Inducing enantioselective crystallization with and self‐assembly of star‐shaped hybrid polymers prepared via “grafting to” strategy

Abstract

Helical polymers present some interesting and distinctive properties, and one of the most distinguished applications of them is the chiral recognition and resolution of enantiomers. In this work, star-shaped hybrid helical poly (phenyl isocyanide) (PPI) with polyhedral oligomeric silsesquioxanes (POSS) as the core was designed and synthesized by "grafting to" strategy. The homoarm star-shaped hybrid POSS-(PPI) 8 was first obtained by the click reaction between azide-modified POSS (POSS-(N 3 ) 8 ) and alkynyl-modified PPI (PPI-Alkynyl). The hybrid POSS-(PPI) 8 was with predominated left-handed helical conformation and exhibited excellent ability in the enantioselective crystallization of racemic compounds. In the meantime, heteroarm star-shaped hybrid (PEG) 4 -POSS-(PPI) 4 was prepared by the click reaction of POSS-(N 3 ) 8 with PPI-Alkynyl and alkynyl-modified poly (ethylene glycol) (PEG-Alkynyl).The hybrid (PEG) 4 -POSS-(PPI) 4 was amphiphilic, and it could self-assemble to form spherical micelles in aqueous solutions.

Recent advances in the field of chiral crystallization

“…Table 2 lists several successful applications of this technique for a variety of compounds. [63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80] Compounds that have similar chemical structures tend to form cocrystals. The first reported cases of chiral cocrystallization were in Water 1981 and used amino acids as additives for the cocrystallization of other amino acids.…”

“…67 Another example of inclusion complex cocrystallization was done with a helical polymeric star-shaped molecule that was shown to have chiral recognition. 80 The hybrid polyhedral oligomeric silsesquioxane helical poly (phenyl isocyanide), (POSS-(PPI) 8 ), star was added to a saturated solution of racemic threonine and allowed to crystallize. The resulting crystals had an enantiomeric excess of 88%.…”

“…This requires the use of enantiomerically pure cocrystallization additives. Table 2 lists several successful applications of this technique for a variety of compounds 63–80 . Compounds that have similar chemical structures tend to form cocrystals.…”

“…The molar ratio of the cyclodextrin, pH, as well as the nature and concentration of the organic cosolvent all had a profound effect on the enantiomeric excess of the product 67 . Another example of inclusion complex cocrystallization was done with a helical polymeric star‐shaped molecule that was shown to have chiral recognition 80 . The hybrid polyhedral oligomeric silsesquioxane helical poly (phenyl isocyanide), (POSS‐(PPI) 8 ), star was added to a saturated solution of racemic threonine and allowed to crystallize.…”