Lead Optimization of Butyrolactone I as an Orally Bioavailable Antiallergic Agent Targeting FcγRIIB.

Food allergy (FA) poses a growing global food safety concern, yet no effective cure exists in clinics. Previously, we discovered a potent antifood allergy compound, butyrolactone I (BTL-I, 1), from the deep sea. Unfortunately, it has a very low exposure and poor pharmacokinetic (PK) profile in rats. Therefore, a series of structural optimizations toward the metabolic pathways of BTL-I were conducted to provide 18 derives (2-19). Among them, BTL-MK (19) showed superior antiallergic activity and favorable pharmacokinetics compared to BTL-I, being twice as potent with a clearance (CL) rate of only 0.5% that of BTL-I. By oral administration, Cmax and area under the concentration-time curve (AUC0-∞) were 565 and 204 times higher than those of BTL-I, respectively. These findings suggest that butyrolactone methyl ketone (BTL-BK) could serve as a drug candidate for the treatment of FAs and offer valuable insights into optimizing the druggability of lead compounds.

Ligustilide covalently binds to Cys703 in the pre-S1 helix of TRPA1, blocking the opening of channel and relieving pain in rats with acute soft tissue injury.

ETHNOPHARMACOLOGICAL RELEVANCE: The natural anodyne Ligustilide (Lig), derived from Angelica sinensis (Oliv.) Diels and Ligusticum chuanxiong Hort., has been traditionally employed for its analgesic properties in the treatment of dysmenorrhea and migraine, and rheumatoid arthritis pain. Despite the existing reports on the correlation between TRP channels and the analgesic effects of Lig, a comprehensive understanding of their underlying mechanisms of action remains elusive. AIM OF THE STUDY: The objective of this study is to elucidate the mechanism of action of Lig on the analgesic target TRPA1 channel. METHODS: The therapeutic effect of Lig was evaluated in a rat acute soft tissue injury model. The analgesic target was identified through competitive inhibition of TRP channel agonists at the animal level, followed by Fluo-4/Ca2+ imaging on live cells overexpressing TRP proteins. The potential target was verified through in-gel imaging, colocalization using a Lig-derived molecular probe, and a drug affinity response target stability assay. The binding site of Lig was identified through protein spectrometry and further analyzed using molecular docking, site-specific mutation, and multidisciplinary approaches. RESULTS: The administration of Lig effectively ameliorated pain and attenuated oxidative stress and inflammatory responses in rats with soft tissue injuries. Moreover, the analgesic effects of Lig were specifically attributed to TRPA1. Mechanistic studies have revealed that Lig directly activates TRPA1 by interacting with the linker domain in the pre-S1 region of TRPA1. Through metabolic transformation, 6,7-epoxyligustilide (EM-Lig) forms a covalent bond with Cys703 of TRPA1 at high concentrations and prolonged exposure time. This irreversible binding prevents endogenous electrophilic products from entering the cysteine active center of ligand-binding pocket of TRPA1, thereby inhibiting Ca2+ influx through the channel opening and ultimately relieving pain. CONCLUSIONS: Lig selectively modulates the TRPA1 channel in a bimodal manner via non-electrophilic/electrophilic metabolic conversion. The epoxidized metabolic intermediate EM-Lig exerts analgesic effects by irreversibly inhibiting the activation of TRPA1 on sensory neurons. These findings not only highlight the analgesic mechanism of Lig but also offer a novel nucleophilic attack site for the development of TRPA1 antagonists in the pre-S1 region.

A gene cluster encoding a nonribosomal peptide synthetase-like enzyme catalyzes γ-aromatic butenolides.

Sea cucumber-derived fungi have attracted much attention due to their capacity to produce an incredible variety of secondary metabolites. Genome-wide information on Aspergillus micronesiensis H39 obtained using third-generation sequencing technology (PacBio-SMRT) showed that the strain contains nonribosomal peptide synthetase (NRPS)-like gene clusters, which aroused our interest in mining its secondary metabolites. 11 known compounds (1-11), including two γ-aromatic butenolides (γ-AB) and five cytochalasans, were isolated from A. micronesiensis H39. The structures of the compounds were determined by NMR and ESIMS, and comparison with those reported in the literature. From the perspective of biogenetic origins, the γ-butyrolactone core of compounds 1 and 2 was assembled by NRPS-like enzyme. All of the obtained compounds showed no inhibitory activity against drug-resistant bacteria and fungi, as well as compounds 1 and 2 had no anti-angiogenic activity against zebrafish.

