Synthesis of novel thiazole, pyranothiazole, thiazolo[4,5-b]pyridines and thiazolo[5′,4′:5,6]pyrano[2,3-d]pyrimidine derivatives and incorporating isoindoline-1,3-dione group

Background Thiazole is a core structural motif presents in a wide range of natural products. Thiazole derivatives also have a wide range of medicinal and biological properties. Results The reaction of hydrazonoyl halides with 2-(1-(4-(1,3-dioxoisoindolin-2-yl)phenyl)ethylidene)hydrazinecarbothioamidein ethanol and triethylamine yielded 2-(4-(1-(2-(4-(2-Arylhydrazono)-5-s-4,5-dihydrothiazol-2-yl)hydrazono)-ethyl)phenyl)isoindoline-1,3-dione and 2-(4-(1-(2-(5-(2-Arylhydrazono)-4-oxo-4,5-dihydrothiazol-2-yl)hydrazono)ethyl)-phenyl)isoindoline-1,3-dione.The reaction of 2-(4-(1-(2-(4-oxo-4,5-dihydrothiazol-2-yl)hydrazono)ethyl)phenyl)isoindoline-1,3-dione with arylidenemalononitrile also yielded 5-amino-2-(2-(1-(4-(1,3-dioxoisoindolin-2-yl)phenyl)ethylidene)hydrazinyl)-7-substituted-7H-pyrano[2,3-d]thiazole-6-carbonitrile. The structures of the newly synthesized compound were elucidated whenever possible on the basis of elemental analysis, spectral data, and alternative synthetic routes. Three of them were evaluated against a breast cancer cell line for their antitumor activity. Conclusions Compound (1) has been shown to be useful in the synthesis of a new series of 1,3-thiazole, pyrano[2,3-d]thiazole and 4,5-dihydrothiazolo[4,5-b]pyridine derivatives using hydrazonoyl halides as precursors. The anticancer efficacy of compounds (9b), (9e), and (9f) against MCF-7, a breast cancer cell line, was also compared to the standard anticancer drug doxorubicin. Electronic supplementary material The online version of this article (10.1186/s13065-019-0559-x) contains supplementary material, which is available to authorized users.


Cytotoxicity evaluations
Through the literary survey it became clear to us that many thiazole derivatives have an excellent anti-tumor activity as shown in Fig. 1 [22,23]. In light of this, antitumor activity was examined for a new series of thiazole substitutes against breast cancer cells line (MCF-7).
In comparison with the well-known anticancer standard drug doxorubicin, the in vitro growth inhibitory activity of the synthesized compounds (9b), (9e), and (9f) was investigated using trypan blue dye viability test. Data generated were used to determine a dose response curve that determined the concentration of test compounds needed to kill 50% of the cell population (IC 50 ). The cytotoxic activity of three independent experiments was expressed as the mean IC 50 . In a concentration-based manner, the results showed that all tested compounds showed an inhibitory activity for tumor cell lines. The small IC 50 values for the compounds selected indicate that, higher concentrations may be used for more anticancer effect. The results are shown in Table 1 and Fig. 2 as follows: The in vitro inhibitory activities of tested compounds against breast cancer cell line (MCF-7) have the following descending order: (9b) > (9e) > (9f ).
Examination of the SAR leads to the following conclusions: • For substituents in position 4 and 5 of the thiazole ring, the following descending order is the in vitro inhibitory activity of tested compounds against the breast cancer cell line. The activity of thiazole (9e) is moderate.
• For substituents at position 4 and 5 of the thiazole ring, the in vitro inhibitory activity of tested compounds against breast cancer cell line has the following descending order: CH 3 , 4-CH 3 C 6 H 4 > 2-C 4 H 3 S, C 6 H 5 > 2-C 10 H 7 , C 6 H 5 group.

Experimental
All of the melting points were determined using a Gallenkamp electrothermal melting point apparatus (Laim George, Calgary, AB, Canada) and, they are uncorrected.

Alternative synthesis of (16a) and (16b)
In acetic acid (25 mL), equimolar amounts of (15a) or (15b), ammonium acetate, and arylidenemalonitrile were heated for 4 h under reflux. The reaction mixture was left at room temperature to cool. The solid formed was filtered off, dried and recrystallized from methanol to obtain an identical product with (16a) and (16b) in all aspects of mp, mixed mp, and spectra.

Evaluation of the antitumor activity using viability assay
The carcinoma cell line utilized during this study, MCF-7, was gotten from the American Kind Culture Group (ATCC, Minnesota, USA). RPMI-1640 environment was utilized for culturing and keeping of the human tumor cell lines [30]. The medium was supplied in a powder form. 10.4 Gram powder and 2 g NaHCO 3 in 1 L distilled H 2 O are dissolved to prepare the working solution. Then, in the Melibor bacteria filter (0.22 μm), the medium was sterilized by filtration. The refrigerator was used at 0-4 °C to maintain the prepared medium. The medium was heated at 37 °C in a water bath and supplemented with 1% penicillin streptomycin and 10% of fetal bovine serum before use. Through the use of the sulforhodamine-B (SRB) assay [31] the cytotoxicity assay was performed. SRB is aminoxanthrene dye with two SO 3 H groups. It is a protein patches that binds to the amino groups of intracellular proteins under slightly acidic conditions to supply a sensitive indicator of cellular protein content. In MCF-7 cells, cytotoxicity was tested for all compounds. At the National Cancer Institute, Cairo, Egypt, by serial subculturing all experiments and data related to the assessment of cellular cytotoxicity were conducted. For the cytotoxicity assay, cells were seeded in 96-well microliter plates at an initial concentration of 3 × 10 3 cells/well in 150 µL of fresh medium and left to attach to the plates for 24 h. At variable concentrations of 0, 5, 12.5, 25 and 50 μg/ mL, the drug was added. Three wells were used for every concentration of drugs and the plates were incubated for 48 h. The cells were fixed by adding 50 μL of cold trichloro acetic acid (10% final concentration) at 4 °C for 1 h. The plates were therefore washed with distilled H 2 O using an automatic washer (Tecan, Germany) and stained with 50 μL of 0.4%. SRB dissolved in 1% acetic acid at room temperature for 30 min. With 1% acetic acid and dried air, the plates were washed. . The values of inhibitory concentration (IC 50 ) (resveratrol concentrations required to inhibit cell growth by 50%) have also been calculated. The relationship between the surviving cells and the concentration of the drug was plotted after treatment with the specified compound to obtain the survival curve of each tumor cell line. The IC 50 , The concentration required by 50% of intact cells to cause toxic effects, was estimated at each concentration from graphical plots of the dose response curve.