Hatsuo Yamamura

Sequence recognition and self-sorting of a dipeptide by cucurbit[6]uril and cucurbit[7]uril

Cucurbit[7]uril forms very strong complex with zwitterionic dipeptide Phe-Gly with affinity exceeding 10(7) M(-1) and effectively recognizes peptide sequence of Phe-Gly over Gly-Phe as well as Tyr-Gly over Gly-Tyr and Trp-Gly over Gly-Trp with relative affinities of 23 000, 18 000 and 2000, respectively.

Assay for the (R)- and (S)-enantiomers of salsolinols in biological samples and foods with ion-pair high-performance liquid chromatography using β-cyclodextrin as a chiral mobile phase additive

A chromatographic procedure was devised for the quantitative determination of the enantiomers of salsolinol and N-methylsalsolinol, which are biologically important alkaloids. The enantiomers of salsolinol and N-methylsalsolinol were completely separated using beta-cyclodextrin in a reversed-phase ion-pair system. The HPLC method was sensitive enough to detect the isoquinolines at a concentration less than 0.1 pmol per injection. The presence of (R)- and (S)-salsolinol was confirmed in fermented foods and beverages, while N-methylsalsolinol was not detected. On the other hand, the (R)-enantiomers of both salsolinol and N-methylsalsolinol were found to predominate in the human brain.

Regioselective allylation and alkylation of electron-deficient alkenes with organogallium and organoindium reagents

Abstract Triorganogallium and -indium reagents reacted with α,β-unsaturated nitrile and carbonyl compounds to give 1,4-addition products regioselectively. The reaction of allylgallium and allylindium sesquihalides with α,β-unsaturated carbonyl compounds proceeded in a 1,2-addition mode, whereas a 1,4-addition took place with α,β-unsaturated nitriles.

Physalins N and O from Physalis alkekengi

Abstract The structures of physalins N and O, isolated from Physalis alkekengi var. francheti , were determined as 7α-hydroxyphysalin B and (25 S )-25,27-dihydrophysalin A, respectively.

Allylindation of Cyclopropenes in Organic and Aqueous Media: Switching the Regio- and Stereoselectivity Based on the Chelation with a Hydroxyl Group and the Crystal Structure of the Cyclopropylindium Product

Hydroxy-bearing cyclopropenes react with allylindium reagents to undergo clean allylindation both in organic and aqueous media, in which the chelation of the hydroxyl group to indium plays the central role. The regio- and stereoselectivity have been regulated both by the location of the hydroxyl group in the molecules and the reaction solvents. In particular, the allylindation in water shows marked differences from that in organic solvents; the regio- and stereoselectivity have totally been reversed compared with those in organic solvents. Unusually stable cyclopropyl-indium compounds have been isolated from the reaction of 1-(omega-hydroxyalkyl)cyclopropenes and the structure has fully been established by X-ray crystallography.

New physalins possessing an additional carbon-carbon bond from Physalis alkekengi var. francheti

Abstract Physalins R and S were isolated from Physalis alkekengi var. francheti and their structures were determined by spectroscopic studies as 15α-hydroxy-11β,15β-cyclo-15-deoxophysalin B and 3α,5α-cyclo-6β-hydroxy-2,3,5,6-tetrahydrophysalin B, respectively. The UV-irradiation of physalin B afforded physalin R, and this photo-induced C(11)-C(15) bond formation was shown to be sensitized intramolecularly by the conjugated enone group in the A ring.

Stereodivergent allylindation of cyclopropenes. Remarkable stereodirection and acceleration by neighbouring carboxyl and hydroxyl groups

Abstract Stereodivergent allylindation of cyclopropene derivatives has been realised regio- and stereoselectively. The coupling occurs exclusively at the γ-carbon of allylic indium reagents and the more substituted carbon of the cyclopropene double bond. The carboxyl and hydroxymethyl groups on the cyclopropene C 3 -carbon exert significant effects in cis -direction and acceleration of the allylindation based on the intramolecular chelation, whereas the ester group directs a trans -addition owing to the steric interaction with incoming allylindium reagents.

The Structure of Physalin T from Physalis alkekengi var. francheti

Abstract A new steroidal constituent named physalin T (3) was isolated from the aqueous extract of Physalis alkekengi var. francheti. Based on 1H and 13C NMR spectral studies the structure was assigned as 2,3-dihydrophysalin D, i.e., 5α,6β-dihydroxy-2,3,5,6-tetrahydrophysalin B, which is the first example of a natural physalin possessing a saturated ring A moiety. The structure was confirmed by the chemical transformation from the known physalin D (2) to physalin T.

Synthesis of a ‘head-to-tail’ type cyclodextrin dimer linked by a disulfide bridge

A ‘head-to-tail’ type cyclodextrin dimer, where C-3 of one cyclodextrin and C-6 of the other are linked by a disulfide bond, is synthesized using 2,2′-dipyridyl disulfide, which is widely applicable to the preparation of other dimers.

Diastereoselective reduction of acyclic hydroxyketones and diketones with an indium hydride reagent

Abstract Hydroxyketones and diketones have been reduced with lithium indium hydride to give meso -diols selectively. α-Hydroxyketones and α-diketones are reduced to meso -1,2-diols with high diastereoselectivities, whereas the selectivities of β-hydroxyketones and β-diketones are less satisfactory.