Two New Pairs of Enantiomeric Butenolides from the Marine Sponge Suberties sp.

Two new pairs of enantiomeric butenolides, (+)- and (-)-suberiteslide A, (+)- and (-)-subertieslide B had been obtained from the marine sponge Suberties sp. The structures with absolute configurations of these compounds were unequivocally determined by spectroscopic analyses and ECD (Electronic Circular Dichroism) method. It was the first separation of butenolides from the marine sponges of genus Suberites. Additionally, the anti-inflammatory, antibacterial and cytotoxic activities of these compounds were evaluated. The result indicated that only (-)-subertieslide B showed weak anti-inflammatory activity with the IC50 value of 40.8 µM.

N-acyl homoserine lactone mediating initial adhesion of microalgal biofilm formation.

While pioneering methods have demonstrated that bacterial N-acyl homoserine lactone (AHL) signaling molecules can influence the growth and self-aggregation of suspended microalgae, whether AHLs can affect the initial adhesion to a carrier has remained an open question. Here we revealed that the microalgae exhibited different adhesion potential under AHL mediation, where the performance was affiliated to both AHL types and concentrations. The result can be well explained by the interaction energy theory, where the energy barrier between the carriers and the cells varied due to AHL mediation. Depth analyses revealed that AHL acted through modifying the properties of the surface electron donor of the cells, which were dependent upon three major components, i.e., extracellular protein (PN) secretion, the PN secondary structure, and the PN amino acid composition. These findings expand the known diversity of AHLs mediation on microalgal initial adhesion and metabolisms, which may interface with other major cycles and become helpful to theoretically guide the application of AHLs in microalgal culture and harvesting.

Synthesis of Gamma-Butyrolactone Hormones Enables Understanding of Natural Product Induction.

Bacteria produce natural products (NPs) via biosynthetic gene clusters. Unfortunately, many biosynthetic gene clusters are silent under traditional laboratory conditions. To access novel NPs, a better understanding of their regulation is needed. γ-Butyrolactones, including the A-factor and Streptomyces coelicolor butanolides, SCBs, are a major class of Streptomyces' hormones. Study of these hormones has been limited due to challenges in accessing them in stereochemically pure forms. Herein, we describe an efficient route to (R)-paraconyl alcohol, a key intermediate for these molecules, as well as a biocatalytic method to access the exocyclic hydroxyl group that differentiates A-factor-type from SCB-type hormones. Utilizing these methods, a library of hormones have been synthesized and tested in a green fluorescent protein reporter assay for their ability to relieve repression by the repressor ScbR. This allowed the most quantitative structure-activity relationship of γ-butyrolactones and a cognate repressor to date. Bioinformatics analysis strongly suggests that many other repressors of NP biosynthesis likely bind similar molecules. This efficient, diversifiable synthesis will enable further investigation of the regulation of NP biosynthesis.

Total Synthesis of Polysubstituted γ-Butyrolactone Lignans (-)-Hinokinin, (-)-Bicubebin B, and (-)-Isodeoxypodophyllotoxin via Oxime Carbonate Formation.

The diverse structures and profound biological activities of lignan natural products have enticed significant effort in the exploration of new methodologies for their total synthesis. We have prepared γ-butyrolactone oximes from readily available δ-nitro alcohols via Boc2O mediated cyclization. The mild conditions are compatible with a wide range of functional groups, and this methodology has been applied to the total synthesis of five lignan natural products.

Detection of Exogenous γ-Hydroxybutyric Acid in Rat Blood Exosomes.

