In order to achieve the diastereo-differentiation of π-faces, we have developed the protected vicinaldiol controller. The striking successes in stereocontrol of diverse organic reactions have been recorded for which the diastereofacial bias constructed by such diol controller should be responsible. We refer to this topological situation as “outside-inside bias”. This review summarizes the application of this concept to nitrone-olefin [3 + 2] cycloaddition reactions which resulted in considerable successes in stereocontrol again, and covers three topics, (1) the substrate-controlled intermolecular asymmetric cycloaddition reactions, (2) intramolecular 1, 3-dipolar cycloaddition reactions of chiral alkenylnitrones, and (3) the synthesis of cyclic chiral nitrones and its intermolecular asymmetric cycloaddition reactions with various olefins. The role of the vicinal diol controller in these processes has been delineated.
Various neutral and cationic monoorganopalladium complexes have been prepared as models of active species involved in palladium-catalyzed catalytic processes. Removal of a halide ligand from monoalkyl- and arylpalladium halide complexes by treatment with a silver salt afforded cationic monoorganopalladium complexes coordinated with a solvent molecule at the vacant site of the cationic palladium center. Generation of the vacant site has been found to be a dominant factor in enhancing the reactivities of organopalladium complexes toward β-hydrogen elimination from alkylpalladium complexes as well as CO and olefin insertions into palladium-carbon bond. Further addition of the silver salt was found to accelerate the CO insertion rate by removing a phosphine ligand from the palladium complexes. Cationic solvent-coordinated Pd (II) complexes also proved to be suitable model compounds for studying the mechanism of nucleophilic attack on coordinated CO. Utility of the concept of the reactivity enhancement by creation of a vacant cationic center at palladium has been demonstrated in catalytic double carbonylation of aryl and allyl halides with a secondary amine to give α-keto amides.
In order to perform selective fluorination using molecular fluorine, mechanistic studies using ab initio MO calculation were carried out. As a result, it was confirmed that both fluorine addition to ethylene and fluorine substitution of methane are electrophilic reactions. These studies suggested that bicyclo [2.2.1] hept-2-ene derivatives would be suitable fluorinating substrates because they have tertiary hydrogens with somewhat lower p-character than sp3 and a more activated double bond. As expected, addition of molecular fluorine to the bicyclo [2.2.1] hept-2-ene derivatives having electronegative substituents on the ethano bridge was found to give exo, exo-difluoro adducts selectively. The difluoro adducts derived from 2-azabicyclo [2.2. 1] kept-5-en-3-one or 7-oxabicyclo [2.2. 1] hept-2-ene derivatives were converted to the difluorinated carbocyclic nucleosides or ribofuranosides. Novel α-fluorination of alkyl phenyl sulfoxides by molecular fluorine was also developed and applied to the synthesis of cis-2-fluorocyclopropane-1-carboxylic acid and fluorine substituted 1-aminocyclopropane-l-carboxylic acid derivatives.
Anti HIV-1 active coumarins with either an alkyl or a phenyl group at the 4 position in the coumarin skeleton were isolated from Calophyllum genus (Guttiferae). This review describes on the chemistry of the anti HIV-1 active Calophyllum coumarins : isolation, structure, relative and absolute stereochemistries, synthesis including asymmetric synthesis, anti HIV-1 activity, and structure-activity relationship. The structural modifications indicated that the stereochemistries of the 2, 3-dimethyl-4-chromanol ring in their molecules should play an important role for the activity. Thus, among Calophyllum coumarins (+) -calanolide A (1) and (+) -inophyllum B (8) with all trans configurations (10R, 11S, 12 S) are the most promising candidates for anti HIV-1 active drugs against AIDS.
To create artificial ion channels using synthetic peptides is one of the challenges of the de novo design of artificial proteins not only to obtain highly functional artificial molecules but also to understand the basic mechanisms of natural ion channel proteins. Amphiphilic helical peptides of 20 amino acid residues were reported to assemble with each other in lipid bilayers to form ion channels. To obtain more organized channels, efforts have been directed toward controlling the assembly by template molecules. Not only α-helical peptides, but also peptide nanotubes and gramicidin-like molecules were developed as channel molecules where the assembly was stabilized by hydrogen bonding between the molecules. We have developed three approaches to construct artificial helical proteins comprising helices with individual amino acid sequences. Using one of these approaches, four helices corresponding to the voltage sensor (S 4 in repeat I-IV) of the sodium channel were tethered on a peptide template to afford a protein having ion channel activity with rectification.
A new method to establish the absolute configurations of organic compounds is reviewed. This method is designated “axial chirality method” because it uses axially chiral biaryls as chiral auxiliaries. Chiral secondary alcohols, α-chiral primary amines and α-chiral carboxylic acids are derivatized with the above reagents. The absolute configurations of original compounds are correlated to the Δδ values, which are defined as Δδ=δaS-δaR for each proton of the diastereomeric derivatives. Some models are described to explain the observed proton shifts and the signs of δas In certain cases, NOEs were observed between the protons of the reagent's moiety and those of substrate's one. The absolute configuration of a sterically hindered tertiary alcohol was determined by this new method using the Δδ values and NOE correlations. One new C-centrochiral reagent was also presented. Versatility and limitation of this method are discussed.