Synthesis and biological evaluation of benzocyclooctene-based and indene-based anticancer agents that function as inhibitors of tubulin polymerization

Article abstract of DOI:10.1039/c6md00459h

The natural products colchicine and combretastatin A-4 (CA4) have been inspirational for the design and synthesis of structurally related analogues and spin-off compounds as inhibitors of tubulin polymerization. The discovery that a water-soluble phosphate prodrug salt of CA4 (referred to as CA4P) is capable of imparting profound and selective damage to tumor-associated blood vessels paved the way for the development of a new therapeutic approach for cancer treatment utilizing small-molecule inhibitors of tubulin polymerization that also act as vascular disrupting agents (VDAs). Combination of salient structural features associated with colchicine and CA4 led to the design and synthesis of a variety of fused aryl-cycloalkyl and aryl-heterocyclic compounds that function as inhibitors of tubulin polymerization. Prominent among these compounds is a benzosuberene analogue (referred to as KGP18), which demonstrates sub-nM cytotoxicity against human cancer cell lines and functions (when administered as a water-soluble prodrug salt) as a VDA in mouse models. Structure activity relationship considerations led to the evaluation of benzocyclooctyl [6,8 fused] and indene [6,5 fused] ring systems. Four benzocyclooctene and four indene analogues were prepared and evaluated biologically. Three of the benzocyclooctene analogues were active as inhibitors of tubulin polymerization (IC₅₀ < 5 μM), and benzocyclooctene phenol 23 was comparable to KGP18 in terms of potency. The analogous indene-based compound 31 also functioned as an inhibitor of tubulin polymerization (IC₅₀ = 11 μM) with reduced potency. The most potent inhibitor of tubulin polymerization from this group was benzocyclooctene analogue 23, and it was converted to its water-soluble prodrug salt 24 to assess its potential as a VDA. Preliminary in vivo studies, which utilized the MCF7-luc-GFP-mCherry breast tumor in a SCID mouse model, demonstrated that treatment with 24 (120 mg kg^?1) resulted in significant vascular shutdown, as evidenced by bioluminescence imaging at 4 h post administration, and that the effect continued at both 24 and 48 h. Contemporaneous studies with CA4P, a clinically relevant VDA, were carried out as a positive control.

Full text of DOI:10.1039/c6md00459h

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DOI: 10.1039/C6MD00459H
Synthesis and Biological Evaluation of
Benzocycloocteneꢀbased and Indeneꢀbased
Anticancer Agents that Function as Inhibitors of
Tubulin Polymerization†
Christine A. Herdmana, Tracy E. Streckera, Rajendra P. Tanpurea, Zhi Chena, Alex
Wintersb, Jeni Gerberichb, Li Liub, Ernest Hamelc, Ralph P. Masonb, David J. Chaplina,d
Mary Lynn Trawicka, and Kevin G. Pinneya*
aDepartment of Chemistry and Biochemistry, Baylor University, One Bear Place #97348,
Waco, Texas 76798ꢀ7348, United States
b Prognostic Imaging Research Laboratory, Department of Radiology, The University of
Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390ꢀ
9058, United States
cScreening Technologies Branch, Developmental Therapeutics Program, Division of
Cancer Treatment and Diagnosis, National Cancer Institute, Frederick National
Laboratory for Cancer Research, National Institutes of Health, Frederick, MD 21702,
United States
dMateon Therapeutics, Inc., 701 Gateway Boulevard, Suite 210, South San Francisco,
California 94080, United States
Keywords: benzocyclooctene analogues, indene analogues, vascular disrupting agents
(VDAs), inhibitors of tubulin polymerization, smallꢀmolecule synthesis, bioluminescence
imaging (BLI)
†A significant portion of the work presented in this manuscript was funded through
Mateon Therapeutics Inc. (formerly OXiGENE Inc.), and this relationship is properly
indicated in the acknowledgement section. One Mateon employee and shareholder Dr.
David Chaplin, is included as a co-author on this manuscript for his valuable
contributions to the overall project. In addition, one of the authors (KGP) is a paid
consultant and shareholder with Mateon. We are pleased with this productive and useful
long-term scientific collaboration and funding relationship with Mateon, and it is
important to note that there is absolutely no actual conflict of interest associated with the
science presented in this manuscript.

