Synthesis of Novel C3-Linked ?-Carboline-Pyridine Derivatives Employing Khronke Reaction: DNA-binding Ability and Molecular Modeling Studies

Morita–Baylis–Hillman reaction of 3-formyl-9H-pyrido[3,4-b]indoles and fluorescence studies of the products

β-Carboline is a privileged class of the alkaloid family and is associated with a broad spectrum of biological properties. 3-Formyl-9H-pyrido[3,4-b]indole is a such potent precursor belonging to this family which can be tailored for installing diversity at various positions of β-carboline to generate unique molecular hybrids of biological importance. The present work is a step towards this and assimilates the results related to the exploration of 3-formyl-9H-β-carbolines for the synthesis of β-carboline C-3 substituted MBH adducts followed by evaluation of their fluorescent characteristic. The effect of contact time, solvent system, concentration and substituents was also studied during investigation of fluorescence properties of these derivatives.

Synthesis and Biological Evaluation of Harmirins, Novel Harmine-Coumarin Hybrids as Potential Anticancer Agents

As cancer remains one of the major health burdens worldwide, novel agents, due to the development of resistance, are needed. In this work, we designed and synthesized harmirins, which are hybrid compounds comprising harmine and coumarin scaffolds, evaluated their antiproliferative activity, and conducted cell localization and cell cycle analysis experiments. Harmirins were prepared from the corresponding alkynes and azides under mild reaction conditions using Cu(I) catalyzed azide–alkyne cycloaddition, leading to the formation of the 1H-1,2,3-triazole ring. Antiproliferative activity of harmirins was evaluated in vitro against four human cancer cell lines (MCF-7, HCT116, SW620, and HepG2) and one human non-cancer cell line (HEK293T). The most pronounced activities were exerted against MCF-7 and HCT116 cell lines (IC₅₀ in the single-digit micromolar range), while the most selective harmirins were 5b and 12b, substituted at C-3 and O-7 of the β-carboline core and bearing methyl substituent at position 6 of the coumarin ring (SIs > 7.2). Further experiments demonstrated that harmirin 12b is localized exclusively in the cytoplasm. In addition, it induced a strong G1 arrest and reduced the percentage of cells in the S phase, suggesting that it might exert its antiproliferative activity through inhibition of DNA synthesis, rather than DNA damage. In conclusion, harmirin 12b is a novel harmine and coumarin hybrid with significant antiproliferative activity and warrants further evaluation as a potential anticancer agent.

β-Carboline-based molecular hybrids as anticancer agents: a brief sketch

Cancer is a huge burden on the healthcare system and is foremost cause of mortality across the globe. Among various therapeutic strategies, chemotherapy plays an enormous role in overcoming the challenges of treating cancer, especially in late stage detection. However, limitations such as extreme side/adverse effects and drug resistance associated with available drugs have impelled the development of novel chemotherapeutic agents. In this regard, we have reviewed the development of β-carboline-based chemotherapeutic agents reported in last five years. The review mainly emphasizes on the molecular hybrids of β-carbolines with various pharmacophores, their synthetic strategies, and in vitro anticancer evaluation. In addition, the mechanisms of action, in silico studies, structural influence on the potency and selectivity among diverse cancer cell lines have been critically presented. The review updates readers on the diverse molecular hybrids prepared and the governing structural features of high potential molecules that can help in the future development of novel cytotoxic agents.

Design and Synthesis of Fluorescent 1,3-Diaryl-β-carbolines and 1,3-Diaryl-3,4-dihydro-β-carbolines

The 1,3-diaryl-β-carboline derivatives, including 3,4-dihydro variants, were synthesized via a multiple-step approach. These compounds possess rigid and twisted configurations, which are expected to exhibit unique optical properties. The absorption and fluorescence properties of the newly synthesized compounds were investigated. These synthetic 1,3-diaryl-β-carbolines displayed strong emission in the range of 387-409 nm and exhibited absolute photoluminescence quantum yields of up to 74%. Density functional theory calculations were performed to better elucidate the geometric, electronic, and optical properties of these novel 1,3-diaryl-β-carbolines.

β-Carbolines as potential anticancer agents

β-Carbolines are indole alkaloids having a tricyclic pyrido[3,4-b]indole ring in their structure. Since the isolation of first β-carboline from Peganum harmala in 1841, the isolation and synthesis of various β-carboline derivatives surged in the following centuries. β-Carboline derivatives due to their widespread availability from natural sources, structural flexibility, quick reactivity and interaction with varied anticancer targets such as DNA (intercalation, groove binding, etc.), enzymes (GPX4, topoisomerases, kinases, etc.) and proteins (tubulin, ABCG2/BRCP1, etc.) have established themselves as promising lead compounds for the synthesis of various anticancer active agents. The current review covers the synthesis and isolation, anticancer activity, mechanism of action and SAR of various β-carboline containing molecules, its derivatives and congeners.

