Substituted benzopyranobenzothiazinones. Synthesis and estrogenic activity on MCF-7 breast carcinoma cells

4-Aminocoumarin derivatives: synthesis and applications

4-Aminocoumarins represent an important class of a versatile scaffold in organic synthesis and have been consistently used as a building block in organic chemistry for the synthesis of different heterocyclic compounds.

Antiestrogenic Activity and Possible Mode of Action of Certain New Nonsteroidal Coumarin-4-acetamides

The preparation of certain 2-(2-oxo-2H-chromen-4-yl)-N-substituted acetamides IIIa-h was planned as a step in the development of new modified nonsteroidal antiestrogens. The purity of target compounds IIIa-h was checked by thin-layer chromatography (TLC), and their structures were confirmed using various spectroscopic tools including IR, 1H-NMR, 13C-NMR, and MS spectroscopy. Viability tests were applied using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay to evaluate the cytotoxic effect of the synthesized compounds against two breast cancer cell lines, MCF-7 and MDA-MB-231. Compound IIIb proved the most active against MCF-7 cells, with an IC50 value of 0.32 μM. The results of an analysis of in vitro antiestrogenic activity indicated that only compound IIIb exhibited antiestrogenic activity; its IC50 value of 29.49 μM was about twice as potent as that of the reference compound, MIBP. The aromatase activity was evaluated for the synthesized target compounds IIIa-g and the intermediates Ib and IIa. A significant aromatase inhibition was observed for the intermediate Ib and compound IIIe, with IC50 values of 14.5 and 17.4 μM, respectively. Compound IIIb, namely 7-methoxy-4-(2-oxo-2-(piperidin-1-yl)ethyl)-2H-chromen-2-one, could be used as an antiestrogen and/or cytotoxic agent with selective activity against tumor cells.

Synthesis and antibacterial activity of new 1,2,3-triazolylmethyl-2H-1,4-benzothiazin-3(4H)-one derivatives

BACKGROUND

A novel series of 1,2,3-triazole derivatives containing 1,4-benzothiazin-3-one ring (7a-9a, 7b-9b), (10a-12a, 10b-12b) and (13-15) were synthesized by 1,3-dipolar cycloaddition reactions of azides α-D-galactopyranoside azide F, 2,3,4,6-tetra-O-acetyl-(D)-glucopyranosyl azide G and methyl-N-benzoyl-α-azidoglycinate H with compounds 4-6.

FINDINGS

Initially, the reactions were conducted under thermal conditions in ethanol. The reaction leads, each time, to the formation of two regioisomers: (Schemes 2, 3) with yields of 17 to 21% for 1,5-disubstituted 1,2,3-triazole-regioisomers (7b-12b) and yields ranging from 61 to 65% for the 1,4-disubstituted regioisomers (7a-12a). In order to report an unequivocal synthesis of the 1,4-regioisomers and confirm the structures of the two regioisomers obtained in thermal conditions (Huisgen reactions), the method click chemistry (Copper-Catalyzed Azide-Alkyne Cycloaddition) has been used.

CONCLUSIONS

The newly synthesized compounds using cycloaddition reactions were evaluated in vitro for their antibacterial activities against some Gram positive and Gram negative microbial strains. Among the compounds tested, the compound 8a showed excellent antibacterial activities against PA ATCC and Acin ESBL (MIC = 31.2 μg/ml).

Synthesis, computational studies and antiproliferative activities of coumarin-tagged 1,3,4-oxadiazole conjugates against MDA-MB-231 and MCF-7 human breast cancer cells

A novel library of coumarin tagged 1,3,4 oxadiazole conjugates was synthesized and evaluated for their antiproliferative activities against MDA-MB-231 and MCF-7 breast cancer cell lines. The evaluation studies revealed that compound 9d was the most potent molecule with an IC₅₀ value of <5 µM against the MCF-7 cell line. Interestingly, compounds 10b and 11a showed a similar trend with lower inhibitory concentration (IC₅₀ = 7.07 µM), in Estrogen Negative (ER-) cells than Estrogen Positive (ER+) cells. Structure-activity relationship (SAR) studies revealed that conjugates bearing benzyl moieties (9b, 9c and 9d) had superior activities compared to their alkyl analogues. The most potent compound 9d showed ∼1.4 times more potent activity than tamoxifen against MCF-7 cell line; while the introduction of sulfone unit in compounds 11a, 11b and 11c resulted in significant cytotoxicity against both MCF-7 and MDA-MB-231 cell lines. These results were further supported by docking studies, which revealed that the stronger binding affinity of the synthesized conjugates is due to the presence of sulfone unit attached to the substituted benzyl moiety in their pharmacophores.

