Numerous biological activities including antioxidant, antitumor, anti-inflammation, and antivirus of the natural product curcumin were reported. However, the clinical application of it was significantly limited by its instability, poor solubility, less body absorbing, and low bioavailability. This review focuses on the structure modification and antioxidant activity evaluation of curcumin. To study the structure-activity relationship (SAR), five series of curcumin analogs were synthesized and their antioxidant activity were evaluated in vitro. The results showed that electron-donating groups, especially the phenolic hydroxyl group are an essential component to improve the antioxidant activity.

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Novel P-stereogenic pincer-Ni complexes {κ P ,κ C ,κ P -3,5-Me 2 -2,6-(Me t BuPCH 2 ) 2 C 6 H}NiCl (3), {κ P ,κ C ,κ P -3,5-Me 2 -2,6-( M e t B u P C H 2 ) 2 C 6 H } N i O T f ( 4 ) , [ { κ P , κ N , κ P -2 , 6 -( M e t B u P C H 2 ) 2 C 5 H 3 N } N i C l ] C l ( 7 ) , [ { κ P , κ N , κ P -2 , 6 -(Me t BuPCH 2 ) 2 C 5 H 3 N}NiCl]BF 4 (8), and [{κ P ,κ N ,κ P -2,6-(Me t BuPCH 2 ) 2 C 5 H 3 N}Ni(NCMe)](BF 4 ) 2 (9) were synthesized in 55−84% yields and characterized by 1 H NMR, 13 C{ 1 H} NMR, 31 P{ 1 H} NMR, 19 F{ 1 H} NMR, and/or single-crystal X-ray diffractions. The ORTEP diagrams of complexes 3, 7, 8, and 9 show that the coordination geometries around the Ni center in all these structures are approximately square planar but have different bond lengths and angles. These complexes were shown to be active catalysts for the asymmetric aza-Michael addition of α,β-unsaturated nitriles.For most examples good to excellent yields (up to 99%) and moderate enantiomeric excesses (up to 46% ee) were obtained. Notably, the PCP complex 3 exhibited higher catalytic activity in the aza-Michael addition than the PNP complexes 7, 8, and 9. Two achiral PCP-type pincer-Ni complexes, {κ P ,κ C ,κ P -3,5-Me 2 -2,6-( t Bu 2 PCH 2 ) 2 C 6 H}NiCl (11) and {κ P ,κ C ,κ P -3,5-Me 2 -2,6-(Ph 2 PCH 2 ) 2 C 6 H}NiCl (13), were also synthesized and fully characterized in order to reveal the structural differences between the chiral and achiral complexes. ■ INTRODUCTIONPincer-type metal complexes have received widespread attention over the last few decades due to their rigid tridentate structural properties and tunable electron density. 1 Such complexes have been used in many types of catalytic reactions. 2 Chiral P-chelated pincer-metal catalysts, such as PCP-3 and PNP 4 -type complexes, are important chiral sources because of their potential application in asymmetric catalysis. However, the chiral centers in these structures are commonly located not on phosphorus atoms but on the pincer skeletons. Reports concerning pincer-metal complexes possessing P-stereogenic centers in which the chiral environment is closer to the metal atom catalytic center are rare. Commonly used examples utilize L-proline-derived phosphorus heterocycles, the structural complexity of which makes them difficult to synthesize (Chart 1, A). 3m,5 Zhang and co-workers developed a class of phenyl-and o-anisyl-substituted P-stereogenic palladium and ruthenium pincer complexes (Chart 1, B). 4b,c These complexes could be applied to asymmetric allylic alkylations and ketone hydrosilylations, providing the desired products in high yields and good enantiomeric excesses. Van Koten 3f,h and MoralesMorales 3g described the synthesis of phenyl-and tert-butyl-or isopropyl-substituted P-stereogenic pincer platinum, palladium, ruthenium, and iridium complexes, but their application in asymmetric hydrogen transfer reactions involving acetophenone gave the corresponding products with only 18% ee (enantiomeric excess) (Chart 1, B). 3h Although the synthesis and application of pincer-type ...

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