Vilsmeier reagent, NaHSe and diclofenac acid chloride: One-pot synthesis of a novel selenoindolinone with potent anticancer activity

Article abstract of DOI:10.1039/d0ra07332f

An effective and straightforward synthesis of 3-seleno functionalized indolinone (5) involving Vilsmeier reagent is presented. Likewise, a procedure to achieve lactamization of diclofenac with excellent yields by using hydrides is also ascertained. Compou

Full text of DOI:10.1039/d0ra07332f

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Vilsmeier reagent, NaHSe and diclofenac acid
chloride: one-pot synthesis of a novel
Cite this: RSC Adv., 2020, 10, 38404
selenoindolinone with potent anticancer activity†
ab
Ana Carolina Ruberte, ab Carlos Aydillo,ab Arun K. Sharma,c Carmen Sanmartın
and Daniel Plano
*
´
ab
Received 26th August 2020
Accepted 12th October 2020
An effective and straightforward synthesis of 3-seleno functionalized indolinone (5) involving Vilsmeier
reagent is presented. Likewise, a procedure to achieve lactamization of diclofenac with excellent yields
by using hydrides is also ascertained. Compound 5 exhibited impressive growth inhibition in most of the
cell lines in an NCI-60 panel, particularly towards resistant breast cancer cells.
DOI: 10.1039/d0ra07332f
rsc.li/rsc-advances
Organoselenium compounds have been broadly studied owing cyclization of the acid chloride 2 through the nucleophilic
to their well-regarded biological activities.1–4 Among the attack of the nitrogen over the acyl chloride (Scheme 1, step 2).
multiple and complex health benets ascribed to organo- Finally, a two-steps reaction to yield the desired compound 4 via
selenium compounds, their role as chemotherapy agents is formation of the selenoamide and the subsequent methylation
greatly-recognized.3 However, their activity is highly dependent of the Se atom (Scheme 1, step 3). Different conditions and
on multiple factors, among which metabolic routes stand out. reagents have been reported for each of these steps, all of them
In this context, methylselenol is one of the main metabolites, being optimized. Next, we will discuss some previously reported
and has received great attention as a key executor of organo- methods along with our conditions and results for each step.
selenium compounds' anticancer activity.5
The chlorination of diclofenac (1) (Scheme 1, step 1) was
A vast number of molecules containing heterocyclic rings attempted under three conditions, as previously reported in the
possess a great variety of biological applications, including literature:10–12 (i) reux conditions with an excess of thionyl
antitumor activity. Accordingly, indole derivatives show potent chloride (SOCl2) for 2 h,10 resulting in the degradation of
1
antitumoral activity against several cancers, such as lung, diclofenac (1), observed by H-NMR spectra; (ii) reaction with
pancreatic and breast, in preclinical models.6–9 Thus, indole can oxalyl chloride [Cl(CO)2Cl] in methylene chloride (DCM) at
be considered as a privileged scaffold for designing novel room temperature,11 that did not yield the acid chloride 2 even
anticancer agents. We hypothesized that the functionalization at long periods of time (up to 72 h); and (iii) the use of few drops
of indole with a methylseleno group would yield a promising of N,N-dimethylformamide (DMF) as catalyst for the reaction for
antitumor agent. Therefore, the objective of this work was the oxalyl chloride, which turned out to be the optimal conditions
synthesis and cytotoxicity evaluation of 1-(2,6-dichlorophenyl)- with quantitative yields (99%).12
2-(methylselanyl)-1H-indole (compound 4 in Scheme 1). The
synthetic procedure designed to obtain the desired derivative is (2,6-dichlorophenyl)indolin-2-one (3) (Scheme 1, step 2), several
illustrated in Scheme 1. procedures have been published on the literature: radical
Regarding to molecular cyclization to render the lactam 1-
The designed synthesis was originally planned in three steps. photoredox cyclization,13,14 acid catalyzed cyclization15,16 and
Firstly, the chlorination of diclofenac (1) to achieve the acid Mn(III)-based oxidative cyclization methods,17 as well as 1-ethyl-
chloride 2 (Scheme 1, step 1). Secondly, the intramolecular 3-(3-dimethylaminopropyl)carbodiimide (EDC)-based carboxyl
activation cyclization,18 among others. Nevertheless, these
methods present limitations, including multiple steps, complex
aUniversidad de Navarra, Facultad de Farmacia y Nutricion, Departamento de
´
catalysis and use of expensive reagents. Thus, the
´
´
´
Tecnologıa y Quımica Farmaceuticas, Irunla-rrea 1, E-31008 Pamplona, Spain.
