Synthesis, flow cytometric evaluation, and identification of highly potent dipyridamole analogues as equilibrative nucleoside transporter 1 inhibitors

Article abstract of DOI:10.1021/jm070311l

Dipyridamole (Persantine) is a clinically used vasodilator with equilibrative nucleoside transporters 1 and 2 (ENT1 and ENT2) inhibitory activity albeit less potent than the prototype ENT1 inhibitor nitrobenzylmercaptopurine riboside (NBMPR). Dipyridamole is a good candidate for further exploration because it is a non-nucleoside and has a proven record of safe use in humans. A series of dipyridamole analogues were synthesized with systematic modification and evaluated as ENT1 inhibitors by flow cytometry. Compounds with much higher potency were identified, the best being 2,6-bis(diethanolamino)-4,8-diheptamethyleneiminopyrimido[5,4-d]pyrimidine (13) with a Ki of 0.49 nM compared to a Ki of 308 nM for dipyridamole. Compound 13 is similar in potency to the prototype potent ENT1 inhibitor NBMPR (0.43 nM). For the first time, a dipyridamole analogue has been identified that is equipotent with NBMPR. The SAR indicated that diethanolamine substituted analogues were more active than monoethanolamine compounds. Also, free hydroxyl groups are not essential for activity.

Full text of DOI:10.1021/jm070311l

3906
J. Med. Chem. 2007, 50, 3906-3920
Synthesis, Flow Cytometric Evaluation, and Identification of Highly Potent Dipyridamole
Analogues as Equilibrative Nucleoside Transporter 1 Inhibitors
Wenwei Lin and John K. Buolamwini*
Department of Pharmaceutical Sciences, College of Pharmacy, UniVersity of Tennessee Health Sciences Center,
847 Monroe AVenue, Suite 327, Memphis, Tennessee 38163
ReceiVed March 19, 2007
Dipyridamole (Persantine) is a clinically used vasodilator with equilibrative nucleoside transporters 1 and
2 (ENT1 and ENT2) inhibitory activity albeit less potent than the prototype ENT1 inhibitor nitrobenzylm-
ercaptopurine riboside (NBMPR). Dipyridamole is a good candidate for further exploration because it is a
non-nucleoside and has a proven record of safe use in humans. A series of dipyridamole analogues were
synthesized with systematic modification and evaluated as ENT1 inhibitors by flow cytometry. Compounds
with much higher potency were identified, the best being 2,6-bis(diethanolamino)-4,8-diheptamethylene-
iminopyrimido[5,4-d]pyrimidine (13) with a Ki of 0.49 nM compared to a Ki of 308 nM for dipyridamole.
Compound 13 is similar in potency to the prototype potent ENT1 inhibitor NBMPR (0.43 nM). For the first
time, a dipyridamole analogue has been identified that is equipotent with NBMPR. The SAR indicated that
diethanolamine substituted analogues were more active than monoethanolamine compounds. Also, free
hydroxyl groups are not essential for activity.
Introduction
Nucleoside transporters are specialized integral membrane
glycoproteins known to mediate the cellular influx or efflux of
physiological nucleosides or nucleobases, as well as many
synthetic analogues.1,2 Currently, nucleoside transporters are
classified into two families: (i) the equilibrative nucleoside
transporter family (ENTs) and (ii) the concentrative nucleoside
transporter family (CNTsa).3,4 The equilibrative family facilitates
the transport of nucleosides or nucleobases down their concen-
tration gradients. In contrast, the concentrative family transports
nucleosides against their concentration gradients by coupling
with a sodium ion gradient. Nucleoside transporter inhibitors
have potential therapeutic applications in ischemic heart disease
and stroke,5-10 in inflammatory disease,11 and as biological
response modifiers in antimetabolite chemotherapy.12 A com-
prehensive summary of nucleoside transport inhibitors as
potential therapeutic agents has been published.13
Equilibrative nucleoside transporters were the first to be
identified because of their broad tissue distribution. They were
initially subdivided into es (equilibrative sensitive) or ENT1
and into ei (equilibrative insensitive) or ENT2 according to their
sensitivities to inhibition by nanomolar concentrations of
4-nitrobenzylmercaptopurine ribonucleoside (NBMPR). Four
subtypes of ENTs (ENT1, ENT2, ENT3, and ENT4) have now
been identified and cloned.3 The ENT1 transporter is the most
widely distributed nucleoside transporter with the highest
abundance in most tissues studied.14,15 This makes it the most
relevant NT target for therapeutic exploration. Several chemical
Figure 1. Representatives of the three main ENT1 inhibitory chemical
classes.
* To whom correspondence should be addressed. Phone: 901-448-7533.
Fax: 901-448-6828. E-mail: Jbuolamwini@utmem.edu.
classes have been shown to inhibit ENT1.13 Among them, three
a Abbreviations: Cbz, carbobenzoxy; CNTs, concentrative nucleoside
transporters; DMSO, dimethylsulfoxide; ENT1, equilibrative nucleoside
transporter 1; ENT2, equilibrative nucleoside transporter 2; ENT3, equili-
brative nucleoside transporter 3; ENT4, equilibrative nucleoside transporter
4; ESI, electrospray ionization; LC, liquid chromatography; MS, mass
spectrometry; NBMPR, nitrobenzylmercaptopurine riboside; NMR, nuclear
magnetic resonance; NTIs, nucleoside transporter inhibitors; SAR, structure-
activity relationship; CDKs, cyclin dependent kinases; TCPP, 2,4,6,8-
tetrachloropyrimido[5,4-d]pyrimidine; TLC, thin-layer chromatography;
TMS, tetramethylsilane.
classes are most significant (Figure 1). These are purine
nucleoside analogues of which NBMPR is the prototype,
pyrimidopyrimidine analogues such as the antithrombotic and
vasodilating agent dipyridamole, and flazine calcium channel
blockers represented by lidoflazine.
NBMPR is a more potent ENT1 inhibitor (e.g., Ki of 0.7
nM)16 than dipyridamole (e.g., Ki of 8.8).17 Draflazine, a
lidoflazine analogue, also exhibits high ENT1 inhibitory activity
10.1021/jm070311l CCC: $37.00 © 2007 American Chemical Society
Published on Web 07/18/2007

Dipyridamole Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3907
Scheme 1a
schizonts; it had an IC50 of 30 nM by itself and lowered the
IC50 of chloroquine from 97.0 to 13.7 nM at a concentration of
0.1 nM.36
In light of these positive attributes of dipyridamole, we
selected it as a candidate for further structure-activity relation-
ship (SAR) exploration for ENT1 transporter inhibitory activity.
Many dipyridamole analogues have been reported and evaluated
for their effects as antiplatelet and cardioprotective agents.37-41
Some dipyridamole analogues have also been synthesized and
evaluated for their inhibitory activities against cyclin dependent
kinases (CDKs), with negative results.42 A more recent publica-
tion disclosed the synthesis and biological evaluation of a series
of dipyprdamole analogues for their ENT1 inhibitory activities,
and some of them showed only slightly higher activities than
dipyridamole.43 In this paper, a series of dipyridamole analogues
were synthesized for a more systematic and comprehensive
evaluation of ENT1 SAR. Some of the compounds showed
activity comparable to that of NBMPR, which is a much more
potent ENT1 inhibitor than dipyridamole.
a Reagents and conditions: (a) NHR1R2, anhydrous THF, 0-5 °C; (b)
NHR3R4, DMSO, 150 °C; (c) R1MgCl, anhydrous THF, 0-5 °C.
(IC50 ) 0.28-10 nM).18 However, NBMPR and the flazine
compounds like draflazine are poor candidates for further
exploration. NBMPR has immunosuppressive and mutagenic
activities derived from its 6-mercaptopurine metabolite.19-21 The
flazines are nosnspecific, having calcium channel antagonist
activity that is thought to contribute significantly to their
cardioprotective effects.22-24 As a potent ENT1 inhibitor,
dipyridamole has broad pharmacological effects. It is an
effective coronary vasodilator (used as an antianginal drug)
through the increasing of extracellular adenosine concentration
stemming from its ENT inhibitory activity.5,25,26 Dipyridamole
also has antiplatelet effects attributed to phosphodiesterase
inhibition.5 Coadministration of ENT1 inhibitors, such as
dipyridamole, and antimetabolites such as 5-fluorouracil has
been shown to result in synergism and might improve the
therapeutic index of antimetabolites, where target cells have a
higher ENT1 expression than normal cells.27,28 Synergism results
not only from inhibition of nucleoside salvage but also from
the increase of the intracellular concentration of 5-fluorodeox-
yuridine caused by blockade of its efflux by dipyridamole. Thus,
the intracellular level of the active product, 5-fluorodeoxyuridine
monophosphate, increases, resulting in higher therapeutic
efficacy.29,30
Besides mammalian tissues, nucleoside transporters are also
found in parasites such as Plasmodium falciparum, the malarial
parasite.31,32 Parasites rely on salvage pathways to meet their
purine and purine nucleoside needs because they do not have
de novo purine biosynthetic pathways.33 Nucleoside transporters
of parasites have limited homologies with the human ENT1 and
have been shown to be inhibited by dipyridamole but not
NBMPR or lidoflazine.34 Some parasites like Toxoplasma gondii
can even transport NBMPR.35 A study of the antimalarial
activity of dipyridamole showed that it was effective against
all of the erythrocytic stages such as rings, trophozoites, and
Chemistry
For the synthesis of these dipyridamole analogues, com-
mercially available starting materials 2,4,6,8-tetrachloropy-
rimido[5,4-d]pyrimidine (TCPP) and dipyridamole were used
on the basis of the structures of individual final products. For
the preparation of the major dipyridamole analogues (com-
pounds 1-8, 11-71, and 73) (Scheme 1), an excess of the
appropriate amine (about 4-fold excess) was reacted with TCPP
in anhydrous THF. The resulting 2,6-dichloro intermediates were
individually reacted with diethanolamine, ethanolamine, or
morpholine at 150 °C in DMSO as solvent to obtain the
target products. For the preparation of compounds 9 and 10
(Scheme 1), the appropriate Grignard reagents were used for
the first step, followed by reaction with diethanolamine in the
second step.
For the preparation of compounds 74-79 (Scheme 2),
dipyridamole was used as starting material. Dipyridamole was
acylated or alkylated44 to afford the desired products. Compound
78 was a dialkylated product, instead of the intended tetraalky-
lated product. It appears that the introduction of the first
isopropyl group at each side of dipyridamole prevented the
introduction of a second isopropyl group on the remaining
hydroxyl groups under the reaction conditions. This could be
possibly due to steric hindrance. In total, 79 dipyridamole
analogues with diverse substituents were synthesized in this
study. The core pyrimido[5,4-d]pyrimidine system and the
symmetrical feature in dipyridamole were maintained with the
exception of compound 8, which had two different substituents
at the at the 4- and 8-positions. Compound 8 was planned to be
Scheme 2a
a Reagents and conditions: (a) HCOOH, 100 °C (compound 74); (b) CH3COCl, DMAP, anhydrous THF, 0-5 °C (compound 75); (c) NaH, R1I, anhydrous
DMF (R2 ) R1 for 76-78; R2 ) H for 79).

3908 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Lin and Buolamwini
Table 1. Inhibitory Activities of Compounds with Different Ring
Systems at the 4- and 8-Positions
Figure 2. Structure of SAENTA-fluorescein.
symmetrical, but the conditions in the second reaction step
caused a loss of one Cbz group to produce the unsymmetrical
compound.
Biological Studies
The compounds and positive controls, dipyridamole, NBMPR,
and lidoflazine were subjected to a flow cytometric assay with
SAENTA-fluorescein (Figure 2) as the fluorescent probe.44 Flow
cytometry has several advantages over the conventional radio-
ligand binding assays in that it eliminates radiation hazards and
disposal problems and allows the use of much fewer cells, as
few as 5000 cells compared to 2 million cells per sample for
comparable radioligand assays. SAENTA-fluorescein is a NB-
MPR analogue, and it was used successfully in several studies
to determine the ENT1 inhibitory activities of NBMPR ana-
logues.16,17 Studies with radiolabeled ligands have shown that
NBMPR, dipyridamole, and lidoflazine displace each other at
the binding sites on the ENT1 transporter.45-47 Thus, we
expected the new compounds would similarly displace SAENTA-
fluorescein from the NBMPR binding site on the ENT1
transporter.
Dipyridamole itself is a fluorescent molecule (excitation λmax
) 280 nm, emmision λmax ) 490 nm),48 but at the experimental
wavelengths sets for SAENTA-fluorescein (exciation λ ) 488
nm, emmision λ ) 533 nm), dipyridamole and its analogues,
with the exception of compounds 9 and 10, had insignificant
absorbance and emission, which did not interfere with the
detection of bound SAENTA-fluorescein. Human erythroleu-
kemia K562 cells were used as the ENT1 transporter source
for the binding experiments. This cell line expresses high levels
of ENT1 protein, with very limited fraction of other nucleoside
transporters,49 and has been used widely for assessing ENT1
binding affinity of compounds.50-53 Compounds were first
screened at 10 µM, and those compounds that showed good
inhibitory activities (% inhibition of >40%) were further tested
at 10 concentration levels to generate dose-dependent curves
from which the IC50 values were derived and used to calculate
the corresponding Ki values. The inhibitory activities of the
highly fluorescent dipyridamole analogues like 9 and 10 could
not be determined by this method.
a ND ) not determined. b For structure of compound 8, see Scheme 1.
Structure-Activity Relationships
All dipyridamole analogues had the core structure of 2,4,6,8-
tetrasubstituted-pyrimido[5,4-d]pyrimidine. They maintained the
symmetric feature as in the case of dipyridamole, with the
exception of compound 8, which had two different substituents
at the 4- and 8-positions of the core pyrimidopyrimidine
structure. The ENT1 inhibitory activities are summarized in
Tables 1-4. In all the tables, the activities of one negative
control (DMSO) and three positive controls, NBMPR, lidofla-
zine, and dipyridamole, are listed for comparison.
midine template. Compounds listed in Table 2 are analogues
with open-chain tertiary amines at the pyrimidopyrimidine
4- and 8-positions. Compounds listed in Table 3 have primary
or secondary amine substituents at the 4- and 8-positions of
the core structure. Compounds listed in Table 4 are derivatives
of dipyridamole. In this study, NBMPR had a Ki of 0.43 nM,
dipyridamole a Ki of 8.18 nM, and lidoflazine a Ki of 279.9
nM, which are in agreement with the literature.
For substituents at the 4- and 8-positions of the pyrimido-
[5,4-d]pyrimidine, nitrogen-containing monocyclic ring struc-
tures usually gave analogues with good inhibitory activities, as
Compounds listed in Table 1 are dipyridamole analogues with
ring structures at the 4- and 8-positions of the pyrimidopyri-

Dipyridamole Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3909
Table 2. Inhibitory Activities of Compounds with Open Chain 4- and
Table 3. Inhibitory Activities of Compounds with Free Hydrogen on
8-Position Substituents
the Nitrogen of 4- and 8-Position Substituents
a ND ) not determined.
in the case of compounds 2, 4, 11, 13, and 15. Increasing ring
size from five (compound 2) to eight (compound 13) increased
inhibitory activity accordingly, with Ki values going from 99.7
to 0.49 nM, about a 200-fold increase in inhibitory activity.
Compound 13 was the most active analogue in the series with
activity comparable to the activity of one of best ENT1
nucleoside analogue inhibitors, NBMPR (Ki ) 0.43 nM).
Compared to dipyridamole (Ki ) 8.18 nM), compound 13 is
16 times more potent. A ring size of eight was optimal because
a further increase in ring size to nine decreased activity as can
be seen with compound 15, which had a Ki of 0.77 nM. The
effect of ring size could be due to an increased hydrophobic
effect because the piperidine ring in dipyridamole (Ki ) 8.18
nM) provided higher inhibitory activity than the morpholino or
piperazine rings in compounds 5 (Ki ) 6956 nM) and 6
(practically inactive), respectively. The binding pocket at the
4- and 8-positions also has limits on the ring size it can
accommodate. Further, not only does the ring size matter but
also the ring flexibility is important, with flexible rings affording
a ND ) not determined.

