Synthesis of aza polycyclic compounds derived from pyrrolidine, indolizidine, and indole via intramolecular Diels-Alder cycloadditions of neutral 2-azadienes

A method for the preparation of novel oxaza and diaza polycyclic 9-oxa-4-azaphenanthrene, 5H-pyrido[2,3-a]pyrrolizine, 5H,6H-pyrido[3,2-g]indolizine, and 5H,6H-indeno[2,1-a]indole is described, based on tandem reactions: aza-Wittig reaction of N-vinylic phosphazenes with functionalized aldehydes and an intramolecular aza-Diels-Alder reaction.     

Another look at the degree‐Kirchhoff index

Let G be an arbitrary graph with vertex set {1,2, …,N} and degrees d_i ≤ D, for fixed D and all i, then for the index R′(G) = ∑_{i < j}d_id_jR_ij we show that We also show that the minimum of R′(G) over all N‐vertex graphs is attained for the star graph and its value is 2N² ? 5N + 3. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Homochirality and chemical evolution: new vistas and reflections on recent models

This report revises and scrutinizes recent arguments, theories, and hypotheses related to the emergence of homochirality. Since the whole treatment would involve multiple and varied scenarios, emphasis is put only on some processes, believed (or claimed) to be prebiotically credible. A particular purpose is to introduce less-travelled paths in which enantioenrichment does not emerge from amplification mechanisms. Some food for thought is provided in an attempt to reduce the gap between existing abiotic hypotheses and the more elusive and conjecturable biotic proposals. A series of novel models have been suggested to reconcile and incorporate chirogenesis into chemical evolution fueled by prebiotic building blocks. All in all, we want to offer new vistas into a never-ending pursuit in the hope that the present considerations will elicit further stimulus, analysis, and experiments in various domains.     

Ugi Reaction on α-Phosphorated Ketimines for the Synthesis of Tetrasubstituted α-Aminophosphonates and Their Applications as Antiproliferative Agents

An Ugi three-component reaction using preformed α-phosphorated N-tosyl ketimines with different isocyanides in the presence of a carboxylic acid affords tetrasubstituted α-aminophosphonates. Due to the high steric hindrance, the expected acylated amines undergo a spontaneous elimination of the acyl group. The reaction is applicable to α-aryl ketimines bearing a number of substituents and several isocyanides. In addition, the densely substituted α-aminophosphonate substrates showed in vitro cytotoxicity, inhibiting the growth of carcinoma human tumor cell line A549 (carcinomic human alveolar basal epithelial cell).     

Directions of uniform rotundity in direct sums of normed spaces

Let {(X_i,|| · || _i)}_{i ? I},\{(X_i,\left \| {\cdot } \right \| _{i})\}_{i\in I}, be an arbitrary family of normed spaces and let (E,|| · || _E)(E,\left \| {\cdot } \right \| _{E}) be a monotonic normed space of real functions on the set I that is an ideal in \Bbb R^I{\Bbb R}^I. We prove a sufficient condition for the direct sum space E(X_i) to be uniformly rotund in a direction. We show that this condition is also necessary for E=l_￥E=\ell _{\infty }, and it is not necessary for E=l₁E=\ell _1. When E is either uniformly rotund in every direction and has compact order intervals, or weakly uniformly rotund respect to its evaluation functionals, we reestablish as a corollary the result that reads: E(X_i)E(X_i) is uniformly rotund in every direction if and only if so are all the X_i.     

Novel Oxime Synthesized from a Natural Product of Senecio nutans SCh. Bip. (Asteraceae) Enhances Vascular Relaxation in Rats by an Endothelium-Independent Mechanism

Senecio nutans Sch. Bip. and its constituents are reported to have antihypertensive effects. We isolated metabolite–1, a natural compound from S. nutans (4-hydroxy-3-(isopenten-2-yl)-acetophenone), and synthesized novel oxime – 1 (4-hydroxy-3-(isopenten-2-yl)-acetophenoxime) to evaluate their effect on vascular reactivity. Compounds were purified (metabolite–1) or synthetized (oxime–1) and characterized using IR and NMR spectroscopy and Heteronuclear Multiple Quantum Coherence (HMQC). Using pharmacological agents such as phenylephrine (PE) and KCl (enhancing contraction), acetylcholine (ACh), L-NAME (nitric oxide (NO) and endothelial function), Bay K8644-induced Ca_V1.2 channel (calcium channel modulator), and isolated aortic rings in an organ bath setup, the possible mechanisms of vascular action were determined. Pre-incubation of aortic rings with 10⁻⁵ M oxime–1 significantly (p < 0.001) decreased the contractile response to 30 mM KCl. EC₅₀ to KCl significantly (p < 0.01) increased in the presence of oxime–1 (37.72 ± 2.10 mM) compared to that obtained under control conditions (22.37 ± 1.40 mM). Oxime–1 significantly reduced (p < 0.001) the contractile response to different concentrations of PE (10⁻⁷ to 10⁻⁵ M) by a mechanism that decreases Cav1.2-mediated Ca²⁺ influx from the extracellular space and reduces Ca²⁺ release from intracellular stores. At a submaximal concentration (10⁻⁵ M), oxime–1 caused a significant relaxation in rat aorta even without vascular endothelium or after pre-incubate the tissue with L-NAME. Oxime–1 decreases the contractile response to PE by blunting the release of Ca²⁺ from intracellular stores and blocking of Ca²⁺ influx by channels. Metabolite–1 reduces the contractile response to KCl, apparently by reducing the plasma membrane depolarization and Ca²⁺ influx from the extracellular space. These acetophenone derivates from S. nutans (metabolite–1 and oxime–1) cause vasorelaxation through pathways involving an increase of the endothelial NO generation or a higher bioavailability, further highlighting that structural modification of naturally occurring metabolites can enhance their intended pharmacological functions.     

A Novel and Adaptive Angle Diversity-Based Receiver for 6G Underground Mining VLC Systems

Visible light communication (VLC) is considered an enabling technology for future 6G wireless systems. Among the many applications in which VLC systems are used, one of them is harsh environments such as Underground Mining (UM) tunnels. However, these environments are subject to degrading environmental and intrinsic challenges for optical links. Therefore, current research should focus on solutions to mitigate these problems and improve the performance of Underground Mining Visible Light Communication (UM-VLC) systems. In this context, this article presents a novel solution that involves an improvement to the Angle Diversity Receivers (ADRs) based on the adaptive orientation of the Photo-Diodes (PDs) in terms of the Received Signal Strength Ratio (RSSR) scheme. Specifically, this methodology is implemented in a hemidodecahedral ADR and evaluated in a simulated UM-VLC scenario. The performance of the proposed design is evaluated using metrics such as received power, user data rate, and bit error rate (BER). Furthermore, our approach is compared with state-of-the-art ADRs implemented with fixed PDs and with the Time of Arrival (ToA) reception method. An improvement of at least 60% in terms of the analyzed metrics compared to state-of-the-art solutions is obtained. Therefore, the numerical results demonstrate that the hemidodecahedral ADR, with adaptive orientation PDs, enhances the received optical signal. Furthermore, the proposed scheme improves the performance of the UM-VLC system due to its optimum adaptive angular positioning, which is completed according to the strongest optical received signal power. By improving the performance of the UM-VLC system, this novel method contributes to further consideration of VLC systems as potential and enabling technologies for future 6G deployments.