow cytometry with Annexin
V-FITC and PI staining. Early apoptotic cells (Annexin-V＋)
were displayed in the lower right quadrant and late apoptotic cells
(Annexin-V＋and PI＋) were shown in the upper right quadrant.
Necrosis cells were shown in the upper left quadrant (PI＋). The
percentages of apoptotic cells were indicated by Annexin-V＋
cells shown as the mean±SD of three independent experiments.
*p＜0.05 vs. control group, **p＜0.01 vs. control group.
Conclusions
Ten platinum(II) complexes with C2-asymmetric
diamines 11a－11e (RR or SS) and six platinum(II)
complexes with C2-symmetric diamines 15a－15c (RR
or SS) were synthesized by convenient methods, in-
volving samarium diiodide induced reductive coupling
as the key step. The results of cytotoxicity showed that
(R,R)-11a and (S,S)-11a exhibited more potent activity
against all leukemia cell lines and less potent activity
against three solid cancer cell lines than that of ox-
aliplatin. This indicated that (R,R)-11a and (S,S)-11a
may selectively inhibit the leukemia cell lines. Further
Figure 2 G2/M cell cycle arrest in K562 cells by (R,R)-11a.
K562 cells were seeded into 6-well plates at a density of 1×104
cells per well. Then, the cells were treated with (R,R)-11a (0, 1, 2
and 4 μmol•L ) for 48 h and analyzed by flow cytometry. Quan-
titative analysis of the apoptotic nuclei was shown in the follows.
Data are expressed as means±SD, *p＜0.05 vs. control group,
**p＜0.01 vs. control group.
－
1
Chin. J. Chem. 2013, 31, 154—158
© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
157

Zhang et al.
NOTE
[2] Wang, D.; Lippard, S. J. Nat. Rev. 2005, 4, 307.
[3] Shah, N.; Dizon, D. S. Future Oncol. 2009, 5, 33.
mechanism study showed that (R,R)-11a increased the
apoptotic K562 cells in a concentration-dependent
manner and arrested K562 cells in G2/M phases in the
flow cytometry assay.
[4] Arnesano, F.; Natile, G. Coord. Chem. Rev. 2009, 253, 2070.
[5] Todd, R. C.; Lippard, S. J. Metallomics 2009, 1, 280.
[6] Holford, J.; Raynaud, F.; Murrer, B. A.; Grimaldi, K.; Hartley, J. A.;
Abrams, M.; Kelland, L. R. Anti-Cancer Drug Des. 1998, 13, 1.
[7] Holford, J.; Sharp, S. Y.; Murrer, B. A. Br. J. Cancer 1998, 77, 366.
[8] Davies, M. S.; Thomas, D. S.; Hegmans, A.; Berners-Price, S. J.;
Farrell, N. P. Inorg. Chem. 2002, 41, 1101.
[9] (a) Galanski, M.; Keppler, B. K. Anti-Cancer Agents Med. Chem.
2007, 7, 55; (b) Dufrasne, F.; Galanski, M. Curr. Pharm. Des. 2007,
13, 2781.
Acknowledgement
Financial support by the National Natural Science
Foundation of China (No. 81172920), the Shanghai
Municipal Committee of Science and Technology (No.
10431903100), and the National Basic Research Pro-
gram of China (973 Program, No. 2010CB912603) are
acknowledged. We would like to thank Prof. G.-Q. Lin
for the guidance of asymmetric synthesis.
[10] Noji, M.; Okamoto, K.; Kidani, Y.; Tashiri, T. J. Med. Chem. 1981,
24, 508.
[11] (a) Dullin, A.; Dufrasne, F.; Gelbcke, M.; Gust, R. ChemMedChem
2006, 1, 644; (b) vom Orde, H. D.; Reile, H.; Muller, R.; Gust, R.;
Bernhardt, G.; Spruss, T.; Schonenberger, H.; Burgemeister, T.;
Mannschreck, A. J. Cancer Res. Clin. 1990, 116, 434.
[12] Zhong, Y. W.; Xu, M. H.; Lin, G. Q. Org. Lett. 2004, 6, 3953.
[13] Zhong, Y. W.; Izumi, K.; Xu, M. H.; Lin, G. Q. Org. Lett. 2004, 6,
4747.
References
[1] Momekov, G.; Bakalova, A.; Karaivanova, M. Curr. Med. Chem.
2005, 12, 2177.
(Lu, Y.)
158
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Chin. J. Chem. 2013, 31, 154—158