Bioactive natural products and chirality

Therapeutic potential of Bergenin in the management of neurological-based diseases and disorders

Originally sourced from plants, Bergenin has been used as a medicinal compound in traditional medicine for centuries, and anecdotal reports suggest a wide range of therapeutic uses. Naturally-occurring and lab-synthesized Bergenin, as well as some of its related compounds, have been shown in in vivo and in vitro studies to alter activity of several enzymes and proteins critical in cellular functioning, including reelin, GSK-3β, Lingo-1, Ten-4, GP-43, Aβ 1-42, P-tau, SOD1,2, GPx, Glx1, NQO1, HO1, PPAR-ɣ, BDNF, VEGF, and STAT6. Additionally, Bergenin alters levels of several cytokines, such as IL-6, IL-1β, TNF-α, and TGF-β. Behavioral and cellular effects of Bergenin have been shown to involve PI3K/Akt, NF-κB, PKC, Nrf2, and Sirt1/FOXO3a pathways. These pathways, enzymes, and proteins have been shown to be important in normal neurological functioning, and/or dysfunctions in these pathways and proteins have been shown to be important in several neuro-based disorders or diseases, which suggests that Bergenin could be therapeutic in management of neuropsychiatric conditions or neurological disorders. In preclinical studies, Bergenin has been shown to be useful for the management of Alzheimer's disease, Parkinson's disease, anxiety, depression, addiction, epilepsy, insomnia, stroke, and potentially, state control. Our review aims to summarize current evidence supporting the conclusion that Bergenin could play a role in treating various neuro-based disorders and that future studies should be conducted to evaluate the mechanisms by which Bergenin could exert its therapeutic effects.

Organocatalytic enantioselective assembly of dispiro-bisoxindoles with vicinal stereocenters

Notwithstanding the rapid development achieved in enantioselective transformations, accessing contiguous quaternary and tertiary stereocenters ubiquitous in natural products and biologically active compounds has been an important and challenging task for synthetic chemists in modern organic chemistry. Drawing inspiration from the huge significance of spirooxindoles featuring a unique spatial structure and incredible medicinal activities, the search for these fascinating compounds in nature and developing new synthetic routes for installing multiple stereocenters remain core areas for synthetic chemists. This mini-review article demonstrates a transitory overview of the organocatalytic enantioselective strategies developed for assembling broad-spectrum dispiro-bisoxindole scaffolds comprising vicinal quaternary and tertiary stereocenters. While addressing the notable advancement accomplished in this intriguing field, we have also discussed the drawbacks and challenges associated with the reaction findings to support more research.

Sex Pheromone of the Azalea Mealybug: Absolute Configuration and Kairomonal Activity

The sex pheromone of the azalea mealybug, Crisicoccus azaleae (Tinsley, 1898) (Hemiptera: Pseudococcidae), includes esters of a methyl-branched medium-chain fatty acid, ethyl and isopropyl (E)-7-methyl-4-nonenoate. These compounds are exceptional among mealybug pheromones, which are commonly monoterpenes. Determination of the absolute configuration is challenging, because both chromatographic and spectrometric separations of stereoisomers of fatty acids with a methyl group distant from the carboxyl group are difficult. To solve this problem, we synthesized the enantiomers via the Johnson-Claisen rearrangement to build (E)-4-alkenoic acid by using (R)- and (S)-3-methylpentanal as chiral blocks, which were readily available from the amino acids L-(+)-alloisoleucine and L-(+)-isoleucine, respectively. Each pure enantiomer, as well as the natural pheromone, was subsequently derivatized with a highly potent chiral labeling reagent used in the Ohrui-Akasaka method. Through NMR spectral comparisons of these derivatives, the absolute configuration of the natural pheromone was determined to be S. Field-trap bioassays showed that male mealybugs were attracted more to (S)-enantiomers and preferred the natural stereochemistry. Moreover, the synthetic pheromones attracted Anagyrus wasps, indicating that the azalea mealybug pheromone has kairomonal activity.

