Synthesis and characterization of side group-modified tetradentate cyclotriphosphazene derivatives

Article abstract of DOI:10.1080/10426507.2011.643434

A series of novel side group-modified cyclotriphosphazene derivatives were synthesized by the reaction of hexachlorocyclotriphosphazene [N ₃P₃Cl₆] with 2,2-diphenol and the potassium salt of 4-hydroxybenzaldehyde, and subsequent reduction of aldehyde groups to alcohol groups by the use of sodium borohydride. The bromination reaction was carried out with PBr₃ to give N₃P₃(O ₂C₁₂H₈) (p-BrCH₂-C₆H ₄-O-)₄. This compound was employed in reactions with macrocyclic polyamides, imidazole, or morpholine to produce title compounds. The target compounds were characterized by ¹H NMR, ³¹P NMR, ¹³C NMR, and electrospray ionization mass spectrometry. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Copyright

Full text of DOI:10.1080/10426507.2011.643434

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Synthesis and Characterization of
Side Group-Modified Tetradentate
Cyclotriphosphazene Derivatives
X. Yang a , R.-Y. Zou a , R. Li a , J.-L. Yang a , Y. Ye a & Y.-F. Zhao a b c
a Department of Chemistry, Phosphorus Chemical Engineering
Research Center of Henan Province , Zhengzhou University ,
Zhengzhou , China
b Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical
Biology (Ministry of Education), Department of Chemistry , Tsinghua
University , Beijing , China
c Department of Chemistry and Key Laboratory for Chemical Biology
of Fujian Province , Xiamen University , Xiamen , China
Accepted author version posted online: 04 Jan 2012.Published
online: 05 Apr 2012.
To cite this article: X. Yang , R.-Y. Zou , R. Li , J.-L. Yang , Y. Ye & Y.-F. Zhao (2012) Synthesis and
Characterization of Side Group-Modified Tetradentate Cyclotriphosphazene Derivatives, Phosphorus,
Sulfur, and Silicon and the Related Elements, 187:6, 722-727, DOI: 10.1080/10426507.2011.643434
To link to this article: http://dx.doi.org/10.1080/10426507.2011.643434
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Phosphorus, Sulfur, and Silicon, 187:722–727, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2011.643434
SYNTHESIS AND CHARACTERIZATION OF SIDE
GROUP-MODIFIED TETRADENTATE
CYCLOTRIPHOSPHAZENE DERIVATIVES
X. Yang,1 R.-Y. Zou,1 R. Li,1 J.-L. Yang,1 Y. Ye,1
and Y.-F. Zhao1,2,3
1Department of Chemistry, Phosphorus Chemical Engineering Research
Center of Henan Province, Zhengzhou University, Zhengzhou, China
2Key Laboratory of Bioorganic Phosphorus Chemistry & Chemical Biology
(Ministry of Education), Department of Chemistry, Tsinghua University,
Beijing, China
3Department of Chemistry and Key Laboratory for Chemical Biology of Fujian
Province, Xiamen University, Xiamen, China
GRAPHICAL ABSTRACT
O
C6H4CH2R
C6H4CH2R
O
N
Cl
Cl
Cl
1) 2,2'-diphenol
K2CO3, THF
Pα
N
Pβ
N
O
N
P
3) NaBH4
4) PBr3
5) HR
P
P
O
Cl
Pβ
N
N
O
Na2CO3
HO
O
O
2)
Cl
Cl
H
C6H4CH2R
RH2CC6H4
1
5
5a c: R= Boc3-cyclen, imdazolyl, morpholino
Abstract A series of novel side group-modified cyclotriphosphazene derivatives were syn-
thesized by the reaction of hexachlorocyclotriphosphazene [N3P3Cl6] with 2,2ꢀ-diphenol and
the potassium salt of 4-hydroxybenzaldehyde, and subsequent reduction of aldehyde groups to
alcohol groups by the use of sodium borohydride. The bromination reaction was carried out
with PBr3 to give N3P3(O2C12H8) (p-BrCH2-C6H4-O-)4. This compound was employed in
reactions with macrocyclic polyamides, imidazole, or morpholine to produce title compounds.
The target compounds were characterized by 1H NMR, 31P NMR, 13C NMR, and electrospray
ionization mass spectrometry.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.
Keywords Macrocyclic polyamide; cyclotriphosphazene derivatives; imidazole; morpholine
Received 10 October 2011; accepted 18 November 2011.
We are grateful for financial support from the NSFC (Nos. 20972143, 20732004, 20972130).
Address correspondence to Yong Ye, Phosphorus Chemical Engineering Research Center of Henan Province,
Department of Chemistry, Zhengzhou University, Zhengzhou 450052, China. E-mail: yeyong03@tsinghua.org.cn
722

