Evaluation of Manassantin A Tetrahydrofuran Core Region Analogues and Cooperative Therapeutic Effects with EGFR Inhibition

Article abstract of DOI:10.1021/acs.jmedchem.0c00151

Tumors adapt to hypoxia by regulating angiogenesis, metastatic potential, and metabolism. These adaptations mediated by hypoxia-inducible factor 1 (HIF-1) make tumors more aggressive and resistant to chemotherapy and radiation. Therefore, HIF-1 is a validated therapeutic target for cancer. In order to develop new HIF-1 inhibitors for cancer chemotherapy by harnessing the potential of the natural product manassantin A, we synthesized and evaluated manassantin A analogues with modifications in the tetrahydrofuran core region of manassantin A. Our structure-activity relationship study indicated that the α,α′-trans-configuration of the central ring of manassantin A is critical to HIF-1 inhibition. We also demonstrated that a combination of manassantin A with an epidermal growth factor receptor inhibitor shows cooperative antitumor activity (～80% inhibition for combination vs ～30% inhibition for monotherapy). Our findings will provide important frameworks for the future therapeutic development of manassantin A-derived chemotherapeutic agents.

Full text of DOI:10.1021/acs.jmedchem.0c00151

pubs.acs.org/jmc
Article
Evaluation of Manassantin A Tetrahydrofuran Core Region
Analogues and Cooperative Therapeutic Effects with EGFR
Inhibition
Seung-Hwa Kwak, Tesia N. Stephenson, Hye-Eun Lee, Yun Ge, Hyunji Lee, Sophia M. Min,
Jea Hyun Kim, Do-Yeon Kwon, You Mie Lee,* and Jiyong Hong*
Cite This: https://dx.doi.org/10.1021/acs.jmedchem.0c00151
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: Tumors adapt to hypoxia by regulating angiogenesis, metastatic potential, and metabolism. These adaptations
mediated by hypoxia-inducible factor 1 (HIF-1) make tumors more aggressive and resistant to chemotherapy and radiation.
Therefore, HIF-1 is a validated therapeutic target for cancer. In order to develop new HIF-1 inhibitors for cancer chemotherapy by
harnessing the potential of the natural product manassantin A, we synthesized and evaluated manassantin A analogues with
modifications in the tetrahydrofuran core region of manassantin A. Our structure−activity relationship study indicated that the α,α′-
trans-configuration of the central ring of manassantin A is critical to HIF-1 inhibition. We also demonstrated that a combination of
manassantin A with an epidermal growth factor receptor inhibitor shows cooperative antitumor activity (∼80% inhibition for
combination vs ∼30% inhibition for monotherapy). Our findings will provide important frameworks for the future therapeutic
development of manassantin A-derived chemotherapeutic agents.
hypoxia-inducible factor 1 (HIF-1) to cope with the stress of
hypoxia.4 HIF-1 is an α/β heterodimeric transcription factor5
and activates several hundred genes involved in angiogenesis
(VEGF), glucose transport (GLUT1), glycolytic pathways
(LDH-A), and other processes.6
HIF-1 helps tumors adapt to hypoxia, subsequently making
tumors more aggressive and resistant to chemotherapy and
radiation,7−11 thereby resulting in poor clinical outcomes.12−14
Histological and clinical evidence suggests that HIF-1 is a
promising drug target for cancer.15 Thus, it is crucial to
advance our understanding of the HIF-1 regulation in tumor
development and progression, which will lead to significant
INTRODUCTION
■
According to estimates from the International Agency for
Research on Cancer (IARC), there were 17.0 million new
cancer cases and 9.5 million cancer deaths worldwide in 2018.1
Globally, about 1 in 6 deaths is due to cancer. By 2040, the
global burden is expected to grow to 27.5 million new cancer
cases and 16.3 million cancer deaths simply due to the growth
and aging of the population. The exact global economic impact
of cancer is unknown but is thought to be in the hundreds of
billions of dollars per year. In the United States alone, the
estimated direct medical cost for cancer in 2015 was $80
billion.2 The estimated annual health care expenditure for
cancer in Europe in 2014 was €83 billion (about $110
billion).3 Therefore, there is an urgent need to develop
effective treatment strategies for a wide range of cancers.
The normal oxygen level in most mammalian tissues is 2−
9%. However, hypoxia is defined by <2% of tissue oxygen
levels, and it occurs in various pathological conditions,
including cancer progression. Mammalian tissues utilize
Received: February 2, 2020
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
© XXXX American Chemical Society
J. Med. Chem. XXXX, XXX, XXX−XXX
A

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
therapeutic benefits. However, our understanding of HIF-1
regulation is still limited due to the complexity of HIF-1
regulatory mechanisms. Therefore, a need exists for chemical
probes with novel mechanisms of action to delineate the
regulatory mechanisms of HIF-1 and hypoxia signaling.
The dineolignan manassantin A (1, Figure 1) is a natural
product isolated from an aquatic plant, Saururuscernuus L.
clinically used epidermal growth factor receptor (EGFR)
inhibitor.
RESULTS AND DISCUSSION
■
Chemistry. Manassantin A (1) consists of two regions
(Figure 1): tetrahydrofuran (THF) core and side chain
regions. Following our previous study on the role of the
manassantin A side chain regions in the HIF-1 inhibition by
1,20 we envisioned the preparation of analogues with
modifications in the THF core region in an effort to complete
a comprehensive SAR of 1. As the asymmetric synthesis of the
THF core of 1 requires a lengthy synthetic sequence,19 we also
aimed to identify manassantin A analogues with reduced
structural complexity and improved chemical tractability. We
anticipated that our effort would help understand the effect of
ring type and size, conformation, heteroatom, and hydrogen
bonding on the HIF-1 inhibition by 1. Such information will
allow structural modifications to increase specificity, decrease
off-target effects, and improve drug performance.
First, to evaluate the effect of the two methyl groups on HIF-
1 inhibition, two tetrahydrofuran analogues (4 and 11) were
designed. Since the C7 and C7′′′ ketone analogue of 1 was as
potent as 1,20 we prepared the corresponding ketone analogues
for SAR studies. Our previous synthesis of 119 provided the
basis for the synthesis of the C8′′ monomethyl THF analogue
4 (Scheme 1A). Starting from the known monomethyl THF
2,19 Bn deprotection followed by BEMP-mediated SN2-
coupling of the resulting bis-phenol with the tosylate 3
provided the desired C8′′ monomethyl THF analogue 4 in
58% for two steps.
To further simplify the structure of manassantin A (1), we
prepared the C8′ and C8′′ desmethyl THF analogue 11
(Scheme 1B). The synthesis began with the cross-metathesis−
isomerization22 of the known allyl alcohol 523 with methyl
acrylate in the presence of Grubbs II and PMHS to afford the
γ-keto ester 6. The Corey−Bakshi−Shibata (CBS) reduction24
of 6 afforded the (S)-γ-hydroxy alcohol 7 (80% ee).25 The
PPTS-catalyzed lactonization of 7 gave the lactone 8 in 86%,
which was converted to the corresponding hemiketal by the
addition of an aryl lithium reagent generated in situ from the
aryl bromide 9.26 The reductive deoxygenation19 of the
resulting hemiketal successfully provided the 2,5-trans-THF
10 as a single diastereomer (49%). The stereochemistry of 10
was determined to be trans by NMR analysis.19 TBS
deprotection and coupling of the resulting bis-phenol with 3
completed the synthesis of the C8′ and C8′′ desmethyl THF
analogue 11.
To gain an insight into the role of the ring size in HIF-1
inhibition, we prepared the tetrahydropyran (THP) analogue
15 of 1 (Scheme 1C). Treatment of the Weinreb amide 1227
with 9 and n-BuLi followed by LiAlH4 reduction of the
resulting 1,5-diketone afforded the 1,5-diol 13 in 56% yield.
Next, for the synthesis of the THP core, the Au(III)-catalyzed
cyclization reaction28 of 13 provided the 2,6-cis-tetrahydropyr-
an 14 as a single diastereomer.29,30 Final TBS deprotection of
14 and coupling with 3 provided the desired THP analogue
15.
Figure 1. Structure and SAR plan of manassantin A.
(Saururaceae).16 Manassantin A (1) is a potent inhibitor of
HIF-1 activity (IC50 ∼ 10 nM) in vitro.17,18 Intrigued by the
great potential of manassantin A as a HIF-1 chemical probe for
studying the hypoxia signaling pathway, we devised a
convergent synthetic route to manassantin A that is amenable
to the development of manassantin A-derived chemical
probes.19 Upon the completion of manassantin A synthesis,
we evaluated the potential of manassantin A as a HIF-1
inhibitor. Manassantin A potently reduces the HIF-1α protein
expression under hypoxia and significantly decreases the
expression of hypoxia-induced HIF-1 downstream target
genes, such as vascular endothelial growth factor (VEGF)
and cyclin-dependent kinase 6 (Cdk6).20 Our preliminary
structure−activity relationship (SAR) study of manassantin A
analogues with modifications in the side chains identified
potent manassantin A analogues with reduced structural
complexity and increased ligand efficiency.20,21
In order to define the pharmacophore of manassantin A and
develop analogues with increased potency and selectivity for
future preclinical and clinical studies, it is required to define
the role of the tetrahydrofuran (THF) core of manassantin A
in HIF-1 inhibition. Herein, we describe our efforts toward the
synthesis and SAR study of manassantin A analogues with
modifications in the THF core region to guide the design of
chemically more tractable manassantin A analogues for
anticancer therapeutic development. We also report the
cooperative antitumor activity of manassantin A with a
The oxygen atom in the THF core of 1 is expected to play
an important role in manassantin’s binding to its molecular
target(s) by functioning as a hydrogen bond acceptor,
mediating polar interactions, or adopting a specific ring
conformation. To explore the role of the oxygen atom in
HIF-1 inhibition, we designed the two pyrrolidine analogues
B
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
a
Scheme 1. Synthesis of the Analogues 4, 11, 15, 20a, and 21
a
Reagents and conditions: (a) Pd/C, H2, EtOAc/EtOH, 25 °C, 24 h, 71%; (b) 3, BEMP, CH2Cl2, 0−25 °C, 1 h, 83%; (c) methyl acrylate, Grubbs’
II, PMHS, toluene, 110 °C, 30 min, 130 °C, 12 h, 45%; (d) (R)-2-Me-CBS-oxazaborolidine, BH3·SMe2, THF, 0 °C, 30 min, 58%, 80% ee; (e)
PPTS, toluene, 70 °C, 12 h, 86%; (f) 9, t-BuLi, THF, −78 °C, 1 h, 20%; (g) BF3·OEt2, NaBH3CN, CH2Cl2/CH3CN, −78 °C, 1 h, 49%; (h) TBAF,
THF, 0−25 °C, 1 h, 88%; (i) 3, BEMP, CH2Cl2, 0 to 25 °C, 1 h, 73%; (j) 9, n-BuLi, THF, −78 °C, 4 h, 64%; (k) LiAlH4, THF, 0 to 25 °C, 10 min,
56%; (l) AuCl3, CH3CN, 25 °C, 10 min, 57%; (m) TBAF, THF, 0−25 °C, 10 min, 47%; (n) 3, BEMP, CH2Cl2, 0−25 °C, 1.5 h, 76%; (o) 9, t-
BuLi, THF, −78 °C, 6 h, 40%; (p) (S)-α,α-diphenyl-2-pyrrolidinemethanol, B(OMe)3, BH3·SMe2, THF, 25 °C, 1 h, 80%, 97% ee; (q) MsCl, Et3N,
CH2Cl2, −20 °C, 3 h; (r) RNH2, 25 °C, 12 h, (19a) 73%, (19b) 64%; (s) TBAF, THF, 0 to 25 °C, 10 min (R = allyl, 55%; R = Bn, 82%); (t) 3,
BEMP, CH2Cl2, 0 to 25 °C, 1 h, (20a) 72%, (20b) 26%; (u) Pd/C, H2, HOAc, 25 °C, 24 h, 50%.
(20a and 21). As shown in Scheme 1D, the addition of an aryl
lithium reagent, generated in situ from 9 and t-BuLi, to the
known Weinreb amide 1631 gave the 1,4-diketone 17 in 40%.
