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Motoo Shiro

Publications and source records attributed to Motoo Shiro.

72 records · Page 4Linked to original sources
PubMed2003

Secondary hypervalent I(III)...O interactions: synthesis and structure of hypervalent complexes of diphenyl-lambda3-iodanes with 18-crown-6.

Reported here for the first time are the synthesis and characterization of supramolecular complexes between diaryl-lambda(3)-iodanes and 18-crown-6 (18C6). Slow evaporation of solvents afforded 1:1 and 2:1 complexes between Ph(2)IBF(4) and 18C6 as stable crystals, depending on the conditions. X-ray crystal structures of these complexes indicated that each iodine atom contacts with the three adjacent oxygen atoms of 18C6 through two hypervalent secondary bonding and a weak interaction. (1)H NMR analyses and CSI-MS spectra showed that, in dichloromethane solution, Ph(2)IBF(4) exclusively forms the 1:1 complex with 18C6 (binding constant K(a), 1.02 x 10(3) M(-)(1)). The binding constants decrease with the increased solvent donor ability (Gutmann's DN). Changing the heteroatom ligand from BF(4) to the less nucleophilic PF(6) and AsF(6) increased the binding constant by about six times. Substitution of an electron-withdrawing group onto the para position of Ph(2)IBF(4) tends to increase in the complex stability. A linear Hammett relationship (rho = 0.59) between log K(a) and sigma(p)(+) values of substituents indicates that the diaryl-lambda(3)-iodanes with electropositive iodine(III) interact more efficiently with 18C6. Decreased binding magnitude was measured with 15C5, dibenzo-18C6, dibenzo-21C7, and dibenzo-30C10.

Journal Article↗
PubMed2003

Artificial metallo-DNA: structural control and discrete metal assembly.

To array Cu2+ ions within a double-stranded DNA along the helix axis in a controllable manner, a series of artificial oligonucleotides, d(5'-GHnC-3') (n = 1-5), were synthesized, where H is a hydroxypyridone nucleobase. Right-handed double helices of the oligonucleotides, nCu2+ x d(5'-GHnC-3')2 (n = 1-5), were quantitatively formed through Cu2+-mediated metallo-base pairing (H-Cu2+-H). The Cu2+ ions incorporated into each duplex were aligned along the helix axes with the Cu2+-Cu2+ distance of 3.7 +/- 0.1 A. The unpaired d electrons of the Cu2+ ions were coupled ferromagnetically with one another to form magnetic chains.

DNA↗
PubMed2002

Syntheses and structure-activity relationships of nonnatural beta-C-nucleoside 5'-triphosphates bearing an aromatic nucleobase with phenolic hydroxy groups: inhibitory activities against DNA polymerases.

Five nonnatural beta-C-nucleoside 5'-triphosphates bearing a 3,4-dihydroxyphenyl (1TP), a 2-hydroxyphenyl (2TP), a 3-hydroxyphenyl (3TP), a 4-hydroxyphenyl (4TP), or a phenyl (5TP) group were synthesized, and their structure-activity relationships were examined for a series of DNA polymerase reactions in vitro under typical polymerase chain reaction conditions. We found that the 5'-triphosphates (1TP-5TP) are not incorporated into DNA strands but inhibit the DNA polymerase reactions in the presence of natural nucleoside 5'-triphosphates (dNTPs). 1TP having two phenolic hydroxy groups at the nucleobase moiety showed the most potent inhibitory effect against DNA synthesis by Ex Taq polymerase (IC(50) = 30 microM). The competition assay indicated that 1TP and dNTPs are most likely to affect DNA polymerase reactions competitively. This finding may raise the appealing possibility that artificial nucleoside 5'-triphosphates having phenolic hydroxy groups could exhibit potent inhibitory activity against DNA-directed enzymatic reactions.

DNA-Directed DNA Polymerase↗
PubMed2002

Efficient incorporation of a copper hydroxypyridone base pair in DNA.

