Metal-(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple-Negative Breast Cancer.

Invited for the cover of this issue are Tatiyana Serebryanskaya, Mikhail Kinzhalov and co-workers at St. Petersburg State University, the Research Institute for Physical Chemical Problems, Belarusian State University, Togliatti State University and Blokhin National Medical Research Center of Oncology. The image depicts the shield of Pallas Athena with the structure of a palladium carbene complex that protects against triple-negative breast cancer. Read the full text of the article at 10.1002/chem.202400101.

Metal-(Acyclic Diaminocarbene) Complexes Demonstrate Nanomolar Antiproliferative Activity against Triple-Negative Breast Cancer.

Hydrolytically stable PdII and PtII complexes supported by acyclic diaminocarbene ligands represent a novel class of structural organometallic anticancer agents exhibiting nanomolar antiproliferative activity in a panel of cancer cell lines (IC50 0.07-0.81 µM) and up to 300-fold selectivity for cancer cells over normal primary fibroblasts. The lead drug candidate was 300 times more potent than cisplatin in vitro and showed higher efficacy in reducing the growth of aggressive MDA-MB-231 xenograft tumors in mice.

Facile synthesis of diiodoheteroindenes and understanding their Sonogashira cross-coupling selectivity for the construction of unsymmetrical enediynes.

Electrophile-promoted cyclizations of functionalized alkynes offer a useful tool for constructing halogen-substituted heterocycles primed for further derivatization. Preinstallation of an iodo-substituent at the alkyne prior to iodo-cyclization opens access to ortho di-iodinated heterocyclic precursors for the preparation of unsymmetrical heterocycle-fused enediynes. This general approach was used to prepare 2,3-diiodobenzothiophene, 2,3-diiodoindole, and 2,3-diiodobenzofuran, a useful family of substrates for systematic studies of the role of heteroatoms on the regioselectivity of cross-coupling reactions. Diiodobenzothiophene showed much higher regioselectivity for Sonogashira cross-coupling at C2 than diiodoindole and diiodobenzofuran. As a result, benzothiophene can be conveniently involved in a one-pot sequential coupling with two different alkynes, yielding unsymmetrical benzothiophene-fused enediynes. On the other hand, the Sonogashira reaction of diiodoindole and diiodobenzofuran formed considerable amounts of di-substituted enediynes in addition to the monoalkyne product by coupling at C2. Interestingly, no C3-monocoupling products were observed for all of the diiodides, suggesting that the incorporation of the 1st alkyne at C2 activates the C3 position for the 2nd coupling. Additional factors affecting regioselectivity were detected, discussed and connected, through computational analysis, to transmetalation being the rate-determining step for the Sonogashira reaction. Several enediynes synthesized showed cytotoxic activity, which is not associated with DNA strand breaks typical of natural enediyne antibiotics.

Acridine-Isoxazole and Acridine-Azirine Hybrids: Synthesis, Photochemical Transformations in the UV/Visible Radiation Boundary Region, and Anticancer Activity.

Easy-to-handle N-hydroxyacridinecarbimidoyl chloride hydrochlorides were synthesized as convenient nitrile oxide precursors in the preparation of 3-(acridin-9/2-yl)isoxazole derivatives via 1,3-dipolar cycloaddition with terminal alkynes, 1,1-dichloroethene, and acrylonitrile. Azirines with an acridin-9/2-yl substituent attached directly or via the 1,2,3-triazole linker to the azirine C2 were also synthesized. The three-membered rings of the acridine-azirine hybrids were found to be resistant to irradiation in the UV/visible boundary region, despite their long-wave absorption at 320-420 nm, indicating that the acridine moiety cannot be used as an antenna to transfer light energy to generate nitrile ylides from azirines for photoclick cycloaddition. The acridine-isoxazole hybrids linked at the C9-C3 or C2-C3 atoms under blue light irradiation underwent the addition of such hydrogen donor solvents, such as, toluene, o-xylene, mesitylene, 4-chlorotoluene, THF, 1,4-dioxane, or methyl tert-butyl ether (MTBE), to the acridine system to give the corresponding 9-substituted acridanes in good yields. The synthesized acridine-azirine, acridine-isoxazole, and acridane-isoxazole hybrids exhibited cytotoxicity toward both all tested cancer cell lines (HCT 116, MCF7, and A704) and normal cells (WI-26 VA4).

3-Arylidene-2-oxindoles as Potent NRH:Quinone Oxidoreductase 2 Inhibitors.

