Green synthesis and biological evaluation of 6-substituted-2-(2-hydroxy/methoxy phenyl)benzothiazole derivatives as potential antioxidant, antibacterial and antitumor agents.

We present a new efficient green synthetic protocol for introduction of substituents to the C-6 position of 2-arylbenzothiazole nuclei. Newly synthesized compounds were designed to study the influence of the hydroxy and methoxy groups on the 2-arylbenzothiazole scaffold, as well as the influence of the type of substituents placed on the C-6 position of benzothiazole moiety on biological activity, including antibacterial, antitumor and antioxidant activity. Modest activity was observed against the tested Gram-positive and Gram-negative bacterial strains for only amidino derivatives 5d and 6d. The tested compounds exhibited moderate to strong antiproliferative activity towards the tumor cell lines tested. The SAR study revealed that the introduction of substituents into the benzene ring of the benzothiazole nuclei is essential for antiproliferative activity, while introduction of the hydroxy group into the 2-aryl moiety of the 2-arybenzothiazole scaffold significantly improved selectivity against tumor cell lines. The observed results revealed several novel 6-substituted-2-arylbenzothiazole compounds, 5b, 5c, 5f and 6f, with strong and selective antiproliferative activity towards HeLa cells in micro and submicromolar concentrations, with the most selective compounds being 6-ammonium-2-(2-hydroxy/methoxyphenyl)benzothiazoles 5f and 6f. The compound 5f bearing the hydroxy group on the 2-arylbenzothiazole core showed the most promising antioxidative activity evaluated by DPPH, ABTS and FRAP in vitro assays. The presence of the amino protonated group attached at the benzothiazole moiety was essential for the antiproliferative and antioxidant activity observed, exerted through a change in the levels of the reactive oxygen species-modulated HIF-1 protein.

Interactions with polynucleotides and antitumor activity of amidino and imidazolinyl substituted 2-phenylbenzothiazole mesylates.

Based on previously reported antiproliferative activity screening, four most promising disubstituted 2-phenylbenzothiazole hydrochlorides were chosen for detailed study. Water solubility, as well as liphophilicity/hydrophilicity balance of organic core were modified by conversion to mesylate salts. For purpose of structure/activity studies their structures were determined by X-ray structure analysis. Detailed analysis of interactions of new compounds with double stranded (ds-) DNA/RNA by UV/Vis and CD titrations, thermal melting and viscometry experiments revealed that most of studied compounds intercalate into ds-RNA but bind into minor groove of AT-DNA, and agglomerate along GC-DNA. Furthermore, compounds also interact with ss-RNA, but only amino-imidazolinyl 2-phenylbenzothiazole, 4b displayed well defined orientation and dominant binding mode (by induced CD signals) with poly A and poly G. Besides, in vitro investigations revealed moderate to high antiproliferative activity of benzothiazoles against seven human cancer cell lines, while in some cases (HTC 116, SW620, MIA PaCa-2) high correlation between the type of the amidino group and cytotoxic activity was observed.

New anticancer active and selective phenylene-bisbenzothiazoles: synthesis, antiproliferative evaluation and DNA binding.

Novel amidino-derivatives of phenylene-bisbenzothiazoles were synthesized and tested for their antiproliferative activity against several human cancer cell lines, as well as DNA-binding properties. The synthetic approach used for preparation of isomeric amidino substituted-phenylene-bis-benzothyazoles 3a-3f was achieved by condensation reaction of isophthaloyl dichloride 1a and terephthaloyl dichloride 1b or with phthalic acid 1c with 5-amidinium-2-aminobenzothiolate 2a and 5-(imidazolinium-2-yl)-2-aminobenzothiolate 2b in good yields. The targeted compounds were converted in the desired water soluble dihydrochloride salts by reaction of appropriate free base with concd HCl in ethanol or acetic acid. All tested compounds (3a-3f) showed antiproliferative effects on tumour cells in a concentration-dependant manner. The strongest activity and cytotoxicity was observed for diimidazolinyl substituted phenylene-bisbenzothiazole compound 3b. These effects were shown to be related to DNA-binding properties, topoisomerase I and II poisoning effects and apoptosis induction. The highest tested selectivity towards tumour cells was observed for the imidazolyl substituted phenylene-benzothiazole 3d that showed no cytotoxic effects on normal fibroblasts making it an excellent candidate for further chemical optimization and preclinical evaluation.

Synthesis and antiproliferative evaluation of some new amidino-substituted bis-benzothiazolyl-pyridines and pyrazine.

Novel diamidino substituted conformationally restricted derivatives of bis-benzothiazolyl-pyridines and pyrazine were synthesized and their antiproliferative activity against several human cancer cell lines were determinated. The synthetic approach used for preparation of isomeric amidinobenzotiazolyl disubstituted pyridines 3a-3k and pyrazine 3l was achieved by condenzation reaction of commercially available pyridine and pyrazine dicarboxylic acids with amidino- 2a and 2-imidazolinyl-substituted 2-aminothiophenol 2b in polyphosphoric acid in moderate to good yield. The condenzation reaction was greatly optimized. The targeted compounds were converted in the desired water soluble dihydrochloride salts by reaction of appropriate free base with concd HCl in ethanol or acetic acid. Antiproliferative assays revealed significant differences in antiproliferative activities of diamidino- and diimidazolinyl-derivatives, the latter exerting stronger concentration-dependent antiproliferative effects on tested tumor cell lines and thus being a prominent compound class for further chemical optimization and biological studies. Biological studies on SW620 cell line and BJ fibroblasts performed for the diimidazolinyl-derivative 3b revealed oxidative stress as a possible mechanism of antiproliferative action and predicted antineoplastic properties for this class of compounds.