3910 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Lin and Buolamwini
Table 4. Inhibitory Activities of Compounds with Modification at the
Hydroxyl Groups of Dipyridamole
Figure 3. Representative regions for dipyridamole analogues.
activity compared to dipyridamole. However, compound 72
exhibited higher activity than compound 1, the N-(monohy-
droxyethyl) counterpart of dipyridamole. This indicates that a
hydrogen atom on the 2- and 6-position nitrogen is unfavorable
for potent activity. Compound 73 has the diethanolamino groups
at the 2- and 6-postions locked into morpholino rings, and this
modification caused a loss of activity. Esterification of dipy-
ridamole (compound 74 and 75) maintained relatively good
activity compared to dipyridamole, which indicates that free
hydroxyl groups are not necessary for activity. Esterification
introduces additional oxygen atoms, which might participate in
additional hydrogen bonding that probably compensates for the
loss of activity caused by an increase in lipophilicity. In contrast,
ether type lipophilic modification at the same positions caused
a decrease in activity as in the case compounds 76-78.
Interestingly, compound 79, which has one free hydroxyl group
at the 2- and 6-positions, exhibited a higher potency than
dipyridamole. The reasons for the higher potency of 79 relative
to dipyridamole are not apparent. Some compounds, namely,
7, 25, and 27, had a percent inhibition above 40%, but no IC50
values could be determined because of low solubility.
These dipyridamole analogues had modifications at two
important regions with regard to ENT1 inhibitory activity (see
Figure 3). Region 1 should be lipophilic to obtain the highest
ENT1 inhibitory activities, with single nitrogen-containing
flexible rings being preferred to carbocyclic, morpholine,
piperazine, or rigid multicyclic ring systems. For the nitrogen-
containing flexible rings, an eight-membered ring is optimal.
Region 2 should be a hydrophilic region with the diethanolamino
group providing optimal activity, although it is not essential;
small lipophilic modifications over the hydroxyl groups are well
tolerated.
a ND ) not determined. b Prepared according to a literature procedure.40
higher activity than rigid ring systems. This is evident in
comparing the activities of compound 15 (Ki ) 13.6 nM) and
compound 17 (Ki ) 3416 nM). Compounds with N-(bis-
hydroxyethyl) substituents at the 2- and 6-positions (type A in
Tables 1-4) were much more potent than the corresponding
N-(monohydroxyethyl) substituted analogues (type B in Tables
1-4).
The open-chain analogues (compound 21-38) were less
active than the cyclic counterparts. Compounds with carbon
chain length from 1 to 4 (compounds 21, 23, 25, and 27)
exhibited low inhibitory activities. Increasing the chain length
(compound 31) or branching it (compounds 29 and 33) led to
a decrease in activity. Compound 35 has polar oxygen atoms
in the side chain, which also resulted in low activity. Compound
37 has dibenzylamino groups at the 4- and 8-positions and was
inactive. In this set also, the N-(monohydroxyethyl) substituted
analogues (compounds 22, 24, 26, 28, 30, 32, 34, 36, and 38)
were less active than the N-(bis-hydroxyethyl) counterparts.
The analogues that contained a primary or secondary amine
(compounds 39-71) at the 4- and 8- positions had lower
inhibitory activities relative to dipyridamole. The most active
compounds in the group, 52, 58, and 64, were only about half
as active as dipyridamole. These are analogues with tert-
butylamino, isopentylamino, and cyclopentylamnio groups at
the 4- and 8-positions. Again, analogues with N-(monohydroxy-
ethyl) substitution were less active than the N-(bis-hydroxyethyl)
counterparts.
Conclusion
In this study, a substantial number of dipyridamole analogues
were synthesized and explored for their inhibitory activity
against ENT1 transporter using a flow cytometric method.
Compounds with much higher activity than dipyridamole were
identified for the first time, with the best, compound 13, being
16 times more active than dipyridamole and having activity
comparable to that of the potent ENT1 standard inhibitor
NBMPR. The study has also revealed important structural
determinants for ENT1 inhibitory activity in this series, among
which are the requirements for a lipophilic medium to large
size nitrogen-containing lipophilic rings at the 4- and 8-positions
and hydrophilic, hydrogen-bond acceptor substituents at the 2-
and 6-positions. The newly identified higher potency dipy-
ridamole analogue, compound 13, may facilitate the therapeutic
exploitation of the ENT1 inhibitory activity of dipyridamole
and related compounds.
Compounds 72-79 are 2- and 6-substituted dipyridamole
analogues. The presence of a 2′-hydroxyethoxy group at the
2- and 6-positions (compound 72) resulted in a steep drop in

Dipyridamole Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3911
1
m/z 477 (M + H)+; H NMR (DMSO-d6) δ 4.688 (m, 4H, 4 ×
Experimental Section
OH, disappeared after D2O exchange), 4.119 (br s, 8H, 2 × N(CH2-
CH2)2), 3.592 (br s, 16H, 2 × N(CH2CH2OH)2), 1.877 (br s, 8H, 2
× N(CH2CH2)2). Anal. (C22H36N8O4) C, H, N.
Chemistry. Thin-layer chromatography (TLC) was conducted
on silica gel plates (Analtech). Compounds were visualized by UV
light (254 and 365 nm). 1D NMR spectra were recorded on a Varian
Inova 500 MHz NMR instrument by using CDCl3 or (CD3)2SO as
solvents and using tetramethylsilane (TMS) as an internal standard.
Flash column chromatography was performed on Fisher silica gel
(170-400 mesh). Melting points were determined using a Fisher-
Johns melting point apparatus and were reported uncorrected. Mass
spectra were obtained on a Bruker-HP ESQUIRE ion trap LC/MS-
(n) system. Elemental analyses were performed by Atlantic Mi-
crolab Inc., Norcross, GA. All solvents and reagents were purchased
from Aldrich or other major chemical companies and used without
further purification. All reactions were carried under argon gas.
2,6-Bis(diethanolamino)-4,8-disubstituted-pyrimido[5,4-d]py-
rimidine or 2,6-Diethanolamino-4,8-disubstituted-pyrimido[5,4-
d]pyrimidine. General Procedure I. To a solution of 2,4,6,8-
tetrachloropyrimido[5,4-d]pyrimidine (TCPP) (0.27 g, 1 mmol) in
anhydrous THF (10 mL), the appropriate amine (4.2 mmol) was
added in this first step. The reaction was stirred on an ice-water
bath for 20 min, and then water (100 mL) was added to precipitate
the reaction intermediate. After drying over P2O5, the intermediate
was dissolved in DMSO (3 mL). An appropriate amine (diethano-
lamine, ethanolamine, or morpholine) (3 mL) was added, and the
mixture was heated at 150 °C for 6 h with stirring. Then the product
was purified by flash silica gel chromatography.
2,6-Diethanolamino-4,8-dipyrrolidinylpyrimido[5,4-d]pyrimi-
dine (3). Compound 3 was prepared by general procedure I with
pyrroline (0.35 mL, 4.2 mmol) at the first step and with ethano-
lamine (3 mL, 50 mmol) at the second step. Product was purified
by flash silica gel chromatography (CH2Cl2/MeOH ) 15/1) to give
a yellow powdery solid (176 mg, 45%). Mp 219-220 °C; MS (ESI)
m/z 389 (M + H)+, 411 (M + Na)+; 1H NMR (DMSO-d6) δ 5.774
(t, 2H, 2 × NH, disappeared after D2O), 4.591 (t, 2H, 2 × OH,
disappeared after D2O exchange), 4.006 (br s, 8H, 2 × N(CH2-
CH2)2), 3.505 (q, 4H, 2 × NHCH2CH2OH, J ) 6 Hz), 3.292 (q,
4H, 2 × NHCH2CH2OH, J1 ) 6 Hz), 1.863 (br s, 8H, 2 ×
N(CH2CH2)2). Anal. (C18H28N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-dimorpholinopyrimido[5,4-d]py-
rimidine (4). Compound 4 was prepared by general procedure I
with morpholine (0.37 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 16/
1) to give a yellow powdery solid (274 mg, 54%). Mp 205-
206 °C; MS (ESI) m/z 509 (M + H)+, 531 (M + Na)+; H NMR
1
(DMSO-d6) δ 4.689 (t, 4H, 4 × OH, disappeared after D2O), 4.121
(br s, 8H, 2 × N(CH2CH2)2O), 3.715 (t, 8H, 2 × N(CH2CH2)2O),
3.573 (br s, 16H, 2 × N(CH2CH2OH)2). Anal. (C22H36N8O6‚0.5H2O)
C, H, N.
2,6-Bis(diethanolamino)-4,8-disubstituted-pyrimido[5,4-d]py-
rimidine. General Procedure II. To a solution of 2,4,6,8-tetra-
chloropyrimido[5,4-d]pyrimidine (TCPP) (0.27 g, 1 mmol) in
anhydrous THF (10 mL), the appropriate Grignard reagent
(2.1 mmol) was added at this first step. The reaction was stirred in
ice-water bath for 20 min, and then water (100 mL) was added to
precipitate the reaction intermediate. After drying over P2O5, the
intermediate was dissolved in DMSO (3 mL), and diethano-
lamine (3 mL) was added. The mixture was heated at 150 °C for
6 h with stirring. Then the product was purified by flash silica gel
chromatography.
2,6-Bis(dialkoxylethylamino)-4,8-disubstituted-pyrimido[5,4-
d]pyrimidine. General Procedure III. NaH (60% in mineral oil,
0.28 g, 7 mmol) was added to a solution of dipyridamole (0.35 g,
0.69 mmol) in anhydrous DMF (10 mL), and the mixture was stirred
at room temperature for 2 h. Then the appropriate alkyl halide (32
mmol) was added, and the mixture was stirred overnight. The
reaction mixture was partitioned between CH2Cl2 (60 mL) and H2O
(50 mL), and the organic layer was separated. The remaining
aqueous solution was extracted with CH2Cl2 (20 mL × 2), and all
organic solutions were incorporated and dried over anhydrous Na2-
SO4. Then the CH2Cl2 was removed under reduced pressure, and
the residue was subjected to flash silica gel chromatography for
purification of the product.
2,6-Diethanolamino-4,8-dimorpholinopyrimido[5,4-d]pyrimi-
dine (5). Compound 5 was prepared by general procedure I with
morpholine (0.37 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 15/
1) to give a yellow powdery solid (211 mg, 50%). Mp 203-
1
204 °C; MS (ESI) m/z 421 (M + H)+, 443 (M + Na)+; H NMR
(DMSO-d6) δ 6.186 (t, 2H, 2 × NH, disappeared after D2O), 4.619
(t, 2H, 2 × OH, disappeared after D2O), 4.128 (br s, 8H, 2 ×
N(CH2CH2)2O), 3.708 (t, 8H, 2 × N(CH2CH2)2O), 3.504 (q, 4H, 2
× NHCH2CH2OH), 3.254 (q, 4H, 2 × NHCH2CH2OH). Anal.
(C18H18N8O4‚0.5H2O) C, H, N.
2,6-Bis(diethanolamino)-4,8-di-(N-methylpiperazino)pyrimido-
[5,4-d]pyrimidine (6). Compound 6 was prepared by general
procedure I with 1-methylpiperazine (0.47 mL, 4.2 mmol) at the
first step and with diethanolamine (3 mL, 30 mmol) at the second
step. Product was purified by flash silica gel chromatography (CH2-
Cl2/MeOH ) 1/1) to give a yellow powdery solid (273 mg, 51%).
Mp 199-200 °C; MS (ESI) m/z 535 (M + H)+, 557 (M + Na)+;
1H NMR (DMSO-d6) δ 4.719 (t, 4H, 4 × OH, disappeared after
D2O), 4.122 (br s, 8H, 2 × N(CH2CH2)2NCH3), 3.591 (br s, 16H,
2 × N(CH2CH2OH)2), 2.434 (t, 8H, 2 × N(CH2CH2)2NCH3), 2.219
(s, 6H, 2 × CH3). Anal. (C24H42N10O4) C, H, N.
2,6-Bis(diethanolamino)-4,8-di-(N-BOC-piperazino)pyrimido-
[5,4-d]pyrimidine (7). Compound 7 was prepared by general
procedure I with N-BOC-piperazine (0.78 g, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 5/1) to give a yellow powdery solid (304 mg, 43%). Mp
2,6-Diethanolamino-4,8-dipiperidinopyrimido[5,4-d]pyrimi-
dine (1). Compound 1 was prepared by general procedure I with
piperidine (0.41 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. The product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 16/1) to give a yellow powdery solid (162 mg, 39%). Mp 152-
1
223-224 °C; MS (ESI) m/z 707 (M + H)+, 729 (M + Na)+; H
1
153 °C; MS (ESI) m/z 417 (M + H)+, 439 (M + Na)+; H NMR
NMR (DMSO-d6) δ 4.749 (br t, 4H, 4 × OH, disappeared after
D2O), 4.121 (br s, 8H, 2 × N(CH2CH2)2N-BOC), 3.611 (s, 16H, 2
× N(CH2CH2OH)2), 3.489 (br s, 8H, 2 × N(CH2CH2)2N-BOC),
1.465 (s, 18H, 6 × CH3). Anal. (C32H54N10O8) C, H, N.
(DMSO-d6) δ 6.016 (t, 2H, 2 × NH, disappeared after D2O, J )
5.5 Hz), 4.606 (t, 2H, 2 × OH, disappeared after D2O, J ) 5.5
Hz), 4.057 (br s, 8H, 2 × N(CH2CH2)2CH2), 3.513 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.269 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 5.5 Hz, J2 ) 6 Hz), 1.641 (br d, 4H, 2 ×
N(CH2CH2)2CH2, J ) 4.5 Hz), 1.592 (br d, 8H, 2 × N(CH2CH2)2-
CH2, J ) 4.5 Hz). Anal. (C20H32N8O2) C, H, N.
2,6-Bis(diethanolamino)-4-piperazino-8-(N-Cbz-piperazino)-
pyrimido[5,4-d]pyrimidine (8). Compound 8 was prepared by
general procedure I with benylpiperazine 1-carboxylate (0.93 g,
4.2 mmol) at the first step and with diethanolamine (3 mL, 30
mmol) at the second step. Product was purified by flash silica gel
chromatography (CH2Cl2/MeOH ) 1.5/1) to give a yellow powdery
solid (77 mg, 12%). Mp 133-134 °C; MS (ESI) m/z 641 (M +
2,6-Bis(diethanolamino)-4,8-dipyrrolidinylpyrimido[5,4-d]py-
rimidine (2). Compound 2 was prepared by general procedure I
with pyrroline (0.35 mL, 4.2 mmol) at the first step and with dietha-
nolamine (3 mL, 30 mmol) at the second step. Product was purified
by flash silica gel chromatography (CH2Cl2/MeOH ) 15/1) to give
a yellow powdery solid (252 mg, 53%). Mp 212-213 °C; MS (ESI)
1
H)+, 663 (M + Na)+; H NMR (DMSO-d6) δ 7.388 (d, 3H, Ar-
H-3, Ar-H-4, Ar-H-5), 7.335 (m, 2H, Ar-H-2, Ar-H-6), 5.121
(s, 2H, PhCH2), 4.699 (t, 4H, 4 × OH, disappeared after D2O),

