Recent development in X-ray crystallography has proved that the crystal structure analysis is a very powerful tool in the elucidation of the reaction mechanism. Two topics are reviewed in this article. One is the observation of the reaction path frozen by the different crystalline fields, comparing many structural fragments in related crystals. The other is the direct observation of the crystalline-state reaction, which proceeds in a crystal without degradation of the crystallinity. The structure at any stage can be obtained by the three dimensional intensity data. These may provide us how to “observe” the structural change in a reaction intermediate.
Preparation and biological activities of macromolecule-anticancer drug conjugates are reviewed under the following headlines : 1) introduction, 2) characteristics of macromolecular drugs, 3) biological activities of conjugates, 3.1) therapeutic effects enhanced by lysosomotropism, 3.2) therapeutic effects enhanced by slow release, 3.3) decreased side effects, 3.4) overcoming of drug resistance, 3.5) effects against metastasis, 3.6) targeting of drugs to tumors, 4) preparation of conjugates, 4.1) selection of macromolecules and drugs, 4.2) preparation and purification of conjugates, and 5) closing remarks.
This account describes the CD exciton chirality method which is useful for determination of absolute stereochemistry of various natural and synthetic chiral compounds. Chiral exciton coupling between two or more chromophores gives rise to two split CD Cotton effects of opposite signs to each other, from the signs of which absolute configuration of chiral compounds is nonempirically determined, if the direction of transition moments in interacting chromophores is known. Applications of this versatile chiroptical method to various organic compounds are exemplified ; in Part II, chiral exciton interaction between different chromophores are discussed.
Recently much attention has been focussed on ene reactions, and their synthetic utility has been increased because of their high regio- and stereospecificity. Ene reaction is based on addition of a compound with electron-deficient multiple bond (an enophile) to an olefin possessing an allylic hydrogen (an ene). Intermolecular ene reactions are classified by functional groups in enophiles. The differences between thermal reactions and Lewis acid catalyzed ones are discussed. Intramolecular ene reactions including metallo-ene systems are reviewd according to the classification (Type I- III) reported by Oppolzer.
This article is intended to give a brief review of synthetic methods of penems, ranging from Woodward's first penem synthesis to the most recent penem synthesis appearing in current papers. The antibacterial in vitro activities of a variety of penem derivatives are also described, together with structure-activity relationships of penems prepared in our laboratories.
Recently, much attention has been focused on the syntesis of dehydrooligopeptides (DHP), containing one or more α-dehydroamino acid (DHA) residues, and the correlation between the structure and the bioactivity of DHP. The synthetic studies on DHP were reviwed according to the following articles : 1. Introduction. 2. Synthesis of dehydrodipeptides. 2.1. Synthesis of DHA as carboxy and amine components. 2.2. Stepwise elongation. 2.3. β-Elimination of dipeptide. 2.4. Synthesis of geometric isomer. 2.5. The other elimination methods. 2.6. The other new synthetic methods. 3. Synthesis of Dehydrooligopeptides. 3. 1. Fragment condensation. 3.2. Synthesis and reactivity of N-carboxy α-dehydroamino acid anhydride (Δ NCA). 3.3 Δ NCA as synthon. 3.4. Application of Δ NCA method. 4. Conclusion.
Recent studies on the ring-opening and recyclization reactions of adenine and its derivatives are reviewed with particular emphasis on the synthetic utility of these transformations. Among the reactions included are Bamberger-type fission, Dimroth rearrangement of 1-alkyladenines, basecatalyzed ring-opening of 1-alkoxyadenines and N6, N6, 3, 9-tetraalkyladenines, recyclization and deformylation of the resulting ring-opened derivatives, synthetic reactions utilizing the ring-opened compounds, and ring-opening and recyclization of Nx, Ny-disubstituted adenines. Examples from the nucleoside and nucleotide series are also summarized.