Several optically active polyacetylenes have also been evaluated as solid
membranes for separating enantiomers [24].
8 Poly(α-amino acids) and Polyamides
Poly(α-amino acid)s (10 and 11 in Fig. 3) are expected to show attractive chiral
recognition due to their helical conformation. However, so far, a high chiral
recognition has not yet been reported [25]. Saigo and coworkers reported optically
active polyamides (12 and 13 in Fig. 3) with attractive structures [26, 27]. These
CSPs can separate polar compounds using hydrogen bonding as the main interaction. The chiral recognition ability of 12 clearly depends on the number of methylene groups, and an odd–even effect was observed. Compound 12 with an even
number of methylene groups showed a higher recognition. We then synthesized a
polyamide 14 derived from (À)-1,2-trans-diaminocyclohexane [28]. The polyamide 14 with the 1,4-phenylene residue showed a better chiral recognition than
the polyamides derived from the same diamine and α,ω-dicarboxylic acids,
HOOC-(CH 2 ) n -COOH.
9 Other Synthetic Polymers
The N-substituted maleimide derivative (7 in Fig. 3) is the monomer that can
produce an optically active polymer by asymmetric polymerization with chiral
initiators such as (À)-sparteine-n-BuLi [29]. The monomeric unit of the polymer
is chiral if the polymerization proceeds in trans-addition by predominantly forming
either an (R,R) or (S,S) center. The polymer 7 with a high optical activity exhibits a
chiral recognition [30].
Various optically active polyurethanes 15 were also synthesized from chiral
diols and various diisocyanates to be used as CSPs [31]. The polyurethanes derived
from aliphatic diisocyanates show better chiral recognitions than those from
aromatic diisocyanate.
10 Natural Polymers and Their Derivatives
Some enzymes are well known to show high chiral recognitions and have been used
as asymmetric catalysts in organic synthesis. A few proteins, such as bovine serum
albumin, α 1 -acid glycoprotein, and ovomucoid, have also been used as CSPs for
HPLC [32–34]. These CSPs can resolve many chiral drugs. Protein-based CSPs are
often not stable because they change their conformation depending on the
conditions such as solvents and temperature. The proteins contain many different
Helical Polymers for Efficient Enantiomer Separation
401
membranes for separating enantiomers [24].
8 Poly(α-amino acids) and Polyamides
Poly(α-amino acid)s (10 and 11 in Fig. 3) are expected to show attractive chiral
recognition due to their helical conformation. However, so far, a high chiral
recognition has not yet been reported [25]. Saigo and coworkers reported optically
active polyamides (12 and 13 in Fig. 3) with attractive structures [26, 27]. These
CSPs can separate polar compounds using hydrogen bonding as the main interaction. The chiral recognition ability of 12 clearly depends on the number of methylene groups, and an odd–even effect was observed. Compound 12 with an even
number of methylene groups showed a higher recognition. We then synthesized a
polyamide 14 derived from (À)-1,2-trans-diaminocyclohexane [28]. The polyamide 14 with the 1,4-phenylene residue showed a better chiral recognition than
the polyamides derived from the same diamine and α,ω-dicarboxylic acids,
HOOC-(CH 2 ) n -COOH.
9 Other Synthetic Polymers
The N-substituted maleimide derivative (7 in Fig. 3) is the monomer that can
produce an optically active polymer by asymmetric polymerization with chiral
initiators such as (À)-sparteine-n-BuLi [29]. The monomeric unit of the polymer
is chiral if the polymerization proceeds in trans-addition by predominantly forming
either an (R,R) or (S,S) center. The polymer 7 with a high optical activity exhibits a
chiral recognition [30].
Various optically active polyurethanes 15 were also synthesized from chiral
diols and various diisocyanates to be used as CSPs [31]. The polyurethanes derived
from aliphatic diisocyanates show better chiral recognitions than those from
aromatic diisocyanate.
10 Natural Polymers and Their Derivatives
Some enzymes are well known to show high chiral recognitions and have been used
as asymmetric catalysts in organic synthesis. A few proteins, such as bovine serum
albumin, α 1 -acid glycoprotein, and ovomucoid, have also been used as CSPs for
HPLC [32–34]. These CSPs can resolve many chiral drugs. Protein-based CSPs are
often not stable because they change their conformation depending on the
conditions such as solvents and temperature. The proteins contain many different
Helical Polymers for Efficient Enantiomer Separation
401