Peroxisome-derived lipids are self antigens that stimulate invariant natural killer T cells in the thymus.

The development and maturation of semi-invariant natural killer T cells (iNKT cells) rely on the recognition of self antigens presented by CD1d restriction molecules in thymus. The nature of the stimulatory thymic self lipids remains elusive. We isolated lipids from thymocytes and found that ether-bonded mono-alkyl glycerophosphates and the precursors and degradation products of plasmalogens stimulated iNKT cells. Synthetic analogs showed high potency in activating thymic and peripheral iNKT cells. Mice deficient in the peroxisomal enzyme glyceronephosphate O-acyltransferase (GNPAT), essential for the synthesis of ether lipids, had significant alteration of the thymic maturation of iNKT cells and fewer iNKT cells in both thymus and peripheral organs, which confirmed the role of ether-bonded lipids as iNKT cell antigens. Thus, peroxisome-derived lipids are nonredundant self antigens required for the generation of a full iNKT cell repertoire.

Discovery of potential novel TRPC5 inhibitors by virtual screening and bioassay.

The transient receptor potential canonical channel 5 (TRPC5), a member of the TRPC family, plays a crucial role in the regulation of various physiological activities and diseases, including those related to the central nervous system, cardiovascular system, kidney, and cancer. As a nonselective cation channel, TRPC5 mainly controls the influx of extracellular Ca2+ into cells, thereby modulating cellular depolarization and intracellular ion concentration. Inhibition of TRPC5 by small molecules presents a promising approach for the treatment of TRPC5-associated diseases. In this study, we conducted a comprehensive virtual screening of more than 1.5 million molecules from the Chemdiv database (https://www.chemdiv.com) to identify potential inhibitors of hTRPC5, utilizing the published structures and binding sites of hTRPC5 as a basis. Lipinski's rule, Veber's rule, PAINS filters, pharmacophore analysis, molecular docking, ADMET evaluation and cluster analysis methods were applied for the screening. From this rigorous screening process, 18 candidates exhibiting higher affinities to hTRPC5 were subsequently evaluated for their inhibitory effects on Ca2+ influx using a fluorescence-based assay. Notably, two molecules, namely SML-1 and SML-13, demonstrated significant inhibition of intracellular Ca2+ levels in hTRPC5-overexpressing HEK 293T cells, with IC50 values of 10.2 µM and 10.3 µM, respectively. These findings highlight SML-1 and SML-13 as potential lead molecules for the development of therapeutics targeting hTRPC5 and its associated physiological activities and diseases.

Strategies for total synthesis of bispyrrolidinoindoline alkaloids.

Covering up to 2021Complex cyclotryptamine alkaloids with a bispyrrolidino[2,3-b]indoline (BPI) skeleton are an intriguing family of natural products, exhibiting wide systematic occurrences, large structural diversity, and multiple biological activities. Based on their structural characteristics, BPI alkaloids can be classified into chimonanthine-type BPI alkaloids, BPI diketopiperazines, and BPI epipolythiodiketopiperazines. These intricate molecules have captivated great attention soon after their isolation and identification in the 1960s. Due to the structural complexity, the total synthesis of these cyclotryptamine alkaloids is challenging. Nevertheless, remarkable progress has been achieved in the last six decades; in particular, several methods have been successfully established for the construction of vicinal all-carbon quaternary stereocenters. In this review, the structural diversity and chemical synthesis of these BPI alkaloids were summarized. BPI alkaloids are mainly synthesized by the methods of oxidative dimerization, reductive dimerization, and alkylation of bisoxindole. The purpose of this review is to present overall strategies for assembling the BPI skeleton and efforts towards controlling the stereocenters.

Synthesis of C2-Carbonyl Indoles via Visible Light-Induced Oxidative Cleavage of an Aminomethylene Group.

A strategy for photochemical oxidative cleavage of the aminomethylene group at the C2 position of indole was developed to synthesize C2-carbonyl indoles. The reaction was initiated by the photochemical oxidation of N1, followed by a water-assisted concerted H-shift by abstracting hydrogen from aminomethylene. Bromopyridine was discovered to play dual roles as an oxidant for the regeneration of photocatalysts and as an accelerant for the single-electron transfer process.

Retro-biosynthetic construction of corynanthe alkaloid skeletons from rhynchophylline alkaloids.

