Chitosan oligosaccharide based Gd-DTPA complex as a potential bimodal magnetic resonance imaging contrast agent.

A new gadolinium diethylenetriamine pentaacetic acid (DTPA) complex (Gd-DTPA-DMABA-CS11) as a potential bimodal magnetic resonance imaging (MRI) contrast agent with fluorescence was synthesized. It was synthesized by the incorporation of 4-dimethylaminobenzaldehyde (DMABA) and chitosan oligosaccharide (CSn; n=11) with low polydispersity index to DTPA anhydride and then chelated with gadolinium chloride. The structure was characterized by Fourier transform infrared (FTIR), (1)H NMR, elemental analysis and size exclusion chromatography (SEC). MRI measurements in vitro were evaluated. The results indicated that Gd-DTPA-DMABA-CS11 provided higher molar longitudinal relaxivity (r1) (12.95mM(-1)·s(-1)) than that of commercial Gd-DTPA (3.63mM(-1)·s(-1)) at 0.5T. Gd-DTPA-DMABA-CS11 also emitted fluorescence, and the intensity was much stronger than that of Gd-DTPA. Therefore, it can be meanwhile used in fluorescent imaging for improving the sensitivity in clinic diagnosis. Gd-DTPA-DMABA-CS11 as a potential contrast agent is preliminarily stable in vitro. The results of thermodynamic action between Gd-DTPA-DMABA-CS11 and bovine serum albumin (BSA) illustrated that the binding process was exothermic and spontaneous, and the main force was van der Waals' interaction and hydrogen bond. The preliminary study suggested that Gd-DTPA-DMABA-CS11 could be used in both magnetic resonance and fluorescent imaging as a promising bimodal contrast agent.

Biomimetic catalytic enantioselective decarboxylative aldol reaction of ß-ketoacids with trifluoromethyl ketones.

We disclose an organocatalyzed enantioselective decarboxylative ketone aldol reaction of ß-ketoacids with trifluoromethyl ketones in the presence of biscinchona alkaloid (DHQD)(2)AQN, affording chiral tertiary alcohols in up to 98% yield and 90% ee.

Asymmetric phase-transfer-catalyzed conjugate addition of glycine imine to exocyclic α,ß-unsaturated ketones: construction of polycyclic imines containing three stereocenters.

We developed a facile, one-pot, multistep transformation between glycine imine and exocyclic α,ß-unsaturated ketones in reactions catalyzed by chiral phase-transfer catalysts (PTC). A series of polycyclic imines containing three adjacent stereocenters were obtained in good to high yields with high diastereo- and enantioselectivities. Further transformation of the imines could afford N-fused polycyclic compounds with four adjacent stereocenters.

A powerful synergistic effect for highly efficient diastereo- and enantioselective phase-transfer catalyzed conjugate additions.

An efficient, catalytic, diastereo- and enantioselective conjugate addition of N-(diphenylmethylene)glycine tert-butyl ester to ß-aryl substituted enones was realized in the presence of 1 mol% of newly desired dinuclear N-spiro-ammonium salts, affording functionalized α-amino acid derivatives in 57-98% yields with high diastereoselectivity (up to 99:1 dr) and enantioselectivity (up to 96.5:3.5 er).

Catalytic stereoselective synthesis of highly substituted indanones via tandem Nazarov cyclization and electrophilic fluorination trapping.

A new catalytic stereoselective tandem transformation via Nazarov cyclization/electrophilic fluorination has been accomplished. This sequence is efficiently catalyzed by a Cu(II) complex to afford fluorine-containing 1-indanone derivatives with two new stereocenters with high diastereoselectivity (trans/cis up to 49/1). Three examples of catalytic enantioselective tandem transformation are presented.