Triphenylphosphine‐Mediated Reduction of Electron‐Deficient Propargyl Ethers to the Allylic Ethers

Semihydrogenation of α,β‐unsaturated ynoates and ‐ynones bearing a γ‐alkoxy group can be performed using triphenylphosphine and water. α,β‐Unsaturated ynoates were reduced to a mixture of cis and trans α,β‐unsaturated enoates, whereas, ynones were reduced to trans α,β‐unsaturated enones as the only products.     

Synthesis,and Helix or Hairpin‐Turn Secondary Structures of ‘Mixed’ α/β‐Peptides Consisting of Residues with Proteinogenic Side Chains and of 2‐Amino‐2‐methylpropanoic Acid (Aib)

Twelve peptides, 1 – 12 , have been synthesized, which consist of alternating sequences of α‐ and β‐amino acid residues carrying either proteinogenic side chains or geminal dimethyl groups (Aib). Two peptides, 13 and 14 , containing 2‐methyl‐3‐aminobutanoic acid residues or a ‘random mix’ of α‐, β²‐, and β³‐amino acid moieties were also prepared. The new compounds were fully characterized by CD (Figs. 1 and 2), and ¹H‐ and ¹³C‐NMR spectroscopy, and high‐resolution mass spectrometry (HR‐MS). In two cases, 3 and 14 , we discovered novel types of turn structures with nine‐ and ten‐membered H‐bonded rings forming the actual turns. In two other cases, 8 and 11 , we found 14/15‐helices, which had been previously disclosed in mixed α/β‐peptides containing unusual β‐amino acids with non‐proteinogenic side chains. The helices are formed by peptides containing the amino acid moiety Aib in every other position, and their backbones are primarily not held together by H‐bonds, but by the intrinsic conformations of the containing amino acid building blocks. The structures offer new possibilities of mimicking peptide–protein and protein–protein interactions (PPI).     

Structural determination and complete NMR spectral assignments of a new diterpenoid obtained from triptonide by biotransformation

A new diterpenoid, 12β,13α‐dihydroxytriptonide, was obtained from the transformed culture of triptonide by Catharanthus roseus cell suspension cultures. The complete ¹H and ¹³C NMR assignments of the compound were carried out by using DEPT, COSY, HSQC, g‐HMBC and NOESY techniques. Copyright © 2003 John Wiley & Sons, Ltd.     

A rare occurrence of a β‐turn in an amyloid βA4 peptide

The fragment β(25–35) of the amyloid β‐peptide, like its parent βA4, has shown neurotrophic and late neurotoxic activities in cultured cells. The 3D structure of this important peptide was examined by ¹H and ¹³C 2D‐NMR and MD simulations in DMSO‐d₆ and water. The NMR parameters of chemical shift, ³J(N,Hα) coupling constants, temperature coefficients of NH chemical shifts and the pattern of intra and inter‐residue NOEs were used to deduce the structures. In DMSO‐d₆, the peptide was found to take up a type I β‐turn around the C‐terminal residues Ile⁸–Gly⁹–Leu¹⁰–Met¹¹, whereas in water at pH 5.5, it adopts a random coil conformation. This is only the second report of a β‐turn in the β‐amyloid class of peptides. The solution structures generated using restrained molecular dynamics were refined by MARDIGRAS to an R factor of 0.33 in the case of DMSO‐d₆ and to 0.56 for water. Copyright © 2002 John Wiley & Sons, Ltd.     

A Mild Isomerization Reaction for β,γ‐Unsaturated Ketone to α,β‐Unsaturated Ketone

A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions.     

Studies on the Mass Spectra of N‐Aryl α,β‐Unsaturated γ‐Lactams

The mass spectra of a series of N‐aryl α,β‐unsaturated γ‐lactams were studied. Besides the molecular ion, the three characteristic fragments such as [M⁺‐29], [M⁺‐55], and [M⁺‐82] were commonly found in a series of N‐Aryl α,β‐unsaturated γ‐lactams in EI/MS. Further more the mechanism for the interpretation of these fragments is also de scribed.     

Billion‐Fold Enhancement in Sensitivity of Nuclear Magnetic Resonance Spectroscopy for Magnesium Ions in Solution

β‐nuclear magnetic resonance (NMR) spectroscopy is highly sensitive compared to conventional NMR spectroscopy, and may be applied for several elements across the periodic table. β‐NMR has previously been successfully applied in the fields of nuclear and solid‐state physics. In this work, β‐NMR is applied, for the first time, to record an NMR spectrum for a species in solution. ³¹Mg β‐NMR spectra are measured for as few as 10⁷ magnesium ions in ionic liquid (EMIM‐Ac) within minutes, as a prototypical test case. Resonances are observed at 3882.9 and 3887.2 kHz in an external field of 0.3 T. The key achievement of the current work is to demonstrate that β‐NMR is applicable for the analysis of species in solution, and thus represents a novel spectroscopic technique for use in general chemistry and potentially in biochemistry.