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Abstract
The natural products colchicine and combretastatin Aꢀ4 (CA4) have been inspirational
for the design and synthesis of structurally related analogues and spinꢀoff compounds as
inhibitors of tubulin polymerization. The discovery that a waterꢀsoluble phosphate
prodrug salt of CA4 (referred to as CA4P) is capable of imparting profound and selective
damage to tumorꢀassociated blood vessels paved the way for the development of a new
therapeutic approach for cancer treatment utilizing smallꢀmolecule inhibitors of tubulin
polymerization that also act as vascular disrupting agents (VDAs). Combination of salient
structural features associated with colchicine and CA4 led to the design and synthesis of
a variety of fused arylꢀcycloalkyl and arylꢀheterocyclic compounds that function as
inhibitors of tubulin polymerization. Prominent among these compounds is a
benzosuberene analogue (referred to as KPG18), which demonstrates subꢀnM
cytotoxicity against human cancer cell lines and functions (when administered as a waterꢀ
soluble prodrug salt) as a VDA in mouse models. Structure activity relationship
considerations led to the evaluation of benzocyclooctyl [6,8 fused] and indene [6,5 fused]
ring systems. Four benzocyclooctene and four indene analogues were prepared and
evaluated biologically. Three of the benzocyclooctene analogues were active as inhibitors
of tubulin polymerization (IC50 < 5 ꢁM), and benzocyclooctene phenol 23 was
comparable to KGP18 in terms of potency. The analogous indeneꢀbased compound 31
also functioned as an inhibitor of tubulin polymerization (IC50 = 11 ꢁM) with reduced
potency. The most potent inhibitor of tubulin polymerization from this group was
benzocyclooctene analogue 23, and it was converted to its waterꢀsoluble prodrug salt 24
to assess its potential as a VDA. Preliminary in vivo studies, which utilized the MCF7ꢀ

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lucꢀGFPꢀmCherry breast tumor in a SCID mouse model, demonstrated that treatment
with 24 (120 mg/kg) resulted in significant vascular shutdown, as evidenced by
bioluminescence imaging at 4 h post administration, and that the effect continued at both
24 and 48 h. Contemporaneous studies with CA4P, a clinically relevant VDA, were
carried out as a positive control.

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1. Introduction
The colchicine site located on the βꢀsubunit of the α,βꢀtubulin heterodimer continues
to serve as a rich and productive target for a wideꢀrange of structurally diverse smallꢀ
molecule anticancer agents. Through a direct binding interaction at the colchicine site,
these compounds inhibit the polymerization of the tubulin heterodimer into microtubules.
Disruption of the inherent dynamic relationship between microtubules and tubulin
heterodimers leads to two mechanistically distinct, yet complementary, cancer treatment
strategies. One approach centers on the well known cytotoxic effect that results when
disruption of the tubulinꢀmicrotubule system, caused by treatment with smallꢀmolecule
inhibitors of tubulin polymerization or depolymerization, impacts the ability of cancer
cells to divide. A wideꢀrange of smallꢀmolecule therapeutic agents has been discovered
and developed that function as antiproliferative agents through this mechanism (Fig. 1).
Figure 1. Representative smallꢀmolecule antiꢀproliferative agents including colchicine,1
paclitaxel,2,3 CA4,4 vinblastine,5,6 OXi6196,7,8 KGP18,9–11 KGP156,10,12,13 OXi8006,14
and BNC105.15,16

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This approach, while productive as an anticancer strategy, has limitations and challenges
since both neoplastic and healthy cells are impacted. Targeting strategies such as the use
of antibodyꢀdrug conjugates (ADCs) bearing active payloads have been successful with
two FDA approved ADCs currently available.17–19 In another example, the targeting of
tumor hypoxia with bioreductively activatable prodrug conjugates (BAPCs) has been
explored20,21 with recent clinical trials involving PRꢀ10422,23 and THꢀ30224–26 serving as
representative examples (Fig. 2).
Figure 2. Structures of PRꢀ104 and THꢀ302.
PRꢀ104 is hydrolyzed to its alcohol parent compound by available phosphatases and,
under hypoxic conditions, is activated by NADPHꢀcytochrome P450 reductases to the
reactive nitrogen mustards that crosslink to DNA and ultimately cause tumor
cytotoxicity.22 THꢀ302 utilizes a similar hypoxia reduction strategy in order to release its
2ꢀnitroimidazole trigger leaving the bromoꢀisophosphoramide mustard to cross link with
DNA.26 The targeting of tumor hypoxia has also been examined with BAPCs that
incorporate the tubulinꢀactive natural product combretastatin Aꢀ4 (CA4).27 These
strategies, along with others, continue to represent areas of ongoing research effort.

