Functional Fluorescence Labeling of Carbohydrates and Its Use for Preparation of Neoglycoconjugates

Abstract

New bifunctional reagents, 2-amino-6-carboxyethylpyridine and 2-amino-6-cyanoethylpyridine, were designed and synthesized in order to provide a novel procedure for preparation of neoglycoconjugates from fluorescence-labeled and purified sugar chains. Labeling of model sugar chains with these reagents was effected by reductive amination using BH₃.Me₂NH to give corresponding 6-carboxyethylpyridylaminated (CEPA-) and 6-cyanoethylpyridylaminated (CNEPA-) derivatives, which were readily purified by reversed phase HPLC. The reagent parts of the labeled products possess the functional groups which then serve as linkers for coupling with matrices such as proteins and polymers. A CEPA-derivative of glucose was directly coupled with the ε-amino group of a Lys derivative to give a neoglycoprotein model. CNEPA-sugars were hydrogenated to give 6-aminopropylpyridylaminated (APPA-) derivatives, which can then be readily used for the preparation of various types of neoglycoconjugates by use of appropriate spacers as exemplified by the coupling of APPA-maltotriose with bovine serum albumin (BSA), biotin, and acrylic acid. The reaction of APPA-maltotriose with succinimidyl 3-(3-nitro-2-pyridyldithio)propionate gave the corresponding amide to be used for a disulfide formation with BSA. Condensation with biotin was effected by use of N-hydroxysuccinimidobiotin. The conjugation of APPA-maltotriose with acrylic acid was carried out by use of 4-acryloyloxyphenyldimethylsulfonium methylsulfate to give the corresponding acrylamide, which can be used for the preparation of sugar-acrylamide copolymers.     

Rational Design for Cooperative Recognition of Specific Nucleobases Using β‐Cyclodextrin‐Modified DNAs and Fluorescent Ligands on DNA and RNA Scaffolds

We propose a binary fluorimetric method for DNA and RNA analysis by the combined use of two probes rationally designed to work cooperatively. One probe is an oligonucleotide (ODN) conjugate bearing a β‐cyclodextrin (β‐CyD). The other probe is a small reporter ligand, which comprises linked molecules of a nucleobase‐specific heterocycle and an environment‐sensitive fluorophore. The heterocycle of the reporter ligand recognizes a single nucleobase displayed in a gap on the target labeled with the conjugate and, at the same time, the fluorophore moiety forms a luminous inclusion complex with nearby β‐CyD. Three reporter ligands, MNDS (naphthyridine–dansyl linked ligand), MNDB (naphthyridine–DBD), and DPDB (pyridine–DBD), were used for DNA and RNA probing with 3′‐end or 5′‐end modified β‐CyD – ODN conjugates. For the DNA target, the β‐CyD tethered to the 3′‐end of the ODN facing into the gap interacted with the fluorophore sticking out into the major groove of the gap site ( MNDS and DPDB ). Meanwhile the β‐CyD on the 5′‐end of the ODN interacted with the fluorophore in the minor groove ( MNDB and DPDB ). The results obtained by this study could be a guideline for the design of binary DNA/RNA probe systems based on controlling the proximity of functional molecules.     

Recent Progress on Nazarov Cyclizations: The Use of Iron Salts as Catalysts in Ionic Liquid Solvent Systems

Nazarov cyclization is an important and versatile method for the synthesis of five‐membered carbocycles, and extensive studies have been conducted to optimize the reaction. Among recent studies, several trends are recognized. One is the combination of different reactions with Nazarov cyclization in a one‐pot reaction system which enables the preparation of unique cyclization products. The second is the use of a transition‐metal catalyst, though Lewis or Brønsted acids have generally been used for the reaction. The third is the realization of the asymmetric Nazarov cyclization. The fourth is the base‐catalyzed Nazarov cyclization. Furthermore, several useful protocols for realizing Nazarov cyclization have also been developed. The recent progress on Nazarov cyclizations is summarized in Section 2. Section 3 is our chronicle in this field. We focused on the use of iron as the catalyst in Nazarov cyclizations and ionic liquids as solvents: Nazarov cyclization of thiophene derivatives using FeCl₃ as the catalyst was accomplished and we succeeded in demonstrating the first example of an iron‐catalyzed asymmetric Nazarov reaction. We next established Nazarov cyclization of pyrrole or indole derivatives using Fe(ClO₄)₃·Al₂O₃ as the catalyst with high trans selectivities in excellent yields. Since the cyclized product was reacted with a vinyl ketone in the presence of the same iron salt, the system allowed realization of the sequential type of Nazarov/Michael reaction of pyrrole derivatives. Furthermore, we demonstrated the recyclable use of the iron catalyst and obtained the desired Nazarov/Michael reaction products in good yields for five repetitions of the reactions without any addition of the catalyst using an ionic liquid, [bmim][NTf₂], as the solvent. We expect that the iron‐catalyzed Nazarov cyclization, in particular, in an ionic liquid solvent might become a useful method to synthesize functional molecules that include cycloalkene moieties.     

