Synthesis and Antiangiogenic Properties of Tetrafluorophthalimido and Tetrafluorobenzamido Barbituric Acids

Article abstract of DOI:10.1002/cmdc.201600496

The development of novel thalidomide derivatives as immunomodulatory and anti-angiogenic agents has revived over the last two decades. Herein we report the design and synthesis of three chemotypes of barbituric acids derived from the thalidomide structure: phthalimido-, tetrafluorophthalimido-, and tetrafluorobenzamidobarbituric acids. The latter were obtained by a new tandem reaction, including a ring opening and a decarboxylation of the fluorine-activated phthalamic acid intermediates. Thirty compounds of the three chemotypes were evaluated for their anti-angiogenic properties in an ex vivo assay by measuring the decrease in microvessel outgrowth in rat aortic ring explants. Tetrafluorination of the phthalimide moiety in tetrafluorophthalimidobarbituric acids was essential, as all of the nonfluorinated counterparts lost anti-angiogenic activity. An opening of the five-membered ring and the accompanying increased conformational freedom, in case of the corresponding tetrafluorobenzamidobarbituric acids, was well tolerated. Their activity was retained, although their molecular structures differ in torsional flexibility and possible hydrogen-bond networking, as revealed by comparative X-ray crystallographic analyses.

Full text of DOI:10.1002/cmdc.201600496

DOI: 10.1002/cmdc.201600496
Full Papers
Synthesis and Antiangiogenic Properties of
Tetrafluorophthalimido and Tetrafluorobenzamido
Barbituric Acids
Agnieszka Ambroz˙ak,[a] Christian Steinebach,[a] Erin R. Gardner,[b] Shaunna L. Beedie,[c]
Gregor Schnakenburg,[d] William D. Figg,[c] and Michael Gꢀtschow*[a]
Dedicated to Professor Dr. Kurt Eger on the occasion of his 75th birthday.
The development of novel thalidomide derivatives as immuno-
modulatory and anti-angiogenic agents has revived over the
last two decades. Herein we report the design and synthesis of
three chemotypes of barbituric acids derived from the thalido-
mide structure: phthalimido-, tetrafluorophthalimido-, and
tetrafluorobenzamidobarbituric acids. The latter were obtained
by a new tandem reaction, including a ring opening and a de-
carboxylation of the fluorine-activated phthalamic acid inter-
mediates. Thirty compounds of the three chemotypes were
evaluated for their anti-angiogenic properties in an ex vivo
assay by measuring the decrease in microvessel outgrowth in
rat aortic ring explants. Tetrafluorination of the phthalimide
moiety in tetrafluorophthalimidobarbituric acids was essential,
as all of the nonfluorinated counterparts lost anti-angiogenic
activity. An opening of the five-membered ring and the accom-
panying increased conformational freedom, in case of the cor-
responding tetrafluorobenzamidobarbituric acids, was well tol-
erated. Their activity was retained, although their molecular
structures differ in torsional flexibility and possible hydrogen-
bond networking, as revealed by comparative X-ray crystallo-
graphic analyses.
Introduction
Angiogenesis, the precisely controlled generation of new
blood vessels from pre-existing vessels, is a complex and im-
portant process. In solid tumor formation, undesired angiogen-
esis is required to sustain the nutrient and oxygen supply for
continued tumor growth and invasion. A direct correlation has
been shown between tumor microvessel density and the inci-
dence of metastasis. Anti-angiogenic drugs have been success-
fully used to restrict vascular supply to the tumor, and are
therefore established drugs for anticancer therapy.[1] Following
the findings that the immunomodulatory drug thalidomide (I,
Figure 1) inhibited the production of tumor necrosis factor-
a (TNF-a) by activated monocytes and macrophages,[2] and
possessed anti-angiogenic properties,[3] interest in thalido-
mide’s biological activities was renewed, leading to the iden-
Figure 1. Structures of thalidomide and selected IMiDs.
tification of a primary target—cereblon—a substrate receptor
of the CRL4 ubiquitin ligase complex.[4] Several analogues of
thalidomide have been developed, sharing and augmenting
the antiproliferative, anti-angiogenic, and TNF-a reducing
properties of the parent compound. They were designated as
immunomodulatory drugs (IMiDs). Lenalidomide (II), for exam-
ple, also interacts with cereblon, leading to differential effects
on T- and B-cells, as compared to thalidomide.[5]
[a] Dr. A. Ambroz˙ak, C. Steinebach, Prof. Dr. M. Gꢀtschow
Pharmaceutical Institute, Pharmaceutical Chemistry I, University of Bonn,
An der Immenburg 4, 53121 Bonn (Germany)
E-mail: guetschow@uni-bonn.de
[b] Dr. E. R. Gardner
Clinical Pharmacology Program, National Cancer Institute, NIH, Bethesda,
MD 20892 (USA)
One successful strategy in the course of the development of
further phthalimide derivatives was the introduction of fluorine
atoms into the molecular structure.[6] For example, the chirally
stable a-fluoro-4-aminothalidomide (III) was found to be
a highly potent inhibitor of TNF-a synthesis.[7] An exchange of
the ÀCHÀCH2ÀCH2À unit in I by ÀC=CHÀNHÀ resulted in the
achiral azathalidomide derivative IV;[8] in the course of an iso-
[c] S. L. Beedie, Dr. W. D. Figg
Molecular Pharmacology Section, National Cancer Institute, NIH, Bethesda,
MD 20892 (USA)
[d] Dr. G. Schnakenburg
Institute of Inorganic Chemistry, University of Bonn, Gerhard-Domagk-Str. 1,
53121 Bonn (Germany)
Supporting information for this article can be found under http://
dx.doi.org/10.1002/cmdc.201600496.
