Palladium(II) Pincer Complexes of Functionalized Amides with S-Modified Cysteine and Homocysteine Residues: Cytotoxic Activity and Different Aspects of Their Biological Effect on Living Cells

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Palladium(II) Pincer Complexes of Functionalized Amides with

S‑Modiﬁed Cysteine and Homocysteine Residues: Cytotoxic Activity

and Di ﬀ erent Aspects of Their Biological E ﬀ ect on Living Cells

Svetlana G. Churusova, Diana V. Aleksanyan,* Ekaterina Yu. Rybalkina, Olga Yu. Susova,

Alexander S. Peregudov, Valentina V. Brunova, Evgenii I. Gutsul, Zinaida S. Klemenkova,

Yulia V. Nelyubina, Valentina N. Glushko, and Vladimir A. Kozlov

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sı Supporting Information

ABSTRACT: In the search for potential new metal-based antitumor

agents, two series of nonclassical palladium(II) pincer complexes

based on functionalized amides with S-modiﬁed cysteine and

homocysteine residues have been prepared and fully characterized

1

13

1

13

by 1D and 2D NMR ( H, C, COSY, HMQC or HSQC, H− C,

1

15

and H− N HMBC) and IR spectroscopy and, in some cases, X-ray

diﬀraction. Most of the resulting complexes exhibit a high level of

cytotoxic activity against several human cancer cell lines, including

colon (HCT116), breast (MCF7), and prostate (PC3) cancers.

Some of the compounds under consideration are also eﬃcient in

both native and doxorubicin-resistant transformed breast cells HBL100, suggesting the prospects for the creation of therapeutic

agents based on the related compounds that would be able to overcome drug resistance. An analysis of diﬀerent aspects of their

biological eﬀects on living cells has revealed a remarkable ability of the S-modiﬁed derivatives to induce cell apoptosis and eﬃcient

cellular uptake of their ﬂuorescein-conjugated counterpart, conﬁrming the high anticancer potential of Pd(II) pincer complexes

derived from functionalized amides with S-donor amino acid pendant arms.

5

INTRODUCTION

media due to much more rapid ligand-exchange processes. A

pincer-type ligation can provide ﬁrm coordination of Pd(II)

ions and thus ensure a high thermodynamic stability of the

resulting complexes. At the same time, the tunable nature of a

tridentate motif oﬀers ample opportunities to achieve the

desired level of kinetic stability.

■

Over a history of about a half-century, pincer complexes have

emerged as some of the most prominent organometallic and

metal−organic compounds, largely contributing to the

1

development of many sustainable chemical processes.

Although catalysis still remains the area of major achievements

for this privileged class of metal complexes featuring highly

tunable tridentate ligands with a meridional geometry that

oﬀer an unprecedented level of control over the complex

Recently, our research group has shown the utility of

nonclassical pincer ligands based on functionalized carbox-

amides for the synthesis of highly cytotoxic Pd(II) complexes.

6

2

It should be noted that pincer ligands with central secondary

amide units are of particular interest owing to their readily

modiﬁable molecular architecture and a possibility of rapid

expansion of libraries of new compounds by simple modular

assembly of building blocksfunctionalized carboxylic acids

properties, they have continuously attracted attention in many

3

other ﬁelds, including medicinal chemistry. A promising line

of research is the creation of new antitumor agents based on

pincer-type complexes, which has already aﬀorded a range of

highly potent gold, ruthenium, copper, palladium, and

platinum derivatives (Figure 1). Some of these complexes

have proven their eﬃciency in in vivo experiments.

Predictably, considerable attention has been paid to Pt(II)

compounds since the development of platinum-based chemo-

therapeutics became a milestone in cancer research. However,

the pincer concept seems to be more beneﬁcial for

palladiumthe closest platinum congener. The point is that

palladium(II) complexes exhibit coordination behavior similar

to that of their platinum(II) counterparts but are highly

susceptible to diﬀerent deactivation processes in biological

7

4

and amines. A rationale behind our project was to provide an

4e,k,n,o

N,S-hemilabile coordination of palladium(II) ions by ancillary

donor groups, incorporating picolinic or 4-chloropicolinic acid

Received: April 13, 2021

Published: June 15, 2021

©

2021 American Chemical Society

https://doi.org/10.1021/acs.inorgchem.1c01138

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Article

Figure 1. Selected examples of potential antitumor agents based on transition-metal pincer complexes (PTA denotes a quaternized

phosphaadamantane derivative).

as an acid component and an S-donor amino acid (S-methyl-L-

cysteine or L-methionine) derivative as an amino component

activity to their S,N,N-counterparts I derived from picoliny-

lamides. Finally, palladium(II) pincer complexes that featured

6

(

compounds I, Figure 2).

The importance of amino acids in tumor metabolism has

a complementary S,N,N-coordination but were deprived of

amino acid residues (compounds VI and VII) also displayed

11

generated great interest in the development of strategies

targeting or involving them in other functions for cancer

therapy. S-donor amino acids play an important role in the

biological activity of the platinum-based antitumor agents and

their palladium analogues. Moreover, the introduction of a

sulfur ancillary donor group into the ligand framework can

facilitate improvement of the bioavailability of potential Pd(II)

chemotherapeutics, which often suﬀers from the strong

binding with sulfur-containing biomolecules such as gluta-

thione. As a conﬁrmation of our rationale, the analogues of

complexes I bearing histidine pendant arms with N-donor

ancillary groups (compounds II, Figure 2) were shown to

exhibit very low antiproliferative activity against several human

lower cytotoxic eﬀects in comparison to I. To further explore

the anticancer potential of these types of Pd(II) pincer

complexes, it seemed reasonable to extend the structural motif

of functionalized amide ligands to S-modiﬁed derivatives

bearing various substituents at the sulfur donor center of the

amino acid residue (S-modiﬁcation of the ligand framework).

Herein, we report on the synthesis of new representatives of

cytotoxic Pd(II) pincer complexes based on picolinylamides

with amino acid pendant arms, where the latter are comprised

by S-substituted cysteine derivatives or their homologues

bearing an additional methylene unitS-modiﬁed homocys-

teine residues. Although homocysteine is a nonproteinogenic

amino acid, it plays a crucial role in methionine metabolism

and serves as a source of cysteine in the body. The discussion

of cytotoxic properties of the resulting complexes against

several human cancer cell lines is supplemented by a deeper

analysis of the action mode of these promising types of

potential antitumor agents.

8

9

4

l

6

cancer cell lines or even facilitated the growth of cancer cells.

Another avenue used to modify the ligand framework was the

variation of an acid component (N-modiﬁcation). The

resulting pincer complexes with S,N,S- and S,N,P-donor sets

10

(

compounds III−V) appeared to be inferior in cytotoxic

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Figure 2. Nonclassical palladium(II) pincer complexes with functionalized carboxamide ligands: strategies for tuning cytotoxic properties.

Scheme 1. Synthesis of Cysteine-Based Ligands 2 and 3

Scheme 2. Synthesis of Homocysteine-Based Ligands 6 and 7

RESULTS AND DISCUSSION

methyl substituents (Scheme 1). A short panel of the alkylating

agents was chosen to endow the ancillary sulfur donor with

diﬀerent steric and electronic proﬁles. Obviously, this strategy

is not restricted to these particular examples and can open the

way to a great variety of S-modiﬁed cysteine derivatives,

providing the proper choice of reaction conditions. The

condensation of free amines generated in situ from hydro-

chlorides 1a−c with picolinyl and 4-chloropicolinyl chlorides

yielded functionalized amide ligands 2a−c and 3a−c,

respectively (Scheme 1). It is noteworthy that in this study,

owing to the application of selective synthetic approaches, the

■

Despite the ostensible similarity of the target compounds to

the key prototypes, the synthesis of S-modiﬁed ligands

required the development of new versatile approaches,

especially in the case of functionalized carboxamides with

elongated S-donor pendant arms.

For the synthesis of the target cysteine-based ligands, L-

cysteine methyl ester hydrochloride was sequentially treated

with di-tert-butyl dicarbonate and diﬀerent alkyl halides

followed by deprotection, which aﬀorded S-modiﬁed cysteine

derivatives 1a−c bearing benzyl, allyl, and methoxycarbonyl-

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aforementioned acylating agents were used in the individual

forms (see the Experimental Section).

Scheme 3. Cyclopalladation of the Picolinylamides with

Cysteine and Homocysteine Pendant Arms

A convenient key precursor for the synthesis of ligands

having elongated coordination arms with diﬀerent substituents

at the sulfur donor atom appeared to be D,L-homocysteine

thiolactone. Its reactions with picolinyl and 4-chloropicolinyl

chlorides smoothly aﬀorded amides 4 and 5 (Scheme 2).

Homocysteine derivatives 4 and 5 readily underwent the

opening of a thiolactone ring under the action of MeONa. The

in situ generated sodium salts of methyl homocysteinates were

alkylated with diﬀerent alkyl halides to aﬀord S-modiﬁed

homocysteine ligands 6a−c and 7a−c in generally good to

high yields (Scheme 2). As in the case of the cysteine-based

derivatives, the alkylating agents used were benzyl, allyl, and

methoxycarbonylmethyl chlorides. Although the target S-

modiﬁed homocysteine derivatives were obtained in the

racemic forms, it is remarkable that the suggested approach

can furnish a whole range of new pincer ligands from a single

key precursor.

frequency shift of the amide group CO stretches (Δν = 37−

−

1

48 and 52−62 cm for the cysteine- and homocysteine-based

1

The identities of all the new compounds were supported by

a combination of spectroscopic techniques and elemental

analyses. The IR spectra of ligands 2, 3, 6, and 7 show the

characteristic absorption bands of the secondary amide units,

associated mainly with CO and N−H stretching in the

derivatives, respectively). Furthermore, the H NMR spectra

1

3

also lacked the doublet signals of NH protons, whereas the C

NMR spectra revealed a signiﬁcant downﬁeld shift of the

C(O)N carbon resonances, reaching up to 9.5 ppm. A

noticeable shift of the amide nitrogen resonance from

−275.0 ppm for ligand 6a to −250.5 ppm for the

corresponding complex (compound 10a) was also consistent

with the N-metalation of the central amide unit. In turn, a

strong upﬁeld shift of the signal of the pyridine nitrogen

−

1

ranges of 1676−1683 and 3373−3383 cm , respectively, and

−

1

in-plane N−H bending (amide II band) at ca. 1517 cm . The

CO stretches of the ester groups are observed at 1739−1746

−

1

cm . The H NMR spectra of the functionalized amide

ligands contain, among other signals, the expected downﬁeld

nucleus (Δδ = −78.7 ppm) clearly indicated the heterocycle

N

doublet resonances of NH protons (δ 8.46−8.74 ppm) with

complexation. In the other cases, the coordination of the

pyridine moiety was deduced from a downﬁeld shift of the

proton resonances of the adjacent CH units (up to 0.53 ppm).

The coordination of S-donor pendant arms was evidenced by

the marked downﬁeld shifts of both carbon and hydrogen

H

coupling constants of about 8.4 Hz, which arise from the

interaction with methine protons. The latter appear as

multiplets in the narrow range of 4.86−5.08 ppm. Note that

in some cases the proton signals of prochiral methylene units

give rise to separate signals. The hydrogen and carbon

resonances of homocysteine derivatives 6a and 7b,c were

unambiguously assigned on the basis of the 2D NMR

experiments (COSY, HMBC, and HMQC or HSQC pulse

sequences) (see, for example, Figures S1 −S15 in the

Supporting Information). In addition, the chemical shifts of

the nitrogen nuclei in representative ligands 6a and 7b were

resonances of the exo methylene units (CH units of benzyl,

2

allyl, and methoxycarbonyl substituents). For example, in the

case of complex 10a, the corresponding values of Δδ reached

7.75 and 0.81 ppm, respectively. Furthermore, the conﬁgura-

tionally stabilized coordinated sulfur atom serves as the second

stereocenter in the complex molecules, giving rise to

1

spectroscopically distinguishable isomers. Thus, the H and

1

15

13

de ﬁ ned from the H− N HMBC correlation spectra (Figure

S16 in the Supporting Information). The amide nitrogen

resonances were readily identiﬁed due to the one-bond direct

NH responses at about −275.0 ppm, whereas the pyrdine

nitrogen nuclei appeared to be coupled with the nearest CH

protons and gave rise to signals at −80.0 (6a) and −85.4 (7b)

ppm.

C NMR spectra of cysteine-based derivatives 8a−c and 9a−c

displayed a double set of signals, which correspond to two

diastereomers resulting from a combination of the coordinated

sulfur atom with a chiral carbon center of the L-amino acid

residue. Depending on the nature of a substituent in the sulﬁde

group, the ratio of diastereomers varied from ∼3/2 to 5/2. The

signals of both major and minor isomers were readily assigned

on the basis of the 2D NMR spectra (see the Experimental

Section). In the case of the homocysteine-based derivatives,

the complexation by the sulfur donor gave rise to four

stereoisomers, since the amino acid precursor (homocysteine

thiolactone) was used in a racemic form. Therefore, two sets of

The direct cyclopalladation of both cysteine- and homo-

cysteine-based ligands was smoothly accomplished under mild

reaction conditions and aﬀorded desired pincer complexes 8−

1

1 in generally good to high yields (Scheme 3).

PdCl (NCPh) was used as a convenient metalating agent.

2

1

13

The reactions were performed in the presence of Et N to trap

signals in the H and C NMR spectra of complexes 10a−c

and 11a−c refer to two pairs of enantiomers. It should also be

noted that the presence of six-membered chelate rings formed

by the elongated S-coordination arms make these compounds

more conformationally labile than their 5,5-membered cysteine

counterparts. This resulted in broadened and unresolved

3

HCl liberated upon metalation and thus avoid potential

deactivation of the pyridine pendant moiety.

Complexes 8−11 are moisture- and air-resistant crystalline

solids, thermally stable at least to 120 °C. Their structures were

unambiguously conﬁrmed by the IR and NMR spectroscopic

data. Thus, the deprotonation and coordination of the

secondary amide unit were supported by the absence of NH

stretching and bending vibrations in the IR spectra of all the

complexes obtained along with a concomitant strong low-

1

signals; in particular, the room-temperature H NMR spectra

provided only limited information on the complex structures.

However, cooling to −40 to −10 °C aﬀorded resolution of

almost all the signals, especially in the congested aliphatic

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Figure 3. Molecular structures of complexes 9a (a) and 10b (b) in representations of atoms via thermal ellipsoids at the 50% probability level.

Table 1. Cytotoxic Eﬀects of the Pd(II) Pincer Complexes under Investigation on Some Human Cell Lines

a

IC₅₀± SD, μM

entry

compound

HCT116

MCF7

PC3

HEK293

NKE

1

2

3

4

5

6

7

8

9

8a

8b

8c

9a

9b

9c

10a

10b

10c

11a

11b

11c

cisplatin

2.5 ± 0.5

6.4 ± 1.4

20.0 ± 2.5

2.2 ± 0.2

5.0 ± 1.0

6.5 ± 1.0

10.5 ± 4.5

12.0 ± 4.0

14.0 ± 4.0

3.5 ± 0.5

8.0 ± 3.0

2.6 ± 0.4

18.0 ± 2.0

12.5 ± 1.5

17.5 ± 2.5

70.0 ± 12.0

6.4 ± 0.4

16.0 ± 4.0

25.0 ± 5.0

15.0 ± 5.0

37.0 ± 3.0

26.0 ± 11.0

12.0 ± 2.5

22.0 ± 4.0

16.2 ± 2.0

25.0 ± 4.0

2.6 ± 0.4

9.0 ± 2.5

28.0 ± 3.6

23.6 ± 1.2

11.0 ± 4.0

7.5 ± 2.5

18.0 ± 3.5

24.0 ± 4.0

12.5 ± 2.5

6.6 ± 0.2

9.0 ± 2.0

3.0 ± 0.5

16.0 ± 3.0

8.2 ± 1.0

9.0 ± 1.0

27.0 ± 3.0

6.6 ± 0.4

7.5 ± 1.5

12.0 ± 6.0

18.0 ± 7.0

15.0 ± 5.0

19.5 ± 4.5

10.0 ± 1.5

19.0 ± 8.0

7.4 ± 0.8

12.5 ± 1.5

14.4 ± 2.4

19.2 ± 2.6

n/d

15.5 ± 1.5

n/d

16.0 ± 2.0

n/d

12.5 ± 1.5

15.2 ± 3.2

n/d

10

11

12

13

n/d

a

SD is the standard deviation of the value. n/d denotes not deﬁned.

region (see, for example, the variable-temperature NMR

spectra of complex 10a in Figure S17 in the Supporting

Information). Again, a complete and unambiguous assignment

of the hydrogen and carbon resonances of homocysteine-based

derivatives 10 and 11 was made using diﬀerent 2D NMR

techniques. Figures S18 −S34 in the Supporting Information

show the NMR spectra for complex 10a used as a

representative example.