ERE-dependent transcription and cell proliferation: Independency of these two processes mediated by the introduction of a sulfone function into the weak estrogen estrothiazine

The synthetic coumestrol derivative 6,12-dihydro-3-methoxy-1-benzopyrano[3,4-b][1,4]benzothiazin-6-one (estrothiazine, ESTZ) has been identified as a weak estrogen receptor α (ERα) ligand unable to compete with tritiated estradiol. The biological activity of this compound, supported by a methoxy group in position 3, seems mainly to result from its capacity to activate ERα dimerization without any participation of coactivators. In support of this view and referring to conventional estrogens, an ESTZ metabolism study conducted with hepatic human microsomes failed to provide any argument in favour of an estrogenic activity dependent on a metabolic conversion of the compound into hydroxylated metabolites with strong receptor activation ability. Interestingly, we failed to detect any oxidation of the sulfur atom of the compound. In the light of pharmacological literature data concerning sulfonylation, we assessed ERα-mediated activities generated by two sulfonylated ESTZ derivatives in which the methoxy group that plays a key role in its mechanism of action was maintained or removed. Sulfonylated ESTZ, even in its demethoxylated form, induced ERE-mediated transcriptions in MCF-7 breast cancer cells, without affecting the ERα turnover rate. In contrast to ESTZ, this compound failed to enhance the proliferation of ERα-positive breast cancer cells, suggesting that its sulfone function confers upon the receptor a capacity to elicit some of the known characteristics associated with estrogenic responses. Moreover, we demonstrated that this sulfone may contribute to ERα dimerization without any requirement of the methoxy group. Nevertheless, it seems to cooperate with this group, as reflected by a weak ability of the sulfonylated form of ESTZ to compete with tritiated estradiol for ERα-binding. Assessment of the docking of this compound within the ligand-binding domain of the receptor by molecular dynamics provided an explanation for this observation since the sulfone is engulfed in a small hydrophobic pocket involving the residues Leu-346, Leu-349, Ala-350 and Leu-384, also known to recruit coactivators. This work not only reports the sulfone functional group as a pharmacophore for estrogenic activity, but also opens new perspectives for the development of estrogenic molecules with therapeutic purpose and devoid of proliferative side effects.

(2Z)-2-Benzylidene-4-octadecyl-3,4-dihydro-2H-1,4-benzothiazin-3-one

The octadecyl chain in the title compound, C33H47NOS, is in the `fully extended' conformation. A puckering analysis of the thiazine ring was performed. The molecules form micellar blocks in the crystal by intercalation of the extended octadecyl chains and association of the dihydro benzothiazine units through C—H...O hydrogen bonds. These blocks are associated through intercalation of the pendant phenyl groups which reside on the outer edges of each block.

(2Z)-2-(4-Chlorobenzylidene)-4-[2-(2-oxooxazoliden-3-yl)ethyl]-3,4-dihydro-2H-1,4-benzothiazin-3-one

In the title molecule, C20H17ClN2O3S, the oxazolidine ring is oriented towards the benzothiazine moiety so that the centroid of the former isca5.05 Å from the sulfur atom of the latter. In the crystal, the molecules are arranged in layers parallel to (101) and held together by the aid of C—H...O interactions, resulting in a three-dimensional network structure.

