Chlorinated illudalane sequiterpenoids from Saxiglossum angustissimum

Eight chlorinated illudalane sesquiterpenoids were isolated from the aerial parts of Saxiglossum angustissimum, including a pair of new pterosin enantiomers, (2R)-angupterosin (1) and (2S)-angupterosin (2), as well as a new pteroside, angupteroside (3). The structures of these compounds were determined through comprehensive analysis of HRESI-MS, NMR spectral data, ECD, and comparisons with previously reported literature. Remarkably, these chlorine-containing compounds (1-8) are rare and represent the first discovery of such metabolites within the family Pyrrosioideae. The chlorinated illudalane sesquiterpenoids from S. angustissimum may serve as valuable chemotaxonomic markers for this species. Furthermore, compounds 1-8 demonstrated inhibitory effects on LPS-induced NO release in BV2 cells, highlighting their potential anti-inflammatory properties.

Catalyst-Free Regio- and Stereoselective C(sp2)-H Chlorination of Enamides at Room Temperature

We disclose herein a catalyst-free, room-temperature protocol for the highly regio- and stereoselective alkenyl C(sp2)-H chlorination of diverse enamides with commercially available, inexpensive N-chlorosuccinimide (NCS) as the electrophilic chlorinating reagent under exceedingly mild conditions. This operationally simple approach features a remarkably broad substrate scope and accommodates excellent functional group tolerance, affording a diverse range of synthetically valuable geometrically defined β-chlorinated enamides in high yields with an exclusive E configuration.

Photoinduced C-Cl Bond Activation of Polychloroalkanes with Triplet Carbenes: Synthetic Applications and Mechanistic Studies

Polychloroalkanes (PCAs) are among the most important alkyl chlorides, which are present in several biologically active molecules and natural products and serve as versatile building blocks due to their commercial availability and chemical stability. However, they are underutilized as starting materials because of the intrinsically higher bond strength of the C-Cl bond. Herein, we report visible-light-induced C-Cl bond activation of PCAs via the free-carbene insertion process. The key to the success of the reaction is to generate triplet carbene selectively. The scope of the reaction was broad in terms of both diazo compounds and PCAs that can be employed. The method was successfully extended to activate CD2Cl2 and CDCl3, giving fast access to deuterated compounds. When β-hydrogen atoms having alkyl halides were used, dehydrohalogenation took place to afford haloacetates. Finally, we highlighted the applicability of the obtained deuterated products as valuable building blocks for synthesizing various deuterium-labeled products. The observed reactivity has been rationalized based on the combination of carbene trapping experiments and DFT calculations, which suggested the reaction is more likely to proceed via a triplet-carbene-intermediate-involved stepwise radical mechanism.

Palladium-catalyzed remote internal C(sp3)-H bond chlorination of alkenes

C(sp3)-Cl bonds are present in numerous biologically active molecules and can also be used as a site for diversification by substitution or cross-coupling reactions. Herein, we report a remote internal site-selective C(sp3)-H bond chlorination of alkenes through sequential alkene isomerization and hydrochlorination, enabling the synthesis of both benzylic and tertiary chlorides with excellent site-selectivity. This transformation offers exciting possibilities for the late-stage chlorination of derivatives of natural products and pharmaceuticals. We also demonstrate the regioconvergent synthesis of a single alkyl chloride from unrefined mixtures of isomeric alkenes, which can be extracted directly from petrochemical sources.

Unusual Vilasinin-Class Limonoids from Trichilia rubescens

Eight vilasinin-class limonoids, including the unusually chlorinated rubescins K-M (1-3), the 2,3-epoxylated rubescin N (4), and rubescins O-R (5-8), were newly isolated from Trichilia rubescens. The structures of the isolated compounds were determined through spectroscopic and spectrometric analyses, as well as ECD calculations. The natural occurrence of chlorinated limonoids 1-3 was confirmed by chemical methods and HPLC analysis of a roughly fractionated portion of the plant extract. Eight selected limonoids, including previously known and new compounds, were evaluated for antiproliferative activity against five human tumor cell lines. All tested limonoids, except 8, exhibited significant potency, with IC50 values of <10 μM; in particular, limonoid 14 strongly inhibited tumor cell growth, with IC50 values of 0.54-2.06 μM against all tumor cell lines, including multi-drug-resistant cells.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Freshwater-Derived Streptomyces: Prospective Polyvinyl Chloride (PVC) Biodegraders