The structures of complexes 9a and 10b were further

corroborated by single-crystal X-ray diﬀraction (Figure 3). In

both compounds, the coordination environment of the

palladium atom was found to be slightly distorted square

planar. The distortions are obviously caused by the

heterodentate nature of the ligand: whereas the Pd−N bond

lengths vary within a narrow range of 1.969(3)−2.049(3) Å for

both the coordinated amide and pyridine units, the Pd−S

bonds are longer and reach up to 2.2646(7) Å (in 10b). In

general, the observed bond lengths are within the expected

norms for these types of complexes. Nevertheless, such a

dissymmetry leads to a slight bend along the S1···N2 line in

inevitably aﬀects their conformations. Thus, the ﬁve-membered

metal-containing ring involving both of the nitrogen

coordination sites is ﬂat (in complex 9a) or adopts a

ﬂattened-envelope conformation (in 10b, with Pd1 atom

deviating by 0.248 Å). In turn, the conformation of the

metallocycle formed by the amino acid pendant arm depends

on its size and varies from an envelope (with atom C10

deviating by 0.464 Å) to a twist (in the case of the six-

membered ring in complex 10b, with C10 and C11 atoms

deviating by 0.683 and 0.337 Å, respectively). It is noteworthy

that slow crystallization of 9a from CH Cl −hexane aﬀorded a

single diastereomer of this complex. Furthermore, the resulting

single crystals of complex 10b appeared to include only one

pair of enantiomers instead of a mixture of the four possible

isomeric forms; in both cases the ester group and allyl

substituent adopt a syn arrangement relative to the

Pd1N1N2Cl1S1 mean plane. This opens up interesting

prospects for the separation of stereoisomers of these types

of nonclassical pincer complexes.

2

The cytotoxic activities of complexes 8−11 were tested

against several human cancer cell lines of diﬀerent origins:

colon (HCT116), breast (MCF7), and prostate (PC3)

cancers. After 48 h exposure, the cell viability was determined

by the conventional MTT assay. Cisplatin was used as a

positive control. The resulting concentrations necessary to

5

,5-membered complex 9a, which almost disappears in its 5,6-

membered counterpart 10b (the corresponding angles are

equal to 167.54(9) and 179.30(6)°, respectively). The

presence of the fused metallocycles formed by the pendant

arms with diﬀerent donor centers and diﬀerent lengths

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inhibit the cellular survival fraction to 50% are given in Table

water and DMSO−PBS solutions: UV−vis spectroscopic

studies conﬁrmed the retention of a pincer structure in

solution over a prolonged period of time (120 h), with the only

conceivable change being the substitution of the auxiliary

chloride ligand for DMSO (Figures S35 −S39 in the

1

.

Most of the complexes obtained exhibited signiﬁcant

antiproliferative activity against all of the cancer cell lines

explored. The only exception was complex 8c (Table 1, entry

6

3

), which demonstrated moderate or even low cytotoxicity and

Supporting Information).

was inferior to the referencecisplatin (entry 13). In most of

the other cases, the compounds under consideration out-

performed this widely used chemotherapeutic agent. In some

cases, especially in the experiments with HCT116 and PC3

cells, the values of IC₅₀reached a low micromolar range (see,

for example, entries 1, 4, 10, and 12). As a rule, MCF7 breast

cancer cells appeared to be less sensitive to Pd(II) complexes

To further evaluate the anticancer potential of Pd(II) pincer

complexes based on functionalized carboxamides with S-donor

amino acid residues, we analyzed the eﬀects of 8a, 9a, 11a−c,

and a representative example of compounds I on the

proliferation of transformed breast cells HBL100 and

doxorubicin-resistant subline HBL100/Dox (Table 2). All of

8

−11.

Table 2. Cytotoxic Eﬀects of the Pd(II) Pincer Complexes

Based on Picolinylamides with S-Donor Amino Acid

Pendant Arms on HBL100 and HBL100/Dox Cells

The S-modiﬁed cysteine-based complexes were found to be

more active than their counterparts with elongated S-donor

pendant arms against all the tested cancer cell lineages. The

order of eﬃciency depending on the substituent at the ancillary

sulfur donor group for the cysteine derivatives was as follows:

CH Ph > All > CH COOMe (entries 1−6). For the

homocysteine-based complexes, methoxycarbonylmethyl de-

rivatives 10c and 11c appeared to be more eﬃcient than their

allyl analogues 10b and 11b (entries 9 and 12 vs entries 8 and

IC₅₀± SD, μM

HBL100/

Dox

compound

HBL100

2

8

9

1

a

1a

1b

1c

8.4 ± 1.4

9.4 ± 2.6

9.6 ± 2.2

11.5 ± 1.0

15.0 ± 0.5

10.2 ± 0.7

9.4 ± 2.2

14.0 ± 3.5

7.8 ± 1.4

14.5 ± 1.5

20.5 ± 3.5

14.6 ± 2.2

1

1). Nevertheless, in both series the highest cytotoxic eﬀects

were exerted by the S-modiﬁed complexes bearing benzyl

substituents. Another general tendency observed for the

S,N,N-complexes under investigation is that the introduction

of a chlorine atom into the pyridine ring facilitated the

improvement of cytotoxic activity: in some examples a

^dⁱ^ﬀ^e^r^eⁿ^c^e^o^f^m^o^r^e^t^h^aⁿ⁴^tⁱ^m^e^s^b^e^t^w^e^eⁿ^t^h^e^I^C⁵0 values of

the corresponding 4-chloropicolinyl- and picolinylamide

derivatives was observed (entries 4−6 vs entries 1−3, entries

compound I (n = 2, X = Cl, L-methionine

derivative)

doxorubicin

0.40 ± 0.14

53.0 ± 7.0

the tested complexes provided almost the same level of growth

inhibition in both native and resistant cells, while the reference,

doxorubicin, exhibited more than a 130-fold drop in the

activity on passing to HBL100/Dox cells. This indicates that

these types of cytotoxic Pd(II) complexes can serve as the basis

for new chemotherapeutic agents that would be able to

overcome drug resistance.

1

0−12 vs entries 7−9). As in the case of prototypes I, the

positive eﬀect of chlorine substituents can be associated with

an increase in the lipophilicity and a possibility of a

nonbonding interaction of the chlorine atom in a binding

1

2

site. The cytotoxic activity of complexes 8−11 was also

estimated against noncancer human embryonic kidney cells

Currently, it is widely recognized that targeting apoptosisa

programmed cell deathranks among the most successful

nonsurgical strategies for cancer treatment. One of the earliest

indicators of apoptosis is the externalization of phospholipid

phosphatidylserine (PS). The exposed PS can readily be

detected by the phospholipid-binding protein annexin V or its

highly luminescent conjugates with ﬂuorochromes such as

phycoerythrin (PE). An Annexin V-PE staining assay was used

to study the ability of the complexes obtained to induce

apoptosis. The investigations were performed with some of the

most active cysteine- and homocysteine-based derivatives

complexes 8a and 11a, respectively. For comparison, the

apoptotic eﬀects of selected representatives of other types of

cytotoxic Pd(II) pincer complexes based on functionalized

amide ligands (compounds I, V, and VI from Figure 2) were

also evaluated. Acute monocytic leukemia cells (THP-1) were

treated with the aforementioned compounds at concentrations

of 10 μM for 20 h. The following analysis by ﬂow cytometry

(Figure 4) revealed that type VI S,N,N-complex lacking an

amino acid residue and S,N,P-complex V with an L-methionine

pendant arm provide almost the same percentages of apoptotic

cells above 30% versus 3.7% in the control experiment but are

considerably less eﬀective in the eﬃciency than the S,N,N-

counterparts derived from the functionalized picolinylamides.

More importantly, the apoptotic eﬃciency increases on passing

from key prototype I to S-modiﬁed analogues 8a and 11a

obtained in this study: the percentages of apoptotic cells

(

HEK293) and kidney epithelial cells (NKE). Unfortunately,

an appreciable level of selectivity in the case of HEK293 cells

was observed only relative to the HCT116 cancer lineage,

although for some complexes the selectivity indices were above

3

.0. Slightly better results were achieved with the selected

examples of S-modiﬁed cyclopalladated derivatives on NKE

cells (the highest selectivity index was 7.0).

It is important to note that free ligands 2, 3, 6, and 7 did not

aﬀord 50% cell growth inhibition even at a concentration as

high as 200 μM, suggesting that the observed cytotoxic

properties of the cyclopalladated complexes are determined by

the coordination with palladium ions, as was the case with

compounds I. In general, the S-modiﬁed derivatives obtained

in this study provide comparable levels of cytotoxic activity and

conform to the main structure−activity relationships observed

for the S-methyl-L-cysteine and methionine prototypes. This

conﬁrms the value of pincer systems based on picolinylamides

bearing S-donor amino acid pendant arms as a potentially

interesting scaﬀold for the development of new antitumor

agents and renders following research in this ﬁeld very

promising.

By the examples of complexes 11a,c, it was demonstrated

that the S-modiﬁed cyclopalladated derivatives, as well as

compounds I bearing methyl substituents at the ancillary S-

donor group, are stable both in neat DMSO and in DMSO−

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Figure 4. Percentages of apoptotic THP-1 cells in the control experiment (a) and after exposure to the complexes from the previous studies VI (n =

2

1

, m = 1 (b)), V (n = 2 (c)), and I (n = 2, X = Cl, L-amino acid derivative (d)) and exposure to the complexes from the present study 8a (e) and

1a (f).

composed 47.0%, 54.0%, and 56.5%, respectively. Thus, the S-

modiﬁcation of the ligand framework can serve as a tool to

improve apoptosis induction by this potent class of cytotoxic

agents.

Interestingly, S-modiﬁed complexes 8a−11a did not aﬀect

the mobility of supercoiled plasmid DNA pHOT1 (Topo-

GEN) at concentrations up to 120 μM in agarose gel

electrophoresis studies (Figure 5 ). The inhibition eﬀect of

their cellular uptake. This characteristic is of high importance

for the application of compounds as therapeutic or diagnostic

agents and is underexplored for the potential metal-based

drugs. Unfortunately, neither complexes 8−11 nor their

prototypes derived from the related ligands display photo-

luminescence properties. Therefore, we decided to obtain a

ﬂuorophore-conjugated analogue of these compounds. Func-

tionalized carboxamide 12 bearing a ﬂuorescein moiety was

obtained according to the general method for the synthesis of

S-modiﬁed homocysteine-based ligands 6 and 7, starting from

homocysteine thiolactone derivative 4 and using 2-chloro-N-

ﬂuoresceinylacetamide as the alkylating agent. The direct

cyclopalladation of 12 under the action of PdCl (NCPh)

2

readily aﬀorded target Pd(II) S,N,N-pincer complex 13

featuring favorable emission properties (for the experimental

details and characterization of compounds 12 and 13,

including their luminescence spectra (Figure S40), see the

Supporting Information). The structure of this complex is

depicted in Figure 7. The ﬂuorescence microscopy images of

PC3 cells treated with compound 13 (Figure 7) show that it is

accumulated mainly in the cytoplasm and, in some cases,

additionally in certain subcellular zones (for the corresponding

images of PC3 cells treated with free ligand 12, see Figure S41

in the Supporting Information). Further studies by ﬂow

cytometry conﬁrmed that compound 13 is indeed taken up

inside PC3 cancer cells despite a large expanse of the ligand.

Figure 8 illustrates its internalization in a time-dependent

manner. It is also noteworthy that this complex is stable to the

intracellular environment, since there is no loss in

luminescence over time. Additionally, the stability of

ﬂuorophore-conjugated derivative 13, in particular, in

DMSO−PBS solution was also conﬁrmed by UV−vis

spectroscopic studies (see Figure S42 in the Supporting

Information).

Figure 5. Gel electrophoresis diagram showing the eﬀect of

complexes 8a−11a on supercoiled pHOT1 DNA.

most of the complexes from this study on human DNA

topoisomerase I was manifested, as a rule, at concentrations

above 10 μM (Figures 6a,b). Some changes in the DNA

relaxation in the electrophoretic patterns obtained after

treatment with the selected compounds at the lower

concentrations were observed only for 9b and 11c starting

from 2.5 μM (Figures 6c,d). These preliminary results on the

binding ability with DNA and Topo I, often serving as the

main targets for metal-based chemotherapeutics, may suggest

diﬀerent action modes of the S-modiﬁed complexes under

consideration and their key prototypes I bearing methyl

substituents at the ancillary sulfur-donor moieties.

To gain further insight into the biological eﬀect of Pd(II)

pincer complexes of picolinylamides with S-donor amino acid

pendant arms on living cells, it seemed interesting to analyze

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Figure 6. Gel electrophoresis diagrams showing the e ﬀ ect of complexes 8a , 9a −c , 10a , and 11a −c on human DNA topoisomerase I.

Figure 7. Fluorescence microscopy analysis of PC3 cells incubated with complex 13: images showing the ﬂuorescence of 13 in the cells obtained

with a blue ﬁlter (a, c) and phase contrast images (b, d) at ×400 magniﬁcation.

There is sometimes an unpredictable interplay between the

structural modiﬁcations and relevant properties. Thus, complex

on the further modiﬁcation of a ligand framework in order to

obtain pincer−(pseudo)dipeptide conjugates.

1

3 appeared to be almost nontoxic toward the tested cancer

lineages: the viabilities of HCT116, MCF7, and PC3 cells after

CONCLUSIONS

■

4

6

8 h exposure to this compound at a concentration as high as

0 μM were above 80%. Nevertheless, ﬁrm evidence for the

A small library of new potential antitumor agents based on

Pd(II) pincer complexes of functionalized carboxamides with

S-modiﬁed cysteine and homocysteine residues has been

synthesized and fully characterized. A preliminary evaluation of

the cytotoxic activities of the resulting complexes against

several human cancer cell lines revealed comparably high levels

of eﬃciency and structure−activity relationships analogous to

uptake into the cellular interior of this particular representative

of nonclassical Pd(II) pincer complexes based on function-

alized carboxamides with amino acid residues is an important

addition to the characteristics of the whole class of these

potential antitumor agents. Our future eﬀorts will be focused

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registered using the JMODECHO mode; the signals for the C nuclei

bearing odd and even numbers of protons had opposite polarities.

1

5

1

15

The N chemical shifts were extracted from the H− N HMBC

spectra. The NMR peak assignments for the representative ligands

1

13

and complexes were based on the analysis of H− H−COSY, H− C

HMBC, HMQC (6a, 7b, 8a, 9b,c, 10a−c, 11b) and/or HSQC (7c,

9

b) spectra. Along with the previously reported data for the related

6

compounds, the results obtained were used to assign the NMR

spectra of the other compounds from this study. The UV−vis spectra

of complexes 11a,c and 13 were registered on a Cary50 spectrometer

in quartz cells with 10 mm path length. The ﬂuorescence emission

spectra of compounds 12 and 13 were recorded on a Cary Eclipse

ﬂuorescence spectrophotometer (λ_e_x= 490 nm, 2.5 nm slit).