Recently, we reported the first artificial nucleoside for alternative DNA base pairing through metal complexation (J. Org. Chem. 1999, 64, 5002-5003). In this regard, we report here the synthesis of a hydroxypyridone-bearing nucleoside and the incorporation of a neutral Cu(2+)-mediated base pair of hydroxypyridone nucleobases (H-Cu-H) in a DNA duplex. When the hydroxypyridone bases are incorporated into the middle of a 15 nucleotide duplex, the duplex displays high thermal stabilization in the presence of equimolar Cu(2+) ions in comparison with a duplex containing an A-T pair in place of the H-H pair. Monitoring temperature dependence of UV-absorption changes verified that a Cu(2+)-mediated base pair is stoichiometrically formed inside the duplex and dissociates upon thermal denaturation at elevated temperature. In addition, EPR and CD studies suggested that the radical site of a Cu(2+) center is formed within the right-handed double-strand structure of the oligonucleotide. The present strategy could be developed for controlled and periodic spacing of neutral metallobase pairs along the helix axis of DNA.

Base Pairing↗
PubMed2002

Metallic conductivity and ferromagnetic interaction of iron(III) d spins in the needle crystals of (ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide)(2).FeBr(4) salt.

The 2:1 charge-transfer (CT) salts (1(2).FeBr(4) and 1(2).GaBr(4)) of ethylenedithiotetrathiafulvalenoquinone-1,3-dithiolemethide (1) with FeBr(4)(-) and GaBr(4)(-) counteranions were obtained as needle crystals, whose structures are almost the same as each other. The 1 molecules form a one dimensionally stacked column with alternation of their molecular axis direction, while the counteranions are aligned in parallel with the 1-stacked columns with the direction of their distorted-tetrahedral geometry maintained. The room-temperature electrical conductivities measured on the single crystals of 1(2).FeBr(4) and 1(2).GaBr(4) were 4.6 and 2.1 S cm(-1), respectively. From the temperature dependences of their electrical conductivities in both cases the electrical conducting properties were metallic between ca. 170 and 300 K, but below ca. 170 K converted to be semiconducting and continued till 5 K, although the activation energies are very small (4-10 meV). For 1(2).FeBr(4) very weak and antiferromagnetic interaction occurred between the d spins of FeBr(4)(-) ions in the temperature range of ca. 1-300 K. However, below ca. 15 K the ferromagnetic interaction was reversely preferential possibly by participation of the pi spin of 1.

Journal Article↗
PubMed2002

Study of pH-dependent zinc(II)-carboxamide interactions by zinc(II)-carboxamide-appended cyclen complexes (cyclen = 1,4,7,10-tetraazacyclododecane).

To elucidate intrinsic recognition of carboxamides by zinc(II) in carbonic anhydrase (CA) (as inhibitors) and carboxypeptidase A (CPA) (as substrates), a new series of Zn(2+)-carboxamide-appended cyclen complexes have been synthesized and characterized (cyclen = 1,4,7,10-tetraazacyclododecane). Two types of Zn(2+)-carboxamide interactions have been found. In the first case represented by a zinc(II) complex of carbamoylmethyl-1,4,7,10-tetraazacyclododecane (L(1)), the amide oxygen binds to zinc(II) at slightly acidic pH (to form ZnL(1)), and the deprotonated amide N(-) binds to zinc(II) at alkaline pH (to form ZnH(-1)L(1)) with pK(a) = 8.59 at 25 degrees C and I = 0.1 (NaNO(3)), as determined by potentiometric pH titrations, infrared spectral changes, and (13)C and (1)H NMR titrations. The X-ray crystal structure of ZnH(-1)L(3) (where L(3) = N-(4-nitrophenyl)carbamoylmethyl cyclen, pK(a) = 7.01 for ZnL(3) <==> ZnH(-1)L(3)) proved that the zinc(II) binds to the amidate N(-) (Zn-N(-) distance of 1.974(3) A) along with the four nitrogen atoms of cyclen (average Zn-N distance 2.136 A). Crystal data: monoclinic, space group P2(1)/n (No. 14) with a = 10.838(1) A, b = 17.210(2) A, c = 12.113(2) A, b = 107.38(1) degrees, V = 2156.2(5) A(3), Z = 4, R = 0.042, and R(w) = 0.038. These model studies provide the first chemical support that carboxamides are CA(-) inhibitors by occupying the active Zn(2+) site both in acidic and alkaline pH to prevent the occurrence of the catalytically active Zn(2+)-OH(-) species. In the second case represented by a zinc(II) complex of 1-(N-acetyl)aminoethylcyclen, ZnL(6), the pendant amide oxygen had little interaction with zinc(II) at acidic pH. At alkaline pH, the monodeprotonation yielded a zinc(II)-bound hydroxide species ZnL(6)(OH(-)) (pK(a) = 7.64) with the amide pendant remaining intact. The ZnL(6)(OH(-)) species showed the same nucleophilic activity as Zn(2+)-cyclen-OH(-). The second case may mimic the Zn(2+)-OH(-) mechanism of CPA, where the nucleophilic Zn(2+)-OH(-) species does not act as a base to deprotonate a proximate amide.

