Showing papers by "Kazuo Nagasawa published in 2016"
TL;DR: DNA methylation of the G-quadruplex and i-motif-forming sequences on genomic DNA can be detected by qPCR and it is demonstrated that the initial elongation efficiency of PCR decreased with increased DNA methylations of the VEGF region on genomicDNA.
Abstract: DNA methylation has been proposed as one of the promising biomarkers for cancer diagnosis. In this study, we developed a DNA methylation detection system utilizing G-quadruplex and i-motif-forming sequences that requires neither sodium bisulfite treatment nor methylated DNA ligands. We hypothesized that G-quadruplex and i-motif structures would be stabilized by DNA methylation and arrest DNA polymerase activity during quantitative polymerase chain reaction (qPCR). The PCR products from VEGF, RET G-quadruplex, and i-motif-forming sequences were used as templates and analyzed by qPCR. Our results indicated that the initial elongation efficiency of PCR decreased with increasing DNA methylation levels in the G-quadruplex and i-motif-forming sequences. Moreover, we demonstrated that the initial elongation efficiency of PCR decreased with increased DNA methylation of the VEGF region on genomic DNA. These results indicated that DNA methylation of the G-quadruplex and i-motif-forming sequences on genomic DNA can ...
30 citations
TL;DR: The first direct demonstration of the biosynthetic route towards saxitoxin and a shunt pathway is provided, suggesting that Int-A’ and Int-C’2 are genuine precursors of PSTs, butInt-C'2 converts partially to Cyclic- C’ which is aShunt product excreted to outside the cells.
Abstract: Saxitoxin, the most potent voltage-gated sodium channel blocker, is one of the paralytic shellfish toxins (PSTs) produced by cyanobacteria and dinoflagellates. Recently, putative biosynthetic genes of PSTs were reported in these microorganisms. We previously synthesized genetically predicted biosynthetic intermediates, Int-A' and Int-C'2, and also Cyclic-C' which was not predicted based on gene, and identified them all in the toxin-producing cyanobacterium Anabaena circinalis (TA04) and the dinoflagellate Alexandrium tamarense (Axat-2). This study examined the incorporation of (15)N-labeled intermediates into PSTs (C1 and C2) in A. circinalis (TA04). Conversions from Int-A' to Int-C'2, from Int-C'2 to Cyclic-C', and from Int-A' and Int-C'2 to C1 and C2 were indicated using high resolution-LC/MS. However, Cyclic-C' was not converted to C1 and C2 and was detected primarily in the extracellular medium. These results suggest that Int-A' and Int-C'2 are genuine precursors of PSTs, but Int-C'2 converts partially to Cyclic-C' which is a shunt product excreted to outside the cells. This paper provides the first direct demonstration of the biosynthetic route towards saxitoxin and a shunt pathway.
27 citations
TL;DR: It is reported that a G-quadruplex-specific compound induced structural changes in G- Quadruple-forming DNA aptamers and stabilized the folded structures, making them suitable for targeted proteins and enhancing their binding properties.
19 citations
Journal Article•
15 citations
TL;DR: The key to the synthesis lies in a Mukaiyama aldol condensation reaction of silyl enol ether with glyoxylate in the presence of an anhydrous fluoride reagent, which directly constructs the crucial C-C bond at the C11 position in SEA.
Abstract: 11-Saxitoxinethanoic acid (SEA) is a member of the saxitoxin (STX) family of paralytic shellfish poisons, and contains an unusual C−C bond at the C11 position. Reported herein is a total synthesis of SEA. The key to our synthesis lies in a Mukaiyama aldol condensation reaction of silyl enol ether with glyoxylate in the presence of an anhydrous fluoride reagent, [Bu4N][Ph3SnF2], which directly constructs the crucial C−C bond at the C11 position in SEA. The NaVCh-inhibitory activities of SEA and its derivatives were evaluated by means of cell-based assay. SEA showed an IC50 value of (47±12) nm, which is approximately twice as potent as decarbamoyl-STX (dcSTX).
14 citations
TL;DR: Molecular mechanics calculations and docking studies indicate that differences arise from the different directions of the side chains in these L2H2-6OTD derivatives, and provide an explanation for the weaker stabilization of telomeric DNA by 2 and 3, compared with 1.
Abstract: New macrocyclic hexaoxazole compounds bearing two side chains on an unsymmetrical macrocyclic ring system, i.e., 4,2-L2H2-6OTD (2) and 5,1-L2H2-6OTD (3), were designed as candidate G-quadruplex (G4) ligands and synthesized. These G4 ligands 2 and 3 induced an anti-parallel topology and a hybrid-type topology of telomeric DNA, respectively, in contrast to the previously reported symmetrical macrocycle 3,3-L2H2-6OTD (1), which induces a typical anti-parallel structure. Molecular mechanics calculations and docking studies indicate that these differences arise from the different directions of the side chains in these L2H2-6OTD derivatives, and provide an explanation for the weaker stabilization of telomeric DNA by 2 and 3, compared with 1.
14 citations
TL;DR: The amaryllidaceae alkaloid (+)-trans-dihydrolycoricidine (1) was synthesized by asymmetric organocatalytic Friedel-Crafts reaction of sesamol with nitro-olefin followed by an intramolecular Henry reaction for construction of the C ring system as discussed by the authors.