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A second mechanistic approach to cancer therapy involving inhibition of the tubulinꢀ
microtubule protein system centers on selective disruption of existing vasculature feeding
tumors, leading to limitation of oxygen and nutrient delivery to the cells and impedance
of the ability of these cells to clear cellular waste products. This ultimately leads to tumor
necrosis. This approach to targeting existing tumorꢀfeeding vasculature utilizes anticancer
agents referred to as vascular disrupting agents (VDAs) and is unique and
mechanistically distinct from the fairly wellꢀestablished and more commonly described
therapeutic approach employing angiogenesis inhibiting agents (AIAs) that impede the
formation of new vessels.28–30 Rapid neovascularization occurs when tumors grow larger
than about 1 mm3, as they can no longer acquire sufficient nutrients from the surrounding
vasculature.31 Such tumors require their own vascular network to supply oxygen and
nutrients and remove waste products.28,29,32 Because of their rapid growth and
development, these vessels feature irregular branching and diameter, poor wall structure,
abnormal bulges, and blind ends.31,33–36 This immature vasculature provides an attractive
target for cancer therapy. Therapeutic agents that target tumor vasculature are referred to
as vascular targeting agents, which can be divided AIAs and VDAs.28,33,30 AIAs inhibit
the growth of new vasculature to the tumor, while VDAs damage already sprouted
vessels.35–40 VDAs are subꢀdivided into biological agents and smallꢀmolecule
therapeutics (Fig. 3),40 and treatment with either of these entities leads to tumor necrosis.

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Figure 3. Several clinically relevant VDAs including CA4P,41–45 CA1P,43,46
BNC105,15,16,43,45,47 AVE8062,43,48–50 and ZD6126.42,43,51
Colchicine, a natural product originally isolated from the autumn crocus, Colchicum
autumnale, and the namesake for the colchicine site on tubulin,52,53 is a potent inhibitor of
tubulin polymerization, but colchicine has a narrow therapeutic window limiting its
development as an anticancer agent.35,54,55 Another natural product binding to the
colchicine site on tubulin is CA4 (Fig. 1).4 Originally isolated from the African
bushwillow tree, Combretum caffrum, and synthesized by Pettit and coꢀworkers, CA4
binds tightly to the colchicine site on tubulin and functions as a VDA.55–58 Combretastatin
Aꢀ4P [(CA4P), Fig. 3] was synthesized as a waterꢀsoluble prodrug salt for therapeutic
use,41,55,56,58 and both CA4 and CA4P are now being evaluated in clinical trials.42,45,59–62
Drawing upon the key structural motifs of colchicine and CA4, the Pinney Research
Group (Baylor University) has a longꢀstanding interest in the discovery and development
of new smallꢀmolecule anticancer agents that function as highly cytotoxic agents and/or

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as potent VDAs. Representative examples within this library include combretastatin,63–66
benzo[b]thiophene,67 dihydronaphthalene,9 benzosuberene,9–12 and indoleꢀbased
analogues.14,68 The Pinney Research Group had previously shown that expansion of the
fused alkyl ring of the dihydronaphthalene anticancer agent known as OXi6196 (Fig. 1)
by one carbon to the fused sevenꢀmembered ring benzosuberene anticancer agent known
as KGP18 (Fig. 1) was an effective design paradigm, since KGP18 was highly cytotoxic
against human cancer cell lines and strongly inhibits tubulin polymerization.
To further elucidate the structure activity relationship (SAR) considerations
associated with functionalized fused arylꢀcarbocyclic ring systems that mimic colchicine
and CA4 and their interaction with the tubulinꢀmicrotubule system, benzocyclooctene
(fused 6,8 ring system) analogues and corresponding indene (fused 6,5 ring system)
analogues were prepared by chemical synthesis and subjected to preliminary biological
evaluation.
2. Results and Discussion
2.1 Synthesis
Four benzocyclooctene analogues and four indene analogues were synthesized to
further investigate SAR considerations associated with fused aliphatic ring structures and
corresponding cytotoxicity and inhibition of tubulin polymerization. These analogues
were prepared utilizing a synthetic strategy reminiscent of that employed for a variety of
benzosuberene analogues developed in the Pinney Research Group.10,11 The synthesis of
each benzocyclooctene analogue was initiated with a Wittig olefination followed by
catalytic hydrogenation to afford carboxylic acids 3 and 4 (Scheme 1). A FriedelꢀCrafts

