Reaction of secondary phosphines with elemental sulfur and hydrazine: atom-economic synthesis of dithiophosphinates

Russian Journal of General Chemistry -     

CuI COMPLEXES BASED ON DI(2-PYRIDYL) (2-AROYLETHENYL)PHOSPHINE OXIDES: SYNTHESIS,STRUCTURE, AND DARK RED PHOTOLUMINESCENCE

Journal of Structural Chemistry - By the interaction of CuI with bis(2-pyridyl)phosphine oxides (2-Py)2RP(O) containing E-1-phenyl-2-aroylethenyl–C(Ph)=CHC(O)R′...     

Floating boundary particle swarm optimization algorithm

A new modification to the particle swarm optimization (PSO) algorithm is proposed aiming to make the algorithm less sensitive to selection of the initial search domain. To achieve this goal, we release the boundaries of the search domain and enable each boundary to drift independently, guided by the number of collisions with particles involved in the optimization process. The gradual modification of the active search domain range enables us to prevent particles from revisiting less promising regions of the search domain and also to explore the areas located outside the initial search domain. With time, the search domain shrinks around a region holding a global extremum. This helps improve the quality of the final solution obtained. It also makes the algorithm less sensitive to initial choice of the search domain ranges. The effectiveness of the proposed Floating Boundary PSO (FBPSO) is demonstrated using a set of standard test functions. To control the performance of the algorithm, new parameters are introduced. Their optimal values are determined through numerical examples.     

MALDI-TOF MS as a label-free approach to rapid inhibitor screening

Mass Spectrometry (MS) has been widely reported for measuring the conversion of substrates to products for enzyme assays. These measurements are typically performed by time-consuming LC-MS to eliminate buffer salts that interfere with electrospray ionization MS. However, matrix-assisted laser desorption ionization, time-of-flight MS (MALDI-TOF MS) offers a label-free and direct readout of substrate and product, a fast sampling rate, and is tolerant of many buffer salts, reagents, and compounds that are typically found in enzyme reaction mixtures. In this report, a demonstration of how MALDI-TOF MS can be used to directly measure ratios of substrates and products to produce IC(50) curves for rapid enzyme assays and compound screening is provided. Typical reproducibility parameters were <7% RSD-a value comparable to ESI MS quantitative assays and well within the acceptable limits for screening assays. The speed of the MALDI readout is currently about 10 s per sample, thus allowing for over 7500 samples/day. From a simplicity standpoint, the enzymatic reaction mixtures are prepared by liquid handling robots, the reactions are stopped by addition of a 10 times volume of acidic matrix solution, and the samples are simultaneously transferred to MALDI target plate for analysis. Importantly, the ratios of substrate to product are of sufficient reproducibility to eliminate the need for internal standards and, thus, minimize the cost and increasing the speed of assay development.     

Synthesis and biological evaluation of aromatic analogues of conduritol F, L-chiro-inositol, and dihydroconduritol F structurally related to the amaryllidaceae anticancer constituents

Pancratistatin is a potent anticancer natural product, whose clinical evaluation is hampered by the limited natural abundance and the stereochemically complex structure undermining practical chemical preparation. Fifteen aromatic analogues of conduritol F, l-chiro-inositol, and dihydroconduritol F that possess four of the six pancratistatin stereocenters have been synthesized and evaluated for anticancer activity. These compounds serve as truncated pancratistatin analogues lacking the lactam ring B, but retaining the crucial C10a-C10b bond with the correct stereochemistry. The lack of activity of these compounds provides further insight into pancratistatin's minimum structural requirements for cytotoxicity, particularly the criticality of the intact phenanthridone skeleton. Significantly, these series provide rare examples of simple aromatic conduritol and inositol analogues and, therefore, this study expands the chemistry and biology of these important classes of compounds.     

Magnetic and vibrational properties and crystal structure of Sr9.2Co1.3(PO4)7 with disordered arrangements of some strontium, cobalt, and phosphate ions

