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Illustrated is the usefulness of keeping track of the directions of atomic orbitals in predicting the shapes of molecules. The application of this technique to all cumulenes and its use in the determination of aromaticity in cyclic systems is discussed. (KR)

A decision tree which can be used to help students determine the proper stereochemical relationship between two isomeric structures is presented. The proper use of this chart is discussed. (CW)

The construction of a model that is useful for teaching stereochemistry from a sealed empty envelope is described. Detailed steps with accompanying diagrams are given. (CW)

The construction of a model that is useful for teaching stereochemistry from two sealed empty envelopes is described. Detailed steps with accompanying diagrams are given. (CW)

This article presents a thorough examination of research on the onion lachrymatory factor (LF), covering aspects such as its structural determination, confirmation of stereochemistry, formation pathways, analytical methods, and its impact on onion flavor. Identified as the onion LF, propanethial S-oxide primarily adopts a (Z)-configuration and is generated through the enzymatic breakdown of its precursor, (+)-S-(E)-1-propenyl-L-cysteine S-oxide, with alliinase serving as the catalyst. Following this, an isomerization process takes place involving an intermediate compound, (E)-1-propenesulfenic acid, catalyzed by lachrymatory factor synthase. To address challenges in conventional gas chromatography (GC) analysis posed by high temperatures, alternative methods such as UV spectroscopy, chemical derivatization, GC with cold injection, high-performance liquid chromatography, direct analysis in real-time mass spectrometry, proton-transfer reaction-mass spectrometry, and secondary electrospray ionization high-resolution orbitrap mass spectrometry have been employed for qualitative and quantitative LF analysis. Beyond its tear-inducing properties, LF significantly contributes to the distinctive onion flavor. This review is crucial for advancing our understanding of the onion LF and sulfur-containing flavor components in the Allium vegetable family. It helps for improving the flavor of onions and refining various onion varieties. [ABSTRACT FROM AUTHOR]

A base-catalyzed O-phosphorylation of aldehyde/ketone with RP-menthyl phenylphosphinate afforded phosphonates. The mechanism was proposed as an intermolecular SN@P reaction of α-hydroxy phosphinate. In an intermediate, the C–P bond was transferred from the equatorial to axial position via Berry pseudorotation, and then was cleaved with the leaving of a carbon anion. The P-retention and C-racemization could be satisfactorily explained by the mechanism. [ABSTRACT FROM AUTHOR]

The stereochemistry of shape‐persistent molecular cages, particularly those resembling prisms, exerts significant influence on their application‐specific functionalities. Although methods exist for fabricating inherently chiral prism‐like cages, strategies for catalytic asymmetric synthesis of these structures in a diversity‐oriented fashion remain unexplored. Herein, we introduce an unprecedented organocatalytic desymmetrization approach for the generation of inherently chiral prism‐like cages via phosphonium‐containing foldamer‐catalyzed SNAr reactions. This methodology establishes a topological connection, enabling the facile assembly of a wide range of versatile stereogenic‐at‐cage building blocks possessing two highly modifiable groups. Furthermore, subsequent stereospecific transformations of the remaining chlorides and/or ethers afford convenient access to numerous functionally relevant chiral‐at‐cage molecules. [ABSTRACT FROM AUTHOR]

Cyclopentene rings possessing a chiral quaternary center are important structural motifs found in various natural products. In this work, we disclose expedient and efficient access to this class of synthetically valuable structures via highly enantioselective desymmetrization of prochiral propargylic alcohols. The efficient chirality induction in this asymmetric gold catalysis is achieved via two‐point bindings between a gold catalyst featuring a bifunctional phosphine ligand and the substrate homopropargylic alcohol moiety—an H‐bonding interaction between the substrate HO group and a ligand phosphine oxide moiety and the gold‐alkyne complexation. The propargylic alcohol substrates can be prepared readily via propargylation of enoate and ketone precursors. In addition to monocyclic cyclopentenes, spirocyclic and bicyclic ones are formed with additional neighboring chiral centers of flexible stereochemistry in addition to the quaternary center. This work represents rare gold‐catalyzed highly enantioselective cycloisomerization of 1,5‐enynes. Density functional theory (DFT) calculations support the chirality induction model and suggest that the rate acceleration enabled by the bifunctional ligand can be attributed to a facilitated protodeauration step at the end of the catalysis. [ABSTRACT FROM AUTHOR]

A strategy for the photosensitized [2+2]‐cycloaddition between styrenyl dihaloboranes and unactivated allylamines to access cyclobutylboronates with control of stereochemistry and regiochemistry is presented. The success of the reaction relies on the temporary coordination between in situ generated dihaloboranes and amines under mild reaction conditions. In addition, cyclobutanes with varying substitution patterns have been prepared using N‐heterocycles as directing group. Manipulation of the C−B bond allows for the synthesis of a diverse class of cyclobutanes from simple precursors. Moreover, these reactions lead to the synthesis of complex amines and heteroaromatic compounds, which have significant utility in medicinal chemistry. Finally, a dearomative [4+2]‐cycloaddition of naphthalenes using a boron‐enabled temporary tethering strategy has also been uncovered to synthesize complex 3‐dimensional borylated building blocks. [ABSTRACT FROM AUTHOR]

