Tadashi Mizutani

Functionalized DMAP catalysts for regioselective acetylation of carbohydrates

Abstract New functionalized DMAPs having carboxylic acid functionality are developed for regioselective acylation of carbohydrates. In these catalysts, DMAP (4-(N,N-dimethylamino)pyridine) is linked with –COOH (–COOMe or –OSO3H in reference catalysts) via methylene spacers of different length at the dimethylamino moiety. Utilizing one of these catalysts, 3-[N-decyl-N-(4-pyridyl)amino]propionic acid ( 1 ), regioselectivity for the primary 6-OH group in acetylation of 1-O-octyl β- d -glucopyranoside is increased from 16% to 89% with rather improved catalytic activity compared with the parent DMAP. Catalyst 1 regioselectively acetylates both anomers of 1-O-octyl glucopyranosides (89% and 88% regioselectivity for β- and α-anomer, respectively) and 1-O-octyl galactopyranosides (100% regioselectivity for both anomers) at position 6 in CHCl3, but gives nearly 1:1 mixtures of 4- and 6-monoacetates in the case of 1-O-octyl mannopyranosides. Control experiments are done to investigate the mechanistic aspects of regiocontrol.

A New Class of Cyclic Hexamer: [Co6L6]24− (H6L=hexaazatriphenylene hexacarboxylic acid)

The construction of nanostructured polynuclear metal complexes with cyclic topologies, particularly those containing multifunctional ligands containing π-electronic structures, is of great interest since they can potentially lead to compounds with unusual electrochemical properties. A novel cyclic module with a hexacarboxylate derivative is described. The results show that the peripheral substituents not only control the electronic structure, but also influence its mode of coordination.

Chiral recognition and chiral sensing using zinc porphyrin dimers

Abstract The chiral zinc porphyrin dimer linked by the ( S )-NMe 2 or ( R )-2,2′-dimethoxy-1,1′-binaphthyl tightly binds diamines via a zinc–nitrogen coordinated ditopic interaction. In particular, the zinc porphyrin displays excellent enantioselectivity towards Lys. The D / L selectivity is determined to be 11–12 for the lysine derivatives. The achiral zinc porphyrin dimers linked by biphenyl unit exhibit a significantly induced CD in the Soret region in the presence of chiral diamines such as lysine amides and cystine diesters, indicating that the chirality of the amino acid derivatives can be monitored upon the complexation with the achiral zinc porphyrin dimer. These results conclude that the zinc porphyrin dimers linked by rigid spacers may be good receptors to discriminate two enantiomers or monitor the absolute configuration of a diamine.

Functionalized cyclodextrins as artificial receptors: guest binding to bisimidazolyl-β-cyclodextrin.zinc

Abstract A systematic investigation of the binding of cyclohexane derivatives to bisimidazolylcyclodextrine zinc was carried out. The basic host-guest interacti and the relative significance of polar and coordination interactions was estimated.

Hydrogen-bonding-based thermochromic phenol–amine complexes

Variable-temperature UV–vis, 13C NMR and IR studies showed that proton-transferred complexes were formed between phenols and amines in apolar solvents at low temperature. Upon cooling a solution of p-nitrophenol and diisopropylamine in toluene, the colour of the solution changed from colourless to yellow. This thermochromism was ascribed to the proton transfer in the hydrogen-bonding complex. Under UV–vis conditions, butylamine and imidazole also caused similar thermochromism upon complexation with p-nitrophenol, while triethylamine, quinuclidine and pyridine did not. The thermochromic behaviour was particularly dependent on the stoichiometry of the amine and the phenol: a solution of 3,3′-dibromo-5,5′-dinitro-2,2′-biphenyldiol and diisopropylamine with a molar ratio of 1:1 showed no thermochromism, while solutions with 1:2 or higher ratios showed thermochromism, indicating that excess amine is required to obtain the proton-transferred species. These results revealed that the proton-transferred species forms in apolar solvents at low temperature if an appropriate hydrogen-bonding network between the phenol and the amine can stabilize it.

Novel approaches to molecular recognition using porphyrins.

Studies of molecular recognition using designed and synthesised molecules provide valuable information on the principle and possible applications of artificial functional molecules. Porphyrin-based receptors have been used to elucidate haem-protein interactions and the basic mechanism of multi-point recognition.