Journal Article↗
PubMed2002

Guanidine is a Zn(2+)-binding ligand at neutral pH in aqueous solution.

We have found the first well-characterized coordination of guanidine with Zn(2+) in a 1:1 complex (ZnL(1)) with cyclen (= 1,4,7,10-tetraazacyclododecane) functionalized with guanidinylethyl group (L(1) = (2-guanidinyl)ethyl-cyclen). The X-ray structure analysis of the 1:1 complex crystallized at pH 7.5 revealed an apical coordination of the pendant guanidinyl group to Zn(2+) ion in ZnL(1). By potentiometrtic pH titration, initial formation of a 1:1 Zn(L(1).H(+)) complex was indicated, where only the cyclen N's bind to Zn(2+) with the complexation constant, log K(s) (K(s) = [Zn(L(1).H(+))]/[Zn(2+)][L(1).H(+)] (M(-1))), being 12.4 +/- 0.1. Facile deprotonation of the guanidinium pendant in the Zn(L(1).H(+)) occurred with a pK(a) value of 5.9 +/- 0.1 at 25 degrees C with I = 0.1 (NaNO(3)) to yield the guanidine-coordinating complex ZnL(1). 4-Nitrophenyl phosphate dianion (NPP(2-)) interacted with ZnL(1) through a new Zn(2+)-phosphate coordination, as indicated by (31)P NMR titration and potentiometric pH titration. An apparent complexation constant for this new species, log K(app)(Zn(L(1).H(+))-NPP), was 4.0 +/- 0.1, which is larger than the log K(app)(ZnL(2)-NPP) value of 3.1 for the 1:1 complex of Zn(2+)-cyclen (ZnL(2)) with NPP at the common pH 5.6. The interaction of ZnL(1) with a phosphate dianion was proven by the X-ray crystal structure analysis of the 1:1 ZnL(1)-PP(2-) complex (PP(2-) is a dianion of phenyl phosphate) obtained from an aqueous solution at pH 6.5. At higher pH, the pendant guanidinium cation is deprotonated to displace the phosphate to yield the Zn(2+)-guanidine bond.

Cations, Divalent↗
PubMed2002

Kinetic study of catalytic CO(2) hydration by water-soluble model compound of carbonic anhydrase and anion inhibition effect on CO(2) hydration.

A kinetic study of CO(2) hydration was carried out using the water-soluble zinc model complex with water-soluble nitrilotris(2-benzimidazolylmethyl-6-sulfonate) L1S, [L1SZn(OH(2))](-), mimicking the active site of carbonic anhydrase, in the presence and absence of anion inhibitors NCS(-) and Cl(-). The obtained rate constants k(cat) for CO(2) hydration were 5.9x10(2), 1. 7x10(3), and 3.1x10(3) M(-1) s(-1) at 5, 10, and 15 degrees C, respectively: the k(cat)=ca. 10(4) M(-1) s(-1) extrapolated towards 25 degrees C has been the largest among the reported k(cat) using zinc model complexes for carbonic anhydrase. It was also revealed that NCS(-), Cl(-) and acetazolamide play a role of inhibitors by the decrease of k(cat): 7x10(2) and 2x10(3) M(-1) s(-1) for NCS(-) and Cl(-) at 15 degrees C, respectively. The sequence of their magnitudes in k(cat) is Cl(-) approximately acetazolamide>NCS(-), where the sequence Cl(-)>NCS(-) is confirmed for native carbonic anhydrase. The difference of k(cat) or k(obs) between NCS(-) and Cl(-) resulted from that between the stability constants K(st)=2x10(3) for [L1SZn(NCS)](2-) and 1x10(2) M(-1) for [L1SZnCl](2-) in D(2)O: for water-insoluble tris(2-benzimidazolylmethyl)amine L1, K(st)=1.8x10(4) for [L1Zn(NCS)](2-) and 1.5x10(3) M(-1) for [L1ZnCl](2-)in CD(3)CN/D(2)O (50% v/v). The crystal structure of anion-binding zinc model complexes [L1Zn(OH(2))](0.5)[L1ZnCl](0.5) (ClO(4))(1.5) 1(0.5)2(0.5)(ClO(4))(1.5) was revealed by X-ray crystallography. The geometry around Zn(2+) in 1 and 2 was tetrahedrally coordinated by three benzimidazolyl nitrogen atoms and one oxygen atom of H(2)O, or Cl(-).

