CD spectral study of Dnp derivatives of amino acids and peptides for their configurational and conformational analysis.

Rules relating the stereochemistry of N-Dnp (Dnp: 2,4-dinitrophenyl) derivatives of alpha-amino acids and peptides and the sign of the Cotton effects at the longest wavelength band (ca. 400 nm) are surveyed. Some new data and insights concerning the CD spectra of Dnp-alpha-amino acids are included: i.e., the spectra of Dnp derivatives as the composite of the corresponding o-nitrophenyl and p-nitrophenyl derivatives; the crystal structure of Dnp-I-phenylalanine and its solid-state CD spectra; the CD spectra of Dnp-alpha-amino acids containing sulfur atom on their side chains; and the theoretical approach to the CD spectra using molecular orbital method-based calculation. Conformational analyses of cyclic and linear peptides by the CD spectra of their Dnp derivatives are also discussed.

MgATP-induced conformational changes in a single myosin molecule observed by atomic force microscopy: periodicity of substructures in myosin rods.

This paper discusses the conformational changes in a single myosin molecule directly observed using atomic force microscopy (AFM). The myosin molecules were pretreated in rigor solutions without MgATP or in relaxed solutions with various concentrations of MgATP. The images of these molecules were obtained using a tapping mode AFM. The results indicate that the orientation of the myosin's heads and tail strongly depend on the MgATP concentration. Without using MgATP, almost all of the myosin molecules are in the extended form; however, when MgATP is used, the molecules bend according to the level of MgATP concentration. The mean-square end-to-end distance of the myosin molecules is significantly shorter with p[MgATP] = 4 than with p[MgATP] = 6. The rod region did not show the same level of intensity along their length in the extended form. The rods exhibited clusters of discontinuity, which were identified as substructures. The size of these substructures change at intervals that are multiples of 14.3-14.5 nm, which reflects the periodicity of the alpha-helical coiled coils. The substructure clusters also correspond to the myosin crossbridge spacing in muscles (14.3 or 43 nm). These results suggest that the myosin's head bends in conjunction with the bending or tilting in the helical substructures. Conformational changes of the myosin molecule induced by MgATP seem to mimic the molecular motions in a muscle's force generation process.

Radical addition of ethers to imines initiated by dimethylzinc.

Ethers undergo addition to imines in the presence of dimethylzinc and air through a radical process. [reaction: see text]

Hemilabile amidomonophosphine ligand-rhodium(I) complex-catalyzed asymmetric 1,4-addition of arylboronic acids to cycloalkenones.

The asymmetric 1,4-addition reaction of arylboronic acids with cycloalkenones was catalyzed by 1 mol % of an amidomonophosphine-rhodium(I) catalyst in a 10:1 mixture of 1,4-dioxane and water at 100 degrees C, affording 3-arylcycloalkanones in reasonably high enantioselectivity and high yields. It was revealed by NMR, IR, and X-ray spectroscopies that this bidentate amidomonophosphine behaves as a hemilabile ligand that contains a hard donor site in addition to the soft donor in a molecule. Phosphorus atom strongly bonds to rhodium(I), and the amide carbonyl oxygen is coordinatively labile. The reaction efficacy of phenylboronic acid with cyclopent-2-en-1-one was significantly dependent on the possibility of coordination of the amide carbonyl oxygen to rhodium(I).

Solution structure of intracellular signal-transducing peptide derived from human beta(2)-adrenergic receptor.

The structure of intracellular third loop peptide (betaIII-2: RRSSKFCLKEKKALK) was studied by CD and NMR spectroscopy. According to the CD study, this peptide forms a helix in the TFE solution. The three-dimensional molecular structure in TFE was determined by the 2D (1)H NMR spectroscopy. The structure consists of a positive charge cluster on the C-terminal side of the peptide chain. This part will be an active site of the peptide interacting with the G-protein.

Palladium(0)-Catalyzed Isomerization Reactions of Aziridines Bearing an alpha,beta-Unsaturated Ester Group: A Thermodynamic Preference for Chiral Alkyl (2E)-4,5-cis-4,5-Epimino-N-(alkyl- or arylsulfonyl) 2-Enoates over the Other Three Stereoisomers.

Palladium(0)-catalyzed reactions of five sets of four stereoisomeric 4,5-epimino-N-(methanesulfonyl) or -N-(arylsulfonyl) 2-enoates reveal that 4,5-cis-(2E)-isomers are thermodynamically more stable than other isomers, in accord with calculations. A highly stereoselective synthesis of (E)-alkene dipeptide isosteres having the desired stereochemistries from unwanted stereoisomeric 4,5-epimino-N-(arylsulfonyl) 2-enoates is also presented.