11 citations
TL;DR: An asymmetric α-amination of β-keto esters with azodicarboxylate in the presence of a guanidine–bisurea bifunctional organocatalyst was investigated and products obtained in up to 99% yield with up to 94% ee.
Abstract: An asymmetric α-amination of β-keto esters with azodicarboxylate in the presence of a guanidine–bisurea bifunctional organocatalyst was investigated. The α-amination products were obtained in up to 99% yield with up to 94% ee.
10 citations
TL;DR: In this paper, an efficient synthesis of α-azido-β-dicarbonyl compounds from trimethylsilyl azide, catalyzed by guanidinium hypoiodite, was presented.
10 citations
TL;DR: Two vitamin D3 derivatives were synthesized via a convergent route employing Julia-Kocienski olefination as a key step, exhibiting about 400- and 30-fold greater binding affinity than the corresponding non-fluorinated derivatives 5a and b.
Abstract: Two vitamin D3 derivatives, namely 24,24-difluoro-1β,3β,25-dihydroxy-19-norvitamin D3 (6a) and 24,24-difluoro-1α,3α,25-dihydroxy-19-norvitamin D3 (6b), were synthesized via a convergent route employing Julia-Kocienski olefination as a key step. Compounds 6a and b bound to vitamin D receptor (VDR) with IC50 values of 64.8 and 57.6 nM, respectively, exhibiting about 400- and 30-fold greater binding affinity than the corresponding non-fluorinated derivatives 5a and b.
6 citations
TL;DR: X‐ray crystallographic analysis revealed that DLAMs induced a large conformational change in the loop region between helices H6 and H7 in the VDR ligand‐binding domain, which suggests that targeting of theloop region may be a new mode of VDR regulation.
TL;DR: The A-ring was coupled with the circular dichroism (CD) ring by means of Julia-Kocienski olefination to construct the diene unit and the structures of the products were confirmed by (1)H-NMR and nuclear Overhauser effect (NOE) experiments.
Abstract: 1β,3β,25-Dihydroxy-19-norvitamin D3 (4a) and 1α,3α,25-dihydroxy-19-norvitamin D3 (4b) were synthesized by employing a new A-ring synthon, (1R,3S)-3-((tert-butyldimethylsilyl)oxy)-5-oxocyclohexyl benzoate (19), which was derived from D-(-)-quinic acid in 12 steps. The A-ring was coupled with the circular dichroism (CD) ring by means of Julia-Kocienski olefination to construct the diene unit. The structures of the products were confirmed by (1)H-NMR and nuclear Overhauser effect (NOE) experiments.
TL;DR: The amaryllidaceae alkaloid (+)-trans-dihydrolycoricidine (1) was synthesized by asymmetric organocatalytic Friedel-Crafts reaction of sesamol with nitro-olefin followed by an intramolecular Henry reaction for construction of the C ring system.
Abstract: The amaryllidaceae alkaloid (+)-trans-dihydrolycoricidine (1) was synthesized by asymmetric organocatalytic Friedel–Crafts reaction of sesamol with nitro-olefin followed by an intramolecular Henry reaction for construction of the C ring system. Construction of the B ring was achieved by a microwave-assisted palladium-catalyzed CO insertion reaction. Finally, regio- and stereoselective introduction of the third hydroxyl group (at C3) on the C ring afforded 1.
TL;DR: In this paper, an efficient synthesis of α-azido-β-dicarbonyl compounds from trimethylsilyl azide, catalyzed by guanidinium hypoiodite, was presented.
Abstract: We present an efficient synthesis of α-azido-β-dicarbonyl compounds from β-dicarbonyl compounds and trimethylsilyl azide, catalyzed by guanidinium hypoiodite. The reaction can be run in air at ambient temperature (up to 40 °C) and is not sensitive to moisture. The substrate scope is broad, including cyclic and linear β-dicarbonyl compounds, and the α-azide products are obtained in 55%–99% yield.
TL;DR: In this paper, the authors revisited the idea of differential activation entropy (ΔΔS) as an important parameter that governs catalytic stereodiscrimination by investigating temperature effects on the basis of the Eyring theory.
Abstract: Differential activation entropy (ΔΔS(≠)) is revisited as an important parameter that governs catalytic stereodiscrimination processes by investigating temperature effects on the basis of the Eyring theory. However, correlating the ΔΔS(≠) effect and the molecular structure of the asymmetric catalyst is still an underdeveloped area. Efforts to identify factors (including catalyst structure, reactants, and reaction conditions) that contribute to the attainment of large ΔΔS(≠) values for enantioselective 1,2-type Friedel-Crafts reactions of phenols with N-tert-butoxycarbonyl aldimines catalyzed by conformationally flexible guanidine bisthioureas are described. First, we uncover an interesting property of the ΔΔS(≠)-driven stereodiscrimination process: maximum enantioselectivity is obtained at around room temperature. Second, a plausible transition-state model accounting for the characteristic ΔΔS(≠) effect and the structural dynamics of the conformationally flexible organocatalyst in the stereodiscrimination process is discussed.