Total synthesis of 4-epi-atpenin A5 as a potent nematode complex II inhibitor

It is clear that atpenins and their analogs are useful chemical tools for elucidation of complex II functionality and that they could act as lead compounds for the development of novel helminth complex II-specific inhibitors. Recently, we discovered 4-epi-atpenin A5 as a potent nematode complex II inhibitor during our SAR studies of atpenin A5. This result led us to embark on a concise total synthesis of 4-epi-atpenin A5. In this study, we describe the total synthesis of 4-epi-atpenin A5. Importantly, this was more concise and practical synthesis than our previous total synthesis of atpenin A5.     

Facile synthesis of a pentasaccharide repeating unit corresponding to the common O-antigen of Salmonella enterica O57 and Escherichia coli O51

A concise chemical synthetic strategy has been developed for the synthesis of a pentasaccharide present in the O-antigen of Salmonella enterica O57 and Escherichia coli O51 strains. A sequential glycosylation strategy has been adopted for the synthesis of the target pentasaccharide. All intermediate steps are high yielding and the glycosylation steps are stereoselective. A number of recently developed methodologies have been used in the synthesis.     

Synthetic studies towards dendridine A: synthesis of hemi-dendridine A acetate by Fischer indolization

A short synthesis of hemi-dendridine A acetate has been accomplished. The synthesis is based on a modified Fischer indolization that represents a rare example of the single-step synthesis of a 7-oxytryptamine from an ortho-oxygenated phenylhydrazine. The synthetic route required developing an efficient synthesis of N-acetyl-2-pyrroline, the key coupling partner for the modified Fischer indolization. Some interesting chemistry associated with the abnormal Fischer indolization has been uncovered, whereby two molecules of the phenylhydrazine substrate combined along the abnormal reaction pathway, affording an unusual N-phenylindoleamine product.     

A flexible organocatalytic enantioselective synthesis of heptadeca-1-ene-4,6-diyne-3S,8R,9S,10S-tetrol and its congeners

A unified enantioselective route is developed for the synthesis of heptadeca-1-ene-4,6-diyne-3S,8R,9S,10S-tetrol and its synthetic congeners. A proline-catalyzed aminoxylation, cross-metathesis, Wittig reaction, and catalytic dihydroxylation are key steps of this synthesis. This new approach is envisioned to facilitate the synthesis of every representative member of the family with skeletal and stereochemical variation.     

Synthesis of cyclitols via ring-closing metathesis

A convenient synthesis of enantiomerically pure and differentially protected l-chiro- and myo-inositols as well as conduritols B and F from 2,3,4-tri-O-benzyl-d-xylopyranose via ring-closing metathesis is reported. The facile synthesis of conduritol B constitutes a short formal synthesis of (−)-cyclophellitol.     

Total synthesis of malayamycin A and analogues

The total synthesis of the bicyclic C-nucleoside malayamycin A is described starting with d-ribonolactone. A new method was developed to obtain preparatively important quantities of β-pseudouridine, which was used as an intermediate. The synthesis of a carba N-nucleoside analogue of malayamycin A is also described.     

Formal total synthesis of aspergillides A and B

The formal total synthesis of the cytotoxic 14-membered macrolides, aspergillides A and B is described. A combination of a chiron approach and an asymmetric synthesis is adopted for the synthesis of the target macrolides. The required 2,6-syn and 2,6-anti tetrahydropyrans were constructed via a tandem Sharpless asymmetric epoxidation and 6-exo cyclization on δ-hydroxy allylic alcohols, as the key steps. The requisite chiral synthon was prepared from l-ascorbic acid.     

Synthesis of the 6′-iso analogues of neplanocin A and 5′-homoneplanocin A

An efficient synthesis of 6′-isoneplanocin A and 6′ -isohomoneplanocin A is reported. The key steps in the synthesis include an enyne metathesis and a regioselective oxidation.     

Development of a scalable synthesis of a nonbasic inhibitor of the serine protease tryptase

A chromatography-free process for the synthesis of a bis(benzimidazole)difluoromethane inhibitor of the serine protease tryptase is described. This synthesis features the introduction of the gem-difluoro moiety using the electrophilic fluorinating reagent N-fluoro-bis(phenylsulfonimide) as well as the stepwise introduction of both benzimidazole rings. A protocol for the destruction of reactive, process-related substances produced in the synthesis is also presented.     

First total synthesis and biological evaluation of the cyclic heptapeptide rhizonin A

The first total synthesis and biological evaluation of the naturally occurring cyclic heptapeptide rhizonin A are described. The synthesis includes solution-phase peptide synthesis and the preparation of NMe-3-(3-furyl)alanine (NMe-FurAla), a unique component of rhizonin A, which was prepared in chiral form via Barton-MacCombie deoxygenation as a key step. The bioactivity was assessed using 3T3-L1 murine adipocytes.     