Rhynchophylline alkaloids are bio-synthesized from corynanthe alkaloids via an oxidative rearrangement. We demonstrate here that corynanthe alkaloids could be generated from rhynchophylline alkaloids in a retro-biosynthetic manner via a Wagner-Meerwein rearrangement. A series of corynanthe analogues were afforded with good functional group tolerance and satisfactory yields.

Enantioselective Total Synthesis of (+)-Flavisiamine†F via Late-Stage Visible-Light-Induced Photochemical Cyclization.

The structural features Kopsia alkaloids, in particular multiple all-carbon quaternary stereocenters in a caged and strained polycyclic skeleton, poses particular challenges for enantioselective total synthesis. Herein, we reported the first total synthesis of (+)-flavisiamine F. The synthetic approach involved a room-temperature Overman rearrangement for introducing the chiral amine at C21, a TMS-promoted ketal Claisen rearrangement for constructing the all-carbon quaternary stereocenter at C20, and a late-stage visible-light-induced photochemical cyclization for establishing the all-carbon quaternary stereocenter at C7.

Enantioselective Radical Cyclization of Tryptamines by Visible Light-Excited Nitroxides.

Nitroxides can absorb both ultraviolet (UV) and visible light, and their electron can be excited from the π-bonding orbital to the antibonding π* orbital or the n-bonding orbital to the antibonding π* orbital, respectively. Despite the reported UV-induced hydrogen atom transfer (HAT) process, the potential of nitroxides for visible light-excited photosynthesis is underexplored. Here we demonstrate that nitroxide can convert indole to its radical through a visible light-induced HAT process. A chiral phosphoric acid-catalyzed cyclization of the in situ-formed imine radical, followed by trapping by another molecule of nitroxide, provides the product in high yield and enantioselectivity. To highlight the novelty and efficiency of this strategy, an asymmetric total synthesis of natural product (-)-verrupyrroloindoline was accomplished in 5 steps.

Vibsanin B preferentially targets HSP90ß, inhibits interstitial leukocyte migration, and ameliorates experimental autoimmune encephalomyelitis.

Interstitial leukocyte migration plays a critical role in inflammation and offers a therapeutic target for treating inflammation-associated diseases such as multiple sclerosis. Identifying small molecules to inhibit undesired leukocyte migration provides promise for the treatment of these disorders. In this study, we identified vibsanin B, a novel macrocyclic diterpenoid isolated from Viburnum odoratissimum Ker-Gawl, that inhibited zebrafish interstitial leukocyte migration using a transgenic zebrafish line (TG:zlyz-enhanced GFP). We found that vibsanin B preferentially binds to heat shock protein (HSP)90ß. At the molecular level, inactivation of HSP90 can mimic vibsanin B's effect of inhibiting interstitial leukocyte migration. Furthermore, we demonstrated that vibsanin B ameliorates experimental autoimmune encephalomyelitis in mice with pathological manifestation of decreased leukocyte infiltration into their CNS. In summary, vibsanin B is a novel lead compound that preferentially targets HSP90ß and inhibits interstitial leukocyte migration, offering a promising drug lead for treating inflammation-associated diseases.

Concise total synthesis of (±)-serotobenine.

A concise total synthesis of (±)-serotobenine via a strategy inspired by the biosynthetic hypothesis for this alkaloid was accomplished. The indolofuran core was constructed by an iron-catalyzed intermolecular oxidative radical cross-coupling reaction developed by our group.

4,5-cis unsaturated α-GalCer analogues distinctly lead to CD1d-mediated Th1-biased NKT cell responses.

The total synthesis of 4,5-cis unsaturated α-GalCer analogues was achieved, and their immune-response altering activity was assessed in vitro as well as in vivo in mice. Using glycosyl iodide as a glycosyl donor, construction of the sphingosine unit was shortened by four steps and single α-stereoselectivity was achieved in good yield (67%). With regard to the therapeutic use of α-GalCer, the novel analogues (1b and 1c) distinctly induced a Th1-biased cytokine response, avoiding induction of a contradictory response and overstimulation.

Total Synthesis of (+)-Chimonanthine, (+)-Folicanthine, and (-)-Calycanthine.