The enzyme NRH:quinone oxidoreductase 2 (NQO2) plays an important role in the pathogenesis of various diseases such as neurodegenerative disorders, malaria, glaucoma, COVID-19 and cancer. NQO2 expression is known to be increased in some cancer cell lines. Since 3-arylidene-2-oxindoles are widely used in the design of new anticancer drugs, such as kinase inhibitors, it was interesting to study whether such structures have additional activity towards NQO2. Herein, we report the synthesis and study of 3-arylidene-2-oxindoles as novel NRH:quinone oxidoreductase inhibitors. It was demonstrated that oxindoles with 6-membered aryls in the arylidene moiety were obtained predominantly as E-isomers while for some 5-membered aryls, the Z-isomers prevailed. The most active compounds inhibited NQO2 with an IC50 of 0.368 µM. The presence of a double bond in the oxindoles was crucial for NQO2 inhibition activity. There was no correlation between NQO2 inhibition activity of the synthesized compounds and their cytotoxic effect on the A549 cell line.

Novel substituted 5-methyl-4-acylaminoisoxazoles as antimitotic agents: Evaluation of selectivity to LNCaP cancer cells.

A series of novel antimitotic agents was designed using the replacement of heterocyclic cores in two tubulin-targeting lead molecules with the acylated 4-aminoisoxazole moiety. Target compounds were synthesized via heterocyclization of ß-aryl-substituted vinylketones by tert-butyl nitrite in the presence of water as a key step. 4-Methyl-N-[5-methyl-3-(3,4,5-trimethoxyphenyl)isoxazol-4-yl]benzamide (1aa) was found to stimulate partial depolymerization of microtubules of human lung carcinoma A549 cells at a high concentration of 100 µM and to totally inhibit cell growth (IC50 = 0.99 µM) and cell viability (IC50 = 0.271 µM) in the nanomolar to submicromolar concentration range. These data provide evidence of the multitarget profile of the cytotoxic action of compound 1aa. The SAR study demonstrated that the 3,4,5-trimethoxyphenyl residue is the key structural parameter determining the efficiency both towards tubulin and other molecular targets. The cytotoxicity of 3-methyl-N-[5-methyl-3-(3,4,5-trimethoxyphenyl)isoxazol-4-yl]benzamide (1ab) to the androgen-sensitive human prostate adenocarcinoma cancer cell line LNCaP (IC50 = 0.301 µM) was approximately one order of magnitude higher than that to the conditionally normal cells lines WI-26 VA4 (IC50 = 2.26 µM) and human umbilical vein endothelial cells (IC50 = 5.58 µM) and significantly higher than that to primary fibroblasts (IC50 > 75 µM).

Selective and Reversible 1,3-Dipolar Cycloaddition of 2-(2-Oxoindoline-3-ylidene)acetates with Nitrones in the Synthesis of Functionalized Spiroisoxazolidines.

The 1,3-dipolar cycloaddition of 2-(2-oxoindoline-3-ylidene)acetates with functionalized aldo- and ketonitrones proceeds with good selectivity to provide new highly functionalized 5-spiroisoxazolidines. A characteristic feature of these reactions is reversibility that allows for the control of the diastereoselectivity of cycloaddition. The reduction of obtained adducts using zinc powder in acetic acid leads to 1,3-aminoalcohols or spirolactones. For a number of the spiro compounds obtained, anticancer activity was found.

Functionalized 10-Membered Aza- and Oxaenediynes through the Nicholas Reaction.

The scope and limitations of the Nicholas-type cyclization for the synthesis of 10-membered benzothiophene-fused heterocyclic enediynes with different functionalities were investigated. Although the Nicholas cyclization through oxygen could be carried out in the presence of an ester group, the final oxaenediyne was unstable under storage. Among the N-type Nicholas reactions, cyclization via an arenesulfonamide functional group followed by mild Co-deprotection was found to be the most promising, yielding 10-membered azaendiynes in high overall yields. By contrast, the Nicholas cyclization through the acylated nitrogen atom did not give the desired 10-membered cycle. It resulted in the formation of a pyrroline ring, whereas cyclization via an alkylated amino group resulted in a poor yield of the target 10-membered enediyne. The acylated 4-aminobenzenesulfonamide nucleophilic group was found to be the most convenient for the synthesis of functionalized 10-membered enediynes bearing a clickable function, such as a terminal triple bond. All the synthesized cyclic enediynes exhibited moderate activity against lung carcinoma NCI-H460 cells and had a minimal effect on lung epithelial-like WI-26 VA4 cells and are therefore promising compounds in the search for novel antitumor agents that can be converted into conjugates with tumor-targeting ligands.