Biomimetic type approach to the tricyclic core of xyloketals. Application to a short, stereocontrolled synthesis of alboatrin and first synthesis of xyloketal G

A convenient approach to the linear tetrahydrofurano benzopyran ring system of xyloketals is described. An orthoester Claisen rearrangement of a chromenol and an intra-molecular cationic cyclization are the key steps in the synthesis. A short, stereocontrolled and high yield synthesis of the phytotoxic metabolite alboatrin was achieved employing this strategy. A unique case of Lewis acid catalyzed isomerization of epi-alboatrin to alboatrin was observed. Subsequently this methodology was extended for the first total synthesis of xyloketal G, where a one pot reaction of three steps viz., acetylation, isomerization and demethylation occurred during acetylation of a mixture of nor-o-methyl xyloketal G and nor-o-methyl epi xyloketal G in presence of AlCl₃ to furnish xyloketal G in very good overall yield.     

Méthodologie de synthèse des analogues à chaînes ouvertes de l’huperzine A

An efficient synthesis of two analogues of huperzine A via a one-step synthesis of E alkene.     

Asymmetric total synthesis of (+)-carneic acid A and structure revision of its natural form

This Letter describes the asymmetric total synthesis of (+)-carneic acid A via the stereoselective IMDA reaction of (E,E,E)-triene, which was prepared from the commercially available methyl (S)-3-hydroxy-2-methylpropionate. By this asymmetric total synthesis, we verified that the reported absolute structure of naturally occurring carneic acid A must be revised.     

Synthesis and Characterization of Preacinetobactin and 5-Phenyl Preacinetobactin

We report the first total synthesis of 5-phenyl preacinetobactin and its characterization. The route was developed for the synthesis of preacinetobactin, the siderophore critical to the Gram-negative pathogen A. baumannii. It leverages a C5-substituted benzaldehyde as a key starting material and should enable the synthesis of similar analogs. 5-Phenyl preacinetobactin binds iron in a manner analogous to the natural siderophore, but it did not rescue growth in a strain of A. baumannii unable to produce preacinetobactin.     

Solid-phase synthesis of benzimidazole N-oxides on SynPhase™ Lanterns

A solid-phase synthesis of benzimidazole N-oxides was developed while attempting to synthesize 1,5-benzodiazepine-2,4-diones. The key step of the synthesis involves the reduction of an arylnitro to a hydroxyamino intermediate which subsequently condenses with an internal carbonyl group to give a benzimidazole N-oxide. A library of nine benzimidazole N-oxides was prepared on SynPhase™ Lanterns using this reduction-cyclization methodology.     

Total synthesis and biological evaluation of marinopyrrole A and analogues

A five-step total synthesis of the antibiotic marinopyrrole A (1) is described. The developed synthetic technology enabled the synthesis of several marinopyrrole A analogs whose antibacterial properties against methicillin-resistant Staphylococcus aureus TCH1516 were evaluated.     

A highly efficient synthesis of unnatural l-sugars from d-ribose

A preparative and short synthesis of l-ribose and l-apiose was accomplished starting from d-ribose via stereoselective cis-dihydroxylation and C2-hydroxymethylation, respectively. These l-sugars can serve as versatile intermediates for the synthesis of l-nucleosides.     

Stereoselective synthesis of cis- and trans-2,3-disubstituted eight-membered medium-ring ethers based on Ireland-Claisen rearrangement of 3-alkoxy-2-propenyl glycolate esters and ring-closing olefin metathesis

A simple stereoselective synthesis of cis- and trans-2,3-disubstituted medium-sized cyclic ethers has been developed based on geometry-selective synthesis of 3-alkoxy-2-propenyl glycolate esters, Ireland-Claisen rearrangement of the glycolate esters, and ring-closing olefin metathesis.     

Total synthesis of maremycins A,B, C1/C2, D1, and D2

The total synthesis of maremycins A, B, C₁/C₂, D₁, and D₂ is achieved starting from the natural amino acids l-isoleucine and S-methyl-l-cysteine, in which the total synthesis of maremycins B, C₁/C₂, and D₂ is accomplished for the first time. The synthesis features a position-selective intramolecular bromination process for the synthesis of key chiral building block, a Pd-catalyzed indole synthesis for the preparation of (2S,3S)-β-methyltryptophan and hydroxylation of oxindoles by molecular oxygen. In addition, the protocol for conversion of maremycins A and B to maremycins C and D was improved.     

Synthesis and structure revision of litseaone A

Litseaone A, isolated from the stem barks of Litsea rubescens and Litsea pedunculata, is a chalcone derivative with a novel spiro-epoxide moiety. The structural revision of litseaone A was achieved by the racemic synthesis of the proposed structure and the asymmetric synthesis of the revised structure. The major tautomeric structure of litseaone A and the relative stereochemistry at the epoxide carbon center were also clarified.