Synthesis,spectroscopic characterization and fungicidal activity of triphenyltin derivatives of N,N-dimethylglycine: Crystal structure of [dimethyl(carboxylatomethyl)ammonium]-chlorotriphenylstannate

The new triorganotin complexes formulated as Me₂HNCH₂COO · Ph₃SnX, X = Cl, NCS were prepared and spectroscopically characterized, and their fungicidal properties against Ceratocystis ulmi were determined. An X-ray structure for [dimethyl(carboxylatomethyl)ammonium] chlorotriphenylstannate is also reported.     

Directed Evolution of a Fluorinase for Improved Fluorination Efficiency with a Non‐native Substrate

Fluorinases offer an environmentally friendly alternative for selective fluorination under mild conditions. However, their diversity is limited in nature and they have yet to be engineered through directed evolution. Herein, we report the directed evolution of the fluorinase FlA1 for improved conversion of the non‐native substrate 5′‐chloro‐5′‐deoxyadenosine (5′‐ClDA) into 5′‐fluoro‐5′‐deoxyadenosine (5′‐FDA). The evolved variants, fah2081 (A279Y) and fah2114 (F213Y, A279L), were successfully applied in the radiosynthesis of 5′‐[¹⁸F]FDA, with overall radiochemical conversion (RCC) more than 3‐fold higher than wild‐type FlA1. Kinetic studies of the two‐step reaction revealed that the variants show a significantly improved k_cat value in the conversion of 5′‐ClDA into S‐adenosyl‐l ‐methionine (SAM) but a reduced k_cat value in the conversion of SAM into 5′‐FDA.     

Neutral loss scan in complement with high-resolution MS/MS: Combination of detection methods for flavonoid and limonoid glycosides analysis

In this study, neutral loss scan and high-resolution MS/MS were used in combination to detect and tentatively identify various flavonoid and limonoid glycosides in navel orange albedo, juice, peel and pulp. These compound classes are of research interest due to their flavour and bioactive properties, and although flavonoid glycosides have been previously studied in other food matrices, to the best of our knowledge, neutral loss scans have not been used for the elucidation of limonoid glycosides. Neutral loss masses of 120, 162 and 308 Da were selected for the detection of hexose, rutinose and neohesperidose-substituted flavonoids, whereas 197 Da was explored for limonoid glycosides due to their tendency to form ammonium adducts. Fragmentation patterns obtained from targeted MS/MS were then used to differentiate rutinose and neohesperidose substituents as well as flavonoid subclasses of flavones, flavanones and flavonols. Additionally, high-resolution MS/MS was also used for the identification of aglycones by accurate mass (to four decimal places), allowing for the differentiation of aglycones with similar unit masses but different chemical formulas. In total, 19 flavonoid glycosides and six limonoid glycosides were detected. This workflow allows for a rapid screening of flavonoid and limonoid glycosides in citrus, which can be further extended to other food products such as tea.     

A new cytotoxic carbazole alkaloid from Clausena excavata

A new carbazole alkaloid, 3-carbomethoxy-2-hydroxy-7-methoxycarbazole, Clausine-TY (1), together with two known carbazole alkaloid, Clausine-H (2) and Clausine-B (3), were isolated from the ethyl acetate extract of the stem bark of the Malaysian Clausena excavata. The structures of these compounds were elucidated by spectroscopic analyses. The new carbazole alkaloid shows significant cytotoxicity against CEM-SS cell line.     

A Chemoenzymatic and Fully Stereocontrolled Total Synthesis of the Antibacterial Natural Product (−)‐Platencin

The natural product (?)‐platencin is a potent antibacterial agent that exerts its effects through a novel mode of action. As such, it is an important lead in the development of next‐generation antibacterials that are urgently needed because of the rapidly developing resistance to current therapies. The work reported here concerns the development of a convergent and chemoenzymatic total synthesis of (?)‐platencin by methods that should provide access to a range of biologically relevant analogues. The key step involves a thermally promoted and facially selective intramolecular Diels–Alder (IMDA) cycloaddition reaction to give an adduct that embodies the tricarbocyclic core of (?)‐platencin. This adduct was elaborated over thirteen steps to the natural product. The substrate for the IMDA reaction was prepared by Stille cross‐coupling of a Z‐configured alkenylstannane with an iodinated diene obtained in an enantiomerically pure form through the whole‐cell biotransformation of iodobenzene.     