SYNTHESIS AND CHARACTERIZATION OF CYCLOTRIPHOSPHAZENE DERIVATIVES 723
INTRODUCTION
With high abilities in recognizing specific DNA sequences and catalyzing the hy-
drolysis of phosphate diester bonds, artificial nucleases have rapidly become an invaluable
research tool in the fields of biology, bioorganic chemistry, therapy, and molecular biol-
ogy.1–3 Although many enzymes have been harnessed for use in the laboratory, there is a
great deal of interest in the design of artificial nucleases, small molecular scissors that can
cleave DNA hydrolytically. Therefore, designing new ligands suitable for cleaving DNA
under hydrolytic conditions is of considerable importance.
Cyclotriphosphazenes have received considerable interest not only due to their wide
spectrum of chemical and physical properties but also due to their importance in synthetic
chemistry. Different side-group structures affect the chemical and physical properties of
ring systems and high polymers based on a phosphazene skeleton.4–11 Recently, we reported
some polydentate cyclotriphosphazene ligands,12–14 which showed good nuclease activity
with hydrolytic cleavage mechanism. To obtain more insight into the selective recognition
and efficient cleavage of DNA by different metal complexes of cyclotriphosphazene, in
this work we synthesized a series of novel tetradentate cyclotriphosphazene derivatives
in good yield via convenient reactions. Their synthetic route is outlined in Scheme 1.
The title compounds were characterized by means of 1H NMR, 31P NMR, 13C NMR, and
mass spectrometry. The DNA cleavage activity of the title compounds is currently being
examined.
O C H CH OH
6
4
2
O
O C H CHO
6
4
O
N
P
Cl
Cl
Cl
1) 2,2'-diphenol
K CO , THF
O
N
P
P
N
P
N
N
P
O
P
N
P
N
O C H CH OH
P
6
4
2
P
2
3
O C H CHO
Cl
6
4
NaBH
N
4
N
O
H
O
O
THF/MeOH
O
O
HO
2)
Cl
Cl
C H CH OH
HOH CC H
6
4
2
2
6
4
C H CHO
OHCC H
6
4
6
4
3
1
2
O
C H CH R
6 4 2
O
O C H CH Br
6
4
2
O
N
α
β
O
P
N
P
P
PBr THF
HR
O
3,
P
N
P
N
O
C H CH R
6
4
2
O C H CH Br
6
4
2
N
N
β
P
Na CO , CH CN
2
3
3
O
O
O
O
C H CH Br
BrH CC H
6
4
2
2
6
4
C H CH R
RH CC H
6
4
2
2
6
4
4
5
N
N
H
CF COOH
3
Boc
O
N
N
R=
N
BocN
N
HN
N
Boc
H
N
N
5c
5b
6a
5a
Scheme 1 Synthesis route of title compounds.

