Synthesis and Biological Evaluation of Tyrphostins As Anticancer Agents

Recent developments in molecular biology have led to a greater understanding of signalling mechanisms which are overexpressed or distorted in the cancer cell, resulting in the identification of a number of new molecular targets for cancer chemotherapy. Protein Tyrosine Kinases (PTKs) are enzymes which play an important role in the signal transduction pathways leading to mitogenesis. Growth factors, such as epidermal growth factor (EGF) are responsible for stimulating cells to synthesise DNA prior to mitosis. The EGF receptor, which is present at elevated levels in certain cancer cells, has been shown to display PTK activity. Tyrphostins are low molecular weight molecules which are structurally similar to tyrosine. These have been shown to display PTK inhibition activity. The earliest reported tyrphostins such as (a) were based upon a benzylidenemalononitile nucleus, but more recently a number of tyrphostins containing a 5-membered heterocyclic nucleus (b) have been reported. Tyrphostins containing a nitrothiophene fragment (c) were prepared using standard methodology. These compounds were shown to display excellent in vitro growth inhibition in cells with a high EGF concentration. More detailed studies later showed that a number of these compounds were not selective for the EGF receptor, and instead displayed wide-spectrum cytotoxicity by an unknown mechanism. The crystal structure of one tyrphostin was solved, showing that the aromatic and cyano groups are cis across the extra-annular double bond. Previous studies had shown that analogues of misonidazole (d) which contained a nitrothiophene group (e) possessed the ability to become reduced to cytotoxic species in hypoxic tumour cells, which have a low oxygen saturation. The reduction potentials of a number of nitrothienyl tyrphostins were measured, and some of these fell within the parameters required for in vivo bioreduction. Pyridyl and quinolyl tyrphostins such as (f) and (g) have been reported to display interesting biological profiles. In particular, 2- and 4-substituted quinolines were particularly active, and this may be perhaps due at least in part to substitution at these electropositive centres. Substitution at the 3-position gave rise to a series of inactive compounds. In order to extend the study of this structure-activity relationship, a series of 6-, 7- and 8-quinolyl tyrphostins (h) were synthesised. Antibody-Directed Enzyme Prodrug Therapy (ADEPT) is a sophisticated method to deliver cytotoxic agents at their preferred site of action. An antibody which recognises surface antigens on a cancer cell also possesses an enzyme which hydrolyses a prodrug molecule such as (i) and leads to the release of the drug molecule. A methodology to synthesise such a prodrug was investigated, but it was not possible to complete the urea linkage between L-glutamate and the benzene ring by attempting to generate an isocyanate at either of the amino groups in the starting materials

Safety evaluation of substituted thiophenes used as flavoring ingredients.

This publication is the second in a series by the Expert Panel of the Flavor and Extract Manufacturers Association summarizing the conclusions of its third systematic re-evaluation of the safety of flavorings previously considered to be generally recognized as safe (GRAS) under conditions of intended use. Re-evaluation of GRAS status for flavorings is based on updated considerations of exposure, structural analogy, metabolism, pharmacokinetics and toxicology and includes a comprehensive review of the scientific information on the flavorings and structurally related substances. Of the 12 substituted thiophenes reviewed here, 11 were reaffirmed as GRAS based on their rapid absorption, metabolism and excretion in humans and animals; the low estimated dietary exposure from flavor use; the wide margins of safety between the conservative estimates of intake and the no-observed-adverse effect levels; and the lack of significant genotoxic and mutagenic potential. For one of the substituted thiophenes, 3-acetyl-2,5-dimethylthiophene, it was concluded that more detailed exposure information, comparative metabolism studies and comprehensive toxicity data, including an in-depth evaluation of the mechanism of action for any adverse effects observed, are required for continuation of its FEMA GRAS™ status. In the absence of these data, the compound was removed from the FEMA GRAS list

Design, Synthesis, and Biological Investigation of Novel Classes of 3-Carene-Derived Potent Inhibitors of TDP1.

Two novel structural types of tyrosyl-DNA phosphodiesterase 1 (TDP1) inhibitors with hexahydroisobenzofuran 11 and 3-oxabicyclo [3.3.1]nonane 12 scaffolds were discovered. These monoterpene-derived compounds were synthesized through preliminary isomerization of (+)-3-carene to (+)-2-carene followed by reaction with heteroaromatic aldehydes. All the compounds inhibit the TDP1 enzyme at micro- and submicromolar levels, with the most potent compound having an IC50 value of 0.65 µM. TDP1 is an important DNA repair enzyme and a promising target for the development of new chemosensitizing agents. A panel of isogenic clones of the HEK293FT cell line knockout for the TDP1 gene was created using the CRISPR-Cas9 system. Cytotoxic effects of topotecan (Tpc) and non-cytotoxic compounds of the new structures were investigated separately and jointly in the TDP1 gene knockout cells. For two TDP1 inhibitors, 11h and 12k, a synergistic effect was observed with Tpc in the HEK293FT cells but was not found in TDP1 -/- cells. Thus, it is likely that the synergistic effect is caused by inhibition of TDP1. Synergy was also found for 11h in other cancer cell lines. Thus, sensitizing cancer cells using a non-cytotoxic drug can enhance the efficacy of currently used pharmaceuticals and, concomitantly, reduce toxic side effects