OBJECTIVES: To find a method to distinguish exogenous gamma-hydroxybutyrate (GHB) from endogenous GHB by establishing ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) based on exosome for quantitative detection of GHB in the rat blood. METHODS: Adult male SD rats were divided into 1 h, 5 h, 10 h administration group and control group. After 1 h, 5 h and 10 h of single precursor of GHB gamma-butyrolactone (GBL) intraperitoneal injection in administration groups, 5 mL blood was collected from the abdominal aorta. Meanwhile, the control group was given a same dose of normal saline, and 5 mL blood was collected at 1 h. Among the 5 mL blood, 0.5 mL was directly detected by HPLC-MS after pretreatment, and exosomes were extracted from the remaining blood by differential centrifugation and detected. RESULTS: The concentration of GHB in the control group was (87.36±33.48) ng/mL, and the concentration with administration at 1 h, 5 h and 10 h was (110 400.00±1 766.35) ng/mL, (1 479.00±687.01) ng/mL and (133.60±12.17) ng/mL, respectively. The results of exosome detection showed that no peak GHB signal was detected in the control group and the 10 h administration group, and the concentrations of GHB at 1 h and 5 h administration groups were (91.47±33.44) ng/mL and (49.43±7.05) ng/mL, respectively. CONCLUSIONS: GHB was detected in blood exosome by UPLC-MS, which indicated that exogenous GHB could be detected in plasma exosomes, while endogenous GHB could not be detected, suggesting that this method may be used as a basis to determine whether there is exogenous drug intake.

γ-Aromatic Butenolides of Microbial Source - A Review of Their Structures, Biological Activities and Biosynthesis.

γ-Aromatic butenolides (γ-AB) are an important type of structures found in many bioactive microbial secondary metabolites (SMs). γ-AB refer to a group of natural products (NPs) containing five-membered (unsaturated) lactones with 3-phenyl and 4-benzyl substituents. Their wide-range biological activities have inspired pharmaceutical chemists to explore its biosynthesis mechanisms and design strategies to construct the γ-AB skeleton. Recently, there are a great deal of interesting research progress on the structures, biological activities and biosynthesis of γ-AB. This review will focus on these aspects and summarize the important achievements of γ-AB from 1975 to 2021.

New Metabolites from the Marine Sponge Scopalina hapalia Collected in Mayotte Lagoon.

The biological screening of 44 marine sponge extracts for the research of bioactive molecules, with potential application in the treatment of age-related diseases (cancer and Alzheimer's disease) and skin aging, resulted in the selection of Scopalina hapalia extract for chemical study. As no reports of secondary metabolites of S. hapalia were found in the literature, we undertook this research to further extend current knowledge of Scopalina chemistry. The investigation of this species led to the discovery of four new compounds: two butenolides sinularone J (1) and sinularone K (2), one phospholipid 1-O-octadecyl-2-pentanoyl-sn-glycero-3-phosphocholine (3) and one lysophospholipid 1-O-(3-methoxy-tetradecanoyl)-sn-glycero-3-phosphocholine (4) alongside with known lysophospholipids (5 and 6), alkylglycerols (7-10), epidioxysterols (11 and 12) and diketopiperazines (13 and 14). The structure elucidation of the new metabolites (1-4) was determined by detailed spectroscopic analysis, including 1D and 2D NMR as well as mass spectrometry. Molecular networking was also explored to complement classical investigation and unravel the chemical classes within this species. GNPS analysis provided further information on potential metabolites with additional bioactive natural compounds predicted.

Butenolides from the Coral-Derived Fungus Aspergillius terreus SCSIO41404.

Five undescribed butenolides including two pairs of enantiomers, (+)-asperteretal G (1a), (-)-asperteretal G (1b), (+)-asperteretal H (2a), (-)-asperteretal H (2b), asperteretal I (3), and para-hydroxybenzaldehyde derivative, (S)-3-(2,3-dihydroxy-3-methylbutyl)-4-hydroxybenzaldehyde (14), were isolated together with ten previously reported butenolides 4-13, from the coral-derived fungus Aspergillus terreus SCSIO41404. Enantiomers 1a/1b and 2a/2b were successfully purified by high performance liquid chromatography (HPLC) using a chiral column, and the enantiomers 1a and 1b were new natural products. Structures of the unreported compounds, including the absolute configurations, were elucidated by NMR and MS data, optical rotation, experimental and calculated electronic circular dichroism, induced circular dichroism, and X-ray crystal data. The isolated butenolides were evaluated for antibacterial, cytotoxic, and enzyme inhibitory activities. Compounds 7 and 12 displayed weak antibacterial activity, against Enterococcus faecalis (IC50 = 25 µg/mL) and Klebsiella pneumoniae (IC50 = 50 µg/mL), respectively, whereas 6 showed weak inhibitory effect on acetylcholinesterase. Nevertheless, most of the butenolides showed inhibition against pancreatic lipase (PL) with an inhibition rate of 21.2-73.0% at a concentration of 50 µg/mL.