Identification of biosynthetic genes for the β-carboline alkaloid kitasetaline and production of the fluorinated derivatives by heterologous expression

β-Carboline alkaloids exhibit a broad spectrum of pharmacological and biological activities and are widely distributed in nature. Genetic information on the biosynthetic mechanism of β-carboline alkaloids has not been accumulated in bacteria, because there are only a few reports on the microbial β-carboline compounds. We previously isolated kitasetaline, a mercapturic acid derivative of a β-carboline compound, from the genetically modified Kitasatospora setae strain and found a plausible biosynthetic gene cluster for kitasetaline. Here, we identified and characterized three kitasetaline (ksl) biosynthetic genes for the formation of the β-carboline core structure and a gene encoding mycothiol-S-conjugate amidase for the modification of the N-acetylcysteine moiety by using heterologous expression. The proposed model of kitasetaline biosynthesis shows unique enzymatic systems for β-carboline alkaloids. In addition, feeding fluorotryptophan to the heterologous Streptomyces hosts expressing the ksl genes led to the generation of unnatural β-carboline alkaloids exerting novel/potentiated bioactivities.

Synthesis of DNA interactive C3-trans-cinnamide linked β-carboline conjugates as potential cytotoxic and DNA topoisomerase I inhibitors

A series of new C3-trans-cinnamide linked β-carboline conjugates has been synthesized by coupling between various β-carboline amines and substituted cinnamic acids. Evaluation of their anti-proliferative activity against a panel of selected human cancer cell lines such as A549 (lung cancer), MCF-7 (breast cancer), B16 (melanoma), HeLa (cervical cancer) and a normal cell line NIH3T3 (mouse embryonic fibroblast cell line), suggested that the newly designed conjugates are considerably active against all the tested cancer cell lines with IC₅₀ values 13-45 nM. Moreover, the conjugates 8v and 8x were the most active against MCF-7 cells (14.05 nM and 13.84 nM respectively) and also even potent on other cell lines tested. Further, detailed investigations such as cell cycle analysis, apoptosis induction study, topoisomerase I inhibition assay, DNA binding affinity and docking studies revealed that these new conjugates are DNA interactive topoisomerase I inhibitors.

Engineered production of kitasetalic acid, a new tetrahydro-β-carboline with the ability to suppress glucose-regulated protein synthesis

β-Carboline alkaloids and related compounds show a broad spectrum of biological activities. We previously identified new members of the β-carboline alkaloid family by using an engineered Kitasatospora setae strain and a heterologous Streptomyces host expressing the plausible biosynthetic genes, including the hypothetical gene kse_70640 (kslB). Here, we elucidated the chemical structure of a new tetrahydro-β-carboline compound (named kitasetalic acid) that appeared in a heterologous Streptomyces host expressing the kslB gene alone. Kitasetalic acid suppressed the expression of glucose-regulated protein 78 (GRP78) without inducing cell death. This is the first report to show that a tetrahydro-β-carboline compound regulates the expression of the GRP78 protein in cancer cell lines.

Synthesis and in vitro cytotoxicity evaluation of β-carboline-linked 2,4-thiazolidinedione hybrids: potential DNA intercalation and apoptosis-inducing studies

A series of β-carboline-linked 2,4-thiazolidinedione hybrids was synthesized and studied for their DNA affinities and cytotoxicities. The most potent compound was 19e with IC₅₀ of 0.97 ± 0.13 μM.

Synthesis of substituted phenanthrene-9-benzimidazole conjugates: Cytotoxicity evaluation and apoptosis inducing studies

A series of new phenanthrene-9-benzimidazole conjugates has been synthesized by condensing phenanthrene aldehydes with various substituted o-phenylenediamines. The title compounds were evaluated for their in vitro cytotoxic potential against various human cancer cell lines like breast (BT-549), prostate (PC-3 and DU145), triple negative breast cancer (MDA-MB-453), and human colon cancer (HCT-116 and HCT-15) cells. Among the tested compounds, 10o displayed significant in vitro cytotoxic activity against PC-3 prostate cancer cells with an IC₅₀ value of 6.32 ± 0.09 μM. Further, the cell cycle analysis indicated that it blocks G2/M phase of the cell cycle in a dose dependent manner. In order to determine the effect of the compound 10o on cell viability; phase contrast microscopy, AO/EB staining, DAPI staining, and DCFDA staining studies were performed. In these studies, apoptotic features were clearly observed indicating that the compound inhibited cell proliferation by apoptosis. JC-1 staining and annexin binding assays indicated the extent of apoptosis in PC-3 cells. Further, relative viscosity measurements and molecular docking studies indicated that these compounds bind to DNA by intercalation.

Design and synthesis of 1,2,3-triazolo-phenanthrene hybrids as cytotoxic agents

A series of new 1,2,3-triazolo-phenanthrene hybrids has been synthesized by employing Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction. These compounds were evaluated for their in vitro cytotoxic potential against various human cancer cell lines viz. lung (A549), prostate (PC-3 and DU145), gastric (HGC-27), cervical (HeLa), triple negative breast (MDA-MB-231, MDA-MB-453) and breast (BT-549, 4T1) cells. Among the tested compounds, 7d displayed highest cytotoxicity against DU145 cells with IC₅₀ value of 1.5±0.09µM. Further, the cell cycle analysis shown that it blocks G0/G1 phase of the cell cycle in a dose dependent manner. In order to determine the effect of compound on cell viability, phase contrast microscopy, AO/EB, DAPI, DCFDA and JC-1 staining studies were performed. These studies clearly indicated that the compound 7d inhibited the cell proliferation of DU145 cells. Relative viscosity measurements and molecular docking studies indicated that these compounds bind to DNA by intercalation.

In(OTf)3 assisted synthesis of β-carboline C-3 tethered imidazo[1,2-a]azine derivatives

Synthesis of β-carboline based natural products and synthetic derivatives is one of the frontier areas of research owing to their medicinal properties.