Zonisamide is a heterocyclic sulfonamide widely employed as anticonvulsant. In this work, we report an efficient process for the preparation of zonisamide, obtained in a six‐step synthesis from phenyl salicylate with an overall 31 % yield. The key step is represented by a base‐promoted intramolecular rearrangement of a β‐ketosultone oxime, leading to the concomitant formation of the benzisoxazole ring and of the exocyclic sulfonic group. This intriguing transformation is investigated with a combination of analytical techniques (NMR, HRMS, PXRD), leading to a preliminary mechanistic proposal. [ABSTRACT FROM AUTHOR]

31P NMR spectroscopy is a consolidated tool for the characterization of organophosphorus compounds and, more recently, for reaction monitoring. The evolution of organic synthesis, mainly due to the combination of elaborated building blocks with enabling technologies, generated great challenges to understand and to optimize the synthetic methodologies. In this sense, 31P NMR experiments also became a routine technique for reaction monitoring, accessing products and side products yields, chiral recognition, kinetic data, intermediates, as well as basic organic parameters, such as acid‐base and hydrogen‐bonding. This review deals with these aspects demonstrating the essential role of the 31P NMR spectroscopy. The recent publications (the last ten years) will be explored, discussing the experiments of 31P NMR and the strategies accomplished to detect and/or quantify distinct organophosphorus molecules, approaching reaction mechanism, stability, stereochemistry, and the utility as a probe. [ABSTRACT FROM AUTHOR]

New nor-isomalabaricanic acids 1 and 2 were isolated from polar fractions of the EtOH extract of the Vietnamese sponge Rhabdastrella globostellata using a combination of column chromatography and reversed-phase HPLC. The chemical structures of the new compounds, which were called stellettins W (1) and X (2), were elucidated by analyzing data from NMR experiments and HR-ESI-MS spectra and by comparison with the structures of associated isolated metabolites. Stellettin W was the first isomalabaricane derivative with a 13,14-epoxide group in its structure. [ABSTRACT FROM AUTHOR]

Scientists are searching for reactive oxygen species, which have been associated with various health issues like heart problems, neurological disorders, inflammation, and aging. Salen complexes have proven to be effective in multiple oxidative stress situations and have been used as catalase and superoxide mimetics. To explore this further, three mixed complexes were synthesized using a Schiff base (salen) and a sugar (d-glucose) with Co(II), Ni(II), and Cu(II) ions. These complexes were then diagnosed by different analytical and spectral techniques. Stoichiometry, stereochemistry, some physical properties, and the method of bonding complexes were measured. Comparisons of the IR and 1HNMR spectra of the ligands with the complexes demonstrated the involvement of the azomethine group of the ligand in the chelation process. The mass spectra and TGA agree with the proposed formula of the complexes, and the conductivity and UV–Vis data supported the octahedral geometry of the complexes, and information was obtained from partial parameter calculations by molecular modeling. The metal complexes exhibited strong antimicrobial and antioxidant properties when compared to standard drugs. The like-superoxide and catalyst mimetic complexes were screened using DPPH ABTS, revealing their effectiveness. [ABSTRACT FROM AUTHOR]

The influence of stereochemistry on the mechanochemistry rate is studied using a new mechanophore based on a benzopinacol (BP) skeleton. Two sets of BP diastereomers, the meso R,S and the R,R/S,S were isolated, incorporated into the center of a poly(methyl acrylate), and their mechanical activation rate was measured in solution. Under mechanical stress, the central C−C bond in BP is cleaved, providing two independent benzophenone molecules with higher UV‐absorption coefficient at 254 nm. Monitoring the reaction rate spectroscopically indicates that the chiral R,R/S,S enantiomers react ~1.4 fold faster compared to the meso R,S diastereomer. In‐silico modeling indicates that a hydrogen bond between the syn hydroxyls in the R,R diastereomer becomes shorter with stress, reducing the maximal force required for C−C bond scission, while this bond is inexistent in the meso diastereomer, as the hydroxyl are anti to each other. Our results indicate that in polymer where free rotation around bonds is possible, non‐covalent interactions between backbone substituents, which are affected by relative stereochemistry, can play a fundamental role in the mechanochemical stability of the polymer. [ABSTRACT FROM AUTHOR]

Stereospecific alternating copolymerization of different chiral cyclic esters is one feasible approach to enrich the structural diversity of copolyesters and tailor their properties. However, dramatically different reactivities of different cyclic esters let a perfectly stereospecific alternating polymerization of these cyclic esters be a challenge, thus the catalyst is required to balance their reactivities. Herein, a remarkable enantiomorphic site effect on chain end control was discovered and successfully utilized to balance the reactivities of highly reactive S, S‐lactide (S, S‐LA) and low reactive R, R‐ethylglycolide (R, R‐EG)/R, R‐propylglycolide (R, R‐PG) during their heterospecific alternating copolymerization. The enantiomorphic site of R, R‐SalenAl complex can increase the relative reactivity of R, R‐EG/R, R‐PG and suppress that of S, S‐LA, then a perfectly alternating sequence of the copolymer of S, S‐LA and R, R‐EG/R, R‐PG can be achieved (Palt=0.96/0.91); inversely, using S, S‐SalenAl complex, the significant enantiomorphic site effect enlarges the reactivity difference of two monomers, the alternating level was just 0.70/0.68 even to 0.61. Poly(S, S‐LA‐alt‐R, R‐EG) with a high alternating regularity exhibits lower glass transition temperatures and a dramatically higher elongation at break (ϵB=449±51 % (Palt=0.96) vs ϵB=6±1% (Palt=0.70)). [ABSTRACT FROM AUTHOR]