724
XIAN YANG ET AL.
RESULTS AND DISCUSSION
In the synthesis of compound 2 (Scheme 1), hexachlorocyclotriphosphazene [N3P3
Cl6] (1) was first reacted with 2,2ꢀ-diphenol at room temperature to give N3P3(O2C12H8)Cl4.
Then, the chlorine atom of N3P3(O2C12H8)Cl4 was substituted by 4-hydroxybenzaldehyde
to afford compound 2, which was further purified by recrystallization from ethyl acetate.
The tetrakis-aldehyde 2 was easily reduced to the corresponding tetrakis-alcohol
3 with sodium borohydride in THF/MeOH. The process was monitored by thin layer
chromatography (TLC). Several reagents are available for converting alcohols to alkyl
bromides. Bromination reagents based on hydrobromic acid–sulfuric acid were found
unemployable, as the reaction was hard to control and formed insoluble intermediates
through reaction with the hydroxyl groups of compound 3. The bromination reaction
1
was achieved using PBr3. Compound 4 was characterized by H NMR, 31P NMR, and
electrospray ionization mass spectrometry (ESI-MS). The 1H NMR spectrum showed that
all four hydroxyl groups were replaced by bromo substituents. Three doublet peaks for
aromatic ring protons appeared at 7.48 ppm, 7.10 ppm, and 6.64 ppm, and a single peak
for the bromomethyl group proton was observed at 4.49 ppm.
Compound 5a was firstly synthesized from compound 4 in CHCl3/Et3N or THF/
Na2CO3. However, as indicated by the 31P NMR spectrum, compound 4 did not disappear
completely. In addition, there were three or four spots in the TLC, which were very
close to each other. After further optimization, the pure compound 5a was obtained in
good yield (54%) when Na2CO3 was selected as base in CH3CN and the reaction time
1
was prolonged to 48 h. The H NMR spectrum of compound 5a exhibits two singlets at
1.42 ppm and 1.46 ppm due to non-equivalency of the Boc groups. The trifluoroacetate of
compound 6a was obtained by deprotection of compound 5a with trifluoroacetic acid in
dichloromethane at room temperature. Subsequent basification with NaOH gave the free
base 6a. Similar to compound 5a, compounds 5b and 5c were produced with 59.6% and
93.4% yield respectively.
1
The target compounds 5b and 5c were characterized by H NMR, 31P NMR, 13C
NMR, IR, and ESI-MS spectra. ESI-MS for all compounds showed the [M+H]+ ion. Their
structures were similar, and compound 5c was chosen as a characteristic example. In its
1H NMR spectrum, two doublet peaks at 7.24 ppm and 7.1 ppm were assigned to protons
on the benzene ring due to their interaction with each other. A single peak at 3.46 ppm
was assigned to the methylene group protons between benzene and morpholine. Two triplet
peaks for the morpholine group protons were observed at 3.67 ppm and 2.41 ppm.
There are two kinds of phosphorus atoms in compounds 2–6. The 31P NMR spectra
of compounds 2–6 are similar and the full spectrum consists of a doublet and a triplet.
Those compounds, where the P atoms have different substituents give two different 31P
signals (here δ = 23.9–25.3 and 8.0–9.4 for α-P and β–P, respectively), each showing the
effect of 31P–31P coupling. For these particular compounds, 2Jpp is 92–95 Hz.
EXPERIMENTAL
General
Melting points were measured using a WC-1 microscopic apparatus and were cor-
rected. Infrared spectra (cm−1) were recorded on a Bruker VECTOR22 spectrophotometer
in KBr pellets. 1H NMR and 31P NMR spectra were measured by using a Bruker AC-P400

