Synthesis and Antitumor Activity of 5-Phenyl-1,3-thiazole-4-sulfonamide Derivatives

A method for the synthesis of 5-phenyl-1,3-thiazole-4-sulfonyl chloride was developed based on the cyclization of ethyl 2-{[1-(benzylsulfanyl)-2-oxo-2-phenylethyl]amino}-2-oxoacetate obtained from available reagents under the action of the Lawesson’s reagent and oxidative chlorination of the intermediate benzyl 5-phenyl-1,3thiazol-4-ylsulfide. The resulting sulfonyl chloride was converted into a series of 5-phenyl-1,3-thiazole-4-sulfonamide derivatives for which in vitro antitumor activity screening studies were performed on 60 cancer cell lines.

DOI: 10.1134/S1070363222020062 Malignant diseases are widespread. They are considered as the main problem of this century, which worries the medical community around the world [1]. The development of resistance to anticancer drugs, leading to their inefficiency, necessitates the search for new highly active and less toxic chemotherapeutic agents. Among drug development strategies, special attention is paid to molecules containing heterocycles with a sulfur atom in their structure, and, in particular, a thiazole ring, since its derivatives have excellent pharmacological characteristics [2][3][4]. The thiazole ring is present in more than 18 FDA-approved drugs [4].
Modification of a thiazole scaffold with carboxyl, sulfonyl, or sulfonamide pharmacophores significantly expands the spectrum of biological activity, making such hybrids ideal candidates for the development of more effective and safer drugs. Among them, the most studied are thiazole-4-and thiazole-5-carboxylic acid derivatives [2,5,6], which include the well-known antitumor drugs bleomycin 1 and dasatinib 2 (Scheme 1). Among thiazole-2-carboxylic acid amides 3, effective inhibitors of ubiquitin-specific peptidase 7 (USP7) were found [7].
Sulfonyl hybrids are widely studied for their anticancer activity, as they are characterized by minimal side effects along with encouraging indicators of the possible development of drug resistance associated with their repeated use [8][9][10]. Thiazolesulfonamides have a wide spectrum of pharmacological activity, among which a number of thiazole-4-(4) and thiazole-5-sulfonamides (5) have been proposed for the prevention or treatment of cancer as inhibitors of ATM and DNA-PK [11], PI3Kα [12], Raf [13] kinases and ATG4B protease [14].
This work is a continuation of our research on the synthesis of thiazole-4-sulfonamides [15] in order to search for effective anticancer agents, and is based on the idea of creating previously unknown sulfonyl hybrids of thiazolecarboxylic acids.
Since compound 10 could not be isolated in pure form, we tried to obtain it in another way, starting from the adduct of formamide and phenylglyoxal. However, unlike 4-chlorophenyl-and 4-methylphenylglyoxals, for which adducts with formamide have been successfully synthesized [17,19], the reaction of phenylglyoxal with formamide was accompanied by significant resin formation, regardless of conditions (when heated or at room temperature, in benzene or THF).
Amination of sulfonyl chloride 11 with ammonia and amines was carried out by heating in dioxane (Scheme 3), which made it possible to obtain a series of sulfonamides 12-15 for further testing for anticancer activity. It should be noted that the list of 2-unsubstituted 1,3-thiazole-4sulfonyl chlorides and 4-sulfonamides described earlier is limited to 5-unsubstituted derivatives and compounds with non-aromatic substituents in position 5 [11,20,21]. For reactions, amines containing pharmacophore fragments (piperidine, morpholine, piperazine or tetrahydrothiophene-1,1-dione) were chosen, since such structural fragments are present in a number of azole sulfonamides, which exhibit a high level of anticancer activity [22,23].
Amination product 12 was formed by the reaction of sulfonyl chloride 11 with aqueous ammonia at room temperature. N-Substituted sulfonamides 13-15 were obtained by heating a reactants mixture with triethylamine Scheme 1. in dioxane. The yields of amination products are practically independent of the amine structure; all sulfonamides were obtained in high yields (70-85%).