ERα dimerization: a key factor for the weak estrogenic activity of an ERα modulator unable to compete with estradiol in binding assays

Estrothiazine (ESTZ) is a weak estrogen sharing structural similarities with coumestrol. ESTZ failed to compete with [³H]17β-estradiol ([³H]17β-E₂) for binding to the estrogen receptor α (ERα), questioning its ability to interact with the receptor. However, detection by atomic force spectroscopy (AFS) of an ESTZ-induced ERα dimerization has eliminated any remaining doubts. The effect of the compound on the proliferation of ERα-positive and negative breast cancer cells confirmed the requirement of the receptor. The efficiency of ESTZ in MCF-7 cells was weak without any potency to modify the proliferation profile of estradiol and coumestrol. Growth enhancement was associated with a proteasomal degradation of ERα without substantial recruitment of LxxLL coactivators. This may be related to an unusual delay between the acquisition by the receptor of an ERE-binding capacity and the subsequent estrogen-dependent transcription. A complementary ability to enhance TPA-induced AP-1 transcription was observed, even at concentrations insufficient to activate the ERα, suggesting a partly independent mechanism. ESTZ also rapidly and transiently activated ERK1/2 likely through membrane estrogenic pathways provoking a reorganization of the actin network. Finally, the systematic absence of biological responses with an ESTZ derivative unable to induce ERα dimerization stresses the importance of this step in the action of the compound, as reported for conventional estrogens. In view of the existence of many other ERα modulators (endocrine disruptors such as, for example, pesticides, environmental contaminants or phytoestrogens) with extremely weak or similar apparent lack of binding ability, our work may appear as pilot investigation for assessing their mechanism of action.

Role of dietary bioactive natural products in estrogen receptor-positive breast cancer

Estrogen receptor (ER)-positive breast cancer, including luminal-A and -B, is the most common type of breast cancer. Extended exposure to estrogen is associated with an increased risk of breast cancer. Both ER-dependent and ER-independent mechanisms have been implicated in estrogen-mediated carcinogenesis. The ER-dependent pathway involves cell growth and proliferation triggered by the binding of estrogen to the ER. The ER-independent mechanisms depend on the metabolism of estrogen to generate genotoxic metabolites, free radicals and reactive oxygen species to induce breast cancer. A better understanding of the mechanisms that drive ER-positive breast cancer will help optimize targeted approaches to prevent or treat breast cancer. A growing emphasis is being placed on alternative medicine and dietary approaches toward the prevention and treatment of breast cancer. Many natural products and bioactive compounds found in foods have been shown to inhibit breast carcinogenesis via inhibition of estrogen induced oxidative stress as well as ER signaling. This review summarizes the role of bioactive natural products that are involved in the prevention and treatment of estrogen-related and ER-positive breast cancer.

Crystal structure of (Z)-2-benzyl-idene-4-methyl-2H-benzo[b][1,4]thia-zin-3(4H)-one

In the title compound, C16H13NOS, the 1,4-thia-zine ring displays a screw-boat conformation. The conformation about the ethene bond [1.344 (2) Å] is Z. The plane of the fused benzene ring makes a dihedral angle of 58.95 (9)° with the pendent phenyl ring, indicating a twisted conformation in the mol-ecule. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming inversion dimers.

Recent progress in the drug development of coumarin derivatives as potent antituberculosis agents

Tuberculosis (TB) is still a challenging worldwide health problem and mycobacterium tuberculosis (MTB) remains one of the most deadly human pathogens. TB is the second leading infectious cause of mortality today behind only HIV/AIDS. The impetus for developing new structural classes of antituberculosis drugs comes from the emergence of multi-drug resistant (MDR) strains. The development of MDR strains to commonly used drugs is due to, longer durations of therapy as results of resistance, and the resurgence of the disease in immune compromised patients. Therefore, there is an urgent need to explore new antitubercular (anti-TB) agents. Ironically, the low number of potentially new chemical entities which can act as anti-TB candidates is of great importance at present situation. Considering the severity of the problem, WHO has prepared a strategic plan in Berlin declaration 2007 to stop TB, globally. Among the oxygen heterocycles, coumarin derivatives are important motifs, which can be widely found in many natural products, and many of them displaying diverse biological activities. This spectacular spectrum of applications has intrigued organic and medicinal chemists for decades to explore the natural coumarins or their synthetic analogs for their applicability as anti-TB drugs. To pave the way for the future research, there is a need to collect the latest information in this promising area. In the present review, we collated published reports on coumarin derivatives to shed light on the insights on different types of methods reported for their preparations, characterizations and anti-TB applications, so that its full therapeutic potential class of compounds can be utilized for the treatment of tuberculosis. Therefore, the objective of this review is to focus on important coumarin analogs with anti-TB activities, and structure-activity relationships (SAR) for designing the better anti-TB agents. It is hoped that, this review will be helpful for new thoughts in the quest for rational designs of more active and less toxic coumarin-based anti-TB drugs.

