The front cover artwork for Issue 19/2019 is provided by Shoji and co‐workers at Nagoya University (Japan). The image shows the concept of their novel high‐pressure reactor which compresses gaseous ...alkanes by pumping liquid forcibly (the person wearing a T‐shirt) into the reaction vessel without an exit (the trunk), and pressurizes up to 10 MPa. See the Communication itself at https://doi.org/10.1002/cctc.201901323.
“ This system can also be adapted for various applications ” This and more about the story behind the research featured on the front cover can be found in this issue's Cover Profile. Read the full text of the corresponding research at https://doi.org/10.1002/cctc.201901323.
A novel fluorescein-containing polymeric photosensitizer (FS-PHEMA) was successfully synthesized and used as an excellent heterogeneous photocatalyst for aerobic photooxidation of thioethers, ...hydroxylation of aryl boric acids, and oxidative self-coupling of amines. All the reactions could run smoothly upon irradiation of blue LED under aerobic conditions at room temperature. This heterogeneous photosensitizer can be easily separated, recovered, and reused at least 5 times without significant loss of catalytic activity, showing a good potential in practical applications.
The fluorescein-containing polymeric heterogeneous photocatalyst (FS-PHEMA) can catalyze the aerobic photooxidation of thioethers, the aerobic photooxidative hydroxylation of aryl boric acids, and the aerobic photooxidative coupling of amines efficiently by visible light to afford a series of sulfoxides, phenols, and imines in good yields with nice substrate tolerance. The gram-scale synthesis indicates the practical application potential of FS-PHEMA. Moreover, this polymeric photocatalyst can be easily separated and reused for 5 times without significant loss of catalytic activity. Display omitted
The direct hydroxylation of benzene is a green and economical-efficient alternative to the existing cumene process for phenol production. However, the undesired phenol selectivity at high benzene ...conversion hinders its wide application. Here, we develop a one-pot synthesis of protonated g-Csub.3Nsub.4 supporting vanadia catalysts (V-pg-Csub.3Nsub.4) for the efficient and selective hydroxylation of benzene. Characterizations suggest that protonating g-Csub.3Nsub.4 in diluted HCl can boost the generation of amino groups (NH/NHsub.2) without changing the bulk structure. The content of surface amino groups, which determines the dispersion of vanadia, can be easily regulated by the amount of HCl added in the preparation. Increasing the content of surface amino groups benefits the dispersion of vanadia, which eventually leads to improved Hsub.2Osub.2 activation and benzene hydroxylation. The optimal catalyst, V-pg-Csub.3Nsub.4-0.46, achieves 60% benzene conversion and 99.7% phenol selectivity at 60 sup.oC with Hsub.2Osub.2 as the oxidant.
Summary
l‐lysine catabolic routes in plants include the saccharopine pathway to α‐aminoadipate and decarboxylation of lysine to cadaverine. The current review will cover a third l‐lysine metabolic ...pathway having a major role in plant systemic acquired resistance (SAR) to pathogen infection that was recently discovered in Arabidopsis thaliana. In this pathway, the aminotransferase AGD2‐like defense response protein (ALD1) α‐transaminates l‐lysine and generates cyclic dehydropipecolic (DP) intermediates that are subsequently reduced to pipecolic acid (Pip) by the reductase SAR‐deficient 4 (SARD4). l‐pipecolic acid, which occurs ubiquitously in the plant kingdom, is further N‐hydroxylated to the systemic acquired resistance (SAR)‐activating metabolite N‐hydroxypipecolic acid (NHP) by flavin‐dependent monooxygenase1 (FMO1). N‐hydroxypipecolic acid induces the expression of a set of major plant immune genes to enhance defense readiness, amplifies resistance responses, acts synergistically with the defense hormone salicylic acid, promotes the hypersensitive cell death response and primes plants for effective immune mobilization in cases of future pathogen challenge. This pathogen‐inducible NHP biosynthetic pathway is activated at the transcriptional level and involves feedback amplification. Apart from FMO1, some cytochrome P450 monooxygenases involved in secondary metabolism catalyze N‐hydroxylation reactions in plants. In specific taxa, pipecolic acid might also serve as a precursor in the biosynthesis of specialized natural products, leading to C‐hydroxylated and otherwise modified piperidine derivatives, including indolizidine alkaloids. Finally, we show that NHP is glycosylated in Arabidopsis to form a hexose‐conjugate, and then discuss open questions in Pip/NHP‐related research.
