Synthetic studies on Ecteinascidin-743: synthesis of building blocks through Sharpless asymmetric dihydroxylation and aza-Michael reactions

Chandrasekhar, S.; Reddy, N. Ramakrishna; Rao, Yadunandana N.

doi:10.1016/j.tet.2006.09.056

Cited by 47 publications

(15 citation statements)

References 72 publications

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“…The selected nitrones 6-15, 18, 19, 21, and 23 in this work have been synthesized using three different methods, as shown in Scheme 1, by reacting the corresponding commercial (1, 4, 17, and 18) or easily available aldehydes by the reported procedures, (2, 12 3, 13 5, 14 20, 15 and 22 16 ), with the corresponding N-substituted hydroxylamines (method A, 5d B 17 ) or with the appropriate nitro compounds (method C) ( Table 1). 18 Nitrones 6 and 8 (Chart 1) are N-alkyl analogues of the well known nitrone 7 (PBN), 2 which has been used here as a reference compound.…”

Section: Synthesismentioning

confidence: 99%

Synthesis, structure, theoretical and experimental in vitro antioxidant/pharmacological properties of α-aryl, N-alkyl nitrones, as potential agents for the treatment of cerebral ischemia

Samadi

Soriano

Revuelta

et al. 2011

Bioorganic & Medicinal Chemistry

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The synthesis, structure, theoretical and experimental in vitro antioxidant properties using the DPPH, ORAC, and benzoic acid, as well as preliminary in vitro pharmacological activities of (Z)-α-aryl and heteroaryl N-alkyl-nitrones 6-15, 18, 19, 21, and 23, is reported. In the in vitro antioxidant activity, for the DPPH radical test, only nitrones bearing free phenol groups gave the best RSA (%) values, nitrones 13 and 14 showing the highest values in this assay. In the ORAC analysis, the most potent radical scavenger was nitrone indole 21, followed by the N-benzyl benzene-type nitrones 10 and 15. Interestingly enough, the archetypal nitrone 7 (PBN) gave a low RSA value (1.4%) in the DPPH test, or was inactive in the ORAC assay. Concerning the ability to scavenge the hydroxyl radical, all the nitrones studied proved active in this experiment, showing high values in the 94-97% range, the most potent being nitrone 14. The theoretical calculations for the prediction of the antioxidant power, and the potential of ionization confirm that nitrones 9 and 10 are among the best compounds in electron transfer processes, a result that is also in good agreement with the experimental values in the DPPH assay. The calculated energy values for the reaction of ROS (hydroxyl, peroxyl) with the nitrones predict that the most favourable adduct-spin will take place between nitrones 9, 10, and 21, a fact that would be in agreement with their experimentally observed scavenger ability. The in vitro pharmacological analysis showed that the neuroprotective profile of the target molecules was in general low, with values ranging from 0% to 18.7%, in human neuroblastoma cells stressed with a mixture of rotenone/oligomycin-A, being nitrones 18, and 6-8 the most potent, as they show values in the range 24-18.4%.

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Section: Synthesismentioning

confidence: 99%

Synthesis, structure, theoretical and experimental in vitro antioxidant/pharmacological properties of α-aryl, N-alkyl nitrones, as potential agents for the treatment of cerebral ischemia

Samadi

Soriano

Revuelta

et al. 2011

Bioorganic & Medicinal Chemistry

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“…This compound could be efficiently transformed into the necessary boronic acid 19 after treatment with n BuLi, quenching with trimethylborate, and subsequent acidic hydrolysis. The second coupling partner, 6‐bromoveratraldehyde 20 , was obtained in only one step from commercially available veratraldehyde following a reported bromination procedure 19. Not unexpectedly, the Suzuki coupling between 19 and 20 provided the biaryl derivative 21 ; however, excellent yields were only obtained when the reaction was carried out in a microwave oven at 120 °C.…”