Wax esters play critical roles in biological systems, serving functions from energy storage to chemical signaling. Their diversity is attributed to variations in alcohol and acyl chains, including their length, branching, and the stereochemistry of double bonds. Traditional analysis by mass spectrometry with collisional activations (CID, HCD) offers insights into acyl chain lengths and unsaturation level. Still, it falls short in pinpointing more nuanced structural features like the position of double bonds. As a solution, this study explores the application of 213-nm ultraviolet photodissociation (UVPD) for the detailed structural analysis of wax esters. It is shown that lithium adducts provide unique fragments as a result of Norrish and Norrish-Yang reactions at the ester moieties and photoinduced cleavages of double bonds. The product ions are useful for determining chain lengths and localizing double bonds. UVPD spectra of various wax esters are presented systematically, and the effect of activation time is discussed. The applicability of tandem mass spectrometry with UVPD is demonstrated for wax esters from natural sources. The UHPLC analysis of jojoba oil proves the compatibility of MS2 UVPD with the chromatography time scale, and a direct infusion is used to analyze wax esters from vernix caseosa. Data shows the potential of UVPD and its combination with CID or HCD in advancing our understanding of wax ester structures. [ABSTRACT FROM AUTHOR]

The stereochemistry of the uncatalyzed chlorolactonization of 4‐phenylpent‐4‐enoic acid at room temperature was examined to probe the reaction's intrinsic diastereoselectivities as a function of chlorenium ion donor, solvent polarity, and reactant concentration ranges. Kinetic studies using Variable Time Normalization Analysis (VTNA) revealed differing reaction orders for the syn and anti alkene addition processes. Aided and illustrated by quantum chemical modeling, this detailed mechanistic analysis of the substrate's intrinsic chlorolactonization reactions points to concerted AdE3‐type paths for both syn and anti additions. By illuminating the factors selecting for syn‐ vs anti‐addition paths, the results provide key reference points for future studies of stereocontrol in halofunctionalization reactions. [ABSTRACT FROM AUTHOR]

The GT99 domain of the membrane‐anchored WbbB glycosyltransferase (WbbBGT99) catalyzes the transfer of 3‐deoxy‐D‐manno‐oct‐2‐acid (β‐Kdo) to an O‐antigen saccharide acceptor with retention of stereochemistry. It has been proposed that the enzyme follows an unprecedented double‐displacement mechanism involving the formation of covalent adduct between the Kdo sugar and an active site residue (Asp232) that is properly oriented for nucleophilic attack. Here we use QM/MM metadynamics simulations on recently reported crystal structures to provide theoretical evidence for the formation of such adduct and unveil the atomic details of the chemical reaction. Our results support the interpretation made on the basis of X‐ray and mass spectrometry analyses. Moreover, we show that the formation of the β‐Kdo‐Asp232 adduct is assisted by the sugar Kdo‐carboxylate group, which mediates the transfer of a proton from Asp232 towards the phosphate leaving group, alleviating electrostatic repulsion between the two negatively charged carboxylate groups. The computed mechanism also explains why His265, previously proposed to act as a general acid, does not impair catalysis. This mechanism can be extended to other related enzymes, expanding the repertoire of GT mechanisms in Nature. [ABSTRACT FROM AUTHOR]

Four new lactones, including hypomonacid A (1) and hypomonone A–C (4–6), as well as nine known polyketide analogues (2–3 and 7–13) were obtained from endophytic fungus Hypomontagnella sp. TX-09 derived from Santalum album. Their planar structures were extensively established by analysing HRESIMS and NMR spectroscopic data. Stereochemistry of new compounds was determined by X-ray diffraction analysis and modified Mosher’s method in combination with quantum-chemical ECD calculation. In addition, compounds 1 and 2 showed anti-inflammatory activity by inhibition of lipopolysaccharide (LPS)-induced NO production in RAW264.7 cells at 50 μmol/L without cytotoxicity. Among them, compound 1 inhibited the production of LPS-stimulated inflammation in mouse macrophage RAW264.7 cells by suppressing the expression of iNOS, TNF-α, IL-1β, and IL-6. [ABSTRACT FROM AUTHOR]

This study investigated the applicability of fluorescent chromophores for exciton‐coupled circular dichroism (ECCD) exploiting fluorescence‐detected circular dichroism (FDCD). FDCD had been previously reported useful in allowing the sensitive detection of ECCD in favorable conditions. However, fluorescence detection may prevent applications of the combined method especially when solutions are polarized in emission. Even without polarization of emission, FDCD deviates from circular dichroism (CD) in some cases when the fluorophore of interest interacts with nonfluorescent chromophore. Herein, it was confirmed that employing 6‐methoxy‐2‐naphthoate always yielded interpretable exciton‐coupled FDCD spectra even when coupling with nonfluorescent p‐substituted benzoates. The 6‐methoxy‐2‐naphthoate chromophore (6‐MN) is prescribed in special cases when only a small amount of sample is available for determining the absolute stereochemistry by the CD exciton chirality method observed by FDCD. [ABSTRACT FROM AUTHOR]