Novel coumarin derivatives containing 1,2,4-triazole, 4,5-dicyanoimidazole and purine moieties: synthesis and evaluation of their cytostatic activity

We report here on the synthesis and in vitro anti-tumor effects of a series of novel 1,2,4-triazole (compounds 3–6), 4,5-dicyanoimidazole (compound 7), and purine (compounds 8–13) coumarin derivatives and their acyclic nucleoside analogues 14–18. Structures of novel compounds 3–18 were deduced from their ¹H- and ¹³C-NMR and corresponding mass spectra. Results of anti-proliferative assays performed on a panel of selected human tumor cell lines revealed that compound 6 had moderate cytostatic activity against the HeLa cell line (IC₅₀ = 35 µM), whereas compound 10 showed moderate activity against the HeLa (IC₅₀ = 33 µM), HepG2 (IC₅₀ = 25 µM) and SW620 (IC₅₀ = 35 µM) cell lines. These compounds showed no cytotoxic effects on normal (diploid) human fibroblasts.

4-Hy-droxy-3-[(4-hy-droxy-2-oxo-2H-3-chromen-yl)(3-thien-yl)meth-yl]-2H-chromen-2-one

The whole mol­ecule of the title compound, C₂₃H₁₄O₆S, is disordered over two sets of sites with refined occupancies of 0.8733 (12):0.1267 (12). The dihedral angle between the mean planes through the chromene ring systems is 56.31 (5) and 55.2 (3)° for the major and minor components, respectively. In both components, a pair of intra­molecular O—H⋯O inter­actions generate rings of S(8) graph-set motif. In the crystal, the mol­ecules are linked by inter­molecular C—H⋯O inter­actions, forming chains along the b axis. The structure is further stabilized by π–π inter­actions with centroid–centroid distances of 3.594 (2) and 3.608 (5) Å.

A review of coumarin derivatives in pharmacotherapy of breast cancer

The coumarin (benzopyran-2-one, or chromen-2-one) ring system, present in natural products (such as the anticoagulant warfarin) that display interesting pharmacological properties, has intrigued chemists and medicinal chemists for decades to explore the natural coumarins or synthetic analogs for their applicability as drugs. Many molecules based on the coumarin ring system have been synthesized utilizing innovative synthetic techniques. The diversity oriented synthetic routes have led to interesting derivatives including the furanocoumarins, pyranocoumarins, and coumarin sulfamates (COUMATES), which have been found to be useful in photochemotherapy, antitumor and anti-HIV therapy, and as stimulants for central nervous system, antibacterials, anti-inflammatory, anti-coagulants, and dyes. Of particular interest in breast cancer chemotherapy, some coumarins and their active metabolite 7-hydroxycoumarin analogs have shown sulfatase and aromatase inhibitory activities. Coumarin based selective estrogen receptor modulators (SERMs) and coumarin-estrogen conjugates have also been described as potential antibreast cancer agents. Since breast cancer is the second leading cause of death in American women behind lung cancer, there is a strong impetus to identify potential new drug treatments for breast cancer. Therefore, the objective of this review is to focus on important coumarin analogs with antibreast cancer activities, highlight their mechanisms of action and structure-activity relationships on selected receptors in breast tissues, and the different methods that have been applied in the construction of these pharmacologically important coumarin analogs.

Synthesis, structure, and estrogenic activity of 4-amino-3-(2-methylbenzyl)coumarins on human breast carcinoma cells

