Products from furans. XXI Synthesis of novel oxygen containing heterocyclic isosteres of tyrosine derivatives

Novel oxygen containing heterocyclic isosteres of tyrosine and tyramine derivatives were synthesized. All new compounds contain the pyran ring as a consequence of their common route of preparation. Furthermore several methyl, ethyl, diethyl and isopropyl derivatives of the prepared amines were synthesized.     

On the solution of steady-state elastodynamic crack problems by using complex variable methods

Summary Solutions in a closed-form, or in a series-expansion form, are given, concerning steady-state elastodynamic crack problems. The configuration of the problems treated consists, either of an infinite body under plane extension, or a strip-like body under anti-plane shear. The loading mode consisted of constant stresses, acting on the crack faces and moving with the velocity of the crack tip. In the domain of elliptic wave-equations, viz. for subsonic crack velocities, the solution of the problems was reduced to a solution of a Dirichlet problem, whereas in the case of hyperbolic wave-equations, viz. for transonic crack velocities, a Riemann-Hilbert problem was formulated and solved.

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Résumé On donne des solutions sous forme explicite ou sous forme de séries infinies pour des problèmes de fissures stables elastodynamiques. La configuration des problèmes traités consiste soit en un corps infini soumis à une extension plane, soit en un corps en forme de bande soumis à un cisaillement anti-plan. Les plaques étaient soumises à un état plan de contraintes constantes, agissant sur les faces de la fissure et suivant l'extrémité de la fissure avec la même vitesse. On a montré que dans le cas où le problème peut être exprimé par des équations d'ondes elliptiques, c.à.d. pour des vitesses de propagation de la fissure d'ordre subsonique, la solution a été réduite à une solution d'un problème de Dirichlet, tandis que dans le cas des équations d'ondes hyperboliques, c.à.d. pour des vitesses transoniques, le problème a été formulé et résolu comme un problème de Riemann-Hilbert.

     

Products from furans. VII. A General Route for the Synthesis of α-(1,2-cis) and β-(1,2-trans) Glycoconjugates via 1-O-Acyl and 1-O-Ethoxycarbonyl-2-azido-2,3-dideoxyglycopyranosides

A methodology for the synthesis of 2,3,6-trideoxy- and 2,3-dideoxy-2-aminoglycosides is presented. 2,3-Dideoxyhex-2-enopyranos-4-uloses (named also as 2H-pyran-3(6H)-ones) were used for the synthesis of 1-O-acetyl, 1-O-ethyloxycarbonyl and 1-S-phenyl-2,3,6-trideoxy-(or 2,3-dideoxy)-2-azidoglycopyranosyl donors. Glycosidation of the above thio-ethers with a variety of alcohols in the presence of N-bromosuccinimide as activator yielded predominantly α-glycosides, while acetates afforded β-glycosides when TMSOTf was used as a promoter. The coupling of carbonates using tin tetrachloride or TMSOTf proved to be the most successful procedure, yielding the β-glycoside as the predominant product. Thus, glycoconjugates of aminosugars, steroids and aminoacids have been synthesized.     

Product (α1, α2)-modulation spaces

We study fundamental properties of product (α₁, α₂)-modulation spaces built by (α₁, α₂)-coverings of ℝⁿ¹ × ℝⁿ². Precisely we prove embedding theorems between these spaces with different parameters and other classical spaces. Furthermore, we specify their duals. The characterization of product modulation spaces via the short time Fourier transform is also obtained. Families of tight frames are constructed and discrete representations in terms of corresponding sequence spaces are derived. Fourier multipliers are studied and as applications we extract lifting properties and the identification of our spaces with (fractional) Sobolev spaces with mixed smoothness.

     

Probing the Mechanism of Allylic Substitution of Morita–Baylis–Hillman Acetates (MBHAs) by using the Silyl Phosphonite Paradigm: Scope and Applications of a Versatile Transformation

A P?C bond‐forming reaction between silyl phosphonites and Morita–Baylis–Hillman acetates (MBHAs) is explored as a general alternative towards medicinally relevant β‐carboxyphosphinic structural motifs. Conversion rates of diversely substituted MBHAs to phosphinic acids 9 or 14 that were recorded by using ³¹P NMR spectroscopy revealed unexpected reactivity differences between ester and nitrile derivatives. These kinetic profiles and DFT calculations support a mechanistic scenario in which observed differences can be explained from the “lateness” of transition states. In addition, we provide experimental evidence suggesting that enolates due to initial P‐Michael addition are not formed. Based on the proposed mechanistic scenario in conjunction with DFT calculations, an interpretation of the E/Z stereoselectivity differences between ester and nitriles is proposed. Synthetic opportunities stemming from this transformation are presented, which deal with the preparation of several synthetically capricious phosphinic building blocks, whose access through the classical P‐Michael synthetic route is not straightforward.     

Control of wireless networks with rechargeable batteries [transactions papers]

We consider the problem of cross-layer resource allocation for wireless networks operating with rechargeable batteries under general arrival, channel state and recharge processes. The objective is to maximize total system utility, defined as a function of the long-term rate achieved per link, while satisfying energy and power constraints. A policy with decoupled admission control and power allocation decisions is proposed that achieves asymptotic optimality for sufficiently large battery capacity to maximum transmission power ratio (explicit bounds are provided). We present first a downlink resource allocation scenario; the analysis is then extended to multihop networks. The policy is evaluated via simulations and is seen to perform very well even in the non-asymptotic regime. This policy is particularly suitable for sensor networks, which typically satisfy the asymptotic conditions required by our methodology.     

A high-throughput, high-resolution strategy for the study of site-selective DNA binding agents: analysis of a "highly twisted" benzimidazole-diamidine

A general strategy for the rapid structural analysis of DNA binding ligands is described as it was applied to the study of RT29, a benzimidazole-diamidine compound containing a highly twisted diphenyl ether linkage. By combining the existing high-throughput fluorescent intercalator displacement (HT-FID) assay developed by Boger et al. and a high-resolution (HR) host-guest crystallographic technique, a system was produced that was capable of determining detailed structural information pertaining to RT29-DNA interactions within approximately 3 days. Our application of the HT/HR strategy immediately revealed that RT29 has a preference for 4-base pair (bp), A.T-rich sites (AATT) and a similar tolerance and affinity for three A-T-bp sites (such as ATTC) containing a G.C bp. On the basis of these selectivities, oligonucleotides were designed and the host-guest crystallographic method was used to generate diffraction quality crystals. Analysis of the resulting crystal structures revealed that the diphenyl ether moiety of RT29 undergoes conformational changes that allow it to adopt a crescent shape that now complements the minor groove structure. The presence of a G.C bp in the RT29 binding site of ATTC did not overly perturb its interaction with DNA-the compound adjusted to the nucleobases that were available through water-mediated interactions. Our analyses suggest that the HT/HR strategy may be used to expedite the screening of novel minor groove binding compounds leading to a direct, HR structural determination.