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steric replacement,[9] the nonpolar analogue V was obtained.[8]
Moreover, in compound VI, the fused benzene ring was fully
fluorinated, leading to a strongly enhanced inhibition of both
TNF-a production by monocytes[8] and microvessel outgrowth
in an angiogenesis model.[10,11] Compound VI was further char-
acterized with regard to its antimyeloma capacity, activation of
the stress kinase p38 pathway, and the effect on blood vessels
depending on their state of maturity.[12] The direct connection
of a cyclic substituent to the phthalimide nitrogen atom was
not requisite for bioactivity, as could be concluded from bio-
data of N-alkylphthalimide derivatives.[13]
A structural modification within the N-substituent of com-
pound IV, i.e., replacement of the uracil by barbituric acid moi-
eties, led to a further class of thalidomide analogues. We de-
signed a small library of barbituric acids in which the barbituric
acid is either connected to a phthalimide or tetrafluorophthali-
mide core, or linked through a carboxamide unit to tetrafluoro-
benzene. We prepared ten compounds of each chemotype
with a consistent substitution pattern. To obtain the tetra-
fluorophthalimides, a synthetic procedure had to be applied
that differed somewhat from that for phthalimides. Moreover,
tetrafluorobenzamides could be obtained in the course of
a new tandem ring opening/decarboxylation sequence. Both
fluorinated chemotypes were characterized by X-ray diffraction
analyses. This report details the syntheses and structural
chemistry of the three chemotypes. Recently, we described the
anticancer properties of two selected tetrafluorophthalimides
and two tetrafluorobenzamides from this library.[14] Herein the
antiangiogenic properties of the entire library[15] are collated
and reported.
Scheme 1. Synthesis of 5-aminobarbituric acids 11 and 12. Reagents and
conditions: a) NaOEt, EtOH, reflux, 3 h; b) HCl (8m), reflux, 7 h for 10a–i, HCl/
dioxane (4m), RT, 2 h; c) NaOH, 08C.
were shown to be suitable substrates for the next reaction
step. An alternative approach was developed for the prepara-
tion of 5-amino-5-ethyl-1-phenylbarbituric acid (12k). Diethyl
[(tert-butyloxycarbonyl)amino]malonate was alkylated with
ethyl bromide,[21] and the resulting malonic ester 3 was reacted
with phenylurea to give the N-protected barbituric acid 10k.
After removal of the Boc group upon treatment with an HCl
solution in 1,4-dioxane at room temperature, the desired
phenyl derivative 12k was liberated from the hydrochloride
11 k.
Results and Discussion
The envisaged method for the preparation of (tetrafluoro)ph-
thalimido barbiturates relied on the condensation of (tetra-
fluoro)phthalic anhydride with free 5-aminobarbituric acids in
glacial acetic acid.[8,16] A new protection–deprotection route to
the desired 5-aminobarbituric acids 12 is outlined in Scheme 1.
The preparation of the 5-acetylaminobarbituric acids 10 includ-
ed the facile alkylation to diethyl acetylaminomalonates 1 and
2,[17] and condensation with appropriate ureas. Some 5-acetyl-
aminobarbituric acids have already been prepared that
way.[18,19] The condensation reaction to 10a–i was performed
under comparable mild conditions to avoid deacetylation and
instantaneous base-catalyzed ring contraction to hydan-
toins.[19,20] Prolonged heating of 10a–i in HCl (8m) was found
to be suitable to provide the corresponding hydrochlorides
11 a–i, which, after cooling, were obtained directly from the re-
action mixtures in pure form. Ensuing treatment with aqueous
NaOH (2m) led to the free aminobarbituric acids 12 f–i. Howev-
er, conversion of the obtained acetylamino derivatives 10 into
the aminobarbituric acids 12 under the above-described condi-
tions was limited. On the one hand, 1-phenyl-5-acetylamino
derivatives 10 (R1 =Me, Et, R2 =Ph, X=Ac) could not be trans-
formed into the corresponding salts 11 (data not shown). On
the other hand, isolation of the bases 12 liberated from the
parent salts 11 a–e was unsuccessful. However, both 11 and 12
With compounds 11 a–e and 12 f–k in hand, their condensa-
tion with both phthalic anhydride and tetrafluorophthalic an-
hydride was studied (Scheme 2). The use of acetic acid as sol-
vent for the reaction of 12 with phthalic anhydride gave unde-
sired N-acetylated barbituric acids to various extents. In con-
trast, boiling DMF proved to be the most suitable solvent for
the preparation of phthalimides 13, which was accomplished
in the presence of additional triethylamine to convert the salts
11 a–e.
To synthesize the tetrafluorophthalimides 14 f–k, aminobar-
bituric acids 12 f–k were condensed with a slight excess of
tetrafluorophthalic anhydride in glacial acetic acid, according
to a published procedure.[8] This methodology was then ap-
plied to hydrochlorides 11 a–e, which were transformed into
14a–e in glacial acetic acid in the presence of triethylamine.
The increased reactivity of the fluorinated anhydride accelerat-
ed the cyclocondensation leading to 14a–k without the com-
peting acetylation, as observed in reactions with the non-fluo-
rinated phthalic anhydride.
In view of the aforementioned acetylation, initial attempts
were made to replace acetic acid with DMF in the reactions
with tetrafluorophthalic anhydride as well. Surprisingly, under
conditions analogous to those established for compounds
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So far, the decarboxylation of fluorine-activated phthalamic
acids has not been used for the synthesis of specific com-
pounds. It was, however, observed as an undesired reaction in
the purification of solution-phase reactions using tetra-
fluorophthalic anhydride,[23] and also observed when tetra-
fluorophthalic anhydride was reacted with an aminoporphyrine
to give the corresponding porphyrin–tetrafluorophenylcarbox-
amide in 3% yield.[24]
Use of the ring opening-decarboxylation reaction enabled us
to access the novel tetrafluorobenzamides 15 with the com-
plete substitution pattern of compounds 13 and 14. The three
series of barbituric acid derivatives were provided for compara-
tive biological investigations.
The structures of 13–15 were unambiguously assigned by
means of 1H and 13C NMR spectroscopy, elemental analyses,
and mass spectrometry. In particular, the 13C NMR spectra of 14
showed three distinct signals—two multiplets and one dou-
blet—for the carbon atoms of the fused tetrafluorobenzene
ring. Tetrafluorobenzamides 15, on the other hand, gave six
distinct shifts of the carbon resonances, which appear as five
multiplets and one doublet. The carbon–fluorine coupling con-
stant of directly bound nuclei was observed between 240–
268 Hz. The proton at position 6 of tetrafluorobenzamides 15
gave a multiplet in the range of 7.51–7.61 ppm.[25]
To confirm the structures of tetrafluorophthalimides and
tetrafluorobenzamides and to characterize the different struc-
tural features, single-crystal X-ray analyses were carried out on
the representative compounds 14c and 15d. In the case of
the tetrafluorophthalimide derivative 14c (Figure 2), a mean
plane calculated through all barbituric acid atoms except H, R1
and R2 makes an angle of 868 with the nearly planar phthali-
mide moiety. This perpendicular orientation is similar to the
crystal structure of thalidomide.[26] The maximum deviation
from planarity in the barbituric acid part of 14c was 0.368 ꢂ.