Preparation of telechelic oligomers by thermal degradation of propylene copolymers

The reactive end groups of nonvolatile oligomers obtained by controlled thermal degradation of poly(propylene-ran-ethylene) and poly(propylene-ran-1-butene) were determined by ¹H and ¹³C NMR spectroscopy. The molar ratio of unsaturated to saturated end groups was found to be about 9:1. The average number of unsaturated end groups per molecule was between 1.6 and 1.8, indicating that 60–80 mol% of the oligomer molecules were telechelic, having two terminal unsaturated end groups. These oligomers had a lower polydispersity than the raw material, despite their lower molecular weight and melting temperature. Although the end groups resulting from each monomer unit could be detected by ¹³C NMR, the end group composition differed from that of the main chains of the raw materials. The end group composition was satisfactorily explained by the differences in bond dissociation energy and activation energy of elementary reactions that occurred during thermal degradation, based on the monomer composition of the raw materials.     

The ruthenium-catalyzed reduction and reductive N-alkylation of secondary amides with hydrosilanes: practical synthesis of secondary and tertiary amines by judicious choice of hydrosilanes

A triruthenium cluster, (mu3,eta2,eta3,eta5-acenaphthylene)Ru3(CO)7 (1) catalyzes the reaction of secondary amides with hydrosilanes, yielding a mixture of secondary amines, tertiary amines, and silyl enamines. Production of secondary amines with complete selectivity is achieved by the use of higher concentration of the catalyst (3 mol %) and the use of bifunctional hydrosilanes such as 1,1,3,3-tetramethyldisiloxane. Acidic workup of the reaction mixture affords the corresponding ammonium salts, which can be treated with a base, providing a facile method for isolation of secondary amines with high purity. In contrast, tertiary amines are formed with high selectivity by using lower concentration of the catalyst (1 mol %) and polymeric hydrosiloxanes (PMHS) as reducing agent. Reduction with PMHS encapsulates the ruthenium catalyst and organic byproducts to the insoluble silicone resin. The two reaction manifolds are applicable to various secondary amides and are practical in that the procedures provide the desired secondary or tertiary amine as a single product. The product contaminated with only minimal amounts of ruthenium and silicon residues. On the basis of the products and observed side products as well as NMR studies a mechanistic scenario for the reaction is also described.     

Binary clusters AuPt and Au6Pt: structure and reactivity within density functional theory

Within density functional theory with the general gradient approximation for the exchange and correlation, the bimetallic clusters AuPt and Au(6)Pt have been studied for their structure and reactivity. The bond strength of AuPt lies between those of Au(2) and Pt(2), and it is closer to that of Au(2). The Pt atom is the reactive center in both AuPt and AuPt(+) according to electronic structure analysis. AuPt(+) is more stable than AuPt. Au(6)Pt prefers electronic states with low multiplicity. The most stable conformation of Au(6)Pt is a singlet and has quasi-planar hexagonal frame with Pt lying at the hexagonal center. The doping of Pt in Au cluster enhances the chemical regioselectivity of the Au cluster. The Pt atom essentially serves as electron donor and the Au atoms bonded to the Pt atom acts as electron acceptor in Au(6)Pt. The lowest triplet of edge-capped rhombus Au(6)Pt clusters is readily accessible with very small singlet-triplet energy gap (0.32 eV). O(2) prefers to adsorb on Au and CO prefers to adsorb on Pt. O(2) and CO have stronger adsorption on AuPt than they do on Au(6)Pt. CO has a much stronger adsorption on AuPt bimetallic cluster than O(2) does. The adsorption of CO on Pt modifies the geometry of AuPt bimetallic clusters.     

Selective chemical vapor deposition synthesis of double-wall carbon nanotubes on mesoporous silica

Double-wall carbon nanotubes (DWNTs) have been selectively synthesized over Fe/Co loaded mesoporous silica by catalytic chemical vapor deposition of alcohol. Several silica materials with desired pore diameter and morphology have been investigated for the DWNT growth. The diameter distribution and selectivity of the DWNT are found to depend on the reaction temperature, pore size, and thermal stability of the support material. A high-yield synthesis of DWNTs has been achieved at 900 degrees C over high-temperature stable mesoporous silica. The outer diameter of DWNTs is found to be in the range of 1.5-5.4 nm with a "d" spacing of 0.38 +/- 0.02 nm between inner and outer layers, which is much larger than those of multiwall carbon nanotubes.     

Structures of a CO adlayer on a Pt(100) electrode in HClO4 solution studied by in situ STM

We have obtained the first in situ STM atomic images of a CO adlayer on a Pt(100)-(1 x 1) electrode in 0.1 M HClO(4) solution, exhibiting a phase transition from c(6 x 2)-10CO to c(4 x 2)-6CO at E > 0.3 V vs. RHE.     

A peptide motif recognizing a polymer stereoregularity

A combinatorial phage display method was applied to films composed of a stereoregular polymer of methacrylates. The phage clones with selective affinity for isotactic (it) poly(methyl methacrylate) (PMMA) were isolated. Greater amounts of the phage clones bound to it-PMMA, compared to other stereoregular PMMAs. The phage expressing ELWRPTR most strongly bound to the polymer, and the selectivity was also the best. The peptide motif essential for the specific interaction with the stereoregular polymer was revealed.