Genome Mining of Oxidation Modules in trans‐Acyltransferase Polyketide Synthases Reveals a Culturable Source for Lobatamides

Bacterial trans‐acyltransferase polyketide synthases (trans‐AT PKSs) are multimodular megaenzymes that biosynthesize many bioactive natural products. They contain a remarkable range of domains and module types that introduce different substituents into growing polyketide chains. As one such modification, we recently reported Baeyer–Villiger‐type oxygen insertion into nascent polyketide backbones, thereby generating malonyl thioester intermediates. In this work, genome mining focusing on architecturally diverse oxidation modules in trans‐AT PKSs led us to the culturable plant symbiont Gynuella sunshinyii, which harbors two distinct modules in one orphan PKS. The PKS product was revealed to be lobatamide A, a potent cytotoxin previously only known from a marine tunicate. Biochemical studies show that one module generates glycolyl thioester intermediates, while the other is proposed to be involved in oxime formation. The data suggest varied roles of oxygenation modules in the biosynthesis of polyketide scaffolds and support the importance of trans‐AT PKSs in the specialized metabolism of symbiotic bacteria.     

Precise pariser-parr-pople molecular orbital calculations using new-γ. A novel guiding principle for the design of functional materials

For precise Pariser-Parr-Pople molecular orbital (PPP MO) calculations, the values of the spectrochemical softness parameter k of a new two-center electron repulsion integral new-γ were evaluated based on an appropriate partial structure of polycyclic aromatic hydrocarbons (PAHs). The spectroactive aromatic sextet resonance system (ASRS) was defined as a spectroactive partial structure of a molecule. The calculated excitation energies of the p-band of PAHs accurately reproduced the observed ones.     

Thermodynamically Induced Conformational Changes of the Cyanobacterial Circadian Clock Protein KaiB

Site-directed spin labeling electron spin resonance (ESR) was applied to investigate the local environment of the cyanobacterial circadian clock protein KaiB. We prepared five cysteine residue-substituted mutants of KaiB labeled with maleimide spin label (MSL). By comparing the ESR spectra of KaiBs carrying MSL at different positions (Thr64, Lys67, Tyr94, Gly98, and Ala101), local conformational changes were identified. The ESR spectra of MSL-T64C and MSL-K67C showed the relatively slow motion of MSL characterized by τ?=?79 and 59?ns at 4°C, respectively. The spectra of MSL-Y94C, MSL-G98C and MSL-A101C showed relatively fast motion characterized by τ?=?8.0, 4.1 and 3.1?ns at 4°C, respectively. These differences were explained by the local environments of the position in KaiB. On incubation at 40°C for 24?h, all ESR spectra of the labeled KaiBs changed, which can be explained by the structural relaxation of KaiB.     

Depth-adaptive regularized reconstruction for reflection diffuse optical tomography

We study reflection diffuse optical tomography using two-dimensional (2D) continuous-wave source-detector arrays on the surface of semi-infinite medium, aiming at imaging the perfusion and the hemoglobin oxygen saturation variation of human cerebral cortex with brain activation. We had previously formulated the inverse problem with Moore-Penrose inversion. When we use simple regularization in this inverse problem, the reconstruction sensitivity decreases markedly with the depth so that the signal in the deep range may be masked by an unwanted signal in the shallow range. In this paper, we propose a depth-adaptive regularized reconstruction, in which we assign a smaller regularization parameter with the depth. We demonstrate improvement of the three-dimensional (3D) reconstruction uniformity using the proposed scheme.     

Analysis of reaction products of cocaine and hydrogen peroxide by high-performance liquid chromatography/mass spectrometry

The change of chemical structure of cocaine in the presence of hydrogen peroxide, a main component of hair dye and decolorant treatments, was studied. High-performance liquid chromatography/mass spectrometry (LC/MS) was used for the separation and identification of cocaine derivatives. After a mixture of cocaine and hydrogen peroxide solutions was incubated at 39 degrees C (this temperature is commonly used when the hair is treated with hair dye or decolorant) for 24 h, six reaction products were detected by LC/MS. Two of them were ecgonine methyl ester and benzoylecgonine, which are metabolites of cocaine. The other reaction products were assumed to be ortho-, meta- and para-hydroxycocaines and dihydroxycocaine, in each of which the benzene ring was hydroxylated by the reaction. These five reaction products (except for dihydroxycocaine) were found immediately after mixing cocaine and hydrogen peroxide. Therefore, the above reaction products might be present in the hair of cocaine users that had treated their hair with hair dye or decolorant.     

Polyaddition reaction of pseudoxazolones with dimercaptans

Polymers having thioether, thiolester, and amide linkages in each repeating unit of a polymer main chain were prepared by the polyaddition reaction of pseudoxazolones (2-isopropylidene-4-alkyl-3-oxazolin-5-ones) and dimercaptans. The polymers had inherent viscosities in a range of 0.08–0.22 and gave transparent films by solution casting.     

Ground-state α-decay of N = 128 isotones 216Ra, 217Ac and 218Th

The α-decay properties of very short-lived N = 128 isotones, ²¹⁶Ra, ²¹⁷Ac and ²¹⁸Th, were investigated by the pulsed-beam method. Alpha emitters of interest were produced in the bombardment of ²⁰⁸Pb or ²⁰⁹Bi with 65–96 MeV ¹²C or ¹⁴N ions and α-decays were measured between natural beam bursts of the cyclotron. The results obtained are _Eα = 9.349±0.008 MeVand $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 182±10}\text{ns for}{}^{216}\text{Ra}\text{, 9.650±0.010}\text{MeV}$ and $\text{111±7}\text{ns for}{}^{217}\text{Ac}\text{, 9.665±0.010}\text{MeV}$ and $\text{96±7}\text{ns for}{}^{218}\text{Th}$. The experimental reduced α-widths of N = 128 isotones from ²¹²Po to ²¹⁸Th are shown to agree well with the simple shell model calculation.     

Chiral phosphinooxazolidine ligands for palladium- and platinum-catalyzed asymmetric Diels-Alder reactions

Cationic palladium (Pd)- and platinum (Pt)-phosphinooxazolidine catalysts 13a-c, 15a-d, 17a-c, and 19a-c were prepared from phosphinooxazolidine ligands 1-3, MCl(2) (M = Pd and Pt), and counterions, and the activities of the catalysts in the asymmetric Diels-Alder (DA) reactions of cyclic or acyclic dienes with imide dienophiles were investigated. These catalysts demonstrated high levels of catalytic activity. The cationic Pd-POZ complex 13c provided particularly excellent enantioselectivity (98% ee) in the DA reactions of cyclopentadiene with acryloyl-, crotonyl-, and fumaroyl-1,3-oxazolidin-2-ones (20a-c).