Highly stereoselective iminopinacol coupling of chiral aromatic imines derived from di- and tripeptides

The reduction of aromatic imines prepared from (S)-Ile-(S)-Ile-OMe, (S)-Val-(S)-Val-OMe, and (S)-Val-(S)-Val-(S)-Val-OMe with Zn-MsOH in THF gave C₂-symmetric (R,R)-diamines in high yields and stereoselectivities.     

Design of allele-specific primers and detection of the human ABO genotyping to avoid the pseudopositive problem

PCR experiments using DNA primers forming mismatch pairing with template lambda DNA at the 3' end were carried out in order to develop allele-specific primers capable of detecting SNP in genomes without generating pseudopositive amplification products, and thus avoiding the so-called pseudopositive problem. Detectable amounts of PCR products were obtained when primers forming a single or two mismatch pairings at the 3' end were used. In particular, 3' terminal A/C or T/C (primer/template) mismatches tended to allow PCR amplification to proceed, resulting in pseudopositive results in many cases. While less PCR product was observed for primers forming three terminal mismatch pairings, target DNA sequences were efficiently amplified by primers forming two mismatch pairings next to the terminal G/C base pairing. These results indicate that selecting a primer having a 3' terminal nucleotide that recognizes the SNP nucleotide and the next two nucleotides that form mismatch pairings with the template sequence can be used as an allele-specific primer that eliminates the pseudopositive problem. Trials with the human ABO genes demonstrated that this primer design is also useful for detecting a single base pair difference in gene sequences with a signal-to-noise ratio of at least 45.     

Mechanistic studies on the catalytic asymmetric Mannich-type reaction with dihydroisoquinolines and development of oxidative Mannich-type reactions starting from tetrahydroisoquinolines

Detailed mechanistic studies on our recently reported asymmetric addition reactions of malonates to dihydroisoquinolines (DHIQs) catalyzed by chiral Pd(II) complexes were carried out. It was found that an N,O-acetal was generated in situ by the reaction of DHIQ with (Boc)2O, and cooperative action of the Pd(II) complex as an acid-base catalyst allowed the formation of a chiral Pd enolate and a reactive iminium ion via alpha-fragmentation. The iminium ion was also accessible via oxidation with DDQ as an oxidant, and a catalytic asymmetric oxidative Mannich-type reaction was achieved with tetrahydroisoquinolines (THIQs) as starting materials. This oxidation protocol was applicable to N-acryloyl-protected THIQs, allowing the efficient synthesis of optically active tetrahydrobenzo[a]quinolizidine derivatives via intramolecular Michael reaction.     

Total synthesis of (+)-achalensolide based on the rh(i)-catalyzed allenic Pauson-Khand-type reaction

The first total synthesis of (+)-achalensolide was achieved from a commercially available d-(-)-isoascorbic acid. The known epoxide, derived from d-(-)-isoascorbic acid, was converted into the allenyne, the Rh(I)-catalyzed Pauson-Khand-type reaction of which directly provided the bicyclo[5.3.0]decane system, a core framework of the title natural product. The construction of the gamma-lactone moiety and some chemical modifications resulted in the completion of the total synthesis of (+)-achalensolide.     

Photochemical reaction and diffusion of caged calcium studied by the transient grating

A photoreaction of caged calcium (Ca²⁺) was investigated by using the time-resolved transient grating (TG) method. The q²-dependent feature of the TG signal was analyzed based on a model that there are two parallel dissociation steps with different rates and Ca²⁺ is released promptly after the fracture of the caged compound. The TG signal representing the presence of Ca²⁺ was appeared by the volume contribution. Although the diffusion coefficients of Cg and the decomposed product are different without Ca²⁺, only one diffusion component was observed after the dissociation of CgCa²⁺, indicating that the caged compounds and Ca²⁺ diffuse together.     

Difference in trafficking of brain-derived neurotrophic factor between axons and dendrites of cortical neurons,revealed by live-cell imaging

Background  

Brain-derived neurotrophic factor (BDNF), which is sorted into a regulated secretory pathway of neurons, is supposed to act retrogradely through dendrites on presynaptic neurons or anterogradely through axons on postsynaptic neurons. Depending on which is the case, the pattern and direction of trafficking of BDNF in dendrites and axons are expected to be different. To address this issue, we analyzed movements of green fluorescent protein (GFP)-tagged BDNF in axons and dendrites of living cortical neurons by time-lapse imaging. In part of the experiments, the expression of BDNF tagged with cyan fluorescent protein (CFP) was compared with that of nerve growth factor (NGF) tagged with yellow fluorescent protein (YFP), to see whether fluorescent protein-tagged BDNF is expressed in a manner specific to this neurotrophin.     

On-bead fluorescence assay for serine/threonine kinases

[chemical reaction: see text]. A novel fluorescence-based assay for serine/threonine kinases is described. Base-mediated beta-elimination of the phosphate moiety and the Michael addition of a thiol-containing fluorescent molecule allows convenient and efficient detection of the enzyme activity. This approach may be broadly applicable to various serine/threonine kinases.