3912 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Lin and Buolamwini
4.119 (br s, 4H, N(CH2CH2)2NH), 4.031 (br s, 4H, N(CH2CH2)2-
NCbz), 3.570 (br s, 21H, 2 × N(CH2CH2OH)2, N(CH2CH2)2NH),
2.789 (br s, 4H, N(CH2CH2)2NCbz). Anal. (C30H44N10O6) C, H,
N.
step. Product was purified by flash silica gel chromatography
(hexane/acetone ) 2/1) to give a yellow powdery solid (246 mg,
43%). Mp 150-151 °C; MS (ESI) m/z 573 (M + H)+, 495 (M +
1
Na)+, 511 (M + K)+; H NMR (DMSO-d6) δ 5.751 (t, 2H, 2 ×
NH, disappeared after D2O, J ) 6 Hz), 4.592 (t, 2H, 2 × OH,
disappeared after D2O, J ) 5.5 Hz), 4.077 (br, s, 8H, 2 × N(CH2-
CH2CH2)2CH2), 3.508 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2
) 5.5 Hz), 3.256 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 6
Hz), 1.786 (br s, 8H, 2 × N(CH2CH2CH2)2CH2), 1.527 (br s, 8H,
2 × N(CH2CH2CH2)2CH2), 1.468 (br s, 4H, 2 × N(CH2CH2-
CH2)2CH2). Anal. (C24H40N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-dicyclohexylpyrimido[5,4-d]py-
rimidine (9). Compound 9 was prepared by general procedure II
with cyclehexylmagnesium chloride solution (2.0 M in diethyl ether,
1.05 mL, 2.1 mmol) at the first step and with diethanolamine (3
mL, 30 mmol) at the second step. Product was purified by flash
silica gel chromatography (CH2Cl2/MeOH ) 24/1) to give a yellow
powdery solid (226 mg, 45%). Mp 226-228 °C; MS (ESI) m/z
503 (M + H)+, 525 (M + Na)+; 1H NMR (DMSO-d6) δ 4.782 (t,
4H, 4 × OH, disappeared after D2O), 3.717 (br s, 8H, 2 × N(CH2-
CH2OH)2), 3.675 (br s, 8H, 2 × N(CH2CH2OH)2), 3.602 (m, 2H,
2 × CH(CH2CH2)2CH2), 1.892-1.815 (m, 8H, 2 × CH(CH2CH2)2-
CH2), 1.753 (d, 2H, 2 × CH(CH2CH2)2CHAHB), 1.589-1.397 (m,
8H, 2 × CH(CH2CH2)2CH2), 1.283 (m, 2H, 2 × CH(CH2CH2)2-
CHAHB). Anal. (C26H42N6O4) C, H, N.
2,6-Bis(diethanolamino)-4,8-dioctomethyleneimino-pyrimido-
[5,4-d]pyrimidine (15). Compound 15 was prepared by general
procedure I with octomethyleneimine (0.54 g, 4.2 mmol) at the
first step and with diethanolamine (3 mL, 30 mmol) at the second
step. Product was purified by flash silica gel chromatography
(hexane/acetone ) 2.5/1) to give a yellow powdery solid (65 mg,
1
11%). Mp 213-214 °C; MS (ESI) m/z 589 (M + H)+; H NMR
(DMSO-d6) δ 4.686 (t, 4H, 4 × OH, disappeared after D2O), 4.055
(br, s, 8H, 2 × N(CH2CH2CH2CH2)2), 3.602 (m, 16H, 2 ×
N(CH2CH2OH)2), 1.811 (s, 8H, 2 × N(CH2CH2CH2CH2)2), 1.648
(s, 8H, 2 × N(CH2CH2CH2CH2)2), 1.451 (s, 8H, 2 × N(CH2CH2-
CH2CH2)2). Anal. Calcd for C30H52N8O4: C 61.20, H 8.90, N 19.03.
Found: C 60.73, H 8.84, N 18.87.
2,6-Bis(diethanolamino)-4,8-diphenylpyrimido[5,4-d]pyrimi-
dine (10). Compound 10 was prepared by general procedure II with
phenylmagnesium chloride solution (2.0 M in tetrahydrofuran, 1.05
mL, 2.1 mmol) at the first step and with diethanolamine (3 mL, 30
mmol) at the second step. Product was purified by flash silica gel
chromatography (CH2Cl2/MeOH ) 9/1) to give a red powdery solid
(29 mg, 5.9%). Mp 208-209 °C; MS (ESI) m/z 491 (M + H)+,
2,6-Diethanolamino-4,8-dioctomethyleneiminopyrimido[5,4-
d]pyrimidine (16). Compound 16 was prepared by general
procedure I with octomethyleneimine (0.54 g, 4.2 mmol) at the
first step and with ethanolamine (3 mL, 50 mmol) at the second
step. Product was purified by flash silica gel chromatography
(hexane/acetone ) 2.5/1) to give a yellow powdery solid (60 mg,
12%). Mp 167 °C; MS (ESI) m/z 501 (M + H)+, 523 (M + Na)+;
1H NMR (DMSO-d6) δ 5.746 (t, 2H, 2 × NH, disappeared after
D2O, J ) 6 Hz), 4.601 (t, 2H, 2 × OH, disappeared after D2O, J
) 5.5 Hz), 4.039 (br, s, 8H, 2 × N(CH2CH2CH2CH2)2), 3.514 (q,
4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.284 (q, 4H,
2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 1.822 (br s, 8H, 2
× N(CH2CH2CH2CH2)2), 1.645 (br s, 8H, 2 × N(CH2CH2CH2-
CH2)2), 1.440 (s, 8H, 2 × N(CH2CH2CH2CH2)2). Anal. (C26H44N8O2)
C, H, N.
2,6-Bis(diethanolamino)-4,8-dinontropanopyrimido[5,4-d]py-
rimidine (17). Compound 17 was prepared by general procedure
I with nontropane54 (0.47 g, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
10/1) to give a yellow powdery solid (250 mg, 45%). Mp 244-
245 °C; MS (ESI) m/z 557 (M + H)+, 579 (M + Na)+; 1H NMR56
(DMSO-d6) δ 6.203 (br s, 2H), 4.908 (br s, 2H), 4.695 (t, 4H, 4 ×
OH, disappeared after D2O), 3.581 (br s, 16H, 2 × N(CH2CH2-
OH)2), 1.942-1.455 (series of br s, 20H). Anal. (C28H44N8O4) C,
H, N.
2,6-Diethanolamino-4,8-dinontropanopyrimido[5,4-d]pyrimi-
dine (18). Compound 18 was prepared by general procedure I with
nontropane54 (0.47 g, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
16/1) to give a yellow powdery solid compound 7 (128 mg, 27%).
Mp 254-255 °C; MS (ESI) m/z 469 (M + H)+, 491 (M + Na)+;
1H NMR57 (DMSO-d6) δ 6.319 (br s, 2H), 5.901 (t, 2H, 2 ×
NHCH2CH2OH, disappeared after D2O, J ) 5.5 Hz), 4.909 (br s,
2H), 4.584 (t, 2H, 2 × OH, disappeared after D2O, J ) 5.5 Hz),
3.515 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.243
(d, 4H, 2 × NHCH2CH2OH, J ) 5.5 Hz), 1.938-1.430 (series of
br s, 20H). Anal. (C24H36N8O2) C, H, N.
1
513 (M + Na)+; H NMR (DMSO-d6) δ 8.470 (m, 4H, 2 × Ar-
H-2, 2 × Ar-H-6), 7.557 (m, 6H, 2 × Ar-H-3, 2 × Ar-H-4, 2
× Ar-H-5), 4.805 (t, 4H, 4 × OH, disappeared after D2O, J ) 5
Hz), 3.793 (br s, 8H, 2 × N(CH2CH2OH)2), 3.708 (t, 8H, 2 ×
N(CH2CH2OH)2, J ) 5 Hz). Anal. (C26H30N6O4) C, H, N.
2,6-Bis(diethanolamino)-4,8-dihexamethyleneiminopyrimido-
[5,4-d]pyrimidine (11). Compound 11 was prepared by general
procedure I with hexamethyleneimine (0.48 mL, 4.2 mmol) at the
first step and with diethanolamine (3 mL, 30 mmol) at the second
step. Product was purified by flash silica gel chromatography
(hexane/acetone ) 2/1) to give a yellow powdery solid (213 mg,
1
40%). Mp 212-213 °C; MS (ESI) m/z 533 (M + H)+; H NMR
(DMSO-d6) δ 4.677 (br t, 4H, 4 × OH, disappeared after D2O),
4.129 (br, s, 8H, 2 × N(CH2CH2CH2)2), 3.572 (s, 16H, 2 ×
N(CH2CH2OH)2), 1.775 (br s, 8H, 2 × N(CH2CH2CH2)2), 1.511
(br s, 8H, 2 × N(CH2CH2CH2)2). Anal. (C26H44N8O4) C, H, N.
2,6-Diethanolamino-4,8-dihexamethyleneiminopyrimido[5,4-
d]pyrimidine (12). Compound 12 was prepared by general
procedure I with hexamethyleneimine (0.48 mL, 4.2 mmol) at the
first step and with ethanolamine (3 mL, 50 mmol) at the second
step. Product was purified by flash silica gel chromatography (CH2-
Cl2/MeOH ) 20/1) to give a yellow powdery solid (106 mg, 24%).
Mp 166-167 °C; MS (ESI) m/z 445 (M + H)+, 467 (M + Na)+;
1H NMR (DMSO-d6) δ 5.787 (q, 2H, 2 × NH, disappeared after
D2O, J ) 5.5 Hz), 4.592 (t, 2H, 2 × OH, disappeared after D2O,
J ) 5.5 Hz), 4.112 (br s, 8H, 2 × N(CH2CH2CH2)2), 3.514 (q, 4H,
2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.246 (t, 4H, 2 ×
NHCH2CH2OH, J1 ) 5.5 Hz, J2 ) 6 Hz), 1.776 (br s, 8H, 2 ×
N(CH2CH2CH2)2), 1.500 (br s, 8H, 2 × N(CH2CH2CH2)2). Anal.
(C22H36N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-diheptamethyleneiminopyrimido-
[5,4-d]pyrimidine (13). Compound 13 was prepared by general
procedure I with heptamethyleneimine (0.53 mL, 4.2 mmol) at the
first step and with diethanolamine (3 mL, 30 mmol) at the second
step. Product was purified by flash silica gel chromatography
(hexane/acetone ) 3/1) to give a yellow powdery solid (219 mg,
1
39%). Mp 204-205 °C; MS (ESI) m/z 561 (M + H)+; H NMR
(DMSO-d6) δ 4.681 (t, 4H, 4 × OH, disappeared after D2O), 4.091
(br, s, 8H, 2 × N(CH2CH2CH2)2CH2), 3.576 (br s, 16H, 2 ×
N(CH2CH2OH)2), 1.782 (br s, 8H, 2 × N(CH2CH2CH2)2CH2), 1.541
(br s, 8H, 2 × N(CH2CH2CH2)2CH2), 1.479 (br s, 4H, 2 × N(CH2-
CH2CH2)2CH2). Anal. (C28H48N8O4) C, H, N.
2,6-Bis(diethanolamino)-4,8-di-(4-azatricyclo[4.3.1.13,8]-
undecane)pyrimido[5,4-d]pyrimidine (19). Compound 19 was
prepared by general procedure I with 4-azatricyclo[4.3.1.13,8]-
undecane55 (0.64 g, 4.2 mmol) at the first step and with diethano-
lamine (3 mL, 30 mmol) at the second step. Product was purified
by flash silica gel chromatography (CH2Cl2/MeOH ) 20/1) to give
a yellow powdery solid (262 mg, 41%). Mp 252-253 °C; MS (ESI)
2,6-Diethanolamino-4,8-diheptamethyleneiminopyrimido[5,4-
d]pyrimidine (14). Compound 14 was prepared by general
procedure I with heptamethyleneimine (0.53 mL, 4.2 mmol) at the
first step and with ethanolamine (3 mL, 50 mmol) at the second
1
m/z 637 (M + H)+, 659 (M + Na)+; H NMR57 (DMSO-d6) δ

