This paper describes the alternating character in the copolymerization of glycidyl phenyl ether (GPE) and 3,4-dihydrocoumarin (DHCM) by 2-ethyl-4-methylimidazole (EMI) as an initiator. DHCM, which is an aromatic lactone that does not undergo its homopolymerization under anionic conditions, underwent the copolymerization with GPE by EMI. In the present copolymerization, formation of the GPE−DHCM alternating sequence and that of the GPE−GPE sequence competed, and the former was always the predominant one. The maximum content of the alternating sequence (90%) was achieved when the feed ratio GPE/DHCM was 1. The obtained copolymer was a polyester, for which the ester linkage was cleavable by reduction with lithium aluminum hydride. The resulting compound inherited the structure of the alternating sequence, and its high yield (90%) supported the high alternating character of the copolymerization.
On the basis of non-covalent bond interactions in nucleic acids, we synthesized the deoxyadenosine derivatives tethering a phenyl group (X) and a naphthyl group (Z) by an amide linker, which mimic a Watson–Crick base pair. Circular dichroism spectra indicated that the duplexes containing X and Z formed a similar conformation regardless of the opposite nucleotide species (A, G, C, T and an abasic site analogue F), which was not observed for the natural duplexes. The ΔG370 values among the natural duplexes containing the A/A, A/G, A/C, A/T and A/F pairs differed by 5.2 kcal mol−1 while that among the duplexes containing X or Z in place of the adenine differed by only 1.9 or 2.8 kcal mol−1, respectively. Fluorescence quenching experiments confirmed that 2-amino purine opposite X adopted an unstacked conformation. The structural and thermodynamic analyses suggest that the aromatic hydrocarbon group of X and Z intercalates into a double helix, resulting in the opposite nucleotide base flipping into an unstacked position regardless of the nucleotide species. This observation implies that modifications at the aromatic hydrocarbon group and the amide linker may expand the application of the base pair-mimic nucleosides for molecular biology and biotechnology.
We have synthesized the deoxyadenosine derivative tethering a phenyl group (X), which mimics the Watson-Crick A/T base pair. The RNA/DNA hybrid duplexes containing X in the middle of the DNA sequence showed a similar thermal stability regardless of the ribonucleotide species (A, G, C, or U) opposite to X, probably because of the phenyl group stacking inside of the duplex accompanied by the opposite ribonucleotide base flipped in an extrahelical position. The RNA strand hybridized with the DNA strand bearing X was cleaved on the 3'-side of the ribonucleotide opposite to X in the presence of MgCl2, and the RNA sequence to be cleaved was not restricted. The site-specific RNA hydrolysis suggests that the DNA strand bearing X has the advantage of the site-selective base flipping in the target sequence and the development of a "universal deoxyribozyme" to exclusively cleave a target RNA sequence.
Anionic copolymerizations of 3,4‐dihydrocoumarin (DHCM) and a series of glycidyl ethers (n‐butyl glycidyl ether, tert‐butyl glycidyl ether, and allyl glycidyl ether) with 2‐ethyl‐4‐methylimidazole as an initiator proceeded in a 1:1 alternating manner to give the corresponding polyesters, whose structures were confirmed by spectroscopic analyses and reductive scission of the ester bonds in the main chain with lithium aluminum hydride, followed by detailed analyses of the resulting fragments. The polyester obtained by the copolymerization of DHCM and allyl glycidyl ether inherited the allyl groups in the side chain, whose applicability to chemical modifications of the polyester was successfully demonstrated by a platinum‐catalyzed hydrosilylation reaction. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4092–4102, 2008
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