Optical activity natural polymer derivatives

Further extensive comparisons of various available options are beyond the scope of this chapter. Readers are referred to a review by Snieckus [59] and other appropriate references [60]. A large number of biaryls, including drugs, natural products and other optically active derivatives, as well as oligomers and polymers of interest in material sciences have been synthesized using Pd- or Ni-catalyzed aryl-aryl coupling, as indicated by the representative examples shown in Schemes 1-17, 1-18, and 1-19). 

In the polymerization of the (—)-monomers with various ee s, enantiomer selection was observed though the selectivity was lower compared with that of the polymerization of IDPDMA.83-87 In this experiment, a nonlinear relation was observed between the ee of the monomer in the feed and the optical activity of the obtained polymer (Figure 6). This indicates that the optical activity of the polymer is not based only on the side chain chirality. Furthermore, the chirality of a one-handed helical part induced by a successive sequence of the (—)-monomeric units (monomeric units derived from a (—)-monomer) can overcome the opposite chiral induction by the sporadic (+)-monomeric units. In other words, once a one-handed helical radical comes under the influence of the (—)-monomeric units, an entering (+)-monomer becomes a part of the one-handed helix whose direction may be unfavorable to the chiral nature of the (+)-monomer. 

PHTP is a chiral host which can be resolved into enantiomers DCA and ACA are (or derive from) naturally occurring optically active compounds. Using these hosts inclusion polymerization can be performed in a chiral environment and can be used for the synthesis of optically active polymers. This line of research has been very fruitful, both on the synthetic and on the theoretical plane. It has been ascertained that asymmetric inclusion polymerization occurs by a "through space" and not by a "through bond" induction only steric host-guest interactions (physical in nature) and not conventional chemical bonds are responsible for the transmission of chirality (W). 

Many optically active polymers exist in nature. Polysaccarides, proteins, enzymes, nucleic acids, polypeptides are some examples. Derivatives of such materials may also exhibit optical activity. This activity is usually preserved throughout the derivatization reactions, provided the reactions do not change the nature of the asymmetric carbon atoms that conferred the chirality to the molecule. 

To synthesize polynucleotide analogues closely resembling natural polymers, we have synthesized several new monomers such as dihydrofuran and dihydropyran derivatives which contained nucleic acid bases (Scheme 1). Copolymerization of the monomers either with maleic anhydride or with vinylene carbonate resulted in the alternating copolymers as shown in Scheme 2. Hydrolysis of the products gave the polymers which were optically active and soluble in water and had alternating sequences along the polymer chain. In this paper we will report synthesis of monomers, their copolymerization either with maleic anhydride or with vinylene carbonate, hydrolysis of the copolymers, and the physicochemical properties of the anhydride and hydrolyzed polymers. 

A chiral host could readily be available from a naturally occurring compound. The use of steroidal acid, deoxycholic acid (Fig. 3d), yielded coinprehensive polymers, particularly, optically active polymers from pro-chiral monomers. Many derivatives of deoxy cholic acid have the corresponding characteristic inclusion abilities. For example, use of apocholic acid (Fig. 3e), cholic acid (Fig. 3f), and chenodeoxycholic acid (Fig. 3g) enabled us to perform one-dimensional inclusion polymerization of various diene and vinyl monomers. 

It is expected that new types of functional phenol polymers with interesting properties in terms of thermal stabiUty or optical and electronic properties will be presented in the next few years. New examples of phenol polymers from natural resources will hopefully broaden the interest for this type of polymerization from a commercial point of view. In this connection, the finding of suitable highly active model complexes could be of increasing interest in reducing the cost of the oxidative polymerization of phenol derivatives. 

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