SYNTHESIS AND CHARACTERIZATION OF CYCLOTRIPHOSPHAZENE DERIVATIVES 725
spectrometer with TMS and 85% H3PO4 as the internal and external references, respec-
tively, and with CDCl3 or DMSO as the solvent. Mass spectra were acquired in positive ion
mode using a Bruker ESQUIRE-LCTM ion trap spectrometer equipped with a gas nebulizer
probe, capable of analyzing ions up to m/z = 20,000. Elemental analyses were carried out
with a Flash EA 1112 instrument. Solvents were purified and dried by standard procedures.
Compound 1 and Boc-cyclen were prepared by the method described previously.15,16
Preparation of 2
To a solution of compound 1 (1.035 g, 3 mmol) in THF (80 mL) K2CO3 (2 g) was
added, and 2,2ꢀ-diphenol solution (0.12 g in 20mL THF) was dropped in at 0 ◦C under N2.
The reaction mixture was stirred for 2 h at room temperature. Then p-hydroxybenzaldehyde
(1.648 g, 13.5 mmol) was added and the mixture was stirred for 48 h. After the removal
of solvent under reduced pressure, the pure 2 was obtained by recrystallization from ethyl
acetate. Yield 80%, m.p.: 137 ◦C–139 ◦C; 1H NMR (CDCl3): δ 9.97 (s, 4H, CHO), 7.82 (d,
8H, J = 8.8 Hz, Har), 7.54 (d, 2H, J = 8 Hz, Har), 7.35 (m, 4H, Har), 7.31 (d, 8H, J = 8.8
Hz, Har), 6.80–6.77 (m, 2H, Har); 13C NMR (CDCl3): δ 190.5, 154.8, 147.6, 133.7, 131.4,
129.8, 128.4, 126.5, 121.5, 121.3; 31P NMR (CDCl3): δ 23.9 [t, P(O2C12H8), J = 95.5 Hz],
8.0 [d, P(OC6H4)2, J = 95.5 Hz]; ESI-MS: m/z 825.9 [M+Na]+.
Preparation of 3
To a solution of compound 2 (2.230 g, 2.7 mmol) in THF/MeOH (40:10 mL) NaBH4
◦
(1.0 g) was added at 0 C under N2. The reaction mixture was stirred for 5 h at room
temperature. After the removal of solvent under reduced pressure, pure 3 was obtained
◦
by recrystallization from ethanol. Yield 64%, m.p.: 79–82 C. 1H NMR (DMSO): δ 7.58
(d, 2H, J = 7.2 Hz, Har), 7.42–7.36 (m, 4H, Har), 7.32 (d, 8H, J = 8.8 Hz, Har), 7.02
(d, 8H, J = 8.8 Hz, Har), 6.59 (d, 2H, J = 7.2 Hz, Har), 4.49 (s, 8H, ArCH2); 13C NMR
(DMSO): δ 149.1, 147.5, 140.1, 130.5, 130.2, 128.3, 128.2, 126.9, 121.8, 120.8, 62.6; 31P
NMR (DMSO): δ 25.3 [t, P(O2C12H8), J = 94.4 Hz], 9.2 [d, P(OC6H4)2, J = 94.4 Hz];
ESI-MS: m/z 812 [M+H]+. Anal. calcd. for C40H36N3O10P3 (811.77): C 59.19, H 4.47, N
5.18. Found: C 59.22, H 4.48, N 5.20.
Preparation of 4
Into a 100-mL round-bottom flask was placed 1.444 g (1.7 mmol) of compound 3
with 30 mL of THF under Ar. Then, 1 mL of PBr3 in 30-mL THF was added drop-wise
at 0 ◦C and the mixture was stirred for 5 h. Aqu. K2CO3 (20 mL) was added. The organic
layer was separated and the aqueous layer was extracted with CHCl3 (3 × 10 mL). The
combined extracts were dried over anhydrous Na2SO4, and the solvent was removed under
reduced pressure to give crude 4, which was purified by silica gel column chromatography
(petr◦oleum ether/CH2Cl2) to yield pure 4 (1.192 g) as a colorless solid. Yield 63.7%, m.p.:
◦
1
139 C–142 C; H NMR (CDCl3): δ 7.48 (d, 2H, J = 7.6 Hz, Har), 7.34–7.28 (m, 12H,
Har), 7.10 (d, 8H, J = 8 Hz, Har), 6.64 (d, 2H, J = 7.6 Hz, Har), 4.49 (s, 8H, ArCH2); 13
C
NMR (CDCl3): δ 150.4, 147.8, 134.7, 130.3, 129.7, 129.5, 128.6, 126.1, 121.7, 121.4, 32.7;
31P NMR (CDCl3): δ 24.8 [t, P(O2C12H8), J = 92.0 Hz], 9.2 [d, P(OC6H4)2, J = 92.0 Hz];
IR: 3027, 2374, 1601, 1502, 1435, 1272, 1178, 1091, 946, 888, 846; ESI-MS: m/z 1085.5

