Total Synthesis of Putative Melognine

Total synthesis of melognine was accomplished. A 10-membered cyclic alkyne was prepared via an intramolecular SN2 reaction of a nosylamide. Enyne metathesis of the cyclic alkyne under an atmosphere of ethylene afforded a 1,3-diene. Intramolecular cycloaddition of a nitrone and an azomethine ylide with the 1,3-diene moiety constructed the characteristic highly fused skeleton. Further transformation, including ring-closing metathesis, resulted in the synthesis of melognine, whose NMR spectra did not match the reported data. Close inspection of the spectra of melognine in the literature suggested that the structure of melognine might be identical with that of a known alkaloid, melodinine L.

Deep learning driven de novo drug design based on gastric proton pump structures

Existing drugs often suffer in their effectiveness due to detrimental side effects, low binding affinity or pharmacokinetic problems. This may be overcome by the development of distinct compounds. Here, we exploit the rich structural basis of drug-bound gastric proton pump to develop compounds with strong inhibitory potency, employing a combinatorial approach utilizing deep generative models for de novo drug design with organic synthesis and cryo-EM structural analysis. Candidate compounds that satisfy pharmacophores defined in the drug-bound proton pump structures, were designed in silico utilizing our deep generative models, a workflow termed Deep Quartet. Several candidates were synthesized and screened according to their inhibition potencies in vitro, and their binding poses were in turn identified by cryo-EM. Structures reaching up to 2.10 Å resolution allowed us to evaluate and re-design compound structures, heralding the most potent compound in this study, DQ-18 (N-methyl-4-((2-(benzyloxy)-5-chlorobenzyl)oxy)benzylamine), which shows a Ki value of 47.6 nM. Further high-resolution cryo-EM analysis at 2.08 Å resolution unambiguously determined the DQ-18 binding pose. Our integrated approach offers a framework for structure-based de novo drug development based on the desired pharmacophores within the protein structure.

Total syntheses of macleanine and lycoposerramine-S

Total syntheses of fawcettimine-class Lycopodium alkaloids having an imino bridge between C5 and C13 were accomplished. Fawcettimine was first prepared in 10 steps from a known compound, and the characteristic structures, including the imino bridge, were constructed via the formation of a bridgehead imine.

Total Syntheses of Malettinins C and E

The total syntheses of tropolone-containing natural products malettinins C and E were accomplished. A nitro compound and a chiral enone were prepared by using palladium-mediated nitromethylation and an organocatalyst-mediated asymmetric aldol reaction, respectively, and were connected via a Michael reaction. Oxidative dearomatization of a phenol having a cyclic acetal moiety produced a spirocyclic dienone, which could be converted into a tropolone via a base-mediated ring-expansion reaction, with elimination of the nitro group, providing entry to malettinins C and E.

Construction of the tetracyclic ring system of diterpene alkaloids via cationic [5 + 2] cycloaddition

The ABCD ring system of C₁₈/C₁₉ diterpene alkaloids was constructed via cationic [5 + 2] cycloaddition to forge a bicyclo[3.2.1]octane, an intramolecular aldol reaction to form a seven-membered ring, oxidation of a phenol at the para-position, and introduction of a one-carbon unit via Stille coupling followed by oxidative cleavage of a furan ring.

Total Synthesis of Kopsone

A total synthesis of kopsone was achieved, featuring stereoselective preparation of an acyclic aldehyde having a protected hydroxylamine moiety via Ireland-Claisen rearrangement and intramolecular cycloaddition of an eight-membered cyclic nitrone to form the 2-azabicyclo[3.3.1]nonane skeleton.

Fluorinated 2,6-Xylenesulfonyl Group: A Protective Group for Amines

We have developed a fluorinated 2,6-xylenesulfonyl group (fluorinated xysyl, ^fXs) as a protective group for amines. The sulfonyl group could be attached to amines by reactions with the corresponding sulfonyl chloride, and survived various conditions, including acidic, basic, and even reductive conditions. The ^fXs group could be cleaved by treatment with a thiolate under mild conditions.

Convergent synthesis of the [5-7-6-3] tetracyclic core of premyrsinane diterpenes

The [5-7-6-3] tetracyclic core of premyrsinane diterpenes was convergently synthesized via the stereoselective three-component coupling of a 2-propenyl unit, an enone, and an aldehyde, followed by the relay ring-closing metathesis with conformation control of the substrate to construct the 7-membered ring.

