Synthesis and S-methylation of 2-thioxopyrido[3′,2′:4,5]thieno[3,2-d]-pyrimidin-4(3H)-ones with and without a phase transfer catalyst

A number of 2-thioxopyrido[3′,2′:4,5]thieno[3,2-H]pyrimdin-4(3H-ones (5) have been synthesized by cyclocondensation of 2-carbethoxy-3-amino-4-phenyl-6-substituted-thieno[2,3-b]pyridines (3) with various isothiocyanates. Compounds 5 were S-methylated routinely and the reactions compared under solid-liquid phase transfer conditions to obtain 2-methylthiopyrido[3′,2′:4,5]thieno[3,2-d]pyrimidin-4(3H)-^ones (6). The new triheterocyclic pyridothienopyrimidines were prepared with the objective to study their pharmacological properties.     

Rate constants of the reactions of O(3P) atoms with Br2 and NO2 over the temperature range 220-950 K

The kinetics of the reactions of Br₂ and NO₂ with ground state oxygen atoms have been studied over a wide temperature range, T = 220-950 K, using a low-pressure flow tube reactor coupled with a quadrupole mass spectrometer: O + NO₂ → NO + O₂ (1) and O + Br₂ → Br + BrO (2). The rate constant of reaction (1) was determined under pseudo–first-order conditions, either monitoring the kinetics of O-atom or NO₂ consumption in excess of NO₂ or of the oxygen atoms, respectively: k₁ = (6.1 ± 0.4) × 10⁻¹² exp((155 ± 18)/T) cm³ molecule⁻¹ s⁻¹ (where the uncertainties represent precision at the 2σ level, the estimated total uncertainty on k₁ being 15% at all temperatures). The temperature dependence of k₁, found to be in excellent agreement with multiple previous low-temperature data, was extended to 950 K. The rate constant of reaction (2) determined under pseudo–first-order conditions, monitoring the kinetics of Br₂ consumption in excess of O-atoms, showed upward curvature at low and high temperatures of the study and was fitted with the following three-parameter expression: k₂ = 9.85 × 10⁻¹⁶ T^1.41 exp(543/T) cm³ molecule⁻¹ s⁻¹ at T = (220-950) K, which is recommended from the present study with an independent of temperature conservative uncertainty of 15% on k₂.     

Pyridopyrimidines. X. Synthesis of 3‐Substituted 2‐Thioxo‐5,7‐dimethylpyrido[2,3‐d] pyrimidin‐4(3H)‐ones and their S‐Alkylation Under Phase Transfer Conditions

2‐Thioxo‐5,7‐dimethylpyrido[2,3‐d]pyrimidin‐4(3H)‐ones 3 were synthesized by the cyclocondensation of 2‐amino‐3‐carbethoxy‐4,6‐dimethylpyridine 1 with methyl‐N‐aryldithiocarbamates 2 and compared with the condensation between 1 and aryl isothiocyanates 4. When a comparative study of N vs S alkylation of ambident 2‐thioxo‐5,7‐dimethylpyrido[2,3‐d]pyrimidin‐4(3H)‐ones 3 was carried out under liquid‐liquid and solid‐liquid phase transfer conditions using various alkylating agents 5 , the S‐alkylated products 6 were obtained exclusively and selectively.     

Stability analysis of structurally unstable man–machine system involving time delays

In this paper, a structurally unstable man–machine system is considered and a rigorous mathematical analysis is performed to study the influence of time delays in the control force on stability of the equilibrium solution of this system. Results on stability, instability and conditions for the preservation of stability (instability), besides the existence of bifurcation are presented.     

Approximating min-cost chain-constrained spanning trees: a reduction from weighted to unweighted problems

We study the min-cost chain-constrained spanning-tree (MCCST) problem: find a min-cost spanning tree in a graph subject to degree constraints on a nested family of node sets. We devise the first polytime algorithm that finds a spanning tree that (i) violates the degree constraints by at most a constant factor and (ii) whose cost is within a constant factor of the optimum. Previously, only an algorithm for unweighted CCST was known (Olver and Zenklusen in Proceedings of the 16th IPCO, pp 324–335, 2013), which satisfied (i) but did not yield any cost bounds. This also yields the first result that obtains an O(1)-factor for both the cost approximation and violation of degree constraints for any spanning-tree problem with general degree bounds on node sets, where an edge participates in a super-constant number of degree constraints. A notable feature of our algorithm is that we reduce MCCST to unweighted CCST (and then utilize Olver and Zenklusen in Proceedings of the 16th IPCO, pp 324–335, 2013) via a novel application of Lagrangian duality to simplify the cost structure of the underlying problem and obtain a decomposition into certain uniform-cost subproblems. We show that this Lagrangian-relaxation based idea is in fact applicable more generally and, for any cost-minimization problem with packing side-constraints, yields a reduction from the weighted to the unweighted problem. We believe that this reduction is of independent interest. As another application of our technique, we consider the k -budgeted matroid basis problem, where we build upon a recent rounding algorithm of Bansal and Nagarajan (Proceedings of IPCO 2016. arXiv:1512.02254, 2015) to obtain an improved \(n^{O(k^{1.5}/\epsilon )}\)-time algorithm that returns a solution that satisfies (any) one of the budget constraints exactly and incurs a \((1+\epsilon )\)-violation of the other budget constraints.     

