RESUMO
Diverse bioactive alkaloids with a tryptophan 2,5-diketopiperazine (DKP) core and an annulated structure forming a methylated pyrroloindoline-DKP assembly have been isolated from various microbial sources. However, little is known about their biosynthesis. In this study, a novel indole C3 methyltransferase from Streptomyces sp. HPH0547 was discovered and characterized. Structural elucidation of the products revealed that this enzyme catalyzed unique pyrroloindoline cyclization in tryptophan-containing cyclodipeptides. This is the first C3 methyltransferase reported to catalyze pyrroloindoline cyclization in cyclic dipeptides, which provides a feasible and simple method to access diverse alkaloids.
Assuntos
Alcaloides/biossíntese , Proteínas de Bactérias/metabolismo , Dipeptídeos/biossíntese , Metiltransferases/metabolismo , Peptídeos Cíclicos/biossíntese , Streptomyces/enzimologia , Ciclização , Dicetopiperazinas/metabolismo , Modelos Químicos , Especificidade por Substrato , Triptofano/química , Triptofano/metabolismoRESUMO
Most of the pharmaceutical co-crystals are formed between drug molecules and small molecular compounds. Here, we demonstrated that a small molecular drug griseofulvin and poly(ethylene glycol) can also form co-crystals.
Assuntos
Griseofulvina/química , Polietilenoglicóis/química , Cristalização , Estrutura Molecular , Peso MolecularRESUMO
A non-suppressed ion chromatographic method by connecting anion-exchange and cation-exchange columns directly was developed for the separation and determination of five inorganic anions (sulfate, nitrate, chloride, nitrite, and chlorate) and three cations (sodium, ammonium, and potassium) simultaneously in explosive residues. The mobile phase was composed of 3.5mM phthalic acid with 2% acetonitrile and water at flow rate of 0.2 mL/min. Under the optimal conditions, the eight inorganic ions were completely separated and detected simultaneously within 16 min. The limits of detection (S/N=3) of the anions and cations were in the range of 50-100 microg/L and 150-320 microg/L, respectively, the linear correlation coefficients were 0.9941-0.9996, and the R.S.D. of retention time and peak area were 0.10-0.29% and 5.65-8.12%, respectively. The method was applied successfully to the analysis of the explosive samples with satisfactory results.
Assuntos
Ânions/análise , Cátions/análise , Cromatografia por Troca Iônica/métodos , Substâncias Explosivas/análise , Indicadores e ReagentesRESUMO
A readily recycled and regenerated heterogeneous catalyst of 9-thiourea epi-quinine supported on mesoporous silica exhibits enhanced enantioselectivity (up to 99.2%) in the asymmetric Friedel-Crafts reaction of imines with indoles.
Assuntos
Alcaloides de Cinchona/química , Quinina/análogos & derivados , Dióxido de Silício/química , Tioureia/análogos & derivados , Catálise , Iminas/química , Indóis/química , Estereoisomerismo , Tioureia/químicaRESUMO
A series of WO3/SBA-15 materials with different Si/W ratios have been prepared by impregnating the host material SBA-15 with aqueous ammonium paratungstate solutions. After temperature-programmed carburization (TPC) in flowing CH4/H2 (20/80 v/v mixture), the materials are converted to the corresponding W2C/SBA-15 species. Both the oxide and carbide materials are characterized using X-ray diffraction, nitrogen adsorption-desorption, 29Si NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and TEM measurements. The XRD results show that after impregnation with different amounts of tungsten and subsequent carburization, the materials retain the mesopore structure of SBA-15. The nitrogen adsorption-desorption results indicate that a thin layer of W2C covers the internal walls of SBA-15. Quantitative 29Si single-pulse excitation MAS experiments and FTIR spectroscopy show that the incorporation of W2C in the channels of SBA-15 is correlated with the formation of Si-O-W bonds. Some Si-O-W bonds are transformed into Si-O-H bonds after carburization. The TEM results show that the thickness of the W2C thin layer is 1.7-1.9 nm in W2C/SBA-15. A model involving a discrete W2C thin layer in the channels of SBA-15 is proposed on the basis of the NMR data. The calculated thickness of the discrete W2C thin layer is consistent with value given by HRTEM.