Synthesis and enhanced DNA cleavage activities of bis-tacnorthoamide derivatives.

A new metal-free DNA cleaving reagent, bis-tacnorthoamide derivative 1 with two tacnorthoamide (tacnoa) units linked by a spacer containing anthraquinone, has been synthesized from triazatricyclo[5.2.1.0(4,10)]decane and characterized by NMR and mass spectrometry. For comparison, the corresponding compounds mono-tacnorthoamide derivative 2 with one tacnorthoamide unit and 6 with two tacnorthoamide units linked by an alkyl (1,6-hexamethylene) spacer without anthraquinone have also been synthesized. The DNA-binding property investigated via fluorescence and CD spectroscopy suggests that compounds 1 and 2 have an intercalating DNA binding mode, and the apparent binding constants of 1, 2 and 6 are 1.3 × 10(7) M(-1), 0.8 × 10(7) M(-1) and 8 × 10(5) M(-1), respectively. Agarose gel electrophoresis was used to assess plasmid pUC19 DNA cleavage activity promoted by 1, 2, 6 and parent tacnoa under physiological conditions, which gives rate constants k(obs) of 0.2126 ± 0.0055 h(-1), 0.0620 ± 0.0024 h(-1), 0.040 ± 0.0007 h(-1) and 0.0043 ± 0.0002 h(-1), respectively. The 50-fold and 15-fold rate acceleration over parent tacnoa is because of the anthraquinone moiety of compound 1 or 2 intercalating into DNA base pairs via a stacking interaction. Moreover, DNA cleavage reactions promoted by compound 1 give 5.3-fold rate acceleration over compound 6, which further demonstrates that the introduction of anthraquinone results in a large enhancement of DNA cleavage activity. In particular, DNA cleavage activity promoted by 1 bearing two tacnoa units is 3.3 times more effective than 2 bearing one tacnoa unit and the DNA cleavage by compound 1 was achieved effectively at a relatively low concentration (0.03 mM). This dramatic rate acceleration suggests the cooperative catalysis of the two positively charged tacnoa units in compound 1. The radical scavenger inhibition study and ESI-MS analysis of bis(2,4-dinitrophenyl) phosphate (BDNPP) and adenylyl(3'-5')phosphoadenine (APA) cleavage in the presence of compound 1 suggest the cleavage mechanism would be via a hydrolysis pathway by cleaving the phosphodiester bond of DNA.

[An epidemiological survey of febrile convulsions among pupils in the Wenzhou region].

OBJECTIVE: To study the prevalence and clinical features of febrile convulsion (FC) among pupils in the Wenzhou region, Zhejiang Province, China. METHODS: Using a random stratified cluster sampling method, 6406 children under 12 years from two primary schools of urban areas and two primary schools of rural areas were surveyed. RESULTS: The prevalence of FC was 3.67% (235/6406). Most children (75.7%) experienced their first onset of FC at 6 months to 3 years of age (median: 16 months). The seizures were generalized (95.3%, 224/235), with a duration of less than 10 minutes (86.4%, 203/235). FC was developed into epilepsy in 13 children (5.5%) who all suffered from complex FC. Relapses were noted in 88 cases (37.4%), among whom 38 patients had only 1 recurrence and 50 patients had 2 or more relapses. EEG was performed in 200 cases, among whom 12(6.0%) showed abnormalities. CONCLUSIONS: The prevalence of FC is 3.67% among pupils in the Wenzhou region. The seizures are generalized, with a short duration. A part of complex FC can be developed into subsequent epilepsy.

Synthesis of 1,2-annulated and 1,2-unsubstituted pyrrolo[2,1,5-de]quinolizin-5-ones (cycl[3.3.2]azin-5-ones) via [3+2] cycloadditions of 1-oxoquinolizinium ylides with cyclic alkenes.