Palladium-Catalyzed Enantioselective γ-Arylation of ß,γ-Unsaturated Butenolides.

γ-Butenolide and γ-butyrolactone scaffolds are two types of important core structures in numerous natural products and bioactive targets. However, methods to construct the chiral quaternary arylated γ-butenolide are rarely explored. We herein report an efficient Pd-catalyzed enantioselective γ-arylation of ß,γ-unsaturated butenolides with aryl bromides, which shows high γ-selectivity, good functional group tolerance and excellent enantioselectivity. Notably, this protocol also allows for facile construction of tricyclic tetrahydroindolines and tetrahydroisoquinolinones in one step. DFT calculations are consistent with the experimental results, suggesting that the γ-arylation is favoured over the α-arylation. Finally, this method is applied to the rapid synthesis of natural product (R)-(+)-boivinianin A.

New Deoxyenhygrolides from Plesiocystis pacifica Provide Insights into Butenolide Core Biosynthesis.

Marine myxobacteria present a virtually unexploited reservoir for the discovery of natural products with diverse biological functions and novel chemical scaffolds. We report here the isolation and structure elucidation of eight new deoxyenhygrolides (1-8) from the marine myxobacterium Plesiocystis pacifica DSM 14875T. The herein described deoxyenhygrolides C-J (1-8) feature a butenolide core with an ethyl residue at C-3 of the γ-lactone in contrast to the previously described derivatives, deoxyenhygrolides A and B, which feature an isobutyl residue at this position. The butenolide core is 2,4-substituted with a benzyl (1, 2 and 7), benzoyl (3 and 4) or benzyl alcohol (5, 6 and 8) moiety in the 2-position and a benzylidene (1-6) or benzylic hemiketal (7 and 8) in the 4-position. The description of these new deoxyenhygrolide derivatives, alongside genomic in silico investigation regarding putative biosynthetic genes, provides some new puzzle pieces on how this natural product class might be formed by marine myxobacteria.

Structural Biology-Guided Design, Synthesis, and Biological Evaluation of Novel Insect Nicotinic Acetylcholine Receptor Orthosteric Modulators.

The development of novel and safe insecticides remains an important need for a growing world population to protect crops and animal and human health. New chemotypes modulating the insect nicotinic acetylcholine receptors have been recently brought to the agricultural market, yet with limited understanding of their molecular interactions at their target receptor. Herein, we disclose the first crystal structures of these insecticides, namely, sulfoxaflor, flupyradifurone, triflumezopyrim, flupyrimin, and the experimental compound, dicloromezotiaz, in a double-mutated acetylcholine-binding protein which mimics the insect-ion-channel orthosteric site. Enabled by these findings, we discovered novel pharmacophores with a related mode of action, and we describe herein their design, synthesis, and biological evaluation.