For the enantioselective reduction of 17, (S)-α,α-diphenyl-2-
pyrrolidinemethanol was used in combination with BH3·SMe2
as a reducing agent to afford the 1,4-syn-diol 18 in 97% ee (see
the Supporting Information for details).32 Mesylate formation
of 18 followed by cyclization in the presence of allylamine or
benzylamine afforded the N-allyl (19a)- and N-benzyl (19b)-
protected pyrrolidines. TBS deprotection of 19a and 19b
followed by BEMP-mediated coupling of the resulting bis-
phenols and 3 successfully provided 20a and 20b, respectively.
Treatment of 20b with Pd/C for debenzylation gave the
pyrrolidine analogue 21.
C
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
a
Scheme 2. Synthesis of the Analogues 25a, 25b, 28, 33, and 38
a
Reagents and conditions: (a) 23, Pd(dppf)Cl2, K2CO3, DMF, 60 °C, 2−4 h, (24a) 99%, (24b) 8%; (b) Pd/C, H2, EtOH, 25 °C, 24 h, X = C:
34%, X = N: 89%; (c) 3, BEMP, CH2Cl2, 0−25 °C, 1 h, (25a) 27%, (25b) 43%; (d) TsNHNH2, MeOH, 60 °C, 15 h, quant.; (e) t-BuXphosAuCl,
LiOt-Bu, NaBArF, 1,2-dichloroethane, reflux, 16 h, 13%; (f) TBAF, THF, 0−25 °C, 1 h, 88%; (g) 3, BEMP, CH2Cl2, 0−25 °C, 1 h, 73%; (h) 30, n-
BuLi, THF, −78 °C, 1 h, 39%; (i) 30, t-BuLi, THF/HMPA, −78 °C, 1 h, 63%; (j) TBAF, THF, 0−25 °C, 40 min, 79%; (k) 3, BEMP, CH2Cl2, 0−
25 °C, 1 h, 86%; (l) PPh3, toluene, reflux, 2 h, 60%; (m) 36, LHMDS, THF, −78 to 0 °C, 5.5 h, 8.4%; (n) TBAF, THF, 0−25 °C, 1 h, 55%; (o) 3,
BEMP, CH2Cl2, 0−25 °C, 1 h, 45%.
We envisioned that a chemically more tractable ring system
that can recapitulate the overall linear-shaped conformation of
the 2,3-cis-3,4-trans-4,5-cis-configuration of the THF core of
manassantin A (1) may retain the potency of 1 toward the
hypoxia signaling pathway. To test this hypothesis, we
prepared several 5- and 6-membered ring analogues, 25a,
25b, 28, and 33 (Scheme 2).
As shown in Scheme 2A, preparation of the benzene (25a)
and pyridine (25b) analogues started with the Suzuki coupling
reaction of boronic acid 23 with 1,3-dibromobenzene (22a)
and 1,3-dibromopyridine (22b), respectively. Debenzylation of
24a,b and BEMP-mediated coupling of the resulting bis-
phenols with 3 provided the desired benzene (25a) and
pyridine (25b) core analogues.
detosylative cyclization33 provided the cyclopentene 27. TBS
deprotection, followed by BEMP-mediated coupling, com-
pleted the synthesis of 28 in 64% in two steps.
To access the dithiane core analogue 33, we used the 1,3-
dithiane umpolung chemistry. Monoalkylation of 1,3-dithiane
(29) with the benzyl bromide 3034 afforded 31, which was
coupled to 30 to give the bis-alkylated dithiane 32 (Scheme
2C). Final TBS deprotection and the BEMP-mediated
coupling reaction accomplished the synthesis of the dithiane
core analogue 33 in a 68% yield.
Next, we replaced the THF core of 1 with a double bond to
determine if the THF core is a side chain tether or serves a
larger role in mediating molecular target interactions. The
known benzyl bromide 3434 was converted to the correspond-
ing phosphonium salt 35 by treating with PPh3 (Scheme 2D).
The Wittig reaction of 35 with aldehyde 36,34 followed by
TBS-deprotection, produced the trans-alkene 37 as determined
For the synthesis of the cyclopentene core analogue 28, the
1,5-diketone 26 was treated with p-toluenesulfonyl hydrazide
to provide the bis-tosylhydrazone intermediate (Scheme 2B).
The subsequent base-promoted/gold-catalyzed intramolecular
D
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
Figure 2. Activity of manassantin A (ManA) and analogues for HIF-1 inhibition. HEK-293T cells were transfected with pGL3-5HRE-VEGF-
luciferase and pRL-SV40 plasmids, and treated with 0, 0.01, 0.1, and 1 μM of ManA (manassantin A) and analogues or 10 μM of 17-AAG (17-
(allylamino)-17-demethoxygeldanamycin), as a positive control under hypoxia for 24 h. Relative luciferase activity was determined after normalized
to the Renilla luciferase activity. Three independent experiments were performed. # P < 0.0001 versus vehicle control group, % P < 0.001 versus
vehicle control group, $ P < 0.01 versus vehicle control group, and * P < 0.1 versus vehicle control group.
Figure 3. Overlays of optimized conformations of manassantin A (1) and analogues (11 and 25b). To avoid any unnecessary complications and/or
exaggeration by the flexible side chains, truncated structures of 1, 11, and 25b were used instead of the full structures. Initial geometries were
determined by conformational search based on MMFF and OPLS3. (A and B) Superimposition of an active manassantin A analog (gray: 1; green:
11). (C and D) Superimposition of an inactive manassantin A analog (gray: 1; sky blue: 25b). (E) Truncated structures 1, 11, and 25b.
by NMR analysis.35 The BEMP-mediated coupling of 37 and 3
assay to assess the effect of manassantin A analogues on HIF-1
transactivation activity. We used HEK-293T cells transiently
transfected with both pGL3-5 × HRE-Luc and pRL-SV40
encoding Renilla-luciferase (pRen-Luc) vectors to investigate
afforded the trans-alkene analogue 38.
Biological Characterization. After the completion of
analogue synthesis, we performed a dual luciferase-reporter
E
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
the effect of manassantin analogues on HIF-1 transactivation
activity. HEK-293T cells were treated with hypoxia (1% O2)
and serially diluted compounds for 24 h. The luciferase signals
were normalized to the activity of Renilla luciferase and
quantified as relative light units (RLU).
results in starvation of the tumor from oxygen and nutrients.40
As tumor vasculatures have leaky and chaotic structures,
hypoxic regions are generated again as tumors grow.41 In turn,
HIF-1α is overexpressed by recurrent hypoxia and increases
the expression of HIF target genes involved in angiogenesis
and chemoresistance. Therefore, we hypothesized that the use
of HIF-1α inhibitors in combination with anticancer agents is
likely to improve the treatment outcome.
Several manassantin analogues such as 4, 11, and 21 reduced
the luciferase signal in a dose-dependent manner (Figure 2).
The luciferase assay provided several valuable insights into the
SAR of 1. First, the C8″ monomethyl (4) and C8′,8″
desmethyl analogues (11) potently inhibited HIF-1 trans-
activation activity. In particular, the potency of 11 was
comparable to that of 1, suggesting the methyl groups of the
THF core of manassantin A are not crucial to HIF-1 inhibition.
These analogues lacking the methyl groups, in particular 11,
significantly shortens the overall synthesis. The 2,6-cis-THP
core analogue 15 was less potent than manassantin A. The lack
of activity of 15 may be attributed to the change in ring size or
conformation by the replacement of 2,5-trans-THF with 2,6-
cis-THP (11 vs 15). The pyrrolidine analogue 21 was slightly
less potent than 11. However, the N-allyl substituted
pyrrolidine analogue 20a was completely inactive. This is
likely due to the loss of hydrogen bonding capability or the
bulkiness of the N-allyl group. This data indicated that the
THF core of manassantin A can be replaced by an α,α′-trans-
disubstituted ring without significant loss of activity, but the
ring is required to have hydrogen bonding capability.
The chemically more tractable analogues such as the
benzene and pyridine analogues (25a and 25b) were
completely inactive due to their flat geometry, confirming
our previous finding that the relative orientation of the side
chains is crucial to the activity of 1. The cyclopentene analogue
28, 1,3-dithiane analogue 33, and trans-alkene analogue 38
were all inactive.
To characterize the effect of ring conformation of
manassantin A (1) on HIF-1 inhibition, we optimized the
conformations of truncated structures36 of manassantin A (1)
To test the hypothesis, we evaluated a combination of
gefitinib (an EGFR inhibitor) and manassantin A in a Lewis
lung carcinoma (LLC) allograft experiment. The tumor
microenvironment including abnormal surrounding blood
vessels is an important factor determining the effect of
anticancer drugs. It is highly challenging to precisely replicate
the tumor microenvironment in an in vitro model. Therefore,
we directly tested the combination of manassantin A and
gefitinib in an in vivo lung cancer model and evaluated the
efficacy of combination therapy. LLC cells were inoculated in
the mouse flank subcutaneously (s.c.) and treated with
manassantin A and/or gefitinib intraperitoneally (i.p.) every
3 days for 15 days. Manassantin A or gefitinib alone inhibited
tumor growth by ∼30% (Figure 4A). However, manassantin A,
together with gefitinib, suppressed tumor growth in a
cooperative manner (∼80% inhibition). Decreased tumor
weight in manassantin A-treated and/or gefitinib-treated mice
showed similar phenomena (Figure 4B), whereas the body
weight did not significantly change (Figure S3). Although
several manassantin A-related compounds are known to be
effective in tumor xenograft models,42−44 there has been no
report of the in vivo antitumor activity of manassantin A. To
the best of our knowledge, this is also the first report of the
cooperative therapeutic effect of a small molecule HIF-1
inhibitor with EGFR inhibition. Our encouraging in vivo
testing result warrants further exploration of the therapeutic
potential of manassantin A in combination with other
treatment methods such as radiation and cancer immunother-
apy.
̈
and analogues (11 and 25b) using Maestro 11.2 (Schrodinger,
NY). As shown in Figure 3, manassantin A (1) adopted a
nearly linear conformation due to the 2,5-trans-configuration of
the THF ring. An active analogue 11 also adopted a linear
conformation like 1. However, an inactive analogue, 25b,
adopted a shape remarkably different from that of 1. The
conformational analysis of 1, 11, and 25b clearly showed that
the side chains are required to position in the correct
orientation for high potency, which suggests that the α,α′-
trans-configuration of 1 is critical to HIF-1 inhibition. Thus,
designing a ligand that mimics the overall conformation of 1
may improve the potency toward the hypoxia signaling
pathway.
Cooperative Therapeutic Effect of Manassantin A
with EGFR Inhibition. Although precision-based targeting of
specific growth factors/receptors and/or pathways has been
effective in certain tumor types, most of the cancers, if not all,
treated with targeted drugs eventually develop resistance. In
addition, intratumoral heterogeneity and clonal evolution,
which are common in solid tumors, are also likely to contribute
to resistance to some targeted therapies. Therefore, the
emergence of resistant cancer cells in several targeted therapies
indicates that simultaneous administration of multiple agents
may be essential for the successful treatment of human
cancers.37−39 In this regard, HIF-1 inhibitors can be extremely
useful in maximizing the therapeutic benefits of standard
treatments. For example, targeting blood vessels in tumors
CONCLUSION
■
To explore the therapeutic potential of manassantin A (1) for
cancer treatment, we prepared and evaluated THF core
analogues of manassantin A. Our SAR study of manassantin A
analogues provided valuable insights into the role of the THF
core of manassantin A in HIF-1 inhibition. Among the
analogues tested, 4, 11, and 21 with reduced structural
complexity and enhanced chemical tractability inhibited HIF-1
transactivation activity under hypoxia. Moreover, manassantin
A cooperatively inhibited tumor growth in combination with
an EGFR inhibitor, demonstrating its therapeutic potential in
combination therapies. We expect that our findings will allow
further structural modifications of manassantin A in order to
enhance the potency and specificity of manassantin A
analogues for novel anticancer drug development.
EXPERIMENTAL SECTION
■
General Chemistry Procedures. All reactions were conducted in
oven-dried glassware under nitrogen. Unless otherwise stated, all
reagents were purchased from commercial suppliers and used without
further purification. All solvents were American Chemical Society
(ACS) grade or better and used without further purification, except
tetrahydrofuran (THF), which was freshly distilled from sodium/
benzophenone each time before use. Analytical thin-layer chromatog-
raphy (TLC) was performed with glass-backed silica gel (60 Å) plates
F
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
mobile phase B = H2O/CH3CN/HCO2H (2:100:0.3). Flow
injections are in 50:50 mobile phase A/mobile phase B at 0.5 mL/
min).