Liver-cell protective pyridones from the fungi Tolypocladium album dws120

Five previously undescribed pyridone derivatives, tolypyridones I-M, were identified from the solid rice medium fermented by Tolypocladium album dws120, along with two known compounds tolypyridone A (or trichodin A) and pyridoxatin. Their planar structures and partial relative configurations have been determined by careful interpretation of their spectroscopic data. The full assignment of the relative and absolute configurations of tolypyridones I-M was achieved by gauge-independent atomic orbital ¹³C NMR calculation, quantitative nuclear Overhauser effects based interatomic distance calculation, and electronic circular dichroism calculation. In addition, we have fully determined the configuration of tolypyridone A by X-ray diffraction analysis. In bioassay, tolypyridones I was able to restore cell viability and inhibit the release of alanine aminotransferase and aspartate aminotransferase for ethanol-induced LO2 cell, suggesting its potential as a liver protective agent.

67 million natural product-like compound database generated via molecular language processing

Natural products are a rich resource of bioactive compounds for valuable applications across multiple fields such as food, agriculture, and medicine. For natural product discovery, high throughput in silico screening offers a cost-effective alternative to traditional resource-heavy assay-guided exploration of structurally novel chemical space. In this data descriptor, we report a characterized database of 67,064,204 natural product-like molecules generated using a recurrent neural network trained on known natural products, demonstrating a significant 165-fold expansion in library size over the approximately 400,000 known natural products. This study highlights the potential of using deep generative models to explore novel natural product chemical space for high throughput in silico discovery.

Natural product evodiamine-inspired medicinal chemistry: Anticancer activity, structural optimization and structure-activity relationship

It is a well-known phenomenon that natural products can serve as powerful drug leads to generate new molecular entities with novel therapeutic utility. Evodiamine (Evo), a major alkaloid component in traditional Chinese medicine Evodiae Fructus, is considered a desirable lead scaffold as its multifunctional pharmacological properties. Although natural Evo has suboptimal biological activity, poor pharmacokinetics, low water solubility, and chemical instability, medicinal chemists have succeeded in producing synthetic analogs that overshadow the deficiency of Evo in terms of further clinical application. Recently, several reviews on the synthesis, structural modification, mechanism pharmacological actions, structure-activity relationship (SAR) of Evo have been published, while few reviews that incorporates intensive structural basis and extensive SAR are reported. The purpose of this article is to review the structural basis, anti-cancer activities, and mechanisms of Evo and its derivatives. Emphasis will be placed on the optimizing strategies to improve the anticancer activities, such as structural modifications, pharmacophore combination and drug delivery systems. The current review would benefit further structural modifications of Evo to discover novel anticancer drugs.

Reverse chemical ecology indicates long-chain aldehydes as new potential semiochemicals for the African elephant Loxodonta africana

Chemical communication between sexes in the elephants has been well studied at the chemical and behavioural levels, but little is known about the proteins mediating the exchange of chemical signals. Two sex pheromones have been identified in Asian elephants: (Z)-7-dodecenyl acetate and frontalin, and their effects on the elephants’ behaviour have been described in detail. The genomes of both the Asian (Elephas maximus) and the African elephant (Loxodonta africana) have been poorly annotated. In particular, the complete sequences of two odorant-binding proteins and a VEG protein are available for the African elephant, together with isoforms and other members of the same families, which however are incomplete or unreliable. In a previous study, we have expressed the OBP1 of both elephant species, and investigated their binding properties. We showed that OBP1 is tuned to the pheromone (Z)-7-dodecenyl acetate and few structurally related linear esters, but also binds (E)-β-farnesene and farnesol with good affinity. In this work we have explored the characteristics of the second OBP of the African elephant (LafrOBP2). This protein, which was not found in the trunk wash, does not bind any of the above listed semiochemicals. Instead, it shows selected affinity to unsaturated linear aldehydes of 16 carbon atoms, specifically (Z)-9-hexadecenal, (Z)-11-hexadecenal and (10E,12Z)-hexadecadienal (bombykal). Fourteen and 18 carbon orthologues show only much reduced binding affinity. Some linear alcohols, fatty acids and esters also weakly bind this protein with dissociation constants about one order of magnitude higher.