Anions↗
PubMed2002

New supramolecular trigonal prisms from zinc(II)- 1,4,7,10-tetraazacyclododecane (cyclen) complexes and trithiocyanurate in aqueous solution.

The multiple bonding between multinuclear zinc(II)-1,4,7,10-tetraazacyclododecane (cyclen, a 12-membered tetraamine) complexes and multidentate ligands is an effective method for constructing supramolecular complexes having well defined and distinct structures in aqueous solution. Herein we present examples of supramolecular D(3h) prisms formed by self-assembly of linearly dimeric or trimeric zinc(II)-cyclen complexes with a potentially trianionic C(3) subunit trithiocyanuric acid (TCA(3-)), wherein Zn(2+)-S(-) or Zn(2+)-N(-) coordination bonds and hydrogen bonds are responsible for stability of the multicomponent architectures in aqueous solution at neutral pH.

Crystallography, X-Ray↗
PubMed2002

Cephalocyclidin A, a novel pentacyclic alkaloid from Cephalotaxus harringtonia var. nana.

A novel alkaloid with an unprecedented fused-pentacyclic skeleton and six-consecutive asymmetric centers, cephalocyclidin A (1), has been isolated from the fruits of Cephalotaxus harringtonia var. nana, and the structure was elucidated on the basis of spectroscopic data. The relative and absolute stereochemistry of 1 was determined by a combination of NOESY correlations, X-ray crystallographic data, and the exciton chirality method.

Alkaloids↗
PubMed2002

A cuboctahedral supramolecular capsule by 4:4 self-assembly of Tris(Zn(II)-cyclen) and trianionic trithiocyanurate in aqueous solution at neutral pH (cyclen=1,4,7,10-tetraazacyclododecane).

A 1:1 mixture of a tris(Zn(II)-cyclen) (1: [Zn(3)L(1)], L(1)=1,3,5-tris(1,4,7,10-tetraazacyclododecan-1-ylmethyl)benzene) and trithiocyanuric acid (TCA) yielded a 4:4 self-assembly complex [(Zn(3)L(1))(4)-(TCA(3-))(4)] (6) through the formation of Zn(II)-S(-) coordination bonds and hydrogen bonds between 1,3,5-triazine N and cyclen NH (cyclen=1,4,7,10-tetraazacyclododecane); the supramolecular capsule structure was revealed by X-ray crystal structure analysis. The capsule exterior represents a twisted cuboctahedral framework containing a nanoscale truncated tetrahedral cavity. The crystal data: formula C(144)H(308)N(72)O(58)S(12)Zn(12) (6[NO(3)](12) x 22 H(2)O), M(r)=5145.75, cubic, space group F432 (No. 209), a=39.182(1) A, V=60153(3) A (3), Z=8, R=0.100, R(w)=0.259. Lipophilic organic molecules with the matching sizes, for example, ([D(4)]-2,2,3,3)-3-(trimethylsilyl)propionic acid (TSP), 1-adamantanecarboxylic acid, 2,4-dinitrophenol (2,4-DNP), adamantane (ADM), or the tetra-n-propylammonium (TPA) cation, are encapsulated in the inner cavity, as revealed by remarkable upfield shifts of the (1)H NMR signals of these guest molecules. The encapsulation of ADM was confirmed by X-ray crystal structure analysis. Crystal data of the ADM-encapsulating complex: formula C(154)H(334)N(72)O(63)S(12)Zn(12) (6-ADM[NO(3)](12) x 27 H(2)O), M(r)=5372.06, cubic, space group F432 (No. 209), a=39.061(1) A, V=59599(3) A(3), Z=8, R=0.103, R(w)=0.263. The 4:4 self-assembly was stabilized by incorporation of one of these guest molecules. The apparent 4:4 self-assembly constants for 6 in the presence of an excess amount of a guest TPA, log K(app) (K(app)=[6-TPA]/[1](4)[TCA](4)) (M(-7))), were determined to be 34.0+/-2.0 and 35.5+/-3.0 by potentiometric pH and UV spectrophotometric titrations, respectively. An apparent encapsulation constant for 2,4-DNP, log K(enc) (K(enc)=[6-2,4-DNP]/[6][2,4-DNP] (M(-1))), was 6.0+/-0.1 at pH 7.0 (50 mM HEPES with I=0.1 (NaNO(3))), as determined by UV titrations. The lipophilicity of the inner cavity was close to that of 2-propanol, as a quantum yield (phi) of 0.24+/-0.1 for the fluorescent emission of 7-diethylaminocoumarin-1-carboxylic acid (20 microM) in the capsule was close to the phi of 0.22 found for 2-propanol. Encapsulation properties of the present Zn(II)-containing cage have been compared with those of cyclodextrins and Fujita's Pd(II)-containing supramolecular cage. The exterior chirality of the 4:4 complex was controlled from within by an encapsulated chiral guest molecule, 2,10-camphorsultam, as indicated by Cotton effects in the circular dichroism spectra.