Dipyridamole Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3913
1
5.765 (br s, 2H), 4.680 (t, 4H, 4 × OH, disappeared after D2O),
3.890 (br s, 4H), 3.589 (br s, 16H, 2 × N(CH2CH2OH)2), 2.299
(br s, 2H), 1.959 (t, 4H), 1.929 (br s, 8H), 1.759-1.733 (br d, 4H),
1.604-1.516 (m, 8H). Anal. (C34H52N8O4‚0.5H2O) C, H, N.
2,6-Diethanolamino-4,8-di(4-azatricyclo[4.3.1.13,8]undecane)-
pyrimido[5,4-d]pyrimidine (20). Compound 20 was prepared by
general procedure I with 4-azatricyclo[4.3.1.13,8]undecane55 (0.64
g, 4.2 mmol) at the first step and with ethanolamine (3 mL, 50
mmol) at the second step. Product was purified by flash silica gel
chromatography (hexane/acetone ) 2.5/1) to give a yellow powdery
solid (198 mg, 36%). Mp 194-196 °C; MS (ESI) m/z 549 (M +
(M + K)+; H NMR (DMSO-d6) δ 4.707 (br s, 4H, 4 × OH,
disappeared after D2O), 3.846 (br s, 8H, 4 × CH2CH2CH3), 3.586
(br s, 16H, 2 × N(CH2CH2OH)2), 1.637 (q, 8H, 4 × CH2CH2CH3,
J ) 7.5 Hz), 0.878 (t, 12H, 4 × CH2CH2CH3, J ) 7.5 Hz). Anal.
(C26H48N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(dipropylamino)pyrimido[5,4-d]py-
rimidine (26). Compound 26 was prepared by general procedure
I with dipropylamine (0.58 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 12/1) to give a yellow powdery solid (85 mg, 19%). Mp 144-
1
1
H)+, 571 (M + Na)+; H NMR55 (DMSO-d6) δ 5.746 (t, 2H, 2 ×
145 °C; MS (ESI) m/z 449 (M + H)+, 471 (M + Na)+; H NMR
NH, disappeared after D2O, J ) 6 Hz), 5.720 (br s, 2H), 4.580 (t,
2H, 2 × OH, disappeared after D2O, J ) 5.5 Hz), 3.834 (br s, 4H),
3.505 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.289
(q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 6 Hz), 2.287 (br s,
2H), 1.951-1.926 (m, 12H), 1.793-1.767 (br d, 4H), 1.605-1.510
(m, 8H). Anal. (C30H44N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-di(dimethylamino)pyrimido[5,4-
d]pyrimidine (21). Compound 21 was prepared by general
procedure I with dimethylamine solution (2.0 M in tetrahydrofuran,
2.1 mL, 4.2 mmol) at the first step and with diethanolamine
(3 mL, 30 mmol) at the second step. Product was purified by flash
silica gel chromatography (CH2Cl2/MeOH ) 12/1) to give a yellow
powdery solid (174 mg, 41%). Mp 207-208 °C; MS (ESI) m/z
425 (M + H)+, 447 (M + Na)+; 1H NMR (DMSO-d6) δ 4.704 (t,
4H, 4 × OH, disappeared after D2O, J ) 5.5 Hz), 3.597 (m, 16H,
2 × N(CH2CH2OH)2, J ) 5.5 Hz), 3.409 (br s, 12H, 4 × CH3).
Anal. (C18H32N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(dimethylamino)pyrimido[5,4-d]py-
rimidine (22). Compound 22 was prepared by general procedure
I with dimethylamine solution (2.0 M in tetrahydrofuran, 2.1 mL,
4.2 mmol) at the first step and with ethanolamine (3 mL, 50 mmol)
at the second step. Product was purified by flash silica gel
chromatography (CH2Cl2/MeOH ) 9/1) to give a yellow powdery
solid (40 mg, 12%). Mp 159-161 °C; MS (ESI) m/z 337 (M +
H)+, 359 (M + Na)+; 1H NMR (DMSO-d6) δ 5.954 (br s, 2H, 2 ×
NH, disappeared after D2O), 4.634 (t, 2H, 2 × OH, disappeared
after D2O), 3.509 (q, 4H, 2 × NHCH2CH2OH), 3.371 (br s, 12H,
4 × CH3), 3.284 (t, 4H, 2 × NHCH2CH2OH). Anal. (C14H24N8O2)
C, H, N.
(DMSO-d6) δ 5.723 (t, 2H, 2 × NH, disappeared after D2O, J )
6 Hz), 4.618 (t, 2H, 2 × OH, disappeared after D2O, J ) 5.5 Hz),
3.837 (br s, 8H, 4 × CH2CH2CH3), 3.518 (q, 4H, 2 × NHCH2CH2-
OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.288 (q, 4H, 2 × NHCH2CH2OH,
J1 ) 6 Hz, J2 ) 6 Hz), 1.644 (m, 8H, 4 × CH2CH2CH3, J ) 7.5
Hz), 0.876 (t, 12H, 4 × CH2CH2CH3, J ) 7.5 Hz). Anal.
(C22H40N8O2) C, H, N.
2,6- Bis(diethanolamino)-4,8-di-(dibutylamino)pyrimido[5,4-
d]pyrimidine (27). Compound 27 was prepared by general
procedure I with dibutylamine (0.71 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 27/1) to give a yellow powdery solid (157 mg, 27%).
Mp 126-127 °C; MS (ESI) m/z 593 (M + H)+, 615 (M + Na)+;
1H NMR (DMSO-d6) δ 4.705 (t, 4H, 4 × OH, disappeared after
D2O, J ) 5 Hz), 3.876 (br s, 8H, 4 × CH2CH2CH2CH3), 3.581
(br s, 16H, 2 × N(CH2CH2OH)2), 1.591 (m, 8H, 4 × CH2CH2-
CH2CH3, J ) 8 Hz), 1.308 (m, 8H, 4 × CH2CH2CH2CH3, J1 ) 8
Hz, J2 ) 7.5 Hz), 0.903 (t, 12H, 4 × CH3, J ) 7.5 Hz). Anal.
(C30H56N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(dibutylamino)pyrimido[5,4-d]py-
rimidine (28). Compound 28 was prepared by general procedure
I with dibutylamine (0.71 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (hexane/acetone ) 5/1)
to give a yellow powdery solid (124 mg, 22%). Mp 129-130 °C;
MS (ESI) m/z 505 (M + H)+; 1H NMR (DMSO-d6) δ 5.687
(t, 2H, 2 × NH, disappeared after D2O, J ) 5.5 Hz), 4.615 (t, 2H,
2 × OH, disappeared after D2O, J ) 5.5 Hz), 3.870 (br s, 8H, 4 ×
CH2CH2CH2CH3), 3.505 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz,
J2 ) 5.5 Hz), 3.267 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 )
6 Hz), 1.596 (m, 8H, 4 × CH2CH2CH2CH3, J ) 7.5 Hz), 1.308
(m, 8H, 4 × CH2CH2CH2CH3, J ) 7.5 Hz), 0.907 (t, 12H, 4 ×
CH3, J ) 7.5 Hz). Anal. (C26H48N8O2‚0.5H2O) C, H, N.
2,6-Bis(diethanolamino)-4,8-di(diethylamino)pyrimido[5,4-d]-
pyrimidine (23). Compound 23 was prepared by general procedure
I with diethylamine (0.44 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 10/
1) to give a yellow powdery solid (187 mg, 39%). Mp 165-166
2,6-Bis(diethanolamino)-4,8-di(diisobutylamino)pyrimido[5,4-
d]pyrimidine (29). Compound 29 was prepared by general
procedure I with diisobutylamine (0.73 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 14/1) to give a yellow powdery solid (59 mg, 10%). Mp
1
°C; MS (ESI) m/z 481 (M + H)+, 503 (M + Na)+; H NMR
(DMSO-d6) δ 4.692 (t, 4H, 4 × OH, disappeared after D2O), 3.914
(br s, 8H, 4 × CH2CH3), 3.589 (br s, 16H, 2 × N(CH2CH2OH)2),
1.205 (t, 12H, 4 × CH2CH3). Anal. (C22H40N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(diethylamino)pyrimido[5,4-d]py-
rimidine (24). Compound 24 was prepared by general procedure
I with diethylamine (0.44 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 16/
1) to give a yellow powdery solid (122 mg, 31%). Mp 127 °C; MS
169-171 °C; MS (ESI) m/z 593 (M + H)+, 615 (M + Na)+; H
1
NMR (DMSO-d6) δ 4.669 (br s, 4H, 4 × OH, disappeared after
D2O), 3.808 (br s, 8H, 4 × CH2CH(CH3)2), 3.528 (br s, 16H, 2 ×
N(CH2CH2OH)2), 1.890 (br s, 4H, 4 × CH2CH(CH3)2), 0.752
(br s, 24H, 4 × CH2CH(CH3)2). Anal. (C30H56N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(diisobutylamino)pyrimido[5,4-d]-
pyrimidine (30). Compound 30 was prepared by general procedure
I with diisobutylamine (0.73 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 18/1) to give a yellow powdery solid (212 mg, 42%). Mp
1
(ESI) m/z 393 (M + H)+, 415 (M + Na)+; H NMR (DMSO-d6)
δ 5.787 (t, 2H, 2 × NH, disappeared after D2O, J ) 5.5 Hz), 4.599
(t, 2H, 2 × OH, disappeared after D2O, J ) 6 Hz), 3.902 (br s,
8H, 4 × CH2CH3), 3.506 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz,
J2 ) 6 Hz), 3.265 (q, 4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 )
5.5 Hz), 1.198 (t, 12H, 4 × CH2CH3). Anal. (C18H32N8O2) C, H,
N.
154 °C; MS (ESI) m/z 505 (M + H)+, 527 (M + Na)+; H NMR
1
2,6-Bis(diethanolamino)-4,8-di(dipropylamino)pyrimido[5,4-
d]pyrimidine (25). Compound 25 was prepared by general
procedure I with dipropylamine (0.58 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 18/1) to give a yellow powdery solid (81 mg, 15%). Mp
150-151 °C; MS (ESI) m/z 537 (M + H)+, 559 (M + Na)+, 575
(DMSO-d6) δ 5.821 (t, 2H, 2 × NH, disappeared after D2O, J )
5.5 Hz), 4.634 (t, 2H, 2 × OH, disappeared after D2O, J ) 5.5
Hz), 3.881 (br s, 8H, 4 × CH2CH(CH3)2), 3.532 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.276 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 1.983 (m, 4H, 4 ×
CH2CH(CH3)2, J ) 6.5 Hz), 0.840 (d, 24H, 4 × CH2CH(CH3)2, J
) 6.5 Hz). Anal. (C26H48N8O2‚0.5H2O) C, H, N.