The interface between chirality and crystallization and mechanisms by which chirality propagates from crystal structure to overall shapes of crystals are a key topic in crystallography and stereochemistry. Recently, nanocrystals attracted attention as useful model systems for this kind of studies. Specifically, tellurium nanocrystals have been used to address questions on relations between chirality of the crystal structure and that of the overall shape. Previous studies of this system did not offer a comprehensive shape diagram and did not survey all the factors that determine whether shapes that form are chiral or not. In the current report, the distribution of chiral and achiral shapes in this system as a function of different physical and chemical parameters is determined experimentally. It is shown that there is a common logic for formation of chiral shapes, that is, growth at conditions that favor the growth of more reactive nuclei. The experiments also reveal more morphologies than previously encountered, suggesting that a systematic change of conditions in nanocrystal growth is key for identifying morphologies that exist only in a narrow range of conditions. [ABSTRACT FROM AUTHOR]

Bacterial infection remains a major complication answering for the failures of various implantable medical devices. Tremendous extraordinary advances have been published in the design and synthesis of antimicrobial materials addressing this issue; however, the clinical translation has largely been blocked due to the challenge of balancing the efficacy and safety of these materials. Here, calcium's biochemical features, natural roles in pathogens and the immune systems, and advanced uses in infection medications are illuminated, showing calcium is a promising target for developing implantable devices with less infection tendency. The paper gives a historical overview of biomedical uses of calcium and summarizes calcium's merits in coordination, hydration, ionization, and stereochemistry for acting as a structural former or trigger in biological systems. It focuses on the involvement of calcium in pathogens' integrity, motility, and metabolism maintenance, outlining the potential antimicrobial targets for calcium. It addresses calcium's uses in the immune systems that the authors can learn from for antimicrobial synthesis. Additionally, the advances in calcium's uses in infection medications are highlighted to sketch the future directions for developing implantable antimicrobial materials. In conclusion, calcium is at the nexus of antimicrobial defense, and future works on taking advantage of calcium in antimicrobial developments are promising in clinical translation. [ABSTRACT FROM AUTHOR]

Enantioenriched 2‐substituted piperidines are very important unit for drug discovery. Ready access to a wide range of such compounds, decorated with functional handles at 2‐position with stereo‐defined centre significantly enhance the quality and diversity of chemical libraries for screening of drug discovery. The ability to control the stereochemistry of piperidine at the 2‐position remains an area of interest in organic synthesis to allow the development of novel, structurally diverse 3D molecules. Among the various ways to obtain enantioenriched 2‐substituted piperidines, asymmetric hydrogenation is widely studied. Asymmetric synthesis, Kinetic resolution, and chiral pool synthesis methodologies are also important ways to obtain the enantioenriched 2‐substituted piperidines. This review article summarized the main four ways to achieve particularly the enantioenriched substituted piperidines only at 2‐position considering the chemical routes, excluding the biocatalytic approach. 1. Introduction 2.1 Asymmetric Hydrogenation of 2‐substituted Pyridines 2.2 Asymmetric Synthesis 2.3. Kinetic resolution of racemic 2‐substituted Piperidine derivatives 2.4. Chiral pool synthesis 3. Conclusions & outlook [ABSTRACT FROM AUTHOR]

The document is the contents list for an issue of the journal Chemical Communications. It includes various articles and communications on topics such as biocatalysis, stereochemistry of natural products, enzyme design, coordination-cage based catalysis, and more. The journal is published by The Royal Society of Chemistry, a leading chemistry community. The document provides a glimpse into the research and advancements in the field of chemistry. [Extracted from the article]

Secondary metabolites from land and marine (micro)organisms have been at the focus of the drug discovery process for many years. One of the reasons for this success is nature's incredible ability to create intricate molecular scaffolds. Such structural richness, however, makes the structural elucidation, and the absolute configuration assignment in particular, a challenging process. Vibrational circular dichroism (VCD) has emerged as one of the most reliable and versatile methods to unambiguously assign both the absolute configuration and conformations of chiral molecules in solution. Although VCD is no longer a curiosity in the field of molecular spectroscopy after 50 years since its first report, it is still underutilized by natural product chemists worldwide for varying reasons. Herein, we highlight the evolution of the application of VCD to natural product chemistry, focusing on its strengths as well as points that still need improvement. General guidelines for the correct application of VCD to stereochemical studies are also provided. [ABSTRACT FROM AUTHOR]

We report the synthesis of alkyl 1,2,6‐triaryl‐4‐arylaminopiperidine‐3‐ene‐3‐carboxylates in acceptable yields (42%–71%) and high trans‐diastereoselectivity (69:31 to 100:0) through a one‐pot multicomponent reaction of aromatic aldehydes, aromatic amines, and β‐ketoesters catalyzed by phosphomolybdic acid in methanol at room temperature. The structure and stereochemistry of tetrahydropyridines were confirmed by X‐ray crystallography. This protocol stands out for its operational simplicity, the use of an inexpensive and commercially available heteropolyacid catalyst, low catalyst loading, and purification via simple filtration, resulting in acceptable yields and high diastereoselectivity. [ABSTRACT FROM AUTHOR]

