Efficient Synthesis of Highly Functionalized Cyclic Aminimides

Simple condensation reactions of various α,β-epoxy or α,β-aziridinyl methyl esters with 1,1-dialkyl hydrazines provided cyclic aminimides (1,1-dialkyl-3-oxopyrazolidines) with a heteroatom substituent at the 4-position in good yields. The reaction proceeds smoothly, without any coreagent, providing the product as an easily isolable precipitate. The reaction is expected to be a good candidate for combinatorial synthesis of a highly functionalized five-membered ring scaffold. The scope and limitations of this reaction were investigated by varying the substituents R1−R5

Efficient Synthesis of Highly Functionalized Cyclic Aminimides

Simple condensation reactions of various α,β-epoxy or α,β-aziridinyl methyl esters with 1,1-dialkyl hydrazines provided cyclic aminimides (1,1-dialkyl-3-oxopyrazolidines) with a heteroatom substituent at the 4-position in good yields. The reaction proceeds smoothly, without any coreagent, providing the product as an easily isolable precipitate. The reaction is expected to be a good candidate for combinatorial synthesis of a highly functionalized five-membered ring scaffold. The scope and limitations of this reaction were investigated by varying the substituents R1−R5

Total Synthesis of (−)-Cylindrocyclophane A via a Double Horner-Emmons Macrocyclic Dimerization Event

Total Synthesis of (−)-Cylindrocyclophane A via a Double Horner-Emmons Macrocyclic Dimerization Even

Synthesis of <i>end</i>- and <i>mid</i>-Phthalic Anhydride Functional Polymers by Atom Transfer Radical Polymerization

Polystyrene (PS) and poly(methyl methacrylate) (PMMA) having a single di-tert-butyl phthalate (DTBP) group either at the chain end or in the middle of the chain were synthesized by Cu(I) ion mediated atom transfer radical polymerization (ATRP). The di-tert-butyl phthalate initiators 7 and 8 (for end-functional polymers) and 11 (for mid-functional polymers) were prepared from commercially available di-tert-butyl acetylene dicarboxylate (1) and myrcene (2) in four and six steps, respectively, with high overall yields. The DTBP functionalized polymers could be cleanly converted to the corresponding phthalic anhydride (PA) functional polymers by pyrolysis. The pyrolysis process could be easily monitored using conventional 1H NMR spectroscopy, by observing the significant chemical shift change of the alkyl linker existing in the initiators. Kinetic study of the pyrolysis revealed that the mechanism of the DTBP group pyrolysis to phthalic anhydride (PA) group follows two first-order consecutive reactions having a phthalic diacid (DA) as an observable intermediate. When the PA-functionalized PMMA was subjected to reactive blending at 180 °C with an amine-functionalized PS, the conversion reached a maximum (>90%) in less than 2 min, which is considerably faster than the corresponding reaction of an aliphatic anhydride (e.g., succinic anhydride)-functionalized PMMA. A competition experiment with small molecules showed that phthalic anhydride reacts ∼5 times faster than succinic anhydride with PS−NH2

Donor−Acceptor−Donor-Type Liquid Crystal with a Pyridazine Core

A new liquid crystalline material having an ethylenedioxythiophene−pyridazine−ethylenedioxythiophene (EDOT−PDZ−EDOT) core with two peripheral long alkyl chains was prepared. The designated donor−acceptor−donor (D−A−D)-type core structure induced a distinct smectic liquid crystalline phase due to the strong intermolecular interaction. The photophysical property and the layer structure of the liquid crystal were investigated by differential scanning calorimetry, polarized light microscopy, X-ray diffraction, and cyclic voltammetry

Macrocyclic Lactam Synthesis via a Ring Expansion Reaction: Construction of the Cripowellin Skeleton

The cripowellin ring skeleton, a macrocyclic [2.3.5]-bicyclic ketolactam, was smoothly generated via construction of a spiro(benzazepin-cyclohexane-1,3-dione) employing oxidative cyclization as a key step and a subsequent ring expansion reaction

