Synthesis, antitumor activity, and cytotoxicity of 4-substituted 1-benzyl-5-diphenylstibano-1H-1,2,3-triazoles.

Trisubstituted 5-organostibano-1H-1,2,3-triazoles (3a-f) were synthesized by the Cu-catalyzed azide-alkyne cycloaddition of various ethynylstibanes (1) with benzylazide (2) in the presence of CuBr (5 mol%) under aerobic conditions. The reaction of 5-stibanotriazoles with HCl afforded C5-unsubstituted 1,2,3-triazoles (4a-f). The antitumor activity of trisubstituted 5-organostibano-1H-1,2,3-triazoles (3a-f) and their 5-unsubstituted 1,2,3-triazoles (4a-f) were evaluated in several tumor cell lines. All 5-stibanotriazoles (3a-f) exerted an excellent antitumor activity. On the contrary, 5-unsubstituted 1,2,3-triazoles (4a-f) without a diphenylantimony group in the molecule exhibited very low antitumor activity compared with 5-stibanotriazoles (3a-f). In compounds of both the series, the substituted 4-butyl group appeared to decrease antitumor activity. However, results suggested that organometal (antimony) in the molecule was required for greater antitumor activity. In addition, all 5-stibanotriazoles (3a-f), but not all 5-unsubstituted 1,2,3-triazoles (4a-f), exhibited cytotoxicity in normal vascular endothelial cells derived from bovine aorta. Among the compounds (3b-e) that exhibited excellent antitumor activity, those with 4-methylphenyl (3b) and 1-cyclohexenyl (3e) showed relatively low cytotoxicity to vascular endothelial cells. Together, these results suggest that trisubstituted 5-organostibano-1H-1,2,3-triazoles, including compounds 3b and 3e, may serve as potential anticancer therapeutic drugs in the future.

Microwave-Assisted Debromination of α-Bromoketones with Triarylstibanes in Water.

Several α-bromoarylketones were reacted with triarylstibanes under microwave irradiation in water to obtain the corresponding debrominated ketones. Under similar reaction conditions, 1,2-elimination of vic-dibromides in water afforded the corresponding E-olefins. This reaction is the first example of organoantimony compounds utilized for organic transformation in water.

Synthesis and photophysical properties of novel benzophospholo[3,2-b]indole derivatives.

The parent benzophospholo[3,2-b]indole was prepared by the reaction of dichlorophenylphosphine with a dilithium intermediate, which was prepared in two steps from 2-ethynyl-N,N-dimethylaniline. Using the obtained benzophosphole-fused indole as a common starting material, simple modifications were carried out at the phosphorus center of the phosphole, synthesizing various functionalized analogs. The X-ray structure analysis of trivalent phosphole and phosphine oxide showed that the fused tetracyclic moieties are planar. The benzophosphole-fused indoles, such as phosphine oxide, phospholium salt, and borane complex, exhibited strong photoluminescence in dichloromethane (Φ = 67-75%).

Copper-catalyzed [3 + 2] cycloaddition of (phenylethynyl)di-p-tolylstibane with organic azides.

Trisubstituted 5-stibano-1H-1,2,3-triazoles were synthesized in moderate to excellent yields by the Cu-catalyzed [3 + 2] cycloaddition of a ethynylstibane with organic azides in the presence of CuBr (5 mol %) under aerobic conditions. The reaction of 5-stibanotriazole with HCl, I2, and NOBF4 afforded 1-benzyl-4-phenyltriazole, 1-benzyl-5-iodo-4-phenyltriazole, and a pentavalent organoantimony compound, respectively.

Pd-catalyzed P-arylation of triarylantimony dicarboxylates with dialkyl H-phosphites without a base: synthesis of arylphosphonates.

The reaction of triarylantimony diacetates [Ar3Sb(OAc)2] with dialkyl H-phosphites [H-PO(OR)2] in the presence of a Pd(PPh3)4 (5 mol%) catalyst led to the formation of arylphosphonates in moderate to excellent yield under base-free conditions. This reaction is the first example of carbon-phosphorus bond formation by using an organoantimony compound as a pseudo-halide.

A novel organobismuth compound, 1-[(2-di-p-tolylbismuthanophenyl)diazenyl]pyrrolidine, induces apoptosis in the human acute promyelocytic leukemia cell line NB4 via reactive oxygen species.

