Anticancer Activities of Some New Synthesized Thiazolo[3,2-a]Pyrido[4,3-d]Pyrimidine Derivatives

Problem statement: This study describes the synthesis and anticancer activities of a new series of thiazolo[3,2-a]pyrimidines derivatives (2 -7) using 3,5-bisarylmethylene-1-methyl-4piperidone and 4-aryl-8-arylmethelene-6-methylpyrid o[4,3-d]pyrimidine-2(1H)thiones as a starting materials. Approach: The antitumor activities of the newly synthesized compounds 4-7 were evaluated utilizing 60 different human tumor cell l ines, representing leukemia, melanoma, lung, colon, brain, ovary, breast and prostate as well as kidney . R sults: Some of the tested compounds exhibited better in vitro antitumor activities at low concent ration (log10 GI 50 = -4.7) against the used human tumor cell lines. Conclusion: From the obtained results, we can conclude that py rimidine moieties fused to N-methylpipredine ring are essential for a ntitumor activities. In the present work, we can suggest that the anticancer activity is due to the presence of nitrogen heterocyclic rings and the presence of sulfur atom generally enhancing the act ivity.


INTRODUCTION
Cancer poses a serious human health problem despite much progress in understanding its biology and pharmacology. Consequently, the design of new lead structures employed as antitumor agents is one of the most urgent research areas in contemporary medicinal chemistry. During our ongoing studies aimed at the discovery of new heterocycles endowed with antitumour activity, we have reported on the synthesis and antitumor activities of a series of heterocyclic compounds (Hammam et al., 2003;Amr et al., 2006;Velusamy and Palaniappan, 2011;Abd El-Salam et al., 2010). Pyrimidine has gained considerable attention because of its diversity in biological activity and widespread applications in pharmaceuticals fields (Katritzky and Rees, 1996;Francis et al., 2011). For instance, as Tie-2 kinase inhibitors (Matloobi and Kappe, 2007;Chengguo et al., 2009), HIV-1 inhibitor (Gadhachanda et al., 2007;Naeem et al., 2009), antimalarial (Ngoy et al., 2011;Khan et al., 2009), adenosine A 1 receptor antagonist (Chang et al., 2004), anticancer (Capdeville et al., 2002), analgesic (Rezvani and Shariati, 2010), cardiovascular (Atwal, 1988 andHasanuzzaman et al., 2010) and antiallergic (Ozeki et al., 1989;Dahmardeh, 2011) activities. On the other hand, the importance of the pyridine ring in the chemistry of biological system has been greatly realized because of their presence as substructure in many natural products of therapeutic importance, involved in oxidation-reduction process. The potent biological activity of various vitamins and drugs (Joule and Mills, 2000;Henry, 2004;Li et al., 1999;Vacher et al., 1999;Nasratun et al., 2009) is primarily contributed by the presence of pyridine ring in their molecular make-up. Furthermore, the pyridine ring is found in the skeleton of many compounds with potent antibacterial, antifungal and anticancer properties (Millet et al., 2004;Mallea et al., 2003;Abou-Ghalia and Amr, 2004;Amr et al., 2009;Jill et al., 2011). In view of these reports and in continuation of our previous work in heterocyclic chemistry, we herein synthesized some new derivatives containing heterocyclic ring fused with Nmethylpiperdion and/or pyrido [4,3-d] pyrimidine structure for the evaluation of their anticancer activities. In view of a beforementioned biological activities and as a part of our interest in the sereach for novel anticancer agents, we report herein the synthesis of several thiazolo [3, 2-a] pyrido [4, 3-d] pyrimidine derivatives and evaluate of their anticancer activities.

MATERIALS AND METHODS
Chemistry: All melting points were determined on open glass capillaries using an Electrothermal IA 9000 digital melting point apparatus and are uncorrected. Elemental analyses were performed on Elementar, Vario El, Microanalytical Unit, National Research Centre, Cairo, Egypt and were found win ± 0.4% of the theoretical values. Infrared (IR) spectra were recorded on Carlzeise Spectrophotometer model 'UR 10' spectrophotometer using the KBr disc technique. 1 H NMR spectra were recorded on Varian Gemini 270 MHz spectrometer (DMSO-d 6 or CDCl 3 ) and the chemical shift are given in δ (parts per million) downfield from Tetramethylsilane (TMS) as an internal standard. The Mass Spectra (MS) were measured using a Finnegan SSQ 7000 mass spectrometer. The anticancer screening occurred in United States National Institute of Health (NIH)/National Cancer Institute (NCI). The starting material, 3,5bisarylmethylene-1-methyl-4-piperidon (1) was synthesized according to the reported procedures (Lyle et al., 1973;Mcelvain and Rorig, 1948;Abdel-Latif and Lamiaa, 2010).

