Stereoselective Approach Research Articles

Stereoselective synthesis of 3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)-one derivatives as PIM kinase inhibitors inspired from marine alkaloids.

We previously demonstrated that natural product-inspired 3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)-ones derivatives delivered potent and selective PIM kinases inhibitors however with non-optimal ADME/PK properties and modest oral bioavailability. Herein, we describe a structure-based scaffold decoration and a stereoselective approach to this chemical class. The synthesis, structure-activity relationship studies, chiral analysis, and pharmacokinetic data of compounds from this inhibitor class are presented herein. Compound 20c demonstrated excellent potency on PIM1 and PIM2 with exquisite kinases selectivity and PK properties that efficiently and dose-dependently promoted c-Myc degradation and appear to be promising lead compounds for further development.

Synthesis , Antibacterial Activity of Sm(III) Complex With L-phenylalanine

Synthesis , Antibacterial Activity of Sm(III) Complex With L-phenylalanine

Stereoselective gold(I)-catalyzed approach to the synthesis of complex \u03b1-glycosyl phosphosaccharides

Glycosyl phosphosaccharides represent a large and important family of complex glycans. Due to the distinct nature of these complex molecules, efficient approaches to access glycosyl phosphosaccharides are still in great demand. Here, we disclose a highly efficient and stereoselective approach to the synthesis of biologically important and complex α-glycosyl phosphosaccharides, employing direct gold(I)-catalyzed glycosylation of the weakly nucleophilic phosphoric acid acceptors. In this work, the broad substrate scope is demonstrated with more than 45 examples, including glucose, xylose, glucuronate, galactose, mannose, rhamnose, fucose, 2-N3-2-deoxymannose, 2-N3-2-deoxyglucose, 2-N3-2-deoxygalactose and unnatural carbohydrates. Here, we show the glycosyl phosphotriester prepared herein was successfully applied to the one-pot synthesis of a phosphosaccharide from Leishmania donovani, and an effective preparation of a trisaccharide diphosphate of phosphosaccharide fragments from Hansenula capsulate via iterative elongation strategy is realized.

Gold-catalyzed hydroarylation reactions: a comprehensive overview.

The hydroarylation of alkynes, alkenes, and allenes is a cost-effective and efficient way to incorporate unsaturated moieties into aromatic substrates. This review focuses on gold-catalyzed hydroarylation, which produces aromatic alkenes, diaryl-alkanes, heterocycles, carbocycles, and arylbutadienes by directly functionalizing C-H bonds. Without the need for prefunctionalization, direct functionalization of aromatic C-H bonds with unsaturated moieties (alkyne, alkene, allene) provides an efficient synthetic strategy with fewer reaction steps. This review offers an overview of the recently developed hydroarylation processes catalyzed by gold. Mechanisms of hydroarylation via alkyne, alkene, allene, and arene activation receive special attention.

A general and stereoselective approach to 14-membered cyclic bis-semicarbazones involving BF3-catalyzed amidoalkylation of 2-(trimethylsilyloxy)propene.

A general and stereoselective five-step approach to 14-membered cyclic bis-semicarbazones, 5,12-diaryl-7,14-dimethyl-1,2,4,8,9,11-hexaazacyclotetradeca-7,14-diene-3,10-diones, starting from aldehyde semicarbazones has been developed. The key intermediates, 4-(3-oxobut-1-yl)semicarbazones, were prepared by BF3-catalyzed amidoalkylation of 2-(trimethylsilyloxy)propene with 4-[(aryl)(methoxy)methyl]- or 4-[(aryl)(tosyl)methyl]semicarbazones. Treatment of these intermediates with excess of hydrazine gave hydrazones of 4-(3-oxobut-1-yl)semicarbazones or 4-(3-oxobut-1-yl)semicarbazides, which in the presence of TsOH were converted into the target macrocycles. All steps of this approach could be scaled up easily to the multi-gram level.

Synthesis of C-Alkynyl Glycosides by Photoredox-Catalyzed Reductive Coupling of Alkynyl Bromides with Glycosyl Bromides.