The IR spectra were recorded on a Nicolet Magna-IR750 FT

−

1

Figure 8. Flow cytometry analysis of PC3 cells incubated with

complex 13 for 1 (yellow), 2 (blue), or 20 h (red) (the gray histogram

denotes control cells).

spectrometer (resolution 2 cm , 128 scans). The assignment of

absorption bands in the IR spectra was made according to ref 19.

Column chromatography was carried out using Macherey-Nagel silica

gel 60 (MN Kieselgel 60, 70−230 mesh). Melting points were

determined with an MPA 120 EZ-Melt automated melting point

apparatus (Stanford Research Systems).

those observed earlier for the related picolinylamide derivatives

with S-methyl-L-cysteine and methionine residues. Further-

more, both the newly prepared and previous representatives of

N-metalated Pd(II) pincer complexes with S-donor amino acid

pendant arms displayed prominent cytotoxic eﬀects on

transformed breast cells HBL100 and their doxorubicin-

resistant clones HBL100/Dox, opening the way for the

creation of metal-based chemotherapeutics that would be

able to overcome drug resistance. The supplemental

mechanistic considerations revealed that the complexes

obtained induce signiﬁcant tumor cell death by apoptosis,

exceeding their key prototypes in the activity, and unlike the

latter did not exhibit high binding aﬃnity to DNA. Hence, the

S-modiﬁcation of the ligand framework can serve as a tool to

improve apoptosis induction ability and modify the action

mode of potential antitumor agents based on these types of

Pd(II) complexes. Finally, additional ﬂuorescence microscopy

and ﬂow cytometry studies with a specially designed

ﬂuorescein-conjugated pincer complex also comprising the S-

modiﬁed derivative discovered its eﬃcient cellular uptake and

stability to the intracellular environment, rendering non-

classical Pd(II) pincer complexes based on picolinylamides

with S-donor amino acid residues worthy of further studies as a

highly potent class of therapeutic agents.

Syntheses. General Procedure for the Synthesis of Ligands 2

and 3. A solution of Et N (0.76 g, 7.51 mmol) in CH Cl (5 mL) was

3

2

added dropwise to a stirred suspension of the corresponding S-

substituted methyl L-cysteinate hydrochloride (3.00 mmol) in CH Cl

(10 mL) at −5 to 0 °C under an argon atmosphere. The resulting

mixture was stirred at 0 °C for 30 min. Then, a suspension of picolinic

or 4-chloropicolinic acid chloride (3.00 mmol) in CH Cl (15 mL)

was added at −5 to +2°C. The reaction mixture was stirred at room

temperature for 12 h, poured into distilled water, sequentially washed

with saturated aqueous NaHCO₃and water, and dried over

anhydrous Na SO . The solvent was removed under vacuum. The

2

4

resulting residue was puriﬁed by column chromatography on silica gel

eluent: CH Cl /MeOH (75/1) (2a−c), CH Cl (3a−c)) to give the

target compounds as yellow (3a,b) or light yellow (2a−c, 3c) viscous

(

2

oils.

Methyl S-Benzyl-N-(pyridin-2-ylcarbonyl)-L -cysteinate (2a).

Yield: 0.44 g (44%). [α ]_D ² ⁰ = −26.6 (c = 0.50, CHCl ). H NMR

1

3

(400.13 MHz, CDCl

): δ 2.95 −3.07 (m, 2H, CH S), 3.79 (s, 2H,

2

3

C H Ph), 3.80 (s, 3H, OMe), 5.02 −5.07 (m, 1H, CH), 7.22 −7.26 (m,

2

3

1

H, H ), 7.28 −7.34 (m, 4H, H ), 7.48 (ddd, 1H, H(C4), J = 7.8

Hz, J = 4.8 Hz, J = 1.1 Hz), 7.88 (dt, 1H, H(C3), J = 7.8

EXPERIMENTAL SECTION

General Remarks. If not mentioned otherwise, all manipulations

were carried out without taking precautions to exclude air and

moisture. Dichloromethane was distilled from P O . Triethylamine

HH

■

4

Hz, J = 1.7 Hz), 8.19 −8.22 (m, 1H, H(C2)), 8.63 −8.65 (m, 1H,

H(C5)), 8.74 (br d, 1H, NH, J = 8.4 Hz) ppm. C{ H} NMR

HH

(

100.61 MHz, CDCl ): δ 33.39 and 36.63 (both s, CH S and

3

2

5

C H Ph), 52.00 and 52.69 (both s, CH and OMe), 122.39 and 126.52

both s, C2 and C4), 127.22 (s, C15), 128.58 and 129.02 (both s,

C13 + C17 and C14 + C16), 137.35 (s, C3), 137.59 (s, C12), 148.42

(s, C5), 149.23 (s, C1), 164.17 (s, C(O)NH), 171.13 (s, C (O)OMe)

ppm. IR (thin ﬁ lm, ν /cm ): 621(w), 702(m), 751(w), 820(vw),

998(w), 1028(vw), 1042(vw), 1072(vw), 1088(vw), 1178(w),

1212(br, m), 1239(w), 1294(w), 1312(w), 1356(w), 1435(m),

2

was distilled from sodium. Methanol for the synthesis of ligands 6 and

was distilled over magnesium turnings activated with iodine.

Picolinyl and 4-chloropicolinyl chlorides were synthesized by the

(

7

1

3

reactions of picolinic acid with SOCl in the presence of Et N and

−1

2

3

14

NaBr, respectively, and directly used in further steps without

puriﬁcation. Methyl S-benzyl-L-cysteinate, methyl S-allyl-L-cystei-

nate, and methyl S-(2-methoxy-2-oxoethyl)-L-cysteinate hydro-

15

16

17

1

454(w), 1466(w), 1515(br, s) (C(O)NH), 1570(w), 1591(w),

chlorides were obtained from methyl L-cysteinate hydrochloride by a

678(br, s) (ν (C O) in C(O)NH), 1746(br, s) (ν (C O) in

sequential treatment with Boc O, the corresponding alkyl halide, and

2

C(O)OMe), 2848(vw), 2924(vw), 2952(w), 3028(vw), 3060(vw),

HCl. 2-Chloro-N-ﬂuoresceinylacetamide used in the synthesis of

ligand 12 was derived from 5-aminoﬂuorescein and chloroacetyl

chloride in the presence of sodium bicarbonate according to the

3

378(br, w) (ν (NH)). Anal. Calcd for C H N O S: C, 61.80; H,

.49; N, 8.48. Found: C, 61.42; H, 5.88; N, 8.13.

Methyl S-Allyl-N-(pyridin-2-ylcarbonyl)-L -cysteinate (2b).

17 18 2 3

5

18

published procedure. For the synthesis and characterization of

ligand 12 and its Pd(II) pincer complex 13, see the Supporting

Information . All other chemicals and solvents were used as purchased.

The NMR spectra were recorded on Bruker Avance 400, Avance

5

00, and Avance 600 spectrometers, and the chemical shifts (δ) were

1

13

referenced internally by the residual ( H) or deuterated ( C) solvent

signals relative to tetramethylsilane or externally to H PO ( P) or

MeNO₂( N). In most cases, the C{ H} NMR spectra were

3

1

Yield: 0.44 g (52%). [α ]_D ² ⁰ = −9.6 (c = 0.26, CHCl ). H NMR

1

3

4

3

15

13

1

(400.13 MHz, CDCl ): δ 2.95 −3.20 (m, 2H, CH S + 2H, C H CH 

3

2

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CH ), 3.78 (s, 3H, OMe), 4.96 −5.01 (m, 1H, CH), 5.06 −5.11 (m,

Methyl S-Allyl-N-[(4-chloropyridin-2-yl)carbonyl]-L-cysteinate

(3b).

2

H, CH CH C H ), 5.68 −5.78 (m, 1H, CH C H CH ), 7.42 −7.45

2

3

(

m, 1H, H(C4)), 7.83 (t, 1H, H(C3), J = 7.7 Hz), 8.15 (d, 1H,

HH

3

H(C2), J = 7.7 Hz), 8.58 (d, 1H, H(C5), J = 4.7 Hz), 8.70 (br

d, 1H, NH, J = 8.4 Hz) ppm. C{ H} NMR (100.61 MHz,

HH

CDCl ): δ 32.49 and 35.08 (both s, CH S and C H CH CH ), 51.99

3

2

and 52.68 (both s, CH and OMe), 118.00 (s, CH CH C H ), 122.32

2

and 126.52 (both s, C2 and C4), 133.61 (s, CH C H CH ), 137.35

Yield: 0.30 g (32%). [α ]_D ² ⁰ = −5.0 (c = 0.50, CH Cl ). H NMR

1

2

(

s, C3), 148.40 (s, C5), 149.16 (s, C1), 164.11 (s, C(O)NH), 171.13

s, C (O)OMe) ppm. IR (thin ﬁ lm, ν /cm ): 598(w), 621(m),

00(w), 751(m), 821(w), 887(vw), 922(w), 998(m), 1020(w),

042(w), 1088(w), 1178(m), 1212(br, m), 1356(m), 1435(m),

466(m), 1517(br, s) (C(O)NH), 1570(w), 1591(w), 1636(w),

678(br, s) (ν (C O) in C(O)NH), 1746(br, s) (ν (C O) in

(

400.13 MHz, CDCl ): δ 2.97 −3.22 (m, 2H, CH S + 2H, C H CH 

−1

3

2

CH ), 3.81 (s, 3H, OMe), 4.97 −5.02 (m, 1H, CH), 5.09 −5.13 (m,

H, CH CH C H ), 5.70 −5.81 (m, 1H, CH C H CH ), 7.47 (dd,

H, H(C4), J = 5.2 Hz, J = 2.0 Hz), 8.19 (d, 1H, H(C2), J

2.0 Hz), 8.52 (d, 1H, H(C5), J = 5.2 Hz), 8.64 (br d, 1H, NH,

J _H _H = 8.4 Hz) ppm. C{ H} NMR (100.61 MHz, CDCl ): δ 32.35

C(O)OMe), 2855(vw), 2921(vw), 2953(w), 3008(vw), 3063(vw),

and 34.97 (both s, CH S and C H CH CH ), 51.89 and 52.62 (both

2

3

383(br, w) (ν (NH)). Anal. Calcd for C H N O S: C, 55.70; H,

13 16 2 3

s, CH and OMe), 117.93 (s, CH CH C H ), 122.88 and 126.52

2

5

.75; N, 9.99. Found: C, 55.74; H, 5.87; N, 9.81.

Methyl S-(2-Methoxy-2-oxoethyl)-N-(pyridin-2-ylcarbonyl)-L-cys-

teinate (2c).

(

both s, C2 and C4), 133.43 (s, CH C H=CH ), 145.73 (s, C3),

2 2

1

49.18 (s, C5), 150.52 (s, C1), 162.84 (s, C(O)NH), 170.82 (s,

C (O)OMe) ppm. IR (thin ﬁ lm, ν /cm ): 526(w), 692(w), 749(m),

81(w), 842(w), 921(w), 994(w), 1019(w), 1097(w), 1178(m),

215(br, m), 1312(w), 1350(m), 1437(m), 1462(m), 1517(br, s)

(

C(O)NH), 1558(m), 1579(m), 1636(w), 1678(br, s) (ν (C O) in

C(O)NH), 1746(br, s) (ν (C O) in C(O)OMe), 2849(vw),

954(w), 3082(vw), 3373(br, w) (ν (NH)). Anal. Calcd for

C H ClN O S: C, 49.60; H, 4.80; N, 8.90. Found: C, 49.50; H,

2

Yield: 0.53 g (57%). [α ]_D ² ⁰ = −11.5 (c = 0.33, CHCl ). H NMR

400.13 MHz, CDCl ): δ 3.17 (dd, 1H, CH S, J = 14.0 Hz, J =

.3 Hz), 3.26 −3.37 (m, 1H, CH S + 2H, C H C(O)OMe), 3.71 (s,

Methyl N-[(4-Chloropyridin-2-yl)carbonyl]-S-(2-methoxy-2-ox-

oethyl)-L-cysteinate (3c ).

2

H, OMe), 3.80 (s, 3H, OMe), 5.03 −5.08 (m, 1H, CH), 7.44 −7.47

3

(

m, 1H, H(C4)), 7.85 (t, 1H, H(C3), J = 7.7 Hz), 8.17 (d, 1H,

HH

3

H(C2), J = 7.7 Hz), 8.60 (d, 1H, H(C5), J = 4.7 Hz), 8.74 (br

d, 1H, NH, J = 8.5 Hz) ppm. C{ H} NMR (100.61 MHz,

HH

CDCl ): δ 33.63 and 34.58 (both s, CH S and C H C(O)OMe),

3

2

5

1.79, 52.51, and 52.82 (three s, CH and OMe in C(O)OMe and

2

CH C(O)OMe), 122.38 and 126.57 (both s, C2 and C4), 137.36 (s,

Yield: 0.43 g (41%). [α ]_D ² ⁰ = −2.6 (c = 0.70, CHCl ). H NMR

1

3

C3), 148.41 (s, C5), 149.10 (s, C1), 164.25 (s, C(O)NH), 170.43

2

3

(

400.13 MHz, CDCl ): δ 3.18 (dd, 1H, CH S, J = 14.1 Hz, J

and 170.95 (both s, C (O)OMe and CH C (O)OMe) ppm. IR (thin

ﬁ lm, ν /cm ): 621(w), 701(vw), 752(m), 821(vw), 998(m), 1173(br,

m), 1214(m), 1281(br, m), 1356(w), 1436(m), 1466(w), 1517(br, s)

2

6

3

.3 Hz), 3.29 and 3.36 (ABq, 2H, C H C(O)OMe, J = 15.0 Hz),

.31 (dd, 1H, CH S, J = 14.1 Hz, J = 5.0 Hz), 3.74 (s, 3H,

2

HH

3

OMe), 3.83 (s, 3H, OMe), 5.06 (ddd, 1H, CH, J = 8.4 Hz, J

C(O)NH), 1570(w), 1591(w), 1676(br, s) (ν (C O) in

C(O)NH), 1740(br, s) (ν (C O) in C(O)OMe), 2850(vw),

954(w), 3007(vw), 3375(br, w) (ν (NH)). Anal. Calcd for

C H N O S: 49.99; H, 5.16; N, 8.97. Found: C, 49.63; H, 5.26;

3

4

.3 Hz, J = 5.0 Hz), 7.48 (dd, 1H, H(C4), J = 5.2 Hz, J

.1 Hz), 8.20 (d, 1H, H(C2), J = 2.1 Hz), 8.52 (d, 1H, H(C5),

J _H _H = 5.2 Hz), 8.68 (br d, 1H, NH, J = 8.4 Hz) ppm. C{ H}

NMR (100.61 MHz, CDCl ): δ 33.63 and 34.54 (both s, CH S and

C H C(O)OMe), 51.85, 52.56, and 52.90 (three s, CH and OMe in

C(O)OMe and CH C(O)OMe), 123.07 and 126.72 (both s, C2 and

C4), 145.91 (s, C3), 149.33 (s, C5), 150.59 (s, C1), 163.13 (s,

3

2

N, 8.86.

Methyl S-Benzyl-N-[(4-chloropyridin-2-yl)carbonyl]-L-cysteinate

3a).

2

(

C(O)NH), 170.40 and 170.78 (both s, C (O)OMe and

−

1

CH C (O)OMe) ppm. IR (thin ﬁ lm, ν /cm ): 527(w), 626(br, vw),

2

6

1

92(w), 748(w), 782(w), 845(w), 904(vw), 995(w), 1009(w),

135(w), 1175(br, w), 1217(br, m), 1283(br, m), 1350(w),

437(m), 1462(w), 1517(br, s) (C(O)NH), 1557(m), 1579(w),

Yield: 1.01 g (92%). [α ]_D ² ⁰ = −10.6 (c = 0.53, CHCl ). H NMR

1

1679(br, s) (ν (C O) in C(O)NH), 1740(br, s) (ν (C O) in

3

C(O)OMe), 2847(vw), 2954(w), 3003(vw), 3059(vw), 3373(br, w)

(

400.13 MHz, CDCl ): δ 2.95 −3.07 (m, 2H, CH S), 3.77 (s, 2H,

ν (NH)). Anal. Calcd for C H ClN O S: C, 45.02; H, 4.36; N,

.08. Found: C, 44.94; H, 4.34; N, 7.91.

