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33 pages, 6573 KiB

Open AccessReview

Stereoselective Synthesis of Flavonoids: A Brief Overview

by Ana Margarida Pereira, Honorina Cidade and Maria Elizabeth Tiritan

Molecules 2023, 28(1), 426; https://doi.org/10.3390/molecules28010426 - 3 Jan 2023

Cited by 21 | Viewed by 8310

Stereoselective synthesis has been emerging as a resourceful tool because it enables the obtaining of compounds with biological interest and high enantiomeric purity. Flavonoids are natural products with several biological activities. Owing to their biological potential and aiming to achieve enantiomerically pure forms, several methodologies of stereoselective synthesis have been implemented. Those approaches encompass stereoselective chalcone epoxidation, Sharpless asymmetric dihydroxylation, Mitsunobu reaction, and the cycloaddition of 1,4-benzoquinone. Chiral auxiliaries, organo-, organometallic, and biocatalysis, as well as the chiral pool approach were also employed with the goal of obtaining chiral bioactive flavonoids with a high enantiomeric ratio. Additionally, the employment of the Diels–Alder reaction based on the stereodivergent reaction on a racemic mixture strategy or using catalyst complexes to synthesise pure enantiomers of flavonoids was reported. Furthermore, biomimetic pathways displayed another approach as illustrated by the asymmetric coupling of 2-hydroxychalcones driven by visible light. Recently, an asymmetric transfer hydrogen-dynamic kinetic resolution was also applied to synthesise (R,R)-cis-alcohols which, in turn, would be used as building blocks for the stereoselective synthesis of flavonoids. Full article

(This article belongs to the Section Bioorganic Chemistry)

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13 pages, 2114 KiB

Open AccessArticle

Identification of Chiral-Specific Carbon Nanotube Binding Peptides Using a Modified Biopanning Method

by Rachel Krabacher, Steve Kim, Yen Ngo, Joseph Slocik, Christina Harsch and Rajesh Naik

Chemosensors 2021, 9(9), 245; https://doi.org/10.3390/chemosensors9090245 - 1 Sep 2021

Cited by 2 | Viewed by 2685

Abstract

Peptides can recognize and selectively bind to a wide variety of materials dependent on both their surface properties and the environment. Biopanning with phage or cell peptide display libraries can identify material-specific binding peptides. However, the limitations with sequence diversity of traditional bacteriophage (phage) display libraries and loss of unique phage clones during the amplification cycles results in a smaller pool of peptide sequences identified. False positive sequences tend to emerge during the biopanning process due to highly proliferating, yet nonspecific, phages. In order to overcome this limitation of traditional biopanning methodology, a modified method using high-throughput next generation sequencing (HTS) was tested to select for unique peptides specific to two types of single wall carbon nanotube (SWNTs) sources with varying diameter distribution and chirality. Here, the process, analysis, and characterization of peptide sequences identified using the modified method is further described and compared to a peptide identified in literature using the traditional method. Selected sequences from this study were incorporated in a SWNT dispersion experiment to probe their selectivity to the nanotube diameter. We show that NHTS can uncover unique binding sequences that might have otherwise been lost during the traditional biopanning method. Full article

(This article belongs to the Special Issue Nanomaterials Synthesis for Both Sensors and Environmental Applications)

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10 pages, 2816 KiB

Open AccessArticle

Scalable Preparation of Enantioenriched (S)-5-methylhept-2-en-4-one. Synthesis and Aroma Properties of Achiral Analogues Thereof

by Eva Puchľová, Michal Dendys, Ivan Špánik and Peter Szolcsányi

Molecules 2019, 24(24), 4497; https://doi.org/10.3390/molecules24244497 - 8 Dec 2019

Cited by 1 | Viewed by 4764

Abstract

(S)-5-Methylhept-2-en-4-one is a key flavour compound in hazelnuts. We have performed its chiral-pool-based chemoenzymatic synthesis with 39% overall yield (73% ee). The four-step aldol-based sequence avoids the use of highly reactive and/or toxic reagents, does not require anhydrous conditions and uses only distillation as the purification method. Thus, such methodology represents a green and scalable alternative to only two stereoselective approaches towards this natural product known so far. In addition, we have designed and prepared a set of new (di)enones as achiral synthetic analogues of the title compound. The results of their sensory analyses clearly show that relatively minor structural changes of the natural molecule significantly alter its olfactory properties. Thus, simple (poly)methylation completely changes the original hazelnut aroma of (S)-5-methylhept-2-en-4-one and shifts the odour of its analogues to eucalyptus, menthol, camphor, and sweet aroma. Full article

(This article belongs to the Special Issue New Insights in Diversity Oriented Synthesis)

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10 pages, 307 KiB

Open AccessArticle

Asymmetric Synthesis of 4,1-Benzoxazepine-2,5-Diones — Effect of the Halogen of (2S)-α-Haloacids

by Syeda Laila Rubab, Bushra Nisar, Abdul Rauf Raza, Nisar Ullah and Muhammad Nawaz Tahir

Molecules 2014, 19(1), 139-148; https://doi.org/10.3390/molecules19010139 - 23 Dec 2013

Cited by 14 | Viewed by 6866

Abstract

Novel chiral 4,1-benzoxazepine-2,5-diones have been unusually synthesized in a single step by exploiting the chiral pool methodology. Substituted anthranilic acids afford N-acylanthranilic acids and (3R)-3-alkyl-4,1-benzoxazepines-2,5-dione upon coupling with α-chloroacids or α-bromoacids, respectively. Full article

(This article belongs to the Section Organic Chemistry)

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52 pages, 320 KiB

Open AccessReview

Muscarinic Receptor Agonists and Antagonists

by Kenneth J. Broadley and David R. Kelly

Molecules 2001, 6(3), 142-193; https://doi.org/10.3390/60300142 - 28 Feb 2001

Cited by 87 | Viewed by 30113

Abstract

A comprehensive review of pharmacological and medical aspects of the muscarinic class of acetylcholine agonists and antagonists is presented. The therapeutic benefits of achieving receptor subtype selectivity are outlined and applications in the treatment of Alzheimer’s disease are discussed. A selection of chemical routes are described, which illustrate contemporary methodology for the synthesis of chiral medicinal compounds (asymmetric synthesis, chiral pool, enzymes). Routes to bicyclic intrannular amines and intramolecular Diels-Alder reactions are highlighted. Full article

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