Core Assembly Mechanism of Quinocarcin/SF-1739: Bimodular Complex Nonribosomal Peptide Synthetases for Sequential Mannich-type Reactions

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On the completeness and the decidability of strictly monadic second-order logic

Regarding strictly monadic second-order logic (SMSOL), which is the fragment of monadic second-order logic in which all predicate constants are unary and there are no function symbols, we show that a standard deductive system with full comprehension is sound and complete with respect to standard semantics. This result is achieved by showing that in the case of SMSOL, the truth value of any formula in a faithful identity-standard Henkin structure is preserved when the structure is “standardized”; that is, the predicate domain is expanded into the set of all unary relations. In addition, we obtain a simpler proof of the decidability of SMSOL.     

Absolute Asymmetric Synthesis of an Aspartic Acid Derivative from Prochiral Maleic Acid and Pyridine under Achiral Conditions

The asymmetric synthesis of an aspartic acid derivative, N‐succinopyridine, from prochiral starting materials involving dynamic enantioselective crystallization was accomplished without using any external chiral source. The aza‐Michael addition reaction of prochiral maleic acid and pyridine afforded racemic conglomerate N‐succinopyridine in water. Continuous stirring of the suspension of the reaction mixture with acetic acid promoted gradual deracemization to afford a crystal with an excellent optical purity of 99 % in 71 % yield.     

Raman amplification characteristics of As2Se3 photonic crystal fibers

We present the dispersion and Raman amplification characteristics of As2Se3 photonic crystal fibers (PCFs). We compare the gain characteristics with conventional As2Se3 fibers and find that the Raman gain efficiency in PCFs can be improved by a factor of more than 4. This allows us to either use a small length of the fiber or to use the low pump power to attain similar gain characteristics. Numerical simulations reveal that a peak gain of 10 dB can be achieved in a 1.1 m long PCF when it is pumped at 1.5 microm in wavelength with an input power of 500 mW.     

Identification of a Conformational Equilibrium That Determines the Efficacy and Functional Selectivity of the μ‐Opioid Receptor

G‐protein‐coupled receptor (GPCR) ligands impart differing degrees of signaling in the G‐protein and arrestin pathways, in phenomena called “biased signaling”. However, the mechanism underlying the biased signaling of GPCRs is still unclear, although crystal structures of GPCRs bound to the G protein or arrestin are available. In this study, we observed the NMR signals from methionine residues of the μ‐opioid receptor (μOR) in the balanced‐ and biased‐ligand‐bound states. We found that the intracellular cavity of μOR exists in an equilibrium between closed and multiple open conformations with coupled conformational changes on the transmembrane helices 3, 5, 6, and 7, and that the population of each open conformation determines the G‐protein‐ and arrestin‐mediated signaling levels in each ligand‐bound state. These findings provide insight into the biased signaling of GPCRs and will be helpful for development of analgesics that stimulate μOR with reduced tolerance and dependence.     

Metalation-induced denitrogenative reductive coupling of isocyanides on a silylene-bridged nickel cluster

The denitrogenative reductive coupling of two molecules of CN^tBu to afford a disilylketenimine with an aza-disilacyclobutane skeleton was achieved on a multinuclear silylene-bridged Ni cluster framework in the absence of any strong reducing reagents. During this reaction, sequential cleavage of a C N bond and formation of a C C bond involving two molecules of CN^tBu were achieved on a nickel cluster surrounded by four silylene moieties. First, the cleavage of the C N bond of one molecule of CN^tBu provided a silylene-supported carbide and an N^tBu moiety on the dinuclear nickel skeleton. Further metalation induced coupling between the carbide moiety and an additional molecule of CN^tBu on the pentanuclear nickel-cluster framework to form a moiety via formation of a C C bond. Thermolysis of this pentanuclear cluster produced a disilylketenimine with an aza-disilacyclobutane skeleton in 58% yield.

The denitrogenative reductive coupling of two molecules of CN^tBu was achieved on a multinuclear silylene-bridged Ni cluster framework, and two possible intermediary Ni clusters were isolated.