C H Ph), 3.80 (s, 3H, OMe), 4.99 −5.04 (m, 1H, CH), 7.22 −7.32 (m,

H, H ), 7.48 (dd, 1H, H(C4), J = 5.2 Hz, J = 2.1 Hz), 8.20

Ar HH HH

4

3

N-(2-Oxotetrahydro-3-thienyl)pyridine-2-carboxamide (4).

d, 1H, H(C2), J = 2.1 Hz), 8.53 (d, 1H, H(C5), J = 5.2 Hz),

.66 (br d, 1H, NH, J = 8.4 Hz) ppm. C{ H} NMR (100.61

MHz, CDCl ): δ 33.34 and 36.62 (both s, CH S and C H Ph), 52.02

3

2

and 52.77 (both s, CH and OMe), 123.06 and 126.67 (both s, C2 and

C4), 127.26 (s, C15), 128.60 and 129.00 (both s, C13 + C17 and

C14 + C16), 137.51 (s, C12), 145.88 (s, C3), 149.32 (s, C5), 150.68

(

s, C1), 163.02 (s, C(O)NH), 170.94 (s, C (O)OMe) ppm. IR (thin

ﬁ lm, ν /cm ): 526(w), 565(vw), 705(m), 749(m), 781(w), 843(w),

A solution of Et N (2.12 g, 21.0 mmol) in CH Cl (5 mL) was added

3 2 2

dropwise to a stirred suspension of DL -homocysteine thiolactone

01(vw), 994(vw), 1028(vw), 1072(vw), 1097(w), 1130(w),

178(m), 1215(br, m), 1312(w), 1350(m), 1437(m), 1454(m),

516(br, s) (C(O)NH), 1557(m), 1579(m), 1680(br, s) (ν (C O)

hydrochloride (1.54 g, 10.0 mmol) in CH Cl (10 mL) at −5 to 0 °C.

2

The resulting mixture was stirred at 0 °C for 15 min. Then, a

suspension of picolinic acid chloride (1.42 g, 10.0 mmol) in CH Cl

2

in C(O)NH), 1746(br, s) (ν (C O) in C(O)OMe), 2952(vw),

(15 mL) was added at −5 to +2 °C. The reaction mixture was poured

3

028(vw), 3060(vw), 3379(br, w) (ν (NH)). Anal. Calcd for

into distilled water, washed with saturated aqueous NaHCO and

3

C H ClN O S: C, 55.96; H, 4.70; N, 7.68. Found: C, 55.58; H,

water, and dried over anhydrous Na SO . The solvent was removed

under vacuum. The resulting residue was puri ﬁ ed by column

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chromatography on silica gel (eluent: CH Cl /MeOH (75/1))

(in the case of ligand 6a after treatment of the resulting yellow viscous

oil with hexane).

Methyl S-Benzyl-N-(pyridin-2-ylcarbonyl)homocysteinate (6a).

2

followed by recrystallization from EtOAc to give compound 4 as

1

grayish crystals. Yield: 2.03 g (91%). Mp: 138 −139 °C. H NMR

(

400.13 MHz, CDCl ): δ 2.10 −2.21 (m, 1H, CH ), 2.92 −2.98 (m,

H, CH ), 3.29 −3.33 (m, 1H, CH S), 3.39 −3.47 (m, 1H, CH S),

2

3

.75 −4.82 (m, 1H, CH), 7.45 (dd, 1H, H(C4), J = 7.7 Hz, J

.8 Hz), 7.83 −7.88 (m, 1H, H(C3)), 8.17 (d, 1H, H(C2), J = 7.8

Hz), 8.45 (br d, 1H, NH, J = 7.2 Hz), 8.56 (d, 1H, H(C5), J

4

=

HH

.8 Hz) ppm. ¹ ³ C{ H} NMR (100.61 MHz, CDCl ): δ 27.59 and

1

3

Yield: 0.58 g (97%). Mp: 42 −43 °C. 1 _H _N _M _R ₍₆ ₀ ₀ _.₂ ₂ _M _H _z _,

CDCl ): δ 2.07 −2.13 (m, 1H, CH ), 2.24 −2.30 (m, 1H, CH ), 2.47 −

3

1.74 (both s, CH and CH S), 59.29 (s, CH), 122.35 and 126.63

2

3

2

(both s, C2 and C4), 137.42 (s, C3), 148.32 (s, C5), 149.07 (s, C1),

2

4

.55 (m, 2H, CH S), 3.73 (s, 2H, C H Ph), 3.77 (s, 3H, OMe), 4.89 −

2

1

64.84 (s, C(O)NH) ppm (the signal of C(O)S carbon nucleus was

.92 (m, 1H, CH), 7.19 −7.21 (m, 1H, H(C16)), 7.24 −7.27 (m, 2H,

−

1

not observed). IR (KBr, ν /cm ): 564(w), 588(w), 621(w), 704(vw),

H(C15) + H(C17)), 7.28 −7.30 (m, 2H, H(C14) + H(C18)), 7.47

7

1

57(m), 826(vw), 841(vw), 930(m), 997(w), 1016(w), 1041(w),

091(vw), 1148(vw), 1277(vw), 1314(w), 1436(w), 1465(w),

512(s) (C(O)NH), 1567(w), 1590(w), 1668(s) (ν (C O) in

3

4

(

ddd, 1H, H(C4), J = 7.7 Hz, J = 4.8 Hz, J = 1.2 Hz), 7.88

dt, 1H, H(C3), J = 7.7 Hz, J = 1.7 Hz), 8.19 (dd, 1H, H(C2),

J _H _H = 7.7 Hz, J = 1.2 Hz), 8.53 (br d, 1H, NH, J = 8.4 Hz),

HH

C(O)NH), 1703(s) (ν (C O) in C(O)S), 2889(vw), 2942(vw),

.61 (dd, 1H, H(C5), J = 4.8 Hz, J = 1.7 Hz) ppm. C{ H}

HH HH

2

995(vw), 3098(vw), 3381(m) (ν (NH)). Anal. Calcd for

NMR (150.93 MHz, CDCl ): δ 26.95 (s, CH S), 32.24 (s, CH ),

3

2

C H N O S: C, 54.04; H, 4.53; N, 12.60. Found: C, 53.94; H,

6.04 (s, C H Ph), 51.60 (s, CH), 52.53 (s, OMe), 122.36 (s, C2),

26.45 (s, C4), 127.00 (s, C16), 128.49 (s, C15 and C17), 128.90 (s,

-Chloro-N-(2-oxotetrahydro-3-thienyl)pyridine-2-carboxamide

C14 and C18), 137.34 (s, C3), 138.05 (s, C13), 148.29 (s, C5),

(5).

1

49.33 (s, C1), 164.18 (s, C(O)NH), 172.09 (s, C (O)OMe) ppm.

1

5

N NMR (60.85 MHz, CDCl ): δ −275.0 (C(O)NH), −80.0 (Py)

3

−

1

ppm. IR (thin ﬁ lm, ν /cm ): 565(vw), 621(w), 702(m), 751(w),

8

1

20(vw), 998(w), 1028(vw), 1042(vw), 1072(vw), 1088(vw),

174(m), 1224(br, m), 1271(w), 1362(w), 1434(m), 1453(m),

466(m), 1516(br, s) (C(O)NH), 1570(w), 1591(w), 1678(br, s)

A solution of Et N (2.12 g, 21.0 mmol) in CH Cl (5 mL) was added

dropwise to a stirred suspension of DL -homocysteine thiolactone

ν (C O) in C(O)NH), 1742(br, s) (ν (C O) in C(O)OMe),

849(vw), 2920(w), 2952(w), 3028(vw), 3060(vw), 3378(br, w)

ν (NH)). Anal. Calcd for C H N O S: C, 62.77; H, 5.85; N, 8.13.

hydrochloride (1.54 g, 10.0 mmol) in CH Cl (10 mL) at −5 to 0 °C.

The resulting mixture was stirred at 0 °C for 15 min. Then, a

suspension of 4-chloropicolinic acid chloride (1.76 g, 10.0 mmol) in

CH Cl (15 mL) was added at 0 °C. The reaction mixture was poured

Found: C, 62.61; H, 5.88; N, 8.04.

Methyl S-Allyl-N-(pyridin-2-ylcarbonyl)homocysteinate (6b).

2

into distilled water, washed with saturated aqueous NaHCO and

3

water, and dried over anhydrous Na SO . The solvent was removed

2

4

under vacuum. The resulting residue was puri ﬁ ed by column

chromatography on silica gel (eluent: CH Cl /MeOH (100/1)) to

2

give compound 5 as light beige crystals. Yield: 2.01 g (78%). Mp:

1

Yield: 0.42 g (82%). H NMR (400.13 MHz, CDCl ): δ 2.07 −2.16

1

2

1

34 −136 °C (EtOAc/hexane). H NMR (400.13 MHz, CDCl ): δ

3

(

m, 1H, CH ), 2.24 −2.33 (m, 1H, CH ), 2.51 −2.63 (m, 2H, CH S),

.09 −2.20 (m, 1H, CH ), 2.97 −3.04 (m, 1H, CH ), 3.32 −3.37 (m,

2

3

4

.16 (d, 2H, C H CH CH , J = 7.2 Hz), 3.81 (s, 3H, OMe),

H, CH S), 3.42 −3.50 (m, 1H, CH S), 4.74 −4.81 (m, 1H, CH), 7.48

.90 −4.96 (m, 1H, CH), 5.05 −5.10 (m, 2H, CH CH C H ), 5.72 −

(

dd, 1H, H(C4), J = 5.2 Hz, J = 2.1 Hz), 8.20 (d, 1H, H(C2),

5.82 (m, 1H, CH C H CH ), 7.47 (ddd, 1H, H(C4), J = 7.6 Hz,

J

HH HH

J _H _H = 2.1 Hz), 8.36 (br d, 1H, NH, J = 6.9 Hz), 8.49 (d, 1H,

= 4.8 Hz, J = 1.2 Hz), 7.86 −7.90 (m, 1H, H(C3)), 8.20 (d,

3 3

H(C5), J = 5.2 Hz) ppm. C{ H} NMR (100.61 MHz, CDCl ):

H, H(C2), J = 7.8 Hz), 8.56 (br d, 1H, NH, J = 8.4 Hz), 8.61

δ 27.59 and 31.66 (both s, CH and CH S), 59.35 (s, CH), 123.00

d, 1H, H(C5), J = 4.8 Hz) ppm. C{ H} NMR (100.61 MHz,

and 126.78 (both s, C2 and C4), 145.95 (s, C3), 149.23 (s, C5),

50.51 (s, C1), 163.69 (s, C(O)NH), 204.64 (s, C(O)S) ppm. IR

HH

CDCl ): δ 26.21 (s, CH S), 32.27 (s, CH ), 34.55 (s, C H CH 

CH ), 51.58 and 52.58 (both s, CH and OMe), 117.26 (s, CH CH 

(KBr, ν /cm ): 528(w), 557(w), 623(vw), 666(w), 688(w), 716(w),

2

C H ), 122.35 and 126.48 (both s, C2 and C4), 134.08 (s, CH C H 

7

1

85(w), 843(w), 899(w), 927(m), 978(w), 1018(vw), 1058(w),

234(vw), 1300(w), 1351(w), 1520(s) (C(O)NH), 1555(m),

578(m), 1656(s) (ν (C O) in C(O)NH), 1692(s) and 1702(s)

2

CH ), 137.37 (s, C3), 148.31 (s, C5), 149.29 (s, C1), 164.21 (s,

2

−

1

C(O)NH), 172.18 (s, C (O)OMe) ppm. IR (thin ﬁ lm, ν /cm ):

6

1

21(w), 700(w), 751(m), 821(vw), 921(w), 998(m), 1042(vw),

088(vw), 1173(m), 1222(br, m), 1271(w), 1292(w), 1362(w),

434(m), 1466(m), 1518(br, s) (C(O)NH), 1570(w), 1591(w),

635(vw), 1677(br, s) (ν (C O) in C(O)NH), 1743(br, s) (ν (C 

(

both ν (C O) in C(O)S), 2856(vw), 2926(vw), 3062(vw),

3093(vw), 3327(m) and 3362(m) (both ν (NH)). Anal. Calcd for

C H ClN O S: C, 46.79; H, 3.53; N, 10.91. Found: C, 46.64; H,

O) in C(O)OMe), 2850(vw), 2919(w), 2952(w), 3008(vw),

General Procedure for the Synthesis of Ligands 6 and 7. The

3

058(vw), 3378(br, w) (ν (NH)). Anal. Calcd for C H N O S: C,

corresponding homocysteine thiolactone derivative (compound 4 or

, 1.74 mmol) was added portionwise to a stirred solution of sodium

14 18 2 3

5

7.12; H, 6.16; N, 9.52. Found: C, 57.32; H, 6.44; N, 9.60.

Methyl S-(2-Methoxy-2-oxoethyl)-N-(pyridin-2-ylcarbonyl)-

homocysteinate (6c ).

5

methoxide obtained in situ from sodium (0.04 g, 1.74 mmol) and

methanol (20 mL) at room temperature under an argon atmosphere.

The resulting mixture was stirred at room temperature for 30 min.

Then, a solution of the corresponding chloride (1.92 mmol) in

MeOH (5 mL) was added dropwise. The reaction mixture was stirred

for 12 h. The solvent was removed under vacuum. A solution of the

resulting residue in CH Cl was washed with water, dried over

2

1

anhydrous Na SO , and evaporated to dryness. The residue obtained

Yield: 0.35 g (62%). H NMR (400.13 MHz, CDCl ): δ 2.12 −2.21

2

4

3

was puriﬁed by column chromatography on silica gel (eleuent:

(m, 1H, CH ), 2.30 −2.39 (m, 1H, CH ), 2.75 −2.78 (m, 2H, CH S),

2

CH Cl /MeOH (75/1)) to give the target compounds as light brown

3.27 (s, 2H, C H COOMe), 3.73 (s, 3H, OMe), 3.82 (s, 3H, OMe),

2

3

(6b,c) or light yellow (7a−c) viscous oils or a beige crystalline solid

4.93 −4.99 (m, 1H, CH), 7.48 (dd, 1H, H(C4), J = 7.7 Hz, J

=

HH

9

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https://doi.org/10.1021/acs.inorgchem.1c01138

Inorg. Chem. 2021, 60, 9880−9898

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4

.8 Hz), 7.86 −7.90 (m, 1H, H(C3)), 8.20 (d, 1H, H(C2), J = 7.8

Methyl N-[(4-Chloropyridin-2-yl)carbonyl]-S-(2-methoxy-2-

oxoethyl)homocysteinate (7c ).