Novel diamidino-substituted derivatives of phenyl benzothiazolyl and dibenzothiazolyl furans and thiophenes: synthesis, antiproliferative and DNA binding properties.

A series of new diamidino-, diisopropylamidino-, and diimidazolinyl-substituted derivatives of phenyl benzothiazolyl and dibenzothiazolyl furans and thiophenes were successfully prepared and evaluated for their antiproliferative activity on tumor cell lines in vitro, DNA binding propensity, and sequence selectivity as well as cellular distribution. A strong antiproliferative effect of the tested compounds was observed on all tested cell lines in a concentration-dependent response pattern. In general, imidazolinyl-substituted derivatives and/or the thiophene core were in correlation with increased antiproliferative activity. Two compounds (2b and 3b) were chosen for biological studies due to their differential antiproliferative properties. The DNA binding properties of this new series of compounds were assessed and evidenced their efficient minor groove binding properties with preferential interaction at AT-rich sites. Both compounds also present nuclear subcellular localization, suggesting that their cellular mode of action implies localization in the DNA compartment and direct inhibition of DNA replication and induction of apoptosis.

Novel amidino substituted 2-phenylbenzothiazoles: synthesis, antitumor evaluation in vitro and acute toxicity testing in vivo.

The efficient synthesis of new bis-substituted nitro-amidino, amino-amidino (10a, 10b-13a, 13b) and previously prepared diamidino 2-phenyl-benzothiazoles (9a, 9b) is described. The compounds 11a and 11b were prepared by recently developed methodology of the key precursors in zwitterionic form 8a and 8b with 4-nitrobenzoylchloride in a very good yield (70%). All compounds except diamidino-substituted 2-phenylbenzothiazole 9a show exceptionally prominent tumor cell-growth inhibitory activity and cytotoxicity, whereby the special selectivity of amino-amidine 2-phenylbenzothiazole 12a towards MCF-7 and H 460 cells makes this compound a prospective lead compound that should be further evaluated in animal models. All in vivo tested compounds (12a, 12b, 13a and 13b) are absorbed from mice gastrointestinal system. LD(50) are between 67.33 and 696.2mg/kg body weight (OECD/EPA toxicity categories 2-3).

S-2-Amino-5-(dimethyl-ammonio)phenyl sulfothio-ate.

The title compound, C(8)H(12)N(2)O(3)S(2), has been isolated as an inter-mediate in the synthesis of methyl-ene blue dye, the best known phenothia-zine dye, and structurally characterized as a zwitterion. The crystal structure is dominated by inter-molecular N-H⋯O hydrogen bonds between the amine and sulfothio-ate groups, with graph-set motif C(9)R(2) (2)(8), involving anti-parallel chains and a centrosymmetric eight-membered ring. A hydrogen bond with graph-set motif R(2) (2)(14) between the ammonium and sulfothio-ate groups completes the two-dimensional network in the ab plane. Inter-molecular C-H⋯O hydrogen bonds are also present in the crystal.

S-5-Amino-2-(dimethyl-ammonio)phenyl sulfothio-ate.

The title compound, C(8)H(12)N(2)O(3)S(2), has been isolated as a by-product in the synthesis of methyl-ene blue dye. The compound crystallizes with four independent mol-ecules in the unit cell (Z'= 4). The zwitterionic form of the mol-ecule was established on the basis of the hydrogen atom located at the dimethyl-amino group. The crystal structure is dominated by inter-molecular hydrogen bonds of the N-H⋯O type formed between amino and ammonio N-H groups and O atoms from the sulfothio-ate group. There are in addition two weak inter-molecular N-H⋯N inter-actions and some non-conventional C-H⋯O hydrogen bonds.

Synthesis and antitumor evaluation of novel derivatives of 6-amino-2-phenylbenzothiazoles.

Novel derivatives of 6-amino-2-phenylbenzothiazole bearing different substituents (amino, dimethylamino or fluoro) on the phenyl ring were prepared as the corresponding hydrochloride salts. 6-Nitro-2-(substituted-phenyl)benzothiazoles (1-6) were synthesized by condensation reactions of substituted benzaldehydes with 2-amino-5-nitrothiophenol. Nitro derivatives were reduced to the amino derivatives with SnCl(2)/HCl. Water soluble hydrochloride salts of 6-amino-2-(substituted-phenyl)benzothiazole (13-19)were prepared using concentrated or gaseous HCl. Compounds 13-19 were found to exert cytostatic activities against malignant human cell lines: cervical (HeLa), breast (MCF-7),colon (CaCo-2), laryngeal carcinoma (Hep-2), and normal human fibroblast cell lines (WI-38).

1,3-Benzothiazole-6-carboxamidinium chloride dihydrate.

The title compound, C(8)H(8)N(3)S(+).Cl(-).2H(2)O, has been synthesized and characterized both spectroscopically and structurally. The structure consists of 1,3-benzothiazole-6-carboxamidinium cations, chloride anions and water molecules, all interconnected by hydrogen bonds into a three-dimensional network. The 1,3-benzothiazole moiety is inclined to the 6-amidine group by 36.71 (9) degrees.