PurA is the main target of aurodox, a type III secretion system inhibitor.

Anti-microbial resistance (AMR) is one of the greatest threats to global health. The continual battle between the emergence of AMR and the development of drugs will be extremely difficult to stop as long as traditional anti-biotic approaches are taken. In order to overcome this impasse, we here focused on the type III secretion system (T3SS), which is highly conserved in many Gram-negative pathogenic bacteria. The T3SS is known to be indispensable in establishing disease processes but not essential for pathogen survival. Therefore, T3SS inhibitors may be innovative anti-infective agents that could dramatically reduce the evolutionary selective pressure on strains resistant to treatment. Based on this concept, we previously identified a polyketide natural product, aurodox (AD), as a specific T3SS inhibitor using our original screening system. However, despite its promise as a unique anti-infective drug of AD, the molecular target of AD has remained unclear. In this paper, using an innovative chemistry and genetic biology-based approach, we show that AD binds to adenylosuccinate synthase (PurA), which suppresses the production of the secreted proteins from T3SS, resulting in the expression of bacterial virulence both in vitro and in vivo experiments. Our findings illuminate the potential of PurA as a target of anti-infective drugs and vaccination and could open a avenue for application of PurA in the regulation of T3SS.

Directing-Group-Assisted Non-Strained Ether C-O Bond Homolysis Mediated by Low-Valent Titanium.

Ether C-O bonds are typical constituents of organic molecules that are seldom regarded as reactive functional groups except when highly strained. With the assistance of appropriate directing groups, low-valent titanium was found to homolytically cleave non-strained C-O bonds. In particular, a newly designed catechol monoether directing group rendered a route toward the activation of non-benzylic C(sp3)-O bonds. This method has been applied to conventional radical addition reactions to alkenes.

Divergent transformation of C,N-cyclic-N'-acyl azomethine imines by reaction with diazo compounds.

C,N-cyclic-N'-acyl azomethine imines with isoquinoline skeletons were investigated for their reactivity with diazo compounds via two different pathways. During the reaction with ethyl diazoacetate, an α-diazoacetate moiety was introduced at the C1-position of the resulting tetrahydroisoquinolines. Alternatively, diazomethane or trimethylsilyldiazomethane was used to synthesize 3-benzazepine derivatives via ring expansion.

Sattahipmycin, a Hexacyclic Xanthone Produced by a Marine-Derived Streptomyces.

Sattahipmycin was isolated from the mycelium of marine-derived Streptomyces sp. GKU 257-1 by following the antibiofilm activity against E. coli NBRC 3972 throughout the purification steps. The structure of sattahipmycin was determined to be a new polycyclic xanthone related to xantholipin but lacking a dioxymethylene and a chlorinated carbon. This compound showed activity toward Gram-positive bacteria and Plasmodium falciparum, antibiofilm formation of Escherichia coli, and cytotoxicity to human cancer cell lines. Using genome sequence data, a biosynthetic pathway leading to sattahipmycin has been proposed involving an uncharacterized type II polyketide synthase biosynthetic gene cluster.

Highly (E)-Selective Trisubstituted Alkene Synthesis by Low-Valent Titanium-Mediated Homolytic Cleavage of Alcohol C-O Bond.

Ti-mediated homolytic C-O bond cleavage was useful for cascade radical-ionic reactions. Benzyl alcohols treated with TiCl4(col) (col = 2,4,6-collidine) and Mn powder generated the corresponding benzyl radicals; in addition, their reaction with 2-carboxyallyl acetates and the subsequent elimination of the acetoxy group yielded α,ß-unsaturated carbonyl compounds with exclusive (E)-stereoselectivity. The simplicity of the procedure and its wide substrate scope represent a solution to the drawbacks associated with the reactions.

Shikinefragalides A-D, new tricyclic macrolides produced by Stachybotryaceae sp. FKI-9632.

Four new tricyclic macrolides, named shikinefragalides A (1), B (2), C (3) and D (4), were isolated by physicochemical (PC) screening from a static culture material of Stachybotryaceae sp. FKI-9632. Their structures were elucidated as new analogs of colletofragarones by MS and NMR analyses. Compounds 1 and 2 showed weak antimalarial activity and cytotoxicity.

Direct and Unified Access to Carbon Radicals from Aliphatic Alcohols by Cost-Efficient Titanium-Mediated Homolytic C-OH Bond Cleavage.

Low-valent Ti-mediated homolytic C-O bond cleavage offers unified access to carbon radicals from ubiquitous non-activated tertiary, secondary, and even primary alcohols. In contrast to the representative Ti reagents, which were ineffective for this purpose, "TiCl2 (cat)"/Zn (cat=catecholate) was found to be specifically active. This method was applied to the addition reactions of radicals to alkenes and exhibited high generality and yields. More than 50 combinations were examined. The excellent cost-efficiency and accessibility of "TiCl2 (cat)"/Zn further enhance its applicability. Control experiments proved the presence of a carbon radical intermediate and excluded the pathway via alkyl chlorides. Further mechanistic study indicated that the 1 : 2 complex of alkoxide (R-O- ) and TiIII is an active species in the C-O cleavage.

