WAVELENGTH-DEPENDENT PROPERTIES OF PHOTOTAXIS IN LARVAE OF Bombyx mori

Phototactic responses of newly hatched silkworm larvae to monochromatic lights and their mixtures were measured to determine wavelength-dependent properties. Each fluence rate-response curve for a monochromatic light was composed of a log-linearly increasing part, a plateau and a decreasing part. Curves were classified into two groups according to the slopes of the linear parts: responses to UV-blue light (364-482 nm) and responses to green-red light (513-681 nm). Different plateau values were found for both groups. The action spectrum had its maximum at 557 nm and showed another large value at about 364 nm, and its minimum was at 447 nm. When green-orange lights (540-577 nm) were added to 557 nm, the silkworms were attracted more by the mixed lights than by the 557 nm component light only. Mixed lights of UV (364 nm) and blue (447 nm) attracted the silkworms more than either component. The magnitude of the response decreased remarkably when green light was mixed with U V or blue light. We conclude that the silkworm possesses colour vision and responds differently to green-red lights (≥ 513 nm) from UV-blue lights (≲ 482 nm).     

Convergent synthesis of the ABCDE ring fragment of ciguatoxins

Synthesis of the ABCDE ring fragment of ciguatoxins has been achieved in a highly stereocontrolled and convergent manner via the B-alkyl Suzuki-Miyaura coupling-based approach.     

De novo design, synthesis, and function of semiartificial myoglobin conjugated with coiled-coil two-alpha-helix peptides

The introduction of a flavin chromophore on the myoglobin (Mb) surface and an effective electron-transfer (ET) reaction through the flavin were successfully achieved by utilizing the self-assembly of heterostranded coiled-coil peptides. We have prepared a semiartificial Mb, named Mb-1alphaK, in which an amphiphilic and cationic alpha-helix peptide is conjugated at the heme propionate (Heme-1alphaK). Heme-1alphaK has a covalently bound iron-protoporphyrin IX (heme) at the N terminus of a 1alphaK peptide sequence. This sequence was designed to form a heterostranded coiled-coil in the presence of a counterpart amphiphilic and anionic 1alphaE peptide sequence in a parallel orientation. Two peptides, Fla(1)-1alphaE and Fla(31)-1alphaE, both incorporating a 10-methylisoalloxazine moiety as an artificial flavin molecule, were also prepared (Fla=2-[7-(10-methyl)isoalloxazinyl]-2-oxoethyl). Heme-1alphaK was successfully inserted into apomyoglobin to give Mb-1alphaK. Mb-1alphaK recognized the flavin-modified peptides and a two-alpha-helix structure was formed. In addition, an efficient ET from reduced nicotinamide adenine dinucleotide to the heme center through the flavin unit was observed. The ET rate was faster in the presence of Fla(1)-1alphaE than in the presence of Fla(31)-1alphaE or the equivalent molecule that has no peptide chain. These results demonstrate that the introduction of a functional chromophore on the Mb surface can be achieved by using specific peptide-peptide interactions. Moreover, the dependence of the ET rate on the position of the flavin indicated that the distance between the heme active site and the flavin chromophore was regulated by the three-dimensional structure of the designed polypeptide.     

Generation of alkoxycarbenium ion pools from thioacetals and applications to glycosylation chemistry

[reaction: see text] Alkoxycarbenium ions have been generated and accumulated as "cation pools" by the low-temperature electrochemical oxidation of alpha-phenylthioethers. Although an unsuccessful attempt to accumulate glycosyl cations was made, a one-pot method for electrochemical glycosylation, which involves anodic oxidation of thioglycosides to generate glycosyl cation equivalents followed by their reactions with glycosyl acceptors, has been developed.     

Enantioselective formation of a dynamic hydrogen-bonded assembly based on the chiral memory concept

In this paper, we report the enantioselective formation of a dynamic noncovalent double rosette assembly 1a(3).(CYA)(6) composed of three 2-pyridylcalix[4]arene dimelamines (1a) and six butylcyanuric acid molecules (BuCYA). The six 2-pyridyl functionalities of the assembly interact stereoselectively with chiral dicarboxylic acids 3a-e via two-point hydrogen-bonding interactions. One of the two enantiomeric assemblies (P- or M-) 1a(3).(CYA)(6) is formed in excess as the result of the complexation of the chiral diacids, resulting in formation of optically active assemblies. The complexations with dibenzoly tartaric acids D-3a and L-3a (3 equivalent), respectively, leading to the formation of diastereomeric assemblies (P)-1a(3).(BuCYA)(6).(D-3a)(3) and (M)-1a(3).(BuCYA)(6).(L-3a)(3) with 90% diastereomeric excess. The diastereomeric excess in (M)-1a(3).(BuCYA)(6).(L-3a)(3) is "memorized" when L-3a is removed by precipitation with ethlylenediamine (EDA). The assembly (M)-1a(3).(BuCYA)(6) is still optically active (90% enantiomeric excess), although none of its individual components are chiral. (M)-1a(3).(BuCYA)(6) has a high kinetic stability toward racemization (E(a) = 119 kJ mol(-)(1), half-life of (M)-1a(3).(BuCYA)(6) is ca. 1 week at 20 degrees C).     