Its four shortened COÀN bonds vary in their lengths between
1.368 and 1.407 ꢂ corresponding to the triketo tautomer with
contributing resonance structures. In compound 14c with all
hydrogen atoms of the phthalimide being replaced by fluorine,
further intermolecular interactions in the crystal unit are ex-
pected. Pairs of centrosymmetrically related molecules are as-
sociated into hydrogen bonded dimers through NÀH···O=C(2)
interactions and make additional CÀH···F and CÀH···O contacts;
the non-peri-substituted fluorines interact with the isopropyl
moiety which is linked to the O=C(4) oxygen atom of a third
molecule.
Scheme 2. Synthesis of 5-phthalimidobarbituric acids 13, 5-tetrafluorophtha-
limidobarbituric acids 14, and 5-(2,3,4,5-tetrafluorobenzamido)barbituric
acids 15. Reagents and conditions: a) phthalic anhydride, Et3N, DMF, 1538C,
5 h; b) phthalic anhydride, DMF, 1538C, 5 h; for 13k, see ref. [8]; c) tetra-
fluorophthalic anhydride, Et3N, AcOH, reflux, 3 h; d) tetrafluorophthalic anhy-
dride, AcOH, reflux, 3 h; e) tetrafluorophthalic anhydride, Et3N, DMSO, 1538C,
5 h; f) tetrafluorophthalic anhydride, DMF, 1538C, 5 h.
13 f–k, a spontaneous decarboxylation of intermediate tetra-
fluorophthalamic acids took place instead of cyclization. This
led to the formation of tetrafluorobenzamides 15 f–k. A similar
approach to provide tetrafluorobenzamides 15a–e from hydro-
chloride substrates 11 a–e in DMF and the presence of triethyl-
amine failed due to an undesired reaction of 15 with dimethyl-
amine (data not shown). Dimethylamine is known to be
formed via thermal decomposition of DMF.[22] In the presence
of triethylamine, and also other tertiary amines, this process
occurred to such an extent that the consecutive nucleophilic
substitution of 15 with dimethylamine gave 4-dimethylamino-
2,3,5-trifluorobenzamides as side products or as the main prod-
uct in the case of 11 a. In the search for an appropriate
reaction medium to obtain sufficient solubility of both sub-
strates and to avoid these side reactions, the use of DMSO at
1538C and equimolar amounts of triethylamine were found to
afford 15a–e from the corresponding hydrochloride substrates
11 a–e.
The molecular structure of 15d was also revealed by X-ray
diffraction (Figure 3). As expected, the amide group is not co-
planar with the tetrafluorobenzene ring, and the dihedral
angle of both is 27.38, a value similar to that of other aromatic
carboxamides.[27] The amide oxygen atom is oriented toward
the aromatic hydrogen, while the amide hydrogen is incorpo-
rated in an intramolecular hydrogen bond of type NÀH···FÀC(2)
with a H···F distance of 2.24 ꢂ. In a related 2,3,4,5-tetrafluoro-
benzamide, the ortho-fluorine also acted as hydrogen bond ac-
ceptor.[28] We observed a significant deviation from planarity
for the barbituric acid part, but the maximum deviation of
0.174 ꢂ was smaller than in the case of 14c. The four COÀN
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Figure 3. Top: Molecular plot of N-(1,5-diethylhexahydro-2,4,6-trioxo-5-pyri-
midinyl)-2,3,4,5-tetrafluorobenzamide (15d) showing the displacement ellip-
soids at the 50% probability level for non-hydrogen atoms. The non-aliphat-
ic hydrogen atoms are depicted as white spheres of arbitrary radii. Bottom:
Packing diagram of 15d along the z-axis. The NÀH···F and NÀH···O contacts
are shown as broken lines.[30]
Figure 2. Top: Molecular plot of 1-isopropyl-5-methyl-5-(4,5,6,7-tetrafluoro-
1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14c)
showing the displacement ellipsoids at the 50% probability level for non-hy-
drogen atoms. Hydrogen atoms are depicted as white spheres of arbitrary
radii. Bottom: Packing diagram of 14c along the y-axis. The CÀH···F, CÀH···O
and NÀH···O contacts are shown as broken lines.[30]
bond lengths vary from 1.366 to 1.392 ꢂ. The planes of the car-
boxamide and barbituric acid part are twisted with respect to
each other by 89.98. As noted for 14c, face-to-face dimeriza-
ated calcium channels and calcium channel-mediated signaling
pathways and known anti-angiogenic agent, was used as posi-
tive control. The vascular outgrowth was quantified as percent-
tion of the barbituric acid motifs of 15d occurs via NÀH···O= age of outgrowth compared with the outgrowth from control
C(2’) contacts. Besides the intramolecular hydrogen bond to
the acceptor fluorine FÀC(2), the amide hydrogen atom forms
an intermolecular contact to carbonyl oxygen O=C(4’). This
three-center (bifurcated) hydrogen bond accounts for the ex-
tended stacking network of 15d. Some structures with unsym-
metrical bifurcated hydrogen bonds to fluorine and oxygen
have been reported.[29]
ring explants (Table 1).
Examination of the biological data clearly indicated that
nearly all phthalimides 13 were inactive as inhibitors of angio-
genesis, independently from substituents at positions C5 and
N1. Out of this subseries, only 13b was weakly active and
showed more than 40% inhibition of the microvessel out-
growth. In contrast, the fluorinated counterparts 14, without
exception, were identified as excellent inhibitors of the vascu-
lar outgrowth. The majority of the compounds 14 exhibited
more than 90% inhibition, with methyl, propyl, and isopropyl
compounds being particularly potent. The activity of the 1-
phenyl derivative 14k was improved due to the introduction
of the cycloaliphatic residue present at this position in com-
pound 14i. Among the new benzamides 15, the most potent
compounds were 15c, 15d, 15e, 15g, and 15i, all leading to
10% or less vascular growth.