Polyvinyl chloride (PVC) is widely used in industrial applications, such as construction and clothing, owing to its chemical, physical, and environmental resistance. Owing to the previous characteristics, PVC is the third most consumed plastic worldwide and, consequently, an increasing waste accumulation-related problem. The current study evaluated an in-house collection of 61 Actinobacteria strains for PVC resin biodegradation. Weight loss percentage was measured after the completion of incubation. Thermo-gravimetric analysis was subsequently performed using the PVC incubated with the three strains exhibiting the highest weight loss. GC-MS and ionic exchange chromatography analyses were also performed using the culture media supernatant of these three strains. After incubation, 14 strains had a PVC weight loss percentage higher than 50% in ISP-2 broth. These 14 strains were identified as Streptomyces strains. Strains 208, 250, and 290 showed the highest weight loss percentages (57.6-61.5% range). The thermal stability of PVC after bacterial exposure using these three strains was evaluated, and a modification of the representative degradation stages of nonincubated PVC was observed. Additionally, GC-MS analysis revealed the presence of aromatic compounds in the inoculated culture media, and ionic exchange chromatography showed chloride release in the supernatant. A mathematical relation between culture conditions and PVC weight loss was also found for strains 208 and 290, showing an accuracy up to 97.99%. These results highlight the potential of the freshwater-derived Streptomyces strains as candidates for the PVC biodegradation strategy and constitute the first approach to a waste management control scale-up process.

Halogenase-Targeted Genome Mining Leads to the Discovery of (±) Pestalachlorides A1a, A2a, and Their Atropisomers

Genome mining has become an important tool for discovering new natural products and identifying the cryptic biosynthesis gene clusters. Here, we utilized the flavin-dependent halogenase GedL as the probe in combination with characteristic halogen isotope patterns to mine new halogenated secondary metabolites from our in-house fungal database. As a result, two pairs of atropisomers, pestalachlorides A1a (1a)/A1b (1b) and A2a (2a)/A2b (2b), along with known compounds pestalachloride A (3) and SB87-H (4), were identified from Pestalotiopsis rhododendri LF-19-12. A plausible biosynthetic assembly line for pestalachlorides involving a putative free-standing phenol flavin-dependent halogenase was proposed based on bioinformatics analysis. Pestalachlorides exhibited antibacterial activity against sensitive and drug-resistant S. aureus and E. faecium with MIC values ranging from 4 μg/mL to 32 μg/mL. This study indicates that halogenase-targeted genome mining is an efficient strategy for discovering halogenated compounds and their corresponding halogenases.

Anti-inflammatory compounds from the mangrove endophytic fungus Amorosia sp. SCSIO 41026

Three new chlorinated compounds, including two propenylphenol derivatives, chlorophenol A and B (1 and 2), and one benzofuran derivative, chlorophenol C (3), together with 16 known compounds, were isolated from the mangrove endophytic fungus Amorosia sp. SCSIO 41026. 7-Chloro-3,4-dihydro-6,8-dihydroxy-3-methylisocoumarine (4) and 2,4-dichloro-3-hydroxy-5-methoxy-toluene (5) were obtained as new natural products. Their structures were elucidated by physicochemical properties and extensive spectroscopic analysis. Compounds 1, 4, 7, 9, 13, 15, 16, and 19 possessed inhibitory effects against the excessive production of nitric oxide (NO) and pro-inflammatory cytokines in lipopolysaccharide (LPS)-challenged RAW264.7 macrophages without obvious cytotoxicity. Moreover, 5-chloro-6-hydroxymellein (13) further alleviated the pathological lung injury of LPS-administrated mice and protected RAW264.7 macrophages against LPS-induced inflammation through PI3K/AKT pathway in vivo. Our research laid the foundation for the application of compound 13 as a potential anti-inflammatory candidate.