Synthesis and reactions of 3-aminotetrachloroquinazolin-2,4-dione

N-phenylsulphonyloxytetrachlorophthalimide was obtained by treatment of N-hydroxy tetrachlorophthalimide with benzenesulphonyl chloride. Also, the titled compound 3 was obtained by reaction of compound 2 with hydrazine hydrate via Lossen rearrangement. Compound 3 used as starting material for the synthesis of new pyrimidine and quinazolinedione derivatives containing four chlorine atoms which have pharmacological activity

Safety evaluation of substituted thiophenes used as flavoring ingredients

AbstractThis publication is the second in a series by the Expert Panel of the Flavor and Extract Manufacturers Association summarizing the conclusions of its third systematic re-evaluation of the safety of flavorings previously considered to be generally recognized as safe (GRAS) under conditions of intended use. Re-evaluation of GRAS status for flavorings is based on updated considerations of exposure, structural analogy, metabolism, pharmacokinetics and toxicology and includes a comprehensive review of the scientific information on the flavorings and structurally related substances. Of the 12 substituted thiophenes reviewed here, 11 were reaffirmed as GRAS based on their rapid absorption, metabolism and excretion in humans and animals; the low estimated dietary exposure from flavor use; the wide margins of safety between the conservative estimates of intake and the no-observed-adverse effect levels; and the lack of significant genotoxic and mutagenic potential. For one of the substituted thiophenes, 3-acetyl-2,5-dimethylthiophene, it was concluded that more detailed exposure information, comparative metabolism studies and comprehensive toxicity data, including an in-depth evaluation of the mechanism of action for any adverse effects observed, are required for continuation of its FEMA GRAS™ status. In the absence of these data, the compound was removed from the FEMA GRAS list

Flavouring Group Evaluation 76 Revision 2 (FGE.76Rev2): Consideration of sulfur-containing heterocyclic compounds, evaluated by JECFA, structurally related to thiazoles, thiophenes, thiazoline and thienyl derivatives from chemical group 29 and miscellaneous substances from chemical group 30 evaluated by EFSA in FGE.21Rev5

The Panel on Food Additives and Flavourings (FAF) was requested to consider the JECFA evaluations of 28 flavouring substances in the Flavouring Group Evaluation 76 (FGE.76Rev2). Twenty-one of these substances have been considered in FGE.76Rev1. Seven substances could not be evaluated, because of concerns with respect to genotoxicity. New genotoxicity data have been provided for 4-methyl-5-vinylthiazole [FL-no: 15.018] and 4,5-dimethyl-2-isobutyl-3-thiazoline [FL-no: 15.032], which are representative substances of [FL-no: 15.005] and [FL-no: 15.029, 15.030, 15.130 and 15.131], respectively. The Panel concluded that the concern for genotoxicity is ruled out for [FL-no: 15.018 and 15.005]. The concerns for gene mutations and clastogenicity are ruled out for [FL-no: 15.032, 15.029, 15.030, 15.130 and 15.131]. In vitro, [FL-no: 15.032] induced micronuclei through an aneugenic mode of action. The available in vivo micronucleus study was not adequate to rule out the concern for potential aneugenicity in vivo. The Panel compared the lowest concentration resulting in aneugenicity in vitro with the use levels reported for [FL-no: 15.032]. Based on this comparison, the Panel concluded that the use of [FL-no: 15.032] at the maximum reported use levels does not raise a concern for aneugenicity. Based on structural similarity, for the remaining four substances [FL-no: 15.029, 15.030, 15.130 and 15.131], an aneugenic potential may also be anticipated. Individual genotoxicity data are needed to establish whether they have aneugenic potential. The Panel agrees with JECFA conclusions for 24 flavouring substances 'No safety concern at estimated levels of intake as flavouring substances' when based on the MSDI approach. For six substances, more reliable information on uses and use levels are needed to refine the mTAMDI estimates. For 15 substances, use levels are needed to calculate the mTAMDIs. For [FL-no: 15.109 and 15.113], information on the actual stereochemical composition is inadequate and the conclusion reached for the named substances cannot be applied to the materials of commerce

Bioisosteric modification on melatonin: synthesis of new naphthalene derivatives, in vitro antioxidant activity and cytotoxicity studies

Melatonin (MLT) is a strong free radical scavenger that protects the body from the deleterious effects of excess oxidants. Synthesis of MLT analogue compounds with antioxidant potency has recently attracted the interest of researchers. In general, the strategy consists of modifying the groups in the different sites of the indole ring or replacing the indole ring with an analogue. As part of our ongoing research, the antioxidant capacity and cytotoxicity of newly synthesized MLT analogue naphthalene derivatives were evaluated. The radical scavenging activity was tested by a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. Most of the synthesized compounds showed significant antioxidant activity in comparison to MLT. The structure-activity relationship was identified. The in vitro cytotoxic effects of the synthesized compounds were also investigated in CHO-K1 cells using the MTT assay