Synthesis of Manassantin A Analogues. General Procedure
for Bn Deprotection (GP1). To a stirred solution of the aryl benzyl
ether (1 equiv) in an appropriate solvent was added 10% palladium
on activated carbon. After stirring for 24 h under a H2 atmosphere at
25 °C, the reaction mixture was filtered through a pad of Celite, and
the filtrate was concentrated in vacuo. The residue was purified as
indicated.
General Procedure for Coupling Reaction (GP2). To a cooled
(−78 °C) solution of a substrate (1 equiv) in an appropriate solvent
was added dropwise n-BuLi (2.5 M in hexanes, 1−4 equiv) or t-BuLi
(1.7 M in pentane, 1−4 equiv). After stirring for 1 h at −78 °C, the
reaction mixture was treated with an electrophile (1−6 equiv) in
anhydrous THF. After stirring for 1−6 h at −78 °C, the reaction was
quenched by the addition of saturated aqueous NH4Cl, and the
resulting mixture was diluted with EtOAc. The layers were separated,
and the aqueous layer was extracted with EtOAc. The combined
organic layers were washed with brine, dried over anhydrous Na2SO4,
and concentrated in vacuo. The residue was purified as indicated.
General Procedure for TBS Deprotection (GP3). To a cooled (0
°C) solution of the TBS silyl ether (1 equiv) in anhydrous THF (0.03
M) was added TBAF (1 M in THF, 3 equiv). After stirring for 5 min
at 0 °C, the reaction mixture was warmed to 25 °C. After stirring for
10 min to 1 h, the reaction was quenched by an addition of saturated
aqueous NH4Cl, and the resulting mixture was extracted with EtOAc.
The combined organic layers were washed with brine, dried over
anhydrous Na2SO4, and concentrated in vacuo. The residue was
purified as indicated.
General Procedure for the Suzuki Coupling Reaction GP4. To a
solution of the 1,3-dibromo benzene or pyridine (1 equiv) in
anhydrous DMF (0.39 M) was added the aryl boronic acid (2 equiv),
K2CO3 (2 equiv), and Pd(dppf)Cl2 (0.5 mol %) at 25 °C. The
resulting mixture was heated to 60 °C and stirred for 2−4 h. After
cooling to 0 °C, the reaction was quenched by the addition of H2O,
and the resulting mixture was diluted with CH2Cl2. The combined
organic layers were washed with brine, dried over anhydrous Na2SO4,
and concentrated in vacuo. The residue was purified as indicated.
General Procedure for the BEMP-Mediated Coupling Reaction
(GP5). To a cooled (0 °C) solution of the bis-phenol (1 equiv) in
anhydrous CH2Cl2 (0.05 M) was added dropwise BEMP (2.3 equiv).
The reaction mixture was stirred at the same temperature for 10 min
before the tosylate 3 (2.5−4 equiv) was added. After stirring for 1 h at
25 °C, the reaction was quenched by the addition of saturated
aqueous NH4Cl and extracted with CH2Cl2. The combined organic
layers were washed with brine, dried over anhydrous Na2SO4, and
concentrated in vacuo. The residue was purified as indicated.
(2R,2′R)-2,2′-((((2S,3R,5S)-3-Methyltetrahydrofuran-2,5-diyl)bis-
(2-methoxy-4,1-phenylene))bis(oxy))bis(1-(3,4-dimethoxyphenyl)-
propan-1-one) (Analogue 4). The bis-phenol was synthesized from
the aryl benzyl ether 2 (13 mg, 0.02 mmol) and 10% palladium on
activated carbon in EtOAc/EtOH (3:1, 3 mL) according to GP1.
Purification by column chromatography (silica gel, hexanes/EtOAc,
Figure 4. Manassantin A (ManA) cooperatively inhibits tumor
growth in combination with an EGFR inhibitor, gefitinib (Gef). Lewis
lung carcinoma cells (2 × 105) were inoculated into both flanks of
C57Bl/6 mice (Day 0). From two days after inoculation, mice (n = 5
per group) were treated intraperitoneally with manassantin A (5 mg/
kg body weight) and/or gefitinib (5 mg/kg body weight) three times
a week for 17 days and then sacrificed. Tumor size (A) and tumor
weight (B) were measured three times a week and on the final day,
respectively. Tumor masses were photographed and shown in a box
right the graph. * P < 0.05 versus vehicle control group.
with a fluorescent indication (Whatman). Visualization was
accomplished by UV irradiation at 254 nm and/or by staining with
p-anisaldehyde solution. Flash column chromatography was per-
formed by using silica gel (particle size 230−400 mesh, 60 Å). All 1H
and 13C NMR spectra were recorded with a Varian 400 (400 MHz)
and a Bruker 500 (500 MHz) spectrometer. All NMR δ values are
given in parts per million (ppm) and are referenced to the residual
solvent signals (δ = 7.26 ppm of CDCl3; δ = 2.05 ppm of
1
4:1) afforded the bis-phenol (6 mg, 71%) as a yellow oil: H NMR
(400 MHz, CDCl3) δ 6.95 (s, 1H), 6.92−6.84 (m, 4H), 6.78 (d, J =
8.1 Hz, 1H), 5.54 (s, 2H), 5.35−5.26 (m, 2H), 3.90 (s, 6H), 2.64−
2.52 (m, 1H), 2.21−2.13 (m, 2H), 0.70 (d, J = 7.0 Hz, 3H); HRMS
(ESI) m/z [M + H]+ calcd for C19H22O5 331.1540, found 331.1543.
The analogue 4 was synthesized from the bis-phenol (10 mg, 0.03
mmol) and the tosylate 3 (44.1 mg, 0.12 mmol) according to GP5.
Purification by column chromatography (silica gel, hexanes/EtOAc,
1:1) afforded the analogue 4 (18 mg, 83%) as a white solid: 1H NMR
(400 MHz, CDCl3) δ 7.86−7.76 (m, 2H), 7.66 (s, 2H), 6.92 (s, 1H),
6.89−6.83 (m, 3H), 6.81−6.73 (m, 3H), 6.70 (d, J = 8.8 Hz, 1H),
5.46 (q, J = 4.0 Hz, 2H), 5.23 (dd, J = 7.2, 5.7 Hz, 2H), 3.95 (s, 6H),
3.93 (s, 6H), 3.83 (s, 6H), 2.55−2.48 (m, 1H), 2.15−2.07 (m, 2H),
1.70 (d, J = 7.0 Hz, 6H), 0.64 (d, J = 7.1 Hz, 3H); HRMS (ESI) m/z
[M + Na]+ calcd for C41H46O11 737.2932, found 737.2941; purity
95.07%, tR 7.693 min.
1
CD3COCD3) for H NMR spectra, or the solvent signals for 13C
spectra. Coupling constants (J) are given in hertz (Hz), and
multiplicities are indicated using the conventional abbreviation (s =
singlet, d = doublet, t = triplet, q = quartet, m = multiplet or overlap
of nonequivalent resonances, br = broad). Electrospray ionization
(ESI) mass spectrometry (MS) was recorded with an Agilent 1100
series (LC/MSD trap) spectrometer in order to obtain the molecular
masses of compounds. Optical rotation values were measured with a
Rudolph Research Analytical (A21102 API/1W) polarimeter. The
purity of final compounds used in bioassays was determined by
analytical HPLC and was found to be 90.7−99.6%. The analysis was
performed on an HPLC (Phenomenex Kinetix C18 column, 3 × 30
mm, mobile phase A = H2O/CH3OH/HCO2H (100:2:0.3), and
G
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
Methyl 4-(4-((tert-Butyldimethylsilyl)oxy)-3-methoxyphenyl)-4-
oxobutanoate (6). To a solution of the allyl alcohol 5 (1.3 g, 4.4
mmol) in anhydrous toluene (100 mL) were added methyl acrylate
(3.9 mL, 44 mmol) and Grubbs’ second-generation catalyst (186 mg,
0.22 mmol). After stirring for 30 min at 110 °C, the remaining methyl
acrylate was removed in vacuo. PMHS (1.3 mL, 0.88 mmol) was
added and stirred for 12 h at 130 °C on reflux conditions. After that,
all volatiles were removed in vacuo, and the residue was purified by
column chromatography (silica gel, hexanes/EtOAc, 8:1) to afford 6
mmol) in anhydrous CH2Cl2 (2 mL) was added NaBH3CN (6 mg,
0.09 mmol) in anhydrous CH3CN (2 mL). After stirring for 10 min at
−78 °C, BF3·OEt2 (18 μL, 0.14 mmol) was added, and the resulting
mixture was stirred for 1 h at −78 °C. The reaction was quenched by
the addition of saturated aqueous NaHCO3, and the resulting mixture
was diluted with EtOAc. The layers were separated, and the aqueous
layer was extracted with EtOAc. The organic layers were washed with
water, dried over anhydrous Na2SO4, and concentrated under reduced
pressure. The residue was purified by column chromatography (silica
gel, hexanes/EtOAc, 8:1) to afford 10 (13 mg, 49%) as a colorless oil:
[α]D22.9 −27.27 (c 0.18, CHCl3); 1H NMR (400 MHz, CDCl3) δ 6.92
(br s, 2H), 6.82 (br s, 4H), 5.16 (t, J = 6.7 Hz, 2H), 3.82 (s, 6H),
2.44−2.40 (m, 2H), 2.02−1.95 (m, 2H), 0.98 (s, 18H), 0.14 (s,
12H); 13C NMR (125 MHz, CDCl3) δ 150.88, 144.17, 137.02,
120.64, 118.04, 109.76, 81.33, 55.53, 35.73, 25.75, 18.46, −4.62;
HRMS (ESI) m/z [M + H]+ calcd for C30H48O5Si2 545.3113, found
545.3114.
1
(700 mg, 45%) as a colorless oil: H NMR (400 MHz, CDCl3) δ
7.56−7.46 (m, 2H), 6.87 (d, J = 8.0 Hz, 1H), 3.84 (s, 3H), 3.69 (s,
3H), 3.27 (t, J = 6.6 Hz, 2H), 2.73 (t, J = 6.6 Hz, 2H), 0.98 (s, 9H),
0.16 (s, 6H); 13C NMR (125 MHz, CD3COCD3) δ 196.14, 172.81,
150.98, 149.65, 131.13, 122.15, 120.27, 111.11, 54.97, 50.83, 32.71,
27.66, 25.15, 18.22, −5.28; HRMS (ESI) m/z [M + H]+ calcd for
C18H28O5Si 353.1785, found 353.1785.
Methyl (S)-4-(4-((tert-Butyldimethylsilyl)oxy)-3-methoxyphenyl)-
4-hydroxybutanoate (7). A solution of (R)-Me-CBS-oxazaborolidine
(1 M in toluene, 0.09 mL, 0.09 mmol) was added to BH3·SMe2 (132
μL, 1.39 mmol), and the reaction mixture was stirred under a nitrogen
atmosphere at 25 °C before cooling to −20 °C. After stirring 10 min,
the solution of γ-keto ester 6 (330 mg, 0.93 mmol) in anhydrous THF
(15 mL) was added dropwise at −20 °C. After stirring for 30 min, the
reaction was quenched by the addition of saturated aqueous NH4Cl,
and the resulting mixture was diluted with EtOAc. The layers were
separated, and the aqueous layer was extracted with EtOAc. The
combined organic layers were washed with H2O, dried over
anhydrous Na2SO4, and concentrated under reduced pressure. The
residue was purified by column chromatography (silica gel, CH2Cl2/
MeOH, 100:1) to afford 7 (190 mg, 58%) as a colorless oil: 1H NMR
(400 MHz, CD3COCD3) δ 7.00 (d, J = 5.1 Hz, 1H), 6.81 (s, 1H),
6.80 (d, J = 5.2 Hz, 1H), 4.69−4.59 (m, 1H), 4.27−4.20 (m, 1H),
3.83 (s, 3H), 3.61 (s, 3H), 2.46−2.32 (m, 2H), 2.01−1.88 (m, 2H),
1.00 (s, 9H), 0.15 (s, 6H); 13C NMR (125 MHz, CD3COCD3) δ
173.38, 150.77, 143.77, 139.40, 120.16, 117.99, 109.85, 72.20, 54.89,
50.71, 34.64, 30.12, 25.30, 18.19, −5.23; HRMS (ESI) m/z [M +
Na]+ calcd for C18H30O5Si 377.1755, found 377.1763 .
