Formal total synthesis of (−)-hamigeran B from a chemo-enzymatically prepared building block with quaternary chiral center

A formal total synthesis of (?)-hamigeran B was achieved in 17 steps from commercially available ethyl 2-oxocyclopentanecarboxylate. Carbonyl reductase-catalyzed asymmetric reduction and the subsequent chemical transformations furnished an enantiomerically pure synthetic intermediate, (R)-5-formyl-2-isopropyl-5-methylcyclopent-1-en-1-yl trifluoromethylsulfonate. Suzuki-Miyaura coupling with Gao's arylboronate [2-(2-formyl-3-methoxy-5-methylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane], under PdCl₂(dppf)?CH₂Cl₂ catalysis, and the subsequent cyclization by way of intramolecular reductive SmI₂-mediated 1,2-diol formation provided a tricyclic skeleton with a tetrasubstituted double bond between C-1 and C-9b. Upon hydrogenation of this double bond, the proper stereochemistry of the remaining chiral centers was established. Exclusive addition of the hydrogen atom from the β-face occurred, owing to the shielding of the α-face with a bulky TBS protective group on the C-4 alcohol. The hydrogenation products were transformed into Clive's synthetic precursor for (?)-hamigeran B.     

1,3-Bis(pyren-1-yliminomethyl)calix[4]arene as a selective fluorescent turn-on sensor for mercury(II) ion

A novel calixarene-based diimine, 1,3-bis(pyren-1-yliminomethyl)calix[4]arene (5), serves as a turn-on-type fluorescent sensor, which selectively detects Hg²⁺ in THF/H₂O (99:1, v/v) in the presence of various other metal ions. Such selectivity is not seen with half salen 1 derived from salicylaldehyde and 1-aminopyrene. ¹H NMR analysis reveals that it is a chemodosimetric sensor based on its hydrolysis mediated by Hg²⁺ to release 1-aminopyrene molecules as fluorescent chromophores.     

Novel and stereocontrolled synthesis of (+/-)-tetrodotoxin from myo-inositol

[reactions: see text] The novel and stereocontrolled synthesis of (+/-)-tetrodotoxin from myo-inositol is described. The key steps involve the stepwise oxidation of hydroxyl groups to the carbonyl function, followed by the addition of specific nucleophiles, including the successive spiro alpha-chloroepoxide formation and its ring-opening with the azide anion, to give the desired branched chain structures (5-->6, 17-->18-->19-->20 and 23-->24-->25) with the desired regio- and stereoselectivities in high yields. The stepwise conversion of the alpha-azido aldehyde 25 to the delta-lactone 29, followed by reduction of the azide, introduction of a guanidine moiety, aldehyde formation, and deprotection, produced the (+/-)-tetrodotoxin.     

Optimal control of ultrafast selection

Optimal laser control for ultrafast selection of closely lying excited states whose energy separation is smaller than the laser bandwidth is reported on the two-photon transition of atomic cesium; Cs(6S-->7D(J), J=5/2 and 3/2). Selective excitation was carried out by pulse shaping of ultrashort laser pulses which were adaptively modulated in a closed-loop learning system handling eight parameters representing the electric field. Two-color fluorescence from the respective excited states was monitored to measure the selectivity. The fitness used in the learning algorithm was evaluated from the ratio of the fluorescence yields. After fifty generations, a pair of nearly transform-limited pulses were obtained as an optimal pulse shape, proving the effectiveness of the "Ramsey fringes" mechanism. The contrast of the selection ratio was improved by approximately 30% from the simple "Ramsey fringes" experiment.     

An air-stable P-chiral phosphine ligand for highly enantioselective transition-metal-catalyzed reactions

A new P-chiral phosphine ligand, (R,R)-2,3-bis(tert-butylmethylphosphino)quinoxaline, has been prepared by the reaction of enantiomerically pure tert-butylmethylphosphine-borane with 2,3-dichloroquinoxaline. This ligand, in contrast to most of the previously reported P-chiral ligands, is an air-stable solid and exhibits excellent enantioselectivities in both Rh-catalyzed asymmetric hydrogenations and Rh- or Pd-catalyzed carbon-carbon bond-forming reactions.     

Photochromic DNA having fluorescent protein-inspired nucleosides

Molecular switches controlled by light stimuli can be applicable to the variety of the biological application. In this study, skeletal structures of a chromophore of fluorescent protein were applied as aglycones of newly designed photochromic nucleosides, “Fluorescent protein-inspired nuceloside: FIN”. Phosphoramidite units of the photochromic nucleosides having imidazolinone derivatives with benzylidene or 3-pyridilidene groups were successfully synthesized for FIN-containing ODNs. Thermodynamic studies of the FIN-containing ODNs revealed that photo-irradiation with specific wavelength induced stability change of the duplexes.     

Nondestructive real-time radioisotope imaging system for visualizing 14C-labeled chemicals supplied as CO2 in plants using Arabidopsis thaliana

We have developed a real-time radioisotope imaging system (RRIS) that can nondestructively trace ¹⁴C-labeled chemicals in plants. In an experiment, after feeding ¹⁴CO₂ to a plant, the plant was fixed inside a box where lighting was regulated, and beta rays emitted from the ¹⁴C in the plant were intermittently imaged using the developed system. As a first step, using a series of standard sources of ¹⁴C, the data depth and detection limits of the ¹⁴C images captured by the RRIS were evaluated for various integral times. As a result, the linearity between the ¹⁴C activity and signal intensity was determined for the range 10³. Next, the linearity was validated using plant (Arabidopsis thaliana) organs, resulting that the linearity was shown in the case of young leaf, but was not maintained in the thick organs, such as a flower, mature leaf, siliques, and stem. Considering the good correlation between the intensity by RRIS and the PSL value by an imaging plate (IP) as well as the relative low energy of beta rays emitted from ¹⁴C, the thickness of the organs would easily affect the quantitativity of the RRIS as well as an IP. Our findings prove that sequential images of ¹⁴C in a living plant sample in a regulated light and air environment can be nondestructively analyzed using the developed system, whose quantitativity is similar to that of an IP.     

Analysis of waveform from perpendicular magnetic printed media

Edge printing is one of the perpendicular magnetic printing methods for writing servo signals with high speed, high accuracy and low cost. Sub-peaks of waveform from edge printed media are concerned as the sub-peaks can cause errors during the read-back process. In this study, in order to reduce sub-peaks, the influence of printing field, bit length and patterned magnetic layer thickness of master medium on sub-peaks is investigated by using a metal-evaporated (ME) tape as a slave medium. The results show that sub-peak to main peak ratio decreases with stronger printing field, smaller bit length and thicker patterned magnetic layer of master media.     

Catalytic Asymmetric Total Synthesis of Exiguolide

The catalytic asymmetric total synthesis of (−)-exiguolide, a complex 20-membered macrolide embedded with a bis(tetrahydropyran) motif, is reported. The convergent synthesis involves the construction of the C1–C11 tetrahydropyran segment via catalytic asymmetric allylation and Prins cyclization, and the formation of the C12–C21 phosphonate segment via catalytic asymmetric cyclocondensation reaction and Johnson–Claisen rearrangement. The synthesis of 15-epi-exiguolide is also described.