Synthesis of 3,6-Dihydro-2H-1,2-oxazines via Dimethylsulfoxonium Methylide Addition to α,ß-Unsaturated Nitrones.

A unique and efficient formation of 3,6-dihydro-2H-1,2-oxazines starting from α,ß-unsaturated nitrones has been achieved. The nucleophilic addition of dimethylsulfoxonium methylide to the C═N bond of an α,ß-unsaturated nitrone to form an aziridine N-oxide followed by the Meisenheimer rearrangement affords 3,6-dihydro-2H-1,2-oxazine in up to 70% yield. Methylene was confirmed to be incorporated at the C3 position of the ring. A wide range of ß-aryl-substituted α,ß-unsaturated nitrones were applicable to this reaction.

Rh-Catalyzed Direct Carboxylation of Alkenyl C-H Bonds of Alkenylpyrazoles.

The Rh-catalyzed direct carboxylation of alkenyl C-H bonds was achieved by using pyrazole as a removable directing group. In the presence of 5 mol% RhCl3 ⋅ 3H2 O, 6 mol% P(Mes)3 , and 2 equiv. of AlMe2 (OMe), the alkenyl C-H bond of various alkenylpyrazoles was directly carboxylated in good yields under CO2 atmosphere. Furthermore, several useful transformations of the pyrazole moiety of the product were achieved to afford synthetically useful carboxylic acid derivatives in good yields.

Enantioselective Dehydroxyhydrogenation of 3-Indolylmethanols by the Combined Use of Benzothiazoline and Chiral Phosphoric Acid: Construction of a Tertiary Carbon Center.

The chiral indole is an important structure in organic chemistry. We have developed an enantioselective hydrogen transfer reaction of indolylmethanol, which is characterized by the combined use of benzothiazoline and a newly synthesized chiral phosphoric acid. The reaction furnished indoles bearing a chiral tertiary carbon center at the 3-position in high to excellent yields and with excellent enantioselectivities, most of which are greater than 95% ee. The chiral indole was converted into an inhibitor of leukotriene production while retaining excellent ee.

New tetrahydroquinoline and indoline compounds containing a hydroxy cyclopentenone, virantmycin B and C, produced by Streptomyces sp. AM-2504.

Two new antibiotics, designated virantmycin B (1) and C (2), were isolated from the cultured broth of Streptomyces sp. AM-2504. Compounds 1 and 2 were purified by Diaion HP-20, silica gel, and octadecylsilane chromatography, followed by high-performance liquid chromatography. The chemical structures of the new compounds, 1 and 2, were determined by nuclear magnetic resonance and mass spectrometry, as containing a terahydroquinoline and an indoline, respectively, each also containing a hydroxy cyclopentenone moiety. Both compounds demonstrated weak antimicrobial (both antibacterial and antifungal) activity and compound 1 also showed antiviral activity against the dengue virus, whereas compound 2 exhibited no antiviral properties.

Nickel-Catalyzed Cross-Electrophile Coupling between Benzyl Alcohols and Aryl Halides Assisted by Titanium Co-reductant.

A nickel-catalyzed cross-electrophile coupling reaction between benzyl alcohols and aryl halides has been developed using a homolytic C-O bond cleavage protocol that has recently been established. The treatment of a benzyl alcohol and aryl halide with a nickel catalyst and low-valent titanium reagent generated from TiCl4(lutidine) (lutidine = 2,6-lutidine) and manganese powder afforded the cross-coupled product in high yield. A mechanistic study indicated the intermediacy of the benzyl radicals that originate from the benzyl alcohols.

Pestiocandin, a new papulacandin class antibiotic isolated from Pestalotiopsis humus.

Secondary metabolites of microorganisms have proven to be an excellent source of drugs. We isolated a new antibiotic, named pestiocandin (1), from a culture broth of a filamentous fungus, Pestalotiopsis humus FKI-7473, using a multidrug-sensitive budding yeast, S. cerevisiae 12geneΔ0HSR-iERG6. The structure of 1 was elucidated by various NMR studies. All geometric isomerisms of 1 were shown to be the E-form and two pyranose units of 1 were found to be glucose and galactose types. Compound 1 showed weak growth inhibition against Gram-positive and Gram-negative bacteria, yeasts and a filamentous fungus. It displayed more potent growth inhibition against multidrug-sensitive yeasts than wild-type yeasts.