Synthesis of the common left-half part of pectenotoxins

The common left-half [C31-C33(OC1-C7)-C40] part of pectenotoxins has been synthesized convergently from the C31-C35, C36-C40, and C1-C7 parts. The C31-C35 part, prepared via a new route shorter than our previous route, was coupled with the C36-C40 part through reductive lithiation and addition reactions to give an adduct stereoselectively, which was converted to a cyclic acetal corresponding to the C31-C40 part. The left-half was synthesized by a three-step process including esterification of the C31-C40 part with the C1-C7 part.     

Cationic carbohydroxylation of alkenes and alkynes using the cation pool method

The reactions of an N-acyliminium ion pool with alkenes and alkynes gave gamma-amino alcohols and beta-amino carbonyl compounds, respectively, after treatment with H(2)O/Et(3)N. The present reaction serves as an efficient method for cationic carbohydroxylation of alkenes and alkynes. When vinyltrimethylsilane was used as an alkene, the reaction was highly diastereoselective and served as an access to an enantiomerically pure alpha-silyl-gamma-amino alcohol. [reaction: see text]     

A novel isomerization on interaction of antitumor-active azole-bridged dinuclear platinum(II) complexes with 9-ethylguanine. Platinum(II) atom migration from N2 to N3 on 1,2,3-triazole

The reactions of the dinuclear platinum(II) complexes, [[cis-Pt(NH(3))(2)](2)(mu-OH)(mu-pz)](NO(3))(2) (1, pz = pyrazolate), [[cis-Pt(NH(3))(2)](2)(mu-OH)(mu-1,2,3-ta-N1,N2)](NO(3))(2) (2, 1,2,3-ta = 1,2,3-triazolate), and a newly prepared [[cis-Pt(NH(3))(2)](2)(mu-OH)(mu-4-phe-1,2,3-ta-N1,N2)](NO(3))(2) (3, 4-phe-1,2,3-ta = 4-phenyl-1,2,3-triazolate), whose crystal structure was determined, with 9-ethylguanine (9EtG) have been monitored in aqueous solution at 310 K by means of (1)H NMR spectroscopy. The dinuclear platinum(II) complexes 1-3 each react with 9EtG in a bifunctional way to form 1:2 complexes, [[cis-Pt(NH(3))(2)(9EtG-N7)](2)(mu-pz)](3+) (4), [[cis-Pt(NH(3))(2)(9EtG-N7)](2)(mu-1,2,3-ta-N1,N3)](3+) (5), and [[cis-Pt(NH(3))(2)(9EtG-N7)](2)(mu-4-phe-1,2,3-ta-N1,N3)](3+) (6). The reactions of 2 and 3 involve a novel isomerization, in which the Pt atom, initially bound to N2 on the 1,2,3-ta, migrates to N3 after the first substitution by N7 of 9EtG. This isomerization reaction has been unambiguously characterized by 1D and 2D NMR spectroscopy and pH titration. The reactions of 2 and 3 with 9EtG show faster kinetics, and the second-order rate constants (k) for the reactions of 1-3are 1.57 x 10(-4), 2.53 x 10(-4), and 2.56 x 10(-4) M(-1) s(-1), respectively. The pK(a) values at the N1H site of 9EtG were determined for 4-6 from the pH titration curves. Cytotoxicity assays of 1-3 were performed in L1210 murine leukemia cell lines, respectively sensitive and resistant to cisplatin. In the parent cell line, 2 and 3 exhibit higher cytotoxicity compared to cisplatin, especially, 2 is 10 times as active as cisplatin. 1 was found to be less cytotoxic than cisplatin, but still in the active range and more active than cisplatin in a cisplatin-resistant cell line.     

Reactivity of hydroperoxide bound to a mononuclear non-heme iron site

The first isolation and spectroscopic characterization of the mononuclear hydroperoxo-iron(III) complex [Fe(H(2)bppa)(OOH)](2+) (2) and the stoichiometric oxidation of substrates by the mononuclear iron-oxo intermediate generated by its decomposition have been described. The purple species 2 obtained from reaction of [Fe(H(2)bppa)(HCOO)](ClO(4))(2) with H(2)O(2) in acetone at -50 degrees C gave characteristic UV-vis (lambda(max) = 568 nm, epsilon = 1200 M(-1) cm(-1)), ESR (g = 7.54, 5.78, and 4.25, S = (5)/(2)), and ESI mass spectra (m/z 288.5 corresponding to the ion, [Fe(bppa)(OOH)](2+)), which revealed that 2 is a high-spin mononuclear iron(III) complex with a hydroperoxide in an end-on fashion. The resonance Raman spectrum of 2 in d(6)-acetone revealed two intense bands at 621 and 830 cm(-1), which shifted to 599 and 813 cm(-1), respectively, when reacted with (18)O-labeled H(2)O(2). Reactions of the isolated (bppa)Fe(III)-OOH (2) with various substrates (single turnover oxidations) exhibited that the iron-oxo intermediate generated by decomposition of 2 is a nucleophilic species formulated as [(H(2)bppa)Fe(III)-O*].