The ten representatives of each chemotype, phthalimidobar-
bituric acids 13, tetrafluorophthalimidobarbituric acids 14, and
tetrafluorobenzamidobarbituric acids 15, were evaluated to de-
termine their anti-angiogenic activities. The compounds were
tested in the rat aortic ring assay at a concentration of 50 mm.
Their inhibitory potency is reflected by a decrease in vascular
outgrowth.
5-Amino-1-{[3,5-dichloro-4-(4-chlorobenzoyl)phe-
nyl]methyl}-1H-1,2,3-triazole-4-carboxamide carboxyamidotria-
zole (CAI), a synthetic, cytostatic inhibitor of non-voltage-oper-
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Based on a comparison of phthalimide derivatives,[14] it has
already been suspected that the chemotype of tetrafluoro-
phthalimidobarbituric acids is privileged not only because of
the fluorine introduction, but also due to the presence of ade-
quate substituents at the phthalimide nitrogen atom. The com-
plete data presented in this report clearly confirm the suitabili-
ty of the structural assembly of chemotype 14. It is likely that
the barbiturate substructure provides their heteroatoms for
potential hydrogen bonding to contribute to protein–ligand
interactions.
Table 1. Inhibitory effects of 5-phthalimidobarbituric acids 13, 5-tetra-
fluorophthalimidobarbituric acids 14, and 5-(2,3,4,5-tetrafluorobenz-
amido)barbituric acids 15 on angiogenesis.
Substitution
pattern
R1
R2
Inhibition [%][a]
Overall, the representatives of chemotype 15 share the bio-
logical activity of derivatives 14. These tetrafluorobenzamide
derivatives, obtained by a formal ring opening and the con-
comitant loss of a CO unit, have an increased degree of confor-
mational freedom which might explain certain differences in
some assays. Tetrafluorophthalimide derivatives 14 exhibit
a molecular structure similar to that of thalidomide as could
be concluded from the X-ray analysis of 14c reported herein.
The X-ray crystal structure of one tetrafluorobenzamide repre-
sentative, 15d, evidencing a deviant molecular geometry, has
also been solved in the course of this study. However, because
of the structural flexibility of compounds 15, they might adopt
a bioactive conformation different from that of the crystalline
form when bound to a protein target. Hence, both chemo-
types are capable of making use of the tetrafluorobenzene as
well as the barbiturate substructure.
13
14
15
a
b
c
d
e
f
g
h
i
Me
Me
Me
Et
Et
Me
Et
Me
Et
Et
Me
nPr
iPr
Et
nPr
Et
n.i.[b]
51
>95
>95
>95
>95
94[d]
94[d]
>95
88
42
77
94[c]
91[d]
n.i.
n.i.
n.i.
n.i.
n.i.
n.i.
n.i.
n.i.[g]
>95
83[e]
90[d]
84[f]
90
iPr
cHex
cHex
Ph
89
76[g]
k
82[h]
[a] Percent inhibition of microvessel outgrowth in the rat aortic ring
assay. Compounds were administered daily at a concentration of 50 mm
for four days. The control was measured with 0.5% DMSO in the absence
of test compounds and was set as 100% growth (0% inhibition). CAI, at
a concentration of 12.5 mgmLÀ1, gave 96Æ8% inhibition of the vascular
outgrowth. Standard deviations were <4% unless stated otherwise.
[b] n.i.: no inhibitory activity (<40% inhibition of microvessel outgrowth
by the indicated compounds). [c] 94Æ8%. [d] Data from ref. [14]. [e] 83Æ
13%. [f] 84Æ9%. [g] Data from ref. [10]. [h] 82Æ16%.
Conclusions
In general, the results summarized in Table 1 clearly show the
presence of the tetrafluoro substitution pattern to be an essen-
tial feature for bioactivity. The structurally analogous non-fluo-
rinated compounds 13 lost the anti-angiogenic properties. Sev-
eral studies have underlined that the introduction of fluorine
in place of hydrogen results in enhanced biological activities,
and the identification of fluorophilic binding areas in protein
targets has emerged as a powerful strategy in medicinal
chemistry.[33] Further investigations to identify the targets of
the tetrafluorinated IMiDs 14 and 15 are underway in our re-
search groups.
The anti-angiogenic activity of the tetrafluorophthalimide
derivative 14k has already been confirmed by the HUVEC tube
formation assay, in which 14k, at a concentration of 12.5 mm,
inhibited the tube formation of human umbilical vein endothe-
lial cells by 93%.[11] A preselection of four tetrafluoro inhibitors
was previously investigated in further assays to characterize
the anti-angiogenic and antiproliferative activities in greater
detail.[14] Using the NCI60 high-throughput screen (NCI, Freder-
ick, MD, USA) for anticancer activity, phthalimides 14e and 14 f
were shown to be more potent than the benzamide deriva-
tives 15d and 15g in 59 tumor cell lines.[31] The GI50 (50%
growth inhibition) values of 14e and 14 f in the NCI60 screen
were 2.21 and 5.12 mm, respectively. Among the four com-
pounds, the tetrafluorophthalimide 14e was most efficient in
inhibiting HUVEC cell proliferation. The anti-angiogenic activity
in transgenic fli1:EGFP zebrafish embryos was investigated, and
the number of intersomitic blood vessels was decreased upon
treatment with 14e, 14 f, and 15g. Notably, the tetrafluoro-
benzamide derivative 15d significantly decreased the tumor
size in a human prostate cancer mouse xenograft model.
Moreover, the tetrafluorophthalimide derivative 14k was
subjected to a study aimed at assessing its antileukemic activi-
ty.[32] Compound 14k was described as a member of a class of
redox-reactive thalidomide analogues with the capacity to up-
regulate nuclear factor of activated T-cells (NFAT) transcription-
al pathways.
Experimental Section
Melting points were determined on a Gallenkamp capillary melting
point apparatus or on a Rapido Boetius apparatus, and are uncor-
rected. The purity of the obtained substances and the composition
of the reaction mixtures were controlled by thin-layer chromatog-
raphy (TLC) using Merck aluminum silica gel plates with 60 F254 in-
dicator. Preparative column chromatography was performed using
Merck silica gel 60 (63–200 mesh). Petroleum ether (PE) used was
a mixture of alkanes boiling between 40–608C, according to the
supplier’s declarations. NMR spectra were recorded on a Bruker
Avance DRX 500 spectrometer at 500 MHz (1H NMR) and 125 MHz
(13C NMR) in [D6]DMSO. Chemical shifts (d) are reported in ppm.