E-mail: sanmartin@unav.es; Tel: +34-948425600 ext. 806388
b
´
Instituto de Investigacion Sanitaria de Navarra (IdiSNA), Irunlarrea, 3, 31008
Pamplona, Spain
cPenn State College of Medicine, Penn State Cancer Institute, CH72, Department of
Pharmacology, 500 University Drive, Hershey, Pennsylvania 17033, USA
† Electronic supplementary information (ESI) available: Experimental details,
compound characterization, NMR spectra. CCDC 1983076. For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/d0ra07332f
Scheme 1 Synthetic route designed for 1-(2,6-dichlorophenyl)-2-
(methylselanyl)-1H-indole (4).
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Table 1 The hydride used for cyclization reaction to obtain lactam 3a
procedure. Hence, we developed novel and efficient method of
intramolecular cyclization with hydrides to obtain lactam 3.
This method was achieved by reaction of acid chloride 2 with
one equivalent of hydride in water and tetrahydrofuran (THF) at
room temperature for 2 h. Besides, we optimized the method
using ve different hydrides, such as LiAlH4, lithium trie-
thylborohydride (LiEt3BH), LiAlH(OtBu)3, NaBH3CN and NaBH4
(Table 1). Luckily, we obtained excellent yields with all hydrides,
but the better yield was with LiAlH(OtBu)3 (Table 1, entry 3).
Finally, we focused on formation of the selenoamide and the
subsequent methylation of the Se atom to yield the desired
compound, 1-(2,6-dichlorophenyl)-2-(methylselanyl)-1H-indole
(4) (Scheme 1, step 3). Concerning the selenoamide formation,
we considered several reported methods gathered in the liter-
ature about the use of hydrogen selenide (H2Se) and hydrogen
sulde (H2S) in the conversion of amides in thioamides;22
thioureas in selenoureas20 and imines in selenones,20 among
others. Thus, amide with H2Se should form the selenoamide.
However, the toxicity of H2Se prompted us to nd safe and
effective alternative in alkali metal salt of hydroselenide
(MHSe), which may be readily prepared in situ by the reaction of
Se and hydride.11,23–25 Another advantage is that hydride was
already used in the intramolecular cyclization (Table 1). Hence,
the reaction conditions to form the lactam 3 (Scheme 1, step 2)
are similar to last step (Scheme 1, step 3), prompting us to
perform step 2 and step 3 in one-pot synthesis.
Entry
Hydride
Yieldb (%)
1
2
3
4
5
AlLiH4
46
53
82
80
78
LiEt3BH
LiAlH(OtBu)3
NaBH3CN
NaBH4
a
All reactions were carried out with compound 2 (6.4 mmol) and the
corresponding hydride (6.4 mmol) in a mixture of water (18 mL) and
b
THF (2 mL) as solvent at RT for 2 h. Estimated yields of 3
determined by 1H-NMR.
