An efficient synthesis of 4-bromo-N-substituted oxindoles by an intramolecular copper-catalyzed amidation reaction

A highly efficient synthetic approach to novel 4-bromo-N-substituted oxindoles is described. The method involves a mild intramolecular copper-catalyzed amidation reaction of N-substituted 2,6-dibromophenylacetamides. In contrast to our recently published palladium-catalyzed amidation reaction, no concomitant dimerization on the 3-position of the formed oxindole occurs.     

Learning to rank: a ROC-based graph-theoretic approach

This note summarizes the main results presented in the author’s Ph.D. thesis, supervised by Luc Boullart and Bernard De Baets. The thesis was defended on 14th October 2008 at Universiteit Gent. It is written in English and available for download at . The work deals with preference learning, with emphasis on the ranking and ordinal regression machine learning settings and their connections to decision theory. Based on receiver operator characteristics analysis and graph theory, new performance measures are proposed to evaluate this type of models, and new algorithms are presented to compute and optimize these performance measures efficiently. Furthermore, the relationship with other settings like pairwise preference learning and multi-class classification is discussed.     

Redshifted and Near‐infrared Active Analog Pigments Based upon Archaerhodopsin‐3

Archaerhodopsin‐3 (AR3) is a member of the microbial rhodopsin family of hepta‐helical transmembrane proteins, containing a covalently bound molecule of all‐trans retinal as a chromophore. It displays an absorbance band in the visible region of the solar spectrum (λmax 556 nm) and functions as a light‐driven proton pump in the archaeon Halorubrum sodomense. AR3 and its mutants are widely used in neuroscience as optogenetic neural silencers and in particular as fluorescent indicators of transmembrane potential. In this study, we investigated the effect of analogs of the native ligand all‐trans retinal A1 on the spectral properties and proton‐pumping activity of AR3 and its single mutant AR3 (F229S). While, surprisingly, the 3‐methoxyretinal A2 analog did not redshift the absorbance maximum of AR3, the analogs retinal A2 and 3‐methylamino‐16‐nor‐1,2,3,4‐didehydroretinal (MMAR) did generate active redshifted AR3 pigments. The MMAR analog pigments could even be activated by near‐infrared light. Furthermore, the MMAR pigments showed strongly enhanced fluorescence with an emission band in the near‐infrared peaking around 815 nm. We anticipate that the AR3 pigments generated in this study have widespread potential for near‐infrared exploitation as fluorescent voltage‐gated sensors in optogenetics and artificial leafs and as proton pumps in bioenergy‐based applications.     

Precursors of biological cofactors from ultraviolet irradiation of circumstellar/interstellar ice analogues

Biological cofactors include functionalized derivatives of cyclic tetrapyrrole structures that incorporate different metal ions. They build up structural partnerships with proteins, which play a crucial role in biochemical reactions. Porphyrin, chlorin, bacteriochlorin, and corrin are the basic structures of cofactors (heme, chlorophyll, bacteriochlorophyll, siroheme, F 430, and vitamin B12). Laboratory and theoretical work suggest that the molecular building blocks of proteins (alpha-amino acids) and nucleic acids (carbohydrates, purines, and pyrimidines) were generated under prebiotic conditions. On the other hand, experimental data on the prebiotic chemistry of cofactors are rare. We propose to search directly for the pathways of the formation of cofactors in the laboratory. Herein we report on the detection of N-heterocycles and amines in the room-temperature residue obtained after photo- and thermal processing of an interstellar ice analogue under high vacuum at 12 K. Among them, hexahydro-1,3,5-triazine and its derivatives, together with monopyrrolic molecules, are precursors of porphinoid cofactors. Hexahydropyrimidine was also detected. This is the first detection of these compounds in experiments simulating circumstellar/interstellar conditions. Except for 2-aminopyrrole and 2,4-diaminofuran, which were only found in 13C-labeled experiments, all the reported species were detected in both 12C- and 13C-labeled experiments, excluding contamination. The molecules reported here might be present in circumstellar/interstellar grains and cometary dust and could be detected by the Stardust and Rosetta missions.     

The synthesis of 3-methyl- and 3,4-dimethyltetrahydroisoquinolines by intramolecular hydroamination with n-butyllithium

The synthesis of 3-methyltetrahydroisoquinolines and 3,4-dimethyltetrahydroisoquinolines from aromatic aminoalkenes using intramolecular hydroamination reactions, mediated by sub-stoichiometric amounts of n-butyllithium, is described.     

The perception of randomness

Psychologists have studied people's intuitive notions of randomness by two kinds of tasks: judgment tasks (e.g., “is this series like a coin?” or “which of these series is most like a coin?”), and production tasks (e.g., “produce a series like a coin”). People's notion of randomness is biased in that they see clumps or streaks in truly random series and expect more alternation, or shorter runs, than are there. Similarly, they produce series with higher than expected alternation rates. Production tasks are subject to other biases as well, resulting from various functional limitations. The subjectively ideal random sequence obeys “local representativeness”; namely, in short segments of it, it represents both the relative frequencies (e.g., for a coin, 50%–50%) and the irregularity (avoidance of runs and other patterns). The extent to which this bias is a handicap in the real world is addressed.     

Exceptionally high in vitro antitumor activity of substituted triphenyltin benzoates including salicylates against a human mammary tumor,MCF-7, and a colon carcinoma,WiDr

Nine new substituted triphenyltin benzoates of the type Ar₃Sn? OOC? C₆H₂XYZ [X = Y = H, Z = 2-OCH₃ and 4-F; X = H, Y = 3-F, Z = 5-F; X = H, Y = 2-OH, Z = 5-Cl, 5-NH₂, 5-OCH₃ and 5-SO₃H; X = 2-OH, Y = 3-CH(CH₃)₂ and Z = 5-CH(CH₃)₂] were prepared and possess considerable in vitro antitumor activity against two human tumor cell lines (MCF-7, a mammary tumor, and WiDr, a colon carcinoma) comparable with that of mitomycin C.     

Synthesis,spectroscopic characterization and in vitro antitumour activity of di-n-butyltin and diethyltin trimethoxybenzoates: X-ray structure analysis of bis[di-n-butyl(3,4,5-trimethoxybenzoato)tin] oxide

Di-n-butyltin(IV) and diethyltin(IV) 2,3,4-, 2,4,5- and 3,4,5-trimethoxybenzoates [(CH₃O)₃C₆H₂COO]₂SnR [Type a] and {[(CH₃O)₃C₆H₂COO]R₂Sn}₂O [Type b] have been synthesized and characterized spectroscopically. The crystal structure of bis[di-n-butyl(3,4,5- trimethoxybenzoato)tin] oxide has been determined. The triclinic unit cell contains one centrosymmetric dimer; a = 15.919(2) Å, b = 11.711(3) Å, c = 13.475(1) Å, and α = 63.63(2)°, β = 67.49(1)°, γ = 76.61(2)°. The geometry of the dimer is very similar to that of bis[di-n-butyl(5-methoxysalicylatotin] oxide), with two different types of five-coordinate tin atoms and one central planar Sn₂O₂ ring.