Spin multiplicities are indicated by the following symbols: s (sin-
glet), brs (broad singlet), d (doublet), t (triplet), q (quartet),
s (sextet), sept (septet), m (multiplet). All multiplets related with
1J(C,F) coupling in 13C NMR spectra are centered. Mass spectra were
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recorded on an MS-50 A.E.I. spectrometer under electron impact
ionization (EI) at 70 eV. Elemental analyses were performed with
a Vario EL apparatus. Compound 13k was available from a previous
study.[10] Isopropylurea (11.15 g, 109.16 mmol) was obtained by
bubbling gaseous NH3 through a solution of isopropylisocyanate
(10.22 g, 120 mmol) in anhydrous CH2Cl2 (200 mL). The resulting
precipitate was collected by suction filtration and washed with
CH2Cl2.
5-Acetylamino-1,5-dimethylbarbituric acid (10a) was prepared
from 1 and methylurea (4); yield 50% (4.80 g); mp: 123–1298C.
5-Acetylamino-5-methyl-1-propylbarbituric acid (10b) was pre-
pared from 1 and n-propylurea (6); yield 37% (3.84 g); mp: 207–
2098C.
5-Acetylamino-1-isopropyl-5-methylbarbituric acid (10c) was ob-
tained from 1 and isopropylurea (7); yield 58% (5.60 g); mp:
>2508C, lit. mp: >2308C.[19]
5-Acetylamino-1,5-diethylbarbituric acid (10d) was obtained
from 2 and ethylurea (5); yield 21% (2.03 g); mp: 189–1948C.
Chemistry
Diethyl 2-acetylamino-2-methylmalonate (1). Diethyl acetylami-
nomalonate (21.72 g, 100 mmol) and methyl iodide (6.9 mL,
15.61 g, 110 mmol) were added to a solution of NaOEt in EtOH
(200 mL, 0.55m, 1.1 equiv). The reaction mixture became orange
and was stirred at reflux for 12 h. EtOH was removed under re-
duced pressure. After the addition of CH2Cl2 (300 mL) the insoluble
material was separated by filtration. The filtrate was evaporated to
dryness and the residue was recrystallized from water to give 1 as
colorless crystals (13.35 g, 58%); mp: 79–858C, lit. mp: 88–908C.[17]
5-Acetylamino-5-ethyl-1-propylbarbituric acid (10e). Reaction of
2 and n-propylurea 6 following the General Procedure gave 10e,
which was purified by recrystallization from EtOH; yield 22%
(2.25 g); mp: 165–1688C.
5-Acetylamino-1-ethyl-5-methylbarbituric acid (10 f) was pre-
pared from 1 and ethylurea (5); yield 51% (4.82 g); mp: 138–
1418C.
5-Acetylamino-5-ethyl-1-isopropylbarbituric acid (10g). Com-
pound 2 was reacted with isopropylurea (7) using the General Pro-
cedure. Extraction with EtOAc (5ꢃ20 mL) gave a yellow oil. Crystal-
lization from EtOAc/hexane afforded 10g; yield 13% (1.33 g); mp:
195–1988C.
Diethyl 2-acetylamino-2-ethylmalonate (2). Diethyl acetylamino-
malonate (21.72 g, 100 mmol) and ethyl bromide (11.99 g,
110 mmol) were added to a solution of NaOEt in EtOH (200 mL,
0.55m, 1 equiv). The reaction mixture was stirred at reflux for 12 h.
EtOH was removed under reduced pressure. After the addition of
CH2Cl2 (300 mL) the insoluble material was separated by filtration.
Silica gel (4 g), Na2SO4 (10 g) and charcoal (4 g) were added to the
filtrate. The mixture was filtered to obtain a colorless solution.
Evaporation of the solvent and drying over CaCl2 gave 2 as a color-
less solid (22.12 g, 82%), which was used without further purifica-
tion; mp: 64–688C, lit. mp: 838C.[17]
5-Acetylamino-1-cyclohexyl-5-methylbarbituric acid (10h). This
compound was obtained from 1 and cyclohexylurea (8) using the
General Procedure to give 10h, which was purified by recrystalliza-
tion from EtOH; yield 45% (5.06 g); mp: >2508C.
5-Acetylamino-1-cyclohexyl-5-ethylbarbituric acid (10i). Reaction
of 2 and cyclohexylurea (8) following the General Procedure yield-
ed 10i, which was purified by recrystallization from EtOH; yield
24% (2.84 g); mp: >2508C, lit. mp: 282–2888C.[34]
Diethyl 2-[(tert-butyloxycarbonyl)amino]-2-ethylmalonate (3). A
solution of diethyl 2-[(tert-butyloxycarbonyl)amino]malonate
(27.53 g, 100 mmol) in EtOH (50 mL) was added dropwise to a solu-
tion of NaOEt in EtOH (122 mL, 0.90m, 1.1 equiv). After 30 min,
ethyl bromide (11.99 g, 110 mmol) was added and the reaction
mixture was held at reflux for 7 h. After removal of the precipitated
NaBr, the resulting filtrate was poured into brine (250 mL) and the
aqueous layer was extracted with EtOAc (5ꢃ100 mL). The com-
bined organic extracts were washed with water (2ꢃ100 mL) and
brine (2ꢃ100 mL), dried over Na2SO4, and filtered after addition of
charcoal. Evaporation to dryness under reduced pressure afforded
3 (11.12 g, 40%) as a yellow oil which was used for the next step
without further purification.
5-[(tert-Butyloxycarbonyl)amino]-5-ethyl-1-phenylbarbituric acid
(10k). This compound was obtained from 3 and phenylurea (9)
using the General Procedure except that the reaction was run for
5 h to give 10k, which was purified by recrystallization from EtOH;
yield 26% (3.61 g); mp: 195–2008C.
Synthesis of 5-aminobarbituric acid hydrochlorides 11a-i: Gen-
eral Procedure. A mixture of the corresponding 5-acetylaminobar-
bituric acid 10 (3.5 mmol) and HCl (25 mL, 8m) was stirred under
reflux for 7 h. The hot, colorless solution was then allowed to cool
down to room temperature, the resulting colorless solid was fil-
tered off and dried under reduced pressure. The filtrate was con-
centrated in vacuo to less than half of its volume and kept at 58C
overnight. The precipitate that formed was collected by filtration,
dried and combined with the first fraction of the product. The
crude material was pure and was used for the next step without
further purification.
