Design, synthesis and structure–activity relationships of antiproliferative 1,3-disubstituted urea derivatives

Catalysis-free synthesis of thiazolidine-thiourea ligands for metal coordination (Au and Ag) and preliminary cytotoxic studies

The reaction of propargylamines with isothiocyanates results in the selective formation of iminothiazolidines, aminothiazolines or mixed thiazolidine-thiourea compounds under mild conditions. It has been observed that secondary propargylamines lead to the selective formation of cyclic 2-amino-2-thiazoline derivatives, while primary propargylamines form iminothiazoline species. In addition, these cyclic thiazoline derivatives can further react with an excess of isothiocyanate to give rise to thiazolidine-thiourea compounds. These species can also be achieved by reaction of propargylamines with isothiocynates in a molar ratio of 1 : 2. Coordination studies of these heterocyclic species towards silver and gold with different stoichiometries have been carried out and complexes of the type [ML(PPh₃)]OTf, [ML₂]OTf (M = Ag, Au) or [Au(C₆F₅)L] have been synthesised. Preliminary studies of the cytotoxic activity in lung cancer cells have also been performed in both ligands and complexes, showing that although the ligands do not exhibit anticancer activity, their coordination to metals, especially silver, greatly enhances the cytotoxic activity.

Novel ureido-dihydropyridine scaffolds as theranostic agents

In this work, the synthesis of interesting urea derivatives 5 based on 1,4-dihydropyridines 3 is described for the first time. Considering that both families exhibit potential as drugs to treat various diseases, their activity as anticancer agents has been evaluated in HeLa (cervix), Jurkat (leukaemia) and A549 (lung) cancer cell lines as well as on healthy mice in vivo. In general, whereas 1,4-dihydropyridines show a moderate cytotoxic activity, their urea analogues cause an extraordinary increase in their antiproliferative activity, specially towards HeLa cells. Because of the chiral nature of these compounds, enantiomerically enriched samples were also tested, showing different cytotoxic activity than the racemic mixture. Although the reason is not clear, it could be caused by a complex amalgam of physical and chemical contributions. The studied compounds also exhibit luminescent properties, which allow performing a biodistribution study in cancer cells. They have emission maxima between 420 and 471 nm, being the urea derivatives in general red shifted. Emission quenching was observed for those compounds containing a nitro group (3e,f and 5e,f). Fluorescence microscopy showed that 1,4-dihydropyridines 3a and 3g localised in the lysosomes, in contrast to the urea derivatives 5h that accumulated in the cell membrane. This different distribution could be key to explain the differences found in the cytotoxic activity and in the mechanism of action. Interestingly, a preliminary in vivo study regarding the acute toxicity of some of these compounds on healthy mice has been conducted, using a concentration up to 7200 times higher than the corresponding IC₅₀ value. No downgrade in the welfare of the tested mice was observed, which could support their use in preclinical tumour models.

Synthesis of unsymmetrical phenylurea derivatives via oxidative cross coupling of aryl formamides with amines under metal-free conditions

A direct transformation of N-aryl formamides to the corresponding phenylurea derivatives via the formation of isocyanate intermediates is achieved in good yields using hypervalent iodine reagents as external oxidants.

Solvent-free synthesis, DNA-topoisomerase II activity and molecular docking study of new asymmetrically N,N'-substituted ureas

A new series of asymmetrically N,N'-substituted ureas 20–25 was prepared using solvent free conditions, which is an eco-friendly methodology, starting with Schiff bases derived from cinnamaldehyde and p-substituted anilines, which are subsequently submitted to reduction reactions that afford the corresponding asymmetric secondary amines. All of the intermediates were prepared using solvent free reactions, which were compared to traditional methodologies. All of the reactions required a remarkably short amount of time and provided good yields when solvent free conditions were employed compared to other methodologies. The DNA-topoisomerase II-α (topo II-α) activity was evaluated in relaxation assays, which showed that all of the compounds inhibited the enzyme activity at 10 μM, except for urea 24. Furthermore, a molecular docking study indicated that the compounds 20–25 binding to the topo II-α are able to interact with the same binding site as the anticancer drug etoposide, suggesting that the ureas could inhibit the enzyme by the same mechanism of action observed for etoposide, which prevents re-ligation of the DNA strands.

Synthesis and evaluation of 1-(substituted)-3-prop-2-ynylureas as antiangiogenic agents

Novel urea derivatives of alkynes have been designed, synthesized, and evaluated as potential cancer therapeutics leads. The most active 1-((3-chloromethyl)phenyl)-3-prop-2-ynylurea (1) exhibited cytotoxic effect against HELA and MCF-7 cell lines with IC(50) values of 1.55 μM and 1.48 μM, respectively. Further investigation on tube formation assay in human vein umbilical cells (HUVEC) demonstrated that 1 and methyl 4-(3-(3-ethynylureido)benzyloxy) benzoate (6) possess antiangiogenic activity, with minimum effective dose of 25 nM (for 1) and 6.25 μM (for 6). The ED(50) of 1 and 6 were found to be 0.26 μM and 17.52 μM, respectively. The results from in vitro tyrosine kinase assay indicated the EGFR inhibition of 1 over other kinases (VEGFR2, FGFR1 and PDGFRβ). The cytotoxicity of 1 against EGFR overexpressing cell line A431 (IC(50) 36 nM) was comparable to that of erlotinib. The binding mode of 1 from docking simulation in the EGFR active site revealed that the urea motif formed hydrogen bonding with Lys745, Thr854 and Asp855 in hydrophobic pocket of EGFR. Compound 1 is considered as a potential lead for further optimization.

Structure-activity relationship of halophenols as a new class of protein tyrosine kinase inhibitors

A series of new benzophenone and diphenylmethane halophenol derivatives were prepared. Their structures were established based on (1)H NMR, (13)C NMR and HRMS data. All prepared compounds were screened for their in vitro protein tyrosine kinase (PTK) inhibitory activities. The effects of modification of the linker, functional groups and substituted positions at the phenyl ring on PTK inhibitory activity were investigated. Twelve halophenols showed significant PTK inhibitory activity. Among them, compounds 6c, 6d, 7d, 9d, 10d, 11d and 13d exhibited stronger activities than that of genistein, the positive reference compound. The results gave a relatively full and definite description of the structure-activity relationship and provided a foundation for further design and structure optimization of the halophenols.