Facile, straightforward, and asymmetric total syntheses of (+)-chimonanthine (1), (+)-folicanthine (2), and (-)-calycanthine (3) were accomplished in four to five steps from commercially available tryptamine. The synthesis features copper-mediated asymmetric cyclodimerization of chiral tryptamine derivative, which established a new entry into constructing the sterically hindered vicinal quaternary stereogenic carbon centers of dimeric hexahydropyrroloindole alkaloids in one procedure. An unprecedented base-induced isomerization from the chimonanthine skeleton to the calycanthine skeleton was observed and facilitated the synthesis of (-)-calycanthine (3).

Semen-Like Floral Scents and Pollination Biology of a Sapromyophilous Plant Stemona japonica (Stemonaceae).

By emitting scent resembling that of organic material suitable for oviposition and/or consumption by flies, sapromyophilous flowers use these flies as pollinators. To date, intensive scent analyses of such flowers have been restricted to Apocynaceae, Annonaceae, and Araceae. Recent studies have suggested that the wide range of volatile organic compounds (VOCs) from sapromyophilous flowers play an important role in attracting saprophagous flies by mimicking different types of decomposing substrates (herbivore and carnivore feces, carrion, and the fruiting bodies of fungi, etc.). In this study, we report the flower visitors and the floral VOCs of Stemona japonica (Blume) Miquel, a species native to China. The flowers do not produce rewards, and pollinators were not observed consuming pollen, thus suggesting a deceptive pollination system. Headspace samples of the floral scent were collected via solid-phase micro-extraction and analysed by gas chromatography coupled with mass spectrometry. Main floral scent compounds were 1-pyrroline (59.2%), 2-methyl-1-butanol (27.2%), and 3-methyl-1-butanol (8.8%), and resulted in a semen-like odor of blooming flowers. The floral constituents of S. japonica were significantly different from those found in previous sapromyophilous plants. An olfaction test indicated that 1-pyrroline is responsible for the semen-like odor in S. japonica flowers. Main flower visitors were shoot flies of the genus Atherigona (Muscidae). Bioassays using a mixture of all identified floral volatiles revealed that the synthetic volatiles can attract Atherigona flies in natural habitats. Our results suggest that the foul-smelling flowers of S. japonica may represent a new type of sapromyophily through scent mimicry.

Construction of tetracyclic 3-spirooxindole through cross-dehydrogenation of pyridinium: applications in facile synthesis of (±)-corynoxine and (±)-corynoxine B.

A facile and straightforward method was developed to construct the fused tetracyclic 3-spirooxindole skeleton, which exists widely in natural products. The formation of the tetracyclic 3-spirooxindole structure was achieved through a transition-metal-free intramolecular cross-dehydrogenative coupling of pyridinium, which were formed in situ by the condensation of 3-(2-bromoethyl)indolin-2-one derivatives with 3-substituted pyridines. As examples of the application of this new methodology, two potentially medicinal natural products, (±)-corynoxine and (±)-corynoxine B, were efficiently synthesized in five scalable steps.

Cyclohexane-fused octahydroquinolizine alkaloids from Myrioneuron faberi with activity against hepatitis C virus.

Investigation of the alkaloids from Myrioneuron faberi, a plant unique to China, gave four pairs of enantiomers (1-4). (±)-ß-Myrifabral A (1) and (±)-α-myrifabral A (2) formed an inseparable mixture of anomers (cluster A), as did (±)-ß-myrifabral B (3) and (±)-α-myrifabral B (4) (cluster B). Their structures were determined by X-ray diffraction and NMR analysis. Compounds 1-4 possessed novel cyclohexane-fused octahydroquinolizine skeletons and represent the first quinolizidine alkaloids from the genus Myrioneuron. The epimers of cluster A (1 and 2) were modified and separated. In vitro, clusters A and B and their derivatives inhibited replication of hepatitis C virus (HCV, IC50 0.9 to 4.7 µM) with cytotoxicity lower than that of telaprevir.

Synthesis and evaluation of immunostimulant plasmalogen lysophosphatidylethanolamine and analogues for natural killer T cells.

Plasmalogen lysophosphatidylethanolamine (pLPE) had been identified as a self antigen for natural killer T cells (NKT cells). It is very important in the development, maturation and activation of NKT cells in thymus. Besides, pLPE is a novel type of antigen for NKT cells. To evaluate the structure-activity relationship (SAR) of this new antigen, pLPE and its analogues referred to different aliphatic chains and linkages at the sn-1 position of the glycerol backbone were synthesized, and the biological activities of these analogues was characterized. It is discovered that the linkages between phosphate and lipid moiety are not important for the antigens' activities. The pLPE analogues 1, 3, 4, 7 and 9, which have additional double bonds on lipid parts, were identified as new NKT agonists. Moreover, the analogues 4, 7 and 9 were discovered as potent Th2 activators for NKT cells.

