Desymmetrization of Prochiral N-Pyrazolyl Maleimides via Organocatalyzed Asymmetric Michael Addition with Pyrazolones: Construction of Tri-N-Heterocyclic Scaffolds Bearing Both Central and Axial Chirality.

The desymmetrization of N-pyrazolyl maleimides was realized through an asymmetric Michael addition by using pyrazolones under mild conditions, leading to the formation of a tri-N-heterocyclic pyrazole-succinimide-pyrazolone assembly in high yields with excellent enantioselectivities (up to 99% yield, up to 99% ee). The use of a quinine-derived thiourea catalyst was essential for achieving stereocontrol of the vicinal quaternary-tertiary stereocenters together with the C-N chiral axis. Salient features of this protocol included a broad substrate scope, atom economy, mild conditions and simple operation. Moreover, a gram-scale experiment and derivatization of the product further illustrated the practicability and potential application value of this methodology.

Fabrication of doxorubicin-loaded ellipsoid micelle based on diblock copolymer with a linkage of enzyme-cleavable peptide.

In this study, a novel micellar drug carrier was fabricated from an amphiphilic diblock copolymer containing poly (ethylene glycol) monomethyl ether (mPEG) and stearic moiety (C18) with a linkage of valine-citrulline (VC), which can be cleaved by cathepsin B (CB) enriched in lysosome of tumor cell. Moreover, the self-assembled micelles were observed as ellipsoid shape with major and minor axis of ca. 169 and 103nm, respectively. Such drug carrier was used to encapsulate anti-cancer drug doxorubicin (DOX), and hence showed a faster drug release behavior in a mimic lysosome condition containing cathepsin B. It was ascribed to the lysosome-sensitivity of the valine-citrulline linkage, which was verified by the size distribution curve shifted to greater size under the same mimic lysosome condition. Furthermore, in comparison with pristine doxorubicin, the encapsulation strategy of as-fabricated micellar carrier resulted in a predominant decrease of cytotoxicity. On the whole, a micellar drug carrier, which can be disassembled by cathepsin B, has been emerging as a potential of specific drug release in lysosome. Additionally, the controlled nanoscale together with elongated structure of such assembled ellipsoid micelles might contribute passive targeting function to tumor tissue and faster cellular uptake behavior (Zhou et al.).