A general, convenient, and highly α stereoselective approach to access C-alkynyl glycosides via the photoredox-catalyzed reductive coupling of alkynyl bromides and glycoside bromides has been developed. Cheap and small-load eosin Y is used as the photocatalyst, and organic base N,N-diisopropylethylamine serves as the reducing reagent. This strategy features readily available starting materials, diverse substrates, mild conditions, and high α stereoselectivity. Moreover, a glycoconjugated peptide could also be achieved using this strategy.

Click generated o-Cresolphthalein linked 1,2,3-triazole derivative for selective Pb(II) ion recognition

Present report describes the “turn-on” absorbance response of a molecular assembly o-Cresolphthalein appended 1,4-disubstituted 1,2,3-triazole (o-CPT) on complexation with Pb(II) ions. Copper (I) catalyzed alkyne-azide cycloaddition reaction, a highly versatile and stereoselective approach to stitch diverse structural units has been employed to generate the designed receptor that has been successfully characterized through IR, NMR (1H, 13C) and mass spectroscopic techniques. UV-Visible absorption spectral behavior of o-CPT was examined with a series of metal ions (Mn (II), Ce (III), Hg (II), Ni (II), Pb (II), Zn (II), Fe (II), Cr (III), Co (II) and Na (I)) in acetonitrile-water (4:1, v/v) solution and the results obtained have marked out the sensitivity of the designed probe exclusively towards Pb(II) ions with a measured detection limit of 13 µM at 2:1 stoichiometry of o-CPT:Pb(II) complex.

Catalytic Carbochlorocarbonylation of Unsaturated Hydrocarbons via C−COCl Bond Cleavage**

Here we report a palladium‐catalysed difunctionalisation of unsaturated C−C bonds with acid chlorides. Formally, the C−COCl bond of an acid chloride is cleaved and added, with complete atom economy, across either strained alkenes or a tethered alkyne to generate new acid chlorides. The transformation does not require exogenous carbon monoxide, operates under mild conditions, shows a good functional group tolerance, and gives the isolated products with excellent stereoselectivity. The intermolecular reaction tolerates both aryl‐ and alkenyl‐substituted acid chlorides and is successful when carboxylic acids are transformed to the acid chloride in situ. The reaction also shows an example of temperature‐dependent stereodivergence which, together with plausible mechanistic pathways, is investigated by DFT calculations. Moreover, we show that benzofurans can be formed in an intramolecular variant of the reaction. Finally, derivatisation of the products from the intermolecular reaction provides a highly stereoselective approach for the synthesis of tetrasubstituted cyclopentanes.

A divergent and stereoselective approach for the syntheses of (–)-zeylenol, (+)-6-O-benzoylzeylenol, (+)-uvarigranol E and (+)-uvarigranol F

A common, divergent, efficient, and stereoselective approach to the total syntheses of four carbasugars, namely, (–)-zeylenol, (+)-6-O-benzoylzeylenol, (+)-uvarigranol E and (+)-uvarigranol F from d-mannose derived key intermediate 14 is described. This intermediate was synthesized using mixed aldol condensation, Grignard reaction and ring closing metathesis as key steps by our previous method in nine steps from d-mannose. From this intermediate, we achieved the syntheses of (+)-6-O-benzoylzeylenol, (+)-uvarigranol F in three steps, (+)-uvarigranol E in four steps and improved synthesis of (–)-zeylenol.

Stereoselective approach to conjugated enone oximes from aliphatic nitro compounds and sulfur ylides

A novel approach to conjugated enone oximes from aliphatic nitro compounds deals with double silylation of N,N-bis(silyloxy) enamines followed by a stereoselective reaction with an ester-stabilized sulfur ylide. The proposed mechanism involves the generation of labile nitrosoalkenes as intermediates, which react with the sulfur ylide to give target enone oximes.

Confinement-Controlled, Either syn- or anti-Selective Catalytic Asymmetric Mukaiyama Aldolizations of Propionaldehyde Enolsilanes.