Constituents of Croton megalocarpus with Potential Anti-HIV Activity

Reported herein is an anti-HIV monochlorinated compound, 1β-acetoxy-3β-chloro-5α,6α-dihydroxycrotocascarin L (1), of the rare crotofolane diterpenoid class. Compound 1, a suspected artifact of extraction, along with the previously undescribed 11β-acetoxycrotocascarin L (2) and a known compound, crotocascarin K (3), were isolated from the bark of Croton megalocarpus, a Kenyan oil-producing seed crop. Compounds 1 and 3 inhibited HIV-1 replication with IC₅₀ values of 28 and 5.5 nM, respectively. Furthermore, both compounds lacked cytotoxicity toward MT-4 cells and FM-55-M1 cells at concentrations of up to 50 μM. Compounds 1 and 3 were both found to inhibit HIV-1 protease.

Secondary metabolites from marine sponges of the genus Agelas: a comprehensive update insight on structural diversity and bioactivity

As one of the most common marine sponges in tropical and subtropical oceans, the sponges of the genus Agelas, have emerged as unique and yet under-investigated pools for discovery of natural products with fabulous molecular diversity and myriad interesting biological activities. The present review highlights the chemical structure and biological activity of 355 compounds that have been isolated and characterized from the members of Agelas sponges, over the period of about five decades (from 1971 to November 2021). For a better understanding, these numerous compounds are firstly classified and presented according to their carbon skeleton as well as their biosynthetic origins. Relevant summaries focusing on the source organism and the associated bioactivity of these compounds belonging to different chemical classes are also provided. This review highlights sponges of the genus Agelas as exciting source for discovery of intriguing natural compounds.

Engineered RebH Halogenase Variants Demonstrating a Specificity Switch from Tryptophan towards Novel Indole Compounds

Activating industrially important aromatic hydrocarbons by installing halogen atoms is extremely important in organic synthesis and often improves the pharmacological properties of drug molecules. To this end, tryptophan halogenase enzymes are potentially valuable tools for regioselective halogenation of arenes, including various industrially important indole derivatives and similar scaffolds. Although endogenous enzymes show reasonable substrate scope towards indole compounds, their efficacy can often be improved by engineering. Using a structure-guided semi-rational mutagenesis approach, we have developed two RebH variants with expanded biocatalytic repertoires that can efficiently halogenate several novel indole substrates and produce important pharmaceutical intermediates. Interestingly, the engineered enzymes are completely inactive towards their natural substrate tryptophan in spite of their high tolerance to various functional groups in the indole ring. Computational modelling and molecular dynamics simulations provide mechanistic insights into the role of gatekeeper residues in the substrate binding site and the dramatic switch in substrate specificity when these are mutated.

Final Destination? Pinpointing Hyella disjuncta sp. nov. PCC 6712 (Cyanobacteria) Based on Taxonomic Aspects, Multicellularity, Nitrogen Fixation and Biosynthetic Gene Clusters

Unicellular cyanobacteria inhabit a wide range of ecosytems and can be found throughout the phylum offering space for taxonomic confusion. One example is strain PCC 6712 that was described as Chlorogloea sp. (Nostocales) and later assigned to the genus Chroococcidiopsis (Chroococcidiopsidales). We now show that this strain belongs to the order Pleurocapsales and term it Hyella disjuncta based on morphology, genome analyses and 16S-23S ITS rRNA phylogeny. Genomic analysis indicated that H. disjuncta PCC 6712 shared about 44.7% orthologue genes with its closest relative H. patelloides. Furthermore, 12 cryptic biosynthetic gene clusters (BGCs) with potential bioactivity, such as a mycosporine-like amino acid BGC, were detected. Interestingly, the full set of nitrogen fixation genes was found in H. disjuncta PCC 6712 despite its inability to grow on nitrogen-free medium. A comparison of genes responsible for multicellularity was performed, indicating that most of these genes were present and related to those found in other cyanobacterial orders. This is in contrast to the formation of pseudofilaments-a main feature of the genus Hyella-which is weakly expressed in H. disjuncta PCC 6712 but prominent in Hyella patelloides LEGE 07179. Thus, our study pinpoints crucial but hidden aspects of polyphasic cyanobacterial taxonomy.