A novel organobismuth compound, 1-[(2-di-p-tolylbismuthanophenyl)diazenyl]pyrrolidine (4), which has 1-(phenyldiazenyl)pyrrolidine (1) substituent in a benzene ring of tri(p-tolyl)bismuthane (2), was synthesized and tested for biological activity toward human tumor cell lines. 4 had a potent anti-proliferative effect on human cancer cell lines, although both 1 and 2 exhibited only weak activity. The sensitivity of leukemic cell lines to 4 was relatively high; IC(50) values for the human leukemia cell line NB4 and cervical cancer cell line HeLa were 0.88 µM and 5.36 µM, respectively. Treatment of NB4 cells with 4 induced apoptosis, loss of mitochondrial membrane potential (ΔΨ(mt)) and the generation of cellular reactive oxygen species (ROS). 1 and 2 did not induce apoptosis and had only a marginal effect on ΔΨ(mt) and the generation of ROS. N-acetyl cysteine (NAC) reduced the generation of ROS and conferred protection against 4-induced apoptosis, indicating a role for oxidative stress. 4 did not inhibit the polymerization of tubulin in vitro. 1-[2-(di-p-tolylstibanophenyl)diazenyl]pyrrolidine (3), which has the same chemical structure as 4 but contains antimony in place of bismuth, did not show any cytotoxic activity. The results suggest that the conjugated structure of the diazenylpyrrolidine moiety and bismuth center are key to the bioactivity of 4.

Pentavalent organoantimony compounds as mild N-arylating agents for amines: Cu-mediated Ullmann-type N-arylation with tetraarylantimony(V) acetates.

Simple and mild Cu-mediated arylation of various amines by use of tetraarylantimony acetate (Ar(4)SbOAc) is described. The Ullmann-type condensation of Ar(4)SbOAc with aliphatic and electron rich aromatic amines proceeded efficiently in the presence of copper(II) acetate. The arylation can be carried out under aerobic conditions without care of exogenous oxygen. This simple procedure exceeds the conventional Ullmann condensation which often requires harsh reaction conditions.

Effect of periodic replacement of the heteroatom on the spectroscopic properties of indole and benzofuran derivatives.

The electronic structures of a homologous series of indole and benzofuran derivatives, in which the nitrogen or oxygen atom is replaced by group 15 and group 16 heavier heteroatoms, have been investigated by means of various spectroscopic techniques coupled with density functional calculations. It was found that the excitation energies of the group 16 benzoheteroles systematically shift to the red in the order of benzofuran (6), benzothiophene (7), benzoselenophene (8), and benzotellurophene (9). In contrast, the electronic absorption spectra of the group 15 benzoheteroles, 1-phenyl derivatives of indole (1b), phosphindole (2b), arsindole (3b), stibindole (4b), and bismuindole (5b), did not exhibit this type of spectral shift. X-ray analysis and density functional theory (DFT) studies revealed that 2b-5b adopt a bent conformation both in the crystalline and in the solution phases. In contrast, planar structures were calculated for the group 16 heterocycles. Using the observed spectroscopic properties and time-dependent density functional theory (TDDFT) calculations, the electronic absorption spectra of the present heterocycles were assigned. A molecular orbital analysis was performed to rationalize the effect of replacement of the heteroatom on the electronic structures. The observed magnetic circular dichroism (MCD) sign patterns of these heterocycles are interpreted according to Michl's perimeter model.

Rhodium catalyzed 1,4-conjugate addition of 1,5-azastibocines with electron deficient olefins.

The rhodium-catalyzed reaction of Sb-aryl-1,5-azastibocines with alpha,beta-unsaturated ketones and esters is described. Exclusive formation of 1,4-conjugate adduct was achieved in aqueous NMP (N-methyl-2-pyrrolidinone) in the presence of 5 mol% of [RhCl(cod)](2), and no formation of Heck adduct was observed in this condition. Reactions with various enones and enoates were also demonstrated to prove generality of the 1,4-conjugate addition.

Carbonylative cross-coupling reaction of ethynylstibane with aryl iodides.

Palladium-catalyzed carbonylative cross-coupling reaction of ethynylstibane (PhSbPh(2)) and aryl iodides (Ar-I) is described. The reaction of the stibanes and the halides under 1 atm of carbon monoxide in N,N-dimethylacetamide using a combination of 5 mol% Pd(OAc)(2) and 4 equivalents (20 mol%) of PPh(3) brought about carbonylative cross-coupling reaction to afford arylethynylketones [ArC(O)Ph] in good yields along with a small amount of directly coupled products, aryl acetylens (ArPh). Formation of the side product was completely suppressed by conducting the reaction under high CO pressure (20 atm) conditions. The present method provides a variety of carbonylated products in good yield even with electron-deficient aryl iodides which usually give inferior results due to their tendency to undergo decarbonylation in the cross-coupling reaction of ethynylstibanes and acyl halides.

Microwave-assisted cross-coupling reaction of alkynylstibanes with aryl iodides in the presence of ammonium salt.

The scope of microwave-assisted coupling reaction of alkynylstibane and aryl iodides to form diarylalkynes is presented. Highly efficient reaction took place smoothly in dimethyl sulfoxide in the presence of cetyltrimethylammonium bromide with much shorter time (1 min) and lower catalyst loading (0.5 mol%) than the conventional method (heating for 24 h with 10 mol% catalyst).