Human serum albumin (HSA) is a multifunctional circulatory protein essential for many physiological processes including oncotic pressure maintenance, ligand/drug binding and transport, antioxidant activity, etc. Abnormal HSA levels in biological fluids have been reported in a variety of clinical disorders, making it a potential biomarker for early diagnosis. Low serum albumin levels have been linked to increased long- and short-term mortality rates in ICU patients. Therefore, quantifying HSA in biofluids such as serum and urine offers a convenient approach for the early identification of underlying clinical conditions and assessing the risk factors. Herein, we report a series of fluorescent 1,4-dihydropyridine (DHP) derivatives for the detection and quantification of HSA in biofluids. Their response towards HSA can be tuned by varying the substituents at the C-4 and the N-1 of the DHP ring. Depending on the nature of the substituents, they generated either a turn-on or ratiometric response with a LoD in low nanomolar or subnanomolar levels. A pair of enantiomers obtained by introducing a chiral center on the N-substituents highlighted the importance of stereochemistry in HSA-ligand interactions. Quantification of HSA in complex biofluids, such as blood serum and urine, was also accomplished using these probes. The high selectivity of some of the probes towards HSA over the homologous BSA allowed the discrimination of these two proteins. The preferred binding location of the probes was the hemin binding site and the detection mechanism was identified as the restriction of intramolecular rotation. Additionally, a prototype of a smartphone-integrated point-of-care device was also fabricated to demonstrate the feasibility of utilizing these probes in clinical settings. [ABSTRACT FROM AUTHOR]

Human 15‐lipoxygenase‐1 (15‐LOX‐1) is a key enzyme that possesses an important role in (neuro)inflammatory diseases. The pocket of the enzyme plays the role of a chiral catalyst, and therefore chirality could be an important component for the design of effective enzyme inhibitors. To advance our knowledge on this concept, we developed a library of the identified chiral 15‐LOX‐1 inhibitors and applied cheminformatic tools. Our analysis highlighted specific structural elements, which we integrated them in small molecules, and employed them as "smart" tools to effectively navigate the chemical space of previously unexplored regions. To this purpose, we utilized the marine derived natural product phosphoeleganin (PE) among with a small library of synthetic fragment derivatives, including a certain degree of stereochemical diversity. Enzyme inhibition/kinetic and molecular modelling studies has been performed in order to characterize structurally novel PE‐based inhibitors, which proved to present a different type of inhibition with low micromolar potency, according to their structural features. We demonstrate that different warheads work as anchor, and either guide specific stereochemistry, or causing a time‐depended inhibition. Finally, we prove that the positioning of the chiral substituents or/and the favorable stereochemistry can be crucial, as it can lead from active to completely inactive compounds. [ABSTRACT FROM AUTHOR]

The study introduces a previously unidentified method for amide bond formation that addresses several limitations of conventional approaches. It uses the β-silyl alkynoate molecule, where the alkynyl group activates the ester for efficient amide formation, while the bulky TIPS (triisopropylsilane) group prevents unwanted 1,4-addition reactions. This approach exhibits high chemoselectivity for amines, making the method compatible with a wide range of substrates, including secondary amines, and targets the specific ε-amino group of lysine among the native amino ester's derivatives. It maintains stereochemistry during amide bond formation and TIPS group removal, allowing a versatile platform for postsynthesis modifications such as click reactions and peptide-drug conjugations. These advancements hold substantial promise for pharmaceutical development and peptide engineering, opening avenues for research applications. [ABSTRACT FROM AUTHOR]

ABSTRACT This study highlights the synergistic interplay between a Lewis acidic copper ion and a dissociated ligand from Cu(triNHC) complexes in the synthesis of cyclic carbonates from CO2 and epoxy compounds. The reactions were found to proceed efficiently under Cu(triNHC)‐catalyzed conditions, yielding significant quantities of cyclic carbonates across various epoxy substrates encompassing amine, sulfide, and ether functionalities. Stereochemical analyses underscore a pronounced propensity for retaining the stereochemistry of epoxy compounds in the resultant carbonates. This suggests a mechanism involving double inversion of stereochemistry during the reaction, which comprises catalyst‐mediated epoxide ring opening, subsequent CO2 addition, and carbonate ring closing. These findings align with established mechanisms for CO2 fixation reactions, shedding light on the intricate pathways underlying this catalytic process. [ABSTRACT FROM AUTHOR]

The catalytic decarboxylation of malonic acid half oxy‐ and thioesters, β‐ketocarboxylic acids, and their related compounds is a straightforward, powerful, and atom‐economical strategy for the in‐situ formation of enolates, which are important and well‐studied synthons for various functional materials and natural products. This strategy, inspired by the biosynthesis of polyketides and fatty acids, is an attractive method for synthesizing enols from carboxyl compounds with less reactive α‐hydrogen atoms under mild conditions. In addition, these reactions are environmentally friendly and are of great interest to chemists because the use of a stoichiometric amount of base can be avoided, and the only byproduct is CO2. Thus far, remarkable progress has been made, especially in the field of organocatalytic enantioselective decarboxylation reactions, allowing for the stereocontrolled formation of new C−H, C−C, C−heteroatom, and C−X bonds. This review provides a comprehensive overview of organocatalytic enantioselective decarboxylation reactions and highlights the significant progress made since 2020. In particular, it focuses on chiral catalyst systems and transition states as key parameters for decarboxylation reactions. [ABSTRACT FROM AUTHOR]

