<Emphasis Type="Italic">Λ</Emphasis>N scattering length from the reaction <Emphasis Type="Italic">γ</Emphasis>d→K<Superscript>+</Superscript><Emphasis Type="Italic">Λ</Emphasis>n

The prospects of utilizing the strangeness production reaction γd→K ⁺ Λn for the determination of the Λn low-energy scattering parameters are investigated. The spin observables that need to be measured in order to isolate the Λn singlet (¹ S ₀) and triplet (³ S ₁) states are identified. Possible kinematical regions where the extraction of the Λn scattering lengths might be feasible are discussed.     

Improving peptide fragmentation by N-terminal derivatization with high proton affinity

An improved method of de novo peptide sequencing based on mass spectrometry using novel N-terminal derivatization reagents with high proton affinity has been developed. The introduction of a positively charged group into the N-terminal amino group of a peptide is known to enhance the relative intensity of b-ions in product ion spectra, allowing the easy interpretation of the spectra. However, the physicochemical properties of charge derivatization reagents required for efficient fragmentation remain unclear. In this study, we prepared several derivatization reagents with high proton affinity, which are thought to be appropriate for peptide fragmentation under low-energy collision-induced dissociation (CID) conditions, and examined their usefulness in de novo peptide sequencing. Comparison of the effects on fragmentation among three derivatization reagents having a guanidino or an amidino moiety, which differ in proton affinity, clearly indicated that there was an optimal proton affinity for efficient fragmentation of peptides. Among reagents tested in this study, derivatization with 4-amidinobenzoic acid brought about the most effective fragmentation. This derivatization approach will offer a novel de novo peptide sequencing method under low-energy CID conditions.     

Synthesis of new Galβ1→4Fuc segments useful for biological investigations

Useful segments (1, 2) for chemical probes embedded in a Galβ1→4Fuc unit were designed and prepared for characterizing sugar-binding proteins in Caenorhabditis elegans. Segment 1 with an amino group terminus was used as a recognition unit in affinity chromatography. It was revealed that some proteins (annexins and galectins) in C. elegans have an affinity for Galβ1→4Fuc.     

Target-specific chemical acylation of lectins by ligand-tethered DMAP catalysts

Because sugar-binding proteins, so-called lectins, play important roles in many biological phenomena, the lectin-selective labeling should be useful for investigating biological processes involving lectins as well as providing molecular tools for analysis of saccharides and these derivatives. We describe herein a new strategy for lectin-selective labeling based on an acyl transfer reaction directed by ligand-tethered DMAP (4-dimethylaminopyridine). DMAP is an effective acyl transfer catalyst, which can activate an acyl ester for its transfer to a nucleophilic residue. To direct the acyl transfer reaction to a lectin of interest, we attached the DMAP to a saccharide ligand specific for the target lectin. It was clearly demonstrated by biochemical analyses that the target-selective labeling of Congerin II, an animal lectin having selective affinity for Lactose/LacNAc (N-acetyllactosamine), was achieved in the presence of Lac-tethered DMAPs and acyl donors containing probes such as fluorescent molecules or biotin. Conventional peptide mapping experiments using HPLC and tandem mass-mass analysis revealed that the acyl transfer reaction site-specifically occurred at Tyr 51 of Cong II. This strategy was successfully extended to other lectins by changing the ligand part of the ligand-tethered DMAP. We also demonstrated that this labeling method is applicable not only to purified lectin in test tubes, but also to crude mixtures such as E. coli lysates or homogenized animal tissue samples expressing Congerin.     

Rh-catalyzed [5+1] and [4+1] cycloaddition reactions of 1,4-enyne esters with CO: a shortcut to functionalized resorcinols and cyclopentenones

We have developed novel Rh-catalyzed [n+1]-type cycloadditions of 1,4-enyne esters, which involve an acyloxy migration as a key step. The efficient preparation of functionalized resorcinols, including biaryl derivatives, from readily available 1,4-enyne esters and CO was achieved by Rh-catalyzed [5+1] cycloaddition accompanied by 1,2-acyloxy migration. When enyne esters had an internal alkyne moiety, the reaction proceeded by a [4+1]-type cycloaddition involving 1,3-acyloxy migration, leading to cyclopentenones.     

Optical resolution of aromatic alcohols using silica nanoparticles grafted with helicene

Optically active silica nanoparticles, with a 70-nm diameter, grafted with (P)-1,12-dimethyl-8-methoxycarbonylbenzo[c]phenanthrene-5-carboxyamide were synthesized, and their use in the kinetic resolution of aromatic alcohols was examined. Up to 61% ee for (S)-2,2-dimethyl-1-phenyl-1-propanol was obtained by a preferential precipitation of aggregates formed with (P)-nanoparticles.     

A short synthesis of 3-oxa- and 3-azabicyclo[3.1.0]hexanes from α,β-unsaturated esters based on the 1,5-CH insertion reaction of cyclopropylmagnesium carbenoids

1-Chlorocyclopropyl p-tolyl sulfoxides bearing an alkoxymethyl group at the 2-position were easily prepared from α,β-unsaturated esters with dichloromethyl p-tolyl sulfoxide and alkylhalides in three steps in good overall yields. Treatment of the 1-chlorocyclopropyl p-tolyl sulfoxides with i-PrMgCl resulted in the formation of 3-oxabicyclo[3.1.0]hexanes in up to 89% yield as a single diastereomer via the 1,5-CH insertion reaction of the generated cyclopropylmagnesium carbenoid intermediates. This procedure provides a good way for the synthesis of 3-oxabicyclo[3.1.0]hexanes from α,β-unsaturated esters in only four steps. 3-Aza- and 3-thiabicyclo[3.1.0]hexanes were also obtained from the corresponding precursors via the 1,5-CH insertion reaction of the cyclopropylmagnesium carbenoid intermediates, though the yields were low to moderate.