Protected aldols (i.e., true aldols derived from aldehydes) with either syn- or anti- stereochemistry are versatile intermediates in many oligopropionate syntheses. Traditional stereoselective approaches to such aldols typically require several nonstrategic operations. Here we report two highly enantioselective and diastereoselective catalytic Mukaiyama aldol reactions of the TBS- or TES- enolsilanes of propionaldehyde with aromatic aldehydes. Our reactions directly deliver valuable silyl protected propionaldehyde aldols in a catalyst controlled manner, either as syn- or anti- isomer. We have identified a privileged IDPi catalyst motif that is tailored for controlling these aldolizations with exceptional selectivities. We demonstrate how a single atom modification in the inner core of the IDPi catalyst, replacing a CF3-group with a CF2H-group, leads to a dramatic switch in enantiofacial differentiation of the aldehyde. The origin of this remarkable effect was attributed to tightening of the catalytic cavity via unconventional C–H hydrogen bonding of the CF2H group.

On the Origin of E-Selectivity in the Ring-Opening Metathesis Polymerization with Molybdenum Imido Alkylidene N-Heterocyclic Carbene Complexes.

The understanding and control of stereoselectivity is a central aspect in ring-opening metathesis polymerization (ROMP). Herein, we report detailed quantum chemical studies on the reaction mechanism of E-selective ROMP of norborn-2-ene (NBE) with Mo(N-2,6-Me2-C6H3)(CHCMe3)(IMes)(OTf)2 (1, IMes = 1,3-dimesitylimidazol-2-ylidene) as a first step to stereoselective polymerization. Four different reaction pathways based on an enesyn or eneanti approach of NBE to either the syn- or anti-isomer of the neutral precatalyst have been studied. In contrast to the recently established associative mechanism with a terminal alkene, where a neutral olefin adduct is formed, NBE reacts directly with the catalyst via [2 + 2] cycloaddition to form molybdacyclobutane with a reaction barrier about 30 kJ mol–1 lower in free energy than via the formation of a catalyst–monomer adduct. However, the direct cycloaddition of NBE was only found for one out of four stereoisomers. Our findings strongly suggest that this stereoselective approach is responsible for E-selectivity and point toward a substrate-specific reaction mechanism in olefin metathesis with neutral Mo imido alkylidene N-heterocyclic carbene bistriflate complexes.

Solvent‐Dependent Chemoselective and Stereoselective Approach to Synthesis of Spiro‐γ‐Lactams with Potent Anticancer Activity

AbstractChemoselective approaches were developed for derivatizing diastereoselective chromanone spiro‐γ‐lactams through the Michael‐type addition by using amide as a weak nucleophile to construct the spiro‐carbon center under basic conditions. To expand the scope of this post‐Ugi cascade reaction, a new series of oxidized chromone derivatives was synthesized by altering solvent from EtOH to DMF. Compounds 7 a and 7 b which could be synthesized in one day, demonstrated comparable anticancer activities with legendary anticancer drug paclitaxel in the PANC and U87 cell lines. This methodology offers a new approach to construct spiro‐carbon centers with functionalized chromanones or chromones under mild reaction conditions.magnified image

Asymmetric Total Synthesis of Hetiamacins A-F.

Herein, we report a concise and stereoselective approach for the asymmetric total synthesis of hetiamacins A–F on the basis of the total synthesis of amicoumacin C, which could be synthesized from a known l-aspartic acid derivative. The synthesis of hetiamacin A was accomplished by an 11-step sequence that featured 1,3-oxazinane ring formation of amicoumacin B followed by amidation in one pot. Hetiamacins B–F were synthesized from amicoumacin A in only one step.

Stereoselective Approaches for Building the C14‐C21 Fragment of Eribulin

AbstractHerein, we report a practical stereoselective synthesis of C14‐C21 and C15‐C21 tetrahydrofuran‐based fragment of eribulin using two different approaches. The approach utilizes iodoetherification and intra molecular oxa‐Michael additions as key steps in individual approaches using R,R‐tartaric acid and L‐ascorbic acids as cost effective chiral starting materials.

Electrochemically driven stereoselective approach to syn-1,2-diol derivatives from vinylarenes and DMF.