RESULTS
In continuation to our search for new heterocyclic chemistry based anticancer, the suggestion, synthesis, structure elucidation of some thiopyrimidine derivatives 2-7 were realized herein using 3,5-bisarylmethylene-1methyl-4-piperidone and 4-aryl-8-arylmethelene-6methylpyrido[4,3-d]pyrimidine-2(1H)thiones as a starting materials. Some of the synthesized compounds were selected and screened for their anticancer activity. Each compound was tested at five different concentrations against 60 cell lines of nine types of human cancers, namely, leukemia, lung, colon, CNS, melanoma, ovarian, renal, prostate and breast cancer. Some of the tested compounds were better exhibited in vitro antitumor activities at low concentration (log 10 GI 50 = -4.7) against the used human tumor cell lines. From the in vitro observed data it has been noticed that, some of the synthesized compounds seem to be the most active prepared derivatives against all the tested cell lines.

Chemistry:
The synthetic strategy to synthesize the target products 2-7 is depicted in Fig. 1 and 2. Preparation of 3, 5-bisarylmethylene-1-methyl-4piperidone (1a-f) was established according to the reported procedure (Lyle et al., 1973;Mcelvain and Rorig, 1948;Pattaraporn and Tharapong, 2009). The corresponding pyrimidine thione derivatives (2a-e) were obtained from condensation of 1a-e with thiourea in ethanolic potassium hydroxide solution under reflux. When compounds 1a-d, f reacted with 2-amino-2thiazoline in butanol/DMSO mixture afforded compounds 3a-e in good yields. Reaction of compounds 2a-e with chloroacetic acid or with 2-bromopropionic acid in the presence of sodium acetate in acetic acid/acetic anhydride mixture gave thiazolopyrimidene derivatives 4a-e and 5a-e, respectively (Fig. 1). Compounds 4a,b,d contain an active methylene group, when these compounds reacted with aromatic aldehydes in the presence of acetic acid/acetic anhydride mixture, the corresponding arylmethylene thiazolopyrimidines derivatives 6a-e were obtained (Fig. 2). The products 6a-e could be also obtained from reaction of 2a,b,d with chloroacetic acid, followed by treatment with aromatic aldehyde in the presence of sodium acetate in refluxing acetic acid/acetic anhydride mixture. Compounds 4a,b,d were coupled with aryldiazonium salts in the presence of pyridine to give arylazo-thiazolopyrimidines derivatives 7a-d (Fig. 2). Antitumor screening: Antitumor activity screening for the synthesized compounds utilizing 59 different human tumor cell lines, representing leukemia, melanoma and cancers of the lung, colon, brain, ovary, breast, prostate as well as kidney, was carried out according to the previously reported standard procedure (Fylaktakidou et al., 2004;Jung et al., 2005;Ngoy et al., 2011 andShuangning et al., 2010). The obtained results ( Table 1) represent concentrations of the used investigated compounds resulting in growth inhibition of 50% (GI 50 ) for the tested human tumor cell lines. From the in vitro observed data it has been noticed that, the selected compounds 3b, 3c, 3d, 4a, 4b, 4d, 5b, 5c, 5d, 6c, 6b, 6d, 7b and 7d seem to be the most active prepared derivatives against all the tested cell lines.

Structural-Activity Relationship (SAR):
From the above-obtained results (Table 1), we can conclude that thiopyrimidine moieties fused to N-methylpipredine ring are essential for antitumor activities. In the present work, we can suggest that the anticancer activity is due to: • The presence of nitrogen heterocyclic rings • The most active compounds being 3b, 3c, 3d, 4a, 4b, 4d, 5b, 5c, 5d, 6c, 6b, 6d, 7b and 7d against all the tested cell lines. • The presence of the nitrogen and sulfur atoms generally enhancing the activity • The difference in activity between the compounds which is due to the indicated subsistents in the phenyl group of the molecule
The antitumor activities of the newly synthesized compounds were evaluated utilizing 60 different human tumor cell lines, representing leukemia, melanoma, lung, colon, brain, ovary, breast, prostate as well as kidney. Some of the tested compounds were better exhibited in vitro antitumor activities at low concentration (log 10 GI 50 = -4.7) against the used human tumor cell lines. In the present work, we can suggest that the anticancer activity is due to the presence of nitrogen heterocyclic rings and the presence of the sulfur atom.