Facile construction of pyrrolo[1,2-: B] isoquinolin-10(5 H)-ones via a redox-amination-aromatization-Friedel-Crafts acylation cascade reaction and discovery of novel topoisomerase inhibitors

Article abstract of DOI:10.1039/c6cc03071h

An efficient redox-amination-aromatization-Friedel-Crafts acylation cascade process from trans-4-hydroxyproline and 2-formylbenzoic acids has been developed for the synthesis of pyrrolo[1,2-b]isoquinolin-10(5H)-ones. Compound 3h was identified as a new potent dual topoisomerase I/II inhibitor.

Full text of DOI:10.1039/c6cc03071h

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: S. Wu, N. Liu, G.
Dong, L. Ma, S. Wang, W. Shi, K. Fang, S. Chen, J. Li, W. Zhang, C. Sheng and W. Wang, Chem. Commun.,
2016, DOI: 10.1039/C6CC03071H.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/chemcomm

Please do not adjust margins
Page 1 of 4
ChemComm
View Article Online
DOI: 10.1039/C6CC03071H
Journal Name
COMMUNICATION
Facile Construction of Pyrrolo[1,2-b]isoquinolin-10(5H)-ones via a
Redox-amination-aromatization-Friedel-Crafts Acylation Cascade
Reaction and Discovery of Novel Topoisomerase Inhibitors
Received 00th January 20xx,
Accepted 00th January 20xx
Shanchao Wu,†,$ Na Liu,†,$ Guoqiang Dong,†,$ Lin Ma,† Shengzheng Wang,† Wencai Shi,§ Kun Fang,†, ≠
DOI: 10.1039/x0xx00000x
Shuqiang Chen†, Jian Li,≠ Wannian Zhang,†,* Chunquan Sheng†,* and Wei Wang‡,≠,
*
www.rsc.org/
An
efficient
redox-amination-aromatization-Friedel-Crafts synthesis of pyrrolo[1,2-b]isoquinolones 3 with a broader
acylation cascade process from trans-4-hydroxyproline and 2- substrate scope (Scheme 1, Eq. 2). The condensation of trans-
formylbenzoic acids has been developed for the synthesis of 4-substituted proline with 2-formylbenzoic acids followed by
pyrrolo[1,2-b]isoquinolin-10(5H)-ones. Compound 3h was intramolecular Friedel-Crafts acylation delivers the molecular
identified as a new potent dual topoisomerase I/II inhibitor.
architectures in an efficient one pot operation.
Pyrrolo[1,2-b]isoquinolone is important scaffold featured in a
number of natural products, such as the lycorine class of
Amaryllidaceae alkaloids1 and the phenanthroindolizidine
alkaloids (Fig. 1).2 Those alkaloids exhibit appealing antitumor
and antiviral properties. By contrast, limited methods are
available for their preparation.3 A commonly used approach
reported by Lete and coworkers employs the Parham-type
cyclization (Scheme 1, Eq. 1).4 A variety of pyrrolo[1,2-
b]isoquinolones can be synthesized in generally good yields by
this method. However, the halogen-lithium exchange
precludes the synthesis of halogen (e.g., Cl and Br) substituted
products.
Scheme 1. Synthesis of Pyrrolo[1,2-b]isoquinolones.
Recently, Seidel and coworkers reported an approach to
the synthesis of N-alkyl pyrroles from trans-4-hydroxy-L-
proline
(1
)
and aldehydes via the redox-amination-
aromatization process (Scheme 2, Eq. 1).5 Inspired by the
interesting work, we envisioned that pyrrolo[1,2-
b]isoquinolones could be efficiently accessed by the redox-
amination-aromatization-Friedel-Crafts acylation cascade
Fig. 1 Representative bioactive natural products containing the
pyrrolo[1,2-b]isoquinolone scaffolds.
Herein we wish to disclose a new alternative route for the
process from trans-4-hydroxyproline
1
and 2-formylbenzolic
could serve as
acids (Eq. 2). The formed pyrroles
2
4
intermediates for the intramolecular Friedel-Crafts acylation.