HH

3

Hz), 8.58 (br d, 1H, NH, J = 8.5 Hz), 8.62 (d, 1H, H(C5), J

=

HH

.8 Hz) ppm. ¹ ³ C{ H} NMR (100.61 MHz, CDCl ): δ 28.41, 31.84,

1

4

3

and 33.13 (three s, CH S, CH and C H C(O)OMe), 51.27, 52.28,

2

and 52.52 (three s, CH and OMe in C(O)OMe and CH C(O)OMe),

2

122.25 and 126.39 (both s, C2 and C4), 137.26 (s, C3), 148.20 (s,

C5), 149.13 (s, C1), 164.16 (s, C(O)NH), 170.61 and 171.91 (both

−

1

s, C (O)OMe and CH C (O)OMe) ppm. IR (thin ﬁ lm, ν /cm ):

1

2

Yield: 0.21 g (33%). H NMR (500.13 MHz, CDCl ): δ 2.13 −2.20

3

6

1

21(w), 700(w), 752(w), 821(vw), 998(m), 1042(w), 1089(w),

172(br, m), 1215(br, m), 1280(br, m), 1362(w), 1435(m),

466(m), 1517(br, s) (C(O)NH), 1570(w), 1591(w), 1677(br, s)

(

m, 1H, CH ), 2.30 −2.37 (m, 1H, CH ), 2.71 −2.80 (m, 2H, CH S),

2

3

.26 (s, 2H, C H COOMe), 3.74 (s, 3H, OMe in CH C (O)OMe),

2

.82 (s, 3H, OMe in C (O)OMe), 4.92 −4.96 (m, 1H, CH), 7.48 (dd,

ν (C O) in C(O)NH), 1739(br, s) (ν (C O) in C(O)OMe),

849(vw), 2953(w), 3002(vw), 3058(vw), 3373(br, w) (ν (NH)).

Anal. Calcd for C H N O S: C, 51.52; H, 5.56; N, 8.58. Found: C,

1H, H(C4), J = 5.3 Hz, J = 2.1 Hz), 8.16 (d, 1H, H(C2), J

= 2.1 Hz), 8.49 −8.52 (m, 2H, NH + H(C5)) ppm. C{ H} NMR

(125.76 MHz, CDCl ): δ 28.47 (s, CH S), 31.86 (s, CH ), 33.24 (s,

1.63; H, 5.96; N, 8.20.

Methyl S-Benzyl-N-[(4-chloropyridin-2-yl)carbonyl]-

homocysteinate (7a ).

C H COOMe), 51.49 (s, CH), 52.43 (s, OMe in CH C(O)OMe),

2

52.72 (s, OMe in C(O)OMe), 123.05 (s, C2), 126.67 (s, C4), 145.94

(s, C3), 149.22 (s, C5), 150.70 (s, C1), 163.12 (s, C(O)NH), 170.69

(

s, CH C (O)OMe), 171.86 (s, C (O)OMe) ppm. IR (thin ﬁ lm, ν /

2

−

1

cm ): 527(w), 693(w), 743(w), 783(w), 814(w), 844(w), 901(vw),

1

009(w), 1134(m), 1160(m), 1220(br, m), 1281(br, m), 1355(m),

393(w), 1436(m), 1520(br, s) (C(O)NH), 1557(m), 1579(m),

683(br, s) (ν (C O) in C(O)NH), 1739(br, s) (ν (C O) in

1

C(O)OMe), 2849(vw), 2953(w), 3060(vw), 3374(br, w) (ν (NH)).

Yield: 0.44 g (67%). H NMR (400.13 MHz, CDCl ): δ 2.05 −2.14

3

Anal. Calcd for C H ClN O S: C, 46.60; H, 4.75; N, 7.76. Found:

m, 1H, CH ), 2.21 −2.30 (m, 1H, CH ), 2.43 −2.55 (m, 2H, CH S),

2

C, 46.61; H, 4.71; N, 7.69.

3

7

.73 (s, 2H, C H Ph), 3.78 (s, 3H, OMe), 4.86 −4.92 (m, 1H, CH),

2

3 4

General Procedure for the Synthesis of Pd(II) Pincer Complexes

.19 −7.31 (m, 5H, H ), 7.48 (dd, 1H, H(C4), J = 5.2 Hz, J

=

Ar

HH

8

−11. A solution of PdCl (NCPh) (76 mg, 0.198 mmol) in 3 mL of

4

2

.1 Hz), 8.20 (d, 1H, H(C2), J = 2.1 Hz), 8.46 (br d, 1H, NH,

HH

dichloromethane was added dropwise to a solution of the

3

13

1

J _H _H = 8.3 Hz), 8.51 (d, 1H, H(C5), J = 5.2 Hz) ppm. C{ H}

HH

corresponding ligand (0.198 mmol) and Et N (28 μL, 0.201 mmol)

3

NMR (100.61 MHz, CDCl ): δ 26.83 (s, CH S), 32.07 (s, CH ),

3

2

in 6 mL of CH Cl . The reaction mixture was left under ambient

2

3

6.00 (s, C H Ph), 51.66 and 52.64 (both s, CH and OMe), 123.02

2

conditions for 12 h and then puriﬁed by column chromatography on

and 126.63 (both s, C2 and C4), 127.03 (s, C16), 128.51 and 128.90

both s, C15 + C17 and C14 + C18), 137.97 (s, C13), 145.90 (s, C3),

49.20 (s, C5), 150.73 (s, C1), 163.01 (s, C(O)NH), 171.94 (s,

silica gel (eluent: CH Cl /MeOH (100/1)) to give the target Pd(II)

2

(

pincer complexes as yellow (8a−c, 9a−c, 10b,c, 11a,c), light yellow

1

(

10a), or dark yellow (11b) crystalline solids.

Complex [κ -S,N,N-(L)Pd Cl] (8a ).

−1

3

II

C (O)OMe) ppm. IR (thin ﬁ lm, ν /cm ): 527(w), 565(vw), 702(m),

7

1

43(w), 783(w), 843(vw), 902(vw), 994(vw), 1072(vw), 1096(w),

175(m), 1223(br, m), 1305(w), 1356(w), 1438(m), 1453(m),

518(br, s) (C(O)NH), 1557(m), 1579(m), 1680(br, s) (ν (C O)

in C(O)NH), 1743(br, s) (ν (C O) in C(O)OMe), 2851(vw),

2921(w), 2952(w), 3028(vw), 3060(vw), 3379(br, w) (ν (NH)).

Anal. Calcd for C H ClN O S: C, 57.06; H, 5.05; N, 7.39. Found:

C, 57.45; H, 5.40; N, 7.08.

Methyl S-Allyl-N-[(4-chloropyridin-2-yl)carbonyl]-

homocysteinate (7b ).

Yield: 70 mg (75%). Mp: 185 −187 °C. H NMR (500.13 MHz,

CDCl , major isomer (M) 66%, minor isomer (m) 34%): δ 2.99 (dd,

S (M), J HH = 11.4 Hz, J HH = 6.5 Hz), 3.13 −3.22 (m, 1H,

CH S (M) + 2H, CH S (m)), 3.74 (s, 3H, OMe (M)), 3.88 (s, 3H,

2

OMe (m)), 4.33 and 4.36 (ABq, 2H, C H Ph (m), J = 13.8 Hz),

2

AB

4

.38 and 4.40 (ABq, 2H, C H Ph (M), J = 13.8 Hz), 4.71 (dd, 1H,

2 AB

3

CH (m), J = 6.9 Hz, J = 3.4 Hz), 4.74 (dd, 1H, CH (M), J

=

HH

3

6.5 Hz, J = 2.1 Hz), 7.36 −7.44 (m, 1H, H(C15) (M) + 1H,

HH

H(C15) (m) + 2H, H(C14) + H(C16) (M) + 2H, H(C14) +

H(C16) (m) + 2H, H(C13) + H(C17) (m)), 7.50 −7.52 (m, 2H,

H(C13) + HC(17) (M)), 7.55 −7.60 (m, 1H, H(C4) (M) + 1H,

H(C4) (m)), 7.90 −7.93 (m, 1H, H(C2) (M) + 1H, H(C2) (m)),

8.04 −8.08 (m, 1H, H(C3) (M) + 1H, H(C3) (m)), 8.89 (d, 1H,

1

Yield: 0.31 g (54%). H NMR (600.22 MHz, CDCl , 253 K): δ 2.06 −

3

2

.12 (m, 1H, CH ), 2.23 −2.29 (m, 1H, CH ), 2.47 −2.56 (m, 2H,

2

3

CH S), 3.14 (d, 2H, C H CH CH , J = 7.3 Hz), 3.80 (s, 3H,

2

HH

OMe), 4.90 −4.94 (m, 1H, CH), 5.03 −5.07 (m, 2H, CH CH C H ),

.69 −5.76 (m, 1H, CH C H CH ), 7.49 −7.50 (m, 1H, H(C4)),

3

2

H(C5) (M), J = 5.2 Hz), 8.91 (d, 1H, H(C5) (m), J = 5.2 Hz)

HH HH

ppm. C{ H} NMR (125.76 MHz, CDCl ): δ 40.96 (s, C H Ph (m)),

3 2

3

.19 (s, 1H, H(C2)), 8.52 (d, 1H, H(C5), J = 5.2 Hz), 8.54 (br d,

H, NH, J = 8.5 Hz) ppm. C{ H} NMR (150.93 MHz, CDCl ,

HH

3

41.01 (s, CH S (m)), 42.54 (s, C H Ph (M)), 43.92 (s, CH S (M)),

2 2 2

53 K): δ 25.56 (s, CH S), 31.78 (s, CH ), 34.26 (s, C H CH CH ),

2

52.98 (s, OMe (M)), 53.04 (s, OMe (m)), 59.36 (s, CH (M)), 61.58

(s, CH (m)), 125.84 (s, C2 (m)), 125.90 (s, C2 (M)), 127.21 (s, C4

(M)), 127.34 (s, C4 (m)), 128.96 (s, C15 (m)), 129.10 (s, C15

1.48 (s, CH), 53.04 (s, OMe), 117.70 (s, CH CH C H ), 123.08 (s,

2

C2), 126.91 (s, C4), 133.87 (s, CH C H CH ), 145.96 (s, C3),

2

1

49.34 (s, C5), 150.36 (s, C1), 163.15 (s, C(O)NH), 172.23 (s,

(

M)), 129.32 (s, C14 + C16 (m)), 129.40 (s, C14 + C16 (M)),

15

C (O)OMe) ppm. N NMR (60.85 MHz, CDCl , 253 K): δ −273.8

C(O)NH), −85.4 (Py) ppm. IR (thin ﬁ lm, ν /cm ): 527(w),

3

129.57 (s, C13 + C17 (m)), 129.87 (s, C13 + C17 (M)), 132.41 (s,

C12 (M)), 132.68 (s, C12 (m)), 140.32 (s, C3 (M)), 140.41 (s, C3

(m)), 147.85 (s, C5 (m)), 147.94 (s, C5 (M)), 155.61 (s, C1 (M +

m)), 169.42 (s, C(O)N (M)), 169.86 (s, C(O)N (m)), 170.22 (s,

C (O)OMe (M)), 171.71 (s, C (O)OMe (m)) ppm. IR (KBr, ν /

cm ): 504(w), 658(vw), 688(m), 706(m), 758(m), 811(vw),

991(vw), 1020(w), 1049(w), 1072(vw), 1096(w), 1172(m),

1213(m), 1292(m), 1389(s), 1435(w), 1453(w), 1477(w),

1494(w), 1569(w), 1600(s), 1630(s) (ν (C O) in C(O)N),

93(w), 743(m), 783(w), 843(w), 919(w), 994(w), 1097(w),

175(m), 1221(br, m), 1259(w), 1305(w), 1356(m), 1438(m),

462(m), 1519(br, s) (C(O)NH), 1557(m), 1579(m), 1634(w),

679(br, s) (ν (C O) in C(O)NH), 1743(br, s) (ν (C O) in

−

1

C(O)OMe), 2850(vw), 2918(w), 2952(w), 3080(vw), 3379(br, w)

(

ν (NH)). Anal. Calcd for C H ClN O S: C, 51.14; H, 5.21; N,

.52. Found: C, 51.04; H, 5.27; N, 8.34.

14 17 2 3

8

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738(s) (ν (C O) in C(O)OMe), 2934(w), 2992(vw), 3056(w).

147.86 (s, C5 (m)), 147.91 (s, C5 (M)), 155.49 (s, C1 (M)), 155.52

Anal. Calcd for C H ClN O PdS: C, 43.33; H, 3.64; N, 5.94.

(s, C1 (m)), 166.28 (s, CH C (O)OMe (m)), 166.58 (s,

Found: C, 43.31; H, 3.69; N, 5.98.

Complex [κ -S,N,N-(L)Pd Cl] (8b ).

CH C (O)OMe (M)), 169.41 (s, C(O)N (M)), 169.72 (s, C(O)N

2

3

II

(m)), 170.07 (s, C (O)OMe (M)), 171.59 (s, C (O)OMe (m)) ppm.

−

1

IR (KBr, ν /cm ): 505(vw), 659(vw), 683(w), 759(w), 809(vw),

8

87(vw), 1015(w), 1094(w), 1170(m), 1202(m), 1274(m),

1

291(m), 1308(m), 1386(m), 1435(m), 1601(s), 1636(s) (ν (C 

O) in C(O)N), 1741(s) (ν (C O) in C(O)OMe), 2853(vw),

2

6

953(w). Anal. Calcd for C H ClN O PdS: C, 34.45; H, 3.34; N,

13 15 2 5

.18. Found: C, 34.48; H, 3.41; N, 6.31.

1

Yield: 68 mg (82%). Mp: 142 −144 °C. H NMR (400.13 MHz,

3

II

Complex [κ -S,N,N-(L)Pd Cl] (9a ).

CDCl , major isomer (M) 72%, minor isomer (m) 28%): δ 3.16 (dd,

H, CH S (M), J = 11.3 Hz, J = 6.7 Hz), 3.26 −3.38 (m, 1H,

2

HH

CH S (M) + 2H, CH S (m)), 3.48 (dd, 1H, C H CH CH (M),

2

3

J

= 13.7 Hz, J = 8.1 Hz), 3.66 (dd, 1H, C H CH CH (m),

HH

2

3

^J HH = 13.5 Hz, J = 5.9 Hz), 3.77 −3.88 (m, 1H, C H CH CH

HH 2 2

(

3

M) + 1H, C H CH CH (m)), 3.78 (s, 3H, OMe (M)), 3.82 (s,

2

1

3

Yield: 91 mg (91%). Mp: 151 −153 °C. H NMR (400.13 MHz,

CDCl , major isomer (M) 64%, minor isomer (m) 36%): δ 2.97 (dd,

H, OMe (m)), 4.70 (dd, 1H, CH (m), J = 6.8 Hz, J = 3.8

HH HH

3

Hz), 4.85 (dd, 1H, CH (M), J = 6.7 Hz, J = 1.7 Hz), 5.36 (d,

H, CH S (M), J = 11.4 Hz, J = 6.5 Hz), 3.13 −3.24 (m, 1H,

CH S (M) + 2H, CH S (m)), 3.75 (s, 3H, OMe (M)), 3.89 (s, 3H,

1

H, CH CH C H (m), J = 17.1 Hz), 5.38 (d, 1H, CH CH 

C H (M), J = 17.0 Hz), 5.45 (d, 1H, CH CH C H (m), J

OMe (m)), 4.30 −4.42 (m, 2H, C H Ph (M) + 2H, C H Ph (m)),

1

5

0.1 Hz), 5.49 (d, 1H, CH CH C H (M), J = 10.1 Hz), 5.89 −

2

HH

4

.70 −4.75 (m, 1H, CH (M) + 1H, CH (m)), 7.35 −7.45 (m, 1H,

.99 (m, 1H, CH C H CH (m)), 6.18 −6.28 (m, 1H, CH C H 

2

H(C15) (M) + 1H, H(C15) (m) + 2H, H(C14) + H(C16) (M) +

CH (M)), 7.54 −7.59 (m, 1H, H(C4) (M) + 1H, H(C4) (m)), 7.90

H, H(C14) + H(C16) (m) + 2H, H(C13) + H(C17) (m)), 7.50 −

(

dd, 1H, H(C2) (m), J = 7.8 Hz, J = 1.5 Hz), 7.93 (dd, 1H,

HH HH

3

4

.53 (m, 2H, H(C13) + H(C17) (M)), 7.55 −7.59 (m, 1H, H(C4)

H(C2) (M), J = 7.9 Hz, J = 1.6 Hz), 8.03 −8.08 (m, 1H,

HH

4

(

M) + 1H, H(C4) (m)), 7.90 (d, 1H, H(C2) (m), J = 2.4 Hz),

.91 (d, 1H, H(C2) (M), J = 2.4 Hz), 8.81 (d, 1H, H(C5) (M),

H(C3) (M) + 1H, H(C3) (m)), 8.85 −8.88 (m, 1H, H(C5), (M) +

H, H(C5) (m)) ppm. C{ H} NMR (100.61 MHz, CDCl ): δ

HH

3

J

= 5.9 Hz), 8.82 (d, 1H, H(C5) (m), J = 5.9 Hz) ppm.

