Synthesis and characterization of N1-(4-toluenesulfonyl)-N1-(9-anthracenemethyl)triamines

Article abstract of DOI:10.1021/jo020331p

A modular synthetic approach was developed to access triamines with varying tether lengths from commercially available aminoalkanols. Initial N-alkylation via reductive amination with anthracene-9-carbaldehyde provided the secondary amines in good yield. Subsequent ditosylation with excess TsC1 yielded the respective bis-N,O-tosylates. The tosylates were reacted with excess putrescine to give the final triamines. X-ray crystallography revealed that the polyamine tail is preferentially oriented over the shielding cone of the anthracene ring.

Full text of DOI:10.1021/jo020331p

Syn th esis a n d Ch a r a cter iza tion of
N1-(4-Tolu en esu lfon yl)-N1-
(9-a n th r a cen em eth yl)tr ia m in es
Chaojie Wang, Khalil A. Abboud,† and
Otto Phanstiel IV*
Department of Chemistry, University of Florida, Gainesville,
Florida 32611, and Department of Chemistry, University of
Central Florida, Orlando, Florida 32816-2366
F IGURE 1. The native polyamines.
ophansti@mail.ucf.edu
Received May 13, 2002
Abstr a ct: A modular synthetic approach was developed to
access triamines with varying tether lengths from com-
mercially available aminoalkanols. Initial N-alkylation via
reductive amination with anthracene-9-carbaldehyde pro-
vided the secondary amines in good yield. Subsequent
ditosylation with excess TsCl yielded the respective bis-N,O-
tosylates. The tosylates were reacted with excess putrescine
to give the final triamines. X-ray crystallography revealed
that the polyamine tail is preferentially oriented over the
shielding cone of the anthracene ring.
F IGURE 2. Acridine-spermidine (4) and anthracene-sper-
midine (5) conjugates.
The naturally occuring linear polyamines 1-3 (pu-
trescine, spermidine, and spermine, respectively) have
attracted attention because of their unique biological
properties and potential as therapeutic templates (Figure
1). Indeed, new polyamine homologues have provided a
better understanding of polyamine transport into leuke-
mia cells.1 Structure-activity relationships have provided
important molecular recognition information about the
transporter, which can facilitate future drug design.
Previous polyamine structural changes included terminal
N-alkylation, alteration of the methylene tether between
nitrogens, and attachment of drug “cargoes” to the
polyamine platform.1-4
Polyamines exist as polycations in vivo and have a high
affinity for biological polyanions such as DNA.2 In addi-
tion, flat polycyclic aromatic systems such as the an-
thracene and acridine nuclei interact with DNA as minor
groove binders or DNA intercalators.3 Indeed, bioconju-
gates involving polyamines and these aromatic nuclei (4
and 5 in Figure 2) have been shown to be efficient
topoisomerase II (Topo-II) inhibitors.4 Interestingly, even
though the acridine conjugates 4 were more potent Topo-
II inhibitors in vitro, the related anthracene conjugates
5 were more efficient in a whole cell assay involving
L1210 murine leukemia cells. Spermidine protection
assays suggested that the affinity of these conjugates for
the L1210 polyamine transporter could be modulated via
alterations in the appended polyamine architecture.4
As part of our continuing investigation of polyamine-
anthracene conjugates, we were interested in the size
limitations of the transporter. In other words, what were
the size constraints of materials with use of the polyamine
transport apparatus? How large a drug cargo could be
delivered via this transporter? Could a polyamine struc-
tural change overcome these constraints? As earlier work
pointed to the fact that one could enhance uptake by
modifying the polyamine structure, homologous spermi-
dine derivatives were synthesized.
* Address correspondence to this author at the University of
Central Florida.
The commercially available amino alcohols were en-
visioned as versatile synthetic intermediates. Previous
reports have shown that successive N-alkylation and
mesylation steps can be used to construct the linear
polyamine chain.5 In this report, a modular synthetic
approach was developed to access polyamine architec-
tures with varying tether distances between the nitro-
gens and a large N-tosyl-N-(9-anthracenemethyl) ap-
pended “cargo”. In this manner, a series of anthracene-
polyamine conjugates were prepared for later biological
evaluation. In addition to introducing large steric con-
straints, the tosyl group also imparted interesting long-
distance effects on the appended polyamine chain.
† University of Florida.
(1) For recent reviews about the synthesis and biological properties
of polyamine derivatives see: (a) Casero, R. A., J r.; Woster, P. M. J .
Med. Chem. 2001, 44, 1-26. (b) Karigiannis, G.; Papaioannou, D. Eur.
J . Org. Chem. 2000, 10, 1841-1863. (c) Kuksa, V.; Buchan, R.; Lin, P.
K. T. Synthesis 2000, 9, 1189-1207. (d) Bergeron, R. J .; Feng, Y.;
Weimar, W. R.; McManis, J . S.; Dimova, H.; Porter, C.; Raisler, B.;
Phanstiel, O., IV J . Med. Chem. 1997, 40, 1475-1494. (e) Seiler, N.;
Delcros, J .-G.; Moulinoux, J . P. Int. J . Biochem. Cell Biol. 1996, 28
(8), 843-861.
(2) Geall, A. J .; Blagbrough, I. S. Tetrahedron 2000, 56, 2449-2460.
(3) (a) Kumar, C. V.; Asuncion, E. H. J . Am. Chem. Soc. 1993, 115,
8547-8553. (b) Burr-Furlong, N.; Sato, J .; Grown, T.; Chavez, F.;
Hurlbert, R. B. Cancer Res. 1978, 38, 1329-1335. (c) Gormley, P. E.;
Sethi, V. S.; Cysyk, R. L. Cancer Res. 1978, 38, 1300-1306.
(4) (a) Phanstiel, O., IV; Price, H. L.; Wang, L.; J uusola, J .; Kline,
M.; Shah, S. M. J . Org. Chem. 2000, 65, 5590-5599. (b) Wang, L.;
Price, H. L.; J uusola, J .; Kline, M.; Phanstiel, O., IV J . Med. Chem.
2001, 44, 3682-3691.
(5) Rajeev, K. G.; Sanjayan, G. J .; Ganesh, K. N. J . Org. Chem. 1997,
62, 5169-5173.
10.1021/jo020331p CCC: $22.00 © 2002 American Chemical Society
Published on Web 10/11/2002
J . Org. Chem. 2002, 67, 7865-7868
7865

SCHEME 1
SCHEME 2
As shown in Scheme 1, the conversion of 6 to 8 was
achieved in two steps via in situ generation of the imine
7. A homologous series of imines (7a -d ) were prepared
from different amino alcohols, 6. The imines were then
reduced to 8 with NaBH4 in good yields without further
purification. The first step did not require scrupulously
dry solvents or molecular sieves as reported for a similar
reaction in the literature.6 Instead, solvent removal by
rotary evaporation at 40-50 °C facilitated the forward
equilibrium step, and provided yields ranging from 68
to 81% of the 2° amines, 8.
In the seemingly routine tosylation step, several condi-
tions were tried to increase the product yields and to
avoid product decomposition. Upon addition of p-toluene-
sulfonyl chloride (TsCl), the color of the solution became
dark even when the reaction was conducted at low
temperature (-20 °C). [Note: This discoloration event
did not occur if the 2° amine was first protected with a
tert-butyloxycarbonyl (Boc) group.] After several modifi-
cations, the desired bis-N,O-tosylates (9a -d ) were iso-
lated in good yields and purified prior to their reaction
with putrescine. While the primary aliphatic tosylates
normally react easily with amines,5 compound 9 required
excess putrescine at elevated temperature (75 °C) and
longer time (overnight) to form the target compounds 10
shown in Scheme 2. This was likely due to steric factors.
aliphatic tosylates (RCH2OTs) appears approximately 0.2
ppm downfield of their alcohol precursors.7 Throughout
the series of 9a -d , the closer the -CH2OTs group was
to the anthracene ring, the further upfield its chemical
shift appeared. For the series 9a -d , even when the
-CH2OTs group and aromatic rings were separated by
six atoms, the chemical shift of the -CH2OTs group
(9d : δ 3.35) was still upfield compared with its alcohol
precursor (8d : δ 3.50). We speculated that the -CH2-
OTs group is still under the strong shielding influence
of the distal anthracene ring.
The triamine analogues, 10a -d , also exhibited this
phenomena. During the conversion from tosylate 9 to
The 1H NMR spectra of the tosylated compounds
revealed interesting chemical shifts. Upon tosylation, the
“benzylic” CH2 of the ditosylated compounds (9) occurred
downfield due to the presence of the strong electron-
withdrawing sulfonyl group as expected. Generally speak-
ing, the other CH2 connected directly to N in 9 is nearly
unperturbed because of the countering effects of the new
sulfonyl group and the shielding cone associated with the
π-system of the aromatic rings.7 A similar phenomenon
was reported for a polyazamacrocycle prepared by Luis
1
triamine 10, the H NMR signals, which belong to the
-CH2OTs group in 9 (δ 3.2-3.4), disappear and new
signals appear between δ 1.6 and 2.7. These signals were
assigned by 1H-1H COSY experiments and were at-
tributed to the CH2 N groups associated with the two free
amines introduced by the putrescine moiety. In short,
certain chemical shift values within the 10 series are
significantly upfield of their normal range and mirrored
the anthracene proximity effect observed with 9. By
1
et al.8 The normal trend is that the H NMR signal of
(7) Silverstein, R. M.; Bassler, G. M.; Morrill, T. C. Spectrometric
Identification of Organic Compounds; J ohn Wiley & Sons: New York,
1981; pp 188 and 220.
(8) Altava, B.; Burguete, M. I.; Escuder, B.; Luis, S. V.; Garc´ıa-
Espan˜a, E.; Mun˜oz, M. C. Tetrahedron 1997, 53, 2629-2640.
(6) Martin, B.; Posse´me´, F.; Le Barbier, C.; Carreaux, F.; Carboni,
B.; Seiler, N.; Moulinoux, J .-P.; Delcros, J .-G. J . Med. Chem. 2001,
44, 3653-3664.
7866 J . Org. Chem., Vol. 67, No. 22, 2002