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intramolecular annulation was accomplished using Eaton’s reagent (7.7 weight percent
H),69 and the reaction was diluted and cooled in order to facilitate the
P
2
O5
in CH
3
SO3
construction of benzocyclooctanones 5 and 6 (Scheme 1). Without dilution and cooling,
the desired product was not formed and only starting material remained.
Scheme 1. Synthesis of benzocyclooctanone analogues 5 and 6.
A similar catalytic reduction was utilized with starting material transꢀ2,3ꢀ
dimethoxycinnamic acid to afford carboxylic acids 9 and 10, which were cyclized with
Eaton’s reagent to their corresponding indanone analogues 11 and 12 (Scheme 2).
Scheme 2. Synthesis of indanone analogues 11 and 12.
Benzocyclooctanone 5 and indanone 11 bearing the ortho dimethoxy motif were each
subjected to a selective demethylation10,11,70 to afford phenolic analogues 13 and 15,
which were subsequently protected with TBS to yield 14 and 16 (Scheme 3).

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Scheme 3. Synthesis of TBSꢀprotected benzocyclooctanone 14 and indanone 16.
Trimethoxyphenyllithium (prepared from the corresponding aryl bromide) underwent a
1,2ꢀaddition reaction to benzocyclooctanone analogues 5, 6 and 14 to afford the
corresponding tertiary alcohols 17, 18, and 19. Subsequent dehydration afforded
benzocyclooctene analogues 20 and 21 and TBSꢀprotected analogue 22, which underwent
deprotection to afford phenolic benzocyclooctene 23 (Scheme 4).
Scheme 4. Synthesis of target benzocyclooctene analogues 20, 21, and 23.

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Phenolic analogue 23 was converted to its corresponding phosphate prodrug salt 24, in
order to increase water solubility for in vivo studies (Scheme 5).
Scheme 5. Conversion of analogue 23 to its corresponding phosphate prodrug salt 24.
Analogous aryl addition reactions were carried out on indanone intermediates 11, 12, and
16 to generate the corresponding tertiary alcohols 25, 26, and 27 (Scheme 6). Subsequent
dehydration afforded indene analogues 28 29, and 30. Removal of the TBS group
afforded phenolic indene 31.
Scheme 6. Synthesis of target indene compounds 28, 29, and 31.
The indene phenol 31 was also converted to its corresponding phosphate salt 32 (Scheme
7). While TEA proved to be an acceptable base (due to ease of removal) for use in the
synthesis of the eight membered ring phosphate salt 24, in the synthesis of the indene

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phosphate salt 32 TEA proved to be hard to remove during purification. Altering the base
to pyridine solved this problem and allowed the waterꢀsoluble phosphate salt 32 to be
synthesized in high purity.
Scheme 7. Synthesis of target indene waterꢀsoluble analogue 32.
Due to their increased size, eight membered rings are the first in the homologous
series (3, 4, 5, 6, 7 – membered rings) that can accommodate both Z and E double bond
configurations.71,72 However, in our hands only the Z configurations were synthesized. Xꢀ
ray crystal structures were obtained for benzocyclooctene analogues 20 and 23 to confirm
their Z double bond configuration (see Supplementary Data).

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Figure 4. Compilation of synthesized benzocyclooctene analogues 20, 21, 23, and 24 and
indene analogues 28, 29, 31, and 32.
2.2 Biological Evaluation
The four target benzocyclooctene and four indene analogues were evaluated for their
cytotoxicity against human cancer cell lines and for their abilities to inhibit tubulin
polymerization and colchicine binding to tubulin.
Table 1. Inhibition of tubulin polymerization [(expressed as half maximal inhibitory
concentration (IC50)] and cytotoxicity [expressed as growth inhibition of 50% (GI50)] of
the eight target analogues synthesized.
Compound
Inhibition of
tubulin
% Inhibition
of
GI50 (ꢁM) SRB
assaya
polymerization
IC50 (ꢁM) ± SD
colchicine
binding ± SD
NCIꢀH460
0.00500c,d
0.00282c
0.0000418g
0.395
DUꢀ145
0.00602c,d
0.00336c
0.0000249 g
0.448
SKꢀOVꢀ3
0.00506d
0.00190
1.0b
>20b
98
± 0.007
CA4
CA4P
KGP18
20
nre
1.4f
0.0000543 g
0.512
nre
4.5 ± 0.5
31 ± 0.6
3.0 ± 0.1
1.2 ± 0.1
29 ± 5
78 ± 4
0.431
0.107
0.570
0.105
0.400
21
23
0.0811