(2R,2′R)-2,2′-((((2S,5S)-Tetrahydrofuran-2,5-diyl)bis(2-methoxy-
4,1-phenylene))bis(oxy))bis(1-(3,4-dimethoxyphenyl)propan-1-
one) (Analogue 11). The bis-phenol was synthesized from 10 (10
mg, 0.01 mmol) according to GP3. Purification by column
chromatography (silica gel, CH2Cl2/MeOH, 50:1) afforded the bis-
phenol (5 mg, 88%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ
6.96 (s, 2H), 6.92−6.85 (m, 4H), 5.57 (br s, 2H), 5.17 (t, J = 6.7 Hz,
2H), 3.91 (s, 6H), 2.50−2.38 (m, 2H), 2.06−1.91 (m, 2H). The
analogue 11 was synthesized from the bis-phenol (5 mg, 0.01 mmol)
and the tosylate 3 (23 mg, 0.06 mmol) according to GP5. Purification
by column chromatography (silica gel, CH2Cl2/MeOH, 50:1)
1
afforded 11 (8.1 mg, 73%) as a white solid: H NMR (400 MHz,
CDCl3) δ 7.82 (d, J = 8.7 Hz, 2H), 7.67 (s, 2H), 6.92 (s, 2H), 6.87
(d, J = 8.6 Hz, 2H), 6.76 (s, 4H), 5.44−5.36 (m, 2H), 5.14−5.06 (m,
2H), 3.93 (s, 6H), 3.91 (s, 6H), 3.85 (s, 6H), 2.41−2.32 (m, 2H),
1.92 (s, 2H), 1.71 (d, J = 7.0 Hz, 6H); 13C NMR (125 MHz, CDCl3)
δ 153.59, 149.87, 148.99, 146.06, 137.56, 127.37, 123.64, 117.90,
115.67, 111.26, 109.81, 81.03, 55.95, 35.49, 19.27; HRMS (ESI) m/z
[M + Na]+ calcd for C40H44O11 723.2913, found 723.2712; purity
93.54%, tR 7.503 min.
(S)-5-(4-((tert-Butyldimethylsilyl)oxy)-3-methoxyphenyl)-
dihydrofuran-2(3H)-one (8). The alcohol 7 (150 mg, 0.42 mmol) in
anhydrous toluene (10 mL) was treated with pyridinium p-toluene
sulfonate (211 mg, 0.84 mmol). After stirring for 12 h at 70 °C, the
reaction was quenched by the addition of H2O, and the resulting
mixture was diluted with EtOAc. The layers were separated, and the
aqueous layer was extracted with EtOAc. The combined organic
layers were and washed with water, dried over anhydrous Na2SO4,
and concentrated under reduced pressure. The residue was purified by
column chromatography (silica gel, hexanes/EtOAc, 6:1) to afford the
1,5-Bis(4-((tert-butyldimethylsilyl)oxy)-3-methoxyphenyl)-
pentane-1,5-diol (13). The 1,5-diketone was synthesized from the
aryl bromide 9 (7.5 g, 24 mmol) in anhydrous THF (36 mL), n-BuLi
(2.5 M in hexanes, 6.4 mL, 16 mmol), and the Weinreb amide 12
(873 mg, 4 mmol) in anhydrous THF (36 mL) according to GP2.
Purified by column chromatography (silica gel, hexanes/EtOAc, 8:1)
afforded the 1,5-diketone (1.47 g, 64%) as a yellow oil: 1H NMR (400
MHz, CDCl3) δ 7.58−7.48 (m, 4H), 6.87 (d, J = 8.0 Hz, 2H), 3.87 (s,
6H), 3.06 (t, J = 7.0 Hz, 4H), 2.22−2.12 (m, 2H), 0.99 (s, 18H), 0.18
(s, 12H); 13C NMR (125 MHz, CD3COCD3) δ 197.74, 150.93,
149.48, 131.48, 122.14, 120.21, 111.18, 54.95, 37.06, 25.12, 19.23,
18.19, −5.31; HRMS (ESI) m/z [M + H]+ calcd for C31H48O6Si2
573.3062, found 573.3069. The 1,5-diketone (200 mg, 0.34 mmol) in
anhydrous THF (20 mL) was added dropwise to a stirred solution of
LiAlH4 (2 M in THF, 0.6 mL, 1.22 mmol) at 25 °C. The cloudy
solution was stirred for 10 min and then cooled to 0 °C. The reaction
was quenched by the addition of 15% NaOH solution, and the
resulting mixture was diluted with EtOAc. The layers were separated,
and the aqueous layer was extracted with EtOAc. The combined
organic layers were dried over anhydrous Na2SO4 and concentrated
under reduced pressure. The residue was purified by column
chromatography (silica gel, CH2Cl2/MeOH, 50:1) to afford the 1,5-
diol 13 (110 mg, 56%) as a needle-shaped white solid: 1H NMR (400
MHz, CDCl3) δ 6.83 (s, 2H), 6.80−6.69 (m, 4H), 4.56 (t, J = 8.0 Hz,
2H), 3.79 (s, 6H), 1.85−1.58 (m, 4H), 1.44−1.33 (m, 2H), 0.98 (s,
18H), 0.13 (s, 12H); 13C NMR (125 MHz, CDCl3) δ 151.36, 144.80,
138.69, 121.00, 118.60, 110.08, 74.86, 55.88, 39.16, 26.13, 18.84,
−4.22; HRMS (ESI) m/z [M + Na]+ calcd for C31H52O6Si2 599.3195,
found 599.3193.
1
lactone 8 (115 mg, 86%) as a colorless oil: H NMR (400 MHz,
CD3COCD3) δ 7.06 (br s, 1H), 6.87 (br s, 2H), 5.52−5.42 (m, 1H),
3.83 (s, 3H), 2.72−2.50 (m, 3H), 2.29−2.21 (m, 1H), 1.01 (s, 9H),
0.16 (s, 6H); 13C NMR (125 MHz, CD3COCD3) δ 176.23, 151.17,
144.99, 133.76, 120.54, 118.44, 110.06, 81.25, 55.01, 30.77, 25.25,
18.18, −5.26; HRMS (ESI) m/z [M + H]+ calcd for C17H26O4Si
323.1673, found 323.1678.
(2S,5S)-2,5-Bis(4-((tert-butyldimethylsilyl)oxy)-3-
methoxyphenyl)tetrahydrofuran (10). Compound 8 (60 mg, 0.18
mmol) in anhydrous THF (1 mL) was reacted with the aryl bromide
9 (79 mg, 0.25 mmol) in anhydrous THF (1 mL) and t-BuLi (1.7 M
in pentane, 0.21 mL, 0.37 mmol) according to GP2. Purification by
column chromatography (silica gel, hexanes/EtOAc, 5:1) afforded the
cyclic hemiketal (20 mg, 20%) as a colorless oil: 1H NMR (400 MHz,
CDCl3) δ 7.50 (d, J = 1.8 Hz, 1H), 7.44 (dd, J = 1.9, 8.2 Hz, 1H),
6.93−6.75 (m, 4H), 4.74 (t, J = 6.5 Hz, 1H), 3.84 (s, 3H), 3.78 (s,
3H), 3.03 (td, J = 6.9, 1.6 Hz, 2H), 2.50 (s, 1H), 2.17 (q, J = 6.8 Hz,
2H), 0.99 (s, 18H), 0.16 (s, 12H); 13C NMR (125 MHz, CDCl3) δ
150.74, 150.50, 150.37, 144.10, 143.64, 140.47, 140.33, 137.05,
120.53, 120.07, 119.95, 118.42, 118.34, 111.17, 110.49, 110.35, 88.75,
81.00, 55.56, 55.42, 55.29, 39.02, 34.96, 25.74, 18.45, −4.61; HRMS
(ESI) m/z [M + H]+ calcd for C30H48O6Si2 561.3062, found
561.3047. To a cooled (−78 °C) solution of hemiketal (27 mg, 0.04
(2R,6S)-2,6-Bis(4-((tert-butyldimethylsilyl)oxy)-3-
methoxyphenyl)tetrahydro-2H-pyran (14). To a solution of 13 (100
mg, 0.17 mmol) in anhydrous CH3CN (30 mL) was added AuCl3 (26
mg, 0.008 mmol). After stirring for 10 min at 25 °C, the reaction
H
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
mixture was filtered through a pad of Celite and concentrated. The
residue was purified by column chromatography (silica gel, hexanes/
EtOAc, 100:1) to afford the 2,6-cis-tetrahydropyran 14 (55 mg, 57%)
as a colorless oil: 1H NMR (400 MHz, CDCl3) δ 6.95 (d, J = 1.9 Hz,
2H), 6.85 (dd, J = 2.0, 8.2 Hz, 2H), 6.79 (d, J = 8.1 Hz, 2H), 4.49 (d,
J = 11.0 Hz, 2H), 3.80 (s, 6H), 1.88 (d, J = 13.5 Hz, 2H), 1.67−1.54
(m, 4H), 0.98 (s, 18H), 0.13 (s, 12H); 13C NMR (125 MHz, CDCl3)
δ 150.69, 144.12, 137.13, 120.55, 118.25, 110.20, 80.26, 55.49, 33.83,
25.77, 18.46, −4.60; HRMS (ESI) m/z [M + H]+ calcd for
C31H50O5Si2 559.3270, found 559.3282.
(2S,5S)-1-Allyl-2,5-bis(4-((tert-butyldimethylsilyl)oxy)-3-
methoxyphenyl)pyrrolidine (19a). To a cooled (−20 °C) solution of
18 (240 mg, 0.42 mmol) in anhydrous CH2Cl2 (10 mL) was added
Et3N (0.29 mL, 2.13 mmol) and MsCl (0.16 mL, 2.13 mmol). After
stirring for 3 h at −20 °C, an excessive amount of allylamine (3.1 mL,
4.2 mmol) was added. The resulting mixture was allowed to warm to
25 °C and stirred for 12 h. The reaction was quenched by an addition
of H2O, and the resulting mixture was diluted with CH2Cl2. The
combined organic layers were washed with brine, dried over
anhydrous Na2SO4, and concentrated in vacuo. Purification by
column chromatography (silica gel, hexanes/EtOAc, 100:1) afforded
19a (492 mg, 73%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ
7.01 (s, 2H), 6.88 (d, J = 8.0 Hz, 2H), 6.79 (d, J = 8.0 Hz, 2H), 5.74−
5.61 (m, 1H), 4.91−4.74 (m, 2H), 3.82 (s, 6H), 3.75−3.67 (m, 2H),
3.01 (d, J = 6.8 Hz, 2H), 2.20−2.06 (m, 2H), 1.81−1.70 (m, 2H),
0.98 (s, 18H), 0.15 (s, 12H); HRMS (ESI) m/z [M + H]+ calcd for
C33 H53NO4Si2 584.3586, found 584.3594.
