Spirobicyclo[2.2.2]octane derivatives: mimetics of baccatin III and paclitaxel (Taxol)

The formylated spirobyclic alcohol was computer modeled to be a mimetic of paclitaxel. In this model, the formyl group was used as a truncated paclitaxel side chain in order to reduce the computational work. Compound , carrying the paclitaxel side chain, was synthesized in six steps from optically active 1,3-diketone . Microtubule stabilization was not observed for , indicating that the model needs to be adjusted.     

Coherent control of the optical nonlinear and luminescence anisotropies in molecular thin films by multiphoton excitations

Photoinduced orientational distributions are implemented with one- and two-photon absorption interference in polymer films containing chromophores that exhibit luminescent and nonlinear properties. The odd- and even-order parameters of the final distribution are probed by simultaneous measurement of second-harmonic generation (SHG) and two-photon fluorescence (TPF). We show the possibility of engineering local SHG and TPF anisotropies by controlling the polarization states and intensities of the writing optical fields. Complex multipolar orders are modeled with an irreducible spherical tensor-based formalism jointly applied to the molecular polarizabilities and field tensors.     

Synthesis and characterization of model compounds of the lysine tyrosyl quinone cofactor of lysyl oxidase

4-n-Butylamino-5-ethyl-1,2-benzoquinone (1(ox)) has been synthesized as a model compound for the LTQ (lysine tyrosyl quinone) cofactor of lysyl oxidase (LOX). At pH 7, 1(ox) has a lambda(max) at 504 nm and exists as a neutral o-quinone in contrast to a TPQ (2,4,5-trihydroxyphenylalanine quinone) model compound, 4, which is a resonance-stabilized monoanion. Despite these structural differences 1(ox) and 4 have the same redox potential (ca. -180 mV vs SCE). The structure of the phenylhydrazine adduct of 1(ox) (2) is reported, and 2D NMR spectroscopy has been used to show that the position of nucleophilic addition is at C(1). UV-vis spectroscopic pH titration of phenylhydrazine adducts of 1(ox) and 4, 2, and 11, respectively, reveals a similar red shift in lambda(max) at alkaline pH with the same pK(a) (approximately 11.8). In contrast, the red shift in lambda(max) at acidic pH conditions yields different pK(a) values (2.12 for 2 vs -0.28 for 11), providing a means to distinguish LTQ from TPQ. Reactions between in situ generated 4-ethyl-1,2-benzoquinone and primary amines give a mixture of products, indicating that the protein environment must play an essential role in LTQ biogenesis by directing the nucleophilic addition of the epsilon-amino group of a lysine residue to the C(4) position of a putative dopaquinone intermediate. Characterization of a 1,6-adduct between an o-quinone and butylamine (3-n-butylamino-5-ethyl-1,2-benzoquinone, 13) confirms the assignment of LTQ as a 1,4-addition product.     

Faber-hypercyclic operators

Let Ω be a bounded domain of the complex plane whose boundary is a closed Jordan curve and (F _n ) _n≥0 the sequence of Faber polynomials of Ω. We say that a bounded linear operator T on a separable Banach space X is Ω-hypercyclic if there exists a vector x of X such that {F _n (T)x: n ≥ 0} is dense in X. We show that many of the results in the spectral theory of hypercyclic operators involving the unit disk or its boundary have Ω-hypercyclic counterparts which involve the domain Ω or its boundary. The influence of the geometry of Ω or the smoothness of its boundary on Faber-hypercyclicity is also discussed.     

Can density functional theory (DFT) be used as an aid to a deeper understanding of tandem mass spectrometric fragmentation pathways?

Prediction of tandem mass spectrometric (MS/MS) fragmentation for non‐peptidic molecules based on structure is of immense interest to the mass spectrometrist. If a reliable approach to MS/MS prediction could be achieved its impact within the pharmaceutical industry could be immense. Many publications have stressed that the fragmentation of a molecular ion or protonated molecule is a complex process that depends on many parameters, making prediction difficult. Commercial prediction software relies on a collection of general heuristic rules of fragmentation, which involve cleaving every bond in the structure to produce a list of ‘expected’ masses which can be compared with the experimental data. These approaches do not take into account the thermodynamic or molecular orbital effects that impact on the molecule at the point of protonation which could influence the potential sites of bond cleavage based on the structural motif. A series of compounds have been studied by examining the experimentally derived high‐resolution MS/MS data and comparing it with the in silico modelling of the neutral and protonated structures. The effect that protonation at specific sites can have on the bond lengths has also been determined. We have calculated the thermodynamically most stable protonated species and have observed how that information can help predict the cleavage site for that ion. The data have shown that this use of in silico techniques could be a possible way to predict MS/MS spectra. Copyright © 2009 John Wiley & Sons, Ltd.