Low-Valent Titanium-Mediated Radical Conjugate Addition Using Benzyl Alcohols as Benzyl Radical Sources.

A concise method to directly generate benzyl radicals from benzyl alcohol derivatives has been developed. The simple and inexpensive combination of TiCl4(collidine) (collidine = 2,4,6-collidine) and manganese powder afforded a low-valent titanium reagent, which facilitated homolytic cleavage of benzylic C-OH bonds. The application to radical conjugate addition reactions demonstrated the broad scope of this method. The reaction of various benzyl alcohol derivatives with electron-deficient alkenes furnished the corresponding radical adducts.

Synthesis of Sterically Fixed Phytochrome Chromophore Derivatives Bearing a 15 E- Fixed or 15 E- Anti- Fixed CD-Ring Component.

To analyze the structure and function of phytochrome chromophores, we have been synthesizing natural and unnatural bilin chromophores of phytochromes. In this manuscript, we report the synthesis of sterically fixed 15 E- fixed 18Et-biliverdin (BV) and 15 E- anti-fixed 18Et-BV derivatives. The key reaction is the introduction of an sp3 carbon alkyl chain bearing a leaving group at the meso-position of the CD-ring component by using the corresponding Grignard reagents in the presence of LiCl.

Pestynol, an Antifungal Compound Discovered Using a Saccharomyces cerevisiae 12geneΔ0HSR-iERG6-Based Assay.

The multidrug-sensitive budding yeast, Saccharomyces cerevisiae 12geneΔ0HSR-iERG6, is very useful in antifungal screens. A novel compound, named pestynol (1), was discovered from a culture of the fungus Pestalotiopsis humus FKI-7473 using the multidrug-sensitive yeast. The structure of 1 was elucidated by NMR studies and modified Mosher's method as (1 R,2 R,3 R,4 R)-( E)-5-(7,11-dimethyl-3-methylenedodeca-6,10-dien-1-yn-1-yl)cyclohex-5-ene-1,2,3,4-tetraol. Compound 1 showed antimicrobial activity against the Gram-positive bacteria, Klebsiella pneumoniae, and S. cerevisiae 12geneΔ0HSR-iERG6 and Mucor racemosus, but displayed only weak cytotoxicity against various human cancer cell lines. Compound 1 displayed antifungal activities against S. cerevisiae 12geneΔ0HSR-iERG6 and Mucor racemosus at 10 µg/disc.

Hamuramicins A and B, 22-membered macrolides, produced by an endophytic actinomycete Allostreptomyces sp. K12-0794.

Two new compounds, designated as hamuramicins A (1) and B (2), were isolated from the cultured broth of an endophytic actinomycete Allostreptomyces sp. K12-0794 by silica gel column chromatography and HPLC. The structures of 1 and 2 were elucidated as 22-membered macrolide containing triene and trienone with an alkyl side chain by spectroscopic analyses including NMR experiments. Both compounds showed growth inhibition activity against Kocuria rhizophia and Xanthomonas oryzae pv. oryzae as well as human cell line toxicity.

Pyrizomicin A and B: structure and bioactivity of new thiazolyl pyridines from Lechevalieria aerocolonigenes K10-0216.

Two new antibiotics, designated pyrizomicin A and B, were isolated from the cultured broth of a rare actinomycete strain, Lechevalieria aerocolonigenes K10-0216, by silica gel and HPLC purification. The chemical structures of pyrizomicin A and B were elucidated as new thiazolyl pyridine compounds by nuclear magnetic resonance and mass spectrometry. Pyrizomicin A and B both showed antimicrobial activity.

Mechanistic study of the rhodium-catalyzed carboxylation of simple aromatic compounds with carbon dioxide.

A detailed mechanism of the Rh(i)-catalyzed carboxylation of simple aromatic compounds via C-H bond activation was investigated. Kinetic studies with model compounds of the postulated key intermediates revealed that 14-electron complexes, RhMe(dcype) and RhPh(dcype), participated in the C-H bond activation step and the carboxylation step, respectively. Interestingly, the undesired carboxylation of RhMe(dcype) to give acetic acid was found to be much faster than the desired C-H bond activation reaction under stoichiometric conditions, however, the C-H bond activation reaction could occur under catalytic conditions. Careful controlled experiments revealed that C-H bond activation using RhMe(dcype) became competitive with its direct carboxylation under the condition that the concentration of CO2 in the liquid phase was rather low. This factor could be controlled to some extent by mechanical factors such as the stirring rate and the shape of the reaction vessel. The resting state of the rhodium species under catalytic conditions was found to be [RhCl(dcype)]2, and the proposed intermediates such as RhMe(dcype) and Rh(OBz)(dcype) were readily converted to the most stable state, [RhCl(dcype)]2, via transmetallation with [Al]-Cl species, thus preventing the decomposition of the active catalytic species.