726
XIAN YANG ET AL.
[M+Na]+. Anal. calcd. for C40H32Br4N3O6P3 (1063.39): C 45.19, H 3.03, N 3.95. Found:
C 45.17, H 3.06, N 3.92.
Preparation of 5
Imidazole (10 mmol), Boc-cyclen or morpholine, and compound 4 were placed in
a 50-mL round-bottom flask with 30 mL of CH3CN and 0.5 g of Na2CO3. The reaction
mixture was heated to reflux and stirred for 72 h under Ar. The solvent was removed by
rotatory evaporation and the residue was chromatographed on a silica gel column with
PE/EA = 2:1 to give pure title compounds 5a–c.
1
Compound 5a: Yield 54%; H NMR (CDCl3): δ 7.49 (d, 2H, J = 8.0 Hz, Har),
7.35–7.29 (m, 4H, Har), 7.19 (d, 8H, J = 8 Hz, Har), 7.10 (s, 8H, Har), 6.72 (s, 2H,
Har), 3.54 (m, 8H, ArCH2), 3.57 (s, 17H, CH2), 3.49–3.39 (m, 32H, CH2), 2.65 (s, 15H,
CH2), 1.42 [s, 54H, 6 C(CH3)3], 1.46 [s, 54H, 6 C(CH3)3]; 13C NMR (CDCl3): δ 155.6,
149.9, 147.9, 133.3, 131.3, 129.6, 129.4, 128.6, 125.9, 121.7, 120.6, 97.3, 61.7, 55.6,
54.6, 49.9, 48.0, 47.5, 47.2, 28.6; 31P NMR (CDCl3): δ 25.1 [t, P(O2C12H8), J = 92.5
Hz], 8.7 [d, P(OC6H4)2, J = 92.5 Hz]; ESI-MS: m/z 2628.4 [M+H]+. Anal. calcd. for
C132H204N19O30P3 (2630.1): C 60.28, H 7.82, N 10.12. Found: C 60.22, H 7.78, N 10.20.
Compound 5b: Yield 59.6%; 1H NMR (CDCl3): δ 7.39 (s, 4H, Har), 7.61 (d, 2H, J =
7.6 Hz, Har), 7.45–7.24 (m, 16H, Har), 7.04–6.98 (m, 12H, Har), 6.48 (d, 2H, J = 7.6 Hz,
Har), 5.22 (s, 8H, ArCH2); 31P NMR (CDCl3): δ 24.8 [t, P(O2C12H8), J = 92.4 Hz], 9.4 [d,
P(OC6H4)2, J = 92.4 Hz]; IR: 3368, 3105, 1606, 1506, 1438, 1272, 1164, 1094, 952, 885;
ESI-MS: m/z 1012 [M+H]+. Anal. calcd. for C52H44N11O6P3 (1011.91): C 61.72, H 4.38,
N 15.23. Found: C 61.75, H 4.36, N 15.20.
1
Compound 5c: Yield 93.4%; H NMR (CDCl3): δ 7.49 (dd, 2H, J = 6.0 Hz,
Har),7.30–7.26 (m, 4H, Har), 7.24 (d, 8H, J = 8.4 Hz, Har), 7.10 (d, 8H, J = 8.4 Hz,
Har), 6.71 (m, 2H, Har), 3.67 (t, 16H, J = 4.8 Hz, OCH2), 3.46 (s, 8H, ArCH2), 2.41 (t, 16H,
J = 4.8 Hz, NCH2); 13C NMR (CDCl3): δ 149.8, 147.9, 134.5, 130.1, 129.5, 129.4, 128.6,
125.9, 121.6, 120.9, 66.9, 62.7, 53.5; 31P NMR (CDCl3) δ 25.2 [t, P(O2C12H8), J = 92.3
Hz], 9.1 [d, P(OC6H4)2, J = 92.3 Hz]; IR: 2853, 1605, 1504, 1439, 1270, 1177, 1116, 952,
884; ESI-MS: m/z 1088.1 [M+H]+. Anal. calcd. for C56H64N7O10P3 (1088.07): C 61.82,
H 5.93, N 9.01. Found: C 61.85, H 5.90, N 9.04.
Preparation of 6a
To a solution of 5a (0.399 g, 0.15 mmol) in dry CH2Cl2 (15 mL) at 0 ◦C, CF3COOH
(2 mL) was added drop-wise under N2. The mixture was stirred for 7 h at room temperature.
After removal of the solvent, the residue was adjusted to pH 12 with aqu. NaOH solution,
and extracted with CHCl3 (5 × 15 mL). The organic phase was collected and dried over
Na2SO4. After removal of the solvent, 6a was obtained as a colorless solid (95.4% yield).
1H NMR (CDCl3): δ 7.47 (d, 2H, J = 7.2 Hz, Har), 7.31–7.28 (m, 3H, Har), 7.25–7.22 (m,
1H, Har), 7.21 (d, 8H, J = 8.4 Hz, Har), 7.11 (d, 8H, J = 8.4 Hz, Har), 6.74 (d, 2H, J = 7.6
Hz, Har), 3.63 (s, 8H, ArCH2), 2.78 (t, 16H, J = 4.8 Hz, CH2), 2.65 (d, 16H, J = 4.4 Hz,
CH2), 2.56 (t, 32H, J = 4.8 Hz, CH2); 13C NMR (CDCl3): δ 149.9, 148.0, 135.2, 130.0,
129.5, 129.4, 128.7, 125.8, 121.9, 120.9, 58.6, 51.1, 47.3, 46.3, 45.0; 31P NMR (CDCl3):
δ 25.3 [t, P(O2C12H8), J = 92.3 Hz], 8.7 [d, P(OC6H4)2, J = 92.3 Hz]; IR: 3405, 2925,
2819, 1605, 1503, 1459, 1271, 1177, 1095, 950, 886; ESI-MS: m/z 1427.7 [M+H]+. Anal.

SYNTHESIS AND CHARACTERIZATION OF CYCLOTRIPHOSPHAZENE DERIVATIVES 727
calcd. for C72H108N19O6P3 (1428.69): C 60.53, H 7.62, N 18.63. Found: C 60.52, H 7.65,
N 18.60.
CONCLUSION
We designed and synthesized three novel tetradentate cyclotriphosphazene derivatives
from hexachlorocyclotriphosphazene. The reactions were convenient and efficient. The
target compounds were characterized by 1H NMR, 31P NMR, 13C NMR, and ESI-MS.
The DNA cleavage activity of the title compounds is currently being examined.
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