Design and Synthesis of Fsp3-Enriched Spirocyclic-Based Biological Screening Compound Arrays via DOS Strategies and Their NNMT Inhibition Profiling

Medicinal chemists are keen to explore tridimensional compounds, especially when it comes to small molecules. It has already been stressed that the majority of known drugs tend to be flat, whereas natural products tend to be more tridimensional and represent a good source of active compounds. 3D metrics have been implemented and computational descriptors are available to evaluate and prioritize compounds based on their 3D geometry. This is usually done by comparing the saturated carbon atoms in a molecule with the total number of its non-hydrogen atoms (the Fsp3 value). While this aspect is clear, still there are not enough synthetic tools that support the realization of novel chemotypes that conform to these criteria. Herein we describe a diversity oriented synthesis (DOS) synthetic cascade technology that starts from two simple reagents, and generates highly enriched Fsp3 novel and diverse spiro-scaffolds with pragmatic synthetic handles (points of diversity). The spiro nature of these scaffolds not only ensures high Fsp3 values but renders the compounds more rigid and therefore more effective in forming precise stereo-interactions with their potential biological targets. These compounds were also profiled for their drug-like properties and as potential modulators of the NNMT enzyme.

Novel methods to characterise spatial distribution and enantiomeric composition of usnic acids in four Icelandic lichens

Usnic acid is an antibiotic metabolite produced by a wide variety of lichenized fungal lineages. The enantiomers of usnic acid have been shown to display contrasting bioactivities, and hence it is important to determine their spatial distribution, amounts and enantiomeric ratios in lichens to understand their roles in nature and grasp their pharmaceutical potential. The overall aim of the study was to characterise the spatial distribution of the predominant usnic acid enantiomer in lichens by combining spatial imaging and chiral chromatography. Specifically, separation and quantification of usnic acid enantiomers in four common lichens in Iceland was performed using a validated chiral chromatographic method. Molecular dynamics simulation was carried out to rationalize the chiral separation mechanism. Spatial distribution of usnic acid in the lichen thallus cross-sections were analysed using Desorption Electrospray Ionization-Imaging Mass Spectrometry (DESI-IMS) and fluorescence microscopy. DESI-IMS confirmed usnic acid as a cortical compound, and revealed that usnic acid can be more concentrated around the algal vicinity. Fluorescence microscopy complemented DESI-IMS by providing more detailed distribution information. By combining results from spatial imaging and chiral separation, we were able to visualize the distribution of the predominant usnic acid enantiomer in lichen cross-sections: (+)-usnic acid in Cladonia arbuscula and Ramalina siliquosa, and (-)-usnic acid in Alectoria ochroleuca and Flavocetraria nivalis. This study provides an analytical foundation for future environmental and functional studies of usnic acid enantiomers in lichens.

Laccase-mediated synthesis of bioactive natural products and their analogues

Laccases are a class of multicopper oxidases that catalyse the one-electron oxidation of four equivalents of a reducing substrate, with the concomitant four-electron reduction of dioxygen to water. Typically, they catalyse many anabolic reactions, in which mostly phenolic metabolites were subjected to oxidative coupling. Alternatively, laccases catalyse the degradation or modification of biopolymers like lignin in catabolic processes. In recent years, laccases have proved valuable and green biocatalysts for synthesising compounds with therapeutic value, including antitumor, antibiotic, antimicrobial, and antioxidant agents. Further up to date applications include oxidative depolymerisation of lignin to gain new biomaterials and bioremediation processes of industrial waste. This review summarizes selected examples from the last decade's literature about the laccase-mediated synthesis of biologically active natural products and their analogues; these will include lignans and neolignans, dimeric stilbenoids, biflavonoids, biaryls and other compounds of potential interest for the pharmaceutical industry. In addition, a short section about applications of laccases in natural polymer modification has been included.