This paper describes a concise, asymmetric and stereodivergent total synthesis of tacaman alkaloids. A key step in this synthesis is the biocatalytic Baeyer–Villiger oxidation of cyclohexanone, which was developed to produce seven‐membered lactones and establish the required stereochemistry at the C14 position (92 % yield, 99 % ee, 500 mg scale). Cis‐ and trans‐tetracyclic indoloquinolizidine scaffolds were rapidly synthesized through an acid‐triggered, tunable acyl‐Pictet–Spengler type cyclization cascade, serving as the pivotal reaction for building the alkaloid skeleton. Computational results revealed that hydrogen bonding was crucial in stabilizing intermediates and inducing different addition reactions during the acyl‐Pictet–Spengler cyclization cascade. By strategically using these two reactions and the late‐stage diversification of the functionalized indoloquinolizidine core, the asymmetric total syntheses of eight tacaman alkaloids were achieved. This study may potentially advance research related to the medicinal chemistry of tacaman alkaloids. [ABSTRACT FROM AUTHOR]

Chemical reactions conducted in the solid phase (specifically, crystalline) are much less numerous than solution reactions, primarily due to reduced motion, flexibility, and reactivity. The main advantage of crystalline‐state transformations is that reactant molecules can be designed to self‐assemble into specific spatial arrangements, often leading to high control over product regiochemistry and/or stereochemistry. In crystalline‐phase transformations, typically only one type of reaction occurs, and a sacrificial template molecule is frequently used to facilitate self‐assembly, similar to a catalyst or enzyme. Here, we demonstrate the first system designed to undergo two chemically unique and orthogonal cycloaddition reactions simultaneously within a single crystalline solid. Well‐controlled supramolecular self‐assembly of two molecules containing different reactive moieties affords orthogonal reactivity without use of a sacrificial template. Using only UV light, the simultaneous [2+2] and [4+4] cycloadditions are achieved regiospecifically, stereospecifically, and products are obtained in high yield, whereas a simultaneous solution‐state reaction affords a mixture of isomers in low yield. Application of dually‐reactive systems toward (supra)molecular solar thermal storage materials is also discussed. This work demonstrates fundamental chemical approaches for orthogonal reactivity in the crystalline state and highlights the complexity and reversibility that can be achieved with supramolecular design. [ABSTRACT FROM AUTHOR]

Numerous zinc complexes based on N‐ and O‐donor Schiff‐base ligands have shown great promise in the ring‐opening polymerization (ROP) of lactides, which are cyclic dimers of lactic acid, to produce poly(lactic acid) (PLA). This is primarily because zinc is a borderline metal, making it non‐cytotoxic, inexpensive, abundant, biocompatible, and environmentally safe. Additionally, Schiff‐based ligands offer stability, stereoselectivity, desirable electronic and steric environments, and resistance to impurities. As a result, zinc complexes are easy to synthesize, colourless, have high reactivity and solubility in organic solvents, and are manageable under typical circumstances. Furthermore, these complexes are free to adopt a variety of coordination numbers since zinc does not have ligand field stabilization energy (LFSC). Zinc complexes possess high catalytic activity due to their distinctive properties, including high Lewis acidity, high electron transfer ability, stability concerning the reactive intermediate, and the ability to monitor polymerization by nuclear magnetic resonance (NMR) spectroscopy. Moreover, these complexes also have reasonable control over stereochemistry, number‐average molecular weight (Mn), and dispersity index (Ð). These advantages make it possible to produce colourless PLA with a high yield, high molecular weight, and narrow dispersity index in bulk and solvent‐based conditions. [ABSTRACT FROM AUTHOR]

Cancer is a leading cause of death worldwide, accounting for about one among six deaths, so the quest for new and improved therapies is of crucial importance. The discovery of cisplatin as an anticancer agent has paved the way for the development of other metal-based therapeutic agents and Re(I)-based candidates have been recently found to show promising results. It is known as well that chirality plays a central role in the interactions of metal-based drugs with intrinsically chiral biomolecules such as membrane transport proteins or DNA. To further exploit this property, we have developed a series of diastereomeric dinuclear Re(I) complexes with chiral ligands containing pinene-bipyridine units. These complexes offer unique insights into the relation between stereochemistry and biological activity. Single-crystal X-ray diffraction studies, spectroscopic analysis, including UV-Vis and circular dichroism (CD), confirmed the chiral structures of these complexes. Biological activity assessments were carried out against various cancer cell lines, with a particular focus on breast and colon cancer. The diastereomers exhibited distinct anticancer activities, with some displaying promising results. Notably, one diastereomer showed exceptional cytotoxicity against HCT116 and MCF-7 cancer cells. This research underscores the significance of chirality in the design of novel anticancer agents, providing insights into the potential of dinuclear Re(I) complexes as effective candidates for cancer treatment. [ABSTRACT FROM AUTHOR]