To probe the feasibility of the proposed cascade reaction,
†Department of Medicinal Chemistry, School of Pharmacy, Second Military Medical
University, 325 Guohe Road, Shanghai 200433, P. R. China
‡Department of Chemistry and Chemical Biology, University of New Mexico,
Albuquerque, NM87131-0001
we examined a model reaction of trans-4-hydroxyproline
1
with 2-formylbenzoic acid 2a in the presence of toluene with
CF3CO2H as the additive (Table 1, entry 1). The acid is used to
facilitate the Friedel-Crafts acylation. To our delight, the
reaction took place and afforded the desired product 3a under
the microwave (μM) irradiation at 150 °C for 40 min albeit low
§Department of Clinical Nutrition, Changhai Hospital, Second Military Medical
University, 168 Changhai Road, Shanghai 200433, P. R. China
≠School of Pharmacy, East China University of Science and Technology, Shanghai
200237, P. R. China
$S.W., N.L., and G.D. contributed equally to this work.
Electronic Supplementary Information (ESI) available: experimental details and
analytical data. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 4
COMMUNICATION
Journal Name
yield (14%). Encouraged by the results, we screened other 9f
additives and solvents. Only a trace amount of product was 10f
detected when PhCO2H was used as the additive (entry 2) and
CH3CO2H
CH3CO2H
-
-
170
170
40
72
72
View Article Online
D2O0I: 10.1039/C6CC03071H
a Microwave reaction conditions (unless otherwise specified):
no reaction was observed using AlCl3 as the acid facilitator
even under the higher temperature (170 °C) (entry 3).
Replacement of the solvent by DCM (entry 4) or DCE (entry 5)
afforded the desired product in similar yield (21%).
Considering the importance of acid additives in this reaction,
acid as reaction medium was explored accordingly. Indeed,
better results were obtained from CH3CO2H (entry 6, 50% yield)
and CH3CH2CO2H (entry 7, 49% yield) under 170 °C for 40 min.
In the presence of CH3CO2H, lower temperature (150 °C) led to
the decrease of the yield (entry 8). Moreover, increasing the
solvent (2.0 mL), substrate
1 (1.0mmol, 1.0 equiv), substrate
b
2a (1.0 mmol, 1.0 equiv). Yield of isolated product after
c
d
column chromatography. Additive (20 mol %). Additive (100
e
f
mol %). No reaction. substrate
1 (1.2 mmol, 1.2 equiv),
substrate 2a (1.0 mmol, 1.0 equiv).
The substrate scope and the generality of the reaction
were probed next (Scheme 3). It appeared that the 2-
formylbenzoic acids
2 bearing different substituted groups
(Scheme 3, 3b 3g) were tolerated. However, the reaction is
-
highly sensitive to the substitution pattern on the phenyl ring.
Generally, higher yields are observed when substituents are
amount of substrate
1 to 1.2 equivalent gave the best yield
(72%, entry 9). The yield was maintained when reducing the
reaction time to 20 min (entry 10). The optimal reaction
condition was identified using CH3CO2H as the solvent under
the microwave irradiation at 170 °C for 20 min.
attached to 3-position in
Nonetheless, the substituents on position 4 or 5 delivered
lower yields (3b 3d 3e and 3f). We found the low reaction
2, as observed in 3c with 85% yield.
,
,
yields were due to the uncyclized Freidel-Crafts acylation
products in ca. 20-30% yield. It is noted that this method is
complementary to Lete’s,4 which is sensitive to Cl and Br
substituted substrates. Besides the halogen and methoxyl
groups, aryl as substitution groups were investigated. A similar
trend is observed. 3-Substituted reactants gave high yields (3j-
t
), while 4- or 5-aryl substrates
using further optimized reaction conditions (see details in
Table S1 in SI) in which the amount substrate was increased
2 gave poorer yields (3g-i) even
2
from 1.0 to 1.2 equiv. Again the low yields resulted from the
incomplete Friedel-Crafts acylation reaction. The structure was
confirmed by X-ray single crystal structure analysis of
compound 3j (Fig. 2).6
Scheme 2. Synthesis of Pyrrolo[1,2-b]isoquinolones by
Integration of the Redox-amination-aromatization and the
Friedel-Crafts Acylation into One-pot Cascade.
Table 1. Optimization of Reaction Conditions.a
entry solvent
add.
