A new cyclopeptide alkaloid from the bark of waltheria douradinha

Waltherine-C (5), a novel 14-membered cyclopeptide alkaloid has been isolated, together with four known cyclopeptide alkaloids, waltherine-A (1) and -B (2), scutianine-B (3) and adouetine-Y' (4), from the bark of Waltheria douradinha (Sterculiaceae) from Rio Grande do Sul, Brazil. The structure and NMR assignments of this new alkaloid were determined by 1D and 2D NMR techniques. The stereochemistry of the ring amino acid residue and the N,N-dimethyl amino acid side-chain has been assigned by gas chromatography employing modified cyclodextrins as chiral stationary phases.     

Theoretical investigation of electronic and optical properties of andalusite within density functional theory

The electronic and optical properties of andalusite were studied by using quantum-mechanical calculations based on the density functional theory (DFT). The electronic structure shows that andalusite has a direct band gap of 5.01 eV. The complex dielectric function and optical constants, such as extinction coefficient, refractive index, reflectivity and energy-loss spectrum, are calculated. The optical properties of andalusite are discussed based on the band structure calculations. It is shown that the O-2p states and Al-3s states play a major role in optical transitions as initial and final states, respectively.     

'Click' cycloaddition catalysts: copper(I) and copper(II) tris(triazolylmethyl)amine complexes

The CuI complex of the 'click' ligand tris(benzyltriazolylmethyl)amine is an unusual dinuclear dication with one triazole unit bridging two metal centers, and is an effective catalyst for the 'click' cycloaddition reaction.     

13C NMR Chemical Shifts of β-Alkoxyvinyl Ketones: III✠-Empirical Substituent Effects in 1-Alkylamino-6-Ethoxy-1,5-Hexadien-3,4-Diones and 1,6-bis(Alkylamino)-1,5-Hexadien-3,4-diones

Evaluation by empirically derived equations for the substituent effect (E_Xn and E_Yn, n = 1 to 6) on the ¹³C NMR chemical shifts for C-1, C-2, C-3, C-4, C-5 and C-6 in 1-alkylamino-6-ethoxy-1,5-hexadien-3,4-diones 1a-f and 1,6-bis(alkylamino)-1,5-hexadien-3,4-diones 2a-f [XCH=CHC(O)-C(O)CH=CHY, where X, Y = OEt, NH₂, PhCH₂NH, n-BuNH, i-PrNH, cyclo-C₆H₁₁NH, t-BuNH], taking as reference the 1,6-diethoxy-1,5-hexadien-3,4-dione (3), is reported. From the calculated values for the E_Xn and E_Yn effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1,2 with excellent precision: 100% of the calculated chemical shifts are found to be within ±0.5ppm. The carbon-13 chemical shifts of C-1, C-2 and C-3 of compounds 1a,2a,3 led a good correlation with carbon charge densities (qr).     

Convenient synthesis of 3-aminomethylenedihydrofuran-2-ones

A simple and convenient synthesis of a series of 3-aminomethylenedihydrofuran-2-ones from the reaction of 3-trichloroacetyl-4,5-dihydrofuran with amines, is presented.     

Synthesis and structural study of a new series of 2‐methylsulfanyl‐tetrahydropyrimidines from β‐alkoxyvinyl trihalomethyl ketones

This work describes the synthesis of a novel series of 2‐methylsulfanyl‐tetrahydropyrimidines, from the cyclocondensation reaction of β‐alkoxyvinyl trihalomethyl ketones with 2‐methyl‐2‐thiopseudourea sulfate, in good yields. A detailed ¹H‐ and ¹³C‐NMR study was performed on the 2‐methylsulfanyl‐tetrahydropyrimidines obtained and 3D structures were proposed based on AM1 calculations supported by ¹H NMR coupling constants and NOESY experiments.     

An ionic liquid as reaction medium for the synthesis of halo-containing β-enaminones at room temperature

A series of twenty halomethylated β-enaminones [RC(O)CH=C(R ¹)NR ³ R ⁴, where R = CF₃,CCl₃, CHCl₂; R ¹ = H, Me, Ph; R ³ = H, Me, Bu, Et; R ⁴ = Me, Et, Bu, allyl, tert-amyl, CH₂CH₂OH, Bn, Ph] were synthesized using the ionic liquid [bmim]BF₄ at room temperature. It is demonstrated that this ionic liquid is a reaction medium suitable for the amination of β-alkoxyvinyl halomethyl ketones. The advantages of this method are the absence of solvents, short reaction times, and good yields. Correspondence: Marcos A. P. Martins, Núcleo de Química de Heterociclos – NUQUIMHE, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.