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.

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.

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.

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).

Xanthone-1,2,4-triazine and Acridone-1,2,4-triazine Conjugates: Synthesis and Anticancer Activity

A total of 21 novel xanthone and acridone derivatives were synthesized using the reactions of 1,2,4-triazine derivatives with 1-hydroxy-3-methoxy-10-methylacridone, 1,3-dimethoxy-, and 1,3-dihydroxanthone, followed by optional dihydrotiazine ring aromatization. The synthesized compounds were evaluated for their anticancer activity against colorectal cancer HCT116, glioblastoma A-172, breast cancer Hs578T, and human embryonic kidney HEK-293 tumor cell lines. Five compounds (7a, 7e, 9e, 14a, and 14b) displayed good in vitro antiproliferative activities against these cancer cell lines. Compounds 7a and 7e demonstrated low toxicity for normal human embryonic kidney (HEK-293) cells, which determines the possibility of further development of these compounds as anticancer agents. Annexin V assay demonstrated that compound 7e activates apoptotic mechanisms and inhibits proliferation in glioblastoma cells.

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.

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.

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 β-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).

Rhodium-Catalyzed Synthesis of 2-Aroylpyrimidines via Cascade Heteropolyene Rearrangement

A one-step synthesis of cytotoxic 2-aroylpyrimidines by the denitrogenative reaction of 1-tosyl-1,2,3-triazoles with isoxazoles under rhodium catalysis has been developed. According to the density functional theory calculations and control experiments, the disclosed reaction proceeds via the rearrangement of an oxadiazatetraene intermediate involving a cascade of intramolecular aza-Diels-Alder and retro-aza-Diels-Alder reactions. The presence of a substituent at C4 of the isoxazole is a prerequisite for the formation of the pyrimidines.

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.

An IMDAF approach to annellated 1,4:5,8-diepoxynaphthalenes and their metathesis reaction leading to novel scaffolds displaying an antiproliferative activity toward cancer cells

A 3,5a-epoxyfuro[2,3,4-de]isoquinoline scaffold, the product of ROCM of 1,4:5,8-diepoxynaphthalenes, is a promising antiproliferative agent toward breast and prostate human cancer cell lines.

Straightforward Three-Component Synthesis of N′,N′′-Disubstituted N-Alkyl-1,3,5-Triazinanes

Efficient approaches towards the synthesis of various N-substituted 1,3,5-triazinanes based on a transformation of N-alkyl-1,5,3-dioxazepanes or on a domino reaction involving condensation of various amines, amides, and paraformaldehyde are described for the first time. Mg(ClO4)2 was shown to be one of the most potent additives for the condensation. The proposed approaches permit the synthesis of a broad spectrum of substituted sym-triazinanes in good yields with relatively easy workup. In the case of the multicomponent reaction, the approach allows the preparation of the target substances from simple and easily accessible reagents. The representatives of the resulting compounds were found to possess no antimicrobial or cytotoxic activity in in vitro bioassays.

Water soluble palladium(ii) and platinum(ii) acyclic diaminocarbene complexes: solution behavior, DNA binding, and antiproliferative activity

Water soluble Pd(ii) and Pt(ii)–ADC species synthesized via the metal-mediated coupling of isocyanides and 1,2-diaminobenzene have demonstrated antitumor potential.

Crystal structures of ethyl {2-[4-(4-iso-propyl-phen-yl)thia-zol-2-yl]phen-yl}carbamate and ethyl {2-[4-(3-nitro-phen-yl)thia-zol-2-yl]phen-yl}carbamate

The title compounds, C21H22N2O2S (I) and C18H15N3O4S (II), are structural analogs of the alkaloid Thio-sporine B. Both mol-ecules adopt a near-planar V-shaped conformation, which is consolidated by intra-molecular N-H⋯N and C-H⋯O hydrogen bonds. The crystal structure of (I) consists of mlecular stacks along the a axis, in which the mol-ecules are linked to each other by π(S)⋯π(C) inter-actions. In the crystal of (II), mol-ecules are linked into chains by C-H⋯O hydrogen bonds and the chains are cross-linked into (100) sheets by π-π stacking inter-actions.

Crystal structures of N-[(4-phenyl-thia-zol-2-yl)carbamo-thio-yl]benzamide and N-{[4-(4-bromo-phen-yl)thia-zol-2-yl]carbamo-thio-yl}benzamide from synchrotron X-ray diffraction

The title compounds, C₁₇H₁₃N₃OS₂, (I), and C₁₇H₁₂BrN₃OS₂, (II), are potential active pharmaceutical ingredients. Compound (I) comprises two almost planar fragments. The first is the central (carbamo-thio-yl)amide (r.m.s. deviation = 0.038 Å), and the second consists of the thia-zole and two phenyl rings (r.m.s. deviation = 0.053 Å). The dihedral angle between these planes is 15.17 (5)°. Unlike (I), compound (II) comprises three almost planar fragments. The first is the central N-(thia-zol-2-ylcarbamo-thio-yl)amide (r.m.s. deviation = 0.084 Å), and the two others comprise the bromo-phenyl and phenyl substituents, respectively. The dihedral angles between the central and two terminal planar fragments are 21.58 (7) and 17.90 (9)°, respectively. Both (I) and (II) feature an intra-molecular N-H⋯O hydrogen bond, which closes an S(6) ring. In the crystal of (I), mol-ecules form hydrogen-bonded layers parallel to (100) mediated by N-H⋯S and C-H⋯O hydrogen bonds. In the crystal of (II), mol-ecules form a three-dimensional framework mediated by N-H⋯Br and C-H⋯O hydrogen bonds, as well as secondary S⋯Br [3.3507 (11) Å] and S⋯S [3.4343 (14) Å] inter-actions.

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 mol­ecules 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, mol­ecules 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] inter­actions.

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 Å for 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.

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.

(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.

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) Å between 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.

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 Å for 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].

(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 phenyl­ethyl­enone [r.m.s. deviation = 0.059 (1) Å] and phenyl­acetyl­ene [r.m.s. deviation = 0.023 (1) Å] fragments form a dihedral angle of 14.16 (7)°. In the crystal, weak C—H⋯O inter­actions link the mol­ecules into zigzag chains propagated in [010].

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.