It is indicated that the introduction of biodegradable segments which are accepted as the substrates for the extracellular enzymes of the environmental microbes into the main chain of the synthetic polymer, is one way to design a biodegradable polymer. In this report oligosaccharides were selected as biodegrading segments in the polymer chain and the relations between the content of the oligosaccharide blocks in the polymer chain and the biodegradability as well as functionality were discussed. High molecular weight poly (sodium carboxylate) s containing variable amount of glycopyranose residues as biodegradable segments were prepared by the partial conversion of the vicinal diols of the glycopyranose groups of polysaccharides into the corresponding dicarboxylates via dialdehydes. These polymers containing sugar groups showed an improved biodegradability, suggesting these functional groups to be useful as biodegrading units in the polymer. The biodegradability and builder effects in detergents of these polymers varied inversely with the degree of dicarboxylation. For the design of a biodegradable polymer, biodegradable segments should be incorporated into the polymer chain in such a manner that they are accepted as substrates in the polymer chain by the corresponding enzymes that are contained in environmental microbes.
Novel methodologies for stereocontrolled synthesis of 2, 6-dideoxy sugars by efficient use of 2, 6-anhydro-2-thio sugar and its application to synthesis of natural products are described. This article involves highly stereocontrolled and powerful glycosylations of 2, 6-anhydro-2-thio sugar for synthesis of 2, 6-dideoxy-α- and β-glycosides and highly sterecontrolled creations of C-3 configuration of 2, 6-dideoxy sugar by an addition of a nucleophilic reagent to 2, 6-anhydro-2-thio sugar. Further, the efficient total synthesis of erythromycin A, which is a most typical and clinically important macrolide antibiotic, from (9S) -9-dihydroerythronolide A is achieved by the successful application of the present novel methodologies.
A method for differentiating allylic diastereofaces of carbon-carbon double bonds has been developed based on the ground state molecular design of allylic compounds in which a protected vicinal (S, S) - or (R, R) -diol unit is incorporated as a controller. The protected vicinal diol groups, if they are the most bulky substituents, should arrange anti to each other and the remaining medium-sized groups involving the allylic carbon-carbon double bonds, for instance, stay gauche accordingly. This situation allows only a pair of diastereofaces exposed outside to be attacked by external reagents because a remaining pair of diastereofaces is mutually shielded from intermolecular processes. Such diastereo-bias has been successfully and diversely employed in diastereoselective processes such as double Michael reaction, osmium tetraoxide-catalyzed vicinal hydroxylation, halo-etherification, and Diels-Alder reaction, giving rise to exceptionally high diastereomeric excess for every case examined, appealing prospect for wide applicability in selective organic syntheses.
Regio- and stereoselective synthesis of (E) - and (Z) -vinyl sulfones, which made it feasible to investigate the stereochemistry of the conversion of vinyl sulfones to the corresponding allyl sulfones under basic conditions, was accomplished via iodosulfonization of 1-alkenes or 1-alkynes. It was found that (E) -vinyl sulfones preferentially afforded (Z) -allyl sulfones as kinetically-controlled products, while (Z) - and α-substituted vinyl sulfones gave (E) -allyl sulfones. Such stereochemical relationship was rationalized by “syn-effect, ” and its relative degree for various substituents was determined by observation of E/Z ratios of the allyl sulfones resulted from the corresponding γ-mono- and disubstituted vinyl sulfones. X-ray crystallography was performed for some vinyl sulfones and the related compounds to reveal the origin of “syn-effect.” On the other hand, the convenient new methods for the preparation of allyl sulfones and desulfonylation of their alkylated derivatives were successfully employed for the syntheses of squalene, (±) -recifeiolide, coenzyme Q10, (±) -lavandulol, and isolavandulol.
This paper reviews the recent development of the fluorinating agents. The agents are classified into two categories -nulceophilic and electrophilic fluorinating agents- and summarized. The agents included are new ammonium, phosphonium, and phosphazenium fluoride salts, hypofluorites, N-fluorosulfonamides, N-fluoropyridinium salts, N-fluoroamides, N-fluoroquinuclidinium salts and some others. The fluorinations with the agents are also described.
Recently, highly efficient and selective methods for constructing various types of organic fluorine compounds have been demanded both in organic synthesis and in organofluorine synthesis. In view of the high versatility of enolate intermediates, fluorine-containing enolates-particularly those bearing a fluorine and/or perfluoroalkyl (Rf) group at the carbon center of their ambident anionic structure-are one of the most useful building blocks capable of synthesizing a variety of molecules which are fluorine-substituted regioselectively and/or stereoselectively. This review describes the generation methods and the reactions of, β-monofluorinated, β, β-difluorinated, β-perfluoroalkylated, β-fluoro-β-perfluoroalkylated, and perfluorinated enolates, together with their applications to the synthesis of the fluoro derivatives of biologically active compounds.