Recent aspect of rhodium-catalyzed reactions is briefly surveyed from the view point of the carbon-carbon bond formation which is attained under almost neutral conditions. Topics focused here are carbene transfer, [4 + 2] cyclocoupling, aldol and Michael type coupling, and carbonylations in which a certain type of rhodium complex behaves efficiently. A unique character of rhodium is demonstrated in the field of incorporation of CO, especially silylformylation which is accomplished by a combined use of triorganosilane, CO, and a rhodium complex in the presence of acetylenic compounds, aldehydes, or epoxides. α-Silylmethylene-β-lactones and lactams are readily derived from the corresponding propargyl alcohol and propargylamine, respectively, under analogous procedure in the presence of a small amount of DBU. Bicyclo [3.3.0] octenone frameworks are also constructed by cyclocarbonylation of 1, 6-diyne derivatives.
Palladium (II) -catalyzed carboxylation of alkanes including propane, ethane, and methane with carbon monoxide has been achieved in the presence of potassium peroxodisulfate and trifluoroacetic acid. Regioselectivity by this method is secondary>primary>tertiary due to steric and electronic factors. Stereochemistry is determined thermodynamically. An equimolar amount of copper additive improves the catalyst activity dramatically and thus gives higher yield than Pd and Cu alone except for the reaction of methane. In contrast, acetic acid synthesis from methane is best promoted by the copper catalyst. The reaction with Pd and Pd-Cu catalysts has been proved to be electrophilic C-H activation, whereas radical process is at work in the carboxylation with Cu catalyst. In the former systems, clear isotope effect has been observed. Spectroscopic investigation of the Pd-Cu mixed catalyst suggests that copper forms a 1 : 1 complex with palladium and enhances the electrophilicity of Pd.
Two new methods for the introduction of a carbon side chain at the C3-position of indoles are presented. The first one is the palladium-catalyzed allylation of 3-bromoindoles with various allyl esters in the presence of hexa-n-butylditin. This is a new type of cross-coupling reaction which does not involve an organometallic reagent as a coupling partner. The second one is the vinylation of bromoindole in the presence of stoichiometric amount of Pd (II) salt. The reaction occurs selectively at the C3-position without affecting the carbon-bromine bond. The first total synthesis of optically acive clavicipitic acid is accomplished by a biomimetic route starting from 4-bromodehydrotryptophan which was prepared in one-step from 4-bromoindole by applying the above selective vinylation.
Nano-scale tubular polymers have been prepared by crosslinking neighbouring cyclodextrins threaded on a poly (ethylene glycol) chain in a polyrotaxane, followed by removing bulky end groups and the polymer chain. Polyrotaxanes consisting of cyclodextrins and poly (ethylene glycol) s were prepared by capping the end groups of the complexes between cyclodextrins and poly (ethylene glycol) bisamine with 2, 4-dinitrofluorobenzene which is large enough to prevent dethreading. Cyclodextrins have been found to form inclusion complexes with various polymers with high specificity to give stoichiometric compounds in crystalline states.
This paper discloses coordination approaches to well-defined organic structures including macrocycles, a three-dimensional cagelike compound, and  catenanes. These supramolecules self-assembled from (en) Pd(NO3)2 (1, en = ethylenediamine) and appropriate polypyridyl-substituted ligands. Treatment of 1 with 4, 4′-bipyridine (2), for example, gave macrocyclic tetranuclear Pd(II) complex [(en) Pd(μ-2)]4(NO3)8 quantitatively, while macrocyclic dinuclear Pd(II) complexes assembled from 1 and flexible ligands such as PyCH2CH2Py (Py =4-pyridyl). From tridentate ligand 1, 3, 5-(PyCH2)3C6H3 and 1 in 2 : 3 ratio, on the other hand, a three-dimensional cagelike compound assembled in high yields only in the presence of certain types of guest molecules, providing an entire model for 'induced-fit'. The coordination approach made it possible to interlock two apparently continuous molecular rings : i.e., a macrocycle assembling from 1 and 1, 4-(PyCH2)2C6H4 was found to be in equilibrium with its catenated dimer, and polar medium strongly pushed the equilibrium toward the catenane up to >99 : 1 ratio.
Although numerous of strategies for the generation of catalytic antibodies have been developed, investigations of the expressed immunoglobulin proteins have resulted in only a limited understanding of antigen-combining site structures and catalytic function. When mice are immunized with a hapten conjugated to a carrier protein, a few, and occasionally several, of the dozens of antibodies that bind the hapten are characterized to be catalytic. Thus, the diversity of the immune response can provide a panel of catalytic antibodies that possess varying degrees of catalytic activity and substrate specificity. However, it is unclear how structural differences in the antigen-combining sites of these antibodies correlate with catalytic activity. For example, how do catalytic and noncatalytic (affinity) antibodies differ on a structural basis ? Are catalytic antibodies derived from noncatalytic antibodies by mechanisms involved in antibody diversification or are they encoded in the germ-line repertoire ? To understand the structure-function relationship and the molecular mechanisms by which catalytic antibodies are generated in immune responses, heavy and light chain variable region primary structures of antibody repertoires (involving catalytic and noncatalytic antibodies) were deduced from cDNA generation, cloning, and sequencing, in addition, three-dimensional molecular models were constructed based on the primary sequence data and kinetic studies using a variety of substrate derivatives.