Synthesis and Anticancer Activity of Some Novel Tetralin-6-yl-pyrazoline, 2-Thioxopyrimidine, 2-Oxopyridine, 2-Thioxo-pyridine and 2-Iminopyridine Derivatives

The title compounds were prepared by reaction of 6-acetyltetralin (1) with different aromatic aldehydes 2a-c, namely 2,6-dichlorobenzaldehyde, 2,6-diflouro-benzaldehyde, and 3-ethoxy-4-hydroxybenzaldehyde, to yield the corresponding α,β-unsaturated ketones 3a-c. Compound 3b was reacted with hydrazine hydrate to yield the corresponding 2-pyrazoline 4, while compounds 3a,b reacted with thiourea to afford the 2-thioxopyrimidine derivatives 5a,b, respectively. The reaction of 1, and the aromatic aldehydes 2a-c with ethyl cyanoacetate, 2-cyano-thioacetamide or malononitrile in the presence of ammonium acetate yielded the corresponding 2-oxopyridines 6a,b, 2-thioxopyridines 7a-c or 2-iminopyridines 8a,b, respectively. The newly prepared compounds were evaluated for anticancer activity against two human tumor cell lines. Compound 3a showed the highest potency with IC50 = 3.5 and 4.5 μg/mL against a cervix carcinoma cell line (Hela) and breast carcinoma cell line (MCF7), respectively.


Introduction
Cancer is presently responsible for about 25% of deaths in developed countries and for 15% of all deaths worldwide. It can therefore be considered as one of the foremost health problems, with about 1.45 million new cancer cases expected yearly. Antitumor chemotherapy is nowadays a very active field of research, and a huge amount of information on the topic is generated every year [1,2].

Anticancer Screening
All the newly synthesized compounds were tested at the Department of Tumor Pathology, National Cancer Institute, Cairo, Egypt. Two cell lines were used for the evaluation -human cervix carcinoma cell line (Hela) and human breast carcinoma cell line (MCF7). The newly synthesized analogs 3a-c, 4, 5a,b, 6a,b, 7a-c and 8a,b were tested for in vitro cytotoxic activity against these cell lines, which were obtained frozen in liquid nitrogen (-180 °C) from the American Type Culture Collection [26]. The tumor cell lines were maintained in the National Cancer Institute, Cairo, Egypt, by serial sub-culturing.
The results ( Table 2) are expressed in the form of the concentration of compound that causes 50% inhibition of cells growth. The in vitro evaluation revealed that all the newly synthesized compounds showed certain activity against tumor cell lines tested, although the activity was generally higher towards the cervical cancer line than the breast cancer one. Compound 3a showed potent and broad antitumor activity against the two tumor cell lines tested (IC 50 = 3.5 against Hela and IC 50 = 4.5 against MCF7) compared to the potent anticancer drug 5-flourouracil (5-FU) used as a reference standard [27]. Substitution of the side chain with different ring systems like in the oxopyridine or thioxopyridine compounds 6a,b and 7a,b resulted in moderate activity against the Hela cell line and marked activity against the MCF-7 cell line. Meanwhile, substitution of the side chain with iminopyridine, thioxopyrimidine and/or pyrazoline rings resulted in low activity against the two tumor cell lines. These results demonstrated that changing the molecular conformation and orientation could influence markedly the antitumor activity against the two tested cell types.

General
Melting points (°C, uncorrected) were measured in open glass capillaries using a Barnstead 9001 electrothermal melting point apparatus. Infrared spectra (ν, cm -1 ) were recorded on a Jasco FT/IR-330E, Fourier Transform Infrared Spectrometer using KBr discs. 1 H-NMR spectra were determined using a Bruker AC 500 Ultra Shield NMR spectrometer operating at 500.13 MHz for 1 H and 125.76 MHz for 13 C, the chemical shifts are expressed in δ (ppm) downfield from tetramethylsilane (TMS) used as internal standard. Electron impact mass spectra (EI-MS) were recorded on a Shimadzu GC-MS-QP 5000 instrument at 70 eV. Elemental analyses (C, H, N) were in full agreement with the proposed structures within ±0.4% of the theoretical values. Monitoring the reactions and checking the purity of the final products were carried out by thin layer chromatography (TLC) using silica gel precoated aluminum sheets (60 F 254 , Merck) and visualization with ultraviolet light (UV) at 365 and 254 nm.

Conclusions
New tetrahydronaphthaline derivatives bearing different heterocyclic moieties were tested for in vitro antitumor activity. The results indicated that the 2,6-dihaloarylchalcone derivatives 3a,b, the cyanopyridone derivatives 6a,b and thioxopyridine derivatives 7a-c were the most effective against the cervix cell line (Hela), showing IC 50 values of 3.5, 10.5, 7.1, 10.9, 8.1, 5.9 and 6.5 μg/mL, respectively. All the tested compounds showed moderate to marginal activity against the breast carcinoma cell line MCF-7. Compound 3a was the most potent, with an IC 50 value of 3.5 μg/mL against Hela and 4.5 μg/mL against MCF7 cell line. Compound 3a seems a promising new lead compound with a novel skeleton for further development towards a new potential clinical trials candidate.