Application of Sugar Phosphonates for the Preparation of Higher Carbon Monosaccharides

ABSTRACT

Reaction of sugar derived phosphonates [Sug-C(O)CH₂P(O)(OMe)₂] with sugar aldehydes (Sug'-CHO) provides the higher enones of the general formula Sug-C(O)CH=CH-Sug' with the trans configuration of the double bond. The phosphonate method is superior to the previously used phosphorane methodology [Sug-C(O)CH=PPh₃ + Sug'-CHO] since sugar phosphonates can be prepared in much higher yields and are much more nucleophilic than corresponding phosphoranes. The sugar enones are reduced to appropriate allylic alcohols with zinc borohydride; the stereoselectivity of this process is >97:3 (with the D-glycero isomer predominating) when the carbonyl group is placed at the α-position to the sugar ring. CD spectroscopy was used for the determination of the configuration of higher sugar allylic alcohols.     

New Synthetic Methods for Nucleotide Analogues Based on H-Phosphonate Chemistry: A Progress Report

New synthetic methods, based on H-phosphonate chemistry, have been developed for functionalization of oligonucleotides and for the preparation of various nucleotide analogues bearing sulfur and selenium at the phosphorus center.     

Silica Phenyl Sulfonic Acid as a Solid Acid Heterogeneous Catalyst for Chemoselective Thioacetalization of Carbonyl Compounds and Dethioacetalization under Mild Conditions

Silica phenyl sulfonic acid (SPSA) is an effective catalyst for chemoselective thioacetalization of aldehydes in the presence of ketones under neutral conditions. In addition, a simple and an efficient procedure for deprotection of 1,3‐dithianes and 1,3‐dithiolanes of aromatic, aliphatic, and α,β‐unsaturated aldehydes and ketones in the solvent‐free to the corresponding parent carbonyl compounds was successfully carried out with SPSA in excellent yields.     

Thermodynamical Approach to the Longest Common Subsequence Problem

We introduce an interacting particle model in a random media and show that this particle process is equivalent to the Longest Common Subsequence (LCS) problem of two binary sequences. We derive a differential equation which links the mean LCS-curve to the average speed of the particles given their density and prove that the average speed of the particles and density converges uniformly on every scale which is somewhat larger than  . All three authors are grateful to SFB 701. M.V. is grateful to CNPq (304561/2006–1 and 471925/2006–3) and FAPESP (thematic grant 04/07276–2) for partial support.     

Elastic properties of multi-cracked composite materials

The problem of predicting the effective elastic properties of multi-cracked and/or composite materials is both fundamental in materials mechanics and of large technological impact. In this paper we develop a continuum elasticity model, based on the Eshelby theory and on the differential homogenization technique, for the effective elastic moduli of a fibro-reinforced system and we address it to elaborate an estimation of the average failure condition of such composites.     

Chiroptical Properties – Structure Relationship in Bicyclic Isoxazolidin‐5‐one Derivatives

The relationship between chiroptical properties of substituted bicyclic isoxazolidin‐5‐one derivatives and their molecular structures was investigated. The chromophoric system in isoxazolidinones was found to be nonplanar with a shallow pyramidal configuration at the N‐atom. The deviation from planarity can be attributed to the strain imposed by the bicyclic skeleton. Due to the nonplanarity, the isoxazolidinone system becomes inherently dissymmetric, which is supported by the high magnitude of the CD band occurring around 210 nm. In addition, the helicity of lactone moiety in investigated bicyclic isoxazolidinones is controlled by the absolute configuration at C(6). On this basis, a helicity rule correlating a positive (negative) helicity expressed by the OC(8) O(9) N(1) torsional angle with a positive (negative) sign of the CD band around 210 nm was formulated.     

Boosting COVID-19 Image Classification Using MobileNetV3 and Aquila Optimizer Algorithm

Currently, the world is still facing a COVID-19 (coronavirus disease 2019) classified as a highly infectious disease due to its rapid spreading. The shortage of X-ray machines may lead to critical situations and delay the diagnosis results, increasing the number of deaths. Therefore, the exploitation of deep learning (DL) and optimization algorithms can be advantageous in early diagnosis and COVID-19 detection. In this paper, we propose a framework for COVID-19 images classification using hybridization of DL and swarm-based algorithms. The MobileNetV3 is used as a backbone feature extraction to learn and extract relevant image representations as a DL model. As a swarm-based algorithm, the Aquila Optimizer (Aqu) is used as a feature selector to reduce the dimensionality of the image representations and improve the classification accuracy using only the most essential selected features. To validate the proposed framework, two datasets with X-ray and CT COVID-19 images are used. The obtained results from the experiments show a good performance of the proposed framework in terms of classification accuracy and dimensionality reduction during the feature extraction and selection phases. The Aqu feature selection algorithm achieves accuracy better than other methods in terms of performance metrics.     

Adler–Finch–Skea Anisotropic Solution in f ( $$\mathcal{G}$$ ) Gravity

In this paper, we develop anisotropic solution for spherically symmetric self-gravitating stellar object by employing Karmarkar embedding constraint in the framework of f($$\mathcal{G}$$) gravity. For this purpose, we use the mass and radius of three compact star models, i.e., Her X-1, SAX J 1808.4-3658, and 4U 1820-30 as well as smooth matching of spherical interior and Schwarzschild exterior spacetime geometries. The physical consistency and stability of the derived model is examined for these star models. We conclude that the resulting anisotropic model is physically viable as well as stable as it satisfies all the necessary requirements of the compact stellar objects.     

Prediction of in-plane elastic properties of graphene in the framework of first strain gradient theory

Meccanica - In the present study, the in-plane elastic stiffness coefficients of graphene within the framework of first strain gradient theory are calculated on the basis of an accurate molecular...