A number of coumarins exhibit interesting pharmacological activities and are therefore of therapeutic use. We report here the synthesis and the structural analysis of new N-substituted 4-amino-3-(2-methylbenzyl)coumarins (compounds 8a-8e) that present structural analogies with estrothiazine and 11- or 7-substituted 17beta-estradiol. These derivatives were tested with respect to estrogenic activity on the estrogen receptor positive (ER+) human MCF-7 breast cancer cell line. Two of the reported compounds (8a and 8b) stimulated specifically the proliferation of MCF-7 cells, but not that of estrogen receptor negative (ER-) human MDA-MB-231 breast cancer cells, suggesting that their mitogenic activity is mediated by ER. Accordingly, the stimulating effect of 8a and 8b was suppressed by the pure antiestrogen fulvestrant. Besides, 8a and 8b induced ER down-regulation similar to that produced by classical ER agonists or pure antagonists. The effects of the compounds under study on ER-mediated transcription were assessed on (ER+) MVLN cells, that is, MCF-7 cells stably transfected with a pVit-tk-Luc reporter plasmid. Derivatives 8a and 8b, and surprisingly compound 8c, enhanced ER-mediated gene transactivation in that model. Finally, no coumarin was able to compete with tritiated 17beta-estradiol ([(3)H]E(2)) for ER binding, suggesting unconventional interactions with the receptor, such as interactions with the second binding pocket or with the coactivator-binding region. To conclude, observations performed in this study on compound 8c reveal that estrogenic activity can be dissociated from enhancement of cell proliferation. Furthermore, ERE-driven transactivation of transcription seems to be a condition necessary, but not sufficient, for estrogen-induced stimulation of cell growth.

Homopterocarpanes as bridged triarylethylene analogues: synthesis and antagonistic effects in human MCF-7 breast cancer cells

A series of new compounds structurally derived from 6a,12a-dihydro-6H,7H-[1]-benzopyran-[4,3-b]-benzopyran (homopterocarpane) was efficiently synthesized by reduction of the corresponding pyrilium salts obtained by treatment of selected flavanones and aldehydes with anhydrous HClO4. Cytotoxic effects on the human breast cancer cell line MCF-7 and antiestrogenic activity (only for compounds which resulted more active than tamoxifen (TAM)) on MCF-7 cells stimulated by 17beta-estradiol were evaluated. In vivo antiestrogenic activity and the relative binding affinity were also assessed. Some of the new compounds (4c, 4h, 4i and 4l) showed a biological activity in the micromolar range, and were more potent than TAM taken as the reference.

Synthesis of 4-hydroxycoumarin and 2,4-quinolinediol derivatives and evaluation of their effects on the viability of HepG2 cells and human hepatocytes culture

We report here the synthesis of aromatic coumarins and aromatic alpha-quinolones which were evaluated in vitro for their protective potentialities against tert-butyl hydroperoxide (t-BHP)-induced oxidative damage on human liver cell death, i.e., human hepatoma HepG2 cell line and human hepatocytes in primary culture. We found that the presence of a benzylidene at the 3-position or a heterocycle with N and S heteroatoms on the benzopyrone or quinolone system was essential for the protective effect of these compounds against t-BHP-induced decrease in viability of cells. We found also that a methoxy group on the aromatic ring systems decreased this potential. t-BHP-induced cytotoxicity in primary cultures of human hepatocytes could be therefore prevented by these compounds suggesting that they could display hepatoprotective effects in humans.

Pharmacological profile of 6,12-dihydro-3-methoxy-1-benzopyrano[3,4-b] [1,4]benzothiazin-6-one, a novel human estrogen receptor agonist

Pharmacological studies were carried out to characterize further the endocrinological profile and the binding mode to the estrogen receptor (ER) of 6,12-dihydro-3-methoxy-1-benzopyrano[3,4-b][1,4]benzothiazin-6-one (1). Binding experiments were conducted with highly purified recombinant human estrogen receptors hERa and beta. Potent estrogenic activity of compound 1 was assessed by testing its ability to down-regulate ERs and to enhance estrogen receptor element (ERE)-dependent transcription. The latest step of our work dealt with the synthesis of the 9-fluorinated derivative 15 for ionic microscopy experiments to determine the intracellular localization of compound 1. Although 1 failed to compete with [3H]E2 for binding to both ER isoforms, evidence was reported that it interacted with hERalpha in MCF-7 cells (ER down-regulation/ERE-dependent luciferase induction). Hence, an appropriate conformation of the hormone binding domain, most probably conferred by co-regulators of ER, is required for the onset of an activity of the compound 1. Estrogenic activity was weak but on the order of magnitude of that of coumestrol (slightly weaker). The synthesis of the 9-methoxylated derivative 16 and its pharmacological evaluation led us to propose a binding mode of 1 on hERalpha. Compound 1 appears to interact with ERa mainly through interactions of its 3-methoxy substituent with the residue His-524 of the hormone binding domain.