The precise synthesis of chiral polymers remains a significant challenge in polymer chemistry, particularly for applications in advanced biomedical and electronic materials. The development of degradable polymers is important for eco‐friendly and advanced materials. Here, we introduce a stereo‐controlled degradable polymer via cascade enyne metathesis polymerization and enantioselective acetal synthesis through Pd‐catalyzed asymmetric hydroamination. This approach allows for the creation of chiral acetal‐based polymers with controlled stereochemistry and degradability, highlighting their potential for use in drug delivery and electronic applications. This concept article reviews the background, development, and potential applications of these stereo‐controlled degradable polymers. [ABSTRACT FROM AUTHOR]

We previously described NMR based fingerprint matching with peptide backbone resonances as a fast and reliable structural dereplication approach for Pseudomonas cyclic lipodepsipeptides (CLiPs). In combination with total synthesis of a small library of configurational CLiP congeners this also allows unambiguous determination of stereochemistry, facilitating structure‐activity relationship studies and enabling three‐dimensional structure determination. However, the on‐resin macrocycle formation in the synthetic workflow brings considerable burden and limits universal applicability. This drawback is here removed altogether by also transforming the native CLiP into a linearized analogue by controlled saponification of the ester bond. This eliminates the need for macrocycle formation, limiting the synthesis effort to linear peptide analogues. NMR fingerprints of such linear peptide analogues display a sufficiently distinctive chemical shift fingerprint to act as effective discriminators. The approach is developed using viscosin group CLiPs and subsequently demonstrated on putisolvin, leading to a structural revision, and tanniamide from Pseudomonas ekonensis COR58, a newly isolated lipododecapeptide that defines a new group characterized by a ten‐residue large macrocycle, the largest to date in the Pseudomonas CLiP portfolio. These examples demonstrate the effectiveness of the saponification‐ enhanced approach that broadens applicability of NMR fingerprint matching for the determination of the stereochemistry of CLiPs. [ABSTRACT FROM AUTHOR]

Synthesis of poison dart frog indolizidine alkaloids (−)‐209D, (−)‐209B and (−)‐223V were accomplished, with a common tricyclic lactone skeleton as the starting compound, in overall yields of 8.8 %, 5.5 %, and 5.2 %, respectively. The construction of the C7−C8 bond in the synthesis of 209D involves simple ring closure metathesis and hydrogenation reactions. However, in the synthesis of 209B and 223V, the C7−C8 bond and the stereochemistry of C8, is achieved through radical cyclization reactions controlled by allylic 1,3‐strain. Cleavage of the excess carbon on the C5 for all the related intermediates were done by Barton decarboxylation protocol. Reduction of the corresponding indolizidin‐3‐ones by LAH completed the total synthesis of these three target molecules. The quantum mechanics calculations were performed on α‐amidyl carbon radical intermediates to account for the observed diastereomeric ratio (~9 : 1) of the key Barton decarboxylation step. Ultimately, the synthesis of 3‐epi‐(−)‐223AB was accomplished in 51.6 % through the cuprate addition to the activated lactam of a late intermediate in the synthesis of (−)‐167B. [ABSTRACT FROM AUTHOR]

Diarylethenes are an important class of photoswitches that usually exist in interconvertible parallel (photoinert) and antiparallel (photochromic) conformational states. Recent research afforded sterically congested diarylethenes that exist as stable and separable configurational atropisomers. Rational manipulation of stereochemistry is a robust strategy for regulating diarylethene photochemistry. Here, we present a brief account of the conformer/atropisomer-dependent photochromism of diarylethene photoswitches, and we discuss a recent advance at the interface of diarylethene photochemistry and polymer mechanochemistry: our group recently introduced a mechanical approach for converting a parallel diarylbenzothiadiazole into its antiparallel configurational diastereomers, thereby turning on its photochromic reactivity. After mechanical activation, UV light changes the converted diarylethene molecule into a colored ring-closed form by a 6π-electrocyclization reaction that permits the visualization of the mechanical activation event. Besides the fundamentally new mechanism of converting a molecule into its configurational diastereomers through force–stereochemistry coupling, the conversion of atropisomer stereochemistry is a noncovalent process and features high mechanical reactivity in comparison to conventional mechanophores, which require covalent bond scission. This new type of configurational mechanophore holds promise for various applications, such as high-sensitivity stress sensing, lithography, and information storage. 1 Diarylethene Conformers and Atropisomers 2 Polymer Mechanochemistry and Configurational Mechanophores 3 Regulating the Stereochemistry and Reactivity of a Diarylethene Atropisomer with Mechanical Force 4 Summary and Future Outlook [ABSTRACT FROM AUTHOR]

A novel, industrially viable synthetic route to (+)‐biotin has been developed starting from L‐cysteine via the known key thiolactone intermediate. The route takes advantage of the in‐built stereochemistry of the cysteine starting material and the best features of the two current industrialized processes. The key transformations are the conversion of L‐cysteine into a hydantoin avoiding racemization followed by catalytic cyanation and thiolactonization to form the required thiolactone intermediate. This known intermediate can be readily further transformed into (+)‐biotin. [ABSTRACT FROM AUTHOR]