Unusual highly diastereoselective Rh(II)-catalyzed dimerization of 3-diazo-2-arylidenesuccinimides provides access to a new dibenzazulene scaffold.

Formation of unusual unsymmetrical dimers or/and indenes via Rh2(esp)2-catalyzed decomposition of 3-diazo-2-arylidenesuccinimides has been investigated. The reaction proceeded under mild conditions, and its result was shown to strongly depend on the nature of the substituents in the diazo substrate. The new reaction provides access to dibenzoazulenodipyrrole and indenopyrrole derivatives in moderate to high yield. Dibenzoazulenodipyrroles bearing alkyl substituents at the nitrogen atom showed pronounced cytotoxocity against the A549 human lung adenocarcinoma cell line while N-aryl analogs were non-cytotoxic.

A Hydroxypyrrole Approach to 2,2'-Bi(4-pyrrolin-3-ones) and Pyrrolone-Based α-Amino Esters.

A high yield synthesis of 2-amino-4-pyrrolin-3-ones including 4-pyrrolin-3-one-based amino esters by the NBS- or TfCl-mediated reaction of 3-hydroxypyrroles with amines has been developed. The reaction of 3-hydroxypyrroles with triflyl chloride in the absence of amine affords 2,2'-bi(4-pyrrolin-3-ones) in excellent yields and diastereoselectivity. The relative configuration of stereocenters in these compounds can be changed from (2RS,2'RS) to (2RS,2'SR) by the action of NaH in THF, while the reverse stereoisomerization occurs in the presence of 2,5-lutidine in MeCN. Bi(4-pyrrolin-3-ones) also can be converted to 2-amino-4-pyrrolin-3-ones in excellent yields. Bi(4-pyrrolin-3-ones) and 2-amino-4-pyrrolin-3-ones were evaluated for their antiproliferative activity toward four human tumor cell lines.

2-Bromo-1-[1-(4-bromo-phen-yl)-5-methyl-1H-1,2,3-triazol-4-yl]ethanone.

The asymmetric unit of the title compound, C11H9Br2N3O, contains two crystallographically independent mol-ecules with similar geometries; the Br-C-C=O torsion angles are 1.2 (4) and -2.8 (4)°, and the benzene and triazole rings are inclined o one another by 51.90 (16) and 51.88 (16)°. The two molecules are related by a pseudo-screw 21 axis directed along [100]. In the crystal, mol-ecules are linked into a three-dimensional network by weak C-H⋯O and C-H⋯N hydrogen bonds and secondary Br⋯Br [3.5991 (8) and 3.6503 (9) Å] inter-actions.

(Z)-N-[1-(Aziridin-1-yl)-2,2,2-tri-fluoro-ethyl-idene]-4-bromo-aniline.

The title compound, C10H8BrF3N2, crystallizes with two independent mol-ecules in the asymmetric unit, which can be considered as being related by a pseudo-inversion center, so their conformations are different; the corresponding N=C-N-C torsion angles are 54.6 (5) and -50.5 (5)°. In the crystal, mol-ecules related by translation in [001] inter-act through short inter-molecular Br⋯F contacts [3.276 (2) and 3.284 (2) Å], thus forming two types of crystallographically independent chains.

3-Bromo-2-[4-(methyl-sulfan-yl)phen-yl]-5,6,7,8-tetra-hydro-1,3-benzo-thia-zolo[3,2-a]imidazole.

In the title mol-ecule, C16H15BrN2S2, the central imidazo[2,1-b]thia-zole fragment is almost planar (r.m.s. deviation = 0.012 Å), and the fused 5,6,7,8-tetra-hydro-benzene ring adopts an unsymmetrical half-chair conformation. The dihedral angle between the imidazo[2,1-b]thia-zole and benzene planes is 18.25 (4)°. The terminal methyl-sulfanyl substituent lies practically within the benzene plane [the dihedral angle between the corresponding planes is 7.20 (10)°] and is turned toward the C-Br bond. In the crystal, mol-ecules form infinite chains along [100] via secondary Br⋯N inter-actions [3.1861 (16) Å]. The chains are arranged at van der Waals distances.

2-Phenyl-5,6,7,8-tetra-hydro-imidazo[2,1-b][1,3]benzo-thia-zole.

