Dynamic covalent chemistry relates to the utilization of chemical equilibrium systems, i.e., reversible cleavage-rebondage of covalent bond, which is effectively applicable to the molecular architectures in supramolecular chemistry and polymer chemistry. This review deals mainly with molecular integration and molecular conversion of supramolecules and polymers in order to prove significance and utility of the dynamic covalent bond by introducing the representative research studies. Equilibria of imine bond, carbon-carbon double bond, disulfide bond, trityl carbon-sulfur bond, ester bond, alkoxyamine bond, and so on are typical dynamic covalent bonds, and several important examples for the constructions of interlocked molecules and polymers are described. In the utilization of the dynamic covalent bond in polymer, utility of a few reversibly cleavable covalent bonds included in polymer main chains is also discussed for the formation and transformation of polymers and cyclic polymers.
Human genome sequencing project and DNA microarray analysis yielded a number of useful results. These are included in an insight into genes possibly associated with diseases and individual's susceptibility to side effects of drugs arising from single nucleotide polymorphisms. For further development of these areas, a simple and convenient analytical means for gene analysis is keenly desired. Among many gene detecting techniques, one that uses an electrochemical method is especially promising from a viewpoint of convenient means with compactification and miniaturization. Ferrocence is a reversible redox active molecule and relatively stable in aqueous solution. Therefore nucleic acids modified with it can be used as an electrochemically active DNA probe. Several modification methods of nucleic acids with ferrocene and electrochemical gene detection methods based on the modified nucleic acids have been studied in this context. Especially, the sensitivity of detection could be improved by the introduction of many ferrocenes in a single DNA probe or by the use of ferrocene as a mediator of enzymatic amplification reaction in the electrochemical gene detecting system. In this article, synthetic methods of ferrocenyl nucleic acids and electrochemical gene detecting methods using their derivatives are summarized. The results described here may lead to an essential technique which enables the development of a DNA analyzer of the next generation.
In the course of the development of a new cyan dye-forming coupler skeleton for color photographic use, we found that 1H-pyrrolo [1, 2-b] [1, 2, 4] triazole having electron-withdrawing groups in the 6, 7 positions could promptly couple with oxidized developing agent to form an azomethine cyan dye. 6-Cyano and 7- (2, 6-di-tert-butyl-4-methyl) cyclohexyloxycarbonyl groups were essential to obtain an excellent hue and stability of the dye. The following synthetic breakthroughs were achieved to lead 1H-pyrrolo [1, 2-b] [1, 2, 4] triazoles to practical couplers. (1) Highly bulky alcohol (Magic alcohol) was efficiently synthesized via two-step reduction of 2, 6-di-tert-butyl-4-methylphenol. (2) Efficient synthesis of highly bulky ester (Magic ester) was accomplished by way of a ketene intermediate generated from triazolylacetic acid derivative. (3) Two types of novel cyclization reactions were developed to construct 5-unsubstituted and 5-acyloxy 1H-pyrrolo [1, 2-b] [1, 2, 4] triazoles from triazole derivatives.
A total synthesis of (±) -nominine 1, a heptacyclic hetisan-type aconite alkaloid isolated from Aconitum sanyoense Nakai, was achieved by use of the palladium-catalyzed intramolecular α-arylation of formyl group. The synthesis is composed of forty steps starting from 1-bromo-2- (2-iodoethyl) -4-methoxybenzene 63 in 0.15% overall yield, and constitutes the first total synthesis of a hetisan-type aconite alkaloid, the sole representative aconite skeleton whose total synthesis has remained unsuccessful. The other key steps include (i) acetal ene-reaction to form the C14-C20 bond 55→56, (ii) stereoselective hydrocyanation 57→58, (iii) LiAlH4 reduction of cyano-enol silyl ether to form the N-C 6 bond 58→59, and (iv) radical cyclization from enyne precursor to construct the methylenebicyclo [2.2.2] octane framework 60→61. Completion of the synthesis was verified unambiguously by single crystal X-ray analysis of the resulting (±) -nominine to confirm its crystal structure as well as its molecular structure.
The development of the synthetic methods of functionalized 2-pyridones is important as a result of the large number of biologically active compounds containing a 2-pyridone structure and as dienes in Diels-Alder cycloadditions. Many methods for the synthesis of 2-pyridones have been reported. We have found a 5-alkoxycarbonyl-2-pyridone synthesis via the nucleophilic addition of malonic esters to alkynyl imines in good yields. It is also found that the reaction of β-keto esters with alkynyl imines give 5-acetyl-2-pyridones in good yields. On the other hand, the reactions of dialkynyl imines instead of alkynyl imines with active methine compounds give 3, 4, 5, 6-tetrasubstituted-2-pyridones. We have found that the reactions of alkynylpyridines, pyrimidine, or thiazoles with malonic esters give bicyclo-2-pyridones in moderate to good yields. The conjugate addition reactions of various cyclic β-keto esters with alkynyl imines proceed and then the intramolecular cyclization reactions take place. The subsequent cleavage reactions give two-atom enlarged carbocyclic products in good yields. We have also found the reactions of malonic esters or β-keto esters with alkynyl ketones give 5-alkoxycarbonyl-2-pyrones or 5-acetyl-2-pyrones in good yields.