Thus, the formation of desired compound 4 from acid
chloride 2 was attempted with oxalyl chloride (0.5 equivalent)
and N,N-dimethylformamide (0.5 equivalent), Se (1.0 equiva-
lent), LiAlH(OtBu)3 (2 equivalent to form lactam 3 and subse-
quently selenamide) and iodomethane (MeI) (3 equivalent) in
water and tetrahydrofuran, under two conditions: (i) room
temperature, up to 8 days; (ii) reux, up to 2 days. Unfortu-
nately, these conditions did not yield desired compound 4. In
fact, this step did not evolve toward any selenocompound and
most of the material recovered was the starting material. This
result can be attributed to the lack of formation of lithium
hydroselenide (Table S4 and Fig. S12, ESI†) necessary to form
selenoamide and subsequently desired compound. Therefore,
we studied the formation of MHSe with the rest of hydrides
used previously (Table S4 and Fig. S10–S14, ESI†). Remarkably,
NaBH4 was the only one that formed MHSe (Table S4 and
Fig. S14, ESI†).
Scheme 2 One-pot synthesis of unexpected derivative 5.
We decided to repeat the previous methods with NaBH4
instead of LiAlH(OtBu)3 (Scheme 2). Surprisingly, desired
compound 4 was not detected at all, unlike lactam 3 with 49% of
yield. Remarkably, we have discovered that the reaction gives
rise to an unexpected 3-alkylidene-2-oxindole with Se ((E)-1-(2,6-
dichlorophenyl)-3-((methylselanyl)methylene)indolin-2-one, 5)
with 10% of yield (Scheme 2). This unexpected derivative was
puried by column chromatography, characterized by NMR and
its structure (Fig. 1) unambiguously determined by X-ray
diffraction (CCDC 1983076, Tables S8–S15, ESI†).
Fig. 1 ORTEP diagram of compound 5 with displacement ellipsoids
drawn at 50% probability level. Crystal Data for C16H11Cl2NOSe (M ¼
383.12 g molꢀ1): monoclinic, space group P21/c (no. 14), a ¼ 8.3923(9)
ꢁ
ꢀ
ꢀ
ꢀ
A, b ¼ 12.7253(14) A, c ¼ 14.6560(15) A, b ¼ 90.072(2) , V ¼ 1565.2(3)
ꢀ3
A , Z ¼ 4, T ¼ 298 K, m(MoKa) ¼ 2.737 mmꢀ1, Dcalc ¼ 1.626 g cmꢀ3
,
13 375 reflections measured (4.24ꢁ # 2Q # 56.66ꢁ), 3859 unique (Rint
¼ 0.0227, Rsigma ¼ 0.0301) which were used in all calculations. The
final R1 was 0.0365 (>2sigma(I)) and wR2 was 0.1049 (all data).
intramolecular reductive cyclization based on hydrides (e.g.
lithium aluminum hydride (LiAlH4); lithium tri-t-butoxy
aluminum hydride (LiAlH(OtBu)3);19 sodium cyanoborohydride
(NaBH3CN)20 and sodium borohydride (NaBH4)21) caught our
attention because of their straightforward and low cost
Since isolated diclofenac lactam 3 did not yield selenated
product 5 under these conditions, the proposed mechanism
(Scheme 3) would need to start from diclofenac carbonyl chlo-
ride 2, and involve the formation of selenocarboxylate A by the
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secondary amine to the activated selenomethyl ester, generating
intermediate D. Leaving methyl selenide can attack nucleo-
philically at aldehyde carbon, generating E, which could easily
undergo water elimination, taking into account the additional
stabilization gained by conjugation with aromatic system and
the lactam in the nal product 5. Low yields of product 5 are
justied as lactamization is a favored process, even more with
activated species, like acid chlorides and selenoesters, which
have been known for acyl activation in peptide synthesis28 and
protein chemical ligation.29
Once that Vilsmeier reagent is suggested to be a key part of
product 5 generation, we attempted to optimize the method
using more equivalents of DMF than in previously used method
(Table 2). Nevertheless, the yield of unexpected derivative 5 and
lactam 3 decreased probably due to the increased solubility of
the organic compounds in the reaction medium and the
subsequent additional issues to isolate the desired compounds.