3914 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Lin and Buolamwini
1
2,6-Bis(diethanolamino)-4,8-di(dipentylamino)pyrimido[5,4-
d]pyrimidine (31). Compound 31 was prepared by general
procedure I with dipentylamine (0.85 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 20/1) to give a yellow powdery solid (145 mg, 22%).
Mp 130-131 °C; MS (ESI) m/z 649 (M + H)+, 671 (M + Na)+;
1H NMR (DMSO-d6) δ 4.706 (t, 4H, 4 × OH, disappeared after
D2O), 3.865 (br s, 8H, 4 × CH2(CH2)3CH3), 3.578 (q, 16H, 2 ×
N(CH2CH2OH)2), 1.604 (m, 8H, 4 × CH2CH2(CH2)2CH3), 1.332-
1.229 (m, 16H, 4 × CH2CH2(CH2)2CH3), 0.869 (t, 12H, 4 × CH3).
Anal. (C34H64N8O4‚0.5H2O) C, H, N.
Na)+; H NMR (DMSO-d6) δ 5.905 (t, 2H, 2 × NHCH2CH2OH,
disappeared after D2O), 4.598 (t, 2H, 2 × NHCH2CH2OH,
disappeared after D2O, J ) 5 Hz), 4.125 (br s, 8H, 4 × CH2CH2-
OCH3), 3.595 (t, 8H, 4 × CH2CH2OCH3), 3.496 (q, 4H, 2 ×
NHCH2CH2OH, J ) 5 Hz), 3.257 (s, 12H, 4 × CH3), 3.235 (br s,
4H, 2 × NHCH2CH2OH). Anal. (C22H40N8O6) C, H, N.
2,6-Bis(diethanolamino)-4,8-bis(dibenzylamino)pyrimido[5,4-
d]pyrimidine (37). Compound 37 was prepared by general
procedure I with dibenzylamine (0.83 g, 4.2 mmol) at the first step
and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 16/1) to give a yellow powdery solid compound 9 (332
mg, 46%). Mp 199 °C; MS (ESI) m/z 729 (M + H)+, 751 (M +
2,6-Diethanolamino-4,8-di(dipentylamino)pyrimido[5,4-d]py-
rimidine (32). Compound 32 was prepared by general procedure
I with dipentylamine (0.85 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (hexane/acetone )
15/1) to give a yellow powdery solid (26 mg, 4.6%). Mp 128-
1
Na)+; H NMR (DMSO-d6) δ 7.324 (t, 8H, 4 × Ar-H-3, 4 ×
Ar-H-5, J1 ) 7.5 Hz, J2 ) 7 Hz), 7.261-7.224 (m, 12H, 4 ×
Ar-H-2, 4 × Ar-H-6, 4 × Ar-H-4), 5.317 (br s, 8H, 4 × CH2-
Ph), 4.564 (t, 4H, 4 × OH, disappeared after D2O, J ) 5 Hz),
3.259 (br d, 16H, 2 × N(CH2CH2OH)2). Anal. (C42H48N8O4) C,
H, N.
1
129 °C; MS (ESI) m/z 561 (M + H)+, 583 (M + Na)+; H NMR
(DMSO-d6) δ 5.659 (t, 2H, 2 × NH, disappeared after D2O, J )
5.5 Hz), 4.619 (t, 2H, 2 × OH, disappeared after D2O, J ) 5.5
Hz), 3.860 (br s, 8H, 4 × CH2(CH2)3CH3), 3.504 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.269 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 1.609 (m, 8H, 4 ×
CH2CH2(CH2)2CH3, J1 ) 7.5 Hz, J2 ) 7 Hz), 1.255 (m, 16H, 4 ×
CH2CH2(CH2)2CH3), 0.871 (t, 12H, 4 × CH3, J ) 7 Hz). Anal.
(C30H56N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-di(diisopentylamino)pyrimido-
[5,4-d]pyrimidine (33). Compound 33 was prepared by general
procedure I with diisopentylamine (0.86 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (hexane/
acetone ) 7/1) to give a yellow powdery solid (156 mg, 24%).
Mp 129 °C; MS (ESI) m/z 671 (M + Na)+; 1H NMR (DMSO-d6)
δ 4.705 (t, 4H, 4 × OH, disappeared after D2O, J ) 5.5 Hz), 3.864
(br s, 8H, 4 × CH2CH2CH(CH3)2), 3.578 (br s, 16H, 2 ×
N(CH2CH2OH)2), 1.603 (m, 8H, 4 × CH2CH2CH(CH3)2), 1.301
(m, 16H, 4 × CH2CH2CH(CH3)2, 4 × CH3), 0.868 (t, 12H, 4 ×
CH3, J ) 7 Hz). Anal. (C34H64N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(diisopentylamino)pyrimido[5,4-d]-
pyrimidine (34). Compound 34 was prepared by general procedure
I with diisopentylamine (0.86 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (hexane/acetone
) 15/1) to give a yellow powdery solid (125 mg, 22%). Mp 97-
98 °C; MS (ESI) m/z 561 (M + H)+; 1H NMR (DMSO-d6) δ 5.727
(m, 2H, 2 × NH, disappeared after D2O, J ) 5.5 Hz), 4.621 (m,
2H, 2 × OH, disappeared after D2O, J ) 5.5 Hz), 3.858 (br d, 8H,
4 × CH2CH2CH(CH3)2), 3.510 (q, 4H, 2 × NHCH2CH2OH, J1 )
6 Hz, J2 ) 5.5 Hz), 3.269 (q, 4H, 2 × NHCH2CH2OH, J1 ) 5.5
Hz, J2 ) 6 Hz), 1.841-1.335 (m, 8H, 4 × CH2CH2CH(CH3)2),
1.321-1.058 (m, 12H, 4 × CH3), 0.884-0.778 (m, 16H, 4 × CH2-
CH2CH(CH3)2), 4 × CH3). Anal. (C30H56N8O2) C, H, N.
2,6-Diethanolamino-4,8-bis(dibenzylamino)pyrimido[5,4-d]-
pyrimidine (38). Compound 38 was prepared by general procedure
I with dibenzylamine (0.83 g, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 20/
1) to give a yellow powdery solid compound 8 (125 mg, 20%).
Mp 215-216 °C; MS (ESI) m/z 641 (M + H)+, 663 (M + Na)+;
1H NMR (DMSO-d6) δ 7.327 (t, 8H, 4 × Ar-H-3, 4 × Ar-H-5,
J1 ) 7 Hz, J2 ) 7.5 Hz), 7.289 (d, 8H, 4 × Ar-H-2, 4 × Ar-
H-6, J ) 7 Hz), 7.247 (t, 4H, 4 × Ar-H-4, J1 ) 7.5 Hz, J2 ) 7
Hz), 5.970 (t, 2H, 2 × NHCH2CH2OH, disappeared after D2O, J
) 5.5 Hz), 4.279 (br s, 8H, 4 × CH2Ph), 4.419 (t, 2H, 2 × NHCH2-
CH2OH, disappeared after D2O, J ) 5.5 Hz), 3.243 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.927(br s, 4H, 2 ×
NHCH2CH2OH). Anal. (C38H40N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-diaminopyrimido[5,4-d]pyrimi-
dine (39). Compound 39 was prepared by general procedure I with
ammonia solution (7 N in methanol, 0.6 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 7/1) to give a yellow powdery solid (63 mg, 17%). Mp
1
225-226 °C; MS (ESI) m/z 369 (M + H)+, 391 (M + Na)+; H
NMR (DMSO-d6) δ 7.194 (br s, 2H, 2 × NHAHB, disappeared after
D2O), 6.663 (br s, 2H, 2 × NHAHB, disappeared after D2O), 4.675
(t, 4H, 4 × OH, disappeared after D2O, J ) 4.5 Hz), 3.625 (t, 8H,
2 × N(CH2CH2OH)2, J ) 5 Hz), 3.584 (t, 8H, 2 × N(CH2CH2-
OH)2, J1 ) 4.5 Hz, J2 ) 5 Hz). Anal. Calcd for C14H24N8O4: C
45.64, H 6.57, N 30.42. Found: C 45.29, H 6.73, N 29.58.
2,6-Bis(diethanolamino)-4,8-dimethylaminopyrimido[5,4-d]-
pyrimidine (40). Compound 40 was prepared by general procedure
I with methylamine solution (2 M in tetrahydrofuran, 2.1 mL, 4.2
mmol) at the first step and with diethanolamine (3 mL, 30 mmol)
at the second step. Product was purified by flash silica gel
chromatography (CH2Cl2/MeOH ) 7/1) to give a yellow powdery
solid (190 mg, 48%). Mp 213-214 °C; MS (ESI) m/z 397 (M +
H)+, 419 (M + Na)+, 435 (M + K)+; 1H NMR (DMSO-d6) δ 7.154
(q, 2H, 2 × NHCH3, disappeared after D2O, J ) 4.5 Hz), 4.675
(br s, 4H, 4 × OH, disappeared after D2O), 3.676 (t, 8H, 2 ×
N(CH2CH2OH)2), 3.619 (t, 8H, 2 × N(CH2CH2OH)2), 2.949
(d, 6H, 2 × NHCH3, J ) 4.5 Hz). Anal. (C16H28N8O4) C, H, N.
2,6-Diethanolamino-4,8-dimethylaminopyrimido[5,4-d]pyri-
midine (41). Compound 41 was prepared by general procedure I
with methylamine solution (2 M in tetrahydrofuran, 2.1 mL, 4.2
mmol) at the first step and with ethanolamine (3 mL, 50 mmol) at
the second step. Product was purified by flash silica gel chroma-
tography (CH2Cl2/MeOH ) 15/1) to give a yellow powdery solid
(176 mg, 57%). Mp 212 °C; MS (ESI) m/z 309 (M + H)+, 331 (M
+ Na)+; 1H NMR (DMSO-d6) δ 7.120 (q, 2H, 2 × NHCH3,
disappeared after D2O, J ) 5 Hz), 5.947 (t, 2H, 2 × NHCH2CH2-
OH, disappeared after D2O, J ) 6 Hz), 4.610 (t, 2H, 2 × NHCH2-
CH2OH, disappeared after D2O, J ) 5.5 Hz), 3.530 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.402 (q, 4H, 2 ×
2,6-Bis(diethanolamino)-4,8-di(bis(2-methoxyethyl)amino)py-
rimido[5,4-d]pyrimidine (35). Compound 35 was prepared by
general procedure I with bis(2-methoxyethyl)amine (0.65 mL, 4.2
mmol) at the first step and with diethanolamine (3 mL, 30 mmol)
at the second step. Product was purified by flash silica gel
chromatography (CH2Cl2/MeOH ) 10/1) to give a yellow powdery
solid (260 mg, 43%). Mp 104-105 °C; MS (ESI) m/z 601 (M +
H)+, 623 (M + Na)+; 1H NMR (DMSO-d6) δ 4.685 (br s, 4H, 4 ×
OH, disappeared after D2O), 4.145 (br s, 8H, 4 × CH2CH2OCH3),
3.594 (t, 8H, 4 × CH2CH2OCH3), 3.557 (br s, 16H, 2 × N(CH2CH2-
OH)2), 3.260 (s, 12H, 4 × CH3). Anal. (C26H48N8O8) C, H, N.
2,6-Diethanolamino-4,8-di(bis(2-methoxyethyl)amino)pyrimido-
[5,4-d]pyrimidine (36). Compound 36 was prepared by general
procedure I with bis(2-methoxyethyl)amine (0.65 mL, 4.2 mmol)
at the first step and with ethanolamine (3 mL, 50 mmol) at the
second step. Product was purified by flash silica gel chromatography
(CH2Cl2/MeOH ) 14/1) to give a yellow powdery solid (100 mg,
20%). Mp 68-69 °C; MS (ESI) m/z 513 (M + H)+, 535 (M +