HH

3

9.47 (s, C H CH CH (m)), 40.43 (s, C H CH CH (M)), 40.93

(s, CH S (m)), 42.78 (s, CH S (M)), 53.00 (s, OMe (m)), 53.04 (s,

C{ H} NMR (100.61 MHz, CDCl

3

): δ 41.01 and 41.05 (both s,

2

OMe (M)), 59.37 (s, CH (M)), 61.50 (s, CH (m)), 122.90 (s,

C H Ph (m) and CH S (m)), 42.57 (s, C H Ph (M)), 43.93 (s, CH S

2

CH CH C H (M)), 123.13 (s, CH CH C H (m)), 125.84 (s, C2

(M)), 53.04 (s, OMe (M)), 53.10 (s, OMe (m)), 59.45 (s, CH (M)),

61.75 (s, CH (m)), 126.30 (s, C2 (m)), 126.35 (s, C2 (M)), 127.35

(s, C4 (M)), 127.47 (s, C4 (m)), 129.03 (s, C15 (m)), 129.19 (s,

C15 (M)), 129.36 (s, C14 + C16 (m)), 129.44 (s, C14 + C16 (M)),

129.57 (s, C13 + C17 (m)), 129.89 (s, C13 + C17 (M)), 132.22 (s,

C12 (M)), 132.52 (s, C12 (m)), 148.46 (s, C5 (m)), 148.54 (s, C5

(M)), 149.12 (s, C3 (M)), 149.22 (s, C3 (m)), 156.73 (s, C1 (M +

m)), 168.31 and 169.98 (both s, C(O)N (M) and C (O)OMe (M))

ppm (the signals of C(O)N (m) and C (O)OMe (m) carbon nuclei

2

(

m)), 125.88 (s, C2 (M)), 127.23 (s, C4 (M)), 127.34 (s, C4 (m)),

1

29.20 (s, CH C H CH (m)), 130.14 (s, CH C H CH (M)),

2

40.32 (s, C3 (M)), 140.43 (s, C3 (m)), 147.77 (s, C5 (m)), 147.85

(s, C5 (M)), 155.59 (s, C1 (m)), 155.64 (s, C1 (M)), 169.45 (s,

C(O)N (M)), 169.81 (s, C(O)N (m)), 170.39 (s, C (O)OMe (M)),

71.40 (s, C (O)OMe (m)) ppm. IR (KBr, ν /cm ): 499(w), 685(w),

67(w), 945(w), 1010(w), 1093(w), 1164(m), 1212(m), 1292(w),

330(w), 1382(m), 1431(w), 1602(s), 1641(s) (ν (C O) in

−

1

C(O)N), 1752(s) (ν (C O) in C(O)OMe), 2951(vw), 2994(vw),

were not observed). IR (KBr, ν /cm ): 533(w), 702(m), 767(m),

843(w), 912(vw), 1021(w), 1107(w), 1171(m), 1202(m), 1252(w),

1364(m), 1422(m), 1454(w), 1495(w), 1553(w), 1595(s), 1641(s)

(ν (C O) in C(O)N), 1742(s) (ν (C O) in C(O)OMe), 2951(w),

3

6

075(vw). Anal. Calcd for C H ClN O PdS: C, 37.07; H, 3.59; N,

13 15 2 3

.65. Found: C, 36.93; H, 3.88; N, 6.75.

3

II

Complex [κ -S,N,N-(L)Pd Cl] (8c ).

3

030(vw), 3065(vw). Anal. Calcd for C H Cl N O PdS: C, 40.38;

17 16 2 2 3

H, 3.19; N, 5.54. Found: C, 40.51; H, 3.28; N, 5.44.

3

II

Complex [κ -S,N,N-(L)Pd Cl] (9b ).

1

Yield: 80 mg (89%). Mp: 136 −138 °C. H NMR (400.13 MHz,

CDCl , major isomer (M) 64%, minor isomer (m) 36%): δ 3.42 (dd,

H, CH S (M), J = 11.4 Hz, J = 6.5 Hz), 3.52 (dd, 1H, CH S

m), J = 14.0 Hz, J = 7.0 Hz), 3.65 (dd, 1H, CH S (m), J =

Yield: 83 mg (92%). Mp: 141 −143 °C. H NMR (500.13 MHz,

4.0 Hz, J = 3.0 Hz), 3.75 (dd, 1H, CH S (M), J = 11.4 Hz,

J _H _H = 1.9 Hz), 3.80 (s, 3H, OMe (M)), 3.81 (s, 3H, OMe (m)), 3.83

CDCl , major isomer (M) 73%, minor isomer (m) 27%): δ 3.15 (dd,

1H, CH S (M), J = 11.3 Hz, J = 6.6 Hz), 3.26 −3.31 (m, 1H,

s, 3H, OMe (m)), 3.84 (s, 3H, OMe (M)), 3.85 −3.89 (m, 1H,

S (m)), 3.37 (dd, 1H, CH

C H C(O)OMe (m)), 4.11 and 4.15 (ABq, 2H, C H C(O)OM (M),

J _A _B = 16.4 Hz), 4.23 (d, 1H, C H C(O)OMe (m), J = 16.4 Hz),

4

Hz, J = 3.6 Hz), 3.47 (dd, 1H, C H CH CH (M), J = 13.8

Hz, J = 8.1 Hz), 3.66 (dd, 1H, C H CH CH (m), J = 13.7

.74 (dd, 1H, CH (m), J = 7.0 Hz, J = 3.0 Hz), 4.83 (dd, 1H,

Hz, J = 5.9 Hz), 3.77 −3.87 (m, 1H, C H CH CH (M) + 1H,

HH

HH 2 2

3

CH (M), J = 6.5 Hz, J = 1.9 Hz), 7.51 −7.59 (m, 1H, H(C4)

C H CH CH (m)), 3.79 (s, 3H, OMe (M)), 3.83 (s, 3H, OMe

(m)), 4.72 (dd, 1H, CH (m), J = 7.0 Hz, J = 3.6 Hz), 4.84 (dd,

M) + 1H, H(C4) (m)), 7.87 −7.90 (m, 1H, H(C2) (m)), 7.94 −7.96

3

m, 1H, H(C2) (M)), 8.03 −8.08 (m, 1H, H(C3) (M) + 1H, H(C3)

1H, CH (M), J = 6.6 Hz, J = 1.7 Hz), 5.37 (d, 1H, CH CH 

m)), 8.74 (d, 1H, H(C5) (M), J = 5.4 Hz), 8.84 (d, 1H, H(C5)

C H (m), J = 17.1 Hz), 5.39 (d, 1H, CH CH C H (M), J

m), J = 5.9 Hz) ppm. C{ H} NMR (100.61 MHz, CDCl ): δ

17.0 Hz), 5.46 (d, 1H, CH CH C H (m), J = 10.1 Hz), 5.51 (d,

7.23 (s, C H C(O)OMe (m)), 40.03 (s, C H C(O)OMe (M)), 43.49

1H, CH CH C H (M),

= 10.0 Hz), 5.89 −5.98 (m, 1H,

2

(

s, CH S (m)), 46.93 (s, CH S (M)), 53.10 (s, OMe (M)), 53.13 (s,

CH C H CH (m)), 6.19 −6.27 (m, 1H, CH C H CH (M)),

2

OMe (m)), 53.38 (s, OMe (m)), 53.43 (s, OMe (M)), 59.66 (s, CH

M)), 61.25 (s, CH (m)), 125.98 (s, C2 (m)), 126.16 (s, C2 (M)),

27.24 (s, C4 (M)), 127.44 (s, C4 (m)), 140.55 (s, C3 (m + M)),

7.54 −7.57 (m, 1H, H(C4) (M) + 1H, H(C4) (m)), 7.90 (d, 1H,

4

(

1

H(C2) (m), J = 2.1 Hz), 7.93 (d, 1H, H(C2) (M), J = 2.2

HH HH

3

Hz), 8.78 (d, 1H, H(C5) (M), J = 5.7 Hz), 8.79 (d, 1H, H(C5)

HH

9

892

https://doi.org/10.1021/acs.inorgchem.1c01138

Inorg. Chem. 2021, 60, 9880−9898

Inorganic Chemistry

pubs.acs.org/IC

Article

1

³ J _H _H = 6.8 Hz), 2.53 −2.58 (m, 1H, CH (m)), 2.60 −2.64 (m, 1H,

(

3

(

m), ³ J _H _H = 5.0 Hz) ppm. ¹ ³ C{ H} NMR (125.76 MHz, CDCl ): δ

3

2

9.56 (s, C H CH CH (m)), 40.52 (s, C H CH CH (M)), 40.98

CH (M)), 3.71 (s, 3H, OMe (M + m)), 4.24 (d, 1H, C H Ph (M),

2

s, CH S (m)), 42.83 (s, CH S (M)), 53.05 (s, OMe (m)), 53.09 (s,

J _H _H = 13.6 Hz), 4.30 (d, 1H, C H Ph (m), J = 13.6 Hz), 4.53 (d,

H, C H Ph (m), J = 13.6 Hz), 4.54 (d, 1H, C H Ph (M), J

2

2 HH

2

OMe (M)), 59.49 (s, CH (M)), 61.67 (s, CH (m)), 123.04 (s,

CH CH C H (M)), 123.27 (s, CH CH C H (m)), 126.32 (s, C2

2

13.6 Hz), 4.57 −4.58 (m, 1H, CH (m)), 4.67 −4.68 (m, 1H, CH

(

1

(

m)), 126.36 (s, C2 (M)), 127.32 (s, C4 (M)), 127.43 (s, C4 (m)),

(

M)), 7.38 −7.46 (m, 5H, H (M) + 5H, H (m)), 7.56 −7.58 (m,

Ar

29.05 (s, CH C H CH (m)), 130.04 (s, CH C H CH (M)),

2

1H, H(C4) (M) + 1H, H(C4) (m)), 7.99 −8.01 (m, 1H, H(C2) (M)

48.38 (s, C5 (m)), 148.45 (s, C5 (M)), 149.10 (s, C3 (M)), 149.22

+

1H, H(C2) (m)), 8.05 −8.07 (m, 1H, H(C3) (M) + 1H, H(C3)

s, C3 (m)), 156.74 (s, C1 (m)), 156.80 (s, C1 (M)), 168.33 (s,

C(O)N (M)), 168.71 (s, C(O)N (m)), 170.15 (s, C (O)OMe (M)),

3

13

1

(m)), 9.13 (d, 1H, H(C5) (M + m), J = 5.5 Hz) ppm. C{ H}

HH

NMR (150.93 MHz, CDCl , 263 K): δ 21.62 (s, CH S (M)), 24.11

71.18 (s, C (O)OMe (m)) ppm. IR (KBr, ν /cm ): 516(w), 541(w),

41(w), 767(m), 856(w), 934(w), 991(w), 1033(w), 1110(m),

166(w), 1202(m), 1251(w), 1348(sh, m), 1359(m), 1416(m),

456(w), 1551(w), 1595(s), 1640(s) (ν (C O) in C(O)N), 1741(s)

(

s, CH S (m)), 30.53 (s, CH (m)), 30.69 (s, CH (M)), 41.64 (s,

2 2 2

C H Ph (M)), 43.79 (s, C H Ph (m)), 52.57 (s, OMe (M + m)), 52.73

2

(

s, CH (M)), 53.61 (s, CH (m)), 125.59 (s, C2 (M + m)), 126.92 (s,

C4 (M + m)), 128.85 (s, C16 (m)), 129.00 (s, C16 (M)), 129.28 (s,

C15 + C17 (m)), 129.43 (s, C15 + C17 (M)), 129.82 (s, C14 + C18

(m)), 129.94 (s, C14 + C18 (M)), 133.01 (s, C13 (M)), 133.33 (s,

C13 (m)), 140.44 (s, C3 (m)), 140.49 (s, C3 (M)), 147.87 (s, C5

(

ν (C O) in C(O)OMe), 2935(w), 3085(vw). Anal. Calcd for

C H Cl N O PdS: C, 34.27; H, 3.10; N, 6.15. Found: C, 34.41; H,

13 14 2 2 3

3

.19; N, 6.28.

3

II

Complex [κ -S,N,N-(L)Pd Cl] (9c ).

(m)), 147.93 (s, C5 (M)), 153.21 (s, C1 (M + m)), 172.28 (s,

C (O)OMe (M)), 172.79 (s, C (O)OMe (m)), 173.15 (s, C(O)N

1

5

(

m)), 173.20 (s, C(O)N (M)) ppm. N NMR (60.85 MHz, CDCl ,

95 K): δ −250.5 (C(O)N), −158.7 (Py) ppm. IR (KBr, ν /cm ):

97(vw), 571(vw), 660(vw), 689(w), 708(m), 755(w), 783(m),

10(vw), 845(vw), 874(vw), 969(vw), 1017(w), 1055(w), 1067(w),

1

1116(w), 1215(m), 1253(m), 1280(w), 1295(w), 1380(m), 1419(w),

436(w), 1481(w), 1570(w), 1597(s), 1625(s) (ν (C O) in

C(O)N), 1718(s) (ν (C O) in C(O)OMe), 2851(vw), 2937(vw),

3027(vw). Anal. Calcd for C 18 PdS · 0.2 CH Cl : C, 43.52;

H, 3.89; N, 5.58. Found: C, 43.33; H, 4.14; N, 5.66.

Yield: 43 mg (45%). Mp: 123 −125 °C. H NMR (500.13 MHz,

1

CDCl , major isomer (M) 61%, minor isomer (m) 39%): δ 3.37 (br s,

H, CH S (M)), 3.49 (dd, 1H, CH S (m), J = 13.9 Hz, J = 6.9

Hz), 3.65 −3.68 (m, 1H, CH S (m)), 3.75 (br d, 1H, CH S (M), J

10.3 Hz), 3.80 (s, 3H, OMe in C(O)OMe (M)), 3.81 (s, 3H, OMe

in C(O)OMe (m)), 3.84 (s, 3H, OMe in CH C(O)OMe (m)), 3.85

2

HH

=

3

II

Complex [κ -S,N,N-(L)Pd Cl] (10b ).