HN NH
Composition and structure of new thiazole derivatives 11-15 were confirmed by elemental analysis, IR, 1 H and 13 C NMR spectroscopy, and mass spectrometry methods. The formation of an azole ring is indicated by the absence in the IR and NMR spectra of the NH signals and carbonyl groups characteristic of the starting acyclic compound 9. Stretching vibrations of the SO 2 group in the IR spectra of compounds 11-15 are observed in the form of two strong bands in the 1143-1193 and 1332-1382 cm -1 regions. A characteristic feature of the 1 H NMR spectra of thiazoles 11-15 is the presence of a singlet of the aromatic proton of the C 2 H thiazole ring in a downfield (9.11-9.29 ppm). In the 13 C NMR spectra, the resonance of the tertiary carbon С 2 of the thiazole ring is observed in a lower field (153.5-155.1 ppm) than the signal of the quaternary carbon С 4 (143.6-150.1 ppm).
As part of the international scientific program of the US National Institutes of Health, testing of the antitumor activity of thiazole-4-sulfonamides 12-15 was carried out. Screening studies were carried out in vitro on 60 cancer cell lines that cover current types of human cancers (lines of lung, kidney, CNS, ovarian, prostate, breast, epithelial cancer, as well as leukemia and melanoma) when exposed to a substance at a concentration of 1× 10 -5 M, as a result of which the growth percentage (GP) of cancer cell lines was determined in comparison with the control (control, 100%) [24][25][26][27]. It was fond that the level of antitumor activity of 5-phenyl-1,3-thiazole-4-sulfonamides 12-15 determines the structure of the amine fragment. Compounds 13, 14d, and 15a-15d, which contain bulky sulfonamide groups in their structure, showed the lowest activity, inhibiting the growth of cancer cells by less than 20% (GP > 80%). The activity of piperazine derivatives 14g-14k is somewhat higher, except for 1-(4-methoxyphenyl)piperazine 14i (Table 1). At the same time, only some cell lines were moderately sensitive to the action of compounds 14g, 14h and 14j, 14k (GP < 80%). The best indicator in this group of thiazolyl-4-sulfonamides was found for the 1-(3-chlorophenyl)piperazine derivative 14h, which Amino-unsubstituted thiazolyl-4-sulfonamide 12 and 2,6-dimethylmorpholinyl derivative 14f had a moderate inhibitory effect (GP < 80%) on the growth of SNB-75 (CNS) and UO-31 (kidney cancer, 14f) cell lines.

EXPERIMENTAL
All reagents and solvents used in synthetic procedures were purchased from Aldrich and used without further purification. Scheme 3. 1 H and 13 C NMR spectra were recorded on a Varian Mercury 400 spectrometer (400 and 126 MHz). The internal standard was TMS. The signals of 13 C atoms (methyl, methylene, methine, and quaternary carbon atoms) were assigned using the APT method, taking into account the known range of chemical shifts of carbon atoms included in the functional groups. IR spectra (KBr) were recorded on a Bruker VERTEX 70 instrument. Mass spectra were recorded on an Agilent 1200 LCMCD SL instrument [chemical ionization (APCI), electrospray ionization (ESI)]. Melting points were determined on a Fisher-Johns apparatus. Elemental analyzes were performed at the Analytical Laboratory of the Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine. The content of carbon and hydrogen was determined by the Pregl gravimetric method, nitrogen-by the gravimetric Dumas micromethod, sulfur-by the Schöniger titrimetric method, and chlorine-by the mercurometric method.   To the residue was added 100 mL of 5% NaOH aqueous solution. The reaction product was extracted from the resulting oil with chloroform (2×100 mL), the extract was dried with CaCl 2 . The solvent was removed in vacuum and the residue was dissolved in 100 mL of ethanol. To a solution containing ethyl 4-(benzylsulfanyl)-5-phenyl-1,3-thiazole-2-carboxylate 9 was added 100 mL of 10% NaOH aqueous solution, boiled for 1 h and left at 20-25°C for 2 h. Next, hydrochloric acid (conc.) was added to the solution to pH 2 and boiled for 1 h. After cooling, the solvent was removed in vacuum and 200 mL of water was added to the residue. The product was extracted with chloroform (2×100 mL), the extract was dried with CaCl 2 . The solvent was removed in vacuum, the residue was dissolved in 80 mL of acetic acid (95%), and gaseous Cl 2 was bubbled through the solution containing benzyl-5-phenyl-1,3-thiazol-4-ylsulfide 10 for 30 min, maintaining the temperature of the reaction mixture within 0-5°С. Next, the solution was kept at 0-5°C for 2 h and then poured into ice (500 g). The formed precipitate was filtered off and dried in a vacuum desiccator over Р 2 О 5 . Compound 11 was purified by recrystallization from toluene. Yield 42.2 g (65%), colorless crystals, mp 114-116°С (toluene). IR spectrum, ν, cm