Reactions of several different kinds of methyl-branched pyranosides were investigated in order to establish new effective routes to carbohydrate chiral synthons having oxygenated dimethyl-branched structure, which are often included in biologically active natural products. While reactions of methyl-branched pyranosides having allylic acetate structure (O-acetylated enopyranosides) and methyl-branched anhydropyranosides with lithium methylcuprates (I) gave 1, 3- and 1, 2- dimethyl structures, respectively, the following three methods were proved to be effective for construction of gem-dimethyl structure in the pyranoside ring : (1) conjugate addition of lithium methylcuprates (I) to methyl-branched enolones, (2) enolate methylation of methyl-branched uloses with lithium diisopropylamide and methyl iodide, and (3) hydrogenolysis of spiro- cyclopropane derivatives, which were derived from corresponding uloses via exomethylene derivatives. Stereochemical aspects in some of these reactions were also discussed.
Divalent sulfur can stabilize both of carbenium ion and carbanion adjacent to the sulfur atom, and hypervalent sulfur functions can strongly stabilize the adjacent carbanions. These sulfur functions can undergo characteristic migration and/or elimination. Single electron transfer onto an aliphatic nitro compound leads to an unstable radical-anion which eliminates the nitrite anion to leave the corresponding free radical. The subsequent reaction of the free radical gives various compounds including denitrated product. And it results a new denitro-hydrogenation reaction. Nitro group can be a good leaving group in allylic system and also for the Friedel-Crafts reaction. Using these characteristics of sulfur and nitro functions twenty-five kinds of convenient synthetic reactions are presented here. The sulfur and nitro functions can assure regio- and stereocontrol of these reactions to give the desired products in most of which no sulfur function or nitro group is remained.
The modified nucleosides or bases from transfer ribonucleic acids and related compounds are reviewed from an organic chemical standpoint with particular emphasis on the fluorescent minor components of eukaryotic phenylalanine transfer ribonucleic acids (tRANsPhe). Structural educidations, syntheses, and chemical properties of these unique tricyclic compounds as well as the use of the chemical properties for modifications of yeast tRNAPhe at the anticodon loop are summarized.
Corticosteroids are commercially produced from deoxycholic acid via a chemical process comprising many steps or from diosgenin and stigmasterol via a process involving a microbiological oxidation step at C-11. Recent advances in the microbiological degradation of cholesterol and abundant soya sterols allowed the production of androst-4-ene-3, 17-dione, 9 α-hydroxyandrost-4-ene-3, 17-dione, androsta-1, 4-diene-3, 17-dione, 21-hydroxy-20-methylpregna-1, 4-dien-3-one and 3-oxopregna-1, 4-diene-20-carboxylic acid which may be potentially useful starting materials for the syntheses of corticoids. In this article, the new syntheses of corticoids from these new steroids have been reviewed.
The properties of 6, 6'-diamino-2, 2'-bipyridine (DABP) as a metal chelating agent are discussed in terms of the electronic and steric effects of the amino groups. Experimental and theoretical studies showed that DABP has higher ability to coordinate metal ions due to the electronic effects of amino groups compared to 2, 2'- bipyridine (bpy) but suffers the steric hindrance between coordinated ligands. Synthesis and photochemical properties of a Ru (II) (DABP) 32+ complex are also discussed. Alkylation of the amino groups of DABP gave oil-soluble alkylamino derivatives of bpy, which showed the ability to undergo selective and uphill transport of metal ions through an organic phase by coupling with a proton gradient. Acylamino derivatives of bpy served as a N2O2 tetradentate planer ligand, and, therfore, is expected to serve as a bis (N-salicylidene) ethylenediamine analogue with higher stability.
Three types of asymmetric reactions induced by chiral sulfoxides are described as follows : (1) 1, 3-Asymmetric induction in the addition of organoaluminum reagents to chiral β-ketosulfoxides. (2) New synthetic method for optically pure α, β-unsaturated sulfoxides, and additive Pummerer reaction of 1-alkenyl sulfoxides with dichloroketene. (3) 1, 4-Asymmetric induction in the rearrangement of α-p-tolylsulfinyl-α, β-enoates. Utility of the present methodologies is illustrated by the asymmetric syntheses of marine prostanoids and bibenzyl lignan lactones.
A new thermoanalytical method is described for the simultaneous recording of the differential thermal analysis (DTA) and the spectrophotometry (SPM) curves on the solution reactions. Simultaneous DTA-SPM curves for the nitration of hydroquinone dimethyl ether (HQDME) are shown to demonstrate the capability of the apparatus.