Dipyridamole Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3915
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 6 Hz), 2.920 (d, 6H, 2 × NHCH3,
J ) 5 Hz). Anal. (C12H20N8O2) C, H, N.
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 14/1) to give a yellow powdery solid (165 mg, 45%). Mp
167 °C; MS (ESI) m/z 365 (M + H)+, 387 (M + Na)+, 403 (M +
2,6-Bis(diethanolamino)-4,8-diethylaminopyrimido[5,4-d]py-
rimidine (42). Compound 42 was prepared by general procedure
I with ethylamine solution (2 M in tetrahydrofuran, 2.1 mL, 4.2
mmol) at the first step and with diethanolamine (3 mL, 30 mmol)
at the second step. Product was purified by flash silica gel
chromatography (CH2Cl2/MeOH ) 10/1) to give a yellow powdery
solid (174 mg, 41%). Mp 188-189 °C; MS (ESI) m/z 425 (M +
H)+, 447 (M + Na)+, 463 (M + K)+; 1H NMR (DMSO-d6) δ 7.151
(br s, 2H, 2 × NHCH2CH3, disappeared after D2O), 4.690 (s, 4H,
4 × OH, disappeared after D2O), 3.668 (br s, 8H, 2 × N(CH2CH2-
OH)2), 3.622 (br s, 8H, 2 × N(CH2CH2OH)2), 3.469 (br s, 4H, 2
× CH2CH3), 1.190 (t, 6H, 2 × CH2CH3). Anal. (C18H32N8O4) C,
H, N.
2,6-Diethanolamino-4,8-diethylaminopyrimido[5,4-d]pyrimi-
dine (43). Compound 43 was prepared by general procedure I with
ethylamine solution (2 M in tetrahydrofuran, 2.1 mL, 4.2 mmol) at
the first step and with ethanolamine (3 mL, 50 mmol) at the second
step. Product was purified by flash silica gel chromatography (CH2-
Cl2/MeOH ) 24/1) to give a yellow powdery solid (205 mg, 61%).
Mp 175-176 °C; MS (ESI) m/z 337 (M + H)+, 357 (M + Na)+,
375 (M + K)+; 1H NMR (DMSO-d6) δ 7.057 (br s, 2H, 2 ×
NHCH2CH3, disappeared after D2O), 5.941 (t, 2H, 2 × NHCH2-
CH2OH, disappeared after D2O, J ) 6 Hz), 4.621 (t, 2H, 2 ×
NHCH2CH2OH, disappeared after D2O, J ) 5.5 Hz), 3.532 (q, 4H,
2 × NHCH2CH2OH, J ) 5.5 Hz), 3.442 (m, 4H, 2 × CH2CH3, J
) 6 Hz), 3.392 (q, 4H, 2 × NHCH2CH2OH, J ) 6 Hz), 1.174 (t,
6H, 2 × CH2CH3, J ) 6 Hz). Anal. (C14H24N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-dipropylaminopyrimido[5,4-d]-
pyrimidine (44). Compound 44 was prepared by general procedure
I with propylamine (0.35 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 8/1)
to give a yellow powdery solid (217 mg, 48%). Mp 145-146 °C;
MS (ESI) m/z 453 (M + H)+, 475 (M + Na)+; 1H NMR (DMSO-
d6) δ 7.154 (t, 2H, 2 × NHCH2CH2CH3, disappeared after D2O),
4.701 (t, 4H, 4 × OH, disappeared after D2O), 3.670 (br d, 8H, 2
× N(CH2CH2OH)2), 3.631 (t, 8H, 2 × N(CH2CH2OH)2), 3.400 (m,
4H, 2 × CH2CH2CH3), 1.607 (m, 4H, 2 × CH2CH2CH3, J ) 7.5
Hz), 0.910 (t, 6H, 2 × CH2CH2CH3, J ) 7.5 Hz). Anal.
(C20H36N8O4) C, H, N.
1
K)+; H NMR (DMSO-d6) δ 6.590 (d, 2H, 2 × NHCH(CH3)2,
disappeared after D2O), 6.008 (t, 2H, 2 × NHCH2CH2OH,
disappeared after D2O, J ) 6 Hz), 4.646 (br s, 2H, 2 × NHCH2-
CH2OH, disappeared after D2O), 4.241 (m, 2H, 2 × NHCH(CH3)2,
J ) 6.5 Hz), 3.535 (br s, 4H, 2 × NHCH2CH2OH), 3.382 (m, 4H,
2 × NHCH2CH2OH, J ) 6 Hz), 1.235 (d, 12H, 2 × NHCH(CH3)2
J ) 6.5 Hz). Anal. (C16H28N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-dibutylaminopyrimido[5,4-d]py-
rimidine (48). Compound 48 was prepared by general procedure
I with butylamine (0.42 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
10/1) to give a yellow powdery solid (82 mg, 17%). Mp 117-
118 °C; MS (ESI) m/z 481 (M + H)+, 503 (M + Na)+, 519 (M +
1
K)+; H NMR (DMSO-d6) δ 7.135 (br s, 2H, 2 × NHCH2CH2-
CH2CH3, disappeared after D2O), 4.693 (br s, 4H, 4 × OH,
disappeared after D2O), 3.658 (br s, 8H, 2 × N(CH2CH2OH)2),
3.617 (br s, 8H, 2 × N(CH2CH2OH)2), 3.431 (br s, 4H, 2 × NHCH2-
CH2CH2CH3), 1.580 (m, 4H, 2 × NHCH2CH2CH2CH3, J ) 7 Hz),
1.350 (m, 4H, 2 × NHCH2CH2CH2CH3, J1 ) 7 Hz, J2 ) 7.5 Hz),
0.919 (t, 6H, 2 × NHCH2CH2CH2CH3, J ) 7.5 Hz). Anal. Calcd
for C22H40N8O4‚0.5H2O: C 53.86, H 8.63, N 22.84. Found: C
54.32, H 8.34, N 22.72.
2,6-Diethanolamino-4,8-dibutylaminopyrimido[5,4-d]pyrimi-
dine (49). Compound 49 was prepared by general procedure I with
butylamine (0.42 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
14/1) to give a yellow powdery solid (70 mg, 18%). Mp 127-
1
128 °C; MS (ESI) m/z 393 (M + H)+, 415 (M + Na)+; H NMR
(DMSO-d6) δ 7.018 (br s, 2H, 2 × NHCH2CH2CH2CH3, disap-
peared after D2O), 5.938 (t, 2H, 2 × NHCH2CH2OH, disappeared
after D2O, J ) 5.5 Hz), 4.618 (br s, 2H, 2 × NHCH2CH2OH,
disappeared after D2O), 3.529 (m, 4H, 2 × NHCH2CH2OH), 3.404
(m, 4H, 2 × NHCH2CH2CH2CH3, J ) 7 Hz), 3.380 (m, 4H, 2 ×
NHCH2CH2OH, J ) 5.5 Hz), 1.556 (m, 4H, 2 × NHCH2CH2CH2-
CH3, J1 ) 7 Hz, J2 ) 7.5 Hz), 1.345 (m, 4H, 2 × NHCH2CH2CH2-
CH3, J1 ) 7.5 Hz, J2 ) 7 Hz), 0.921 (t, 6H, 2 × NHCH2CH2-
CH2CH3, J ) 7 Hz). Anal. (C18H32N8O2) C, H, N.
2,6-Diethanolamino-4,8-dipropylaminopyrimido[5,4-d]pyri-
midine (45). Compound 45 was prepared by general procedure I
with propylamine (0.35 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
10/1) to give a yellow powdery solid (196 mg, 54%). Mp 147-
2,6-Bis(diethanolamino)-4,8-diisobutylaminopyrimido[5,4-d]-
pyrimidine (50). Compound 50 was prepared by general procedure
I with isobutylamine (0.36 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 9/1)
to give a yellow powdery solid (58 mg, 12%). Mp 162-163 °C;
MS (ESI) m/z 481 (M + H)+, 503 (M + Na)+, 519 (M + K)+; 1H
NMR (DMSO-d6) δ 7.145 (br s, 2H, 2 × NHCH2CH(CH3)2,
disappeared after D2O), 4.703 (br s, 4H, 4 × OH, disappeared after
D2O), 3.649 (d, 8H, 2 × N(CH2CH2OH)2), 3.619 (d, 8H, 2 ×
N(CH2CH2OH)2), 3.278 (t, 4H, 2 × NHCH2CH(CH3)2, J ) 6.5
Hz), 1.957 (m, 2H, 2 × NHCH2CH(CH3)2, J1 ) 6.5 Hz, J2 ) 7
Hz), 0.917 (d, 12H, 2 × NHCH2CH(CH3)2, J ) 7 Hz). Anal.
(C22H40N8O4) C, H, N.
2,6-Diethanolamino-4,8-diisobutylaminopyrimido[5,4-d]pyri-
midine (51). Compound 51 was prepared by general procedure I
with isobutylamine (0.36 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
12/1) to give a yellow powdery solid (78 mg, 20%). Mp 141-
142 °C; MS (ESI) m/z 393 (M + H)+, 415 (M + Na)+, 431 (M +
K)+; 1H NMR (DMSO-d6) δ 7.019 (t, 2H, 2 × NHCH2CH(CH3)2,
disappeared after D2O), 5.980 (t, 2H, 2 × NHCH2CH2OH,
disappeared after D2O, J ) 5.5 Hz), 4.631 (t, 2H, 2 × NHCH2-
CH2OH, disappeared after D2O, J ) 5.5 Hz), 3.537 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.377 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 5.5 Hz, J2 ) 6 Hz), 3.255 (t, 4H, 2 × NHCH2-
CH(CH3)2, J ) 6.5 Hz), 1.954 (m, 2H, 2 × NHCH2CH(CH3)2, J1
1
148 °C; MS (ESI) m/z 365 (M + H)+, 387 (M + Na)+; H NMR
(DMSO-d6) δ 7.055 (br s, 2H, 2 × NHCH2CH2CH3, disappeared
after D2O), 5.957 (br s, 2H, 2 × NHCH2CH2OH, disappeared after
D2O), 4.636 (br s, 2H, 2 × NHCH2CH2OH, disappeared after D2O),
3.544 (br s, 4H, 2 × NHCH2CH2OH), 3.376 (br s, 8H, 2 × NHCH2-
CH2OH, 2 × CH2CH2CH3), 1.591 (m, 4H, 2 × CH2CH2CH3, J )
7.5 Hz), 0.901 (t, 6H, 2 × CH2CH2CH3, J ) 7.5 Hz). Anal.
(C16H28N8O2) C, H, N.
2,6-Bis(diethanolamino)-4,8-diisopropylaminopyrimido[5,4-
d]pyrimidine (46). Compound 46 was prepared by general
procedure I with isopropylamine (0.36 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 8/1) to give a yellow powdery solid (201 mg, 44%). Mp
1
188-190 °C; MS (ESI) m/z 453 (M + H)+, 475 (M + Na)+; H
NMR (DMSO-d6) δ 6.547 (d, 2H, 2 × NHCH(CH3)2, disappeared
after D2O), 4.706 (br s, 4H, 4 × OH, disappeared after D2O), 4.218
(m, 2H, 2 × NHCH(CH3)2), 3.662 (t, 8H, 2 × N(CH2CH2OH)2),
3.620 (br s, 8H, 2 × N(CH2CH2OH)2), 1.264 (d, 12H, 2 × NHCH-
(CH3)2). Anal. (C20H36N8O4) C, H, N.
2,6-Diethanolamino-4,8-diisopropylaminopyrimido[5,4-d]py-
rimidine (47). Compound 47 was prepared by general procedure
I with isopropylamine (0.36 mL, 4.2 mmol) at the first step and

3916 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Lin and Buolamwini
) 6.5 Hz, J2 ) 7 Hz), 0.914 (d, 12H, 2 × NHCH2CH(CH3)2, J )
7 Hz). Anal. Calcd for C18H32N8O2: C 55.08, H 8.22, N 28.55.
Found: C 54.46, H 8.15, N 28.22.
2,6-Diethanolamino-4,8-diisopentylaminopyrimido[5,4-d]py-
rimidine (57). Compound 57 was prepared by general procedure
I with isopentylamine (0.49 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 30/1) to give a yellow powdery solid (235 mg, 56%). Mp 132-
2,6-Bis(diethanolamino)-4,8-di(tert-butylamino)pyrimido[5,4-
d]pyrimidine (52). Compound 52 was prepared by general
procedure I with tert-butylamine (0.44 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 6/1) to give a yellow powdery solid (173 mg, 36%). Mp
1
133 °C; MS (ESI) m/z 421 (M + H)+, 443 (M + Na)+; H NMR
(DMSO-d6) δ 6.999 (br s, 2H, 2 × NHCH2CH2CH(CH3)2, disap-
peared after D2O), 5922 (t, 2H, 2 × NHCH2CH2OH, disappeared
after D2O), 4.621 (br s, 2H, 2 × NHCH2CH2OH, disappeared after
D2O), 3.538 (q, 4H, 2 × NHCH2CH2OH), 3.422 (q, 4H, 2 ×
NHCH2CH2OH), 3.384 (m, 4H, 2 × NHCH2CH2CH(CH3)2), 1.614
(m, 2H, 2 × NHCH2CH2CH(CH3)2), 1.490 (m, 4H, 2 × NHCH2CH2-
CH(CH3)2), 0.931 (d, 12H, 2 × NHCH2CH2CH(CH3)2). Anal.
(C20H36N8O2‚H2O) C, H, N.
1
244-245 °C; MS (ESI) m/z 481 (M + H)+, 503 (M + Na)+; H
NMR (DMSO-d6) δ 6.475 (s, 2H, 2 × NHC(CH3)3, disappeared
after D2O), 4.748 (t, 4H, 4 × OH, disappeared after D2O), 3.643
(br s, 16H, 2 × N(CH2CH2OH)2), 1.474 (s, 18H, 2 × NHC(CH3)3).
Anal. (C22H40N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(tert-butylamino)pyrimido[5,4-d]-
pyrimidine (53). Compound 53 was prepared by general
procedure I with tert-butylamine (0.44 mL, 4.2 mmol) at the first
step and with ethanolamine (3 mL, 50 mmol) at the second
step. Product was purified by flash silica gel chromatography
(CH2Cl2/MeOH ) 9/1) to give a yellow powdery solid (190 mg,
48%). Mp 154 °C; MS (ESI) m/z 393 (M + H)+, 415 (M + Na)+;
1H NMR (DMSO-d6) δ 6.456 (s, 2H, 2 × NHC(CH3)3, disap-
peared after D2O), 6.135 (t, 2H, 2 × NHCH2CH2OH, disappeared
after D2O, J ) 6 Hz), 4.652 (br s, 2H, 2 × NHCH2CH2OH,
disappeared after D2O), 3.536 (q, 4H, 2 × NHCH2CH2OH, J )
5.5 Hz), 3.338 (q, 4H, 2 × NHCH2CH2OH, J1 ) 5.5 Hz, J2 ) 6
Hz), 1.477 (s, 18H, 2 × NHC(CH3)3). Anal. (C18H32N8O2) C, H,
N.
2,6-Bis(diethanolamino)-4,8-di(tert-amylamino)pyrimido[5,4-
d]pyrimidine (58). Compound 58 was prepared by general
procedure I with tert-amylamine (0.49 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 14/1) to give a yellow powdery solid (245 mg, 48%).
Mp 212-213 °C; MS (ESI) m/z 509 (M + H)+, 531 (M + Na)+,
1
547 (M + K)+; H NMR (DMSO-d6) δ 6.432 (s, 2H, 2 × NHC-
(CH3)2CH2CH3, disappeared after D2O), 4.757 (d, 4H, 4 × OH,
disappeared after D2O), 3.637 (s, 16H, 2 × N(CH2CH2OH)2), 1.841
(q, 4H, 2 × NHC(CH3)2CH2CH3, J ) 7.5 Hz), 1.415 (s, 12H, 2 ×
NHC(CH3)2CH2CH3), 0.833 (t, 6H, 2 × NHC(CH3)2CH2CH3, J )
7.5 Hz). Anal. (C24H44N8O4) C, H, N.
2,6-Bis(diethanolamino)-4,8-diamylaminopyrimido[5,4-d]py-
rimidine (54). Compound 54 was prepared by general procedure
I with amylamine (0.49 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
12/1) to give a yellow powdery solid (190 mg, 37%). Mp 128 °C;
MS (ESI) m/z 509 (M + H)+, 531 (M + Na)+, 547 (M + K)+; 1H
NMR (DMSO-d6) δ 7.139 (br s, 2H, 2 × NHCH2CH2(CH2)2CH3,
disappeared after D2O), 4.690 (br s, 4H, 4 × OH, disappeared after
D2O), 3.662 (br s, 8H, 2 × N(CH2CH2OH)2), 3.624 (d, 8H, 2 ×
N(CH2CH2OH)2), 3.423 (br s, 4H, 2 × NHCH2CH2(CH2)2CH3),
1.598 (m, 4H, 2 × NHCH2CH2(CH2)2CH3), 1.320 (m, 8H, 2 ×
NHCH2CH2(CH2)2CH3), 0.882 (t, 6H, 2 × NHCH2CH2(CH2)2CH3).
Anal. (C24H44N8O4) C, H, N.
2,6-Diethanolamino-4,8-di(tert-amylamino)pyrimido[5,4-d]py-
rimidine (59). Compound 59 was prepared by general procedure
I with tert-amylamine (0.49 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 18/1) to give a yellow powdery solid (196 mg, 47%). Mp 167-
1
168 °C; MS (ESI) m/z 421 (M + H)+, 443 (M + Na)+; H NMR
(DMSO-d6) δ 6.391 (s, 2H, 2 × NHC(CH3)2CH2CH3, disappeared
after D2O), 6.143 (t, 2H, 2 × NHCH2CH2OH, disappeared after
D2O, J ) 6 Hz), 4.653 (br s, 2H, 2 × NHCH2CH2OH, disappeared
after D2O), 3.552 (q, 4H, 2 × NHCH2CH2OH, J ) 5.5 Hz), 3.328
(q, 4H, 2 × NHCH2CH2OH, J1 ) 5.5 Hz, J2 ) 6 Hz), 1.881 (q,
4H, 2 × NHC(CH3)2CH2CH3, J ) 7.5 Hz), 1.414 (s, 12H, 2 ×
NHC(CH3)2CH2CH3), 0.814 (t, 6H, 2 × NHC(CH3)2CH2CH3, J )
7.5 Hz). Anal. Calcd for C20H36N8O2‚0.5H2O: C 55.92, H 8.68, N
26.09. Found: C 56.02, H 8.67, N 25.62.
2,6-Diethanolamino-4,8-diamylaminopyrimido[5,4-d]pyrimi-
dine (55). Compound 55 was prepared by general procedure I with
amylamine (0.49 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH )
17/1) to give a yellow powdery solid (155 mg, 37%). Mp 147-
2,6-Bis(diethanolamino)-4,8-dicyclopropylaminopyrimido[5,4-
d]pyrimidine (60). Compound 60 was prepared by general
procedure I with cyclopropylamine (0.31 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 14/1) to give a yellow powdery solid (220 mg, 49%).
1
148 °C; MS (ESI) m/z 421 (M + H)+, 443 (M + Na)+; H NMR
(DMSO-d6) δ 7.032 (t, 2H, 2 × NHCH2CH2(CH2)2CH3, disappeared
after D2O), 5.931 (t, 2H, 2 × NHCH2CH2OH, disappeared after
D2O), 4.620 (t, 2H, 2 × NHCH2CH2OH, disappeared after D2O),
3.530 (q, 4H, 2 × NHCH2CH2OH), 3.382 (m, 8H, 2 × NHCH2-
CH2(CH2)2CH3, 2 × NHCH2CH2OH), 1.582 (m, 4H, 2 ×
NHCH2CH2(CH2)2CH3), 1.309 (m, 8H, 2 × NHCH2CH2(CH2)2-
CH3), 0.882 (t, 6H, 2 × NHCH2CH2(CH2)2CH3). Anal. (C20H36N8O2‚
0.5H2O) C, H, N.
1
Mp 225 °C; MS (ESI) m/z 449 (M + H)+, 471 (M + Na)+; H
NMR (DMSO-d6) δ 7.060 (d, 2H, 2 × NHCH(CH2)2, disappeared
after D2O, J ) 3.5 Hz), 4.688 (s, 4H, 4 × OH, disappeared after
D2O), 3.681 (t, 8H, 2 × N(CH2CH2OH)2), 3.627 (d, 8H, 2 ×
N(CH2CH2OH)2), 2.796 (m, 2H, 2 × NHCH(CH2)2), 0.783 (m, 4H,
2 × NHCH(CH2)2-H2a,3a), 0.622 (m, 4H, 2 × NHCH(CH2)2-
H2e,3e). Anal. (C20H32N8O4‚0.25H2O) C, H, N.
2,6-Bis(diethanolamino)-4,8-diisopentylaminopyrimido[5,4-d]-
pyrimidine (56). Compound 56 was prepared by general procedure
I with isopentylamine (0.49 mL, 4.2 mmol) at the first step and
with diethanolamine (3 mL, 30 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 22/1) to give a yellow powdery solid (346 mg, 68%). Mp 124-
125 °C; MS (ESI) m/z 509 (M + H)+, 531 (M + Na)+, 547 (M +
2,6-Diethanolamino-4,8-dicyclopropylaminopyrimido[5,4-d]-
pyrimidine (61). Compound 61 was prepared by general procedure
I with cyclopropylamine (0.31 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 17/1) to give a yellow powdery solid (156 mg, 43%). Mp
1
199 °C; MS (ESI) m/z 361 (M + H)+, 383 (M + Na)+; H NMR
1
K)+; H NMR (DMSO-d6) δ 7.131 (t, 2H, 2 × NHCH2CH2CH-
(DMSO-d6) δ 6.983 (d, 2H, 2 × NHCH(CH2)2, disappeared after
D2O, J ) 3.5 Hz), 5.003 (t, 2H, 2 × NHCH2CH2OH, disappeared
after D2O, J ) 6 Hz), 4.633 (t, 2H, 2 × NHCH2CH2OH,
disappeared after D2O, J1 ) 5 Hz, J2 ) 5.5 Hz), 3.525 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.396 (q, 4H, 2 ×
NHCH2CH2OH, J ) 6 Hz), 2.869 (m, 2H, 2 × NHCH(CH2)2),
(CH3)2, disappeared after D2O), 4.679 (t, 4H, 4 × OH, disappeared
after D2O), 3.666 (t, 8H, 2 × N(CH2CH2OH)2), 3.621 (d, 8H, 2 ×
N(CH2CH2OH)2), 3.454 (q, 4H, 2 × NHCH2CH2CH(CH3)2), 1.621
(m, 2H, 2 × NHCH2CH2CH(CH3)2), 1.505 (m, 4H, 2 × NHCH2CH2-
CH(CH3)2), 0.936 (d, 12H, 2 × NHCH2CH2CH(CH3)2). Anal.
(C24H44N8O4‚0.5H2O) C, H, N.