Chirality is traditionally a problematic subject for undergraduate students at the beginning of learning organic chemistry, yet it is of great importance in life sciences. If the initial introduction of chirality is conducted carelessly, students will face ambiguity through the rest of the course and education every time they come across chirality-related subjects. Although there are numerous methods for overcoming the problems of visualization of chiral molecules in 3D space, the connection of chirality with molecular changes like vibrations and conformations is usually not explained thoroughly. In this work, chirality is introduced on dynamic (real) systems, because students from the start should perceive molecules in their natural state of constant motion and change. Apart from the proposition of the lecture concept, exercises are also included, that employ free and readily available software. [ABSTRACT FROM AUTHOR]

The hydrolase-catalyzed kinetic resolution of fluorinated racemates of 3-arylcarboxylic acids is described. Hydrolysis of ethyl esters of fluorinated acids by esterases and hydrolases in all cases resulted in the formation of hydrolyzed (S)-carboxylic acids and unreacted (R)-esters in high yields and high enantiomeric purity. The influence of separation conditions on the efficiency and enantioselectivity of biocatalytic conversion was also studied. The reactions were carried out under normal conditions (stirring with a magnetic stirrer at room temperature) and microwave irradiation in the presence of hydrolases. Amano PS showed excellent selectivity and good yields in the hydrolysis of fluorinated aromatic compounds. The absolute configuration of the resulting compounds was based on biokinetic studies and the use of chiral HPLC. A molecular modeling of the kinetic resolution of carboxylic acid esters was carried out. [ABSTRACT FROM AUTHOR]

A series of five novel copper(II) complexes with imidazole derivatives having general core Cu(R-Im)2(Macr)2 (Macr = methacrylate anion; R-Im = 2-methylimidazole/2-MeIm, 4-methylimidazole/4-MeIm, 2-ethylimidazole/2-EtIm, 2-isopropylimidazole/2-iPrIm) has been synthesized and characterized by elemental analysis, Fourier Transform Infrared spectroscopy (FTIR), electronic reflectance spectroscopy, cyclic voltammetry, thermal analysis and single crystal X-ray diffraction. All complexes crystalize in a monoclinic crystal system and form a complex supramolecular network developed through hydrogen bonds. The stereochemistry of the copper ion is distorted octahedral except for the compound with 4-methylimidazole for which the geometry is square-pyramidal. The imidazole derivatives act as unidentate while methacrylate ions are chelated except for compound with 4-methylimidazole where is unidentate. All ligands and complexes inhibited B16 murine melanoma cells in a micromolar range, but the complex with 2-isopropylimidazole was more active. Furthermore, all species do not affect the healthy BJ cells in the concentration range used for assays. [ABSTRACT FROM AUTHOR]

The quadridentate tetraaza ligand (H2L) containing dioxime function groups and its palladium (II) complex [PdL] were synthesized and structurally characterized by analytical and various spectroscopic techniques (MS‐ES, 1HNMR, FTIR, UV–Vis, and PXRD in addition to SEM and EDX analysis). Processing powder X‐ray diffraction data and DFT calculations coupled with spectroscopic measurements revealed slightly distorted square planar stereochemistry. The anticancer activity of the newly synthesized dioxime palladium (II) complex, [PdL], has been studied and the findings of this study emphasize that [PdL] complex potentially combats cancer by exhibiting diverse cytotoxic impacts. These effects include reduced cell mitosis, decreased metastasis of MDA‐MB‐231 cancer cells, inhibition of topoisomerase II, and induction of apoptotic cell death. In conclusion, the present palladium (II) complex could be a potential therapeutic drug in breast cancer because it can reduce topoisomerase II expression, which is essential in metastasis. This inhibition also reduces the expression of CDK1, which plays an important role in cell cycle regulation. [ABSTRACT FROM AUTHOR]

The maverick American chemist Russell Earl Marker (1902–1995) is known for his studies on the fragmentation of organic mercury compounds, establishing the concept of the octane number, investigating the rearrangements of hydrocarbons and exploring the relationship between optical rotation and the configuration of organic compounds. His greatest achievement, however, is the elaboration of seminal isolation and synthetic methods of an important class of natural products that helped found a new industry, based on the pharmaceutical chemistry of steroids. The nomadic life of this extraordinary man demonstrates that the enormous obstacles thwarting the progress of science and technology can be surmounted by serendipity, acumen and devotion. However, his premature retirement from chemistry is a warning sign that every scientist is vulnerable and even the toughest man's perseverance can fade if the conditions worsen. [ABSTRACT FROM AUTHOR]

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Curcuminoids are widely studied due to their well-recognized therapeutic properties. These molecules are often derivatized with metals, producing their corresponding homoleptic metal complexes. Numerous crystal structures of homoleptic symmetric curcuminoids with physiologically essential metals are known, although the literature lacks reports of homoleptic metal complexes of unsymmetric curcuminoids (or hemi-curcuminoids) as ligands. Three unknowns must be solved when an unsymmetric curcuminoid ligand is reacted with a metal ion: (a) the degree of coordination (MLn); (b) the spatial geometry; and (c) the conformational nature (syn or anti) of the complex. Herein, we report the structure of the anti-isomer of the Zn complex of the hemi-curcuminoid 5-hydroxy-1-(4-methoxyphenyl)hexa-1,4-dien-3-one. While the NMR shows only one set of signals for this homoleptic complex, the unambiguous stereochemistry was established through single-crystal X-ray diffractometry, revealing an anti-hexacoordinated octahedral ML2 structure. [ABSTRACT FROM AUTHOR]