Optical sensing in microfluidic lab-on-a-chip by femtosecond-laser-written waveguides

We use direct femtosecond laser writing to integrate optical waveguides into a commercial fused silica capillary electrophoresis chip. High-quality waveguides crossing the microfluidic channels are fabricated and used to optically address, with high spatial selectivity, their content. Fluorescence from the optically excited volume is efficiently collected at a 90° angle by a high numerical aperture fiber, resulting in a highly compact and portable device. To test the platform we performed electrophoresis and detection of a 23-mer oligonucleotide plug. Our approach is quite powerful because it allows the integration of photonic functionalities, by simple post-processing, into commercial LOCs fabricated with standard techniques. Figure Femtosecond laser written waveguides can selectively excite fluorescence in a microfluidic channel of a commercial lab-on-a-chip. A compact scheme for on-chip detection by laser induced fluorescence is applied to capillary electrophoresis of a 23-mer Cy3-labeled oligonucleotide     

1,3‐Dimethyl‐2‐oxo‐4,6‐diphenyl‐1,2,3,4‐tetrahydropyridine‐3‐carbonitrile

The crystal structure of the title compound, C₂₀H₁₈N₂O, reveals a distorted half‐chair conformation of the central tetra­hydro­pyridine (THP) ring, with the cyano‐ and adjacent phenyl‐substituted C atoms displaced by 0.329 (1) and ?0.315 (1) Å, respectively, from the THP best plane. Steric interactions force the phenyl rings out of the THP plane by 49.21 (9) and 65.76 (5)°. The cyano moiety is coplanar with the THP plane.     

C—H⋯N and C—H⋯π interactions in 2‐ethoxy‐4,6‐diphenylpyridine‐3‐carbonitrile

The title compound, C₂₀H₁₆N₂O, has two mol­ecules in the asymmetric unit and the crystal structure shows that the central pyridine ring of each mol­ecule has a flat boat conformation. The terminal C atom in one of the mol­ecules is disordered over two positions, with relative occupancies of 0.594 (14) and 0.398 (14). Intermolecular C—H?N and C—H?π interactions and π–π stacking, along with intramolecular C—H?N and C—H?π interactions, help to stabilize the structure.     

Synthesis of isomeric triazolopyrrolopyrimidines

4‐Hydrazino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 4 ) were cyclocondensed with formic acid or triethyl orthoformate to give 7H‐1,2,4‐triazolo[1,5‐c]pyrrolo[3,2‐e]pyrimidines ( 5 ) and 7H‐1,2,4‐triazolo[4,3‐c]pyrrolo‐[3,2‐e]pyrimidines ( 6 ) respectively. The [4,3‐c]‐isomers ( 6 ) were rearranged into thermodynamically more stable [1,5‐c]‐isomers ( 5 ). The identical compounds ( 5 ) were prepared using another route by reacting 3‐amino‐4‐imino‐7H‐pyrrolo[2,3‐d]pyrimidines ( 3 ) with formic acid or triethylorthoformate. Reaction of 2‐amino‐3‐cyanopyrroles ( 1 ) with triethyl orthoformate followed by hydrazinolysis afforded ( 3 ) via the formation of N‐ethoxymethylene‐2‐amino‐3‐cyanopyrroles ( 2 ).     

Fluorogenic ratiometric dipodal optode containing imine-amide linkages: Exploiting subtle thorium (IV) ion sensing

The (13E,19E)-N1′,N3′-bis[4-(diethylamino)-2-hydroxybenzylidene]malonohydrazide (L) has been developed for the detection of Th⁴⁺ ions using dual channel signalling system. The UV–vis absorbance and fluorescence spectroscopic data revealed the formation of L–Th⁴⁺ complex in 1:1 equilibrium. The density functional theory (DFT) also confirms the optimum binding cavity for the recognition of metal ion. The binding constant computed from different mathematical models for an assembly of L–Th⁴⁺. The detection limit of L for Th⁴⁺ recognition is to a concentration down to 0.1 μM (0.023 μg g⁻¹). The present sensing system is also successfully applied for the detection of Th⁴⁺ ion present in soil near nuclear atomic plants.