2

(

s, 3H, OMe in CH C(O)OMe (M)), 3.85 −3.88 (m, 1H,

2

C H C(O)OMe (m)), 4.00 (d, 1H, C H C(O)OMe (M),

6.3 Hz), 4.13 (d, 1H, C H C(O)OMe (M), J = 16.3 Hz), 4.22 (d,

2 HH

2

H, C H C(O)OMe (m), J = 16.4 Hz), 4.75 −4.77 (m, 1H, CH

m)), 4.85 (br s, 1H, CH (M)), 7.54 (dd, 1H, H(C4) (M), J = 5.9

Hz, J = 2.1 Hz), 7.56 (dd, 1H, H(C4) (m), J = 5.9 Hz, J =

2

H(C2) (M), J = 2.1 Hz), 8.74 (d, 1H, H(C5) (M), J = 5.9

Hz), 8.77 (d, 1H, H(C5) (m), J = 5.9 Hz) ppm. C{ H} NMR

HH

4

.2 Hz), 7.89 (d, 1H, H(C2) (m), J = 2.2 Hz), 7.93 (d, 1H,

Yield: 70 mg (81%). Mp: 152 −154 °C. H NMR (600.22 MHz,

CDCl , 263 K, major isomers (M) 51%, minor isomers (m) 49%): δ

3

HH

1

.83 −1.88 (m, 1H, CH (M)), 2.03 −2.07 (m, 1H, CH (m)), 2.14 −

(

100.61 MHz, CDCl ): δ 37.26 (s, C H C(O)OMe (m)), 39.97 (s,

2

3

2

.20 (m, 1H, CH S (M) + 1H, CH S (m)), 2.38 (dd, 1H, CH S (m),

C H C(O)OMe (M)), 43.50 (s, CH S (m)), 47.00 (s, CH S (M)),

2

3

2

^J HH = 14.5 Hz, J = 5.3 Hz), 2.46 (dd, 1H, CH S (M), J = 12.8

5

3.16 (s, OMe (M)), 53.20 (s, OMe (m)), 53.42 (s, OMe (m)),

3.49 (s, OMe (M)), 59.71 (s, CH (M)), 61.41 (s, CH (m)), 126.42

Hz, J HH = 6.5 Hz), 2.61 −2.70 (m, 1H, CH

3.46 (dd, 1H, C H

3.74 (s, 3H, OMe (m)), 3.75 (s, 3H, OMe (M)), 3.74 −3.79 (m, 1H,

C H

(M) + 1H, CH

(m)),

(M), J HH = 13.5 Hz, J HH = 8.0 Hz),

2

3

(

s, C2 (m)), 126.51 (s, C2 (M)), 127.41 (s, C4 (M)), 127.54 (s, C4

m)), 148.46 (s, C5 (m)), 148.55 (s, C5 (M)), 149.29 (s, C3 (M)),

2

CH CH

1

49.38 (s, C3 (m)), 156.67 (s, C1 (m + M)), 166.15 (s,

2

CH CH

2

(m)), 3.82 −3.85 (m, 1H, C H

CH C (O)OMe (m)), 166.42 (s, CH C (O)OMe (M)), 168.29 (br

(M), J HH = 13.5 Hz, J HH = 6.9 Hz), 4.63 −

2

s, C(O)N (M)), 168.63 (br s, C(O)N (m)), 169.85 (s, C (O)OMe

4.64 (m, 1H, CH (M)), 4.66 −4.67 (m, 1H, CH (m)), 5.27 (d, 1H,

CH

(m), J HH = 16.9 Hz), 5.39 −5.42 (m, 1H, CH

(M)), 171.39 (s, C (O)OMe (m)) ppm. IR (KBr, ν /cm ): 534(w),

2

CH C H

2

(M), J HH = 16.9 Hz), 5.34 (d, 1H, CH

CH C H

C H =CH

(M)), 7.53 −7.56 (m, 1H, H(C4) (M) +

96(vw), 767(w), 846(w), 912(vw), 1015(w), 1033(w), 1107(w),

170(m), 1202(m), 1273(br, m), 1308(m), 1365(m), 1423(m),

435(m), 1553(w), 1596(s), 1640(s) (ν (C O) in C(O)N), 1741(s)

2

CH C H

(m)), 5.95 −6.02 (m, 1H, CH

ν (C O) in C(O)OMe), 2849(vw), 2953(w), 3000(vw), 3087(vw).

1H, H(C4) (m)), 7.97 −7.99 (m, 1H, H(C2) (M) + 1H, H(C2)

Anal. Calcd for C H Cl N O PdS: C, 32.02; H, 2.89; N, 5.74.

(m)), 8.03 −8.06 (m, 1H, H(C3) (M) + 1H, H(C3) (m)), 9.06 −9.08

(m, 1H, H(C5) (M) + 1H, H(C5) (m)) ppm. ¹ C{ H} NMR

3

1

Found: C, 32.07; H, 2.91; N, 5.49.

3

II

Complex [κ -S,N,N-(L)Pd Cl] (10a ).

(150.93 MHz, CDCl

CH S (M)), 30.41 (s, CH (M)), 31.24 (s, CH (m)), 41.18 (s,

3

, 263 K): δ 22.11 (s, CH S (m)), 23.09 (s,

2

C H CH CH (m)), 42.07 (s, C H CH CH (M)), 52.57 (s, OMe

2

(

1

M)), 52.61 (s, OMe (m)), 52.69 (s, CH (m)), 53.11 (s, CH (M)),

22.10 (s, CH CH C H (M)), 122.70 (s, CH CH C H (m)),

2

25.56 (s, C2 (M + m)), 126.91 (s, C4 (M + m)), 130.57 (s,

CH C H CH (m)), 130.95 (s, CH C H CH (M)), 140.44 (s, C3

2

(

1

M)), 140.49 (s, C3 (m)), 147.74 (s, C5 (m)), 147.84 (s, C5 (M)),

53.03 (s, C1 (M)), 153.17 (s, C1 (m)), 172.35 (s, C (O)OMe (m)),

72.60 (s, C (O)OMe (M)), 173.14 (br s, C(O)N (M + m)) ppm. IR

1

−1

Yield: 90 mg (90%). Mp: >250 °C. H NMR (600.22 MHz, CDCl ,

(KBr, ν /cm ): 500(w), 659(vw), 683(w), 759(w), 809(vw), 933(w),

991(vw), 1053(w), 1073(w), 1094(w), 1121(w), 1171(m), 1199(m),

1293(w), 1376(m), 1426(w), 1440(w), 1481(vw), 1571(w), 1599(s),

1621(s) (ν (C O) in C(O)N), 1743(m) (ν (C O) in C(O)OMe),

2849(vw), 2949(w), 2975(w), 3077(vw). Anal. Calcd for

3

2

63 K, major isomers (M) 59%, minor isomers (m) 41%): δ 1.81 −

1

(

.86 (m, 1H, CH (m)), 1.90 −1.95 (m, 1H, CH (M)), 1.98 −2.07

2

m, 1H, CH S (M) + 1H, CH S (m)), 2.13 (dd, 1H, CH S (M), J

14.5 Hz, J = 5.2 Hz), 2.27 (dd, 1H, CH S (m), J = 13.0 Hz,

HH 2 HH

9

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Inorg. Chem. 2021, 60, 9880−9898

Inorganic Chemistry

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Article

C H ClN O PdS: C, 38.63; H, 3.94; N, 6.44. Found: C, 38.70; H,

(M)), 53.64 (s, CH (m)), 126.05 (s, C2 (M + m)), 127.06 (s, C4 (M

+ m)), 128.95 (s, C16 (m)), 129.10 (s, C16 (M)), 129.33 (s, C15 +

C17 (m)), 129.49 (s, C15 + C17 (M)), 129.85 (s, C14 + C18 (m)),

Complex [κ -S,N,N-(L)Pd Cl] (10c ).

3

II

1

(

1

29.96 (s, C14 + C18 (M)), 132.82 (s, C13 (M)), 133.14 (s, C13

m)), 148.50 (s, C5 (m)), 148.57 (s, C5 (M)), 149.09 (s, C3 (m)),

49.14 (s, C3 (M)), 154.13 (s, C1 (m)), 154.25 (s, C1 (M)), 172.03

(

s, C (O)OMe or C(O)N (m)), 172.07 (s, C (O)OMe or C(O)N

M)), 172.09 (s, C (O)OMe or C(O)N (M)), 172.57 (s, C (O)OMe

(

−

1

or C(O)N (m)) ppm. IR (KBr, ν /cm ): 571(vw), 658(vw), 708(m),

7

1

63(m), 783(m), 849(w), 900(vw), 945(vw), 967(vw), 1015(w),

065(w), 1115(w), 1196(m), 1216(m), 1254(m), 1298(w), 1325(w),

1

Yield: 86 mg (93%). Mp: 159 −161 °C. H NMR (600.22 MHz,

1359(m), 1423(m), 1494(vw), 1557(w), 1597(s), 1618(s) and

1628(s) (both ν (C O) in C(O)N), 1717(s) (ν (C O) in

C(O)OMe), 2851(vw), 2953(vw), 3028(vw), 3075(vw). Anal.

Calcd for C H Cl N O PdS: C, 41.60; H, 3.49; N, 5.39. Found:

CDCl , 233 K, major isomers (M) 51%, minor isomers (m) 49%): δ

3

1

2

.83 −1.89 (m, 1H, CH (m)), 2.09 −2.14 (m, 1H, CH (M)), 2.24 −

2

.34 (m, 1H, CH S (M) + 1H, CH S (m)), 2.65 −2.74 (m, 1H, CH

M) + 1H, CH (m) + 1H, CH S (m)), 2.99 (dd, 1H, CH S (M),

2

C, 41.43; H, 3.66; N, 5.48.

2

3

II

^J HH = 12.8 Hz, J = 6.4 Hz), 3.76 (s, 3H, OMe in C(O)OMe

m)), 3.79 (s, 3H, OMe in C(O)OMe (M)), 3.82 (s, 3H, OMe in

HH

Complex [κ -S,N,N-(L)Pd Cl] (11b ).

(

CH C(O)OMe (M)), 3.83 (s, 3H, OMe in CH C(O)OMe (m)),

2

3

.97 (d, 1H, C H C(O)OMe (m), J = 16.6 Hz), 4.01 (d, 1H,

2 HH

2

C H C(O)OMe (M), J _H _H = 16.7 Hz), 4.20 −4.26 (m, 1H,

2

C H C(O)OMe (M) + 1H, C H C(O)OMe (m)), 4.63 −4.65 (m,

2

1

H, CH (m)), 4.67 −4.68 (m, 1H, CH (M)), 7.54 −7.58 (m, 1H,

H(C4) (M) + 1H, H(C4) (m)), 7.97 −7.99 (m, 1H, H(C2) (M) +

1

(

H, H(C2) (m)), 8.06 −8.09 (m, 1H, H(C3) (M) + 1H, H(C3)

1

Yield: 88 mg (95%). Mp: 146 −148 °C. H NMR (600.22 MHz,

3

m)), 9.01 (d, 1H, H(C5) (m), J = 5.5 Hz), 9.04 (d, 1H, H(C5)

HH

CDCl , 253 K, isomers A 50%, isomers B 50%): δ 1.81 −1.87 (m, 1H,

M), J = 5.6 Hz) ppm. C{ H} NMR (150.93 MHz, CDCl , 233

HH

3

CH (A)), 2.01 −2.06 (m, 1H, CH (B)), 2.11 −2.16 (m, 1H, CH S

2

K): δ 24.58 (s, CH S (m)), 26.66 (s, CH S (M)), 30.86 (s, CH (M +

A) + 1H, CH S (B)), 2.36 (dd, 1H, CH S (B), J = 14.5 Hz, J

2 2 HH HH

m)), 38.16 (s, C H C(O)OMe (m)), 41.42 (s, C H C(O)OMe (M)),

5.4 Hz), 2.45 (dd, 1H, CH S (A), J = 12.9 Hz, J = 6.5 Hz),

2 HH HH

5

2.68 (s, CH (M)), 52.98 (br s, OMe in C(O)OMe (M + m)), 53.07

2

.60 −2.68 (m, 1H, CH (A) + 1H, CH (B)), 3.41 (dd, 1H,

2

(

s, CH (m)), 53.86 (br s, OMe in CH C(O)OMe (M + m)), 125.75

s, C2 (m)), 125.79 (s, C2 (M)), 127.20 (s, C4 (M + m)), 140.76 (s,

2

3

2

C H CH CH (A), J = 13.5 Hz, J = 8.0 Hz), 3.72 and 3.73

2

HH

(

both s, 3H + 3H, OMe (A and B)), 3.72 −3.83 (m, 2H, C H CH 

2

C3 (M)), 140.85 (s, C3 (m)), 147.91 (s, C5 (M + m)), 152.79 (s, C1

m)), 152.85 (s, C1 (M)), 167.17 (s, CH C (O)OMe (m)), 167.30 (s,

2

3

CH (B)), 3.87 (dd, 1H, C H CH CH (A), J = 13.5 Hz, J

.8 Hz), 4.58 −4.59 (m, 1H, CH (A)), 4.61 −4.63 (m, 1H, CH (B)),

CH C (O)OMe (M)), 172.37 (s, C (O)OMe (m)), 172.96 (s,

.26 (d, 1H, CH CH C H (A), J = 16.8 Hz), 5.33 (d, 1H,

2

HH

C (O)OMe (M)), 173.28 (s, C(O)N (M + m)) ppm. IR (KBr, ν /

(B), J HH = 16.9 Hz), 5.38 −5.42 (m, 1H, CH

2

CH 

cm ): 496(vw), 685(w), 755(w), 972(vw), 1013(w), 1054(vw),

C H (A) + 1H, CH CH C H (B)), 5.92 −5.99 (m, 1H, CH C H 

2

1

117(w), 1170(w), 1213(m), 1264(m), 1294(m), 1380(m),

436(m), 1481(vw), 1570(w), 1597(s), 1625(s) (ν (C O) in

CH (B)), 6.12 −6.19 (m, 1H, CH C H CH (A)), 7.51 −7.52 (m,

2

1

H, H(C4) (A) + 1H, H(C4) (B)), 7.93 −7.95 (m, 1H, H(C2) (A) +

H, H(C2) (B)), 8.94 −8.96 (m, 1H, H(C5) (A) + 1H, H(C5) (B))

C(O)N), 1718(s) and 1734(s) (both ν (C O) in C(O)OMe),

2

843(vw), 2929(w), 2950(w), 2999(vw). Anal. Calcd for

1

3

1

ppm. C{ H} NMR (150.93 MHz, CDCl , 253 K): δ 22.02 (s, CH S

3

2

C H ClN O PdS: C, 35.99; H, 3.67; N, 6.00. Found: C, 36.14;

B)), 23.01 (s, CH S (A)), 30.29 (s, CH (A)), 31.11 (s, CH (B)),

2 2 2

H, 3.71; N, 5.91.

Complex [κ -S,N,N-(L)Pd Cl] (11a ).

3

II

41.22 (s, C H CH CH (B)), 42.06 (s, C H CH CH (A)), 52.67 −

2

52.70 (m, overlapping signals of OMe (A and B) and CH (B)), 53.12

(

s, CH (A)), 122.32 (s, CH CH = C H (A)), 122.97 (s, CH CH 

2

C H (B)), 125.98 (s, C2 (A + B)), 127.05 (s, C4 (A + B)), 130.36 (s,

2

CH C H CH (B)), 130.81 (s, CH C H CH (A)), 148.37 and

2

148.47 (both s, C5 (A and B), 149.04 and 149.10 (both s, C3 (A and

B)), 154.06 and 154.19 (both s, C1 (A and B), 172.00 (br s, C(O)N

A and B)), 172.13 (s, C (O)OMe (B)), 172.38 (s, C (O)OMe (A))

(

−

1

ppm. IR (KBr, ν /cm ): 503(vw), 536(w), 698(vw), 739(w),

58(m), 785(w), 833(w), 945(vw), 961(vw), 1010(w), 1035(vw),

1071(vw), 1112(w), 1125(w), 1160(m), 1174(m), 1197(m),

7

1

Yield: 85 mg (83%). Mp: 208 −210 °C dec. H NMR (500.13 MHz,

1

254(w), 1329(w), 1353(m), 1427(m), 1435(w), 1557(w),

595(s), 1619(s) (ν (C O) in C(O)N), 1747(m) (ν (C O) in

CDCl , 253 K, major isomers (M) 59%, minor isomers (m) 41%): δ

3

1

.80 −2.05 (m, 1H, CH (M) + 1H, CH (m) + 1H, CH S (M) + 1H,

2

3

C(O)OMe), 2948(w), 3072(vw). Anal. Calcd for

C

H, 3.75; N, 5.62.

CH S (m)), 2.12 (dd, 1H, CH S (M), J = 14.2 Hz, J = 5.3

Hz), 2.27 (dd, 1H, CH S (m), J = 12.9 Hz, J = 5.3 Hz), 2.53 −

PdS: C, 35.80; H, 3.43; N, 5.96. Found: C, 36.12;

2

HH

2

.59 (m, 1H, CH (m)), 2.60 −2.65 (m, 1H, CH (M)), 3.70 (s, 3H,

2

3

II

OMe (m)), 3.71 (s, 3H, OMe (M)), 4.24 (d, 1H, C H Ph (M), J

=

HH

Complex [κ -S,N,N-(L)Pd Cl] (11c ).

