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Lindsay Kinyon
Final Report
Background
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Beginning in the early 1980's, researchers began examining the
zinc, iron, cobalt, chromium, rhodium, osmium, and, especially,
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interactions of octahedrally coordinated complexes of copper, nickel,
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ruthenium
with
DNA.
Octahedrally
coordinated
organometallic
Figure 1:
compounds (see Figure 1) are molecules which contain a metal center
Octahedral coordination
with six binding sites occupied by small organic molecules (ligands).
of three diimene ligands
The generic compound formulation [M(N-N)3]n+ will be used to
to a metal center.
represent molecules of this type. These compounds have demonstrated
site-specific DNA interaction (intercalation, groove-binding or electrostatic) and some have been shown to
engage in photolytic strand cleavage. Notably absent from this collection of transition metal DNA probes were
the octahedrally coordinated platinum family analogs, [Pt(N-N)3]4+ & [Pd(N-N)3]4+, most likely due to the
difficulty of solvating the high charge density of the platinum (4+) & palladium (4+) ions.
Early in the summer of 1996, Dr. Robert Granger developed a new, versatile scheme for the synthesis of
homoleptic (only one type of ligand) water-soluble octahedrally-coordinated platinum(IV) complexes with
intercalative ligands1,2. Dr. Granger then obtained a three year grant from the Jeffress Memorial Trust to study
the synthesis and characterization of these new Pt(IV) and Pd(IV) diimene complexes. That research focused
primarily on the synthesis of Pt(IV) and Pd(IV) complexes of 1,10-phenanthroline and 2,2’-dipyridine (see
Figure 2).
R. Granger et al. “Synthesis and Characterization of (1,10-phenanthroline)platinum tetrachloride” The Virginia Journal of Science.
Vol. ? Pp. ? (1999)
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[M (p hen)3]4+; M = Pt & Pd
[M (dip y )3]4+; M = Pt & Pd
[M (dione)(phen)2]4+; M = Pt & Pd
Figure 2:
Although many metal complexes are used as DNA markers, only compounds of the platinum family are
widely used medically as chemotherapeutic agents. Cisplatin (cis-diamminedichloroplatinum, a square-planar
Pt(II) compound) is widely used alone or in combination with other chemotherapeutic drugs in the treatment of
several aggressive cancers, including ovarian, lung, testicular and bladder carcinomas.
Unfortunately,
resistance to cisplatin can develop and the drug itself is toxic to the patient, with the kidneys, gastrointestinal
tract, bone marrow and nervous system all experiencing distress resulting from treatment and not all tumors
respond to cisplatin, so there is of course the hope that new drugs might be found which would be effective
against cisplatin-resistant tumors.
To date, none of the other octahedrally coordinated metal center complexes have shown to have anticancer activity, but because of the importance of platinum in other forms as anti-cancer drugs, Dr. Granger
wished to explore the bioactivity of his new platinum(IV) and palladium(IV) complexes against malignant cells.
In the summer of 1997, Dr. Robin Davies began preliminary cell culture experiments using Dr. Granger’s novel
platinum (IV) and palladium (IV) complexes. To their surprise, these new platinum (IV) and palladium (IV)
complexes were extremely active against malignant cell lines (see Figure 3).
R. Granger et al. “The Synthesis and Characterization of tris(1,10-phenanthroline)platinum(IV) hexafluorophosphate” Polyhedron.
Submitted June 1999
2
Figure 3: Cell count vs. Time for human leukemia cells exposed to drug.
These results serve to indicate that further investigation of the cytotoxic effects of these novel Pt(IV) and
Pd(IV) diimene complexes is warranted and to suggest that the proposed investigations are likely to prove
fruitful. These investigations are currently underway in Dr. Davies research group.
In addition, Dr. Granger has also completed studies on the binding mode of [Pt(phen)3]4+ with DNA and
has been able to demonstrate that the (4+) charge on these complexes bends the DNA strand upon binding (see
figure 4).
Viscosity:
If metal probe intercalates 
DNA lengthens 
Viscosity increases
If metal probe binds electrostatically 
No effect on DNA length 
No effect on viscosity
If metal probe kinks DNA 
DNA shortens 
Viscosity decreases.