(2R,2′R)-2,2′-((((2R,6S)-Tetrahydro-2H-pyran-2,6-diyl)bis(2-me-
thoxy-4,1-phenylene))bis(oxy))bis(1-(3,4-dimethoxyphenyl)-
propan-1-one) (Analogue 15). The bis-phenol was synthesized from
14 (55 mg, 0.09 mmol) according to GP3. Purification by column
chromatography (silica gel, hexanes/EtOAc, 2:1) afforded the bis-
phenol (19 mg, 47%) as a colorless oil: 1H NMR (400 MHz, CDCl3)
δ 6.97 (s, 2H), 6.93−6.84 (m, 4H), 5.58 (s, 2H), 4.49 (d, J = 11.0 Hz,
2H), 3.89 (s, 6H), 2.05−1.99 (m, 1H), 1.93−1.84 (m, 3H), 1.70−
1.60 (m, 2H); 13C NMR (125 MHz, CDCl3) δ 146.33, 144.78,
135.60, 118.88, 114.01, 108.78, 80.29, 55.90, 33.69, 24.46, 14.21;
HRMS (ESI) m/z [M + H]+ calcd for C19H22O5 331.1540, found
331.1549. The analogue 15 was synthesized from the bis-phenol (19
mg, 0.05 mmol) and the tosylate 3 (83.8 mg, 0.23 mmol) according
to GP5. Purification by column chromatography (silica gel, CH2Cl2/
(2R,2′R)-2,2′-((((2S,5S)-1-Allylpyrrolidine-2,5-diyl)bis(2-methoxy-
4,1-phenylene))bis(oxy))bis(1-(3,4-dimethoxyphenyl)propan-1-
one) (Analogue 20a). The bis-phenol was synthesized from 19a (20
mg, 0.03 mmol) according to GP3. Purification by column
chromatography (silica gel, hexanes/EtOAc, 1:1) afforded the bis-
phenol (11 mg, 55%) as a colorless oil: 1H NMR (400 MHz,
CD3COCD3) δ 7.38 (s, 2H), 7.15 (s, 2H), 6.92 (d, J = 7.9 Hz, 2H),
6.79 (dd, J = 8.0, 8.0 Hz, 2H), 5.84−5.67 (m, 1H), 4.94−4.79 (m,
2H), 3.88 (s, 6H), 3.81−3.73 (m, 4H), 3.04 (d, J = 6.8 Hz, 2H),
2.19−2.08 (m, 2H), 1.80−1.68 (m, 2H); 13C NMR (125 MHz,
CD3COCD3) δ 147.42, 145.45, 136.25, 134.24, 119.87, 116.34,
114.57, 110.49, 66.41, 55.26, 52.37, 34.03; HRMS (ESI) m/z [M +
H]+ calcd for C21H25NO4 356.1856, found 356.1864. The analogue
20a was synthesized from the bis-phenol (44 mg, 0.12 mmol) and the
tosylate 3 (270.63 mg, 0.74 mmol) according to GP5. Purification by
column chromatography (silica gel, hexanes/EtOAc, 1:1) afforded the
1
MeOH, 50:1) afforded 15 (30 mg, 76%) as a beige solid: H NMR
(400 MHz, CD3COCD3) δ 7.84 (d, J = 8.5 Hz, 2H), 7.65 (d, J = 2.2
Hz, 2H), 7.11−7.00 (m, 4H), 6.87−6.81 (m, 2H), 6.80−6.74 (m,
2H), 5.65−5.56 (m, 2H), 4.47 (d, J = 11.4 Hz, 2H), 3.89 (s, 6H),
3.85 (s, 6H), 3.82 (s, 6H), 2.01−1.90 (m, 2H), 1.87−1.80 (m, 2H),
1.59 (d, J = 6.7 Hz, 6H), 1.55−1.41 (m, 2H); 13C NMR (125 MHz,
CD3COCD3) δ 196.49, 154.00, 149.80, 149.26, 146.10, 137.90,
127.51, 123.34, 117.74, 115.14, 111.23, 110.55, 79.49, 76.75, 55.13,
33.67, 18.21; HRMS (ESI) m/z [M + Na]+ calcd for C41H46O11
737.2932, found 737.2937; purity 99.59%, tR 7.813 min.
1
analogue 20a (40 mg, 72%) as a white solid: H NMR (400 MHz,
CD3COCD3) δ 7.86 (dd, J = 8.5, 2.1 Hz, 2H), 7.66 (s, 2H), 7.17 (d, J
= 8.2 Hz, 2H), 7.05 (d, J = 8.4 Hz, 2H), 6.89 (ddd, J = 10.4, 8.3, 1.9
Hz, 2H), 6.78 (dd, J = 8.1, 4.4 Hz, 2H), 5.82−5.54 (m, 3H), 4.82 (dd,
J = 10.6, 18.2 Hz, 2H), 3.92−3.81 (m, 18H), 3.76 (t, J = 6.4 Hz, 2H),
2.98 (d, J = 6.9 Hz, 2H), 2.13−2.06 (m, 2H), 1.72−1.65 (m, 2H),
1.60 (d, J = 6.7 Hz, 6H); 13C NMR (125 MHz, CD3COCD3) δ
196.53, 154.00, 150.13, 149.27, 146.04, 138.81, 134.15, 127.57,
123.36, 119.31, 116.47, 115.39, 115.24, 111.62, 111.49, 111.26,
110.70, 76.74, 66.33, 55.33, 33.99, 18.24; HRMS (ESI) m/z [M +
H]+ calcd for C43H49NO10 740.3429, found 740.3446; purity 94.21%,
tR 6.147 min.
(2S,5S)-1-Benzyl-2,5-bis(4-((tert-butyldimethylsilyl)oxy)-3-
methoxyphenyl)pyrrolidine (19b). To a cooled (−20 °C) solution of
18 (240 mg, 0.42 mmol) in anhydrous CH2Cl2 (10 mL) were added
Et3N (0.29 mL, 2.13 mmol) and MsCl (0.16 mL, 2.13 mmol). After
stirring for 3 h at −20 °C, an excessive amount of benzylamine (4.58
mL, 42 mmol) was added. The resulting mixture was allowed to warm
to 25 °C and stirred for 12 h. The reaction was quenched by the
addition of H2O, and the resulting mixture was diluted with CH2Cl2.
The combined organic layers were washed with brine, dried over
anhydrous Na2SO4, and concentrated in vacuo. Purification by column
chromatography (silica gel, hexanes/EtOAc, 100:1) afforded 19b
(170 mg, 64%) as a colorless oil: 1H NMR (400 MHz, CD3COCD3)
δ 7.26−7.05 (m, 4H), 6.99−6.90 (m, 4H), 6.83−6.76 (m, 3H), 3.83
(s, 3H), 3.73 (s, 3H), 3.71−3.65 (m, 2H), 3.58 (s, 2H), 2.14−2.01
(m, 2H), 2.00−1.87 (m, 2H), 1.00 (s, 18H), 0.16 (s, 12H); HRMS
(ESI) m/z [M + H]+ calcd for C37H55NO4Si2 634.3742, found
634.3756.
1,4-Bis(4-((tert-butyldimethylsilyl)oxy)-3-methoxyphenyl)-
butane-1,4-dione (17). The 1,4-diketone was synthesized from the
aryl bromide 9 (927 mg, 2.93 mmol) in anhydrous THF (3 mL), t-
BuLi (1.7 M in pentane, 1.15 mL, 1.95 mmol), and the known
Weinreb amide 16 (100 mg, 0.48 mmol) in anhydrous THF (4 mL)
according to GP2. Purification by column chromatography (silica gel,
hexanes/EtOAc, 8:1) afforded the 1,4-diketone 17 (108 mg, 40%) as
a yellow solid: 1H NMR (400 MHz, CD3COCD3) δ 7.67 (dd, J = 8.2,
2.0 Hz, 2H), 7.61 (d, J = 2.0 Hz, 2H), 7.00 (d, J = 8.2 Hz, 2H), 3.91
(s, 6H), 3.45−3.35 (m, 4H), 1.01 (s, 18H), 0.20 (s, 12H); 13C NMR
(125 MHz, CD3COCD3) δ 150.64, 143.52, 140.20, 120.02, 118.05,
109.91, 73.26, 54.84, 36.10, 25.26, 18.16, −5.28; HRMS (ESI) m/z
[M + H]+ calcd for C30H46O6Si2 559.2906, found 559.2914.
(1R,4R)-1,4-Bis(4-((tert-butyldimethylsilyl)oxy)-3-
methoxyphenyl)butane-1,4-diol (18). To a solution of (S)-α,α-
diphenyl-2-pyrrolidinemethanol (3.8 mg, 0.01 mmol) in anhydrous
THF (1 mL) was added B(OMe)3 (1.98 μL, 0.01 mmol). The
resulting mixture was stirred under a nitrogen atmosphere at 25 °C
for 1 h and transferred to a solution of 17 (50 mg, 0.08 mmol) and
BH3·SMe2 (2 M in THF, 0.53 mL, 1.06 mmol) in anhydrous THF (1
mL). After stirring for 1 h, the reaction was quenched by the addition
of 2 M HCl solution, and the resulting mixture was diluted with
EtOAc. The layers were separated, and the aqueous layer was
extracted with EtOAc. The combined organic layers were dried over
anhydrous Na2SO4 and concentrated under reduced pressure. The
residue was purified by column chromatography (silica gel, CH2Cl2/
MeOH, 50:1) to afford the 1,4-diol 18 (40 mg, 80%) as a white solid:
1H NMR (400 MHz, CD3COCD3) δ 6.98 (br s, 2H), 6.81−6.75 (m,
4,4′-((2S,5S)-1-Benzylpyrrolidine-2,5-diyl)bis(2-methoxyphenol)
(20b). The bis-phenol was synthesized from 19b (100 mg, 0.15
mmol) according to GP3. Purification by column chromatography
(silica gel, CH2Cl2/MeOH, 50:1) afforded the bis-phenol (50 mg,
82%) as a colorless oil: 1H NMR (400 MHz, CD3COCD3) δ 7.38 (s,
1H), 7.23−7.06 (m, 4H), 7.03−6.89 (m, 3H), 6.85−6.74 (m, 3H),
3.88 (s, 6H), 3.80 (s, 2H), 3.71−3.66 (m, 4H), 2.11−1.99 (m, 2H),
1.80−1.68 (m, 2H); HRMS (ESI) m/z [M + H]+ calcd for
4H), 4.59 (br s, 2H), 4.22 (d, J = 4.0 Hz, 2H), 3.80 (s, 6H), 1.90−
1.78 (m, 2H), 1.73−1.63 (m, 2H), 1.00 (s, 18H), 0.14 (s, 12H); 13C
NMR (125 MHz, CD3COCD3) δ 150.64, 143.53, 140.22, 120.02,
118.07, 109.91, 73.28, 54.83, 36.22, 25.25, 18.15, −5.29; HRMS
(ESI) m/z [M + Na]+ calcd for C30H50O6Si2 585.3219, found
585.3041. The enantiomeric excess of 18 was determined by chiral
HPLC separation (see Figure S2 for details).
I
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
C25H27NO4 406.2013, found 406.2018. Compound 20b was
synthesized from the bis-phenol (33 mg, 0.08 mmol) and the tosylate
3 (116 mg, 0.32 mmol) according to GP5. Purification by column
chromatography (silica gel, hexanes/EtOAc, 1:1) afforded 20b (35
mg, 26%) as a white solid: 1H NMR (400 MHz, CD3COCD3) δ 7.88
(d, J = 8.5 Hz, 2H), 7.74−7.64 (m, 2H), 7.18 (dd, J = 9.3, 2.1 Hz,
2H), 7.10−7.03 (m, 5H), 6.97−6.88 (m, 3H), 6.86−6.72 (m, 3H),
5.67−5.56 (m, 2H), 4.07 (q, J = 7.2 Hz, 2H), 3.94−3.82 (m, 18H),
3.53 (s, 2H), 2.13−2.02 (m, 2H), 1.77−1.68 (m, 2H), 1.63−1.58 (m,
6H).
tosyl ketone 3 (99 mg, 0.27 mmol) according to GP5. Purification by
column chromatography(silica gel, hexanes/EtOAc, 1:1) afforded the
analogue 25b (21 mg, 43%) as a colorless oil: H NMR (400 MHz,
1
CDCl3) δ 7.86 (ddd, J = 8.6, 2.0, 1.1 Hz, 2H), 7.78 (dd, J = 2.2, 1.1
Hz, 2H), 7.73−7.67 (m, 3H), 7.57−7.44 (m, 4H), 6.88 (ddd, J = 8.5,
3.6, 1.1 Hz, 4H), 5.49 (q, J = 6.8 Hz, 2H), 3.97 (s, 6H), 3.95 (s, 6H),
3.93 (s, 6H), 1.78 (dd, J = 6.9, 1.2 Hz, 6H); HRMS (ESI) m/z [M +
H]+ calcd for C41H41NO10 708.2803, found 708.2819; purity 91.50%,
tR 7.711 min.
1,5-Bis(4-((tert-butyldimethylsilyl)oxy)-3-methoxyphenyl)-
pentane-1,5-dione (26). The 1,5-diketone 26 was synthesized from
the aryl bromide 9 (7.5 g, 24 mmol) in anhydrous THF (36 mL), n-
BuLi (2.5 M in hexanes, 6.4 mL, 16 mmol), and the Weinreb amide
12 (873 mg, 4 mmol) in anhydrous THF (36 mL) according to GP2.
Purified by column chromatography (silica gel, hexanes/EtOAc, 8:1)
afforded 26 (1.47 g, 64%) as a yellow oil: 1H NMR (400 MHz,
CDCl3) δ 7.58−7.48 (m, 4H), 6.87 (d, J = 8.0 Hz, 2H), 3.87 (s, 6H),
3.06 (t, J = 7.0 Hz, 4H), 2.22−2.12 (m, 2H), 0.99 (s, 18H), 0.18 (s,
12H); 13C NMR (125 MHz, CD3COCD3) δ 197.74, 150.93, 149.48,
131.48, 122.14, 120.21, 111.18, 54.95, 37.06, 25.12, 19.23, 18.19,
−5.31; HRMS (ESI) m/z [M + H]+ calcd for C31H48O6Si2 573.3062,
found 573.3069.
(2R,2′R)-2,2′-((((2S,5S)-Pyrrolidine-2,5-diyl)bis(2-methoxy-4,1-
phenylene))bis(oxy))bis(1-(3,4-dimethoxyphenyl)propan-1-one)
(Analogue 21). The analogue 21 was synthesized from the aryl benzyl
ether 20b (21 mg, 0.02 mmol) and 10% palladium on activated
carbon in HOAc (1 mL) according to GP1. Purification by column
chromatography (silica gel, CH2Cl2/MeOH, 50:1) afforded the
1
analogue 21 as a beige solid (6.9 mg, 50%): H NMR (400 MHz,
CD3COCD3) δ 7.85 (ddd, J = 8.4, 2.0, 1.2 Hz, 2H), 7.65 (d, J = 2.1
Hz, 2H), 7.27 (s, 2H), 7.10−7.01 (m, 2H), 6.92 (dd, J = 8.2, 2.0 Hz,
2H), 6.76 (d, J = 8.2 Hz, 2H), 5.64−5.57 (m, 2H), 4.32 (br s, 2H),
3.94−3.75 (m, 18H), 2.26−2.19 (m, 2H), 1.84−1.77 (m, 2H), 1.60
(d, J = 6.8 Hz, 6H); HRMS (ESI) m/z [M + H]+ calcd for
C40H45NO10 700.3116, found 700.3128; purity 98.39%, tR 5.877 min.
4,4′′-Bis(benzyloxy)-3,3′′-dimethoxy-1,1′:3′,1′′-terphenyl (24a).
The coupling of 22a (0.04 mL, 0.39 mmol) and 23 (203 mg, 0.78
mmol) was carried out according to GP4. Purification by column
chromatography (silica gel, hexanes/EtOAc, 10:1) afforded 24a (199
1,2-Bis(4-((tert-butyldimethylsilyl)oxy)-3-methoxyphenyl)-
cyclopent-1-ene (27). To the 1,5-diketone 26 (802 mg, 1.5 mmol) in
MeOH was added TsNHNH2 (701 mg, 3.7 mmol). After stirring for
15 h at 60 °C, the reaction mixture was concentrated under reduced
pressure. The resulting solid was used in the next step without further
purification. To a solution of the above hydrazide in 1,2-dichloro-
ethane (20 mL) were added LiOt-Bu (185 mg, 2.3 mmol), t-
BuXphosAuCl (12.5 mg, 0.01 mmol), and NaBArF (16.8 mg, 0.01
mmol). The reaction mixture was heated to 80 °C and stirred for 16 h
under reflux conditions. The reaction mixture was cooled to 25 °C;
the solvent was removed, and the residue was purified by column
chromatography (silica gel, hexanes/EtOAc, 50:1) to afford 27 (52
1
mg, 99%) as a white solid: H NMR (400 MHz, CDCl3) δ 7.70 (s,
1H), 7.54−7.28 (m, 12H), 7.22−7.05 (m, 4H), 7.04−6.89 (m, 3H),
5.21 (d, J = 8.6 Hz, 4H), 3.97 (s, 6H); HRMS (ESI) m/z [M + H]+
calcd for C34H30O4 503.2217, found 503.2219.
(2R,2′R)-2,2′-((3,3′′-Dimethoxy-[1,1′:3′,1′′-terphenyl]-4,4′′-diyl)-
bis(oxy))bis(1-(3,4-dimethoxyphenyl)propan-1-one) (Analogue
25a). The bis-phenol was synthesized from the aryl benzyl ether
24a (28 mg, 0.04 mmol) in EtOH (0.5 mL) and 10% palladium on
activated carbon according to GP1. Purification by column
chromatography (silica gel, hexanes/EtOAc, 3:1) afforded the bis-
phenol (5 mg, 34%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ
7.68 (s, 1H), 7.52−7.41 (m, 3H), 7.18−7.08 (m, 4H), 7.01 (dd, J =
8.2, 2.2 Hz, 2H), 5.65 (s, 2H), 3.96 (s, 6H); HRMS (ESI) m/z [M +
H]+ calcd for C20H18O4 323.1278, found 323.1269. The analogue 25a
was synthesized from the bis-phenol (5 mg, 0.01 mmol) and the tosyl
ketone 3 (14.13 mg, 0.03 mmol) according to GP5. Purification by
column chromatography (silica gel, hexanes/EtOAc, 20:1) afforded
the analogue 25a (3 mg, 27%) as a colorless oil: 1H NMR (400 MHz,
CDCl3) δ 7.85 (dd, J = 8.4, 2.0 Hz, 1H), 7.76−7.66 (m, 5H), 7.60 (s,
1H), 7.56−7.50 (m, 3H), 7.43 (d, J = 1.6 Hz, 2H), 7.10 (d, J = 2.1
Hz, 1H), 7.03 (dd, J = 8.3, 2.1 Hz, 1H), 6.93−6.82 (m, 2H), 5.51−
5.43 (m, 2H), 4.09 (s, 3H), 4.07 (s, 3H), 3.94 (s, 6H), 3.92 (s, 3H),
3.89 (s, 3H), 1.76 (d, J = 6.8 Hz, 6H); HRMS (ESI) m/z [M + H]+
calcd for C42H42O10 707.2851, found 707.2865; purity 92.45%, tR
7.921 min.
2,6-Bis(4-(benzyloxy)-3-methoxyphenyl)pyridine (24b). The cou-
pling of 22b (50.2 mg, 0.21 mmol) and 23 (219 mg, 0.85 mmol) was
carried out according to GP4. Purification by column chromatography
(silica gel, hexanes/EtOAc, 10:1) afforded 24b (9 mg, 8%) as a white
solid: 1H NMR (400 MHz, CDCl3) δ 7.79−7.73 (m, 2H), 7.48 (dd, J
= 7.8, 1.0 Hz, 2H), 7.43−7.36 (m, 7H), 7.35−7.28 (m, 5H), 7.23 (d, J
= 6.9 Hz, 1H), 6.79−6.73 (m, 2H), 5.76 (s, 4H), 4.01 (s, 6H).
(2R,2′R)-2,2′-((Pyridine-2,6-diylbis(2-methoxy-4,1-phenylene))-
bis(oxy))bis(1-(3,4-dimethoxyphenyl)propan-1-one) (Analogue
25b). The bis-phenol was synthesized from the aryl benzyl ether
24b (41 mg, 0.08 mmol) in EtOH (0.67 mL) and 10% palladium on
activated carbon according to GP1. Purification by column
chromatography (silica gel, hexanes/EtOAc, 2:1) afforded the bis-
phenol (23 mg, 89%) as a white solid: 1H NMR (400 MHz, CDCl3) δ
7.79 (s, 2H), 7.74 (t, J = 7.8 Hz, 1H), 7.62−7.54 (m, 4H), 7.02 (d, J =
8.2 Hz, 2H), 5.76 (br s, 2H), 4.02 (s, 6H); HRMS (ESI) m/z [M +
H]+ calcd for C19H17NO4 324.1230, found 324.1248. The analogue
25b was synthesized from the bis-phenol (22 mg, 0.06 mmol) and the
1
mg, 13%): H NMR (400 MHz, CDCl3) δ 6.76−6.65 (m, 6H), 3.54
(s, 6H), 2.85 (t, J = 7.2 Hz, 4H), 2.05−1.96 (m, 2H), 0.98 (s, 18H),
0.12 (s, 12H).
(2R,2′R)-2,2′-((Cyclopent-1-ene-1,2-diylbis(2-methoxy-4,1-
phenylene))bis(oxy))bis(1-(3,4-dimethoxyphenyl)propan-1-one)
(Analogue 28). The bis-phenol was synthesized from 27 (51 mg, 0.09
mmol) according to GP3. Purification by column chromatography
(silica gel, hexanes/EtOAc, 2:1) afforded the bis-phenol (25.5 mg,
88%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ 6.82−6.75 (m,
4H), 6.69−6.60 (m, 2H), 3.65 (s, 6H), 2.85 (t, J = 7.2 Hz, 4H),
2.02−1.96 (m, 2H). Analogue 28 was synthesized from the bis-phenol
(11 mg, 0.03 mmol) and the tosylate 3 (51 mg, 0.14 mmol) according
to GP5. Purification by column chromatography (silica gel, hexanes/
1
EtOAc, 1:1) afforded analogue 28 (18 mg, 73%): H NMR (400
MHz, CDCl3) δ 7.80 (d, J = 8.0 Hz, 2H), 7.65 (s, 2H), 6.88 (d, J =
8.8 Hz, 2H), 6.68−6.66 (m, 6H), 5.39 (q, J = 4.0 Hz, 2H), 3.94 (s,
6H), 3.91 (s, 6H), 3.51 (s, 6H), 2.79 (t, J = 7.2 Hz, 4H), 1.98−1.94
(m, 2H), 1.69 (d, J = 6.7 Hz, 6H); HRMS (ESI) m/z [M + Na]+
calcd for C41H44O10 719.2827, found 719.2842; purity 94.57%, tR
8.094 min.
(4-((1,3-Dithian-2-yl)methyl)-2-methoxyphenoxy)(tert-butyl)-
dimethylsilane (31). Compound 31 was synthesized from 1,3-
dithiane (29) (58 mg, 0.48 mmol) in anhydrous THF (4 mL), n-BuLi
(2.5 M in hexanes, 0.19 mL, 0.48 mmol), and the benzyl bromide 30
(161 mg, 0.48 mmol) in anhydrous THF (0.9 mL) according to GP2.
Purification by column chromatography (silica gel, hexanes/EtOAc,
1
20:1) afforded 31 (71 mg, 39%) as a colorless oil: H NMR (400
MHz, CDCl3) δ 6.77 (d, J = 7.9 Hz, 1H), 6.72 (d, J = 2.0 Hz, 1H),
6.69 (dd, J = 8.0, 2.1 Hz, 1H), 4.21 (t, J = 7.3 Hz, 1H), 3.79 (s, 3H),
2.93 (d, J = 7.3 Hz, 2H), 2.90−2.77 (m, 4H), 2.17−2.06 (m, 1H),
1.92−1.79 (m, 1H), 0.98 (s, 9H), 0.14 (s, 6H); HRMS (ESI) m/z [M
+ H]+ calcd for C18H30O2S2Si 371.1529, found 371.1532.
((((1,3-Dithiane-2,2-diyl)bis(methylene))bis(2-methoxy-4,1-
phenylene))bis(oxy))bis(tert-butyldimethylsilane) (32). Compound
32 was synthesized from the dithiane 31 (21 mg, 0.05 mmol) in
THF/HMPA (10:1, 0.7 mL), t-BuLi (1.7 M in pentane, 33 μL, 0.05
J
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
mmol), and the benzyl bromide 30 (28 mg, 0.08 mmol) in anhydrous
THF (0.4 mL) according to GP2. Purification by column
chromatography (silica gel, hexanes/EtOAc, 20:1) afforded 32 (22
mg, 63%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ 6.86 (d, J
= 1.7 Hz, 2H), 6.81−6.71 (m, 4H), 3.78 (s, 6H), 3.11 (s, 4H), 2.79−
2.68 (m, 4H), 1.89−1.77 (m, 2H), 0.99 (s, 18H), 0.15 (s, 12H);
HRMS (ESI) m/z [M + H]+ calcd for C32H52O4S2Si2 621.2918,
found 621.2904.