1,2-Annulated pyrrolo[2,1,5-de]quinolizin-5-ones (cycl[3.3.2]azin-5-ones) 6a-6k, 8a-8b and 9 have been synthesized by one pot tandem reactions of 2-acetyl-N-phenacylpyridinium bromides (1a-1d) with electron-deficient cyclic alkenes (N-alkyl(aryl)maleimides, benzoquinones and naphthoquinone) in the presence of sodium carbonate as a base and tetrakispyridinecobalt(II) dichromate (TPCD) as an oxidant. These products are formed by 1.3-dipolar cycloaddition of the 1-oxoquinolizinium ylides generated in situ from 1a-1d with the alkene followed by dehydrogenation of the primary cycloadduct under the action of TPCD. Similar reactions of the ylides generated in situ from 1a-1f with maleic anhydride gave the 1,2-unsubstituted pyrrolo[2,1,5-de]quinolizin-5-ones 7a-7f via oxidative bisdecarboxylation and dehydrogenation of the primary cycloadducts under the action of TPCD.

Regioselective synthesis of 3-acylindolizines and benzo- analogues via 1,3-dipolar cycloadditions of N-ylides with maleic anhydride.

3-Acylindolizines (5a-5f) and their benzo- analogues 1-acylpyrrolo[1,2-a]quinolines (6a-6f) and 1-acylpyrrolo[2,1-a]isoquinolines (7a-7i) are regioselectively synthesized by a convenient one pot reaction of the corresponding pyridinium (quinolinium, isoquinolinium) ylide with maleic anhydride (MA) in the presence of the mild oxidant tetrakispyridinecobalt(ii) dichromate (TPCD). These reactions proceed via a tandem reaction sequence of 1,3-dipolar cycloaddition of azomethine ylide with MA, anhydride hydrolysis and oxidative bisdecarboxylation of the primary cycloadducts followed by dehydrogenative aromatization of the dihydroindolizines. TPCD serves as both decarboxylation and dehydrogenation reagent in the reactions. These results show that TPCD is a promising new reagent for bisdecarboxylation of aliphatic carboxylates.

Intermolecular photocyclizations of N-(omega-hydroxyalkyl)tetrachlorophthalimide with alkenes leading to medium- and large-ring heterocycles--reaction modes and regio- and stereoselectivity of the 1,n-biradicals.

A new photocyclization strategy by using intermolecular tandem reactions between N-(omega-hydroxyalkyl)-4,5,6,7-tetrachlorophthalimides (1, 2, and 3) and a series of acyclic and cyclic alkenes is reported. Electron transfer of the triplet-excited phthalimide with the alkene and regioselective trapping of the alkene cation radical by the hydroxyl group at the phthalimide side chain gives a triplet 1,n-biradical, which after intersystem crossing (ISC) leads to regio- and diastereoselective synthesis of polycyclic heterocycles with an N,O-containing medium to large ring. Regio- and diastereoselectivity in the cyclizations are clarified by unambiguous steric structure assignments of the products by X-ray diffraction or extensive 2D NMR measurements. The diastereoselectivity is decided by the stereochemical course of the ISC process of the triplet 1,n-biradicals. These intermolecular photoreactions also furnish a new strategy to generate triplet 1,n-biradicals. Therefore, in photoreactions of 1 and 2 with phenylcyclohexene, the unprecedented stereoselective formation of products by intramolecular hydrogen-atom transfer in the 1,n-biradical intermediate was found (9 and 23). These facts provide direct verification to the reaction pathways of the 1,n-biradicals and give a new insight into the factors deciding reaction-pathway partitioning and stereoselectivity.

2-[3-((Z)-2-{4-[Bis(2-chloro-eth-yl)amino]-phen-yl}ethen-yl)-5,5-dimethyl-cyclo-hex-2-en-1-yl-idene]propane-dinitrile.

The highly conjugated title compound, C(23)H(25)Cl(2)N(3), is nearly planar (the mean deviation from the plane being 0.049 Å), except for the -C(CH(3))(2) group on the cyclo-hexene ring and the two CH(2)Cl groups. The cyclo-hexene ring has an envelope configuration. In the crystal, the packing is stabilized by C-H⋯Cl inter-actions and C-H⋯π inter-actions involving the benzene ring.

2-(2-Chloro-3-quinol-yl)-3-phenyl-thia-zolidin-4-one.