Photocatalytic Alkyl Addition to Access Quaternary Alkynyl α‑Amino Esters

A regioselective alkylation of β,γ-alkynyl-α-imino esters by visible-light photocatalysis has been developed. This method enables 1,2-addition of methyl, primary, secondary, and tertiary alkyl radicals to the conjugated imines under mild conditions to produce a variety of quaternary alkynyl α-amino acid and cyclic amino acid motifs. Alkyl radicals are generated from alkyl bis­(catecholato)­silicates with an organic photocatalyst. This process is effective under an air atmosphere, providing operational benefits compared to conventional alkylation using organometallic reagents

Donor−Acceptor−Donor-Type Liquid Crystal with a Pyridazine Core

Donor−Acceptor−Donor-Type Liquid Crystal with a Pyridazine Cor

Structural Effect of Cyclic Olefin Cross-Linkers on Long-Wave Infrared-Transmitting Sulfur Polymers

The structural characteristics of the organic cross-linker greatly affect the potential infrared (IR) optics applications of sulfur polymers synthesized through the inverse vulcanization reaction. Unlike elemental sulfur, organic cross-linkers induce various absorptions in the IR region and leave organic moieties that affect the IR transmittance, even after inverse vulcanization. Most of the cyclic olefin cross-linkers [e.g., dicyclopentadiene (DCPD)] investigated so far are expected to produce side reactions and form byproducts during inverse vulcanization. The side reactions caused by differences in reactivity between the reaction sites can result in the deterioration of the optical properties of sulfur polymers. In this study, thiol groups were introduced as a cross-linker to effectively control the side reactions and byproducts that may occur in inverse vulcanization. The sulfur and thiol cross-linkers reacted rapidly and uniformly at all reaction sites to form sulfur polymers without unwanted side reactions. Optical windows prepared with the sulfur polymer exhibited enhanced IR transparency and achieved thermal imaging of the human body in the long-wave IR (LWIR) region. By design of a cross-linker for LWIR transparent sulfur polymers, these results provide a useful solution for IR optics applications

TEMPO-Assisted Free-Radical-Initiated Peptide Sequencing Mass Spectrometry for Ubiquitin Ions: An Insight on the Gas-Phase Conformations

TEMPO ((2,2,6,6-tetramethylpiperidine-1-yl)­oxyl)-assisted free-radical-initiated peptide sequencing mass spectrometry (FRIPS MS) is applied to the top-down tandem mass spectrometry of guanidinated ubiquitin (UB­(Gu)) ions, i.e., p-TEMPO–Bn–Sc–guanidinated ubiquitin (UBT­(Gu)), to shed a light on gas-phase ubiquitin conformations. Thermal activation of UBT­(Gu) ions produced protein backbone fragments of radical character, i.e., a-/x- and c-/z-type fragments. It is in contrast to the collision-induced dissociation (CID) results for UB­(Gu), which dominantly showed the specific charge-remote CID fragments of b-/y-type at the C-terminal side of glutamic acid (E) and aspartic acid (D). The transfer of a radical “through space” was mainly observed for the +5 and +6 UBT­(Gu) ions. This provides the information about folding/unfolding and structural proximity between the positions of the incipient benzyl radical site and fragmented sites. The analysis of FRIPS MS results for the +5 charge state ubiquitin ions shows that the +5 charge state ubiquitin ions bear a conformational resemblance to the native ubiquitin (X-ray crystallography structure), particularly in the central sequence region, whereas some deviations were observed in the unstable second structure region (β2) close to the N-terminus. The ion mobility spectrometry results also corroborate the FRIPS MS results in terms of their conformations (or structures). The experimental results obtained in this study clearly demonstrate a potential of the TEMPO-assisted FRIPS MS as one of the methods for the elucidation of the overall gas-phase protein structures