2

1

7

3.6 Hz), 4.29 (d, 1H, C H Ph (m), J = 13.5 Hz), 4.48 −4.55 (m,

2

HH

H, C H Ph (M) + 1H, C H Ph (m) + 1H, CH (m)), 4.64 −4.65 (m,

2

H, CH (M)), 7.38 −7.45 (m, 5H, H (M) + 5H, H (m)), 7.54 −

.56 (m, 1H, H(C4) (M) + 1H, H(C4) (m)), 7.98 (d, 1H, H(C2)

Ar

4

(

m), J = 2.4 Hz), 7.98 (d, 1H, H(C2) (M), J = 2.4 Hz), 9.03

HH HH

3 3

(

dd, 1H, H(C5) (M), J = 6.0 Hz), 9.04 (dd, 1H, H(C5) (m), J

6.4 Hz) ppm. ¹ C{ H} NMR (125.76 MHz, CDCl , 253 K): δ

1.58 (s, CH S (M)), 24.05 (s, CH S (m)), 30.42 (s, CH (m)),

2 2 2

1

0.61 (s, CH (M)), 41.70 (s, C H Ph (M)), 43.75 (s, C H Ph (m)),

Yield: 55 mg (55%). Mp: 168 −170 °C. H NMR (500.13 MHz,

2

2.69 −52.73 (m, overlapping signals of OMe (M and m) and CH

CDCl , 253 K, major isomers 53%, minor isomers 47%): δ 1.81 −1.88

3

9

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Article

Table 3. Crystal Data and Structure Reﬁnement Parameters for 9a and 10b

9

a

10b

empirical formula

C H Cl N O PdS

C H ClN O PdS

1

7

16

2

3

14 17

2

3

formula wt

505.68

435.20

cryst syst

orthorhombic

monoclinic

space group

P2 2 2

1 1

C2/c

1

Z

4

8

a, Å

b, Å

c, Å

8.8569(6)

11.2668(7)

18.4710(11)

90

1.822

12.5700(16)

15.674(2)

17.247(3)

90

109.428(3)

1.804

β, deg

V, Å³

D_c_a_l_c, g cm⁻

linear absorption μ, cm⁻

F(000)

3

1

14.3

1008

14.67

1744

2

θ_m_a_x, deg

58

no. of rﬂns measd

no. of indep rﬂns

22435

4898

13115

4257

no. of obsd rﬂns (I > 2σ(I))

4694

3550

no. of params

236

200

R1

wR2

0.0262

0.0567

1.110

0.0305

0.0725

1.017

GOF

Δρ_m_a_x/Δρ_m_i_n, e Å⁻

3

1.013/−0.517

0.629/−0.647

(

m, 1H, CH (m)), 2.06 −2.13 (m, 1H, CH (M)), 2.27 −2.38 (m,

in Table 3. All calculations were performed using the SHELXTL

20

2

1

H, CH S (M) + 1H, CH S (m)), 2.66 −2.73 (m, 1H, CH (M) +

software. CCDC 1887955 and 1887957 contain the supplementary

crystallographic data for 10b and 9a, respectively.

2

H, CH (m) + 1H, CH S (m)), 2.96 (dd, 1H, CH S (M), J =

2

HH

3

2.7 Hz, J = 6.5 Hz), 3.76 (s, 3H, OMe in C(O)OMe (m)), 3.79

Cytotoxicity Assays. The cytotoxicities of ligands 2, 3, 6, and 7

and complexes 8−11 were explored against human colon (HCT116),

breast (MCF7), and prostate (PC3) cancer cell lines, as well as

noncancerous human embryonic kidney cells (HEK293) and kidney

epithelial cells (NKE). In the case of complexes 8a,b and 11a−c,

additional experiments were carried out with the transformed breast

cell line HBL100 and its doxorubicin-resistant subline HBL100/Dox.

RPMI-1640 and DMEM media were obtained from Gibco. Fetal

bovine serum (FBS) was purchased from HyClone. Cells were

cultured in RPMI-1640 (in the case of PC3 and HBL100) or DMEM

(in the other cases) media supplemented with 10% FBS and 50 μg/

mL of gentamicin in a humidiﬁed incubator with a 5% CO₂

atmosphere. The eﬀect of the compounds on cell viability was

evaluated by the standard MTT assay (ICN Biomedicals, Germany).

HH

(

s, 3H, OMe in C(O)OMe (M)), 3.83 (s, 3H, OMe in

CH C(O)OMe (M)), 3.84 (s, 3H, OMe in CH C(O)OMe (m)),

3

2

.93 (d, 1H, C H C(O)OMe (m), J = 16.4 Hz), 4.00 (d, 1H,

2

2 HH

2

C H C(O)OMe (M), J _H _H = 16.7 Hz), 4.17 −4.23 (m, 1H,

C H C(O)OMe (M) + 1H, CH C(O)OMe (m)), 4.64 −4.65 (m,

2

1

H, CH (M)), 4.67 −4.68 (m, 1H, CH (m)), 7.52 −7.54 (m, 1H,

H(C4) (M) + 1H, H(C4) (m)), 7.97 −7.98 (m, 1H, H(C2) (M) +

1

CDCl , 253 K): δ 24.79 (s, CH S (m)), 26.65 (s, CH S (M)), 30.86

(

4

3

H, H(C2) (m)), 8.96 (d, 1H, H(C5) (m), J = 6.1 Hz), 8.97 (d,

H, H(C5) (M), J = 6.1 Hz) ppm. C{ H} NMR (125.76 MHz,

HH

3

2

s, CH (M)), 30.96 (s, CH (m)), 38.34 (s, C H C(O)OMe (m)),

2 2 2

1.28 (s, C H C(O)OMe (M)), 52.67 (s, CH (m)), 52.81 (br s, OMe

2

in C(O)OMe (M + m)), 53.02 (s, CH (M)), 53.68 (s, OMe in

CH C(O)OMe (M)), 53.71 (s, OMe in CH C(O)OMe (m)),

3

Cells were seeded in triplicate at a cell density of 5 × 10 /well in 96-

2

1

26.11 (s, C2 (M)), 126.13 (s, C2 (m)), 127.10 (s, C4 (M + m)),

48.52 (s, C5 (M)), 148.57 (s, C5 (m)), 149.22 (s, C3 (M)), 149.30

well plates in 100 μL of complete medium and preincubated for 24 h.

The tested compounds were initially dissolved in DMSO. Then the

compounds at various concentrations were added to the media. The

well plates were incubated for 48 h followed by the addition of MTT

solution (Sigma; 20 μL, 5 mg/mL). The cells were incubated at 37 °C

for a further 3 h; then the culture medium was removed, and

formazan crystals were dissolved in DMSO (70 μL). The absorbances

of the resulting solutions were measured on a multiwell plate reader

(Multiskan FC, Thermo scientiﬁc) at 530 nm to determine the

percentage of surviving cells. The reported values of IC₅₀are the

averages of three independent experiments (Tables 1 and 2).

Cisplatin (in the initial form of an infusion concentrate in natural

saline solution) and doxorubicin from commercial sources were used

as the references.

DNA Binding Experiments. The DNA binding abilities of the

selected complexes from this study were investigated by agarose gel

electrophoresis. In each experiment, a solution of 0.15 μg of

supercoiled pHOT1 plasmid DNA (TopoGEN) in water and the

aforementioned amount of the complex (used as a stock solution in

DMSO; the ﬁnal concentration of the complexes ranged from 40 to

120 μM) was incubated in the dark at 37 °C for 30 min. The samples

of free DNA were used as controls. After incubation, 10 μL aliquots of

the resulting solutions were loaded onto 0.8% agarose gel. The

(s, C3 (m)), 154.09 (s, C1 (M)), 154.16 (s, C1 (m)), 166.96 (s,

CH C (O)OMe (m)), 167.07 (s, CH C (O)OMe (M)), 172.01 −

2

172.04 (m, overlapping signals of C (O)OMe (M and m) and C(O)N

−1

(M or m)), 172.57 (s, C(O)N (m or M)) ppm. IR (KBr, ν /cm ):

5

1

17(vw), 537(vw), 754(w), 786(w), 841(vw), 942(vw), 979(vw),

011(vw), 1034(vw), 1121(w), 1173(m), 1207(m), 1232(w),

291(m), 1355(m), 1388(w), 1433(m), 1558(w), 1594(s), 1626(s)

(

ν (C O) in C(O)N), 1725(s) and 1737(s) (both ν (C O) in

C(O)OMe), 2953(vw), 3061(vw). Anal. Calcd for:

C H Cl N O SPd: C, 33.52; H, 3.21; N, 5.58. Found: C, 33.76;

X-ray Diﬀraction. Single crystals of compounds 9a and 10b were

obtained by slow crystallization from CH Cl /hexane. X-ray

2

diﬀraction experiments were carried out with a SMART APEX2

DUO CCD diﬀractometer using graphite-monochromated Mo Kα

radiation (λ = 0.71073 Å, ω-scans) at 120 K. The structures were

solved by the direct method and reﬁned by full-matrix least squares

2

against F in the anisotropic approximation for non-hydrogen atoms.

The positions of hydrogen atoms were calculated and reﬁned in the

isotropic approximation in a riding model. The crystal data and

structure reﬁnement parameters for the complexes explored are given

9

895

https://doi.org/10.1021/acs.inorgchem.1c01138

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Inorganic Chemistry

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Article

electrophoresis was carried out at 1.5−2.0 V/cm for 8−10 h in TAE

buﬀer. The gels were stained with ethidium bromide (0.5 μg/mL) and

visualized under UV light.

Topoisomerase I Activity Inhibition Studies. The modulation

of topoisomerase I activity by the selected complexes from this study

was explored using a TopoGEN Topoisomerase I Drug Screening Kit.

In the experiments, each speciﬁed complex and one unit of the

puriﬁed topoisomerase from calf thymus (Fermentas, Lithuania) were

incubated with 0.13 μg of supercoiled pHOT1 plasmid DNA

emailing data_request@ccdc.cam.ac.uk , or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

AUTHOR INFORMATION

Corresponding Author

■

Diana V. Aleksanyan − Nesmeyanov Institute of

Organoelement Compounds, Russian Academy of Sciences,

Moscow 119991, Russia; orcid.org/0000-0002-7083-

(

TopoGEN) in a reaction buﬀer (10 mM Tris-HCl, pH 7.9, 1 mM

EDTA, 0.15 M NaCl, 0.1% BSA, 0.1 mM spermidine, 5% glycerol) for

0 min at 37 °C. The reactions were stopped with SDS. After

2537 ; Email: aleksanyan.diana@ineos.ac.ru

3

digestion with proteinase K (50 μg/mL, 30−60 min at 37 °C), the

samples were mixed with a DNA loading buﬀer and loaded onto 0.9%

agarose gel. The electrophoresis was performed at the maximum

voltage of 2−3 V/cm in a TAE buﬀer (2 M Tris base, 0.05 M EDTA,

Authors

Svetlana G. Churusova − Nesmeyanov Institute of

Organoelement Compounds, Russian Academy of Sciences,

Moscow 119991, Russia

1.56 M acetic acid). The gels were stained with ethidium bromide

Ekaterina Yu. Rybalkina − Blokhin National Medical

Research Center of Oncology of the Ministry of Health of the

Russian Federation, Moscow 115478, Russia

Olga Yu. Susova − Blokhin National Medical Research Center

of Oncology of the Ministry of Health of the Russian

Federation, Moscow 115478, Russia

Alexander S. Peregudov − Nesmeyanov Institute of

Organoelement Compounds, Russian Academy of Sciences,

Moscow 119991, Russia

Valentina V. Brunova − Nesmeyanov Institute of

Organoelement Compounds, Russian Academy of Sciences,

Moscow 119991, Russia

Evgenii I. Gutsul − Nesmeyanov Institute of Organoelement

Compounds, Russian Academy of Sciences, Moscow 119991,

Russia

(

0.5 μg/mL) and visualized via UV ﬂuorescence at wavelengths in the

range of 240−360 nm using a GelDoc-It TS imaging system. In the

absence of inhibitors, topoisomerase I relaxed scDNA through the

formation of a series of topoisomers. Topoisomerase I inhibition was

revealed by the ability of the complexes under investigation to retard

scDNA relaxation, which was observed as a decrease in the amount of

topoisomers and a retention of scDNA.

Apoptosis Induction Assay. To deﬁne the ability of the

complexes explored to promote apoptosis, acute monocytic leukemia

cells THP-1, preincubated overnight in a CO incubator at 37 °C,

2

were cultured in a medium containing 10 μM of 8a or 11a for 20 h.

After exposure, the cells were washed with cold PBS and incubated

with annexin V-PE (BD PharMingen) according to the supplier’s

protocol for 15 min at room temperature in the dark. The apoptotic

rates of the resulting cell samples were analyzed on a FACScan ﬂow

cytometer (Becton Dickinson, USA) using CellQuest software. For

comparison, the apoptotic activities of representative examples of

cytotoxic complexes I, V, and VI were also evaluated under the same

conditions.

Zinaida S. Klemenkova − Nesmeyanov Institute of

Organoelement Compounds, Russian Academy of Sciences,

Moscow 119991, Russia

Cell Uptake Studies. PC3 cells were seeded on glass plates in the

culture medium and incubated for 24 h under the standard

conditions. Then, complex 13 was added at a concentration of 6 ×

Yulia V. Nelyubina − Nesmeyanov Institute of Organoelement

Compounds, Russian Academy of Sciences, Moscow 119991,

Russia; orcid.org/0000-0002-9121-0040

Valentina N. Glushko − Institute of Chemical Reagents and

High Purity Chemical Substances of the National Research

Centre “Kurchatov Institute”, Moscow 107076, Russia

Vladimir A. Kozlov − Nesmeyanov Institute of Organoelement

Compounds, Russian Academy of Sciences, Moscow 119991,

Russia

−

5

1

0

μM. This is a subtoxic concentration that leads to less than 10%

cell death. The cells were incubated in the presence of the

aforementioned compound for 24 h. Then, the plates were washed

twice with the neat medium and observed under an Axioplan 2

ﬂuorescence microscope (Zeiss).

For the ﬂow cytometry analysis, PC3 cells were seeded on Petri

dishes and cultured for 24 h under the standard conditions. Then,

complex 13 was added to a ﬁnal concentration of 6 × 10 M, and the

resulting samples were incubated for the speciﬁed time spans. After

the required period of time, the cells were detached by trypsinization

−5

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.inorgchem.1c01138

(

with Trypsin-Versene) and analyzed on a FACSCanto II ﬂow

cytometer.

Notes

The authors declare no competing ﬁnancial interest.

ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01138.

■

*

ACKNOWLEDGMENTS

■

This work was supported by the Russian Science Foundation,

project no. 20-73-00282. X-ray diﬀraction and NMR

spectroscopic data were collected with ﬁnancial support from

the Ministry of Science and Higher Education of the Russian

Federation using the equipment of the Center for Molecular

Composition Studies of INEOS RAS.

Synthesis and characterization of ﬂuorescein-conjugated

derivatives 12 and 13, NMR ( H, C{ H}, and diﬀerent

1

13

1

2

D NMR) spectra of ligand 6a and complex 10a, UV−

vis spectra of complexes 11a,c and 13, luminescence

spectra of compounds 12 and 13, and ﬂuorescence

microscopic images of PC3 cells treated with ligand 12

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Article Doi

Palladium(II) Pincer Complexes of Functionalized Amides with S-Modified Cysteine and Homocysteine Residues: Cytotoxic Activity and Different Aspects of Their Biological Effect on Living Cells

DOI: 10.1021/acs.inorgchem.1c01138

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Full text of DOI:10.1021/acs.inorgchem.1c01138

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