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>20
>20
0.0260
0.0410
34.6
0.0366
9.46
24
28
29
31
ndh
ndh
42.2
4.02
>20
4.66
6.15
ndh
11 ± 2
>20
17 ± 5
0.388
1.50
0.362
3.34
0.704
0.334
ndh
32
a Average of n ≥ 3 independent determinations
b Data from ref. 73
c For additional data, see ref. 73
d Data from ref. 13
e nr = not reported
f For additional data, see ref. 12
g For additional data, see ref. 9
h nd = not determined
Among the seven compounds synthesized for this study and analyzed biologically, only
the target benzocyclooctene analogues (20, 21, and 23) had activities as inhibitors of
tubulin polymerization similar to those of CA4 and KGP18. Benzocyclooctene phenol 23
demonstrated the lowest IC50 value (1.2 ꢁM) among the compounds evaluated in this
study. A binding study utilizing radiolabeled colchicine demonstrated that at a
concentration 5 ꢁM, phenol 23 inhibited colchicine binding by 78%, 20% less than the
activity obtained with 5 µM CA4 (used as a positive control). Considering the three
indene analogues, only phenolic indene 31 demonstrated modest inhibition of tubulin
polymerization, with an IC50 value of 11 ꢁM.

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Benzocyclooctene phenol 23 and its corresponding phosphate prodrug salt 24 were
the most cytotoxic analogues in these series against the three human cancer cell lines
examined (for example, GI50 = 0.105 and 0.0410 ꢀM against DUꢀ145 (prostate) for
analogues 23 and 24, respectively). While structurally similar to KGP18, differing by the
addition of one carbon to the aliphatic ring, the phenolic benzocyclooctene analogue is
dramatically less cytotoxic than its benzosuberene counterpart. Compounds 23 and 24
had GI50 values in the submicromolar range, while the values obtained with KGP18 were
all subnanomolar.
2.3 Dynamic bioluminescence imaging
Bioluminescence imaging (BLI) is a highly valuable modality with diverse
applications in a wide range of biological models and systems.74–76 BLI is a particularly
useful tool for assessing and quantifying in vivo blood flow reduction following treatment
with a VDA.54,76–79 In the current study MCF7 human breast cancer cells, which had been
previously transfected stably to express the enzyme luciferase, as well as two fluorescent
proteins, as designated by MCF7ꢀlucꢀGFPꢀmCherry, were implanted in SCID mice, as
described previously.78 Since the luciferase substrate luciferin can be delivered to the
tumor via the blood stream, damage to the vessels by a VDA can be quantified by
measurement of reduced bioluminescence upon injection of luciferin.54 In the study
shown in Fig. 5, three mice bearing the MCF7ꢀlucꢀGFPꢀmCherry breast tumor were
injected ip with analogue 24 (120 mg/kg), and BLI assessment was performed at baseline
(0 h, preꢀadministration) and at 4, 24 , and 48 h after administration of 24. In a
contemporaneous study, one mouse was treated with CA4P (120 mg/kg) as a positive

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control, and an additional mouse was treated with saline alone. A limited dose escalation
study with analogue 24 in nonꢀtumor bearing SCID mice (60ꢀ150 mg/kg, unpublished
data) suggested that a dose of 120 mg/kg was tolerated and likely below the maximum
tolerated dose (MTD), which has not yet been determined. The optimal CA4P dose in
SCID mice for evaluation of VDA efficacy has been previously established at 120
mg/kg.76 Single dose treatment with both analogue 24 and CA4P resulted in a significant
reduction in bioluminescence (approximately 80% decrease as compared to baseline or
saline control; p<0.05) at 4 h after compound injection. While bioluminescence intensity
in the mouse treated with compound 24 recovered somewhat at 24 and 48 h, it remained
significantly below baseline values (p<0.005). In this study, the BLI data for both
analogue 24 and CA4P at 4 h were statistically different from the saline control, but not
from each other or from the data obtained at other time points. Following the 48 h time
point BLI mice were sacrificed and tumors excised and prepared for histology. Routine
staining using H&E indicated much more extensive necrosis throughout the tumors
following administration of 24 or CA4P each at 120 mg/kg, as compared with saline
control (Fig. 6). Thus, analogue 24 is a good candidate for further assessment and may be
a therapeutically useful VDA.