A1c
A2c
A3d
A1c
A1c
-
T (°C)
150
150
170
150
150
170
170
150
t (min)
40
40
40
40
40
40
40
40
yieldb (%)
14
Trace
N.R.e
21
21
50
49
34
1
2
3
4
5
6
7
8
PhMe
PhMe
PhMe
DCM
DCE
CH3CO2H
EtCO2H
CH3CO2H
-
-
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Please do not adjust margins
Page 3 of 4
ChemComm
Journal Name
COMMUNICATION
showed some selectivity toward the HeLa cells and was
View Article Online
identified as a promising antitumor leadDcOoIm: 1p0o.10u3n9d/Cf6oCrCf0u3r0th71eHr
optimization.
Scheme 3. Substrate Scope of the 2-Formylbenzoic acid
Involved in the Synthesis of Pyrrolo[1,2-b]isoquinolin-10(5H)-
a
ones. Unless specified, reaction conditions, see Table 1.
Microwave reaction conditions (unless otherwise specified):
solvent (2.0 mL), substrate
1 (1.0mmol, 1.0 equiv), substrate
b
2a (1.0 mmol, 1.0 equiv). Yield of isolated product after
c
column chromatography. substrate
1 (1.2 mmol, 1.2 equiv)
and substrate (1.0 mmol, 1.0 equiv) used.
2
Fig. 3 Gel electrophoresis of Top1-induced and Top2-induced
DNA cleavage assay for pyrrolo[1,2-b]isoquinolin-10(5H)-ones.
(A) Inhibition of Top1 relaxation activity at 100 μM: lane 1,
supercoiled plasmid DNA; lane 2, DNA + Top1; lane 3, DNA +
Fig. 2 X-ray single crystal structure of compound 3j
.
Top1 + CPT; lanes 4-8, DNA + Top1 + compound (3g, 3h, 3k, 3n
To the best of our knowledge, the biological activity of the
pyrrolo[1,2-b]isoquinolin-10(5H)-one scaffold has not been
investigated. The planar conformation and structural feature
led us to study their biological activity toward topoisomerase
and 3o, respectively). (B) Inhibition of Top1 relaxation activity
at 50 μM: lane 1, supercoiled plasmid DNA; lane 2, DNA + Top1;
lane 3, DNA + Top1 + CPT; lanes 4-7, DNA + Top1 + compound
( , 3h, 3k and 3n, respectively). (C) Inhibition of Top2
3g
relaxation activity at 100 μM: lane 1, supercoiled plasmid DNA;
their Top inhibitory activities by Top1-mediated and Top2- lane 2, DNA + Top2; lane 3, DNA + Top1 + Etoposide; lanes 4-
11, DNA + Top2 + compound 3b 3f 3h 3i and 3q
(Top).7 Accordingly, the new compounds
3 were screened for
mediated DNA cleavage assays.8 As shown in Fig. 3A, 3 out of
20 compounds (3g 3h and 3k) were active against Top1
(
-
,
,
,
respectively). (D) Inhibition of Top2 relaxation activity at 50
μM: lane 1, supercoiled plasmid DNA; lane 2, DNA + Top2; lane
3, DNA + Top2 + Etoposide; lanes 4-11, DNA + Top2 +
,
mediated relaxation of supercoiled DNA at the concentration
of 100 μM. At a lower concentration of 50 μM, two
compounds (3h and 3n) were still active (Fig. 3B). Notably, the
activity of compound 3n was comparable to that of classical
compound (3b-3f, 3h, 3i and 3q, respectively).
Table 3. In Vitro Antitumor Activities of the Pyrrolo[1,2-
b]isoquinolin-10(5H)-ones (IC50, μM)
Top1 inhibitor camptothecin. Moreover,
8 out of 20
compounds were active against Top2 mediated relaxation of
supercoiled DNA at the concentration of 100 μM and 50 μM,
respectively (Fig. 3C and 3D) and several of them (e.g., 3f, 3h)
Compound
3h
Camptothecin 0.83 0.084
Etoposide 4.12 1.91
HeLa HCT116
4.86 14.02
HepG2 A549
HUVEC
10.01
0.031
0.78
14.37
2.31
7.58
0.12
68.01
were comparable to classical Top2 inhibitor etoposide. The
above results highlighted compound 3h as a novel Top1/Top2
dual inhibitor. Dual Top1/Top2 inhibitors are highly sought in
new antitumor drug development because they can
simultaneously target two enzymes at different points of cell
cycle and thus have a broader cell cycle activity and antitumor
efficacy.9 Encouraged by the results, in vitro antitumor activity
of compound 3h against four types of human cancer cell lines
(HeLa cervical cancer cell, HCT116 colon cancer cell, HepG2
hepatoma cell and A549 non-small cell lung cancer cell) and
the human normal cells (HUVEC human umbilical vein
endothelial cell) were tested using the standard CCK8 method.