2H), 7.27 (d, J = 1.9 Hz, 1H), 7.12 (dd, J = 8.5, 1.4 Hz, 2H), 7.09 (d,
J = 1.5 Hz, 1H), 7.02 (d, J = 8.4 Hz, 1H), 6.86 (dd, J = 8.4, 1.4 Hz,
5H), 5.78−5.68 (m, 2H), 3.97 (s, 6H), 3.94 (s, 6H), 3.93 (s, 6H),
1.69 (d, J = 6.7 Hz, 6H); HRMS (ESI) m/z [M + Na]+ calcd for
C38H40O10 679.2519, found 679.2522; purity 90.65%, tR 7.557 min.
Dual Luciferase-Reporter Assay. HEK-293T cells were seeded
on 96-well plates at a density of 5 × 103 cells/well and allowed to
attach for 24 h. Cells were transfected with a pGL3-5 × HRE-Luc
plasmid containing five copies of HREs in human VEGF promoter
and pRL-SV40 plasmid encoding Renilla luciferase using the
Vivamagic Transfection Reagent (Vivagene, Seongnam, Korea),
according to the manufacturer’s instructions. Cells were treated
with hypoxia (1% O2) and serially diluted compounds for 24 h after
transfection. The luciferase-reporter assay was performed using the
Dual-Glo Luciferase Assay System (Promega, Madison, WI, USA)
according to the manufacturer’s instructions. Briefly, an equal volume
of the Dual-Glo Reagent to the culture medium was added to each
well, and the mixture was incubated for 10 min. The firefly
luminescence was measured using a microplate reader (Infinite
(2R,2′R)-2,2′-((((1,3-Dithiane-2,2-diyl)bis(methylene))bis(2-me-
thoxy-4,1-phenylene))bis(oxy))bis(1-(3,4-dimethoxyphenyl)-
propan-1-one) (Analogue 33). The bis-phenol was synthesized from
32 (20 mg, 0.03 mmol) according to GP3. Purification by column
chromatography (silica gel, hexanes/EtOAc, 3:1) afforded bis-phenol
(10 mg, 79%) as a colorless oil: 1H NMR (400 MHz, CDCl3) δ 6.93−
6.74 (m, 6H), 5.55 (br s, 2H), 3.87 (s, 6H), 3.13 (s, 4H), 2.89−2.77
(m, 4H), 1.98−1.79 (m, 2H); HRMS (ESI) m/z [M + H]+ calcd for
C20H24O4S2 393.1189, found 393.1184. Analogue 33 was synthesized
from the bis-phenol (10 mg, 0.02 mmol) and the tosyl ketone 3 (35
mg, 0.1 mmol) according to GP5. Purification by column
chromatography (silica gel, hexanes/EtOAc, 1:1 to 1:2) afforded
1
̈
M200 Pro, TECAN, Mannedorf, Switzerland). The Dual-Glo Stop &
analogue 33 (17 mg, 86%) as a colorless oil: H NMR (400 MHz,
Glo Reagent was added, and the mixture was incubated for 10 min
before the measurement of Renilla luminescence. The firefly
luminescence signals were normalized to the activity of Renilla
luciferase. Three independent experiments were performed.
Molecular Overlay. The molecular overlay of manassantin A
analogues was generated based on a total number of 2 analogues that
were tested for their activity against HIF-1 (Figure 2). The molecular
CDCl3) δ 7.81 (d, J = 8.4 Hz, 2H), 7.66 (s, 2H), 6.87 (d, J = 8.5 Hz,
2H), 6.85 (s, 1H), 6.77−6.61 (m, 4H), 5.40 (q, J = 4.0 Hz, 2H), 3.93
(s, 6H), 3.91 (s, 6H), 3.79 (s, 6H), 3.04 (s, 4H), 2.82−2.63 (m, 4H),
1.86−1.76 (m, 2H), 1.71 (d, J = 6.7 Hz, 6H); HRMS (ESI) m/z [M +
H]+ calcd for C42H48O10S2 777.2762, found 777.2764; purity 92.42%,
tR 7.780 min.
Bromo(4-((tert-butyldimethylsilyl)oxy)-3-methoxybenzyl)-
triphenyl-l5-phosphane (35). To a solution of the benzyl bromide 34
(675 mg, 2.04 mmol) in anhydrous toluene (8 mL) was added PPh3
(1.6 g, 6.11 mmol). The reaction mixture was heated to 80 °C and
stirred for 2 h under reflux conditions. The reaction mixture was
cooled to 25 °C, and the precipitate was filtered and purified by
column chromatography (silica gel, CH2Cl2/MeOH 20:1) to afford
̈
structures were sketched and built with Maestro 11.2 (Schrodinger,
NY). Low-energy conformations of manassantin A analogues were
generated by LigPrep. LigPrep used the force field OPLS3e and
charges in all ligand preparation steps. All possible protonation and
ionization states were enumerated for each ligand at pH 7.4. Only the
lowest energy conformer was kept for each ligand. Ligand
conformation sampling was done by using the MacroModel module
of Maestro. The extended cutoff of the MacroModel (van der Waals,
8.0; electrostatic, 20.0; and H-bond, 4.0) was used. The superimpose
model was generated by using the Structure Alignment module of
1
the phosphonium salt 35 (720 mg, 60%) as a white solid: H NMR
(400 MHz, CDCl3) δ 7.84−7.50 (m, 15H), 6.84 (t, J = 2.2 Hz, 1H),
6.59 (d, J = 8.1 Hz, 1H), 6.43 (dt, J = 8.2, 2.5 Hz, 1H), 5.27 (d, J =
13.7 Hz, 2H), 3.46 (s, 3H), 1.93 (m, 9H), 0.07 (m, 6H).
(E)-1,2-Bis(4-((tert-butyldimethylsilyl)oxy)-3-methoxyphenyl)-
ethene (37). To a cooled (−78 °C) solution of 35 (211 mg, 0.36
mmol) in anhydrous THF (2 mL, 0.5 M) was added LHMDS (1 M in
THF, 0.36 mL, 0.36 mmol) dropwise. The resulting mixture was
stirred at the same temperature for 20 min and treated with a solution
of aldehyde 36 (142 mg, 0.53 mmol) in anhydrous THF (1 mL).
After stirring for 5.5 h at 0 °C, the reaction was quenched by the
addition of saturated aqueous NH4Cl solution and diluted with
EtOAc. The layers were separated, and the aqueous layer was
extracted with EtOAc. The combined organic layers were washed with
brine, dried over anhydrous Na2SO4, and concentrated in vacuo. The
residue was purified by column chromatography (silica gel, hexanes/
EtOAc 30:1) to afford the corresponding TBS-protected trans-alkene
̈
Schrodinger Glide. The superimposition of conformers was developed
with the “atom pair” method in the Structure Alignment module.
Mice. Animal experiments were performed using C57BL/6J mice
(Japan SLC, Shizuoka, Japan), which were handled in strict
compliance with the guidelines for care and use of laboratory animals
issued (KNU 2017-145) by the Institutional Ethical Animal Care
Committee of Kyungpook National University (Daegu, Korea).
In Vivo Animal Study. To generate a Lewis lung carcinoma
(LLC) allograft tumor model, suspensions of LLC cells (2 × 105 cells
in 200 μL of serum-free culture media) were implanted subcuta-
neously into the dorsal flank regions of 5−6 week old male C57BL/6
mice (Day 0). From 2 days after inoculation, mice (n = 5 per group)
were treated with manassantin A (5 mg/kg body weight) and/or
gefitinib (5 mg/kg body weight) intraperitoneally three times a week
for 17 days. Body weights were measured three times a week for 17
days. Tumor volumes (cm3) were calculated by multiplying the height
by length by depth. Eventually, the mice were anesthetized, and their
tumor tissues were harvested at the completion of the study period.
1
(15 mg, 8.4%) as a white solid: H NMR (400 MHz, CDCl3) δ 7.01
(d, J = 1.9 Hz, 2H), 6.95 (dd, J = 2.0, 8.2 Hz, 2H), 6.90 (s, 2H), 6.82
(d, J = 8.1 Hz, 2H), 3.86 (s, 6H), 1.00 (s, 18H), 0.17 (s, 12H);
HRMS (ESI) m/z [M + NH4]+ calcd for C28H44O4Si2 518.3116,
found 518.3124. The bis-phenol 37 was synthesized from the TBS-
protected trans-alkene (83 mg, 0.16 mmol) according to GP3.
Purification by column chromatography (silica gel, hexanes/EtOAc
2:1) afforded 37 as a white solid (24 mg, 55%): 1H NMR (400 MHz,
CD3COCD3) δ 7.64 (s, 2H), 7.17 (d, J = 1.7 Hz, 2H), 6.98 (s, 2H),
6.97−6.96 (m, 2H), 6.79 (d, J = 8.1 Hz, 2H), 3.88 (s, 6H); HRMS
(ESI) m/z [M + H]+ calcd for C16H16O4 273.1121, found 273.1120.
(S)-1-(3,4-Dimethoxyphenyl)-2-(4-((E)-4-(((R)-1-(3,4-dimethoxy-
phenyl)-1-oxopropan-2-yl)oxy)-3-methoxystyryl)-2-
methoxyphenoxy)propan-1-one (Analogue 38). Analogue 38 was
synthesized from the bis-phenol 37 (25 mg, 0.09 mmol) and the
tosylate 3 (134 mg, 0.36 mmol) according to GP5. Purification by
column chromatography (silica gel, hexanes/EtOAc, 10:1) afforded
the analogue 38 (27 mg, 45%) as a white solid: 1H NMR (400 MHz,
CD3COCD3) δ 7.91 (dd, J = 8.4, 1.7 Hz, 2H), 7.72 (d, J = 2.0 Hz,
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jmedchem.0c00151.
Determination of enantiomeric excess of 7 and 18, body
weight, and HPLC traces of final compounds (PDF)
SMILES representations and relative luciferase activity
(CSV)
K
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
AUTHOR INFORMATION
ABBREVIATIONS USED
■
■
BEMP, 2-tert-butylimino-2-diethylamino-1,3-dimethylperhy-
dro-1,3,2-diazaphosphorine; CDK6, cyclin-dependent kinase
6; EGFR, epidermal growth factor receptor; GLUT1, glucose
transporter 1; HEK, human embryonic kidney; HIF-1,
hypoxia-inducible factor; HRE, hypoxia response element;
i.p., intraperitoneally; LLC, Lewis lung carcinoma; PMHS,
polymethylhydrosiloxane; RLU, relative light unit; SAR,
structure−activity relationship; s.c., subcutaneously; THF,
tetrahydrofuran; THP, tetrahydropyran; VEGF, vascular
endothelial growth factor
Corresponding Authors
You Mie Lee − College of Pharmacy, BK21 Plus KNU Multi-
Omics Creative Drug Research Team, Research Institute of
Pharmaceutical Sciences, Kyungpook National University, Buk-
gu, Daegu 41566, Republic of Korea; orcid.org/0000-0002-
5756-7169; Phone: 82-53-950-8566; Email: lym@knu.ac.kr;
Fax: 82-53-950-8557
Jiyong Hong − Department of Chemistry, Duke University,
Durham, North Carolina 27708, United States; Department of
Pharmacology and Cancer Biology, Duke University Medical
Center, Durham, North Carolina 27710, United States;
orcid.org/0000-0002-5253-0949; Phone: 1-919-660-
1545; Email: jiyong.hong@duke.edu; Fax: 1-919-660-1605
REFERENCES
■
(1) Bray, F.; Ferlay, J.; Soerjomataram, I.; Siegel, R. L.; Torre, L. A.;
Jemal, A. Global cancer statistics 2018: GLOBOCAN estimates of
incidence and mortality worldwide for 36 cancers in 185 countries.
Ca-Cancer J. Clin. 2018, 68, 394−424.
(2) Agency for Healthcare Research and Quality. Total expenditures
in millions by condition, U.S., 2015. Medical Expenditure Panel Survey.
https://www.meps.ahrq.gov/mepstrends/hc_cond/.
(3) Jonsson, B.; Hofmarcher, T.; Lindgren, P.; Wilking, N. The cost
and burden of cancer in the European Union 1995−2014. Eur. J.
Cancer 2016, 66, 162−170.
(4) Semenza, G. L. Oxygen sensing, homeostasis, and disease. N.
Engl. J. Med. 2011, 365, 537−547.
(5) Wang, G. L.; Jiang, B. H.; Rue, E. A.; Semenza, G. L. Hypoxia-
inducible factor 1 is a basic-helix-loop-helix-PAS heterodimer
regulated by cellular O2 tension. Proc. Natl. Acad. Sci. U. S. A. 1995,
92, 5510−5514.