Structural properties and evaluation of the antiproliferative activity of limonene-1,2-diol obtained by the fungal biotransformation of R-(+)- and S-(-)-limonene

Limonene-1,2-diol is a limonene oxygenated metabolite that possesses eight different stereoisomers, which could result in different biological properties. Nonetheless, the relation between its spatial configuration and biological function is still little explored. The present study aimed to perform the stereoisomers identification using nuclear magnetic resonance (NMR) investigation of the limonene-1,2-diol produced via R-(+)- and S-(-)-limonene biotransformation by Colletotrichum nymphaeae and S-(-)-limonene biotransformation by Fusarium oxysporum 152B. Besides, in vitro antiproliferative activity was evaluated against human tumor and nontumor cell lines. The NMR analysis showed that R-(+)-limonene biotransformation afforded exclusively (+)-(1S,2S,4R-limonene-1,2-diol), whereas S-(-)-limonene biotransformation afforded exclusively (-)-(1R,2R,4S-limonene-1,2-diol) independent on the fungi used. Despite no significant cytostatic effects, a possible influence of stereogenic center on the antiproliferative activity of these limonene biotransformation products was evidenced. Moreover, the lack of in vitro antiproliferative effect of limonene-1,2-diol against nontumor cells suggested a safe dose range for further in vivo evaluations, including food applications.

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world's most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage "If you don't seek, you don't find". Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

Detecting multiple chiral centers in chiral molecules with high harmonic generation

Characterizing chiral is highly important for applications in the pharmaceutical industry, as well as in the study of dynamical chemical and biological systems. However, this task has remained challenging, especially due to the ongoing increasing complexity and size of the molecular structure of drugs and active compounds. In particular, large molecules with many active chiral centers are today ubiquitous, but remain difficult to structurally analyze due to their high number of stereoisomers. Here we theoretically explore the sensitivity of high harmonic generation (HHG) to the chiral of molecules with a varying number of active chiral centers. We find that HHG driven by bi-chromatic non-collinear lasers is a sensitive probe for the stereo-configuration of a chiral molecule. We first show through calculations (from benchmark chiral molecules with up to three chiral centers) that the HHG spectrum is imprinted with information about the handedness of each chiral center in the driven molecule. Next, we show that using both classical- and deep-learning-based reconstruction algorithms, the composition of an unknown mixture of stereoisomers can be reconstructed with high fidelity by a single-shot HHG measurement. Our work illustrates how the combination of non-linear optics and machine learning might open routes for ultra-sensitive sensing in chiral systems.

Chiral Polythiophenes: Part I: Syntheses of Monomeric Precursors

The purpose of this mini-review is to comprehensively present the synthetic approaches used for the preparation of non-racemic mono- and multi-substituted thiophenes, which, in turn, can be applied as precursors for the synthesis of chiral polythiophenes isolated as a single chemical entity or having supramolecular thin-layer architectures.

Using (+)-Carvone to access novel derivatives of (+)-ent-Cannabidiol: the first asymmetric syntheses of (+)-ent-CBDP and (+)-ent-CBDV

(-)-Cannabidiol [(-)-CBD] has recently gained prominence as a treatment for neuro-inflammation and other neurodegenerative disorders; interest is also developing in its synthetic enantiomer, (+)-CBD, which has a higher affinity to CB1 / CB2 receptors than the natural stereoisomer. We have developed an inexpensive, stereoselective route to access ent-CBD derivatives using (+)-carvone as a starting material. In addition to (+)-CBD, we report the first syntheses of (+)-cannabidivarin, (+)-cannabidiphorol as well as C-6 / C-8 homologues.

