A convergent synthesis of the right-hand fragment of ciguatoxin CTX3C

A convergent synthesis of the right-hand fragment of ciguatoxin CTX3C was investigated. The first and second generation stereocontrolled syntheses of the LM ring fragment were achieved via spiroacetalization as a key step, respectively. The polyether framework of the HIJKLM ring fragment was constructed in a convergent manner by using intramolecular allylation, ring-closing metathesis, and stereoselective hydrogenation to form the 36-methyl substituent as the key transformations.     

Stereoselective synthesis of the C94-C104 fragment of symbiodinolide

Stereoselective synthesis of the C94-C104 fragment of symbiodinolide which is a polyol marine natural product with a molecular weight of 2860 has been accomplished. The synthetic route features Achmatowicz rearrangement and RuO₄-catalyzed dihydroxylation for the construction of the tetrahydropyran moiety and the dithiane addition to the aldehyde for the introduction of the side chain.     

Growth of protein crystals in hydrogels prevents osmotic shock

High-throughput protein X-ray crystallography offers a significant opportunity to facilitate drug discovery. The most reliable approach is to determine the three-dimensional structure of the protein-ligand complex by soaking the ligand in apo crystals. However, protein apo crystals produced by conventional crystallization in a solution are fatally damaged by osmotic shock during soaking. To overcome this difficulty, we present a novel technique for growing protein crystals in a high-concentration hydrogel that is completely gellified and exhibits high strength. This technique allowed us essentially to increase the mechanical stability of the crystals, preventing serious damage to the crystals caused by osmotic shock. Thus, this method may accelerate structure-based drug discoveries.     

First-principles study on superconductivity of the gold–indium alloy under high pressure

The superconductivity of gold–indium alloys has been investigated using first-principles calculations based on the density functional theory. At ambient pressure, the calculated superconducting transition temperature (T _c) is 0.04 μ K in pure gold, but T _c dramatically increases by substituting indium atoms for gold atoms. The gold–indium alloy having 12.5 atomic percent indium (Au_0.875In_0.125) shows T _c of 0.1 K, and Au_0.75In_0.25 marks 1.7 K. The dramatic increase in T _c owing to the alloying effect is caused by the enhancement of the electron–phonon coupling. The superconductivity of gold is predicted to be drastically weakened with increasing pressure and virtually disappear at 10 GPa, but it continues up to at least 30 GPa by the inclusion of indium atoms.     

Total synthesis of mycestericin A and its 14-epimer

The total synthesis of mycestericin A (1) and its 14-epimer 34 is described herein. The Overman rearrangement of an allylic trichloroacetimidate derived from l-tartrate generated a tetra-substituted carbon with nitrogen and subsequent stereoselective transformations afforded the highly functionalized left-half segment, vinyl iodide. Cross-coupling of the vinyl iodide with a chiral organometallic species synthesized from d-tartrate under the Negishi or Suzuki-Miyaura coupling conditions, followed by deprotection, completed the total synthesis of 1. The 14-epimer of mycestericin A was also synthesized, and a comparison of [α]_D values of peracetyl γ-lactone derivatives of mycestericin A and its 14-epimer as well as degradation studies of 1 and 34 fully confirmed the proposed absolute structure of mycestericin A.     

Large time behavior of solutions of Hamilton–Jacobi equations with periodic boundary data

We study the large time behavior of viscosity solutions of Hamilton–Jacobi equations with periodic boundary data on bounded domains. We establish a result on convergence of viscosity solutions to state constraint asymptotic solutions or periodic asymptotic solutions depending on the sign of critical value as time goes to infinity.