Autophagy is a highly conserved lysosomal degradation pathway for maintaining cellular homeostasis. Its dysregulation is implicated in various diseases, including cancer, neurodegeneration, and infections, making precise modulation of autophagy a potentially promising therapeutic strategy. Artificial peptide-based autophagy modulators have emerged as a promising alternative to conventional small molecules, offering several advantages in terms of specificity, biocompatibility, and functional versatility. This review summarizes recent advances in artificial peptide-based autophagy monitoring tools, autophagy inducers, and autophagy inhibitors.

The first enantioselective copper-catalyzed conjugate addition of alpha-substituted benzyl nitriles to alkyl acrylates is described. This protocol allows the direct and 100% atom-economic generation of a nitrile-containing quaternary stereogenic center in a highly enantioselective manner. The practical application of our methodology was demonstrated through the concise formal synthesis of (-)-aphanorphine.

Rocaglaol, a representative flavagline, has attracted significant attention because of its unique chemical structure and biological activities. This paper reports a mild and scalable copper-catalyzed enantioselective conjugate addition of benzofuran-3(2H)-ones to α,β-unsaturated thioamides. This method allows for the concise synthesis of all possible stereoisomers of a key intermediate of rocaglaol and its derivatives in a highly diastereo- and enantioselective manner using different chiral phosphine ligands. Theoretical insights into the reaction mechanism and the origin of ligand-dependent diastereodivergence were obtained using density functional theory calculations.

Butyrolactones are prevalent structural elements in many natural products. Vinylogous conjugate additions of butenolides are among the most promising synthetic methods for generating natural products and/or natural product-like compounds with potential biological activities. In this report, direct 1,6-conjugate addition of butenolide to p-quinone methides via Bronsted base catalysis was performed, which provides an efficient route to interesting molecules. The reaction proceeds with a regioselective gamma-attack of butenolide and shows good functional group tolerance.

A copper-catalyzed asymmetric vinylogous conjugate addition of butenolide to 2-ester-substituted chromones is described, and it delivers syn- or anti-chromanone lactones with high stereoselectivities. The enantioselectivity-determining step varied with the use of B(OMe)3 as an additive, resulting in enhanced stereoselectivities, as revealed by density functional theory calculations, which also provided theoretical insight into the origin of the ligand-dependent diastereodivergence.

A gram-scale syn-selective asymmetric vinylogous addition of butenolides to chromones, catalyzed by an Al-Li-BINOL (ALB) complex, was developed in this study. For various combinations of substrates, the observed diastereoselectivity approached 20:1 with 84-98% ee. This protocol is complementary to previously reported ones and improves the selectivity for several chromones. This methodology can be applied to a quinolone substrate, affording another type of heterocyclic scaffolds substituted with five-membered lactones. Computational studies support the role of ALB as a bifunctional catalyst in this reaction and provide insights into the origin of the observed stereoselectivity.

Selective modulation of autophagy is a promising therapeutic strategy, especially for cancer treatment. However, the lack of specific autophagy inhibitors limits this strategy. The formation of the ATG12-ATG5-ATG16L1 complex is essential for targeting the ATG12-ATG5 conjugate to proper membranes and to generate LC3-II for the progression of autophagy. Thus, targeting ATG5-ATG16L1 protein-protein interactions (PPIs) might inhibit early stage autophagy with high specificity. In this paper, we report that a stapled peptide derived from ATG16L1 exhibits potent binding affinity to ATG5, striking resistance to proteolysis, and significant autophagy inhibition activities in cells.

Vicinal oxygen-containing tetra- and tri-substituted stereocenters exist widely in chromanone lactone and tetrahydroxanthone natural products. Their enantioselective construction in a single step remains elusive and poses a formidable challenge for chemical synthesis. Here, we report the first copper(I)-catalyzed asymmetric vinylogous additions of siloxyfurans to 2-ester-substituted chromones, which enable concise and enantioselective assembly of chromanone lactones. Both syn and anti adducts can be accessed with excellent diastereo- and enantioselectivity by judicious choice of the chiral ligands. Our approach allowed for the efficient synthesis of (-)-blennolide B with precise stereochemical control, which provides a formal synthesis of secalonic acid A.