Fine tuning by human CD1e of lipid-specific immune responses.

CD1e is a member of the CD1 family that participates in lipid antigen presentation without interacting with the T-cell receptor. It binds lipids in lysosomes and facilitates processing of complex glycolipids, thus promoting editing of lipid antigens. We find that CD1e may positively or negatively affect lipid presentation by CD1b, CD1c, and CD1d. This effect is caused by the capacity of CD1e to facilitate rapid formation of CD1-lipid complexes, as shown for CD1d, and also to accelerate their turnover. Similar results were obtained with antigen-presenting cells from CD1e transgenic mice in which lipid complexes are assembled more efficiently and show faster turnover than in WT antigen-presenting cells. These effects maximize and temporally narrow CD1-restricted responses, as shown by reactivity to Sphingomonas paucimobilis-derived lipid antigens. CD1e is therefore an important modulator of both group 1 and group 2 CD1-restricted responses influencing the lipid antigen availability as well as the generation and persistence of CD1-lipid complexes.

Adaptability of the semi-invariant natural killer T-cell receptor towards structurally diverse CD1d-restricted ligands.

The semi-invariant natural killer (NK) T-cell receptor (NKTcr) recognises structurally diverse glycolipid antigens presented by the monomorphic CD1d molecule. While the alpha-chain of the NKTcr is invariant, the beta-chain is more diverse, but how this diversity enables the NKTcr to recognise diverse antigens, such as an alpha-linked monosaccharide (alpha-galactosylceramide and alpha-galactosyldiacylglycerol) and the beta-linked trisaccharide (isoglobotriaosylceramide), is unclear. We demonstrate here that NKTcrs, which varied in their beta-chain usage, recognised diverse glycolipid antigens with a similar binding mode on CD1d. Nevertheless, the NKTcrs recognised distinct epitopic sites within these antigens, including alpha-galactosylceramide, the structurally similar alpha-galactosyldiacylglycerol and the very distinct isoglobotriaosylceramide. We also show that the relative roles of the CDR loops within the NKTcr beta-chain varied as a function of the antigen. Thus, while NKTcrs characteristically use a conserved docking mode, the NKTcr beta-chain allows these cells to recognise unique aspects of structurally diverse CD1d-restricted ligands.

Water-mediated radical C-H tosylation of alkenes with tosyl cyanide.

The water-mediated tosylation of alkenes with tosyl cyanide was discovered. Experimental investigations revealed that the reaction was initiated by the in situ formation of sulfinyl sulfone in the presence of water. The sulfinyl sulfone species decomposed to a sulfonyl radical and a sulfinyl radical through homolytic fission. The vinyl sulfone was afforded via sequential addition of the alkene to the sulfonyl radical and the sulfinyl radical, followed by ß-elimination of a sulfinyl moiety.

Redox-Neutral Intramolecular Dearomative Spirocyclization of Phenols Induced by Visible Light.

Described herein is a redox-neutral intramolecular dearomative spirocyclization induced by visible light. The photochemical cyclization was catalyzed by a phenolate anion-derived photocatalyst and delivered the spirocyclohexadienone. Mechanistic experiments revealed that the aryl halide was reduced to aryl radical via the single-electron transfer (SET) process under visible light irradiation. The electrophilic addition of an aryl radical with the phenolate anion moiety gave a radical anion intermediate, which recycled the photocatalyst by a second SET process.

Nickel/photoredox dual catalyzed arylalkylation of nonactivated alkenes.

Alkene dicarbofunctionalization is an efficient strategy and operation-economic fashion for introducing complexity in molecules. A nickel/photoredox dual catalyzed arylalkylation of nonactivated alkenes for the simultaneous construction of one C(sp3)-C(sp3) bond and one C(sp3)-C(sp2) bond has been developed. The mild catalytic method provided valuable indanethylamine derivatives with wide substrate scope and good functional group compatibility. An enantioselective dicarbofunctionalization was also achieved with pyridine-oxazoline as a ligand. The efficiency of metallaphotoredox dicarbofunctionalization was demonstrated for the concise synthesis of pharmaceutically active compounds.