Retinoid X receptor-antagonistic diazepinylbenzoic acids

Several dibenzodiazepine derivatives were identified as novel retinoid X receptor (RXR) antagonists on the basis of inhibitory activity on retinoid-induced cell differentiation of human promyelocytic leukemia cells HL-60 and transactivation assay using retinoic acid receptors (RARs) and RXRs in COS-1 cells. 4-(5H-2,3-(2,5-Dimethyl-2,5-hexano)-5-n- propyldibenzo[b,e][1,4]diazepin-11-yl)benzoic acid (HX603, 6c) is an N-n-propyl derivative of an RXR pan-agonist HX600 (6a), and exhibited RXR-selective antagonistic activity. Similar RXR-antagonistic activities were observed with 4-(5H-2,3-(2,5-dimethyl-2,5-hexano)-5-methyl- 8-nitrodibenzo[b,e][1,4]diazepin-11-yl)benzoic acid (HX531, 7a) and 4-(5H-10,11-dihydro-5,10-dimethyl-2,3-(2,5-dimethyl- 2,5-hexano)-dibenzo[b,e][1,4]diazepin-11-yl)benzoic acid (HX711, 8b), which also inhibited transactivation of RARs induced by an RAR agonist, Am80. These compounds inhibited HL-60 cell differentiation induced by the combination of a low concentration of the retinoid agonist Am80 with an RXR agonist (a retinoid synergist, HX600). These results indicated that HX603 (6c), and the related RXR antagonists inhibit the activation of RAR-RXR heterodimers as well as RXR homodimers, which is a distinct characteristic different from that of the known RXR antagonist, LG100754 (9).     

Water‐Exchange Mechanism for Zinc(II), Cadmium(II), and Mercury(II) Ions in Water as Studied by Umbrella‐Sampling Molecular‐Dynamics Simulations

Umbrella‐sampling molecular‐dynamics simulations were performed to investigate the water‐exchange reactions of zinc(II), cadmium(II), and mercury(II) ions in aqueous solution. The dissociation of a coordinating water molecule to the M? O distance at 3.34, 3.16, and 3.26 Å for Zn^II, Cd^II, and Hg^II, respectively, leads the system to a transition state. For Zn^II, the first hydration shell is occupied by five spectator water molecules in the transition state, indicating that the water‐exchange reaction proceeds via a dissociative mode of activation. In contrast, the number of spectator water molecules of 5.85 and 5.95 for Cd^II and Hg^II, respectively, suggests an associative exchange for these larger metal ions. The average M? O distance of the spectator molecules is shortened by 0.06 Å for the dissociative exchange of Zn^II, while it is elongated by 0.04 and 0.03 Å for Cd^II and Hg^II, respectively. The water‐exchange rate constants of 4.1×10⁸, 6.8×10⁸, and 1.8×10⁹ s^?1 are estimated for Zn^II, Cd^II, and Hg^II, respectively, at 298 K in terms of the transition‐state theory based on the assumption of a transmission coefficient of unity.     

Stannic chloride‐induced unsymmetrical C?Se bond cleavage of bis(N,N‐dimethylcarbamoylseleno)methanes: Novel generation of selenoaldehydes

Treatment of bis(N,N‐dimethylcar‐ bamoylseleno)methanes with SnCl₄ afforded β‐1,3,5‐triselenanes in moderate to high yields, and the key intermediates of the reactions, i.e., acylselonium ions and selenoaldehydes, were successfully trapped by using allyltrimethylsilane or 2,3‐dimethyl‐1,3‐butadiene to obtain the allylation products or the cycloadducts, respectively. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:125–135, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20190     

Effect and Mechanism of a New Photodynamic Therapy with Glycoconjugated Fullerene

When irradiated, fullerene efficiently generates reactive oxygen species (ROS) and is an attractive photosensitizer for photodynamic therapy (PDT). Ideally, photosensitizers for PDT should be water-soluble and tumor-specific. Because cancer cells endocytose glucose more effectively than normal cells, the characteristics of fullerene as a photosensitizer were improved by combining it with glucose. The cytotoxicity of PDT was studied in several cancer cell lines cultured with C₆₀-(Glc)1 (d -glucose residue pendant fullerene) and C₆₀-(6Glc)1 (a maltohexaose residue pendant fullerene) subsequently irradiated with UVA₁. PDT alone induced significant cytotoxicity. In contrast, PDT with the glycoconjugated fullerene exhibited no significant cytotoxicity against normal fibroblasts, indicating that PDT with these compounds targeted cancer cells. To investigate whether the effects of PDT with glycoconjugated fullerene were because of the generation of singlet oxygen (¹O₂), NaN₃ was added to cancer cells during irradiation. NaN₃ extensively blocked PDT-induced apoptosis, suggesting that PDT-induced cell death was a result of the generation of ¹O₂. Finally, to investigate the effect of PDT in vivo, melanoma-bearing mice were injected intratumorally with C₆₀-(Glc)1 and irradiated with UVA₁. PDT with C₆₀-(Glc)1 suppressed tumor growth. These findings indicate that PDT with glycoconjugated fullerene exhibits tumor-specific cytotoxicity both in vivo and in vitro via the induction of ¹O₂.     

