Stellatolide H,a cytotoxic peptide lactone from a deep-sea sponge Discodermia sp.

Stellatolide H (1) was isolated from a deep-sea sponge Discodermia sp. as the cytotoxic constituent. The planar structure of 1 was elucidated on the basis of the NMR spectroscopic and mass spectrometric data. The absolute configurations of the constituent amino acid residues were determined by the Marfey’s method. Stellatolide H (1) is a peptide lactone of the callipeltin class with its N-terminus blocked by 3-hydroxy-6,8-dimethyldeca-(4Z,6E)-dienoic acid (Hdda).     

An Efficient Method for the Conjugation of Hydrophilic and Hydrophobic Components by Solid‐Phase‐Assisted Disulfide Ligation

Chemical conjugation between hydrophilic and hydrophobic components is difficult because of their extremely different solubility. Herein, we report a new versatile method with a solid‐phase‐assisted disulfide ligation to overcome the difficulty of conjugation attributed to solubility. The method involves two steps in a one‐pot process: 1) loading of a hydrophobic molecule onto a resin in an organic solvent, and 2) release of the solid‐supported hydrophobic molecule as a conjugate with a hydrophilic molecule into an aqueous solvent. This strategy allows the use of a suitable solvent system for the substrates in each step. Conjugates of a water‐insoluble drug, plinabulin, with hydrophilic carriers that could not be prepared by solution‐phase reactions were obtained in moderate yields (29–45 %). This strategy is widely applicable to the conjugation of compounds with solubility problems.     

Heavily Doped and Highly Conductive Hierarchical Nanoporous Graphene for Electrochemical Hydrogen Production

Heavy chemical doping and high electrical conductivity are two key factors for metal‐free graphene electrocatalysts to realize superior catalytic performance toward hydrogen evolution. However, heavy chemical doping usually leads to the reduction of electrical conductivity because the catalytically active dopants give rise to additional electron scattering and hence increased electrical resistance. A hierarchical nanoporous graphene, which is comprised of heavily chemical doped domains and a highly conductive pure graphene substrate, is reported. The hierarchical nanoporous graphene can host a remarkably high concentration of N and S dopants up to 9.0 at % without sacrificing the excellent electrical conductivity of graphene. The combination of heavy chemical doping and high conductivity results in high catalytic activity toward electrochemical hydrogen production. This study has an important implication in developing multi‐functional electrocatalysts by 3D nanoarchitecture design.     

Total Synthesis of the Nonribosomal Peptide Surugamide B and Identification of a New Offloading Cyclase Family

The cathepsin B inhibitor surugamide B ( 2 ), along with structurally related derivatives (A and C–E), has previously been isolated from the marine actinomycete Streptomyces sp. JAMM992. The biosynthetic genes are unexpectedly part of a cluster of four non‐ribosomal peptide synthetase (NRPS) genes, two of which are responsible for the biosynthesis of the additional linear decapeptide surugamide F. However, the thioesterase domain required for the later stage of the biosynthesis of the cyclic peptides surugamides A–E is not present in any module architecture of the surugamide NRPSs. Herein, we report the first total synthesis of surugamide B ( 2 ) through the macrocyclization at the biomimetic position, which not only alleviated the Cα epimerization in the macrolactamization process, but also efficiently provided 2 in 34 % yield for 18 steps. Furthermore, both the chemical and enzymatic studies with the biosynthetic precursor mimics revealed that the stand‐alone enzyme SurE, which belongs to the penicillin‐binding protein family, is responsible for macrocyclization of the tethered octapeptidyl intermediate.     

Structure of liquid-crystalline phases formed by N-acetyl-L-glutamic acid oligomeric benzyl esters –2H NMR study

A series of N-acetyl-L-glutamic acid oligopeptide benzyl esters with exact residue numbers 4, 6, and 12 has been synthesized by a stepwise procedure. For these oligopeptide–dioxane binary systems, the behavior of the liquid-crystalline phases has been examined␣by the use of ²H NMR, and the results indicate that highly ordered aggregates formed by these oligopeptides in dioxane are in an alignment similar to that in a nematic mesophase. Received: 27 February 2001 Accepted: 8 May 2001     

Reverse aromatic cope rearrangement of 2-allyl-3-alkylideneindolines driven by olefination of 2-allylindolin-3-ones: synthesis of alpha-allyl-3-indole acetate derivatives

The reverse aromatic Cope rearrangement of 2-allyl-3-alkylideneindolines obtained by Horner-Wadsworth-Emmons olefination of 2-allylindolin-3-ones was performed. When 2-allylindolin-3-ones were treated with phosphonium ylides in refluxing toluene, domino Wittig reaction and reverse aromatic Cope rearrangement took place to give alpha-allyl-3-indole acetate derivatives in good yields. The aromatization as a new driving force in the Cope rearrangement is preferable to the conjugation with the carbonyl and cyano groups and also to the alkyl substitution pattern, which are well-known driving forces.     

Phlomisflavosides A and B, new flavonol bisglycosides from Phlomis spinidens

From the aerial parts of Phlomis spinidens, two new flavonol bisglycosides, phlomisflavosides A (1) and B (2), were isolated together with the known compounds, astragalin, isoquercitrin, lamiridoside, phlomoside A, shanzhiside methyl ester, 8-O-acetylshanzhiside methyl ester, phlorigidoside C, rodioloside (=salidroside), forsythoside B, citroside A and lariciresinol-4'-O-beta-D-glucoside. The structures of the new compounds were elucidated based on spectral and chemical evidence.     

Temperature dependent control of the solubility of gallium nitride in supercritical ammonia using mixed mineralizer

Using a mass-loss method, we investigated the solubility change of gallium nitride (GaN) in supercritical ammonia with mixed mineralizers [ammonium chloride (NH₄Cl)?+?ammonium bromide (NH₄Br) and NH₄Cl?+?ammonium iodide (NH₄I)]. The solubilities were measured over the temperature range 450–550 °C, at 100 MPa. The solubility increased with NH₄Cl mole fraction at 450 °C and 100 MPa. The temperature dependence of the solubility curve was then measured at an equal mole ratio of the two mineralizers. The slope of the solubility–temperature relationship in the mixed mineralizer was between those of the individual mineralizers. These results show that the temperature dependence of the solubility of GaN can be controlled by the mineralizer mixture ratio. The results of the van’t Hoff plot suggest that the solubility species were unchanged over the investigated temperature range. Our approach might pave the way to realizing large, high-quality GaN crystals for future gallium-nitride electronic devices, which are increasingly on demand in the information-based age.