Triphenyltin Esters of N-(2-Carboxybenzylidene)anilines: Synthesis,Spectroscopic Characterization,X-ray Structure Analysis and Fungicidal Activity

Four triphenyltin carboxylates formulated as o- Ph₃SnOCOC₆H₄CH=N–Ar (Ar=C₆H₅; p -CH₃C₆H₄; o -CH₃C₆H₄; o -HOC₆H₄) were prepared and spectroscopically characterized. The crystal structure of o -Ph₃SnOCOC₆ H₄CH=NC₆H₅ indicates that the tin atom, in each of the two molecules comprising the asymmetric unit, exists in a distorted tetrahedral geometry owing to an intramolecular acyl O. . .Sn contact. These new triphenyltin carboxylates display marked toxicity against the fungus Ceratocystis ulmi .     

Biogenic Synthesis of Silver Nanoparticles with High Antimicrobial and Catalytic Activities using Sheng Di Huang (Rehmannia glutinosa)

Silver nanoparticles (AgNPs) are widely sought after for a variety of biomedical and environmental applications due to their antimicrobial and catalytic properties. We present here a green and simple synthesis of AgNPs utilizing traditional Chinese medicinal herbs. The screening of 20 aqueous herb extracts shows that Sheng Di Huang (Rehmannia glutinosa) had the most promising potential in producing AgNPs of 30±6 nm, with narrow size distribution and high crystallinity. The antimicrobial activities of these AgNPs conducted on E. coli cells were found to be superior in comparison to poly(vinylpyrrolidone)-capped AgNPs synthesized using common chemical method. Additionally, the AgNPs obtained possess excellent catalytic performance in the reduction of 4-nitrophenol to 4-aminophenol. We compared the phytochemical and FTIR spectral analyses of the herb extract before and after synthesis, in order to elucidate the phytochemicals responsible for the reduction of Ag⁺ ions and the capping of the AgNPs produced.     

Phylattrin, a new cytotoxic xanthone from Calophyllum soulattri

Our continuing studies on secondary metabolites from the stem bark of Calophyllum soulattri has led to the isolation of another new diprenylated xanthone, phylattrin (1), in addition to five other xanthones and two common sterols. The xanthones are soulattrin (2), caloxanthone C (3), macluraxanthone (4), brasixanthone B (5) and trapezifolixanthone (6) while the sterols are stigmasterol (7) and β-sitosterol (8). The structures of these compounds were determined on the basis of spectroscopic analyses such as 1D and 2D-NMR, HRESIMS, IR and UV. Compounds 1-7 exhibited moderate cytotoxic activities against SNU-1, HeLa, Hep G2, NCI-H23, K562, Raji, LS174T, IMR-32 and SK-MEL-28 cells.     

Xanthones from Garcinia mangostana (Guttiferae)

Studies on the stem of Garcinia mangostana have led to the isolation of one new xanthone mangosharin (1) (2,6-dihydroxy-8-methoxy-5-(3-methylbut-2-enyl)-xanthone) and six other prenylated xanthones, alpha-mangostin (2), beta-mangostin (3), garcinone D (4), 1,6-dihydroxy-3,7-dimethoxy-2-(3-methylbut-2-enyl)-xanthone (5), mangostanol (6) and 5,9-dihydroxy-8- methoxy-2,2-dimethyl-7-(3-methylbut-2-enyl)-2H,6H-pyrano-[3,2-b]-xanthene-6-one (7). The structures of these compounds were determined by spectroscopic methods such as 1H NMR, 13C NMR, mass spectrometry (MS) and by comparison with previous studies. All the crude extracts when screened for their larvicidal activities indicated very good toxicity against the larvae of Aedes aegypti. This article reports the isolation and identification of the above compounds as well as bioassay data for the crude extracts. These bioassay data have not been reported before.     

An adaptive GRP scheme for compressible fluid flows

This paper presents a second-order accurate adaptive generalized Riemann problem (GRP) scheme for one and two dimensional compressible fluid flows. The current scheme consists of two independent parts: Mesh redistribution and PDE evolution. The first part is an iterative procedure. In each iteration, mesh points are first redistributed, and then a conservative interpolation formula is used to calculate the cell-averages and the slopes of conservative variables on the resulting new mesh. The second part is to evolve the compressible fluid flows on a fixed nonuniform mesh with the Eulerian GRP scheme, which is directly extended to two-dimensional arbitrary quadrilateral meshes. Several numerical examples show that the current adaptive GRP scheme does not only improve the resolution as well as accuracy of numerical solutions with a few mesh points, but also reduces possible errors or oscillations effectively.