An anti-selective catalytic asymmetric Michael-type vinylogous addition of β,γ-butenolides to chromones was developed.

The average conformation of the methyl-branched chains of archaeal lipid phosphatidyl glycerophosphate methyl ester (PGP-Me) was examined in a hydrated bilayer membrane based on the 2H nuclear magnetic resonance (NMR) of enantioselectively 2H-labeled compounds that were totally synthesized for the first time in this study. The NMR results in combination with molecular dynamics simulations revealed that the PGP-Me chain appeared to exhibit behavior different from that of typical membrane lipids such as dimyristoylphosphatidylcholine (DMPC). The C-C bonds of the PGP-Me chain adopt alternative parallel and tilted orientations to the membrane normal as opposed to a DMPC chain where all of the C-C bonds tilt in the same way on average. This characteristic orientation causes the intertwining of PGP-Me chains, which plays an important role in the excellent thermal and high-salinity stabilities of archaeal lipid bilayers and membrane proteins.

The direct catalytic asymmetric aldol reaction is an emerging catalytic methodology that provides atom-economical access to functionalized chiral building blocks. Thioamides are useful aldol donors due to their high-fidelity chemoselective enolization and divergent post-aldol transformations. Herein we describe the incorporation of an α-vinyl appendage on a thioamide, which expands the utility of aldol adducts for natural product synthesis. This vinylated thioamide was not accommodated under the previously identified catalyst settings, but the newly developed catalytic conditions furnished aldol products containing the pendant vinyl group.

Four new macrolactones, leptolyngbyolides A-D, were isolated from the cyanobacterium Leptolyngbya sp. collected in Okinawa, Japan. The planar structures of leptolyngbyolides were determined by extensive NMR studies, although complete assignment of the absolute configuration awaited the catalytic asymmetric total synthesis of leptolyngbyolide C. The synthesis took advantage of the catalytic asymmetric thioamide-aldol reaction using copper(I) complexed with a chiral bidentate phosphine ligand to regulate two key stereochemistries of the molecule at the outset. The present total synthesis demonstrates the utility of this reaction for the construction of complex chemical entities. In addition to the total synthesis, this work reports that leptolyngbyolides depolymerize filamentous actin (F-actin) both in vitro and in cells. Detailed biological studies suggest the probable order of F-actin depolymerization and apoptosis caused by leptolyngbyolides.

Abstract Catalytic asymmetric synthesis of the C1–C15 fragment of spirastrellolide A, a naturally occurring PP2A inhibitor, was achieved. To construct the 1,3-polyol system in a stereodefined manner, we took advantage of an iterative aldol strategy comprising the catalytic asymmetric thioamide-aldol reaction, and a diastereoselective crotylation process. A potential segment for the total synthesis of spirastrellolide A was thus accessed through a 14-step procedure.

We achieved a formal total synthesis of scytophycin C. The synthesis demonstrates the utility of the catalytic asymmetric direct thioamide-aldol reaction for the preparation of polyketide structures, and was accomplished via diastereoselective allylation, and allylative cyclization as other key transformations. The reported process accesses Miyashita’s key fragment corresponding to the C7–C18 framework in fewer steps (14 steps) than in previously reported syntheses.

Sphingomyelin (SM) and cholesterol (chol)-rich domains in cell membranes, called lipid rafts, are thought to have important biological functions related to membrane signaling and protein trafficking. To visualize the distribution of SM in lipid rafts by means of Raman microscopy, we designed and synthesized an SM analog tagged with a Raman-active diyne moiety (diyne-SM). Diyne-SM showed a strong peak in a Raman silent region that is free of interference from intrinsic vibrational modes of lipids and did not appear to alter the properties of SM-containing monolayers. Therefore, we used Raman microscopy to directly visualize the distribution of diyne-SM in raft-mimicking domains formed in SM/dioleoylphosphatidylcholine/chol ternary monolayers. Raman images visualized a heterogeneous distribution of diyne-SM, which showed marked variation, even within a single ordered domain. Specifically, diyne-SM was enriched in the central area of raft domains compared with the peripheral area. These results seem incompatible with the generally accepted raft model, in which the raft and nonraft phases show a clear biphasic separation. One of the possible reasons is that gradual changes of SM concentration occur between SM-rich and -poor regions to minimize hydrophobic mismatch. We believe that our technique of hyperspectral Raman imaging of a single lipid monolayer opens the door to quantitative analysis of lipid membranes by providing both chemical information and spatial distribution with high (diffraction-limited) spatial resolution.

