An optically active, amphiphilicmeta-phenylene ethynylene (m-PE) bearing a chiral amide pendant was designed and synthesized. Living polymerization ofm-PE using alkyne-Pd(II) as the initiator afforded well-defined poly(meta-phenylene ethynylene) (m-PPE). Thesem-PPEs were found to have a stable helical conformation in THF, 1,4-dioxane, and CH3CN and showed split Cotton effects over the range of 245–400 nm. The positive first Cotton effect was observed at a wavelength of approximately 308 nm, and the negative second Cotton effect was observed at a wavelength of approximately 289 nm. Them-PPEs exhibited helical conformational changes in different mixed solvents and showed effective solvent-dependent helix inversion in CHCl3/THF solutions. The sign of the Cotton effect ofm-PPE was inverted at 25 °C by varying the mixing ratio of THF and CHCl3. Finally, amphiphilic poly(meta-phenylene ethynylene)-block-polyisocyanide containing hydrophilic PPE and hydrophobic PPI segments were facilely prepared using Pd(II)-terminatedm-PPE as the macroinitiator. This block copolymer can self-assemble into well-defined spherical nanostructures in a selective THF/CH3OH solution. This efficient polymerization will open up enormous opportunities for the preparation of functional amphiphilic block copolymers in a wide variety of fields.
N -substituted β-amino esters as an important class of chiral amines, are widely used as building blocks in pharmaceuticals. A novel imine reductase Sv IRED was identified through gene mining from Streptomyces viridochromogenes with high enantioselectivity of > 99 % ee (1 R , 2 S ), 95 % de ( cis:trans ), towards 2-oxocyclohexane-1-carboxylate and cyclopropylamine. Sv IRED exhibited the highest activity at pH 7.0 and 40 °C. A variety of amine donors could be used by Sv IRED and produce chiral N -substituted β-amino esters with different enantioselectivity. Employing methylamine ( i ) and pyrrolidine ( n ) as amine donors, Sv IRED exhibited reversed enantioselectivity of 23 % ee (1 S , 2 R ) and 79 % ee (1 S , 2 R ) respectively. Through alanine scanning, M183 and H244 were identified with remarkable roles in governing enantioselectivity towards i and n . Compared with WT Sv IRED, the enantioselectivity of M183A was inverted to ee value of >99 % (1 R , 2 S ) and de value of >99 % ( cis:trans ) towards i , and the enantioselectivity of H244A was inverted to ee value of 88 % (1 R , 2 S ) and de value of >99 % ( cis:trans ) towards n . Interaction analysis indicated the orientation of ester group was vital for manipulation of enantioselectivity. This study provides novel Imine reductase mutants for enantioselective synthesis of N -substituted β -amino esters with different amine donors.
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