Detection of Exogenous γ-Hydroxybutyric Acid in Rat Blood Exosomes / 法医学杂志

OBJECTIVES@#To find a method to distinguish exogenous gamma-hydroxybutyrate (GHB) from endogenous GHB by establishing ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS) based on exosome for quantitative detection of GHB in the rat blood.@*METHODS@#Adult male SD rats were divided into 1 h, 5 h, 10 h administration group and control group. After 1 h, 5 h and 10 h of single precursor of GHB gamma-butyrolactone (GBL) intraperitoneal injection in administration groups, 5 mL blood was collected from the abdominal aorta. Meanwhile, the control group was given a same dose of normal saline, and 5 mL blood was collected at 1 h. Among the 5 mL blood, 0.5 mL was directly detected by HPLC-MS after pretreatment, and exosomes were extracted from the remaining blood by differential centrifugation and detected.@*RESULTS@#The concentration of GHB in the control group was (87.36±33.48) ng/mL, and the concentration with administration at 1 h, 5 h and 10 h was (110 400.00±1 766.35) ng/mL, (1 479.00±687.01) ng/mL and (133.60±12.17) ng/mL, respectively. The results of exosome detection showed that no peak GHB signal was detected in the control group and the 10 h administration group, and the concentrations of GHB at 1 h and 5 h administration groups were (91.47±33.44) ng/mL and (49.43±7.05) ng/mL, respectively.@*CONCLUSIONS@#GHB was detected in blood exosome by UPLC-MS, which indicated that exogenous GHB could be detected in plasma exosomes, while endogenous GHB could not be detected, suggesting that this method may be used as a basis to determine whether there is exogenous drug intake.

Ligand-controlled divergent dehydrogenative reactions of carboxylic acids via C-H activation.

Dehydrogenative transformations of alkyl chains to alkenes through methylene carbon-hydrogen (C­H) activation remain a substantial challenge. We report two classes of pyridine-pyridone ligands that enable divergent dehydrogenation reactions through palladium-catalyzed ß-methylene C­H activation of carboxylic acids, leading to the direct syntheses of α,ß-unsaturated carboxylic acids or γ-alkylidene butenolides. The directed nature of this pair of reactions allows chemoselective dehydrogenation of carboxylic acids in the presence of other enolizable functionalities such as ketones, providing chemoselectivity that is not possible by means of existing carbonyl desaturation protocols. Product inhibition is overcome through ligand-promoted preferential activation of C(sp3)­H bonds rather than C(sp2)­H bonds or a sequence of dehydrogenation and vinyl C­H alkynylation. The dehydrogenation reaction is compatible with molecular oxygen as the terminal oxidant.

A general and concise stereodivergent chiral pool approach toward trans-(4S,5R)- and cis-(4R,5R)-5-alkyl-4-methyl-γ-butyrolactones: Syntheses of (+)-trans- and (+)-cis-whisky and cognac lactones from d-(+)-mannitol.

A straightforward synthesis of (+)-trans-(4S,5R)- and (+)-cis-(4R,5R)-whisky lactones starting from d-(+)-mannitol has been reported here in fewer number of efficient steps compared to existing literature processes involving d-mannitol as the chiral pool starting material. Chiron approach directly translated chirality of d-mannitol to one of the two chiral centers in these target molecules. Toward this end, stereoisomerically pure trans- and cis-iodomethyl-γ-lactones were formed in the penultimate step. These two acted as versatile advanced common intermediates as they were also converted to the (+)-trans-(4S,5R)- and (+)-cis-(4R,5R)-cognac lactones, respectively. To the best of our knowledge, till date no synthesis of cognac lactones starting from d-mannitol has been reported. All these lactones are identified as the key aroma components of aged alcoholic beverages.

Construction of Enantioenriched γ,γ-Disubstituted Butenolides Enabled by Chiral Amine and Lewis Acid Cascade Cocatalysis.

Herein we report a cascade cocatalysis strategy for the facile construction of chiral γ,γ-disubstituted butenolides. The synthetic manifold employs simple alkynoic acids instead of the preformed silyloxy furans or 5-substituted furan-2(3H)-ones. In situ formed 5-substituted furan-2(3H)-ones by AgNO3 or Ph3PAuCl/AgOTf catalyzed cyclization of alkynoic acids can smoothly engage in the subsequent chiral diphenylprolinol TMS-ether catalyzed Michael and Michael-aldol reactions. The cascade process serves as a general approach to chiral quaternary γ,γ-disubstituted butenolides.

Ozonolysis of α-angelica lactone: a renewable route to malonates.

Industrially relevant intermediates such as malonic acid, malonates and 3-oxopropionates can be easily accessed by ozonolysis of α-angelica lactone, derived from the platform chemical levulinic acid. The roles of the solvent and of the quenching conditions are of key importance for the outcome of the reaction.