The title compound, C15H14N2S, crystallizes with two independent mol-ecules in the asymmetric unit. The central imidazo[2,1-b][1,3]benzo-thia-zole unit is planar (r.m.s. deviations of 0.010 and 0.008 Šfor the two independent mol-ecules). The fused tetra-hydro-hexane ring adopts a half-chair conformation. The phenyl substituent is twisted by 16.96 (13) and 22.89 (12)° relative to the central imidazo[2,1-b][1,3]benzo-thia-zole unit in the two mol-ecules. In the crystal, there are no significant intermolecular interactions present.

2-Bromo-4-phenyl-1,3-thia-zole.

In the title mol-ecule, C9H6BrNS, the planes of the 2-bromo-1,3-thia-zole and phenyl rings are inclined at 7.45 (10)° with respect to each other. In the crystal, mol-ecules related by a centre of symmetry are held together via π-π inter-actions, with a short distance of 3.815 (2) Šbetween the centroids of the five- and six-membered rings. The crystal packing exhibits short inter-molecular S⋯Br contacts of 3.5402 (6) Å.

7-Nitro-2-phenyl-imidazo[2,1-b][1,3]benzo-thia-zole.

In the title mol-ecule, C15H9N3O2S, the central imidazo[2,1-b][1,3]benzo-thia-zole heterotricyclic unit is essentially planar (r.m.s. deviation = 0.021 Å). The terminal phenyl ring and nitro group are twisted by 9.06 (1) and 11.02 (4)°, respectively, from the mean plane of the heterotricycle. In the crystal, mol-ecules are linked by π-π stacking inter-actions into columns along [100]; the inter-planar distance between neighboring imidazo[2,1-b][1,3]benzo-thia-zole planes within the columns is 3.370 (2) Å. Furthermore, the columns interact with each other by secondary S⋯O [2.9922 (10) and 3.1988 (11) Å] inter-actions, forming a three-dimensional framework.

(E)-1,5-Di-phenyl-pent-2-en-4-yn-1-one.

The title compound, C17H12O, has an E conformation about the C=C bond. The C-C C-C torsion angle is 7.7 (2)°, and the mean planes of the phenyl-ethyl-enone [r.m.s. deviation = 0.059 (1) Å] and phenyl-acetyl-ene [r.m.s. deviation = 0.023 (1) Å] fragments form a dihedral angle of 14.16 (7)°. In the crystal, weak C-H⋯O inter-actions link the mol-ecules into zigzag chains propagated in [010].

6-(4-Chloro-phen-yl)-3-methyl-imidazo[2,1-b]thia-zole.

In the title compound, C12H9ClN2S, the imidazo[2,1-b]thia-zole fragment is planar (r.m.s. deviation = 0.003 Å), and the benzene ring is twisted slightly [by 5.65 (6)°] relative to this moiety. In the crystal, mol-ecules are linked by π-π stacking inter-actions into columns along [010]. The mol-ecules within the columns are arranged alternatively by their planar rotation of 180°. Thus, in the columns, there are the two types of π-π stacking inter-actions, namely, (i) between two imidazo[2,1-b]thia-zole fragments [inter-planar distance = 3.351 (2) Å] and (ii) between an imidazo[2,1-b]thia-zole fragment and the phenyl ring [inter-planar distance = 3.410 (5) Å]. There are no short contacts between the columns.

2-(Adamantan-1-yl)-N-(6-meth-oxy-1,3-benzo-thia-zol-2-yl)acetamide.

The asymmetric unit of the title compound, C20H24N2O2S, contains two independent mol-ecules having very similar geometries. The main N-(6-meth-oxy-1,3-benzo-thia-zol-2-yl)acetamide moiety adopts an almost planar structure (r.m.s. deviations of 0.091 and 0.051 Šfor the two independent molecules). The adamantyl substituent occupies the gauche position relative to the C-N bond of the acetamide moiety [the corresponding N-C-C-C dihedral angles are -100.3 (3) and -96.5 (3)° for the two independent mol-ecules]. In the crystal, the two independent mol-ecules form a dimer via a pair of N-H⋯N hydrogen bonds. The dimers are further linked by C-H⋯O hydrogen bonds and attractive S⋯S [3.622 (2) Å] inter-actions into ribbons along [100].

3-Bromo-7-meth-oxy-2-phenyl-imidazo[2,1-b][1,3]benzothia-zole.

In the title mol-ecule, C16H11BrN2OS, the central imidazo[2,1-b][1,3]benzothia-zole tricycle is essentially planar (r.m.s. deviation = 0.021 Å). The terminal phenyl ring is twisted at 36.18 (5)° from the mean plane of the tricycle. In the crystal, pairs of eak C-H⋯O hydrogen bonds link mol-ecules into centrosymmetric dimers, which are further packed into stacks along the a axis.