Exp er im en ta l Section
Ma ter ia ls. Silica gel (32-63 µm) was purchased from Sci-
entific Adsorbents Inc. Chemical reagents were purchased from
commercial sources and used without further purification. All
solvents were distilled prior to use. 1H and 13C NMR spectra
were recorded at 300 and 75 MHz, respectively. TLC solvent
systems are based on volume percent and NH4OH refers to
concentrated aqueous NH4OH. Elemental analyses were per-
formed by Atlantic Microlabs (Norcross, GA). High-resolution
mass spectrometry was performed by Dr. David Powell at the
University of Florida Mass Spectrometry facility.
Gen er a l P r oced u r e for th e Syn th esis of (An th r a cen -9-
ylm eth yl)a m in o Alcoh ols, 8a -d . To a stirred solution of
amino alcohol (12 mmol) in 10 mL of 25% MeOH/CH2Cl2 was
added a solution of 9-anthraldehyde (10 mmol) in 10 mL of 25%
MeOH/CH2Cl2 under N2. The mixture was stirred at room
temperature overnight, until the imine formation was complete
(monitored by TLC). The solvent was evaporated under vacuum
to give the crude imine as a bright green solid, which was used
for reduction without further purification.
NaBH4 (30 mmol) was added in small portions to the solution
of imine in 20 mL of 1:1 CH3OH-CH2Cl2 at 0 °C. The mixture
was stirred at room temperature overnight, then concentrated
under vacuum. The residue was dissolved in 50 mL of CH2Cl2
and washed three times with 50 mL of aq Na2CO3 (pH 10). The
organic layer was separated, dried over anhydrous Na2SO4,
filtered, and concentrated under vacuum. The residue was
purified by flash chromatography on silica gel and NMR data
were collected in CDCl3.
F IGURE 3. X-ray crystal structure of 9c.
Gen er a l P r oced u r e for th e Ditosyla tion of N-(An th r a -
cen -9-ylm eth yl)a m in o Alcoh ols, 9a -d . The solution of N-(an-
thracen-9-ylmethyl)amino alcohol (5 mmol) in 25 mL of dry
pyridine was stirred at -20 °C for 10 min. p-Toluenesulfonyl
chloride (TsCl, 15 mmol) was added in small portions over an
hour period. The mixture was stirred for one additional hour
more, and the temperature gradually rose to 0 °C. The reaction
flask was placed in a refrigerator (0-5 °C) overnight. The
mixture was added into 200 mL of ice-water, and a solid (or
viscous liquid) typically precipitated. The solid (or viscous liquid)
was washed with deionized water several times. Then the
washed solid (or viscous liquid) was recrystallized from CH2-
Cl2-methanol or purified by flash chromatograph on silica gel.
Note: The viscous liquids became foamlike solids after pumping.
NMR data were collected in CDCl3.
Gen er a l P r oced u r e for th e P r ep a r a tion of Mon otosy-
la ted Ben zylic Tr ia m in es, 10a -d . The ditosylated product 9
(1 mmol) and 1,4-diaminobutane (10 mmol) were dissolved in
acetonitrile (10 mL), then stirred at 75 °C under N2 overnight.
After checking the disappearance of ditosylated products by TLC,
the solution was concentrated under reduced pressure. The
residue was dissolved in CH2Cl2 (20 mL) and washed three times
with saturated aqueous sodium carbonate. The organic layer was
separated, dried over anhydrous sodium sulfate, filtered, and
concentrated under vacuum. The residue was purified by flash
chromatography on silica gel.
X-r a y Cr ysta llogr a p h y w ith 9c. The bis-tosylate 9c (0.2 g)
was dissolved in 10 mL 1:1 (v/v) acetone-methanol. The solvent
was slowly evaporated in air at room temperature over several
days. The single crystal appeared as a pale green prism.
Data were collected at 173 K on a Siemens SMART PLAT-
FORM equipped with A CCD area detector and a graphite
monochromator utilizing Mo KR radiation (λ ) 0.71073 Å). Cell
parameters were refined with up to 8192 reflections. A full
sphere of data (1381 frames) was collected with the ω-scan
method (0.3° frame width). The first 50 frames were remeasured
at the end of data collection to monitor instrument and crystal
stability (maximum correction on I was <1%). Absorption
corrections by integration were applied based on measured
indexed crystal faces.
assigning the chemical shifts of the homologous series
9a -d and 10a -d , one can estimate that the shielding
cone of the anthracene nucleus effected CH signals, which
were 3-9 atoms away from the anthracene core. Before
and beyond this six-atom “window”, the CH chemical
shifts appear near their expected positions. For example,
the most distal position from the anthracene core (i.e.,
the terminal CH2NH2 group) varied from δ 2.43 for 10a
to δ 2.70 for 10d .
To assign this effect to a particular conformation, a
single crystal of the ditosylate system, 9c, was obtained.9
As shown in Figure 3, the butylene fragment is prefer-
entially oriented toward the anthracene ring system as
anticipated. This arrangement places the aliphatic chain
over the shielding cone of the anthracene. A priori one
may have expected the polyamine tail in 10 to impart
this conformational bias due to electronic factors. How-
ever, the conformation of 9c (Figure 3) suggested that
the conformational bias of the N-tosyl-N-anthracenylm-
ethyl group is likely due to steric factors, which require
a near anti alignment of the bulky tosyl group and the
anthracene ring system. As shown in Figure 3, the
N-alkyl ligand (N-C23) is oriented toward the an-
thracene ring via the dihedral angle C2-C1-N-C23
(-30°). In short, the N-tosyl-N-anthracenylmethyl
terminus introduces a conformational constraint on
the appended N-alkyl chain, which preferentially
orients the N-alkyl ligand over the anthracene ring
system.
In conclusion, an efficient modular method was devel-
oped that allows ready access to the polyamines with
different tethers between the nitrogen centers. In addi-
tion, a novel conformational constraint was introduced
via the N-tosyl-N-anthracenemethyl subunit. Whether
this interesting corollary translates to unique biological
activity remains to be seen and will be the subject of
future work.
The structure was solved by the Direct Methods in SHELX-
TL5, and refined with full-matrix least squares.9 The non-H
(9) Sheldrick, G. M. SHELXTL5: Bruker-AXS: Madison, WI, 2000.
J . Org. Chem, Vol. 67, No. 22, 2002 7867

