Isolation and Biosynthesis of an Azoxyalkene Compound Produced by a Multiple Gene Disruptant of Streptomyces rochei

Streptomyces rochei 7434AN4 predominantly produces lankacidin and lankamycin under normal culture conditions, suggesting that other biosynthetic gene clusters for secondary metabolites are silent. To exploit silent metabolites of strain 7434AN4, we constructed mutant KA57, a multiple disruptant of the transcriptional repressor gene srrB together with the biosynthesis genes for both antibiotics. Mutant KA57 accumulated a compound (KA57-A) with a strong UV absorption at 235 nm, which was not detected in the parent strain or other mutants. Various spectroscopic analyses revealed that KA57-A is an azoxyalkene compound of a molecular formula of C10H20N2O3 with the R configuration at C-2. Biosynthesis of KA57-A was also studied by feeding with labeled acetates, amino acids, and 1-hexylamine. The hexenyl moiety (C1’-C6’) was derived from fatty acid, while the 3-amino-butan-1,2-diol moiety (C1-C4) was derived from C-2 of acetate (C1) and serine (C2-C4). Incorporation of [1,1-2H2]1-hexylamine indicated that C1’-C2’ dehydrogenation occurs at the final step of biosynthesis.アクセプト後にアブストラクト等変更あり。This work was supported by a Grants‐in‐Aid for Scientific Research on Innovative Areas from the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), and a Noda Institute for Scientific Research Grant.Supporting information for this articleis available on the WWW under http://dx.doi.org/10.1002/cbic.201500393

Greener Preparation of 5-Ethyl-4a-hydroxyisoalloxazine and Its Use for Catalytic Aerobic Oxygenations

Isoalloxazine ring systems are found in flavin cofactors in nature, and the simulation of their redox catalyses is an important task for developing sustainable catalytic oxidation reactions. Although 5- ethyl-4a-hydroxyisoalloxazines are among the most promising candidates as catalyst for such purposes, the use of them for laboratorial as well as industrial synthetic chemistry has so far been quite limited presumably due to the lack of their preparation methods readily, safely, and inexpensively available. In this communication, we introduce an environmentally benign and practical preparation of 5-ethyl-4a-hydroxy-3,7,8,10-tetramethylisoalloxazine (1EtOH) from 3,7,8,10-tetramethylisoalloxazine (1), in which conventional synthetic requirements, including (i) operations under inert conditions, (ii) risky or expensive chemicals, and (iii) isolation of labile intermediates, have all been dissolved. In addition, we have presented that 1EtOH could be an effective catalyst for Baeyer-Villiger oxidation as well as sulfoxidation with molecular oxygen (O2) as a terminal oxidant under suitable conditions, which is the first report on aerobic oxygenations catalyzed by 5-alkyl-4a-hydroxyisoalloxazines

Observation of finite excess noise in the voltage-biased quantum Hall regime as a precursor for breakdown

We performed noise measurements in a two-dimensional electron gas to investigate the nonequilibrium quantum Hall effect (QHE) state. While excess noise is perfectly suppressed around the zero-biased QHE state reflecting the dissipationless electron transport of the QHE state, considerable finite excess noise is observed in the breakdown regime of the QHE. The noise temperature deduced from the excess noise is found to be of the same order as the energy gap between the highest occupied Landau level and the lowest empty one. Moreover, unexpected finite excess noise is observed at a finite source-drain bias voltagesmaller than the onset voltage of the QHE breakdown, which indicates finite dissipation in the QHE state and may be related to the prebreakdown of the QHE.Comment: 8 pages, 8 figure

Brønsted Acid Catalysed Aerobic Reduction of Olefins by Diimide Generated In Situ from Hydrazine

Aerobic reduction of olefins with hydrazine was proven to be efficiently catalysed by readily available Brønsted acids, such as p-toluenesulfonic acid monohydrate, providing hydrogenated products in very good yields and chemoselectivity under mild conditions