Dipyridamole Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3917
0.748 (m, 4H, 2 × NHCH(CH2)2-H2a,3a), 0.633 (m, 4H, 2 ×
NHCH(CH2)2-H2e,3e). Anal. (C16H24N8O2‚0.25H2O) C, H, N.
2,6-Bis(diethanolamino)-4,8-dicyclobutylaminopyrimido[5,4-
d]pyrimidine (62). Compound 62 was prepared by general
procedure I with cyclobutylamine (0.37 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 16/1) to give a yellow powdery solid (212 mg, 45%).
Mp 222-223 °C; MS (ESI) m/z 477 (M + H)+, 499 (M + Na)+;
1H NMR (DMSO-d6) δ 6.992 (br s, 2H, 2 × NHCH(CH2)2CH2,
disappeared after D2O), 4.701 (s, 4H, 4 × OH, disappeared after
D2O), 4.467 (br s, 2H, 2 × NHCH(CH2)2CH2), 3.615 (br d, 16H,
2 × N(CH2CH2OH)2, 2.295 (m, 4H, 2 × NHCH(CH2)2CH2-H2a,4a),
2.196 (m, 4H, 2 × NHCH(CH2)2CH2-H2e,4e), 1.729 (m, 4H, 2 ×
NHCH(CH2)2CH2). Anal. (C22H36N8O4) C, H, N.
D2O), 3.891 (m, 2H, 2 × NHCH(CH2CH2)2CH2), 3.637 (m, 16H,
2 × N(CH2CH2OH)2), 1.916 (m, 4H, 2 × NHCH(CHaxHeqCH2)2-
CH2), 1.729 (m, 4H, 2 × NHCH(CH2CHaxHeq)2CH2), 1.593 (m,
2H, 2 × NHCH(CH2CH2)2CHaxHeq), 1.442-1.330 (m, 8H, 2 ×
NHCH(CH2CHaxHeq)2CH2, 2 × NHCH(CHaxHeqCH2)2CH2), 1.248
(m, 2H, 2 × NHCH(CH2CH2)2CHaxHeq). Anal. (C26H44N8O4) C,
H, N.
2,6-Diethanolamino-4,8-dicyclohexylaminopyrimido[5,4-d]py-
rimidine (67). Compound 67 was prepared by general procedure
I with cyclohexylamine (0.48 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 15/1) to give a yellow powdery solid (44 mg, 10%). Mp
1
163 °C; MS (ESI) m/z 445 (M + H)+, 467 (M + Na)+; H NMR
(DMSO-d6) δ 6.589 (d, 2H, 2 × NHCH(CH2CH2)2CH2, disappeared
after D2O), 6.033 (t, 2H, 2 × NHCH2CH2OH, disappeared after
D2O), 4.632 (t, 2H, 2 × NHCH2CH2OH, disappeared after D2O),
3.915 (q, 2H, 2 × NHCH(CH2CH2)2CH2), 3.525 (q, 4H, 2 ×
NHCH2CH2OH), 3.355 (q, 4H, 2 × NHCH2CH2OH), 1.901 (m,
4H, 2 × NHCH(CHaxHeqCH2)2CH2), 1.735 (m, 4H, 2 × NHCH-
(CH2CHaxHeq)2CH2), 1.600 (m, 2H, 2 × NHCH(CH2CH2)2CHaxHeq),
1.399-1.304 (m, 8H, 2 × NHCH(CH2CHaxHeq)2CH2, 2 × NHCH-
(CHaxHeqCH2)2CH2), 1.225 (m, 2H, 2 × NHCH(CH2CH2)2CHaxHeq).
Anal. (C22H36N8O2) C, H, N.
2,6-Diethanolamino-4,8-dicyclobutylaminopyrimido[5,4-d]py-
rimidine (63). Compound 63 was prepared by general procedure
I with cyclobutylamine (0.37 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 19/1) to give a yellow powdery solid (183 mg, 47%). Mp 189-
1
190 °C; MS (ESI) m/z 389 (M + H)+, 411 (M + Na)+; H NMR
(DMSO-d6) δ 7.052 (d, 2H, 2 × NHCH(CH2)2CH2, disappeared
after D2O, J ) 8 Hz), 5.971 (t, 2H, 2 × NHCH2CH2OH,
disappeared after D2O, J ) 5.5 Hz), 4.645 (t, 2H, 2 × NHCH2-
CH2OH, disappeared after D2O, J1 ) 4.5 Hz, J2 ) 5.5 Hz), 4.555
(m, 2H, 2 × NHCH(CH2)2CH2, J1 ) 8 Hz, J2 ) 8.5 Hz), 3.533 (q,
4H, 2 × NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.405 (q, 4H,
2 × NHCH2CH2OH, J1 ) 5.5 Hz, J2 ) 6 Hz), 2.272 (m, 4H, 2 ×
NHCH(CH2)2CH2-H2a,4a), 2.097 (m, 4H, 2 × NHCH(CH2)2CH2-
H2e,4e), 1.675 (m, 4H, 2 × NHCH(CH2)2CH2). Anal. (C18H28N8O2)
C, H, N.
2,6-Bis(diethanolamino)-4,8-diphenylaminopyrimido[5,4-d]-
pyrimidine (68). Compound 68 was prepared by general procedure
I with aniline (0.39 mL, 4.2 mmol) at the first step and with
diethanolamine (3 mL, 30 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 14/
1) to give a yellow powdery solid (186 mg, 36%). Mp 209-
1
210 °C; MS (ESI) m/z 519 (M - H)-; H NMR (DMSO-d6) δ
8.918 (s, 2H, 2 × NHAr, disappeared after D2O), 7.916 (d, 4H, 2
× Ar-H-2, 2 × Ar-H-6, J ) 8 Hz), 7.404 (t, 4H, 2 × Ar-H-3,
2 × Ar-H-5, J ) 8 Hz), 7.105 (t, 2H, 2 × Ar-H-4), 4.753 (t, 4H,
4 × OH, disappeared after D2O, J ) 5.5 Hz), 3.789 (br s, 8H, 2 ×
N(CH2CH2OH)2), 3.689 (q, 8H, 2 × N(CH2CH2OH)2, J ) 5.5 Hz).
Anal. (C26H32N8O4) C, H, N.
2,6-Bis(diethanolamino)-4,8-dicyclopentylaminopyrimido[5,4-
d]pyrimidine (64). Compound 64 was prepared by general
procedure I with cyclopentylamine (0.42 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 10/1) to give a yellow powdery solid (97 mg, 19%). Mp
2,6-Diethanolamino-4,8-diphenylaminopyrimido[5,4-d]pyri-
midine (69). Compound 69 was prepared by general procedure I
with aniline (0.39 mL, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 16/
1) to give a yellow powdery solid compound 4 (138 mg, 32%).
Mp 233-234 °C; MS (ESI) m/z 433 (M + H)+, m/z 455 (M +
Na)+; 1H NMR (DMSO-d6) δ 8.937 (s, 2H, 2 × NHAr, disappeared
after D2O), 8.010 (d, 4H, 2 × Ar-H-2, 2 × Ar-H-6, J ) 8 Hz),
7.388 (t, 4H, 2 × Ar-H-3, 2 × Ar-H-5, J1 ) 7.5 Hz, J2 ) 8.5
Hz), 7.092 (t, 2H, 2 × Ar-H-4, J1 ) 7.5 Hz, J2 ) 7 Hz), 6.564
(br s, 2H, 2 × NHCH2CH2OH, disappeared after D2O), 4.694 (t,
2H, 2 × OH, disappeared after D2O, J ) 5.5 Hz), 3.613 (q, 4H, 2
× NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.526 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 5.5 Hz, J2 ) 6 Hz). Anal. Calcd for
C22H24N8O2‚0.5H2O): C 59.85, H 5.71, N 25.38. Found; C 60.31,
H 5.69, N 25.23.
1
211-212 °C; MS (ESI) m/z 505 (M + H)+, 527 (M + Na)+; H
NMR (DMSO-d6) δ 6.619 (d, 2H, 2 × NHCH(CH2CH2)2, disap-
peared after D2O), 4.704 (br s, 4H, 4 × OH, disappeared after D2O),
4.296 (m, 2H, 2 × NHCH(CH2CH2)2), 3.657 (t, 8H, 2 × N(CH2-
CH2OH)2), 3.615 (d, 8H, 2 × N(CH2CH2OH)2), 2.016 (m, 4H, 2
× NHCH(CHaxHeqCH2)2), 1.720 (m, 4H, 2 × NHCH(CH2-
CHaxHeq)2), 1.587 (m, 8H, 2 × NHCH(CH2CHaxHeq)2, 2 × NHCH-
(CHaxHeqCH2)2). Anal. (C24H40N8O4) C, H, N.
2,6-Diethanolamino-4,8-dicyclopentylaminopyrimido[5,4-d]-
pyrimidine (65). Compound 65 was prepared by general procedure
I with cyclopentylamine (0.42 mL, 4.2 mmol) at the first step and
with ethanolamine (3 mL, 50 mmol) at the second step. Product
was purified by flash silica gel chromatography (CH2Cl2/MeOH
) 18/1) to give a yellow powdery solid (175 mg, 42%). Mp 203-
1
204 °C; MS (ESI) m/z 417 (M + H)+, 439 (M + Na)+; H NMR
(DMSO-d6) δ 6.678 (d, 2H, 2 × NHCH(CH2CH2)2, disappeared
after D2O), 6.028 (t, 2H, 2 × NHCH2CH2OH, disappeared after
D2O, J ) 6 Hz), 4.651 (t, 2H, 2 × NHCH2CH2OH, disappeared
after D2O, J ) 5 Hz), 4.337 (q, 2H, 2 × NHCH(CH2CH2)2),
3.534 (q, 4H, 2 × NHCH2CH2OH, J ) 5 Hz), 3.380 (q, 4H, 2 ×
NHCH2CH2OH, J ) 6 Hz), 1.998 (m, 4H, 2 × NHCH(CHaxHeq-
CH2)2), 1.708 (m, 4H, 2 × NHCH(CH2CHaxHeq)2), 1.559 (m, 8H,
2 × NHCH(CH2CHaxHeq)2, 2 × NHCH(CHaxHeqCH2)2). Anal.
(C20H32N8O2‚0.5H2O) C, H, N.
2,6-Bis(diethanolamino)-4,8-bis(dibenzylamino)pyrimido[5,4-
d]pyrimidine (70). Compound 70 was prepared by general
procedure I with dibenzylamine (0.83 g, 4.2 mmol) at the first step
and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 16/1) to give a yellow powdery solid compound 9 (332
mg, 46%). Mp 199 °C; MS (ESI) m/z 729 (M + H)+, 751 (M +
1
Na)+; H NMR (DMSO-d6) δ 7.324 (t, 8H, 4 × Ar-H-3, 4 ×
Ar-H-5, J1 ) 7.5 Hz, J2 ) 7 Hz), 7.261-7.224 (m, 12H, 4 ×
Ar-H-2, 4 × Ar-H-6, 4 × Ar-H-4), 5.317 (br s, 8H, 4 × CH2-
Ph), 4.564 (t, 4H, 4 × OH, disappeared after D2O, J ) 5 Hz),
3.259 (br d, 16H, 2 × N(CH2CH2OH)2). Anal. (C42H48N8O4) C,
H, N.
2,6-Bis(diethanolamino)-4,8-dicyclohexylaminopyrimido[5,4-
d]pyrimidine (66). Compound 66 was prepared by general
procedure I with cyclohexylamine (0.48 mL, 4.2 mmol) at the first
step and with diethanolamine (3 mL, 30 mmol) at the second step.
Product was purified by flash silica gel chromatography (CH2Cl2/
MeOH ) 12/1) to give a yellow powdery solid (320 mg, 60%).
Mp 198-199 °C; MS (ESI) m/z 533 (M + H)+, 555 (M + Na)+;
1H NMR (DMSO-d6) δ 6.586 (d, 2H, 2 × NHCH(CH2CH2)2CH2,
disappeared after D2O), 4.708 (t, 4H, 4 × OH, disappeared after
2,6-Diethanolamino-4,8-bis(dibenzylamino)pyrimido[5,4-d]-
pyrimidine (71). Compound 71 was prepared by general procedure
I with dibenzylamine (0.83 g, 4.2 mmol) at the first step and with
ethanolamine (3 mL, 50 mmol) at the second step. Product was

