Some new methods and practical strategies for the efficient resolution of a wide variety of organic componds by means of such crystallization procedures as preferential crystallization, diastereomeric salt formation and their combination are described. Utilizing the organic compounds with high optical purities thus obtained, application study in the following field has been performed;1) verification of the Brewster's theory of optical activity, 2) syntheses of pharmaceutical, agricultural and perfuming chemicals, 3) preparation of optical purity determining agents, 4) preparation of atropisomeric bis (triarylphosphine) as a catalyst for asymmetric hydrogenation, 5) syntheses of ferroelectric liquid crystals. In this article, an outline of our investigation in the above mentioned fields is also described.
This review article describes preparation and modification of oligonucleotides by condensation in aqueous solution. Nucleotides and oligonucleotides are generally soluble in water, but not in organic solvents. Reactions in aqueous solution are therefore indispensable. Condensation in aqueous media is thermodynamically unfavorable. Several methods have been devised to overcome this problem. Large amount of water soluble condensing agents such as EDC or cyanogen bromide are employed for the condensation of oligonucleotides. Use of imidazole-activated nucleotides is an another approach for the preparation and the modification of oligonucleotides. The control of pH of the reaction media is necessary to accomplish the efficient and regioselective condensation. Metal ions or polynucleotide template, wihch organize the substrate nucleotides by complex formation promote the target condensation.
Cyclic silicon compounds containing heteroatoms (N, P, S), as cyclosilazanes, cyclosilaphosphanes, and cyclosilthianes have been energetically investigated as synthetic targets in a field of silicon chemistry. In the interest of chemical industry, cyclosilazanes as well as cyclosiloxanes are useful in the preparation of linear polymer. The importance of polysilazanes as preceramic materials is well-konwn. But the possibility of cyclosilaphosphanes and cyclosilthianes as the industrial materials have not been discussed in detail. In this review, the recent developments in the field of cyclic silicon compounds containing heteroatoms (N, P, S) are summarized from the above point of view.
Various organosilicon compounds act as synthetic equivalents of unstable active chemical species, especially novel 1, 3-dipolar reagents such as azomethine ylides, thiocarbonyl ylides and related reagents, are designed and synthesized. These compounds activated by a Lewis acid or fluoride ion react with a variety of dipolarophiles and hetero-dipolarophiles in highly regio- and stereospecific mode. It has been found that this methodology can be extended to the design and preparations of tailor-made 1, 3-dipolar reagents. The highly selective synthesis of heterocycles are described.
The first enantioselective total synthesis of neooxazolomycin (1), structurally unique antitumor agent isolated from streptomyces sp., is described. The key steps of the synthesis involve the following newly developed synthetic methods : i) the novel dianion cyclocondensation reaction of amide-malonate 3 with ester 36 followed by stereoselective lactonization to give the fused bicyclic lactam-lactone terminus, ii) the four carbon homologation of aldehyde 41 to E, E-dienamide 45 via vinyliodide 43 by means of the mild Pd-catalyzed coupling with the vinylstannane 13, (iii) the diastereoselective Reformatsky type aldol reaction of Z-enal 48 with the tin (II) enolate derived from chiral oxazolidinone 15 to give R, S-oxazinedione 51. Utilizing the above key reactions and further manipulations afforded the right half amine 71 and the left half acid 68 in proper chiral form. Finally, the amide formation of them followed by deprotection gave the synthetic neooxazolomycin (1).