Atsuo Kuki

A simple method for the synthesis of cyclic α-amino acids

Abstract The benzylidene derivative of glycine ethyl ester was alkylated with various electrophiles to synthesize cyclic α- amino acids bearing aromatic and aliphatic side chains.

Friedel-Crafts Approach to Electron Deficient Cyclic α- Amino Acids

An electron deficient 2,2-dimethyl-1-H-phenalene-1,3-dione based cyclic α-amino acid was synthesized in 7 steps using Friedel-Crafts acylation as the key step. A new recipe was found to deprotect the required phthalimide protecting group in highly hindered substrates.

Improved methods for path integral Monte Carlo integration in fermionic systems

We generalize the discretized Feynman path integral expansion by replacing the path through pure states with a path through idempotent density matrices. The transformed expression converges to the ordinary path integral, but is computationally more flexible than the ordinary form. By introducing a particular choice of these idempotent density matrices, based on rotational averaging around the two‐particle center of mass, we greatly reduce the sign problem for systems of two fermions in three dimensions. In the ordinary path integral Monte Carlo approach, low temperature simulation of fermions is inefficient as the integral decays exponentially faster than the integrand (and its variance) as the temperature decreases. The new rotationally averaged algorithm dramatically retards this relative decay. Fermionic simulations of the model system of Kestner and Sinanoglu, and of the harmonic oscillator, demonstrate this improvement, as integrals calculated at temperatures much lower than the singlet–triplet split...

Photoinduced electron transfer and long-lived charge separation in rigid peptide architectures

Two novel architectures, a cyclic dipeptide and a helical nonapeptide rich in α-aminoisobutyric acid (Aib), provide the rigid structural framework for the study of intramolecular, photoinduced electron transfer between two custom-designed redox α-amino acids (donor and acceptor).

Synthesis of a novel constrained α-amino acid with quinoxaline side chain: 7-amino-6,7-dihydro-8H-cyclopenta[g]quinoxaline-7-carboxylic acid

A novel constrained 7-amino-6,7-dihydro-8H-cyclopenta[g]quinoxaline-7-carboxylic acid derivative was prepared starting from 4,5-dimethyl-o-phenylenediamine.

Synthesis and reactions of 3,4-dihydro-2H-1,4-benzoxazine derivatives

Several 3,4-dihydro-2H-1,4-benzoxazine derivatives were prepared from commercially available benzoxazoles by use of an efficient two step sequence. Aryl functionalization reactions allowing access to further benzoxazine derivatives are also described

Modelling ab initio non-bonded interactions for sigma bond, pi bond, and lone pair orbitals

Abstract Ab initio eigenvalue splittings between symmetric and anti-symmetric combinations of energetically degenerate and environmentally equivalent molecular orbitals (MOs) are presented for pairs of ethane molecules and pairs of formaldehyde molecules in various geometrical configurations and as a function of separation. These weak non-bonded orbital interactions are computed for the MO of CC sigma bond character in ethane, and for MOs of CO pi bond character and those of axial and perpendicular oxygen lone pair character in formaldehyde. The relationship between simple orbital overlaps and the Hartree—Fock splittings in this beyond-van-der-Waals distance range is examined using overlaps based on valence bond wavefunctions constructed from single zeta Slater type orbitals. The role of the hydrogen atoms interposed in the region between the interacting MOs is examined. The suitability of the computed interactions as calibrations of effective transfer integrals needed in macromolecular electronic analyses is discussed.

A new synthetic approach to unusually electron rich α-amino acids

An electron rich dihydrobenzoxazine based α-amino acid has been synthesized using the Schollkopf chiral auxiliary giving a new adaptation of the standard Cα–Cβ bond formation strategy, as required by the electron rich nature of the side chain.

Long‐Range Electron Transfer in Rigid 310‐Helical Oligopeptides Containing Redox Cyclic a‐Amino Acids

Intrahelical photoinduced electron transfer processes (ET) in conformationally restricted oligopeptides have been studied by nanosecond time‐resolved transient spectroscopy. The helical peptides were constructed from ste‐rically hindered a‐aminoisobutyric acid (Aib) and two cyclic a‐amino acids (Aib class) bearing electron acceptor and donor side chains (DkNap, ThQx). This helical backbone design provides high conformation stability, as previously demonstrated, and yields reliable 310‐helical architectures in solution. The forward ET between ThQx and 3DkNap is followed by a slow back ET thus giving rise to an accumulation of the charge‐separated ion pairs for hundreds of nanoseconds. We demonstrate the modulation of electronic interactions by the number of intervening Aib residues separating acceptor‐donor side chains and propose modifications of the peptide framework by inclusion of a non‐Aib amino acid residue. These well‐defined and sterically stable frameworks are suited for the precise evaluation of intrahelical electron transfer processes mediated by peptides.