Construction of the [7-5-5] Tricyclic Core of Daphniphyllum Alkaloids via a Cationic Cascade Reaction

The [7-5-5] tricyclic core of daphniphyllum alkaloids, containing contiguous stereogenic centers at C14 and C15 and a tetrasubstituted alkene moiety between C9 and C10, was constructed via a cascade reaction that involved an electrocyclic reaction of a pentadienyl cation and intramolecular interception of the resultant cyclopentenyl cation.

Formal Synthesis of Ecteinascidin 743 via an Intramolecular Cascade Heck Reaction to Construct the Diazabicyclo[3.3.1]nonane Framework

A synthetic route to ecteinascidin 743 has been established via an intramolecular cascade Heck reaction to construct the diazabicyclo[3.3.1]nonane skeleton while controlling the two contiguous stereogenic centers. The strategically formed five-membered ring was oxidatively cleaved to generate a dialdehyde intermediate, from which the B ring of ecteinascidin 743 was constructed.

Substitution of α-Azido Sulfones with Thiolates to Form α-Azido Sulfides

Upon treatment of α-azido sulfones with a thiol in the presence of 1,1,3,3-tetramethylguanidine, substitution of the sulfonyl group with a thiolate occurred, resulting in the formation of α-azido sulfides. Based on experimental results and DFT calculations, a reaction mechanism that involves the addition of a thiolate to the azido group and generation of an alkylidene triazene is proposed.

Photoinduced rearrangement of α-(2-nitrophenyl)ketones

Photoirradiation of α-(2-nitrophenyl)ketones produced cyclic hydroxamates. The reaction proceeded via photoinduced oxygen transfer from the nitro group to the benzylic position, forming an α-hydroxyketone having a nitroso group. Subsequent addition of the nitroso group to the ketone moiety and the concomitant cleavage of the C-C σ bond between the carbonyl group and the benzyl position produced hydroxamic acid, which underwent formation of a hemiacetal to give cyclic hydroxamate.

Synthetic Approach toward (–)-Tetrodotoxin via Construction of the Bicyclo[2.2.2]octane Skeleton

A synthetic approach toward (–)-tetrodotoxin (TTX) is described. Our approach features a stereoselective construction of the TTX core structure using the bicyclo[2.2.2]octane skeleton which was constructed via intramolecular Diels–Alder reaction of an o-quinone monoketal having the key functional groups. The robust asymmetric synthesis was achieved by an iridium-catalyzed dynamic kinetic resolution (DKR) of the aryl vinyl carbinol that could be easily prepared from a simple aromatic compound.

Total Synthesis of Haliclonin A

The total synthesis of haliclonin A was accomplished. Starting from 3,5-dimethoxybenzoic acid, a functionalized cyclohexanone fused to a 17-membered ring was prepared through a Birch reduction/alkylation sequence, ring-closing metathesis, intramolecular cyclopropanation, and stereoselective 1,4-addition of an organocopper reagent to an enone moiety. Reductive C-N bond formation via an N,O-acetal forged the 3-azabicyclo[3.3.1]nonane core. The allyl alcohol moiety was constructed by a sequence involving stereoselective α-selenylation of an aldehyde via an enamine, syn-elimination of a selenoxide, and allylation of the aldehyde with an allylboronate. Formation of the 15-membered ring containing a skipped diene was achieved by ring-closing metathesis, and final transformations led to the synthesis of haliclonin A.

Photo-oxygenation by a biocompatible catalyst reduces amyloid-β levels in Alzheimer's disease mice

Amyloid formation and the deposition of the amyloid-β peptide are hallmarks of Alzheimer's disease pathogenesis. Immunotherapies using anti-amyloid-β antibodies have been highlighted as a promising approach for the prevention and treatment of Alzheimer's disease by enhancing microglial clearance of amyloid-β peptide. However, the efficiency of antibody delivery into the brain is limited, and therefore an alternative strategy to facilitate the clearance of brain amyloid is needed. We previously developed an artificial photo-oxygenation system using a low molecular weight catalytic compound. The photocatalyst specifically attached oxygen atoms to amyloids upon irradiation with light, and successfully reduced the neurotoxicity of aggregated amyloid-β via inhibition of amyloid formation. However, the therapeutic effect and mode of actions of the photo-oxygenation system in vivo remained unclear. In this study, we demonstrate that photo-oxygenation facilitates the clearance of aggregated amyloid-β from the brains of living Alzheimer's disease model mice, and enhances the microglial degradation of amyloid-β peptide. These results suggest that photo-oxygenation may represent a novel anti-amyloid-β strategy in Alzheimer's disease, which is compatible with immunotherapy.