AXIAL CHIRALITY INDUCTION IN FLEXIBLE BIPHENOLS BY HYDROGEN BONDING AND STERIC INTERACTIONS

Abstract Chiral induction in biphenols was studied as a model for intermolecular information transmission. Upon complexation with chiral trans -1,2-cyclohexanediamines (C 6 H 10 (NHR) 2 , R = H, CH 3 , CH 2 CH 2 Bu t ), axial chirality was induced in biphenols in toluene, CHCl 3 and THF. The induced chirality varies as the alkyl groups on the amino groups vary from H, CH 3 to CH 2 CH 2 Bu t . The bulky diamine (R = CH 2 CH 2 Bu t ) induced the opposite chirality to that induced by the less bulky diamine (R = CH 3 , H.

Nature of force field operating in molecular recognition by cyclodextrins. Contribution of nonpolar and polar interactions

Abstract Significance of polar interaction (ΔHpol.) and non-polar interaction (ΔHdisp.) operating in guest cyclodextrin complexes in water is investigated. Force field calculation of α-cyclodextrin·p-nitrophenol complex gives ΔH disp= -13.7 kcal mol and ΔHpol of -0.2 kcal mol . Minor contribution of ΔHp between cyclodextrin and even an ionic guest is confirmed by the observed ΔH° (-4.6 kcal mol ) for Trp-ionic cyclodextrin 1 complexation. ΔHpol between a cyclodextrin bearing cations and anions on C6 carbons and Trp is calculated to be in a range from -2.0 to -5.9 kcal mol , depending on the local dielectric constant.

Linear tetrapyrroles as functional pigments in chemistry and biology

1,19,21,24-tetrahydro-1,19-bilindione is the framework of pigments frequently found in nature, which includes biliverdin IX α, phytochromobilin and phycocyanobilin. 1,19-bilindiones have unique features such as (1) photochemical and thermal cis-trans isomerization, (2) excited energy transfer, (3) chiroptical properties due to the cyclic helical conformation, (4) redox activity, (5) coordination to various metals, and (6) reconstitution to proteins. 1,19-bilindione can adopt a number of conformations since it has exocyclic three double bonds and three single bonds that are rotatable thermally and photochemically. In solution, biliverdin and phycocyanobilin adopt a cyclic helical ZZZ, syn, syn, syn conformation, but other conformations are stabilized depending on the experimental conditions and substituents on the bilin framework. The conformational changes in 1,19-bilindiones are related to the biological functions of a photoreceptor protein, phytochrome. Structural and conformational studies of bilindiones are summarized both in solution and in protein. The conformational changes of bilins can be used for other functions such as a chirality sensor. The bilindiones and the zinc complexes of bilindiones can be employed as a chirality sensor due to the helically chiral structure and the dynamics of racemization of enantiomers. In this paper, we discuss the conformational equilibria and dynamics of bilindiones and its implications in photobiology and materials science.

NEW APPROACH TO THE CONSTRUCTION OF AN ARTIFICIAL HEMOPROTEIN COMPLEX

Abstract Modified prosthetic metalloporphyrin, having a total of eight carboxylate groups at the terminal of two peripheral propionate side chains, was inserted into apomyoglobin to yield a new reconstituted myoglobin. The cluster of substituted carboxylates acts as the binding domain for cationic compounds such as methyl viologen and cytochrome c. Fluorescence spectroscopic analysis indicates that the reconstituted myoglobin formed a stable complex with methyl viologen and photoinduced singlet electron transfer (ET) occurred within the complex; k et =2.1×10 9 s −1 and k cr =3.3×10 8 s −1 . Cytochrome c with a positively charged domain also interacted with the reconstituted myoglobin with an association constant of 6.5×10 4 M −1 . The photoinduced triplet ET from the zinc reconstituted myoglobin to ferricytochrome c occurred through diprotein complex with a rate constant of 2.2×10 3 s −1 . Furthermore, compared to native myoglobin, the ferryl state of the reconstituted myoglobin generated by hydrogen peroxide revealed the peroxidase activity with the acceleration of the oxidation of ferrocytochrome c via complex formation. The present approach could be very useful for constructing practical protein–protein complex systems to elucidate the biological ET via noncovalently linked biomolecules.