Synthesis of barbituric acids 10a–k: General Procedure. Diethyl
2-acetylamino-2-methylmalonate 1 (9.25 g, 40 mmol) or diethyl 2-
acetylamino-2-ethylmalonate 2 (9.81 g, 40 mmol) or diethyl 2-[(tert-
butyloxycarbonyl)amino]-2-ethylmalonate 3 (12.13 g, 40 mmol) and
40 mmol of the appropriate urea (methylurea 2.96 g; ethylurea
3.52 g; n-propylurea 4.09 g; isopropylurea 4.09 g; cyclohexylurea
5.69 g; phenylurea 5.45 g) were added to a solution of NaOEt in
EtOH (200 mL, 0.24m, 1.2 equiv). The resulting mixture was stirred
at 788C for 3 h. The clear, yellow solution was then evaporated in
vacuo. The oily residue was dissolved in a minimum amount of
water, subsequently acidified to pH 2–3 by dropwise addition of
HCl (2m) and kept overnight at 58C. The precipitated product was
isolated by filtration and dried under reduced pressure. If no pre-
cipitation occurred, the solution was extracted with EtOAc (5ꢃ
20 mL). The organic layer was separated, dried (Na2SO4), filtered,
and evaporated to dryness. Pure products were used in the next
step without further purification. Otherwise, further treatment or
recrystallization was performed as indicated below.
5-Amino-1,5-dimethylbarbituric acid hydrochloride (11a). Yield
66% (0.48 g); mp: >2508C.
5-Amino-5-methyl-1-propylbarbituric acid hydrochloride (11b).
Yield 73% (0.65 g); mp: >2508C.
5-Amino-1-isopropyl-5-methylbarbituric
acid
hydrochloride
(11c). Yield 50% (0.41 g); mp: >2508C.
5-Amino-1,5-diethylbarbituric acid hydrochloride (11d). Yield
75% (0.62 g); mp: >2508C.
5-Amino-5-ethyl-1-propylbarbituric acid hydrochloride (11e).
Yield 79% (0.69 g); mp: >2508C.
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5-Amino-1-ethyl-5-methylbarbituric acid hydrochloride (11 f).
Yield 65% (0.50 g); mp: >2508C.
1,5-Diethyl-5-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-
2,4,6(1H,3H,5H)-pyrimidinetrione (13d). Yield 28% (0.14 g). An
analytical sample was obtained by column chromatography using
PE/EtOAc (4:1); mp: 201–2058C.
5-Amino-5-ethyl-1-isopropylbarbituric acid hydrochloride (11g).
Yield 42% (0.37 g); mp: 248–2528C.
5-(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)-5-ethyl-1-propyl-
2,4,6(1H,3H,5H)-pyrimidinetrione (13e). Yield 21% (0.11 g); mp:
185–1878C.
5-Amino-1-cyclohexyl-5-methylbarbituric acid hydrochloride
(11h). Yield 64% (0.62 g); mp: >2508C.
5-Amino-1-cyclohexyl-5-ethylbarbituric acid hydrochloride (11i).
This compound was prepared according to the General Procedure
except that the starting 10i was dissolved in EtOH (25 mL) and
then HCl (200 mL, 8m) was added; yield 64% (0.65 g); mp:
>2508C.
Preparation of 5-phthalimidobarbituric acids 13 f–i from 5-ami-
nobarbituric acids 12 f–i: General Procedure. A mixture of the
corresponding 5-aminobarbituric acid 12 (1.50 mmol), phthalic an-
hydride (0.22 g, 1.50 mmol) in DMF (11 mL) was stirred under reflux
for 5 h. The reaction mixture was then cooled to room temperature
and poured into water (50 mL). The colorless precipitate that
formed was collected by filtration, washed with water and dried
under reduced pressure. The obtained material was pure unless
stated otherwise.
5-Amino-5-ethyl-1-phenylbarbituric acid hydrochloride (11k).
Compound 10k (1.22 g, 3.5 mmol) was dissolved in a solution of
HCl in 1,4-dioxane (14 mL, 4m) and stirred at room temperature
for 2 h. The colorless solid that formed was filtered off, washed
with PE and dried under reduced pressure to give 11 k (0.93 g,
88%); mp: 227–2338C.
5-(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)-1-ethyl-5-methyl-
2,4,6(1H,3H,5H)-pyrimidinetrione (13 f). Yield 48% (0.23 g); mp:
235–2388C.
Synthesis of 5-aminobarbituric acids 12 f–k: General Procedure.
The corresponding 5-aminobarbituric acid hydrochloride 11
(3.5 mmol) was dissolved in a minimum volume of water. The in-
soluble material was separated by filtration and the acidic filtrate
(pH 2–3) was adjusted to pH 6 by dropwise addition of aqueous
NaOH (2m) under stirring in an ice-bath. The resulting colorless
solid was collected by filtration and dried under reduced pressure.
The obtained material was pure and was directly used in the next
step unless stated otherwise.
5-(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)-5-ethyl-1-isopropyl-
2,4,6(1H,3H,5H)-pyrimidinetrione (13g). Yield 23% (0.12 g). An
analytical sample was obtained by column chromatography using
PE/EtOAc (4:1); mp: 212–2158C.
1-Cyclohexyl-5-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-5-
methyl-2,4,6(1H,3H,5H)-pyrimidinetrione (13h). The crude materi-
al was recrystallized from PE/EtOAc (4:3); yield 49% (0.27 g); mp:
241–2448C.
5-Amino-1-ethyl-5-methylbarbituric acid (12 f). Yield 39%
(0.25 g); mp: 185–1918C.
1-Cyclohexyl-5-(1,3-dihydro-1,3-dioxo-2H-isoindol-2-yl)-5-ethyl-
2,4,6(1H,3H,5H)-pyrimidinetrione (13i). This compound was pre-
pared according to the General Procedure from 12i (0.38 g,
1.50 mmol) and phthalic anhydride (0.22 g, 1.50 mmol). The crude
product was recrystallized from EtOH to give 81 mg of 13i. After
the removal of the crude product, N-(1-cyclohexyl-5-ethylhexahy-
dro-2,4,6-trioxopyrimidin-5-yl)phthalamic acid precipitated from
the DMF/H2O filtrate after standing at room temperature for three
days. The isolated compound (0.45 g, 1.12 mmol) was transformed
into the desired phthalimidobarbituric acid 13i by heating at 858C
for 10 min in Ac2O (7 mL). After cooling, the precipitated material
was collected and washed with a mixture of hexane/Et2O (1:1) to
give 0.34 g of the final product 13i. Total yield 73%; mp: 245–
2508C, lit. mp: 248–2538C.[8]
5-Amino-5-ethyl-1-isopropylbarbituric acid (12g). Yield 52%
(0.39 g); mp: 140–1428C.