Section: Resultsmentioning

confidence: 99%

“…The second coupling partner, 6-bromoveratraldehyde 20, was obtained in only one step from commercially available ve-ratraldehyde following a reported bromination procedure. [19] Not unexpectedly, the Suzuki coupling between 19 and 20 provided the biaryl derivative 21; however, excellent yields were only obtained when the reaction was carried out in a microwave oven at 120 8C. Subsequent transformation of the aldehyde moiety into the corresponding terminal alkyne 22 by the Ohira-Bestmann reaction set the stage for the key platinum-catalyzed 6-endo-dig cycloisomerization to the desired phenanthrene 23 by employing 6 g as precatalyst.…”

Section: Synthetic Applicationsmentioning

confidence: 99%

Coordination Chemistry of Cyclopropenylidene‐Stabilized Phosphenium Cations: Synthesis and Reactivity of Pd and Pt Complexes

Kozma

Deden

Carreras

et al. 2014

Chemistry A European J

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A straightforward synthesis of cyclopropenylidene-stabilized phosphenium cations 1 a–g through the reaction of [(iPr₂N)₂C₃⁺Cl]BF₄ with secondary phosphines is described. Their donor ability was evaluated by analysis of the CO stretching frequency in Rh complexes [RhCl(CO)L₂](BF₄)₂ and electrochemical methods. The cyclopropenium ring induces a phosphite-type behavior that can be tuned by the other two substituents attached to the phosphorus atom. Despite of the positive charge that they bear, phosphenium cations 1 a–g still act as two-electron donor ligands, forming adducts with Pd^II and Pt^II precursors. Conversely, in the presence of Pd⁰ species, an oxidative insertion of the Pd atom into the C_carbene–phosphorus bond takes place, providing dimeric structures in which each Pd atom is bonded to a cyclopropenyl carbene while two dialkyl/diaryl phosphide ligands serve as bridges between the two Pd centers. The catalytic performance of the resulting library of Pt^II complexes was tested; all of the cationic phosphines accelerated the prototype 6-endo-dig cyclization of 2-ethynyl-1,1′-biphenyl to afford pentahelicene. The best ligand 1 g was used in the synthesis of two natural products, chrysotoxene and epimedoicarisoside A

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“…To begin with o-bromobenzaldehydes or o-bromoacetophenones 1 were identified as suitable starting materials. 16 Since, ethyl cinnamates 13 undergo smooth condensation to give 2-benzoxepin-3(1H)-ones 7, the palladium-catalyzed intermolecular Heck coupling using 1a and 1aa as model substrates with ethyl acrylate was examined under different conditions (Table 1). 17 Performing the reaction of 1a with ethyl acrylate with palladium(II) acetate (5 mol%) as the catalyst and triphenylphosphine (10 mol%) as the ligand in acetonitrile with cesium carbonate as the base gave the aldol product 3 exclusively, albeit in poor yield (entry 1).…”

Section: Syn Thesismentioning

confidence: 99%

Concise Three-Step Strategy for the Synthesis of 2-Benzoxepin-3(1H)-ones

2015

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A short and efficient method was developed for the synthesis of 2-benzoxepin-3(1H)-ones. The synthetic sequence comprises of initial intermolecular Heck coupling, followed by reduction of the carbonyl functionality of the Heck product and finally base-induced intramolecular condensation. Notably, the final condensation may proceed by an interesting oxy-Michael addition, cycloreversion via double bond isomerization and intramolecular condensation.

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Synthetic studies on Ecteinascidin-743: synthesis of building blocks through Sharpless asymmetric dihydroxylation and aza-Michael reactions

Cited by 47 publications

References 72 publications

Synthesis, structure, theoretical and experimental in vitro antioxidant/pharmacological properties of α-aryl, N-alkyl nitrones, as potential agents for the treatment of cerebral ischemia

Synthesis, structure, theoretical and experimental in vitro antioxidant/pharmacological properties of α-aryl, N-alkyl nitrones, as potential agents for the treatment of cerebral ischemia

Coordination Chemistry of Cyclopropenylidene‐Stabilized Phosphenium Cations: Synthesis and Reactivity of Pd and Pt Complexes

Concise Three-Step Strategy for the Synthesis of 2-Benzoxepin-3(1H)-ones

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