Copper-Mediated Conversion of Alkynes into Nitriles via Iodotriazoles

We disclose our studies on a copper-mediated reaction of alkynes with trimethylsilyl azide to afford nitriles, and proposed a reaction mechanism, which involves an iodoalkyne and an iodotriazole as intermediates.

A novel translation inhibitor, mersicarpine, inhibits S-phase progression and induces apoptosis in HL60 cells

Mersicarpine is an aspidosperma alkaloid isolated from the Kopsia genus of plants. Its intriguing structural features have attracted much attention in synthetic organic chemistry, but no biological activity has been reported. Here, we report the effects of mersicarpine on human leukemia cell line HL60. At concentrations above 30 µm, mersicarpine reversibly arrested cell cycle progression in S-phase. At higher concentrations, it induced not only production of reactive oxygen species, but also apoptosis. Macromolecular synthesis assay revealed that mersicarpine specifically inhibits protein synthesis. These results suggest that mersicarpine is a novel translation inhibitor that induces apoptosis.

Synthesis of Polycyclic Natural Products through Skeletal Rearrangement

Construction of rings through reliable reactions followed by changes in the ring size or the connectivity through skeletal rearrangement provides molecules with a wide range of skeletons. In this account, our syntheses of polycyclic natural products through skeletal rearrangement are discussed.

1 Introduction

2 Synthesis through Changes in the Ring Size

3 Synthesis by Biomimetic Strategies

4 Synthesis through Metathesis

5 Synthesis through Temporary Formation of a Ring

6 Conclusion

Structure-Activity Relationship Study of Majusculamides A and B and Their Analogues on Osteogenic Activity

We discovered that majusculamide A (1) and majusculamide B (2), isolated from a marine cyanobacterium collected in Okinawa, induced osteoblast differentiation in MC3T3-E1 cells. Although majusculamide A (1) has a different configuration only at the C-19 stereocenter, bearing a methyl group, compared to majusculamide B (2), the effect of 1 was stronger than that of 2. We synthesized some analogues of the majusculamides (3-15) and evaluated osteogenic activities of these analogues. The structure-activity relationship study of majusculamide analogues suggested that the number of methyls and configuration at C-19 and the nature of the substituent at C-20 of majusculamide A (1) may be important for the osteoblast differentiation-inducing effect of 1.

Synthetic Studies on Bilobalide

We disclose our synthetic studies on bilobalide, which features a Diels–Alder reaction of a cyclic anhydride to form two contiguous quaternary carbon centers, desymmetrization of a symmetric diol, and construction of a cyclic acetal under acidic conditions with inversion of configuration at an allylic position.

Total Synthesis of Lycoposerramine-R

A total synthesis of lycoposerramine-R was accomplished. The synthesis featured a Claisen–Ireland rearrangement to install a two-carbon unit, and a hetero-Diels–Alder reaction to form a cyclic enol ether that reacted with an ethynyl group to construct a cis-hydrindane core containing a quaternary carbon. A 2-pyridone synthesis using 2-(phenylsulfinyl)acetamide was used to complete the synthesis.

Synthesis of Cardiopetaline via a Wagner-Meerwein Rearrangement without Preactivation of the Pivotal Hydroxy Group

A synthesis of cardiopetaline has been accomplished via a Wagner-Meerwein rearrangement of a diol having the denudatine skeleton. The Wagner-Meerwein rearrangement could be facilitated simply by heating the diol with p-toluenesulfonic acid in pivalic acid, without preactivating the pivotal hydroxy group. This strategy does not require differentiation of several hydroxy groups in the substrate for the Wagner-Meerwein rearrangement and could be applied to the synthesis of more highly oxygenated aconitine-type diterpenoid alkaloids.