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The localized charge on the metal center “pulls” the
anionic phosphates towards the metal.
As the charge on the metal center increases, intercalkinking increases.
Late in the summer of 1999, Dr.
H2 SO4
HNO3
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Granger began to focus his synthetic efforts
KBr
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Dr.
Granger
has
begun
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H2 N
NH2
- 2H2 O
DNA backbone (see Scheme 1 for additional
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developing a series extended ligand systems
that will be able to insert deeper into the
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5,6-dione-1,10-phenanthroline
on modifications to the intercalating ligand.
Specifically,
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dpz
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H2 N
NH2
- 2H2 O
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dppz
possible ligand systems).
Use of these
extended ligands will hold the metals (4+)
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charge farther away from the DNA’s
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H2 N
NH2
- 2H2 O
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backbone, thus promoting an intercalative
developed a synthetic scheme that will allow
for the exact placement of individual ligands.
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dpnz
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binding mode. Also, Dr. Granger has
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H2 N
NH2
- 2H2 O
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phehat
S cheme 1:
Synthesis of phendione and several dppz analogs
This is the portion of the overall project that I have focused my summer's research efforts upon.
Lindsay Kinyon's Summer Research 2000
The goal for my summer research was to synthesize a series of ligands similar to the ligand dppz (see
scheme 1). The first thing I had to do was to synthesize the necessary template molecule 5,6-dione-1,10phenanthroline (see scheme 2).
Scheme 2
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1,10-phenanthroline
H2SO4; HNO 2; KBr
Boil for 3 hours
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5,6-dione-1,10-phenanthroline
Following a literature preparation, this was completed during the first week. I then selected three commercially
available diamene compounds for use in synthesizing three new dppz-like ligands (see scheme 3).
Each of these syntheses involved refluxing (boiling) the 5,6-dione-1,10-phenanthroline ligand with the
requisite diamine. A classic condensation reaction between the dione oxygen and the amine hydrogens occurs
yielding water and our desired compound. The products of the three condensation reactions were confirmed by
GC-Mass spectrometry (GC-MS). This technique allows for the determination of the exact mass of the
molecule in addition to identifying fragmentation products (see figures 5 & 6)
GC-MS of bdppz
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C
OCH2CH3
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C
OCH2CH3
Figure 5: GC-MS of bdppz. The parent peak at 355 represents the ethyl ester of the expected product. The
two peaks at 281 and 73 represent the two fragmentation products dppz and -CO2CH2CH3.
GC-MS of dpnpz
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NO2
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C2H5O
C2H5
OC 2H5
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C2H5O
OC 2H5
Figure 6: GC-MS of dpnpz. The parent peak at 415 shows the ethyl ester of the expected product. The peak
at 327 shows the expected product.
A surprise we encountered during this project occurred in the analysis of the product bdppz. The GCMS did not find the expected product bdppz but instead we found the ethyl ester of bdppz. In retrospect, this is
not surprising. By the same condensation reaction used to make dppz-like ligands, carboxylic acids will
condense with alcohols to form esters. Since the reaction was conducted in ethanol, this is not a surprising
result (see scheme 4).
-H2O
Scheme 4: Esterification of bdppz
HO-CH2CH3
O OH
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H2N
HO-CH2CH3
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H2N
Reflux
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-H2O
O O-CH CH
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The discovery of the ethyl ester of bdppz has lead us to make some exciting conjectures. I then tried to
repeat the bdppz synthesis in a non-alcolhol solvent, which would verify the stability of bdppz. However, I
could not find a non-alcohol solvent that my starting materials were both soluble in. Once I find a sutable
solvent, my next step would be to attempt to place a metabolite such as a simple sugar onto the bdppz ligand.
Since our goal is to make cancer drugs, it only makes sense to exploit the exaggerated metabolism of cancer
cells in order to actively transport our DNA drugs into the cancer cells (see scheme 5).
Once this scheme is (scheme 5) successful, we will want to place this ligand onto a metal center and
create our DNA drugs (see figure 8).
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Figure 8: Glucosified bdppz complex of palladium (II)
HO
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OH C
H2
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OH
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Pd
HO
HO
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O O
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H2
C HO
OH
OH
2+