We have developed an electrochemically driven strategy for the stereoselective synthesis of protected syn-1,2-diols from vinylarenes with N,N-dimethylformamide (DMF). The newly developed system obviates the need for transition metal catalysts or external oxidizing agents, thus providing an operationally simple and efficient route to an array of protected syn-1,2-diols in a single step. This reaction proceeds via an electrooxidation of olefin, followed by a nucleophilic attack of DMF. Subsequent oxidation and nucleophilic capture of the generated carbocation with a trifluoroacetate ion is proposed, which gives rise predominantly to a syn-diastereoselectivity upon the second nucleophilic attack of DMF.

Regio- and Stereoselective Photoredox-Catalyzed Atom Transfer Radical Addition of Thiosulfonates to Aryl Alkynes.

Despite extensive investigations, altering the regioselectivity of atom transfer radical addition (ATRA) to alkynes remains a highly desirable yet unachieved challenge. Guided by computational predictions, thiosulfonates were found herein as a tunable radical precursor for thiyl radicals instead of well-recognized sulfonyl radicals. Merging such a finding with ATRA to phenylacetylenes leads to a highly regio- and stereoselective approach to (E)-β-arylsulfonylvinyl sulfides. This protocol is feathered by mild conditions, low photocatalyst loading, no transition-metal catalyst required, and broad functional group compatibility. The successful application of our protocol in the late-stage functionalization of bioactive natural product derivatives demonstrates its synthetic utility. Mechanistic studies corroborate the photoredox-catalyzed ATRA pathway and reveal the pivotal role of thiyl radical, to which unprecedented regioselectivity was attributed.

Synergistic Catalysis for Stereodivergent Synthesis of trans- and cis-Skipped Dienes

Catalytic, stereoselective synthesis of skipped dienes is an important topic in organic synthesis. Summarized here are the transition-metal-catalyzed stereoselective approaches and a new, photoinduced stereodivergent strategy reported by our group recently. Our strategy utilizes a synergistic photoredox/nickel protocol to enable the cross-electrophile coupling of allylic carbonates and vinyl triflates to construct 1,4-dienes, the stereoselectivity of which was tuned by the triplet energy (E T) photocatalysts employed, offering a convenient and stereodivergent solution to (E)- and (Z)-1,4-dienes from one set of substrates.

Synthesis of 3-substituted isoxazolidin-4-ols using hydroboration-oxidation reactions of 4,5-unsubstituted 2,3-dihydroisoxazoles.

Isoxazolidines represent a very important class of N/O-containing heterocycles used as the key intermediates in the synthesis of more complex cyclic and acyclic compounds, including various biologically active molecules. Here, we present a fast and highly stereoselective approach towards both C-3/4-cis and C-3/4-trans isomers of 3-substituted isoxazolidin-4-ols. The strategy relies on a highly regio- and trans-stereoselective hydroboration–oxidation reaction of the 4,5-unsubstituted 2,3-dihydroisoxazoles with basic hydrogen peroxide. The consecutive oxidation/reduction route, sequentially employing Dess–Martin periodinane and ʟ-selectride, is used for the inversion of the C-3/4-trans relative configuration of the isoxazolidine ring. The significance of the method lies in its variability and applicability to a concise synthesis of various 4-hydroxyisoxazolidines, starting from the readily available C-alkyl/aryl-nitrones. The resemblance to 3-hydroxypyrrolidines certainly makes the 4-hydroxyisoxazolidines important and valuable structural fragments in drug discovery.

Stereoselective approach to access 3-tert-Butyl-Dimethylsiloxy-2,6-Substituted piperidines through nucleophilic addition of N,O-acetals with organozinc reagents

An efficient approach to access chiral 3-tert-butyl-dimethylsiloxy 2,6-disubstituted 6-benzyl piperidines was developed through nucleophilic addition of N,O-acetals with organozinc reagents. A number of substituted benzyl zinc reagents could react with N,O-acetals 6a-6e, affording the desired products 7a-7j and 9a-9q in good to excellent yields and with high diastereoselectivities.