A Kinetic Evidence for the Nitroxyl Radicals Recycling Mechanism in the Photostabilizing Process of HALS

The photoinduced bulk polymerization of a reactive-hindered amine light stabilizers (r-HALS), 4-acryloyl-2, 2, 6,6-tetramethylpiperidinyl (ATMP), was performed at 80 C by using a DPC technique. An unique periodic exponential attenuation-type oscillating curve was found when the polymerization was carried out in air, but this phenomenon was not found in nitrogen. It is supposed that this unique kinetic performance may be attributed to nitroxyl radicals that are produced in situ from the oxidation of ATMP. ATMP polymer with narrow polydispersity (d = 1.03) can be obtained by photoinduced solution polymerization of ATMP. The signal detected in ESR may be assigned to the nitroxyl radicals in the matrix of ATMP polymer. Since this kind of recycling of nitroxyl radicals is well documented for the photostabilizing mechanism of HALS, the present results may serve as a kinetic evidence for this mechanism.

An efficient electrocatalytic system composed of nickel oxide and nitroxyl radical for the oxidation of bio-platform molecules to dicarboxylic acids

Selective oxidation of biomass and its derivatives to dicarboxylic acids represents a promising route for biomass valorization.However,the co-presence of multiple functional groups in biomass molecules makes the selective oxidation of particular functional a challenging task.Here,we demonstrate an efficient electrocatalytic system consisting of nickel oxide(NiO)and a nitroxyl radical,i.e.,2,2,6,6-tetrame thylpiperidine-1-oxyl(TEMPO)or 4-acetamido-TEMPO(ACT),for the selective oxidation of key bioplatform molecules including glucose,xylose and 5-hydroxymethylfurfural(HMF)into corresponding dicarboxylic acids,i.e.,glucaric acid,xylaric acid,and 2,5-furandicarboxylic acid(FDCA).NiO is clarified as the active catalyst for the oxidation of aldehyde in bio-platform molecules to carboxylic acid,while TEMPO or ACT is responsible for the oxidation of primary alcohol to aldehyde.The combination of NiO and TEMPO or ACT significantly accelerated the tandem oxidation of aldehyde and hydroxyl groups in glucose,xylose and HMF,thus achieving excellent yields(83%-99%)of dicarboxylic acids.Moreover,the combination catalyst enables the selective oxidation of glucose and xylose with high concentrations(e.g.,20 wt%),which offers a promising strategy for biomass valorization.

Anticancer Drugs ( Ⅳ )——New Derivatives of Podophyllotoxin

Four new derivatives of podophyllotoxin, N'-podophyllic acid-N-[3-(2, 2, 5, 5-te-tramethyl-pyrrolinenyloxy)] semicarbazide(GP-11, 6), podophyllic acid [3-(2,2,5,5-te-tramethyl-pyrrolinenyloxy)]hydrazone (GP-12, 7), podophyllic acid-[4-(2, 2, 6, 6-tetramethyl-1-hydroxy piperidine)]hydrazone(GP-1-OH, 8) and podophyllic acid[4-(2,2, 6, 6-tetramethyl piperidine)]hydrazone(GP-1-H, 9) were synthesized. The inhibition effect of the four new compounds on L-1210 cells were determined. The antitumor activity and toxicity of GP-1(2), GP-1-OH(8), GP-1-H(9) and VP-16-213(1) were discussed.

Anticancer Drugs (V)─—Synthesis of Etoposide Derivatives

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Synthesis and Biological Activity of Novel Spin Labeled Derivatives of 4′-Demethyl-4-deoxypodophyllotoxin

Seven novel spin labeled derivatives of 4＇-demethyl-4-deoxypodophyllotoxin with nitroxyl radi- cals（TMHPO and TMPRO） were prepared and their cytotoxic and antioxidative activities were tested. Their cytotoxic activities were tested against two tumor cell lines（A-549 and HL-60） in vitro. Among them, five compounds show higher inhibition activity against A-549 cells compared with the clinical drug VP-16（2） and parent compound 4＇-demethyl-4-deoxypodophyllotoxin（DDPT, 6）. Compounds 8, 10 and 13 show excellent inhibition activity against HL-60 cells. Furthermore, the antioxidative activities of them were tested. All the seven spin labeled compounds show stronger antioxidative activity compared with VP-16（2） and DDPT（6）. The partition coefficients P of these derivatives were determined.

Crystal Structure of trans－2－（1－Naphthyl）－1－（p－（4＇，4＇，5＇，5＇－tetramethyl－4＇，5＇－dihydro－1＇H－imidazolyl－1＇－oxy－3＇－oxide）－phenyl）－imine，C_（24）H_（24）N_3O_2

The crystal structure of the title compound was determined by X-ray diffraction method at room temperature.The crystal belongs to triclinic space group P1 with the following crystallographic parameters:a=13.942(2),b=15.540(2),c=10.007(1) A,a=105.16(1)°,β=92.42(1)°,γ=88.12(1)°,V=2090.2(4) Z=4,Dc=1.23g cm-3,F(000)=820,μ(MoKα)=0.74 cm-1,and final R= 0.054 for 3208 observations.Two molecules , which are slightly different in conformation,coexist in an asymmetric unit. Some intermolecular distances are fairly short.The packing arrangement of the molecules in the crystal is also discussed.

Synthesis and Cytotoxic Activities of Spin-labeled Derivatives of Cinobufagin

Two series of novel spin-labeled derivatives of Cinobufagin（compounds 5 and 8a--8f in series 1 with five-membered ring nitroxyl free radical and compounds 6 and 9a-9f in series 2 with six-membered ring nitroxyl free radical） were synthesized. The cytotoxic activities in vitro against two tumor cell lines（HepG2 and HeLa） were evaluated, and the results indicate that all compounds display potent cytotoxicity against HepG2 and HeLa cells, and most compounds show better activities on HeLa cells than on HepG2 cells except for compounds 8a and 9d. Gene- rally, the compounds in series 2 have more potent cytotoxic activity against HepG2 than the compounds in series 1. Especially, compounds 6 and 9f in series 2 exhibit even more potent activities against the two tumor cell lines than Cinobufagin. Thus incorPoration of different L-amino acids as the linker changed the cytotoxic profile of the spin-labeled Cinobufagin. In addition, the representative compound 9f significantly changed the cell cycle distribution and led to HeLa cell cycle arrested at G2/M phase.