atoms were treated anisotropically, whereas the hydrogen atoms
were calculated in ideal positions and were riding on their
respective carbon atoms. The chain between N1 and O3 is
disordered and was refined in two positions (both of which are
oriented toward the anthracene ring). Both conformers are
present in the crystal. Their site occupation factors refined to
0.77(1) for the major part (Figure 3) and, consequently, 0.23(1)
for the minor part. A total of 385 parameters were refined in
the final cycle of refinement using 4824 reflections with I >
2σ(I) to yield R1 and wR2 of 4.05% and 10.55%, respectively.
Refinement was done with F2.
was sponsored in part by the Elsa U. Pardee Foundation
and the Florida Hospital Gala Endowed Program for
Oncologic Research. K.A.A. wishes to acknowledge the
National Science Foundation and the University of
Florida for funding of the purchase of the X-ray equip-
ment. C.W. was partially supported by the China
Scholarship Council.
Su p p or tin g In for m a tion Ava ila ble: Complete charac-
terization data (1H NMR, 13C NMR, mass spectral data, and
elemental analyses) for the synthetic intermediates (8a -d and
9a -d ) and products 10a -d , and crystallographic information
for 9c. This material is available free of charge via the Internet
at http://pubs.acs.org.
Ack n ow led gm en t. The authors wish to thank Dr.
David Powell at the University of Florida Mass Spec-
trometry facility and the UCF Presidential Initiative to
Fund Major Equipment for the acquisition of the UCF
300 and 500 MHz NMR facility. In addition, this work
J O020331P
7868 J . Org. Chem., Vol. 67, No. 22, 2002