Studies on the mechanism of 1,2-dihydropyrazin-2-one ring formation from dipeptidyl chloromethyl ketone and its chemical properties: immediate deamination during catalytic hydrogenation

1,2-Dihydropyrazin-2-one derivatives, which have two aminoalkyl groups at the positions 3 and 6, were found to be efficient tools for the construction of potent, selective and long-acting opioid mimetics. During the course of preparation, we found that the catalytic hydrogenation of 3,6-bis(benzyloxycarbonylaminomethyl)-5-methyl-1,2-dihydropyrazin-2-one to remove the benzyloxycarbonyl groups resulted in a side reaction. By MS and NMR studies and by preparation of additional 1,2-dihydropyrazin-2-one derivatives, the structure of the by-product was identified as 3-aminomethyl-5,6-dimethyl-1,2-dihydropyrazin-2-one. Preparation of additional compounds substituted with deuterium provided us with sufficient information to confirm the structure of the product and to support a cyclization mechanism in its formation.     

Triethylborane-induced radical allylation reaction with zirconocene-olefin complex

[reaction: see text] Allylzirconium reagents are effective for radical allylation of alpha-halo carbonyl compounds. The key steps would be homolytic cleavage of the zirconium-carbon bond and halogen abstraction by the resulting Cp(2)ZrCl(III). Zirconocene-olefin complex can be also utilized for the allylation of alpha-halo compounds.     

Induction of a remarkable conformational change in a human telomeric sequence by the binding of naphthyridine dimer: inhibition of the elongation of a telomeric repeat by telomerase

The binding of a dimeric form of the 2-amino-1,8-naphthyridine derivative (naphthyridine dimer) to a human telomeric sequence, TTAGGG, was investigated by UV melting, CD spectra, and CSI-MS measurements. Both the 9-mer d(TTAGGGTTA) and the 15-mer d(TTAGGGTTAGGGTTA) showed apparent melting temperatures (T(m)) of 45.6 and 63.6 degrees C, respectively, in the presence of naphthyridine dimer (30 microM) in sodium cacodylate buffer (50 mM, pH 7.0) containing 100 mM NaCl. The CD spectra at 235 and 255 nm of the 9-mer increased in intensity accompanied with strong induced CDs at 285 and 340 nm upon complex formation with naphthyridine dimer. UV titration of the binding of naphthyridine dimer to the 9-mer at 320 nm showed a hypochromism of the spectra. A Scatchard plot of the data showed the presence of multiple binding sites with different association constants. Cold spray ionization mass spectrometry of the complex between naphthyridine dimer and the 9-mer clearly showed that one to three molecules of the ligand bound to the dimer duplex of the 9-mer. Telomeric repeat elongation assay showed that the binding of naphthyridine dimer to the telomeric sequence inhibits the elongation of the sequence by telomerase.     

Basic peptides as functional components of non-viral gene transfer vehicles

Improving the performance of non-viral gene-delivery vehicles that consist of synthetic compounds and nucleic acids is a key to successful gene therapy. Supplementing synthetic vehicles with various biological functions by using natural or artificial peptides is a promising approach with which to achieve this goal. One of the obstacles hindering this effort is that some of the potentially useful peptides, especially those with many basic amino acid residues, interfere with the formation of the complex owing to strong electrostatic interactions with the nucleic acid. In this review, we describe our recent work in examining the potential of these peptides in gene delivery, using a recombinant lambda phage particle as the model for the gene-delivery complex. Lambda phage encapsulates large duplex DNA in a rigid polyplex-like shell with a diameter of 55 nm, and can display various peptides on this capsid, independently of particle formation. By examining the expression of marker genes encapsulated in the phage capsid, we have demonstrated that the protein transduction domain of HIV Tat protein and the nuclear localization signal derived from SV40 T antigen can remarkably facilitate the delivery of these marker genes across the two major barriers, the cell membrane and the nuclear membrane, respectively. Our results indicate that these basic peptides can constitute effective components of synthetic gene-transfer complexes, as long as sufficient copies are displayed on the outer surface of the complex.     