5-Amino-1-cyclohexyl-5-methylbarbituric acid (12h). Yield 96%
(0.80 g); mp: 202–2038C.
5-Amino-1-cyclohexyl-5-ethylbarbituric acid (12i). Yield 97%
(0.86 g); mp: 160–1648C, lit. mp: 171–1738C.[19]
5-Amino-5-ethyl-1-phenylbarbituric acid (12k). The crude prod-
uct was recrystallized from EtOH; yield 37% (0.32 g); mp: 214–
2178C, lit. mp: 192–1938C.[19]
Preparation of 5-phthalimidobarbituric acids 13a–e from 5-ami-
nobarbituric acid hydrochlorides 11a–e: General Procedure. A
mixture of the corresponding 5-aminobarbituric acid hydrochloride
11 (1.50 mmol), phthalic anhydride (0.22 g, 1.50 mmol) and Et3N
(0.15 g, 1.50 mmol) in DMF (11 mL) was stirred under reflux for 5 h.
The reaction mixture was then allowed to cool down to room tem-
perature and poured into water (50 mL). The colorless precipitate
that formed was collected by filtration, washed with water and
dried under reduced pressure. The obtained material was pure
unless stated otherwise.
Preparation of 5-(tetrafluorophthalimido)barbituric acids 14a–
e from 5-aminobarbituric acid hydrochlorides 11a–e: General
Procedure. A mixture of the corresponding 5-aminobarbituric acid
hydrochloride 11 (1.50 mmol), tetrafluorophthalic anhydride
(0.40 g, 1.80 mmol) and Et3N (0.15 g, 1.50 mmol) in glacial AcOH
(11 mL) was stirred under reflux for 3 h. The yellow solution was
then allowed to cool down to room temperature and evaporated
to dryness under reduced pressure. The oily residue was recrystal-
lized from 70% EtOH to give 5-tetrafluorophthalimides 14a–e as
colorless crystals.
5-(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)-1,5-dimethyl-
2,4,6(1H,3H,5H)-pyrimidinetrione (13a). Yield 40% (0.18 g); mp:
>2508C.
1,5-Dimethyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-dioxo-2H-iso-
indol-2-yl)-2,4,6-(1H,3H,5H)-pyrimidinetrione (14a). Yield 47%
(0.22 g); mp: 168–1728C.
5-(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)-5-methyl-1-propyl-
2,4,6(1H,3H,5H)-pyrimidinetrione (13b). Yield 40% (0.20 g); mp:
188–1908C.
5-Methyl-1-propyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-dioxo-
2H-isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14b). Yield
42% (0.25 g); mp: 173–1778C.
5-(1,3-Dihydro-1,3-dioxo-2H-isoindol-2-yl)-1-isopropyl-5-methyl-
2,4,6(1H,3H,5H)-pyrimidinetrione (13c). Yield 36% (0.18 g); mp:
221–2248C.
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1-Isopropyl-5-methyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-
dioxo-2H-isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14c).
Yield 42% (0.25 g); mp: 184–1878C.
from PE/EtOAc (3:1); yield 13% (0.10 g); light brown crystals; mp:
163–1678C.
N-(5-Ethyl-hexahydro-2,4,6-trioxo-1-propyl-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15e). Yield 12% (0.10 g); colorless
crystals; mp: 79–828C.
1,5-Diethyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-dioxo-2H-isoin-
dol-2-yl)-2,4,6-(1H,3H,5H)-pyrimidinetrione (14d). Yield 23%
(0.14 g); mp: 152–1548C.
Preparation of 5-(2,3,4,5-tetrafluorobenzamido)barbituric acids
5-Ethyl-1-propyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-dioxo-2H-
isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14e). Yield 47%
(0.29 g); mp: 137–1408C.
15 f–k from 5-aminobarbituric acids 12 f–k: General Procedure.
A
mixture of the corresponding 5-aminobarbituric acid 12
(2 mmol), tetrafluorophthalic anhydride (0.44 g, 2 mmol) and DMF
(14 mL) was stirred under reflux for 5 h. The yellow solution was
then allowed to cool down to room temperature and poured into
water (50 mL). The precipitate that formed was collected by filtra-
tion and dried under reduced pressure. The obtained material was
pure unless stated otherwise.
Preparation of 5-(tetrafluorophthalimido)barbituric acids 14 f–k
from 5-aminobarbituric acids 12 f–k: General Procedure. A mix-
ture of the corresponding 5-aminobarbituric acid 12 (1.50 mmol)
and tetrafluorophthalic anhydride (0.40 g, 1.80 mmol) in glacial
AcOH (11 mL) was stirred under reflux for 3 h. The yellow solution
was then cooled and evaporated to dryness under reduced pres-
sure. The oily residue was recrystallized from EtOH to give 5-tetra-
fluorophthalimides 14 f–k as colorless crystals.
N-(1-Ethyl-hexahydro-5-methyl-2,4,6-trioxo-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15 f). Yield 87% (0.63 g); colorless
crystals; mp: 207–2128C.
1-Ethyl-5-methyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-dioxo-2H-
isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14 f). Yield 55%
(0.32 g); mp: 178–1848C.
N-(5-Ethyl-hexahydro-1-isopropyl-2,4,6-trioxo-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15g). Yield 91% (0.71 g), colorless
crystals; mp: 166–1718C.
5-Ethyl-1-isopropyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-dioxo-
2H-isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14g). Yield
56% (0.35 g); mp: 134–1398C.
N-(1-Cyclohexyl-hexahydro-5-methyl-2,4,6-trioxo-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15h). Yield 92% (0.76 g); yellow
crystals; mp: 232–2348C.
1-Cyclohexyl-5-methyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-
dioxo-2H-isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14h).
Yield 46% (0.31 g); mp: 208–2118C.