Significance Statement
Metabolism of l‐lysine to N‐hydroxypipecolic acid consists of a three‐step biochemical reaction sequence induced upon pathogen inoculation and regulated by feedback amplification. N‐hydroxypipecolic acid induces systemic acquired resistance by enhancing immune‐regulatory gene expression, amplifying resistance responses, synergizing with salicylic acid and priming plants for enhanced defense capacity.
Under conditions of hypoxia, cancer cells with hypoxia inducible factor-1alpha (HIF-1alpha) from heterogeneous tumor cells show greater aggression and progression in an effort to compensate for harsh ...environmental conditions. Extensive study on the stability of HIF-1alpha under conditions of acute hypoxia in cancer progression has been conducted, however, understanding of its involvement during the chronic phase is limited. In this study, we investigated the effect of SIRT1 on HIF1 stability in a typical chronic hypoxic conditon that maintains cells for 24 h under hypoxia using Western blotting, co-IP, measurement of intracellular NAD + and NADH levels, semi-quantitative RT-PCR analysis, invasion assay, gene knockdown. Here we demonstrated that the high concentration of pyruvate in the medium, which can be easily overlooked, has an effect on the stability of HIF-1alpha. We also demonstrated that NADH functions as a signal for conveyance of HIF-1alpha degradation via the SIRT1 and VHL signaling pathway under conditions of chronic hypoxia, which in turn leads to attenuation of hypoxically strengthened invasion and angiogenic activities. A steep increase in the level of NADH occurs during chronic hypoxia, leading to upregulation of acetylation and degradation of HIF-1alpha via inactivation of SIRT1. Of particular interest, p300-mediated acetylation at lysine 709 of HIF-1alpha is recogonized by VHL, which leads to degradation of HIF-1alpha via ubiquitin/proteasome machinary under conditions of chronic hypoxia. In addition, we demonstrated that NADH-elevation-induced acetylation and subsequent degradation of HIF-1alpha was independent of proline hydroxylation. Our findings suggest a critical role of SIRT1 as a metabolic sensor in coordination of hypoxic status via regulation of HIF-1alpha stability. These results also demonstrate the involvement of VHL in degradation of HIF-1alpha through recognition of PHD-mediated hydroxylation in normoxia and p300-mediated HIF-1alpha acetylation in hypoxia.
Because of the electron-rich property of indoles, direct functionalization strategies towards indoles generally involve electrophilic substitutions. In this paper, an efficient protocol for ...nucleophilic hydroxylation, halogenation and esterification of indoles
the aromatic Pummerer process was developed. With the advantages of readily accessible starting materials, simple operation and mild conditions, this protocol should be of interest to synthetic scientists.
Many flavoenzymes catalyze hydroxylation of aromatic compounds especially phenolic compounds have been isolated and characterized. These enzymes can be classified as either single‐component or ...two‐component flavin‐dependent hydroxylases (monooxygenases). The hydroxylation reactions catalyzed by the enzymes in this group are useful for modifying the biological properties of phenolic compounds. This review aims to provide an in‐depth discussion of the current mechanistic understanding of representative flavin‐dependent monooxygenases including 3‐hydroxy‐benzoate 4‐hydroxylase (PHBH, a single‐component hydroxylase), 3‐hydroxyphenylacetate 4‐hydroxylase (HPAH, a two‐component hydroxylase), and other monooxygenases which catalyze reactions in addition to hydroxylation, including 2‐methyl‐3‐hydroxypyridine‐5‐carboxylate oxygenase (MHPCO, a single‐component enzyme that catalyzes aromatic‐ring cleavage), and HadA monooxygenase (a two‐component enzyme that catalyzes additional group elimination reaction). These enzymes have different unique structural features which dictate their reactivity toward various substrates and influence their ability to stabilize flavin intermediates such as C4a‐hydroperoxyflavin. Understanding the key catalytic residues and the active site environments important for governing enzyme reactivity will undoubtedly facilitate future work in enzyme engineering or enzyme redesign for the development of biocatalytic methods for the synthesis of valuable compounds.
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