Structural characterisation of natural products by means of quantum chemical calculations of NMR parameters: new insights

In this review, we focus in all aspects of NMR simulation of natural products, from the fundamentals to the new computational toolboxes available, combining advanced quantum chemical calculations with upstream data processing and machine learning.

Bioguided Fractionation of Local Plants against Matrix Metalloproteinase9 and Its Cytotoxicity against Breast Cancer Cell Models: In Silico and In Vitro Study

Matrix metalloproteinase9 (MMP9) is known to be highly expressed during metastatic cancer where most known potential inhibitors failed in the clinical trials. This study aims to select local plants in our state, as anti-breast cancer agent with hemopexin-like domain of MMP9 (PEX9) as the selective protein target. In silico screening for PEX9 inhibitors was performed from our in house-natural compound database to identify the plants. The selected plants were extracted using methanol and then a step-by-step in vitro screening against MMP9 was performed from its crude extract, partitions until fractions using FRET-based assay. The partitions were obtained by performing liquid–liquid extraction on the methanol extract using n-hexane, ethylacetate, n-butanol, and water representing nonpolar to polar solvents. The fractions were made from the selected partition, which demonstrated the best inhibition percentage toward MMP9, using column chromatography. Of the 200 compounds screened, 20 compounds that scored the binding affinity −11.2 to −8.1 kcal/mol toward PEX9 were selected as top hits. The binding of these hits were thoroughly investigated and linked to the plants which they were reported to be isolated from. Six of the eight crude extracts demonstrated inhibition toward MMP9 with the IC₅₀ 24 to 823 µg/mL. The partitions (1 mg/mL) of Ageratum conyzoides aerial parts and Ixora coccinea leaves showed inhibition 94% and 96%, whereas their fractions showed IC₅₀ 43 and 116 µg/mL, respectively toward MMP9. Using MTT assay, the crude extract of Ageratum exhibited IC₅₀ 22 and 229 µg/mL against 4T1 and T47D cell proliferations, respectively with a high safety index concluding its potential anti-breast cancer from herbal.

Determination of Oxyphylla A Enantiomers in the Fruits of Alpinia oxyphylla by a Chiral High-Performance Liquid Chromatography-Multiple Reaction Monitoring-Mass Spectrometry Method and Comparison of Their In Vivo Biological Activities

(R)-Oxyphylla A, a natural product isolated from Alpinia oxyphylla Miquel as a food and medicinal plant, has been reported previously as a novel chiral compound that possesses a potential therapeutic value for Parkinson's disease (PD). A chiral high-performance liquid chromatography-multiple reaction monitoring-mass spectrometry method was developed to separate oxyphylla A enantiomers and to identify the presence of natural (S)-oxyphylla A for the first time. Twelve samples of dried A. oxyphylla fruits were analyzed in which a large variation in the abundance of enantiomers was observed. Moreover, (S)-oxyphylla A was less abundant in all tested samples, whereas fruits harvested from Hainan and Guangdong tended to have relatively higher total concentrations of enantiomers. Additionally, enantiomers exhibited comparable neuroprotective effects in the zebrafish model of PD without observed toxicity phenotype. The optimized enantioseparation method will be crucial for the quality control of A. oxyphylla and research on bioactivities facilitates the development of oxyphylla A as a potential therapeutic for neurodegenerative diseases.

Beyond Chiral Organic (p-Block) Chromophores for Circularly Polarized Luminescence: The Success of d-Block and f-Block Chiral Complexes