Three abietane diterpenes and two diterpenes incorporated sesquiterpenes from the bark of Cryptomeria japonica

Three new abietane diterpenes, sugikurojins D (1), E (2), and F (3), and two new abietanes which incorporate cadinane, sugikurojins G (4) and H (5) were isolated from the bark of Cryptomeria japonica. These structures were elucidated primarily by extensive NMR experiments. The structure of sugikurojin D (1) was deduced to be 6alpha-acetoxy-7beta,11-dihydroxy-12-methoxy-8,11,13-abietatriene. Sugikurojin E (2) was deduced to be 6alpha-acetoxy-7beta,12-dihydroxy-8,11,13-abietatriene. Sugikurojin F (3) was 7alpha-methoxy-8,13-abietadien-11,12-dione. Sugikurojins G (4) and H (5) had a unique skeleton incorporating an alpha-cadinol or a 1alpha-hydroxy-T-cadinol in ferruginol, respectively. Also obtained in this investigation were the known diterpenes (6-14). An antibacterial activity of ten among these against Staphylococcus aureus and Escherichia coli was inactive at the (MIC: 125 microg/ml) level. Meanwhile, in the cytotoxic activity against HL-60, compounds 4, 8, and 11 showed moderate (IC50: 4, 35.4; 8, 28.0; 11, 52.4 microM) though weak (IC50: 4, 100; 8, 80.8; 11, 100 microM) activity against HCT-15.     

Asymmetric radical cyclization of (2S,3S)-2,3-butanediyl, (2S,4S)-2,4-pentanediyl,and (2S,5S)-2,5-hexanediyl bis(4-vinylbenzoate)s as a model reaction for asymmetric cyclocopolymerization

The asymmetric cyclocopolymerization of bis(4-vinylbezoate) of a chiral diol with styrene is a promising method for the preparation of optically active polystyrene derivatives because of main-chain chirality. However, the mechanism for chirality induction from the chiral diol to the main chain is still unknown. To clarify the chirality induction mechanism, we carried out the radical cyclizations of (2S,3S)-2,3-butanediyl bis(4-vinylbenzoate), (2S,4S)-2,4-pentanediyl bis(4-vinylbenzoate), and (2S,5S)-2,5-hexanediyl bis(4-vinylbenzoate) with tri-n-butyltin hydride or allyltri-n-butyltin as a chain-transfer reagent as model reactions for asymmetric cyclocopolymerization. The absolute configuration was determined with single-crystal X-ray crystallography and a circular dichroism exciton chirality method. The distribution of the stereoisomer showed (R)-configuration selectivity (21–34% diastereomeric excess) in the intramolecular cyclization and an extremely low extent (<1%) of the (S,S)-cyclized product among the four stereoisomers. Therefore, chirality induction is caused by the selective inhibition of the (S,S)-racemo configuration. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4671–4681, 2004     

Nef Reaction with Molecular Oxygen in the Absence of Metal Additives,and Mechanistic Insights

A Nef reaction has been developed that is conducted under mildly basic conditions with molecular oxygen as an oxidant, without the need for metal additives. Whereas nitroalkanes are converted into ketones in good yield, nitroalkenes are transformed into α,β‐unsaturated ketones in one‐pot by double‐bond isomerization followed by the oxygen‐mediated Nef reaction. The reaction protocol is both mild and general, and tolerates acid‐ and base‐labile functionality or protecting groups. When oxygen‐saturated solvents are employed, the reaction completes within 20 min. Mechanistically, the addition of nitronate ion and molecular oxygen is proposed to proceed initially through a single‐electron transfer event, as indicated by radical clock experiments. This ultimately generates a putative 1,1‐dioxirane, which reacts further with another nitronate ion to generate the ketone. Involvement of a 1,1‐dioxirane is supported by intramolecular trapping experiments with sulfide at the γ‐position of the nitro‐moiety.     

Palladium‐Catalyzed Direct C?H Arylation of Isoxazoles at the 5‐Position

A palladium‐catalyzed direct arylation of isoxazoles with aryl iodides has been achieved. The C H bond at the 5‐position is activated selectively to give coupling products in moderate to good yields. This direct arylation was applied to the synthesis of a spiro‐type chiral ligand, which proved to be most effective to the palladium‐catalyzed tandem cyclization of a dialkenyl alcohol.     

Synthesis and photophysical properties of Rhodamine B dye‐bearing poly(isobutyl methacrylate‐co‐2,2,2‐trifluoroethyl methacrylate) as a temperature‐sensing polymer film

To develop a novel temperature‐sensitive paint, methacrylamide monomers bearing Rhodamine B dye (two regioisomers, 3a and 3b ) were synthesized and polymerized with isobutyl methacrylate and 2,2,2‐trifluoroethyl methacrylate to afford Rhodamine B‐pendant polymers 4a and 4b . The methacrylamide monomers 3a and 3b showed photophysical properties almost identical with those of Rhodamine B. The temperature sensitivity of the luminescence intensity of 3a and 3b was also similar to that of Rhodamine B. The polymers 4a and 4b have excellent solubility in nonpolar organic solvents and are suitable for application as paint. Films of polymers 4a and 4b showed temperature‐dependent luminescence, which is applicable for temperature‐sensing. The temperature sensitivity of the film of 4a was estimated to be ?0.37% °C^?1, and was independent of pressure. The film of 4b showed higher temperature sensitivity, but its temperature sensitivity was slightly pressure‐dependent. Hence, polymer 4a is expected to be superior for practical use in paints having temperature‐sensing functionality. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2876–2885, 2007