Journal Article↗
PubMed2002

Facile palladium(0)-catalyzed ring expansion reactions of hydroxy methoxyallenyl cyclic compounds via hydropalladation.

Palladium(0)-catalyzed one-atom ring expansion of various hydroxy methoxyallenyl compounds has been achieved in excellent yields without the use of aryl halides. Hydroxy methoxyallenylisoindolinones, -indanones, and -phthalans have been readily converted to the corresponding isoquinolones, naphthoquinones, and isochromanones in the presence of P(o-tolyl)(3).

Journal Article↗
PubMed1998

Optically Active Axially Chiral Anilide and Maleimide Derivatives as New Chiral Reagents: Synthesis and Application to Asymmetric Diels-Alder Reaction.

New axially chiral N-acryl-N-allyl-o-tert-butylanilide and N-(o-tert-butylphenyl)-2-methylmaleimide with high optical purity and definite absolute configurations were prepared from o-tert-butylaniline and (S)-O-acetyl lactic acid or (R)-2-methylsuccinic acid, respectively. Iodine- or Lewis acid-mediated asymmetric Diels-Alder reaction of these axially chiral compounds with various dienes proceeded with high endo and diastereofacial selectivity.

Journal Article↗
PubMed1997

Nucleophilic Vinylic Substitutions of (Z)-(beta-Haloalkenyl)phenyliodonium Salts with Sodium Benzenesulfinate: First Evidence of a Michael Addition of Nucleophiles to Alkenyliodonium Salts at the C(beta) Atom.

Evidence for a Michael addition of a nucleophile to alkenyl(phenyl)iodonium salts at the C(beta) atom is reported here for the first time. Nucleophilic vinylic substitutions of (Z)-(beta-chloroalkenyl)- 2b and (Z)-(beta-bromoalkenyl)iodonium tetrafluoroborates 3b with sodium benzenesulfinate in THF afforded stereoselectively (Z)-1,2-bis(benzenesulfonyl)alkene 5b with retention of configuration. Intermediate formation of (Z)-(beta-(benzenesulfonyl)alkenyl)iodonium salt 9b in these reactions was established by (1)H NMR experiments in CDCl(3). The formation of (Z)-9b involves a hitherto unobserved Michael addition of benzenesulfinate anion to the alkenyliodonium salts at the C(beta) atom, followed by halogen extrusion. The formation of a stereoisomeric mixture of (Z)- and (E)-bis-sulfones 5b, and 1-(benzenesulfonyl)cyclopentene 11 that was observed in the reaction of (Z)-(beta-fluoroalkenyl)iodonium salt 4b in CDCl(3), strongly suggests the intermediacy of 9b in this nucleophilic vinylic substitution.

Journal Article↗
PubMed1996

Synthesis of Novel Chiral Diazole Derivative Ligands for the Enantioselective Addition of Diethylzinc to Benzaldehyde.

The high-pressure-promoted reaction of epoxides with pyrazoles and imidazoles provided access to a variety of chiral diazole derivative ligands such as 11-23. Furthermore, chiral pyrazoles 26 and 27, which have a primary alcohol side chain, were also prepared from (+)-camphopyrazole 4. Each of these chiral diazole ligands was used for the catalytic enantioselective addition of diethylzinc to benzaldehyde. The best results were obtained for 16 and 18: 93% ee was achieved in both cases, and reversed asymmetric induction was observed. A plausible mechanism for this efficient asymmetric induction is offered on the basis of X-ray crystallographic data.

Journal Article↗