Chiral molecules are essential for the development of advanced technological applications in spintronic and photonic. The best systems should produce large circularly polarized luminescence (CPL) as estimated by their dissymmetry factor (g _lum), which can reach the maximum values of -2 ≤ g _lum ≤ 2 when either pure right- or left-handed polarized light is emitted after standard excitation. For matching this requirement, theoretical considerations indicate that optical transitions with large magnetic and weak electric transition dipole moments represent the holy grail of CPL. Because of their detrimental strong and allowed electric dipole transitions, popular chiral emissive organic molecules display generally moderate dissymmetry factors (10^-5 ≤ g _lum ≤ 10^-3). However, recent efforts in this field show that g _lum can be significantly enhanced when the chiral organic activators are part of chiral supramolecular assemblies or of liquid crystalline materials. At the other extreme, chiral Eu^III- and Sm^III-based complexes, which possess intra-shell parity-forbidden electric but allowed magnetic dipole transitions, have yielded the largest dissymmetry factor reported so far with g _lum ~ 1.38. Consequently, 4f-based metal complexes with strong CPL are currently the best candidates for potential technological applications. They however suffer from the need for highly pure samples and from considerable production costs. In this context, chiral earth-abundant and cheap d-block metal complexes benefit from a renewed interest according that their CPL signal can be optimized despite the larger covalency displayed by d-block cations compared with 4f-block analogs. This essay thus aims at providing a minimum overview of the theoretical aspects rationalizing circularly polarized luminescence and their exploitation for the design of chiral emissive metal complexes with strong CPL. Beyond the corroboration that f-f transitions are ideal candidates for generating large dissymmetry factors, a special attention is focused on the recent attempts to use chiral Cr^III-based complexes that reach values of g _lum up to 0.2. This could pave the way for replacing high-cost rare earths with cheap transition metals for CPL applications.

Stereodivergent Synthesis of 1-Hydroxymethylpyrrolizidine Alkaloids

A first stereodivergent strategy for the asymmetric synthesis of all stereoisomers of 1-hydroxymethylpyrrolizidine alkaloids is developed using an asymmetric self-Mannich reaction as a key step. An anti-selective self-Mannich reaction of methyl 4-oxobutanoate with the PMP-amine catalyzed by a chiral secondary amine is successfully optimized for the asymmetric synthesis of (+)-isoretronecanol and (-)-isoretronecanol. A syn-selective self-Mannich reaction catalyzed by proline is utilized for the asymmetric synthesis of the diastereomer, (+)-laburnine, and its enantiomer, (-)-trachelanthamidine.

Absolute Configuration Assignment to Chiral Natural Products by Biphenyl Chiroptical Probes: The Case of the Phytotoxins Colletochlorin A and Agropyrenol

The application of flexible biphenyls as chiroptical probes for the absolute configuration assignment to chiral natural products is described. The method is straightforward and reliable and can be applied to conformationally mobile and ECD silent compounds, not treatable by computational analysis of chiroptical data. By this approach, the (6'R) absolute configuration of the phytotoxin colletochlorin A (1) was confirmed, while the absolute configuration of the phytotoxin agropyrenol (2), previously assigned by the NMR Mosher method, was revised and assigned as (3'S,4'S). Moreover, with the biphenyl method the configurational assignment can be obtained simply by the sign of a diagnostic Cotton effect at 250 nm in the ECD spectrum, thus allowing application without the need of advanced knowledge of chiroptical spectroscopy and computational protocols.

Challenges in the configuration assignment of natural products. A case-selective perspective

An overview by a case study approach on the currently available methods for the configurational analysis of natural products.

Unprecedented homochiral 3D lanthanide coordination polymers with triple-stranded helical architecture constructed from a rigid achiral aryldicarboxylate ligand

Luminescence and second harmonic generation activity of a series of homochiral 3D Ln-CPs were studied.

Enantiomeric ratios: Why so many notations?

The correct quantification of enantiomers is pivotal in a variety of fields, such as pharmacokinetic studies, enantioselective syntheses, chemical characterization of natural products, authentication of fragrance and food, biodegradation behavior, accurate evaluation of environmental risk, and it can also provide information for sentencing guidance in forensic field. Enantioselective chromatography is the first choice to assess the composition of an enantiomeric mixture. Different notations have been used to express the measured enantiomeric ratios, which compromise the results and represent a challenge for data comparison. This manuscript critically discusses the currently used notations and exemplifies with applications in different fields indicating the advantages and disadvantages of one of the adopted systems. In order to simplify the notations, the use of enantiomeric ratio (e.r.%) as standardization for nonchiroptical methods is proposed.