Solid solutions of Sr_9+xCo_1.5−x(PO₄)₇ were found in the compositional range of 0.05?x?0.30. The structure of Sr_9.2Co_1.3(PO₄)₇ (x=0.2) was determined from single crystal X-ray diffraction (space group (No. 166); Z=3; and ; ; ; ) and refined to R₁=0.0343 and wR₂=0.0633 for 586 reflections with I>2σ(I). Sr_9.2Co_1.3(PO₄)₇ is structurally related to β-Ca₃(PO₄)₂ and Sr₃(PO₄)₂ and has disordered arrangements of some Sr²⁺, Co²⁺, and PO₄³⁻ ions. Sr²⁺ ions at a 9e site are statistically disordered among four positions near the center of symmetry. Co²⁺ and Sr²⁺ ions are split along the c-axis to occupy a 6c site that is 75% vacant. The P1O₄ tetrahedra are orientationally disordered. Sr²⁺ ions at an 8-fold coordinated 18h site, Co²⁺ ions at an octahedral 3a site, and the P2O₄ tetrahedra are ordered in the structure of Sr_9.2Co_1.3(PO₄)₇. Features of Raman spectra are discussed in relation to the crystallographic structure of Sr_9.2Co_1.3(PO₄)₇ and in comparison with Raman spectra of β-Ca₃(PO₄)₂-type and Sr₃(PO₄)₂-type compounds. Sr_9.2Co_1.3(PO₄)₇ is paramagnetic between 2 and 300 K with an effective magnetic moment of 4.98μ_B per Co²⁺ ion.     

Selectivity guidelines and a reductive elimination-based model for predicting the stereochemical course of conjugate addition reactions of organocuprates to gamma-alkoxy-alpha,beta-enoates

Current models used to predict the stereochemical outcome of organocopper conjugate addition processes focus on the nucleophilic addition step as stereochemistry-determining. Recent kinetic, NMR, kinetic isotope effect, and theoretical density functional studies strongly support the proposal that stereochemical preferences in these processes are dictated by the reductive elimination step, transforming Cu(III) to Cu(I) intermediates. A new model that considers various steric and stereoelectronic factors involved in the transition state of the reductive elimination step is proposed and then used to interpret the results of systematic studies of arylcuprate conjugate addition reactions with cis and trans gamma-alkoxy-alpha,beta-enoates. The results give rise to the following selectivity guidelines for this process. To achieve high anti-addition diastereoselectivities the use of trans esters with a bulky nonalkoxy substituent at the gamma-position is recommended. While stereoelectronics disfavor syn-addition, a judicious choice of properly sized gamma-substituents may lead to the predominant formation of syn-products, especially with cis enoates. However, high syn-selectivities may be achieved by using gamma-amino-alpha,beta-enoates.     

Ring opening and ring closure in an indolizine structure activated through S(N)Ar coupling with superelectrophilic 4,6-dinitrobenzofuroxan, an unusual intramolecular oxygen transfer from a N-oxide functionality

Coupling of superelectrophilic 4,6-dinitrobenzofuroxan with a pi-excessive indolizine structure affords a strongly dipolar substitution product which undergoes a facile but unusual rearrangement induced by an intramolecular oxygen atom transfer from the N-oxide functionality of the DNBF moiety.     

SEAr-SNAr couplings of indolizines and related pyrrole derivatives with superelectrophilic nitrobenzoxadiazoles

The nucleophilic aromatic substitutions of 7-chloro-4,6-dinitrobenzofurazan (DNBZ-Cl) and 7-chloro-4,6-dinitrobenzofuroxan (DNBF-Cl) with a series of differently substituted indolizines (5a-f) and a series of dihyropyrroloisoquinolines (11a-f) have been investigated. In accord with previous reports emphasizing the superelectrophilic character of these compounds in σ-complexation processes, DNBZ-Cl and DNBF-Cl react very readily and quantitatively with the weak carbon nucleophiles 5a-f and 11a-f at room temperature in acetonitrile. In the case of DNBZ-Cl, the resulting products (7Z,a-f and 12Z,a-f) are those expected from the displacement of the chlorine atom through a S_EAr-S_NAr mechanism. A significant result is that these compounds, despite the lack of coplanarity of the two rings, are characterized by an intense intramolecular charge transfer between the donor pyrrole-type moiety and the electron-deficient acceptor DNBZ moiety. Contrasting with this behaviour, the DNBF-Cl reactions show a totally different pattern, proceeding with loss of the N-oxide functionality and expansion of the pyrrole moiety to afford stable zwitterionic spiro adducts (8F,a-f and 13F,a-f) of a so far unknown type. Rapid NMR recordings have revealed that the formation of these adducts occurs after initial formation of the expected substitution products 7F,a-f and 12F,a-f. A mechanism accounting for the overall rearrangement leading to the spirobenzofurazan adducts is suggested. It is based on an initial nucleophilic attack of the oxygen atom of the N-oxide functionality at the electron-deficient and strongly olefinic C-C coupling bond generated by the aforementioned intramolecular charge transfer. This results in the formation of an unstable five-membered isoxazole ring whose decomposition goes along with loss of the N-oxide functionality and enlargement of the pyrrole moiety into a pyridine one. Also discussed are the factors accounting for the high thermodynamic stability of the spiro adducts, and their relevance to the stability of previously reported spiro adducts.