Mitsuhiko Ikura

Chemical constitution of safflor yellow B. A quinochalcone C-glycoside from the flower petals of Carthamus tinctorius L.

Abstract The chemical constitution of safflor yellow B, a quinochalcone glycoside from the flower petals of Carthamus tinctorius L , has been characterized as 1, mainly on the basis of spectral means.

Sequence‐specific assignments of downfield‐shifted amide proton resonances of calmodulin Use of two‐dimensional NMR analysis of its tryptic fragments

Two‐dimensional NMR methods were applied to assign the extremely downfield‐shifted amide‐proton resonances in the 500‐MHz 1H‐NMR spectra of the NH2‐terminal fragment of residues 1–75 of calmodulin. The low‐field resonances of the 1H‐NMR spectra of intact calmodulin were assigned to specific amino acid residues by comparison with spectra of the tryptic fragments of residues 1–75 and 78–148, in both the Ca2+‐free and Ca2+‐bound states. The hydrogen bonding of glycine residues connecting the two amino acid residues at the Z and − Y positions in the octahedral Ca2+ coordination site was investigated. The Gly 134 in site IV showed a different property from the other glycines, 25, 61 and 98, involved in sites I, II and III, respectively.

Glycinoeclepin A, a natural hatching stimulus for the soybean cyst nematode

A large-scale of isolation of glycinoeclepin A, a natural hatching stimulus for the soybean cyst nematode, and its structure elucidation by spectroscopic and X-ray methods are described.

Structure revision of okamurallene and structure elucidation of further C15 non-terpenoid bromoallenes from Laurencia intricata

Abstract The structures of okamurallene related metabolites, which have previously been isolated from the red alga Laurencia intricata , have been revised. In addition, two new C 15 non-terpenoid bromoallenes with a halohydrin moiety have also been obtained, and their structures determined by chemical and spectroscopic methods.

Glycinoeclepins B and C, nortriterpenes related to glycinoeclepin a

Abstract The structure of two new nortriterpenes, glycinoeclepins B and C, isolated from the aqueous extracts of roots of kidney bean and related structurally to glycinoeclepin A, a natural hatching stimulus for the soybean cyst nematode, has been elucidated to be formulas 2 and 3, respectively.

113Cd-NMR evidence for cooperative interaction between amino- and carboxyl-terminal domains of calmodulin

113Cd-NMR experiments were performed to characterize the nature of Cd2+ binding to calmodulin in the presence of a tetradecapeptide mastoparan or a 26-residue peptide M13 (calmodulin-binding region of skeletal muscle myosin light-chain kinase). The results indicate that binding of these peptides to calmodulin induces a positive cooperativity between Ca2+ binding to C- and N-terminal domains. The results imply that the activation of myosin light-chain kinase caused by the increase in Ca2+ concentration occurs as a result of cooperative interactions not only between two Ca2+ binding sites in each domain but also between the two domains. The interdomain interaction manifests itself only in the presence of such peptides.

Gymnopilins, bitter principles of the big-laughter mushroom Gymnopilus spectabilis

Abstract Planar structures of main bitter principles of Gymnopilus spectabilis have been determined to be 1 , 2 and 3 , mainly on the basis of spectroscopic evidence.

Dictymal, a new Seco-fusicoccin type diterpene from the brown alga dictyota dichotoma

The structure of dictymal, a new seco-fusicoccin type diterpene isolated from the brown alga Dictyota dichotoma, has been determined mainly on the basis of the 2D NMR studies.

Multinuclear n.m.r. studies on sol-gel transition of κ-carrageenan. Selective interaction of group I cations

Abstract Multinuclear n.m.r. experiments were carried out to study a selective interaction between group I cations and κ-carrageenan. It was found that the n.m.r. intensity of gel-forming cations undergoes a rapid change in the vicinity of sol-gel transition temperature. On the other hand, the n.m.r. intensity of a non-gel forming cation which coexists with a gel-forming cation does not show any singular behaviour at the sol-gel transition. These results strongly suggest that gel-forming cations selectively interact with κ-carrageenan.

New steroidal alkaloids having a novel seven ring skeleton from fritillaria ussuriensis maxim

Abstract Two new steroidal alkaloids having a novel seven ring skeleton, ussurienine ( 1 ) and ussurienone ( 2 ), were isolated from the HCI-MeOH hydrolyzed alkaloid fraction of Fritillaria ussuriensis Maxim. (Ping-bei-mu). Continuous study on the same plant, however, showed that 1 and 2 were the artifacts derived from ussuriedine ( 3 ) and ussuriedinone ( 4 ), which were isolated from the free alkaloids fraction. Their structures were elucidated on the basis of spectral data, X-ray crystal analysis and chemical conversion.