3918 Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16
Lin and Buolamwini
purified by flash silica gel chromatography (CH2Cl2/MeOH ) 20/
1) to give a yellow powdery solid compound 8 (125 mg, 20%).
Mp 215-216 °C; MS (ESI) m/z 641 (M + H)+, 663 (M + Na)+;
1H NMR (DMSO-d6) δ 7.327 (t, 8H, 4 × Ar-H-3, 4 × Ar-H-5,
J1 ) 7 Hz, J2 ) 7.5 Hz), 7.289 (d, 8H, 4 × Ar-H-2, 4 × Ar-
H-6, J ) 7 Hz), 7.247 (t, 4H, 4 × Ar-H-4, J1 ) 7.5 Hz, J2 ) 7
Hz), 5.970 (t, 2H, 2 × NHCH2CH2OH, disappeared after D2O, J
) 5.5 Hz), 4.279 (br s, 8H, 4 × CH2Ph), 4.419 (t, 2H, 2 × NHCH2-
CH2OH, disappeared after D2O, J ) 5.5 Hz), 3.243 (q, 4H, 2 ×
NHCH2CH2OH, J1 ) 6 Hz, J2 ) 5.5 Hz), 3.927(br s, 4H, 2 ×
NHCH2CH2OH). Anal. (C38H40N8O2) C, H, N.
2,6-Bis[N,N-di-(2′-ethoxy)ethylamino]-4,8-dipiperidinopyrimido-
[5,4-d]pyrimidine (77). Compound 77 was prepared by general
procedure III with ethyl bromide (2.4 mL, 32 mmol) as the alkyl
halide. The residue was subjected to flash silica gel chromatography
(hexane/acetone ) 12:1) to give yellow fluorescent powdery
compound 57 (520 mg, 84%). Mp 58-59 °C; MS (ESI) m/z 639
1
(M + Na)+, 617 (M + H)+; H NMR (DMSO-d6) δ 4.049 (br s,
8H, 2 × N(CH2CH2)2CH2), 3.776 (br s, 8H, 2 × N(CH2CH2OCH2-
CH3)2), 3.624 (br s, 8H, 2 × N(CH2CH2OCH2CH3)2), 3.500 (q,
8H, 4 × CH2CH3), 1.708 (br s, 12H, 2 × N(CH2CH2)2CH2), 1.194
(t, 12H, 4 × CH2CH3). Anal. (C32H56N8O4) C, H, N.
2,6-Bis[N,N-di-(2′-propoxy)ethylamino]-4,8-dipiperidinopy-
rimido[5,4-d]pyrimidine (78). Compound 78 was prepared by
general procedure III with propyl bromide (2.9 mL, 32 mmol) as
the alkyl halide. The residue was subjected to flash silica gel
chromatography (hexane/acetone ) 13:1) to give yellow fluorescent
powdery compound 58 (570 mg, 85%). Mp 32-34 °C; MS (ESI)
m/z 695 (M + Na)+, 673 (M + H)+; 1H NMR (DMSO-d6) δ 4.056
(br s, 8H, 2 × N(CH2CH2)2CH2), 3.779(br s, 8H, 2 × N(CH2CH2-
OCH2CH2CH3)2), 3.616 (br s, 8H, 2 × N(CH2CH2OCH2CH2CH3)2),
3.399(t, 8H, 4 × CH2CH2CH3, J ) 6.5 Hz), 1.699 (br s, 12H, 2 ×
N(CH2CH2)2CH2), 1.578 (m, 8H, 4 × CH2CH2CH3, J1 ) 6.5 Hz,
J2 ) 7.5 Hz), 0.915 (t, 12H, 4 × CH2CH2CH3, J ) 7.5 Hz). Anal.
(C36H64N8O4) C, H, N.
2,6-Di-(2′-hydroxyethoxy)-4,8-dipiperidinopyrimido[5,4-d]py-
rimidine (72). Compound 72 was prepared according to a literature
procedure.43
2,6-Dimorpholino-4,8-dipiperidinopyrimido[5,4-d]pyrimi-
dine (73). Compound 73 was prepared by general procedure I with
piperidine (0.41 mL, 4.2 mmol) at the first step and with morpholine
(3 mL, 34 mmol) at the second step. Product was purified by flash
silica gel chromatography (hexane/acetone ) 10/1) to give a yellow
powdery solid (173 mg, 37%). Mp 203-204 °C; MS (ESI) m/z
469 (M + H)+, 491 (M + Na)+; 1H NMR (DMSO-d6) δ 4.076 (br
s, 8H, 2 × N(CH2CH2)2CH2), 3.663 (t, 8H, 2 × N(CH2CH2)O, J
) 5 Hz), 3.542 (t, 8H, 2 × N(CH2CH2)O, J ) 5 Hz), 1.664
(br d, 4H, 2 × N(CH2CH2)2CH2, J ) 4.5 Hz), 1.608 (br d, 8H, 2
× N(CH2CH2)2CH2, J ) 4.5 Hz). Anal. (C24H36N8O2) C,
H, N.
2,6-Bis[N,N-di-(2′-formyloxy)ethylamino]-4,8-dipiperidinopy-
rimido[5,4-d]pyrimidine (74). Dipyridamole (0.51 g, 1 mmol) was
dissolved in formic acid (10 mL, 0.25 mole). The mixture was
stirred at reflux for 6 h, and then the solvent was evaporated under
reduced pressure. The residue was dissolved in methylene chloride
(50 mL) and washed with 10% NaHCO3 solution, and then the
organic layer was separated and dried by anhydrous Na2SO4. After
the solvent was removed, the residue was subjected to flash silica
gel chromatography (hexane/acetone ) 6:1) to give a yellow
fluorescent powdery compound 74 (0.567 g, 92%). Mp 129-
130 °C (lit25 128-130 °C); MS (ESI) m/z 639 (M + Na)+, 617 (M
+ H)+; 1H NMR (DMSO-d6) δ 8.225 (s, 4H, 4 × CHO), 4.289 (t,
8H, 2 × N(CH2CH2OCHO)2, J ) 5.5 Hz), 4.052 (m, 8H, 2 ×
N(CH2CH2)2CH2), 3.784 (t, 8H, 2 × N(CH2CH2OCHO)2, J ) 5.5
Hz), 1.646 (m, 4H, 2 × N(CH2CH2)2CH2), 1.599 (m, 8H, 2 ×
N(CH2CH2)2CH2). Anal. (C28H40N8O8) C, H, N.
2,6-Bis[N,N-di-(2′-acetoxy)ethylamino]-4,8-dipiperidinopy-
rimido[5,4-d]pyrimidine (75). In an ice-water bath, acetyl chloride
(1.45 mL, 20 mmol) was added to a solution of dipyridamole (0.51
g, 1 mmol) and a catalytic amount of DMAP in anhydrous THF
(30 mL). The mixture was stirred for 3 h, and then the solvent was
evaporated under reduced pressure. The residue was dissolved in
methylene chloride (50 mL) and washed with 10% NaHCO3 solu-
tion, and then the organic layer was separated and dried by anhy-
drous Na2SO4. After the solvent was removed, the residue was
subjected to flash silica gel chromatography (hexane/acetone ) 10:
1) to give a yellow fluorescent needle-like compound 75 (0.64 g,
95%). Mp 121-122 °C (lit25 123-124 °C); MS (ESI) m/z 695 (M
+ Na)+, 673 (M + H)+; 1H NMR (DMSO-d6) δ 4.191 (t, 8H, 2 ×
N(CH2CH2OCOCH3)2, J ) 5.5 Hz), 4.046 (m, 8H, 2 × N(CH2-
CH2)2CH2), 3.746 (t, 8H, 2 × N(CH2CH2OCOCH3)2, J ) 5.5 Hz),
1.982 (s, 12H, 4 × CH3), 1.649 (m, 4H, 2 × N(CH2CH2)2CH2),
1.598 (m, 8H, 2 × N(CH2CH2)2CH2). Anal. (C32H48N8O8) C, H,
N.
2,6-[N-(2-Hydroxyethyl)-N-(2-isopropoxyethyl)amino]-4,8-
dipiperidinopyrimido[5,4-d]pyrimidine (79). Compound 79 was
prepared by general procedure III with isopropyl bromide (3 mL,
32 mmol) as the alkyl halide. The residue was subjected to flash
silica gel chromatography (hexane/acetone ) 2:1) to give yellow
fluorescent powdery compound 58 (326 mg, 55%). Mp 56-58 °C;
MS (ESI) m/z 611 (M + Na)+, 589 (M + H)+; 1H NMR (DMSO-
d6) δ 4.574 (m, 2H, 2 × OH, disappeared after D2O), 4.058 (br s,
8H, 2 × N(CH2CH2)2CH2), 3.631 (t, 4H, 2 × CH2OH), 3.570 (br
s, 8H, 2 × (CH3)2CHOCH2CH2NCH2CH2OH), 3.525 (m, 6H, 2 ×
(CH3)2CHOCH2), 1.646 (br s, 4H, 2 × N(CH2CH2)2CH2), 1.597
(br s, 8H, 2 × N(CH2CH2)2CH2), 1.075 (d, 12H, 4 × CH3). Anal.
(C30H52N8O4) C, H, N.
Flow Cytometric Assays. The compounds were tested to
determine their ENT1 nucleoside transporter binding ability by a
flow cytometric assay.44 Briefly, human leukemia K562 cells
growing in RPMI 1640 medium were washed once, resuspended
at 1.6 × 106 cells/mL in phosphate-buffered saline at pH 7.4, and
incubated with 5-(SAENTA)-X8-fluorescein (30 nM) in the pres-
ence or absence of varying concentrations of test compounds at
room temperature for 45 min. Flow cytometric measurements of
cell-associated fluorescence were then performed with a FACS-
Calibur instrument (Becton Dickinson, San Jose, CA) equipped
with a 15 mW argon laser (Molecular Resources Flow Cyto-
metry Facility, University of Tennessee Health Sciences Center).
In each assay, 5000 cells were analyzed from suspensions
of 4 × 105 cells/mL. The units of fluorescence were arbitrary
channel numbers. Percentage (%) of control (i.e., ENT1 trans-
porter-specific fluorescence in the presence of SAENTA-fluores-
cein without test compounds) was calculated for each sample
by
(SFs)
% inhibition ) 100 -
× 100
(1)
[
]
(SFf)
where SFs is the ENT1 transporter-specific fluorescence of test
samples and whre SFf is the ENT1 transporter-specific fluorescence
of the SAENTA-fluorescein ligand standard in mean channel
numbers. The results were fed into the PRISM program (GraphPad,
San Diego, CA) to derive concentration-dependent curves. From
these curves, the IC50 values were obtained and used to calculate
inhibition constants (Ki):
2,6-Bis[N,N-di-(2′-methoxy)ethylamino]-4,8-dipiperidinopy-
rimido[5,4-d]pyrimidine (76). Compound 76 was prepared by
general procedure III with MeI (2 mL, 32 mmol) as the alkyl halide.
The residue was subjected to flash silica gel chromatography
(hexane/acetone ) 8:1) to give yellow fluorescent powdery
compound 56 (247 mg, 64%). Mp 64-65 °C; MS (ESI) m/z 583
1
(M + Na)+, 561 (M + H)+; H NMR (DMSO-d6) δ 4.052 (br s,
8H, 2 × N(CH2CH2)2CH2), 3.766 (t, 8H, 2 × N(CH2CH2OCH3)2,
J ) 6 Hz), 3.574 (t, 8H, 2 × N(CH2CH2OCH3)2, J ) 6 Hz), 3.351
(s, 12H, 4 × CH3), 1.683 (s, 12H, 2 × N(CH2CH2)2CH2). Anal.
(C28H48N8O4) C, H, N.
IC50
Ki )
(2)
1 + [L]/KL

Dipyridamole Analogues
Journal of Medicinal Chemistry, 2007, Vol. 50, No. 16 3919
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where [L] and KL are the concentration and the Kd value of the
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transporter-specific ligand 5-(SAENTA)-X8-fluorescein24 and, for
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Acknowledgment. Financial support from the National
Cancer Institute (Grant Nos. CA101856 and CA105327) and
the National Institute of Allergy and Infectious Diseases (Grant
No. AI065372) is hereby acknowledged.
Supporting Information Available: Elemental analysis data.
This material is available free of charge via the Internet at http://
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