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Figure 5. Dynamic bioluminescence with respect to vascular disruption. A) Graphs show
evolution of light emission from individual MCF7ꢀlucꢀGFPꢀmCherry breast tumors
following administration of luciferin substrate subcutaneously in the foreꢀback region of
each mouse at time 0. Respective curves are baseline (blue), 4 h (red), 24 h (green) and
48 h (purple) post administration of VDA. Left hand panel shows representative mouse
with 120 mg/kg analogue 24 and right hand panel shows CA4P (120 mg/kg). B)
Photographs show selected images at the 10 min. time point. Left hand group for
analogue 24 and right hand group for CA4P for the same mice used to generate the
curves for part A. Respective images are each scaled to same values.

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Figure 6. Histological assessment of tumor necrosis. H&E stained tumor cross sections
showing necrotic (pink) and viable (purple) regions at 48 h post treatment for A:
Analogue 24 (120 mg/kg) B: CA4P (120 mg/kg) C: Saline.
3. Conclusions
These studies, which focused on indene and benzocyclooctene ring systems,
expanded the known SAR associated with the effect that fused aliphatic ring size plays in
regard to cytotoxicity and inhibition of tubulin polymerization. From the group of eight
analogues prepared by chemical synthesis with seven compounds evaluated biologically,
three benzocyclooctene analogues were strong inhibitors of tubulin polymerization and
one indene analogue was a modest inhibitor. The most promising compound
(benzocyclooctene analogue 23) was prepared and evaluated as its corresponding waterꢀ
soluble phosphate salt 24. It demonstrated significant in vivo reduction of blood flow (as
evidenced by BLI) in an MCF7ꢀlucꢀGFPꢀmCherry tumor model in SCID mice, and the
results indicated that 24 should undergo further evaluation as a VDA for potential cancer
treatment.
4. Acknowledgements
The authors are grateful to the National Cancer Institute of the National Institutes of
Health (Grant No. 5R01CA140674 to K.G.P, M.L.T, and R.P.M), the Cancer Prevention
and Research Institute of Texas (CPRIT, Grant No. RP140399 to K.G.P., M.L.T., and

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R.P.M.), and Mateon Therapeutics, Inc. (grant to K.G.P. and M.L.T.) for their financial
support of this project. The content is solely the responsibility of the authors and does not
necessarily reflect the official views of the National Institutes of Health. The authors
would also thank Dr. Craig Moehnke and Dr. Michelle Nemec (Director) for the use of
the shared Molecular Biosciences Center at Baylor University, Dr. Alejandro Ramirez
(Mass Spectrometry Core Facility, Baylor University) and Dr. Kevin Klausmeyer and Dr.
Marissa Penney (Xꢀray analysis). The authors are grateful to Mr. Jack Littlejohn and Mr.
Jake Lofman (Baylor University) for their contributions to the synthesis of certain
analogues. John Shelton (JAR Molecular Pathology core, UTSW) prepared the H&E
stained sections. Imaging was facilitated with the assistance of resources of the Harold C.
Simmons Cancer Center supported through a National Institutes of Health National
Cancer Institute Cancer Center Support Grant [Grant 1P30 CA142543], specifically, the
Southwestern Small Animal Imaging Resource, and Live Cell Imaging Resource. The
IVIS Spectrum was purchased with support of 1S10RR024757.
5. Supplementary Data
Supplementary data including experimental procedures (synthesis, SRB assay,
colchicine binding assay, inhibition of tubulin polymerization, in vivo BLI, and
histology), 1H NMR, 13C NMR, 31P NMR, HPLC, HRMS for target compounds and
intermediates (1H NMR, 13C NMR, only) and Xꢀray crystallography for compound 20
and 23 associated with this article can be found in the online Supplementary data file. All
animal procedures were approved by the University of Texas
Southwestern Medical Center Institutional Animal Care and Use Committee.

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Vascular Disrupting Agents (VDAs): Correlation of Structure with Function
OCH3
OCH3
O
H3CO
H3CO
OCH3
H3CO
CHO
H3CO
OCH3
OCH3
O
R
H3CO
H3CO
H3CO
R
R
R
R = OCH3, OH, H, OPO3Na2
R = OCH3, H, OH