Raman scattering microscopy identifies molecular species in a sample by optically detecting molecular vibration, and provides spatial distribution of molecules in a specimen. Our developed slit-scanning Raman microscopy improved imaging speed more than 100 times faster than that of conventional point-scanning Raman microscopy, by providing both diffraction-limited high spatial resolution and chemical information. It allows us to observe dynamic behavior of biomolecules in a living cell during various biological processes, such as cytokinesis, mitosis, and apoptosis [1,2].

Raman scattering microscopy has been utilized for visualizing molecular distribution of a specimen. Our developed slit-scanning Raman microscopy achieves more than 100 times faster imaging speed than that of conventional point-scanning Raman microscopy, which allows us to observe biological samples at high spacio-temporal resolution [1]. Here, we utilized slit-scanning Raman microscopy to observe lipid rafts in an artificial monolayer membrane [2]. Lipid raft is a micro-domain in bio-membranes, formed by sphingomyelin (SM) and cholesterol (chol). It has been thought to work for various biological functions, such as membrane signaling and protein trafficking. For the analysis of lipid rafts, artificial ternary membrane of SM/phosphatidylcholine(PC)/chol has been widely used as a model. Phase separation of this membrane can be visualized by fluorescently-labeled lipids, however, observation of SM inside of the domain has been challenging, because the steric effect of bulky fluorophore disturbs the entry of labeled lipids into tightly packed micro-domain. We directly observed the distribution of SM inside of micro-domain by using Raman microscopy. For the specific observation of SM, we synthesized SM analogue modified with diyne tag (Fig. A). Diyne moiety shows characteristic Raman peak at silent region of biomolecules (Fig. B), and it keeps the original property of SM to be incorporated into micro-domain due to its tiny chemical structure. Raman image of diyne-SM in ternary membrane monolayer visualized micro-domain (Fig. C). We found out that the diyne-SM was enriched in central area compared with the peripheral area of the domain. Raman imaging of lipid membrane, achieved here with single lipid-layer sensitivity, high spatial-resolution and hyper-spectral imaging capability, will widely contribute to lipid membrane research.

Phosphatidylglycerophosphate methyl ester (PGP-Me), a major constituent of the archaeal purple membrane, is essential for the proper proton-pump activity of bacteriorhodopsin (bR). We carried out the first synthesis of the bisphosphate head group of PGP-Me using H-phosphonate chemistry that led to the production of a simplified PGP-Me analogue with straight alkyl chains. To investigate the role of this head group in the structural and functional integrity of bR, the analogue was used to reconstitute bR into liposomes, in which bR retained the original trimeric structure and light-induced photocycle activity. Enhanced ordering of an alkyl chain of the (2)H-labelled analogue was observed in (2)H NMR spectra upon interaction with bR. These results together suggest that the bisphosphate moiety plays a role in the proper functioning of bR through the lipid-protein interaction.

Correction for 'Stereoselective synthesis of the head group of archaeal phospholipid PGP-Me to investigate bacteriorhodopsin-lipid interactions' by Jin Cui, et al., Org. Biomol. Chem., 2015, DOI: 10.1039/c5ob01252j.

Lipid organization has been at the center of research on lipid rafts. Dioleoylphosphatidylcholine (DOPC) is a typical unsaturated lipid. Very few studies have reported its thermodynamics in raft-like membranes. Herein, we have developed a highly efficient synthetic method for [C6-2H2] oleic acid, and newly synthesized [C6-2H2] DOPC. In raft-like oriented bilayers, [C6-2H2] DOPC shows clear phase separation and characteristic phase behavior at various temperature. It has been successfully utilized for the comparison of membrane properties between sphingomyelin (SM) and dihydrosphingomyelin (DHSM) membranes.