Asymmetric Michael addition of malonic diesters to acrylates by phase-transfer catalysis toward the construction of quaternary stereogenic α-carbons

A highly enantioselective construction of an all-carbon quaternary stereogenic center at the α-position of malonic diesters has been achieved by Michael addition using phase-transfer catalysis. The reaction of α-monosubstituted malonates with acrylates in the presence of N-(9-anthracenylmethyl)quininium chloride as a phase-transfer catalyst afforded the corresponding α,α-disubstituted malonic diesters in high chemical yields (up to >95% yield) with high enantioselectivities (up to 95% ee). Furthermore, the product was amenable to chemoselective transformation and could be successfully converted to the corresponding α,α-disubstituted amino acid derivatives through Curtius rearrangement.     

Short-step synthesis and structure-activity relationship of cortistatin A analogs

An improved method for synthesizing structurally simplified analogs of cortistatin A (1), a novel anti-angiogenic steroidal alkaloid from a marine sponge, was developed. In contrast to previous methods, step- and redox-economical synthesis was achieved using a known α-bromoketone as the starting material. The structure-activity relationship study revealed that the isoquinoline portion was strictly recognized by the target molecule. Surprisingly, the introduction of the acetamide moiety on the A-ring structure dramatically enhanced the selective antiproliferative activity against endothelial cells. This new method can be easily applied to gram-scale synthesis and enabled us to prepare various analogs, which were focused on the participation of the side chain and A-ring structure.     

Total synthesis of miraziridine A and identification of its major reaction site for cathepsin B

The synthesis of miraziridine A, a pentapeptide derivative isolated from marine sponge, and its truncated analogs has been achieved. To construct the backbone of miraziridine A, a side-chain-unprotected vinylogous arginine was condensed with an aziridine-containing fragment prepared by a conventional solid-phase procedure. An analog lacking the vinylogous arginine site showed comparable inhibitory activity with miraziridine A, whereas an analog lacking the aziridine site showed remarkably weak inhibitory activity for cathepsin B.     

Synthesis of an insecticidal tetrahydroisocoumarin, (3R,4S,4aR)-4,8-dihydroxy-3-methyl-3,4,4a,5-tetrahydro-1H-2-benzopyran-1-one

The insecticidal tetrahydroisocoumarin, (3R,4S,4aR)-4,8-dihydroxy-3-methyl-3,4,4a,5-tetrahydro-1H-2-benzopyran-1-one, was synthesized as a racemate and as an optically active form using one-pot esterification-Michael addition-aldol reaction of δ-hydroxy-α,β-unsaturated aldehyde and diketene as a key step.     

Role of xanthurenic acid 8-O-beta-D-glucoside,a novel fluorophore that accumulates in the brunescent human eye lens

We have been able to identify a blue fluorophore from the low-molecular weight soluble fraction of human adult nondiabetic brunescent cataract lenses as xanthurenic acid 8-O-beta-D-glucoside (XA8OG) (excitation = 338 nm and emission = 440 nm). To determine the role of this fluorophore in the lens, we have examined its photophysical and photodynamic properties. We found XA8OG to have a fluorescence quantum yield (phi) of 0.22 and a major emission lifetime of 12 ns. We found it to be a UVA-region sensitizer, capable of efficiently generating singlet oxygen species but little of superoxide. We also demonstrated that XA8OG oxidizes proteins when irradiated with UVA light, causing photodynamic covalent chemical damage to proteins. Its accumulation in the aging human lens (and the attendant decrease of its precursor O-beta-D-glucoside of 3-hydroxykynurenine) can, thus, add to the oxidative burden on the system. XA8OG, thus, appears to be an endogenous chromophore in the lens, which can act as a cataractogenic agent.     

Site specificity of metal ions in heterodinuclear complexes derived from an "end-off" compartmental ligand

A phenol-based "end-off" compartmental ligand, 2-[N-[2-(dimethylamino)ethyl]iminomethyl]-6-[N,N-di(2-pyridylmethyl)aminomethyl]-4-methylphenol (HL), having a bidentate arm and a tridentate arm attached to the 2 and 6 positions of the phenolic ring, has afforded the following heterodinuclear M(a)(II)M(b)(II) complexes: [CuM(L)(AcO)(2)]ClO(4) (M = Mn (1), Fe (2), Co (3), Ni (4), Zn (5)), [ZnM(L)(AcO)(2)]ClO(4) (M = Co (6), Ni (7)), and [CuNi(L)(AcO)(NCS)(2)] (8). 1.MeOH (1'), 2.MeOH (2'), 3.MeOH (3'), 4.MeOH (4'), 5.MeOH (5'), and 7.MeOH (7') are isostructural and have a heterodinuclear core bridged by the phenolic oxygen atom of L(-) and two acetate groups. In 1'-5' the Cu(II) is bound to the bidentate arm and has a square-pyramidal geometry with one acetate oxygen at the apical site. The M(II) is bound to the tridentate arm and has a six-coordinate geometry together with two acetate oxygen atoms. In the case of 7' the Zn is bound to the bidentate arm and the Ni is bound to the tridentate arm. 8.2-PrOH (8') has a dinuclear core bridged by the phenolic oxygen atom of L(-) and one acetate group. The Cu bound to the bidentate arm has a square-pyramidal geometry with an isothiocyanate group at the apical site. The Ni bound to the tridentate arm has a six-coordinate geometry with further coordination of an isothiocyanate group. The site specificity of the metal ions is discussed together with the crystal structure of [Cu(4)(L)(2)(AcO)(3)](ClO(4))(3).H(2)O (9) prepared in this work.     

An oxidative carbon-carbon bond formation system in cycloalkane-based thermomorphic multiphase solution

A selective anodic oxidation system in which a carbocation intermediate is generated exclusively by use of a temperature-controlled multiphase solution to separate the different stages of the reaction from each other and from the products is described. The formation of a thermomorphic middle layer in an electrolytic solution composed of c-Hex and LPC/MeNO2 results in enhanced interaction between aliphatic alkenes and polar unstable cation.     

Curve-structured phenalenyl chemistry: synthesis, electronic structure, and bowl-inversion barrier of a phenalenyl-fused corannulene anion

We have demonstrated the features of curve-structured phenalenyl chemistry, for the first time. A phenalenyl-fused corannulene anion has been designed by the annelation of a six-memberd ring across peri-positions of corannulene and generated as a stable species in a degassed solution. The 1H and 13C NMR spectra have shown the highly symmetrical structure and high-field shifts of protons and carbons at the asterisked positions in the chemical structure, indicating the occurrence of large negative charge densities at these positions. These results well agree with the HOMO picture and the electrostatic potential surface, demonstrating the phenalenyl anion-type electronic structure is retained in the curved-surface pi-system. The calculated bowl-inversion barrier of the anion (11.3 kcal/mol) is larger than that of corannulene (9.2 kcal/mol) because of peri-annelation of the corannulene skeleton. The calculations of the barriers of the neutral radical (12.6 kcal/mol), radical dianion (8.1 kcal/mol), and trianion (5.4 kcal/mol) of the phenalenyl-fused corannulene have exhibited a stepwise flattening of the curvature with increase in negative charge. Therefore, we have revealed that the bowl-inversion barrier of the anion is governed by the setoff of the peri-annelation and negative charge effects.