An easy ABD→ABCD strategy to indolo[2,3-a]quinolizin-4-one. Synthesis of deplancheine and yohimbane

The efficient synthesis of indolo[2,3-a]quinolizin-4-ones 2 is described in two steps via formal [3+3] cycloaddition reaction of α-sulfonyl tryptaminylacetamide 4 with various α,β-unsaturated esters 5 and the regioselective reduction of the resulting glutarimides 3 with sodium borohydride then sequent further dehydrated cyclization in the presence of boron trifluoride etherate. The useful building block is applied to synthesize deplancheine (1a) and yohimbane (1b).     

Quantum algebraic–combinatoric study of the conformational properties of n‐alkanes. I

Based on quantum chemical calculation results, four rules were previously derived for the numbers and the sequences of the conformers of free alkane molecules. This paper builds up first an algebra to handle the conformational problem of alkanes. Partitioning the set of all sequences, the whole problem is then subdivided into three independent subcases. With the help of an equivalence relation, the sequences can be classified. According to the quantum chemical rules, certain equivalence classes do not represent conformers. A welldefined subcase of the whole problem is solved.     

Tuning a High Transmission Ion Guide to Prevent Gas-Phase Proton Exchange During H/D Exchange MS Analysis

Hydrogen/deuterium exchange (HDX) mass spectrometry (MS) for protein structural analysis has been adopted for many purposes, including biopharmaceutical development. One of the benefits of examining amide proton exchange by mass spectrometry is that it can readily resolve different exchange regimes, as evidenced by either binomial or bimodal isotope patterns. By careful analysis of the isotope pattern during exchange, more insight can be obtained on protein behavior in solution. However, one must be sure that any observed bimodal isotope patterns are not artifacts of analysis and are reflective of the true behavior in solution. Sample carryover and certain stationary phases are known as potential sources of bimodal artifacts. Here, we describe an additional undocumented source of deuterium loss resulting in artificial bimodal patterns for certain highly charged peptides. We demonstrate that this phenomenon is predominantly due to gas-phase proton exchange between peptides and bulk solvent within the initial stages of high-transmission conjoined ion guides. Minor adjustments of the ion guide settings, as reported here, eliminate the phenomenon without sacrificing signal intensity. Such gas-phase deuterium loss should be appreciated for all HDX-MS studies using such ion optics, even for routine studies not focused on interpreting bimodal spectra.

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Synthesis and characterization of open-framework niobium silicates: Rb2(Nb2O4)(Si2O6).H2O and the dehydrated phase Rb2(Nb2O4)(Si2O6)

A new niobium(V) silicate, Rb(2)(Nb(2)O(4))(Si(2)O(6)).H(2)O, has been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and solid-state NMR spectroscopy. It crystallizes in the tetragonal space group P4(3)22 (No. 95) with a = 7.3431(2) A, c = 38.911(3) A, and Z = 8. Its structure contains tetrameric units of the composition Nb(4)O(18), which share corners to form a layer of niobium oxide. The Nb-O layer is a slice of the pyrochlore structure. Neighboring Nb-O layers are linked by vierer single-ring silicates generating eight-ring and six-ring channels running parallel to <100> directions, in which the Rb(+) cations and water molecules reside. The tantalum analogue was prepared and characterized by powder X-ray diffraction. Upon heating to 500 degrees C, Rb(2)(Nb(2)O(4))(Si(2)O(6)).H(2)O loses lattice water molecules, while the framework structure is retained to give the anhydrous compound Rb(2)(Nb(2)O(4))(Si(2)O(6)), whose structure was also characterized by single-crystal X-ray diffraction. The dehydrated sample absorbs water reversibly, as indicated by powder X-ray diffraction. Rb(2)(Nb(2)O(4))(Si(2)O(6)) crystallizes in the tetragonal space group I4(1) (No. 80) with a = 10.2395(6) A, c = 38.832(3) A, and Z = 16.     

Shape-Selective Alkylation of Isopropylnaphthalene over HM Zeolite. A Theoretical Study

A first principle quantum chemical method for determining the shape of molecules has been elaborated and its value in interpreting the experimentally found shape selectivity in isopropylation of isopropylnaphthalene on H-mordenite zeolite is demonstrated. In line with experimental results, it is found that 2,6-diisopropylnaphthalene is the most feasible product since it diffuses through the main channels of mordenite the easiest among the possible isomers.     

Representations of generalized inverses via full-rank QDR decomposition

Numerical Algorithms - In this paper, novel representations of generalized inverses of rational matrices are developed. Therefore, a unified approach for the computation of {1,2,3} and {1,2,4}...     

Transient and First Passage Time Distributions of First- and Second-order Multi-regime Markov Fluid Queues via ME-fication

We propose a numerical method to obtain the transient and first passage time distributions of first- and second-order Multi-Regime Markov Fluid Queues (MRMFQ). The method relies on the observation that these transient measures can be computed via the stationary analysis of an auxiliary MRMFQ. This auxiliary MRMFQ is constructed from the original one, using sample path arguments, and has a larger cardinality stemming from the need to keep track of time. The conventional method to approximately model the deterministic time horizon is Erlangization. As an alternative, we propose the so-called ME-fication technique, in which a Concentrated Matrix Exponential (CME) distribution replaces the Erlang distribution for approximating deterministic time horizons. ME-fication results in much lower state-space dimensionalities for the auxiliary MRMFQ than would be with Erlangization. Numerical results are presented to validate the effectiveness of ME-fication along with the proposed numerical method.

     

Effect of the naphthalene moiety on the mesogenic properties of ferroelectric liquid crystals containing diastereomeric propionic acids

Two ferroelectric liquid crystals containing the naphthalene moiety were synthesized from 2(S)-[2(R)-methylhexyloxy]propionic acid and its (S, S)-diastereomer. Their mesogenic properties are compared with those of the analogous mesogens containing the biphenyl ring.     

Traceless polymer-supported divergent synthesis of quinoxalinones by microwave irradiation

A novel protocol for rapid assemble of quinoxalinones framework has been demonstrated. This method incorporated with soluble polymer support provides a convenient approach for diversification of heterocyclic compounds and for easy purification via facile precipitation from reaction matrix. The key transformation of this study involves in situ reduction of aromatic nitro compound, tandem lactamization concomitant with traceless cleavage of the polymer support under microwave irradiation in a one-pot fashion. Moreover, forward synthetic routes were introduced to maximize complexity of the master intermediate on which further chemical elaboration was applied. The strategy is envisaged to apply for establishment of drug-like small-molecule libraries for high-throughput screening.