Finally, this unexpected new organoselenium derivative 5
with the code NSC: 811012 was submitted to the National
Cancer Institute's (NCI) Developmental Therapeutics Program
(DTP), to be tested at a single dose of 10 mM in a panel of NCI-60
human tumor cell lines. These cell lines include nine cancer
types (leukemia, melanoma, non-small cell lung, colon, CNS,
ovarian, renal, prostate and breast cancers).30 The results
(Fig. S1, ESI†) were expressed in growth percent (GP), that is the
growth of treated cells compared to the growth of an untreated
cells. GP (%) values between 0 and 50 means antiproliferative
properties and between ꢀ100 and 0 stand for cytotoxic prop-
erties. Compound 5 demonstrated antitumor activity in most
NCI-60 cell lines, with a GP mean value towards all cell lines of
17.48% (Fig. S1, ESI†). In addition, compound 5 showed potent
cytotoxic activity with GP lower than ꢀ30.80% in 6 out of the 60
tumor cell lines tested, including renal (UO-31 and SN12C),
breast (BT-549), CNS (SNB-75), melanoma (MDA-MB-435) and
leukemia (HL-60 (TB)) cancers (Fig. 2). In this context,
compound 5 exhibited the most cytotoxic activity (GP equal to
ꢀ96.55%) towards UO-31, a renal cancer cell line. Additionally,
this new derivative showed great cytotoxic activity (GP equal to
Scheme
unexpected derivative 5.
3 Proposed reaction mechanism one-pot synthesis of
attack of in situ generated hydroselenide (HSeꢀ), and posterior
esterication with MeI to form B. Vilsmeier reagent generated
by DMF and oxalyl chloride present in the reaction mixture is
attacked by selenomethyl ester enolate, probably mediated by
the presence of NaBH4, generating aer hydrolysis the for-
mylated intermediate C. Examples of related formylation of
esters with alkyl formats in presence of base (hydrides26 and
alkoxides27) have been previously reported. The next step would
involve the intramolecular amide formation by the attack of
Table 2 Optimization of reaction conditions of unexpected derivative 5a
Cl(CO)2Cl
(equiv.)
Entry
DMF (equiv.)
Yield (%) comp. 3b
Yield (%) comp. 5b
1
2
3
4
0
0.5
1
0
78
58
49
47
NRc
14
2
0.5
0.5
0.5
1.5
1<
a
All reactions were carried out with compound 2 (6.4 mmol), oxalyl chloride (3.2 mmol) and DMF (0, 3.2, 6.4 or 9.6 mmol), elemental selenium (6.4
mmol) and NaBH4 (12.8 mmol) in a mixture of water and THF (9 : 1) at RT. Aer 30 min, MeI (19.2 mmol) was added to the reaction and stirred at RT
for 24 h. Estimated yields of 3 and 5 determined by 1H-NMR. c No reaction.
b
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melanoma, CNS and leukaemia cancer cell lines.
ꢀ35.63%) in the most resistant breast cancer cell of NCI panel
towards more than 20 000 compounds tested (BT-549).30
In conclusion, we developed a novel and efficient method of
intramolecular cyclization with hydrides to obtain lactam 3.
Besides, we report an unexpected and unprecedented Vilsmeier
reagent application to afford a selenated lactam 5 with potent
cytotoxic activity in resistant breast cancer cells. Hence, this
new synthesis may be an attractive approach for the discovery of
new potent antitumoral agents, particularly for therapy of
resistant breast cancers.
Conflicts of interest
There are no conicts to declare.
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The authors thank Dr Hemant Yennawar at the X-ray diffraction
facility at Penn State University for the determination of the
crystal structure. C. S. and D. P. wish to express their gratitude
to PIUNA (refs 2014–26 and 2018–19) and UNED–Pamplona,
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Fundacion Bancaria “La Caixa”, and “Fundacion Caja Navarra”
for nancial support for the project. A. C. R. acknowledges the
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support of the Asociacion de Amigos de la Universidad de
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24 C. Sanmartın, D. Plano, E. Domınguez, M. Font, A. Calvo,
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