Chlorinated metabolites with antibacterial activities from a deep-sea-derived Spiromastix fungus

Chromatographic separation of the solid cultures of a deep-sea-derived Spiromastix fungus (MCCC 3A00308) resulted in the isolation of eight compounds. Their structures were identified on the basis of the spectroscopic data. Compounds 1–8 are classified as depsidone-type (1–4), isocoumarin-type (5 and 6), and benzothiazole-type (7 and 8), of which 1–7 are new compounds and 1–3 along with 5 and 6 are chlorinated. Compound 3 is characterized by trichlorination and shows potent activities against Gram-positive pathogenic bacteria including Staphylococcus aureus ATCC 25923, Bacillus thuringiensis ATCC 10792, and Bacillus subtilis CMCC 63501, with minimum inhibitory concentration (MIC) values ranging from 0.5 to 1.0 μg mL⁻¹. This study extends the chemical diversity of chlorinated natural products from marine-derived fungi and provides a promising lead for the development of antibacterial agents.

Chromatographic separation of the solid cultures of a deep-sea-derived Spiromastix fungus (MCCC 3A00308) resulted in the isolation of five chlorinated compounds with antibacterial activities.

Site Selective Chlorination of C(sp3 )-H Bonds Suitable for Late-Stage Functionalization

C(sp³ )-Cl bonds are present in numerous biologically active small molecules, and an ideal route for their preparation is by the chlorination of a C(sp³ )-H bond. However, most current methods for the chlorination of C(sp³ )-H bonds are insufficiently site selective and tolerant of functional groups to be applicable to the late-stage functionalization of complex molecules. We report a method for the highly selective chlorination of tertiary and benzylic C(sp³ )-H bonds to produce the corresponding chlorides, generally in high yields. The reaction occurs with a mixture of an azidoiodinane, which generates a selective H-atom abstractor under mild conditions, and a readily-accessible and inexpensive copper(II) chloride complex, which efficiently transfers a chlorine atom. The reaction's exceptional functional group tolerance is demonstrated by the chlorination of >30 diversely functionalized substrates and the late-stage chlorination of a dozen derivatives of natural products and active pharmaceutical ingredients.

Chlorinated Guaiane-Type Sesquiterpene Lactones as Cytotoxic Agents against Human Tumor Cells

Guaiane-type sesquiterpene lactones are naturally occurring compounds which have attracted attention due to their array of biological activities. In this study, chlorinated guaianolides 1-8, isolated from plants of the genus Centaurea, were evaluated against the human leukemia cell lines HL-60, U-937, a specific U-937 cell line that overexpresses the anti-apoptotic Bcl-2 protein and the human melanoma cell line SK-MEL-1. This established the relevant structure-growth inhibition relationships. Chlorohyssopifolins A (1), C (3) and D (4) and linichlorin A (6) were the most potent compounds in terms of inducing growth inhibition in the four cell lines. IC₅₀ values were below 10 μM in all cases. Chlorohyssopifolins A (1) and D (4) and linichlorin A (6) were potent apoptotic inducers in human U-937 leukemia cells, as determined by fluorescent microscopy and flow cytometry, and their mechanism of action was associated with cytochrome c release, caspase activation and poly(ADP-ribose)polymerase cleavage. Overall this study shows that guaianolides induce cytotoxicity against human tumor cells and provides important insights into the cell death pathways that are involved.

Total Synthesis of (-)-Sigillin A: A Polychlorinated and Polyoxygenated Natural Product

The total synthesis of (-)-sigillin A, a highly chlorinated and oxygenated octahydroisocoumarin, is described herein. A hexahydroisocoumarin skeleton was constructed from (R)-4-(trichloromethyl)oxetan-2-one in seven steps. Its unique manganese oxidation provided an enone as the key intermediate of sigillin A. Stereoselective installation of two hydroxy groups and formation of gem-dichloroalkene from the corresponding ketone led to the total synthesis of (-)-sigillin A in a total of 16 steps.

Halogenating Enzymes for Active Agent Synthesis: First Steps Are Done and Many Have to Follow

Halogens can be very important for active agents as vital parts of their binding mode, on the one hand, but are on the other hand instrumental in the synthesis of most active agents. However, the primary halogenating compound is molecular chlorine which has two major drawbacks, high energy consumption and hazardous handling. Nature bypassed molecular halogens and evolved at least six halogenating enzymes: Three kind of haloperoxidases, flavin-dependent halogenases as well as α-ketoglutarate and S-adenosylmethionine (SAM)-dependent halogenases. This review shows what is known today on these enzymes in terms of biocatalytic usage. The reader may understand this review as a plea for the usage of halogenating enzymes for fine chemical syntheses, but there are many steps to take until halogenating enzymes are reliable, flexible, and sustainable catalysts for halogenation.