N-(1-Cyclohexyl-5-ethyl-hexahydro-2,4,6-trioxo-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15i). Yield 72% (0.62 g); colorless
crystals; mp: 210–2128C.
1-Cyclohexyl-5-ethyl-5-(4,5,6,7-tetrafluro-1,3-dihydro-1,3-dioxo-
2H-isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14i). Yield
73% (0.50 g); mp: 172–1768C.
N-(5-Ethyl-hexahydro-2,4,6-trioxo-1-phenyl-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15k). The crude material was re-
crystallized from PE/EtOAc (2:1); yield 32% (0.28 g); yellow crystals;
mp: 210–2158C.
5-Ethyl-1-phenyl-5-(4,5,6,7-tetrafluoro-1,3-dihydro-1,3-dioxo-2H-
isoindol-2-yl)-2,4,6(1H,3H,5H)-pyrimidinetrione (14k). Yield 59%
(0.40 g); mp: 209–2158C, lit. mp: 218–2208C.[8]
Biological investigations
Preparation of 5-(2,3,4,5-tetrafluorobenzamido)barbituric acids
15a–e from 5-aminobarbituric acid hydrochlorides 11a–e: Gen-
eral Procedure. A mixture of the corresponding 5-aminobarbituric
acid hydrochloride 11 (2 mmol), tetrafluorophthalic anhydride
(0.44 g, 2 mmol), Et3N (0.20 g, 2 mmol) and DMSO (3 mL) was
stirred and heated on an oil bath at 1538C for 5 h. The reaction
mixture was then allowed to cool down to room temperature and
poured into water (10 mL). The oil that immediately formed was
carefully removed from the solution, from which a solid precipitat-
ed after four days standing at room temperature. The precipitate
was collected by filtration, washed with water and dried under re-
duced pressure. The obtained material was pure unless stated
otherwise.
Rat aortic ring assay: To determine the extent of the anti-angio-
genic effects of the test compounds, the rat aortic ring assay was
carried out as described elsewhere.[10,14] Briefly, 12-well tissue cul-
ture plates were covered with 250 mL of Matrigel (Becton-Dickin-
son) and allowed to gel for 30 to 45 min at 378C and 5% CO2. Sec-
tions of thoracic aorta were removed from 8- to 10-week-old male
Sprague–Dawley rats. Following excision of fibroadipose tissue, the
aortic sections were cut into 1-mm-long cross-sections, placed on
Matrigel-coated wells, and layered with additional Matrigel
(250 mL). These were then allowed to set, after which the cross-sec-
tional rings were covered with endothelial cell growth media
(EGM-II) and incubated under 5% CO2 at 378C overnight. EGM-II
consists of endothelial cell basal medium (EBM-II) and endothelial
cell growth factors. After 24 h, the medium was removed and re-
placed with EBM-II (1 mL), supplemented with fetal bovine serum
(2%), amphotericin B (0.25 mgmLÀ1), and gentamicin (1 mgmLÀ1).
The aortic rings were treated daily with vehicle (0.5% DMSO), CAI
(12.5 mgmLÀ1; positive control), test compounds, each at a dose of
50 mm, for four days. This was replicated four times using aortas
from four different rats. The area of angiogenic sprouting was
quantified using Adobe Photoshop.
N-(Hexahydro-1,5-dimethyl-2,4,6-trioxo-5-pyrimidinyl)-2,3,4,5-
tetrafluorobenzamide (15a). Yield 29% (0.21 g); yellow crystals;
mp: 219–2228C.
N-(Hexahydro-5-methyl-2,4,6-trioxo-1-propyl-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15b). Yield 17% (0.14 g); yellow
crystals; mp: 83–878C.
N-(Hexahydro-1-isopropyl-5-methyl-2,4,6-trioxo-5-pyrimidinyl)-
2,3,4,5-tetrafluorobenzamide (15c). The crude material was re-
crystallized from PE/EtOAc (1:1); yield 7% (54 mg); colorless crys-
tals; mp: 225–2298C.
Disclosure of Potential Conflicts of Interest: A.A., E.R.G., W.D.F.,
and M.G. have ownership interests on a patent on the novel com-
pounds assessed in this study [Patent No. US8143252 B2 (March
27, 2012)].[15] No potential conflicts of interest were disclosed by
the other authors.
N-(1,5-Diethyl-hexahydro-2,4,6-trioxo-5-pyrimidinyl)-2,3,4,5-tet-
rafluorobenzamide (15d). The crude material was recrystallized
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Full Papers
[15] W. D. Figg, E. Lepper, M. Gꢀtschow, A. Ambroz˙ak (US Dept. of Health
and Human Services), US Pat. No. US8143252 B2, 2012.
Disclaimer: The content of this publication does not necessarily re-
flect the views or policies of the US Department of Health and
Human Services, nor does the mention of trade names, commercial
products, or organization imply endorsement by the US Govern-
ment.
[16] a) G. W. Muller, R. Chen, S. Y. Huang, L. G. Corral, L. M. Wong, R. T. Patter-
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Acknowledgements
G.S. thanks Prof. A. C. Filippou for support.
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Keywords: angiogenesis · barbituric acids · phthalimides ·
tetrafluorobenzamides · tetrafluorophthalimides
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Received: September 29, 2016
Revised: October 18, 2016
Published online on && &&, 0000
ChemMedChem 2016, 11, 1 – 10
www.chemmedchem.org
9
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
These are not the final page numbers! ÞÞ

FULL PAPERS
A. Ambroz˙ak, C. Steinebach, E. R. Gardner,
S. L. Beedie, G. Schnakenburg, W. D. Figg,
M. Gꢀtschow*
&& – &&
Synthesis and Antiangiogenic
Properties of Tetrafluorophthalimido
and Tetrafluorobenzamido Barbituric
Acids
Tetrafluorinated anti-angiogenic
agents: Synthetic entries to phthali-
mides, tetrafluorophthalimides and
tetrafluorobenzamides, all of which con-
tain barbituric acid moieties, were ach-
ieved and thirty derivatives of these
three subseries were tested for their
antiangiogenic properties in rat aortic
ring assays. Despite differences in mo-
lecular structure and conformational
flexibility, all representatives of the two
fluorine-containing subseries were
shown to be biologically active.
&
ChemMedChem 2016, 11, 1 – 10
www.chemmedchem.org
10
ꢁ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!