Synthetic Studies of Haliclonin A: Construction of the 3-Azabicyclo[3.3.1]nonane Skeleton with a Bridge that Forms the 17-Membered Ring

The core structure of haliclonin A, a 3-azabicyclo[3.3.1]­nonane with a bridge that forms a 17-membered ring, was constructed. The synthesis features a ring-closing metathesis that constructs the macrocyclic ring, the stereoselective introduction of carbon units via the intra­molecular cyclopropanation of a diazoester, the conjugate addition of an organocopper reagent, and the formation of 3-azabi­cyclo­[3.3.1]­nonane skeleton via an unexpected 1,5-hydride shift.

Synthesis of the [7-5-5] tricyclic core of Daphniphyllum alkaloids

The [7-5-5] tricyclic core of the Daphniphyllum alkaloids was constructed, featuring a Claisen-Ireland rearrangement to install the two contiguous stereogenic centers, E1cB elimination to form the tetrasubstituted C–C double bond, and a 2,3-Wittig rearrangement to construct the quaternary carbon.

Discovery of novel 2-(3-phenylpiperazin-1-yl)-pyrimidin-4-ones as glycogen synthase kinase-3β inhibitors

We herein describe the results of further evolution of glycogen synthase kinase (GSK)-3β inhibitors from our promising compounds containing a 2-phenylmorpholine moiety. Transformation of the morpholine moiety into a piperazine moiety resulted in potent GSK-3β inhibitors. SAR studies focused on the phenyl moiety revealed that a 4-fluoro-2-methoxy group afforded potent inhibitory activity toward GSK-3β. Based on docking studies, new hydrogen bonding between the nitrogen atom of the piperazine moiety and the oxygen atom of the main chain of Gln185 has been indicated, which may contribute to increased activity compared with that of the corresponding phenylmorpholine analogues. Effect of the stereochemistry of the phenylpiperazine moiety is also discussed.

Total Synthesis of Huperzine Q

The total synthesis of huperzine Q was accomplished. The synthesis features the construction of the cis-hydrindane skeleton via a Diels-Alder reaction and a ring contraction reaction of an epoxyketone.

Eudistomin C, an Antitumor and Antiviral Natural Product, Targets 40S Ribosome and Inhibits Protein Translation

Eudistomin C (EudiC), a natural product, shows potent antitumor and antiviral activities, but the target molecule and the mechanism of action remain to be revealed. Here, we show that the 40S ribosome is the target in EudiC cytotoxicity. We isolated EudiC-resistant mutants from a multidrug-sensitive yeast strain, and a genetic analysis classified these YER (yeast EudiC resistance) mutants into three complementation groups. A genome-wide study revealed that the YER1-6 mutation is in the uS11 gene (RPS14A). Biotinylated EudiC pulled down Rps14p-containing complexes from 40S and 80S ribosomes, but not from the 60S ribosome. EudiC strongly inhibited translation of the wild-type strain but not of YER1-6 in cells and in vitro. These results indicate that EudiC is a protein synthesis inhibitor targeting the uS11-containing ribosomal subunit, and shows cytotoxicity by inhibiting protein translation.

Morphological Evaluation of Nonlabeled Cells to Detect Stimulation of Nerve Growth Factor Expression by Lyconadin B

The success of drug development is greatly influenced by the efficiency of drug screening methods. Recently, phenotype-based screens have raised expectations, based on their proven record of identifying first-in-class drugs at a higher rate. Although fluorescence images are the data most commonly used in phenotype-based cell-based assays, nonstained cellular images have the potential to provide new descriptive information about cellular responses. In this study, we applied morphology-based evaluation of nonlabeled microscopic images to a phenotype-based assay. As a study case, we attempted to increase the efficiency of a cell-based assay for chemical compounds that induce production of nerve growth factor (NGF), using lyconadin B as a model compound. Because the total synthesis of lyconadin B was accomplished very recently, there is no well-established cell-based assay scheme for further drug screening. The conventional cell-based assay for evaluating NGF induction requires two types of cells and a total of 5 days of cell culture. The complexity and length of this assay increase both the risk of screening errors and the cost of screening. Our findings show that analysis of cellular morphology enables evaluation of NGF induction by lyconadin B within only 9 h.