Insight into and Computational Studies of the Selective Synthesis of 6H-Dibenzo[b,h]xanthenes

Multicomponent Reactions (MCRs) with o-Quinone Methides

This article presents a comprehensive overview of multicomponent reactions (MCRs) that proceed via ortho-quinone methide intermediates (o-QM) generated in the reaction medium. Examples of applications involving these highly reactive intermediates in organic synthesis and biological processes (e. g., biosynthetic pathways, prodrug cleavage and electrophilic capture of biological nucleophiles) are also described. QMs are often generated by eliminative processes of phenol derivatives or by photochemical reactions, including reversible generation in photochromic substances. This class of compounds can undergo various reaction types, including nucleophilic attack at the methide carbon, with subsequent rearomatization, and react with electron-rich dienophiles in inverse-electron demand hetero-Diels-Alder reactions. Its versatile reactivity has been explored in the context of cascade reactions for the construction of several classes of substances, including complex natural products.

Recent progress on the synthesis of henna-based dibenzoxanthenes

Xanthenes are a class of natural and synthetic heterocyclic compounds that exhibit a broad spectrum of biological properties and synthetic applications.

Hetero-Diels-Alder Reactions of Quinone Methides: The Origin of the α-Regioselectivity of 3-Methylene-1,2,4-naphthotriones

The regioselective formation of α- and β-lapachone via hetero-Diels-Alder reactions was investigated by experimental and computational approaches. The experimentally observed α-selectivity was explored in detail, revealing that the lower energy barrier for the formation of α-lapachone is a result of lower Pauli repulsion throughout the reaction path, when compared to the β-isomer. By comparing equivalent points on both α- and β-lapachone potential energy surfaces (PES), according to the activation strain model (ASM) and energy decomposition analysis (EDA), we were able to demonstrate that the Pauli repulsion term increases more significantly when going from reactants to TS_β than to TS_α, resulting in lower interaction energy in the early stages of the reaction path and in a later transition state for β-lapachone. Moreover, we confirmed that regio- and diastereoselectivity trends previously reported for other quinone methide intermediates are also observed for 3-methylene-1,2,4-naphthotriones, such as small endo/exo diastereoselectivity, as well as pronounced ortho/meta regioselectivity for reactions performed with dienophile containing electron-releasing groups. The results presented here provide a deeper understanding of the reactivity of quinone methide derivatives, aiding the future rational design of the reaction condition, structural modification of possible quinone methide intermediates, and the development of more selective synthetic routes for quinone derivatives.

Design, Synthesis and Biological Evaluation of 1H-1,2,3-Triazole-Linked-1H-Dibenzo[b,h]xanthenes as Inductors of ROS-Mediated Apoptosis in the Breast Cancer Cell Line MCF-7

BACKGROUND

Low molecular weight 1,2,3-triazoles and naphthoquinones are endowed with various types of biological activity, such as against cancer, HIV and bacteria. However, in some cases, the conjugation of these two nuclei considerably increases their biological activities.

OBJECTIVE

In this work, we decided to study the synthesis and screening of bis-naphthoquinones and xanthenes tethered to 1,2,3-triazoles against cancer cell lines, specifically the human breast cancer cell line MCF-7.

RESULTS

Starting from lawsone and aryl-1H-1,2,3-triazole-4-carbaldehydes (10a-h) several new 7- (1-aryl-1H-1,2,3-triazol-4-yl)-6H-dibenzo[b,h]xanthene-5,6,8,13(7H)-tetraones (12a-h) and 3,3'- ((1-aryl-1H-1,2,3-triazol-4-yl)methylene)bis(2-hydroxynaphthalene-1,4-diones) 11a-h were synthesized and evaluated for their cytotoxic activities using the human breast cancer cell line MCF-7 and the non-tumor cell line MCF10A as control. We performed test of cell viability, cell proliferation, intracellular ATP content and cell cytometry to determine reactive oxygen species (ROS) formation.

CONCLUSIONS

Based on these results, we found that compound 12a promotes ROS production, interfering with energy metabolism, cell viability and proliferation, and thus promoting whole cell damage.

Potential cytotoxic and selective effect of new benzo[b]xanthenes against oral squamous cell carcinoma

Aim: The current work shows a new synthetic methodology to obtain 21 naphthoquinones that have been evaluated against oral cavity cancer. The compounds were obtained by a three-component reaction involving lawsone, dimedone and aromatic aldehydes catalyzed by lithium chloride under microwave irradiation to produce families of 1,4- and 1,2-naphthoquinones. Results: A clonogenic assay was performed on SCC9 cell line cultures with all compounds, revealing five very active compounds. In the 3,4,5-dimethylthiazol-2,5-diphenyltetrazolium bromide cell viability assay using three different cell lines (SCC9, SCC4 and SCC25), 8c had an average IC50 of approximately 1.45 μM capable of reducing tumor cell viability, approximately 90-times higher than carboplatin.Conclusion: Therefore, the xanthene-naphthoquinone derivatives show promising bioactivity for oral cavity cancer treatment.

Synthesis and Cytotoxicity of N-Substituted Dibenzo[a,j]xanthene-3,11-dicarboxamide Derivatives

In order to study the structure-activity relationships of xanthene derivatives, four series of N-substituted 14-aryl-14H-dibenzo[a,j]xanthene-3,11-dicarboxamide derivatives were synthesized. The structures of all compounds were identified by ¹H-NMR, HR-MS and IR spectra, in which compounds 6a-h were further identified by ¹³C-NMR spectra. The in vitro antitumor activity of the synthesized compounds was tested by MTT assay. Most of them displayed strong inhibitory activity on human hepatocellular carcinoma cell lines (SK-HEP-1, HepG2 and SMMC-7721 cells) and acute promyelocytic leukemia NB4 cells. Compounds 6c-6e exhibited significant inhibitory activity against NB4 cells with IC₅₀ values of 0.52 μM and 0.76 μM, respectively, much lower than 5.31 μM of the positive control As₂O₃.