Catalytic Desymmetrizing Baeyer-Villiger Oxidation of Quaternary Carbon-Containing Cyclobutane-1,3-diones.

The first highly enantioselective Baeyer-Villiger oxidation of quaternary carbon-containing cyclobutane-1,3-diones using chiral phosphoric acid catalysis and commercially available oxidants was reported. According to the structure of the substrates, two optimized reaction conditions were developed to afford the corresponding chiral tetronic acid products in ≤93% and ≤95% ee values. This reaction offers the first catalytic asymmetric approach to chiral 5,5-disubstituted tetronic acid derivatives. The synthetic potential of this method has been demonstrated by the formal asymmetric synthesis of (-)-vertinolide and the first catalytic asymmetric total synthesis of plakinidone B.

Kinetic resolution of 2-substituted 2,3-dihydro-4-pyridones by palladium-catalyzed asymmetric allylic alkylation: catalytic asymmetric total synthesis of indolizidine (-)-209I.

The kinetic resolution of 2-substituted-2,3-dihydro-4-pyridones was realized via a Pd-catalyzed allylic substitution reaction using a commercially available (S)-P-Phos as a ligand, affording optically active dihydropyridones and C-allylated dihydropyridones in high yields and good enantioselectivities with the S-factor up to 43. With this protocol, a catalytic asymmetric total synthesis of indolizidine (-)-209I was realized for the first time.

Palladium-catalyzed regio-, diastereo-, and enantioselective allylation of nitroalkanes with monosubstituted allylic substrates.

Pd-catalyzed asymmetric allylic alkylation of nitroalkanes and monosubstituted allylic substrates was performed to afford products with two adjacent chiral centers and with excellent regio-, diastereo-, and enantioselectivities. The usefulness of the protocol in organic synthesis was demonstrated by transformation of the product to an optically active homoallylamine, a 2,3-disubstituted tetrahydropyridine, and an α,ß-disubstituted amino acid derivative.

[Effects of multiwall carbon nano-onions on platelet aggregation and hemostatic function].

OBJECTIVE: To observe the effects of multiwall carbon nano-onions (MWCNOs) on platelet aggregation and hemostatic function. METHODS: The platelet aggregation was determined with Born's method at different concentration of MWCNOs (0, 0.2, 2.0, 20.0 microg/ml) in vitro. Twenty male SD rats were randomly divided into 4 groups which were exposed to 0, 2, 4 and 8 mg/kg MWCNOs, respectively. Then platelet count, platelet aggregation, activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT), bleeding time (BT) and platelet count (PC) were measured at 12 h after receiving tail intravenous injection of MWCNOs. The effects of MWCNOs (4 mg/kg) on platelet aggregation and platelet count at different time points were observed. RESULTS: In vitro, MWCNOs exhibited the potent inhibitory effects on rat platelet aggregation caused by ADP in a concentration-dependent manner. The platelet aggregation in the highest dosage of 20.0 microg/ml group was 50.0% +/- 6.9% which was significantly lower than that (73.2% +/- 4.3%) in control group (P<0.01). In vivo, the highest inhibitory was up to 20.4%, but there was no significant difference, as compared with control group. MWCNOs did not affect the APTT, PT, TT, BT and PC. CONCLUSION: Under this experimental condition, MWCNOs might inhibit platelet aggregation but not affect hemostatic function.