Compound 3h showed potent activity with an IC50 value in the
range of 4.86 μM to 14.37 μM (Table 3). Moreover, it was less
toxic than campthothecin and etoposide. Compound 3h
13.71
In summary, we have developed a new redox-amination-
aromatization-Friedel-Crafts acylation acylation cascade
process for the preparation of pyrrolo[1,2-b]isoquinolin-
10(5H)-ones. The process displays a relatively broad substrate
scope. Their preliminary biological activity as Top inhibitors
was explored for the first time. Compound 3h was a potent
dual inhibitor of Top1 and Top2 with good antitumor activity,
which represents a promising lead compound as anticancer
agent for drug discovery. Further exploration of the biological
properties of these compounds and the new reagents in
synthesis are under investigation in our laboratories.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 4
COMMUNICATION
Journal Name
This work was supported by the 863 Hi-Tech Program of
China (2014AA020525 to C.S.), the National Basic Research
Program of China (2014CB541800 to C.S.) and the National
Natural Science Foundation of China (81573283 to C.S., and
21372073 to W.W.).
View Article Online
DOI: 10.1039/C6CC03071H
Notes and references
1
2
3
O. Hoshino, Chapter 4 The Amaryllidaceae Alkaloids.
Alkaloids Chemistry & Biology, 1998, 51, 323.
(a) Z. Li, Z. Jin and R. Huang, Synthesis, 2001, 2001, 2365; (b)
J. P. Michael, Nat. Prod. Rep., 2003, 20, 458.
(a) M. Iwao, K. Mahalanabis, M. Watanabe, S. De Silva and V.
Snieckus, Tetrahedron, 1983, 39, 1955; (b) A. J. Clark, R. P.
Filik, J. L. Peacock and G. H. Thomas, Synlett, 1999, 441; (c) I.
S. Cho, C. L. Tu and P. S. Mariano, J. Am. Chem. Soc., 1990,
112, 3594; (d) P. C. Belanger, J. G. Atkinson, C. S. Rooney, S.
F. Britcher and D. C. Remy, J. Org. Chem., 1983, 48, 3234.
(a) A. Ardeo, E. Lete and N. Sotomayor, Tetrahedron Lett.,
2000, 41, 5211; (b) J. Ruiz, N. Sotomayor and E. Lete, Org.
4
Lett., 2003,
5
, 1115; (c) J. Ruiz, A. Ardeo, R. Ignacio, N.
Sotomayor and E. Lete, Tetrahedron, 2005, 61, 3311; (d) S.
Lage, U. Martínez
Synth. Catal., 2009, 351, 2460.
‐
Estíbalez, N. Sotomayor and E. Lete, Adv.
5
6
(a) I. Deb, D. J. Coiro and D. Seidel, Chem. Commun., 2011,
47, 6473; (b) A. V. Kumar and K. R. Rao, Tetrahedron Lett.,
2011, 52, 3237; (c) Z. Zou, Z. Deng, X. Yu, M. Zhang, S. Zhao,
T. Luo, X. Yin, H. Xu and W. Wang, Sci. China-Chem., 2012,
55, 43.
The structure was determined by X-ray crystal structure
analysis of compound 3j
. CCDC-1465987 contains the
supplementary crystallographic data for this paper. These
data can be obtained free of charge via www.ccdc.cam.ac.uk
and see Supporting Information.
7
8
(a) Y. Pommier, Chem. Rev., 2009, 109, 2894; (b) Y. Pommier,
ACS Chem. Biol., 2013, 8, 82.
(a) S. Wang, K. Fang, G. Dong, S. Chen, N. Liu, Z. Miao, J. Yao,
J. Li, W. Zhang and C. Sheng, J. Med. Chem., 2015, 58, 6678;
(b) G. Dong, S. Wang, Z. Miao, J. Yao, Y. Zhang, Z. Guo, W.
Zhang and C. Sheng, J. Med. Chem., 2012, 55, 7593.
S. Dallavalle, S. Gattinoni, S. Mazzini, L. Scaglioni, L. Merlini,
S. Tinelli, G. L. Beretta and F. Zunino, Bioorg. Med. Chem.
Lett., 2008, 18, 1484.
9
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins