11H-Benzo[4,5]imidazo[1,2-a]indol-11-one as a New Precursor of Azomethine Ylides: 1,3-Dipolar Cycloaddition Reactions with Cyclopropenes and Maleimides.

The possibility of generating azomethine ylides from 11H-benzo[4,5]imidazo[1,2-a]indol-11-one and amino acids is shown for the first time. Based on the cycloaddition reactions of these azomethine ylides with cyclopropenes and maleimides, cyclopropa[a]pyrrolizines, 3-azabicyclo[3.1.0]hexanes, and pyrrolo[3,4-a]pyrrolizines spiro-fused with a benzo[4,5]imidazo[1,2-a]indole fragment were synthesized. Spirocyclic compounds were obtained in moderate to good yields, albeit with poor diastereoselectivity. Density functional theory calculations were performed to obtain an insight into the mechanism of the 1,3-dipolar cycloaddition of 11H-benzo[4,5]imidazo[1,2-a]indol-11-one-derived azomethine ylides to cyclopropenes. The cytotoxic activity of some of the obtained cycloadducts against the human erythroleukemia (K562) cell line was evaluated in vitro by MTS-assay.

Biological Evaluation of 3-Azaspiro[Bicyclo[3.1.0]Hexane-2,5'-Pyrimidines] as Potential Antitumor Agents.

A series of heterocyclic compounds containing spirofused barbiturate and 3-azabicyclo[3.1.0]hexane frameworks have been studied as potential antitumor agents. Antiproliferative activity of products was screened in human erythroleukemia (K562), T lymphocyte (Jurkat), and cervical carcinoma (HeLa) as well as mouse colon carcinoma (CT26) and African green monkey kidney epithelial (Vero) cell lines. The most effective among the screened compounds show IC50 in the range from 4.2 to 24.1 µM for all tested cell lines. The screened compounds have demonstrated a significant effect of the distribution of HeLa and CT26 cells across the cell cycle stage, with accumulation of cells in SubG1 phase and induced apoptosis. It was found, using a confocal microscopy, that actin filaments disappeared and granular actin was distributed diffusely in the cytoplasm of up to 90% of HeLa cells and up to 64% of CT26 cells after treatment with tested 3-azaspiro[bicyclo [3.1.0]hexane-2,5'-pyrimidines]. We discovered that the number of HeLa cells with filopodium-like membrane protrusions was reduced significantly (from 91% in control cells to 35%) after treatment with the most active compounds. A decrease in cell motility was also noticed. Preliminary in vivo experiments on the impact of the studied compounds on the dynamics of CT26 tumor growth in Balb/C mice were also performed.

Synthesis of bis-spirocyclic derivatives of 3-azabicyclo[3.1.0]hexane via cyclopropene cycloadditions to the stable azomethine ylide derived from Ruhemann's purple.

A reliable method for the synthesis of bis-spirocyclic derivatives of 3-azabicyclo[3.1.0]hexanes through the 1,3-dipolar cycloaddition (1,3-DC) reactions of cyclopropenes to the stable azomethine ylide - protonated form of Ruhemann's purple (PRP) has been developed. Both 3-substituted and 3,3-disubstituted cyclopropenes reacted with PRP, affording the corresponding bis-spirocyclic 3-azabicyclo[3.1.0]hexane cycloadducts in moderate to good yields with high diastereofacial selectivity. Moreover, several unstable 1,2-disubstituted cyclopropenes were successfully trapped by the stable 1,3-dipole under mild conditions. The mechanism of the cycloaddition reactions of cyclopropenes with PRP has been thoroughly studied using density functional theory (DFT) methods at the M11/cc-pVDZ level of theory. The cycloaddition reactions have been found to be HOMOcyclopropene-LUMOylide controlled while the transition-state energies for the reaction of 3-methyl-3-phenylcyclopropene with PRP are fully consistent with the experimentally observed stereoselectivity.

Identification of Spiro-Fused Pyrrolo[3,4-a]pyrrolizines and Tryptanthrines as Potential Antitumor Agents: Synthesis and In Vitro Evaluation.

A series of heterocyclic compounds containing a spiro-fused pyrrolo[3,4-a]pyrrolizine and tryptanthrin framework have been synthesized and studied as potential antitumor agents. Cytotoxicity of products was screened against human erythroleukemia (K562) and human cervical carcinoma (HeLa) cell lines. Among the screened compounds. 4a, 4b and 5a were active against human erythroleukemia (K562) cell line, while 4a and 5a were active against cervical carcinoma (HeLa) cell line. In agreement with the DNA cytometry studies, the tested compounds have achieved significant cell-cycle perturbation with higher accumulation of cells in G2/M phase and induced apoptosis. Using confocal microscopy, we found that with 4a and 5a treatment of HeLa cells, actin filaments disappeared, and granular actin was distributed diffusely in the cytoplasm in 76-91% of cells. We discovered that HeLa cells after treatment with compounds 4a and 5a significantly reduced the number of cells with filopodium-like membrane protrusions (from 63 % in control cells to 29% after treatment) and a decrease in cell motility.

Identification of Spiro-Fused [3-azabicyclo[3.1.0]hexane]oxindoles as Potential Antitumor Agents: Initial In Vitro Evaluation of Anti-Proliferative Effect and Actin Cytoskeleton Transformation in 3T3 and 3T3-SV40 Fibroblast.

Novel heterocyclic compounds containing 3-spiro[3-azabicyclo[3.1.0]hexane]oxindole framework (4a, 4b and 4c) have been studied as potential antitumor agents. The in silico ADMET (adsorption, distribution, metabolism, excretion and toxicity) analysis was performed on 4a-c compounds with promising antiproliferative activity, previously synthetized and screened against human erythroleukemic cell line K562 tumor cell line. Cytotoxicity of 4a-c against murine fibroblast 3T3 and SV-40 transformed murine fibroblast 3T3-SV40 cell lines were evaluated. The 4a and 4c compounds were cytotoxic against 3T3-SV40 cells in comparison with those of 3T3. In agreement with the DNA cytometry studies, the tested compounds have achieved significant cell-cycle perturbation with higher accumulation of cells in G0/G1 phase. Using confocal microscopy, we found that with 4a and 4c treatment of 3T3 cells, actin filaments disappeared, and granular actin was distributed diffusely in the cytoplasm in 82-97% of cells. The number of 3T3-SV40 cells with stress fibers increased to 7-30% against 2% in control. We discovered that transformed 3T3-SV40 cells after treatment with compounds 4a and 4c significantly reduced the number of cells with filopodium-like membrane protrusions (from 86 % in control cells to 6-18% after treatment), which indirectly suggests a decrease in cell motility. We can conclude that the studied compounds 4a and 4c have a cytostatic effect, which can lead to a decrease in the number of filopodium-like membrane protrusions.

Stereo- and Regioselective 1,3-Dipolar Cycloaddition of the Stable Ninhydrin-Derived Azomethine Ylide to Cyclopropenes: Trapping of Unstable Cyclopropene Dipolarophiles.

A stereo- and regioselective 1,3-dipolar cycloaddition of the stable ninhydrin-derived azomethine ylide [2-(3,4-dihydro-2 H-pyrrolium-1-yl)-1-oxo-1 H-inden-3-olate, DHPO] to differently substituted cyclopropenes has been established. As a result, an efficient synthetic protocol was developed for the preparation of biologically relevant spiro[cyclopropa[ a]pyrrolizine-2,2'-indene] derivatives. DHPO has proved to be an effective trap for such highly reactive and unstable substrates as parent cyclopropene, 1-methylcyclopropene, 1-phenylcyclopropene, and 1-halo-2-phenylcyclopropenes. It has also been found that 3-nitro-1,2-diphenylcyclopropene undergoes a nucleophilic substitution reaction in alcohols and thiols to afford 3-alkoxy- and 3-arylthio-substituted 1,2-diphenylcyclopropenes, which can be captured as corresponding 1,3-dipolar cycloadducts in the presence of DHPO. These new approaches provide a straightforward strategy for the synthesis of functionally substituted cyclopropa[ a]pyrrolizine derivatives. The factors governing regio- and stereoselectivity have been revealed by means of quantum mechanical calculations (M11 density functional theory), including previously unreported Nylide- Hcyclopropene second-orbital interactions. The outcome of this work contributes to the study of 1,3-dipolar cycloaddition, as well as enriches chemistry of cyclopropenes and methods for the construction of polycyclic compounds with cyclopropane fragments.

Synthesis of Functionalized 3-Spiro[cyclopropa[a]pyrrolizine]- and 3-Spiro[3-azabicyclo[3.1.0]hexane]oxindoles from Cyclopropenes and Azomethine Ylides via [3 + 2]-Cycloaddition.

3-Spiro[cyclopropa[a]pyrrolizine]- and 3-spiro[3-azabicyclo[3.1.0]hexane]oxindoles were prepared in moderate to high yields via one-pot three-component reactions using substituted isatins, α-amino acids, and cyclopropenes. The key step is an intramolecular [3 + 2]-cycloaddition reaction of an in situ generated azomethine ylide onto a cyclopropene. Both N-substituted and N-unsubstituted α-amino acids, dipeptide Gly-Gly, and also benzylamine were used as the amine component for the azomethine ylide generation. The anticancer activity of some of the obtained compounds against human leukemia K562 cell line was evaluated by flow cytometry in vitro.