Isolation, structure elucidation and racemization of (+)- and (-)-pratensilins A-C: unprecedented spiro indolinone-naphthofuran alkaloids from a marine Streptomyces sp

Three pairs of new enantiomeric alkaloids with an unprecedented spiro indolinone-naphthofuran skeleton were isolated from a marine Streptomyces sp. The pure enantiomers had a marked difference in the enantiomerization processes for the three compounds. DFT calculations in combination with chemical derivatization were performed to corroborate the racemization process via a keto-enol-type tautomerism.

Enantiomeric Mixtures in Natural Product Chemistry: Separation and Absolute Configuration Assignment

Chiral natural product molecules are generally assumed to be biosynthesized in an enantiomerically pure or enriched fashion. Nevertheless, a significant amount of racemates or enantiomerically enriched mixtures has been reported from natural sources. This number is estimated to be even larger since the enantiomeric purity of secondary metabolites is rarely checked in the natural product isolation pipeline. This latter fact may have drastic effects on the evaluation of the biological activity of chiral natural products. A second bottleneck is the determination of their absolute configurations. Despite the widespread use of optical rotation and electronic circular dichroism, most of the stereochemical assignments are based on empirical correlations with similar compounds reported in the literature. As an alternative, the combination of vibrational circular dichroism and quantum chemical calculations has emerged as a powerful and reliable tool for both conformational and configurational analysis of natural products, even for those lacking UV-Vis chromophores. In this review, we aim to provide the reader with a critical overview of the occurrence of enantiomeric mixtures of secondary metabolites in nature as well the best practices for their detection, enantioselective separation using liquid chromatography, and determination of absolute configuration by means of vibrational circular dichroism and density functional theory calculations.

Chiral Hypervalent, Pentacoordinated Phosphoranes

This review presents synthetic procedures applied to the preparation of chiral (mainly optically active) pentacoordinated, hypervalent mono and bicyclic phosphoranes. The mechanisms of their stereoisomerization and their selected interconversions are also presented.

Synthesis and bioassay of the eight analogues of the CH503 male pheromone (3-acetoxy-11,19-octacosadien-1-ol) of the Drosophila melanogaster fruit fly

Eight analogues of (3R,11Z,19Z)-CH503 (3-acetoxy-11,19-octacosadien-1-ol), the anti-aphrodisiac pheromone of male Drosophila melanogaster, were synthesized for a bioassay. These were the enantiomers of 3-acetoxy-11,19-octacosadiyn-1-ol (1), 3-acetoxyoctacosan-1-ol (2), (Z)-3-acetoxy-11-octacosen-1-ol (3), and (Z)-3-acetoxy-19-octacosen-1-ol (4). None of them were pheromonally active, indicating that the two double bonds at C-11 and C-19 were necessary for bioactivity.

Dirigent proteins: molecular characteristics and potential biotechnological applications

Dirigent proteins (DIRs) are thought to play important roles in plant secondary metabolism. They lack catalytic activity but direct the outcome of bimolecular coupling reactions toward regio- and stereospecific product formation. Functionally described DIRs confer specificity to the oxidative coupling of coniferyl alcohol resulting in the preferred production of either (+)- or (-)-pinoresinol, which are the first intermediates in the enantiocomplementary pathways for lignan biosynthesis. DIRs are extracellular glycoproteins with high β-strand content and have been found in all land plants investigated so far. Their ability to capture and orientate radicals represents a unique naturally evolved concept for the control of radical dimerization reactions. Although oxidative coupling is commonly used in biological systems, its wider application in chemical synthesis is often limited by insufficient selectivity. This minireview gives an overview of functionally described DIRs and their molecular characteristics and wants to inspire further research for their use in biotechnological applications.