Synthetic and structural studies of [6]-, [7]- and [10]metacyclophanes

A new preparative sequence from 2,3-polymethylene-2-cyclopentenone 5 to 2,6-polymethylenebromobenzenes 3 (n = 6, 7, 10) and 2,6-polymethylenephenyllithiums 6 has been found. The reaction of 6 with various electrophiles produces a number of new compounds to disclose the unique reactivity of the aryl C-Li moiety surrounded by the polymethylene chain. Photolysis of 3a and 3b provides transannular products 8, 10 and 11, all arising from the proximity between the aromatic bromine and the aliphatic hydrogen intraannularly opposed to be removed as HBr. Spectrometric study gives quantitative data of the dependence of the molecular geometry upon the chain length and the aromatic substituents. The energy barriers ΔG_c^≠ of the conformational flipping are 17·4 kcal/mol (T_c 76·5°) for [6]metacyclophane (7a), 11·5 kcal/mol (T_c ?28°) for [7]metacyclophane (7b), ·8 kcal/mol for [10]metacyclophane (7c). The lower-energy process of the aliphatic chain in [6]metacyclophane derivatives is the pseudorotation with substituent-dependent barrier ΔG_c^≠ 11·1 kcal/mol (T_c ?31·5°) for 7a, 12·4 kcal/mol (T_c ?4·5°) for 3a and 12·7 kcal/mol (T_c 1·0°) for 12a. The rather large rotational barrier is attributed to the compressed structure of each system. The benzene ring distortion of the cyclophanes is deduced from the bathochromic shift of the B-band and the diamagnetic shift of the benzene proton signals in the PMR.     

Efficiently Synthesizing Lacto-Ganglio-Series Gangliosides by Using a Glucosyl Ceramide Cassette Approach: The Total Synthesis of Ganglioside X2

The first total synthesis of the hybrid ganglioside X2, which consisted of a highly branched octasaccharide and ceramide moieties, was accomplished by using a glucosyl ceramide cassette approach. With a disaccharyl donor, the heptasaccharide could not be constructed by glycosylation of the C4 hydroxy group of galactose at the reducing end of the pentasaccharide. In contrast, through an alternative approach with two branched glycan units, a GM2-core trisaccharide, and a lacto-ganglio tetrasaccharide, the heptasaccharyl donor could be prepared and subsequently joined with a glucosyl ceramide cassette to afford the protected ganglioside, X2. Finally, global deprotection completed the synthesis, thus affording the pure ganglioside X2.     

Compressed Corannulene in a Molecular Cage

Self‐assembled coordination cages can be employed as a molecular press, where the bowl‐shaped guest corannulene (C₂₀H₁₀) is significantly flattened upon inclusion within the hydrophobic cavity. This is demonstrated by the pairwise inclusion of corannulene with naphthalene diimide as well as by the dimer inclusion of bromocorannulene inside the box‐like host. The compressed corannulene structures are unambiguously revealed by single‐crystal X‐ray analysis.     

New Synthetic Method for Bicyclic Compounds Through a Sequence of Ene-Type Chlorination,Palladium Catalyzed Dehydrochlorination,and Intramolecular Diels-Alder Reaction

A sequence of ene-type chlorination, palladium catalyzed dehydrochlorination, and the intramolecular Diels-Alder reaction afforded a new method for conversion of prenyl derivatives into bicyclic compounds.     

Development of a stable isotope dilution UPLC‐MS/MS method for quantification of dexmedetomidine in a small amount of human plasma

Dexmedetomidine (Dex) is a selective central α2‐agonist with anesthetic properties and has been used in clinical practice for sedation in the intensive care unit (ICU) after operations. In this study, an analytical assay for the determination of Dex in a small amount of plasma was developed for the application to pediatric ICU trials. The quantification of Dex was constructed using the original stable isotope Dex‐d₃ for electrospray ionization‐tandem mass spectrometry (ESI‐MS/MS) in the selected reaction monitoring mode. A rapid ultra‐performance liquid chromatography technique was adopted using ESI‐MS/MS with a runtime of 3 min. Efficacious concentration levels (50 pg/mL to 5 ng/mL) could be evaluated using a very small amount of plasma (10 μL) from patients. The lower limit of the quantification was 5 pg/mL in the plasma (100 µL). For sample preparation, a solid‐phase extraction was used along with the OASIS‐HLB cartridge type. Recovery values ranged from 98.8 to 100.3% for the intra‐ [relative standard deviation (RSD), 0.9–1.3%] and inter‐ (RSD, 0.9–1.5%) day assays. A stable test had recovery values that ranged from 97.8 to 99.7% with an RSD of 1.0–1.9% for the process/wet extract, bench‐top, freeze–thaw and long‐term tests. This method was used to measure the Dex levels in plasma from pediatric ICU patients. In the clinical ICU trial, the small amount of blood (approximate plasma volume, 200 μL) remaining from blood gas analysis was reused and targeted for the clinical analysis of Dex in plasma. Copyright © 2013 John Wiley & Sons, Ltd.