(6) Lisy, K.; Peet, D. J. Turn me on: regulating HIF transcriptional
activity. Cell Death Differ. 2008, 15, 642−649.
(7) Vaupel, P. Tumor microenvironmental physiology and its
implications for radiation oncology. Semin. Radiat. Oncol. 2004, 14,
198−206.
Authors
Seung-Hwa Kwak − Department of Chemistry, Duke University,
Durham, North Carolina 27708, United States
Tesia N. Stephenson − Department of Chemistry, Duke
University, Durham, North Carolina 27708, United States
Hye-Eun Lee − College of Pharmacy, BK21 Plus KNU Multi-
Omics Creative Drug Research Team, Research Institute of
Pharmaceutical Sciences, Kyungpook National University, Buk-
gu, Daegu 41566, Republic of Korea
Yun Ge − College of Pharmacy, BK21 Plus KNU Multi-Omics
Creative Drug Research Team, Research Institute of
Pharmaceutical Sciences, Kyungpook National University, Buk-
gu, Daegu 41566, Republic of Korea
Hyunji Lee − Department of Chemistry, Duke University,
Durham, North Carolina 27708, United States
Sophia M. Min − Department of Chemistry, Duke University,
Durham, North Carolina 27708, United States
Jea Hyun Kim − Department of Chemistry, Duke University,
Durham, North Carolina 27708, United States
Do-Yeon Kwon − Department of Chemistry, Duke University,
Durham, North Carolina 27708, United States
(8) Aebersold, D. M.; Burri, P.; Beer, K. T.; Laissue, J.; Djonov, V.;
Greiner, R. H.; Semenza, G. L. Expression of hypoxia-inducible factor-
1a: a novel predictive and prognostic parameter in the radiotherapy of
oropharyngeal cancer. Cancer Res. 2001, 61, 2911−2916.
(9) Moeller, B. J.; Cao, Y.; Li, C. Y.; Dewhirst, M. W. Radiation
activates HIF-1 to regulate vascular radiosensitivity in tumors: role of
reoxygenation, free radicals, and stress granules. Cancer Cell 2004, 5,
429−441.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.jmedchem.0c00151
Author Contributions
(10) Koukourakis, M. I.; Giatromanolaki, A.; Sivridis, E.;
Simopoulos, C.; Turley, H.; Talks, K.; Gatter, K. C.; Harris, A. L.
Hypoxia-inducible factor (HIF1A and HIF2A), angiogenesis, and
chemoradiotherapy outcome of squamous cell head-and-neck cancer.
Int. J. Radiat. Oncol., Biol., Phys. 2002, 53, 1192−1202.
(11) Schito, L.; Semenza, G. L. Hypoxia-inducible factors: master
regulators of cancer progression. Trends Cancer 2016, 2, 758−770.
(12) Brizel, D. M.; Sibley, G. S.; Prosnitz, L. R.; Scher, R. L.;
Dewhirst, M. W. Tumor hypoxia adversely affects the prognosis of
carcinoma of the head and neck. Int. J. Radiat. Oncol., Biol., Phys.
1997, 38, 285−289.
S.-H.K., T.N.S., H.L., S.M.M., J.H.K., and D.-Y.K. synthesized
manassantin A and analogues used in in vitro and in vivo
testing. S.-H.K. performed conformational analysis. H.-E.L.
performed in vivo testing of manassantin A. Y.G. performed the
in vitro luciferase assay of manassantin A and analogues. Y.M.L.
designed in vitro and in vivo testing and analyzed the data. J.H.
conceived the project, designed the overall experimental
strategy, and analyzed and discussed the results. J.H., Y.M.L.,
and S.-H.K. wrote the manuscript with input from all of the
authors.
(13) Hockel, M.; Schlenger, K.; Aral, B.; Mitze, M.; Schaffer, U.;
Vaupel, P. Association between tumor hypoxia and malignant
progression in advanced cancer of the uterine cervix. Cancer Res.
1996, 56, 4509−4915.
Notes
The authors declare no competing financial interest.
(14) Moon, E. J.; Brizel, D. M.; Chi, J. T.; Dewhirst, M. W. The
potential role of intrinsic hypoxia markers as prognostic variables in
cancer. Antioxid. Redox Signaling 2007, 9, 1237−1294.
(15) Wigerup, C.; Pahlman, S.; Bexell, D. Therapeutic targeting of
hypoxia and hypoxia-inducible factors in cancer. Pharmacol. Ther.
2016, 164, 152−169.
(16) Rao, K. V.; Alvarez, F. M. Manassantins A/B and saucerneol:
novel biologically active lignoids from Saururus cernuus. Tetrahedron
Lett. 1983, 24, 4947−4950.
ACKNOWLEDGMENTS
■
This work was supported by the American Cancer Society
(122057-RSG-12-045-01-CDD to J.H.) and the Korean
National Research Foundation (NRF-2017R1A2B3002227 to
Y.M.L.). T.N.S. was supported by the NSF Graduate Research
Fellowship Program.
L
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX

Journal of Medicinal Chemistry
pubs.acs.org/jmc
Article
(17) Hodges, T. W.; Hossain, C. F.; Kim, Y. P.; Zhou, Y. D.; Nagle,
D. G. Molecular-targeted antitumor agents: the Saururus cernuus
dineolignans manassantin B and 4-O-demethylmanassantin B are
potent inhibitors of hypoxia-activated HIF-1. J. Nat. Prod. 2004, 67,
767−771.
(18) Hossain, C. F.; Kim, Y. P.; Baerson, S. R.; Zhang, L.; Bruick, R.
K.; Mohammed, K. A.; Agarwal, A. K.; Nagle, D. G.; Zhou, Y. D.
Saururus cernuus lignanslpotent small molecule inhibitors of hypoxia-
inducible factor-1. Biochem. Biophys. Res. Commun. 2005, 333, 1026−
1033.
(19) Kim, H.; Kasper, A. C.; Moon, E. J.; Park, Y.; Wooten, C. M.;
Dewhirst, M. W.; Hong, J. Nucleophilic addition of organozinc
reagents to 2-sulfonyl cyclic ethers: stereoselective synthesis of
manassantins A and B. Org. Lett. 2009, 11, 89−92.
(20) Kwon, D. Y.; Lee, H. E.; Weitzel, D. H.; Park, K.; Lee, S. H.;
Lee, C. T.; Stephenson, T. N.; Park, H.; Fitzgerald, M. C.; Chi, J. T.;
Mook, R. A., Jr.; Dewhirst, M. W.; Lee, Y. M.; Hong, J. Synthesis and
biological evaluation of manassantin analogues for hypoxia-inducible
factor 1alpha inhibition. J. Med. Chem. 2015, 58, 7659−7671.
(21) Kasper, A. C.; Moon, E. J.; Hu, X.; Park, Y.; Wooten, C. M.;
Kim, H.; Yang, W.; Dewhirst, M. W.; Hong, J. Analysis of HIF-1
inhibition by manassantin A and analogues with modified
tetrahydrofuran configurations. Bioorg. Med. Chem. Lett. 2009, 19,
3783−3786.
(22) Schmidt, B.; Hauke, S. Cross metathesis of allyl alcohols: how
to suppress and how to promote double bond isomerization. Org.
Biomol. Chem. 2013, 11, 4194−4206.
(23) Strych, S.; Trauner, D. Biomimetic synthesis of santalin A, B
and santarubin A, B, the major colorants of red sandalwood. Angew.
Chem., Int. Ed. 2013, 52, 9509−9512.
(37) Atkins, M. B.; Larkin, J. Immunotherapy combined or
sequenced with targeted therapy in the treatment of solid tumors:
current perspectives. J. Natl. Cancer Inst. 2016, 108, No. djv414.
(38) Lee, S. Y.; Oh, S. C. Changing strategies for target therapy in
gastric cancer. World J. Gastroenterol. 2016, 22, 1179−1189.
(39) Camidge, D. R.; Pao, W.; Sequist, L. V. Acquired resistance to
TKIs in solid tumours: learning from lung cancer. Nat. Rev. Clin.
Oncol. 2014, 11, 473−481.
(40) Sherwood, L. M.; Parris, E. E.; Folkman, J. Tumor
angiogenesis: therapeutic implications. N. Engl. J. Med. 1971, 285,
1182−1186.
(41) Carmeliet, P.; Jain, R. K. Angiogenesis in cancer and other
diseases. Nature 2000, 407, 249−257.
(42) Lang, L.; Liu, X.; Li, Y.; Zhou, Q.; Xie, P.; Yan, C.; Chen, X. A
synthetic manassantin A derivative inhibits hypoxia-inducible factor 1
and tumor growth. PLoS One 2014, 9, No. e99584.
(43) Li, J.; Zhao, K.; Wang, F.; Cai, J.; Li, Z.; Zou, L. X609, a novel
manassantin A derivative, exhibits antitumor activity in MG-63 human
osteosarcoma cells in vitro and in vivo. Mol. Med. Rep. 2015, 12,
3115−3120.
(44) Lai, F.; Liu, Q.; Liu, X.; Ji, M.; Xie, P.; Chen, X. LXY6090 - a
novel manassantin A derivative - limits breast cancer growth through
hypoxia-inducible factor-1 inhibition. OncoTargets Ther. 2016, 9,
3829−3840.
(24) Corey, E.; Bakshi, R. K.; Shibata, S. Highly enantioselective
borane reduction of ketones catalyzed by chiral oxazaborolidines.
mechanism and synthetic implications. J. Am. Chem. Soc. 1987, 109,
5551−5553.
(25) The enantiomeric excess of 7 was determined by Mosher ester
analysis. See the Supporting Information for details.
(26) Ghavimi, B.; Magnus, P. Total synthesis of 8,14-dihydromor-
phinandienone alkaloids. Org. Lett. 2014, 16, 1708−1711.
(27) Kang, F.-A.; Jain, N.; Sui, Z. Stereoselective synthesis of rac-
(8R,13S,14S)-7-oxa-estra-4,9-diene-3,17-dione. Tetrahedron Lett.
2006, 47, 9021−9024.
(28) Jiang, X.; London, E. K.; Morris, D. J.; Clarkson, G. J.; Wills, M.
Gold-catalysed cyclic ether formation from diols. Tetrahedron 2010,
66, 9828−9834.
(29) Inagi, S.; Takei, N.; Fuchigami, T. Synthesis of 4-
iodotetrahydropyran-containing polymers via TMSI-promoted Prins
cyclization. Polym. Chem. 2013, 4, 1221−1227.
(30) Brown, D. S.; Bruno, M.; Davenport, R. J.; Ley, S. V.
Substitution reactions of 2-benzenesulphonyl cyclic ethers with
carbon nucleophiles. Tetrahedron 1989, 45, 4293−4308.
(31) Harding, M.; Hodgson, R.; Nelson, A. J. Sequential kinetic
resolution of C2-symmetric compounds as a key step in two-
directional synthesis: structural requirements for efficient resolution of
difuryl diols. J. Chem. Soc., Perkin Trans. 1 2002, 21, 2403−2413.
(32) Hasdemir, B. Asymmetric synthesis of some chiral aryl and
hetero aryl-substituted β-, γ-, δ-hydroxy esters. Synth. Commun. 2015,
45, 1082−1088.
(33) Zhu, C.; Qiu, L.; Xu, G.; Li, J.; Sun, J. Base-promoted/gold-
catalyzed intramolecular highly selective and controllable detosylative
cyclization. Chem. - Eur. J. 2015, 21, 12871−12875.
(34) Singh, S. B.; Pettit, G. R. Synthesis of ( )-isocombretastatins
AC. Synth. Commun. 1987, 17, 877−892.
̀
(35) Hitce, J.; Crutizat, M.; Bourdon, C.; Vives, A.; Marat, X.;
Dalko-Csiba, M. Flash-metathesis for the coupling of sustainable
(poly) hydroxyl β-methylstyrenes from essential oils. Green Chem.
2015, 17, 3756−3761.
(36) To avoid any unnecessary complications and/or exaggeration
by the flexible side chains, truncated structures of 1, 11, and 25b were
used instead of the full structures.
M
https://dx.doi.org/10.1021/acs.jmedchem.0c00151
J. Med. Chem. XXXX, XXX, XXX−XXX