In the title compound, C(18)H(13)ClN(2)OS, the thia-zolidinone ring is slightly distorted and adopts a envelope conformation. The basal plane is nearly perpendicular to the quinoline ring, forming a dihedral angle of 86.1 (1)°, and makes a dihedral angle of 14.9 (1)° to the benzene ring. The benzene ring is also nearly perpendicular to the quinoline ring, forming a dihedral angle of 89.4 (1)°. In the crystal, non-classical C-H⋯O and C-H⋯N hydrogen bonds link the mol-ecules, forming polymers along b.

Photoinduced three-component reactions of tetracyanobenzene with alkenes in the presence of 1,3-dicarbonyl compounds as nucleophiles.

Photoinduced three-component reactions between tetracyanobenzene (TCNB), an aromatic olefin, and a beta-dicarbonyl compound afford products composed of the three components via formal elimination of hydrogen cyanide, leading to the vicinal dialkylation of the olefin and the alpha-alkylation of the beta-dicarbonyl compounds. It is shown that these reactions are initiated by photoinduced electron transfer (PET) from the olefin to the singlet excited TCNB and proceed by a nucleophile-olefin combination, aromatic substitution (NOCAS) reaction sequence with the enolized beta-dicarbonyl compound as a nucleophile. Therefore, aromatic olefins are suitable substrates in photo-NOCAS reactions when TCNB is used as the electron acceptor. In addition, these results show that the enol of beta-dicarbonyl compound serves as a carbon nucleophile to trap the alkene cation radical in PET reactions to lead to C-C bond formation.

Reaction modes and mechanism in indolizine photooxygenation reactions.

Photooxygenations of 1,2-, 1,3-, and 2,3-di- and 1,2,3-trisubstituted indolizines 1a-1f under different reaction conditions in methanol and acetonitrile have been investigated to establish the general reaction pattern and mechanism in indolizine photooxygenation in view of the influence of the ring substituents and substitution pattern. Photooxygenations of 1-acyl-2-phenylindolizines 1a and 1b and 1,3-dibenzoyl-2-phenylindolizine (1d) are self-sensitized, while those of 1-(p-nitrobenzoyl)-2-phenylindolizine (1c) and 2-phenyl-3-(p-chlorobenzoyl)indolizine (1e) need to be sensitized by rose bengal (RB) or methylene blue (MB). These reactions proceed via a singlet oxygen mechanism yet follow different pathways in methanol and in acetonitrile, with peroxidic zwitterion D (in methanol) and dioxetane E across the indolizine C2-C3 bond (in acetonitrile) as the intervening intermediates. Methanol trapping of the peroxidic zwitterion results in C3-N bond cleavage and pyrrole ring opening to give the corresponding (E)- and (Z)-3-(2-pyridinyl)-3-benzoylpropenoic acid methyl esters (2 and 3) and 4-(2-pyridinyl)-3-phenyl-5-aryl-5-hydroxyfuran-2-one (4) as products in methanol, while O-O bond homolysis of the dioxetane furnishes 3-(2-pyridinyl)-3-benzoyl-2-phenyloxirane-2-carboxaldehyde (6) and 1-(6-methyl-2-pyridinyl)-2-phenylethanedione (5) as products in acetonitrile. 3-Benzoyl-1-indolizinecarboxylic acid methyl ester (1f) is unreactive toward singlet oxygen; however, it could be photooxygenated under electron transfer conditions with 9,10-dicyanoanthracene (DCA) as a sensitizer. This reaction takes place by the combination of the indolizine cation radical with the superoxide anion radical (or molecular oxygen) to give the pyridine ring oxidized methyl 3-benzoyl-5-methoxy-8-hydroxy-1-indolizinecarboxylate (9f), dimethyl 2-(2-pyridinyl)fumarate (8f), and dimethyl 2-(2-pyridinyl)maleate (7f) as products.

2,3-bis(2-methylphenylimino)-1,4-dithiacyclohexane.

An N,N'-disubstituted dithiooxamide derivative reacts with 1,2-dibromoethane to produce the title compound, C(18)H(18)N(2)S(2), a heterocycle with a double Schiff base. In the crystal structure, the molecule of the title compound lies on a twofold axis. Weak C-H...pi interactions are the principal intermolecular forces, mediating the formation of layers parallel to the ab plane. Each molecule participates as donor and acceptor in two such contacts.