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Tetrahedron Letters

Ihsan Erden, Cindy J Gleason
Herein, we describe two independent and non-pyrolytic syntheses of an important C12H12 hydrocarbon which had been prepared previously by gas phase thermolysis of compound 6. The first method is based on an unusual dipolar cycloaddition of dichloroketene onto bullvalene. After reductive dechlorination, a Shapiro-Heath reaction of the tosylhydrazone gave the title compound. Alternatively, compound 13 is also obtained from its isomer 6 by a Ag+ catalyzed reaction.
January 17, 2018: Tetrahedron Letters
Maciej J Stawikowski, Gregg B Fields
A novel and convenient method for the synthesis of C -terminally branched collagen-model peptides has been achieved using tricine ( N -[tris(hydroxymethyl)methyl]glycine) as a branching scaffold and 1,2-diaminoethane or 1,4-diaminobutane as a linker. The peptide sequence was incorporated directly onto the linker and scaffold during solid-phase synthesis without additional manipulations. The resulting branched triple-helical peptides exhibited comparable thermal stabilities to the parent, unbranched sequence, and served as substrates for matrix metalloproteinase-1 (MMP-1)...
January 10, 2018: Tetrahedron Letters
Humberto E Ortega, João M Batista, Weilan G P Melo, Jon Clardy, Mônica T Pupo
The known antibiotic and cytotoxic compounds griseorhodin A ( 1 ) and griseorhodin C ( 2 ) were produced in solid culture by Streptomyces puniceus AB10, which was isolated from the leaf-cutter ant Acromyrmex rugosus rugosus . Their absolute configurations were unambiguously established as 6 S ,6a R ,7 S ,8 S and 6 R ,6a R ,7 S ,8 R , respectively, using vibrational circular dichroism (VCD) and density functional theory (DFT) calculations.
December 13, 2017: Tetrahedron Letters
Nurul H Ansari, Björn C G Söderberg
Treatment of 2-nitro- N -(2-methyl-1-propen-1-yl)benzenamines with potassium tert -butoxide in tert -butanol followed by the addition of an electrophile affords N -alkoxy-2 H -benzimidazoles. Electrophiles including methyl iodide, allylic bromides, propargylic bromides, benzyl bromide, and acetyl chloride gave good to excellent yields of product while 1-iodo- and 2-iodo-butane afforded very low yields.
December 13, 2017: Tetrahedron Letters
Heather A Hintz, Nicholas J Sortedahl, Samantha M Meyer, Daniel A Decato, Bart J Dahl
Two triply lactone-bridged 1,3,5-triphenylbenzene derivatives with solubilizing moieties have been synthesized in five and six steps from commercially available starting materials. Compounds containing the 1,3,5-triphenylbenzene core with two atom bridges are relatively unknown. This new class of pi-expanded coumarins contain triskelion architectures and X-ray crystallographic studies of one of the triskelions indicates that the 1,3,5-triphenylbenzene core adopts a near-planar geometry. This is the only known example of a two atom-bridged 1,3,5-triphenylbenzene derivative to adopt a planar structure...
December 13, 2017: Tetrahedron Letters
James T Fletcher, Joseph A Christensen, Eric M Villa
A tandem method for preparing 4-formyl-1,2,3-triazoles via a two-step one-pot acetal cleavage/CuAAC reaction was developed. Using this method, 4-formyl-1,2,3-triazole analogs with both electron-withdrawing and electron-donating substituents were prepared in good yield and purity. Expansion of this method to a three-step tandem reaction that incorporates an additional step of azide substitution was also successful, circumventing the need for organic azide isolation. This one-pot method, noteworthy in its simplicity and mild conditions, utilizes practical, readily available reactants and relies on protic solvent to promote acid-catalyzed acetal cleavage...
November 22, 2017: Tetrahedron Letters
Galina Lepesheva, Plamen Christov, Gary A Sulikowski, Kwangho Kim
The study and development of azole-based CYP51 inhibitors is an active area of research across disciplines of biochemistry, pharmacology and infectious disease. Support of in vitro and in vivo studies require the development of robust asymmetric routes to single enantiomer products of this class of compounds. Herein, we describe a scalable and enantioselective synthesis to VNI and VFV, the two potent inhibitors of protozoan sterol 14α-demethylase (CYP51) that are currently under consideration for clinical trials for Chagas disease...
November 8, 2017: Tetrahedron Letters
Arun K Ghosh, Emilio L Cárdenas, Margherita Brindisi
Enantioselective syntheses of tert-butyl ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate and ((S)-2-(3,5-difluorophenyl)-1-((R)-oxiran-2-yl)ethyl)carbamate are described. We utilized asymmetric syn- and anti-aldol reactions to set both stereogenic centers. We investigated ester-derived Ti-enolate aldol reactions as well as Evans' diastereoselective syn-aldol reaction for these syntheses. We have converted optically active ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate to a potent β-secretase inhibitor...
October 25, 2017: Tetrahedron Letters
Daniel Polyak, Ngan Phung, Jian Liu, Robert Barrows, Thomas J Emge, Spencer Knapp
Homophthalic anhydride (HPA) typically reacts rapidly with benzalimines to afford the formal [4+2] adduct, a 1,2,3,4-tetrahydroisoquinolin-1-one-4-carboxylic acid. The stereochemical outcome of this reaction is consistent with an open transition state comprising an iminium species and enolized HPA, leading to a short-lived amino-anhydride intermediate. In the case of N-tert-butylbenzalimine, this Mannich-type intermediate, which would normally cyclize at low temperature to a single isomer of the delta-lactam, is intercepted by base treatment to afford beta-lactam products...
October 4, 2017: Tetrahedron Letters
Khanh G Tang, Greggory T Kent, Ihsan Erden, Weiming Wu
cis-β-Bromostyrene derivatives were synthesized stereospecifically from cinnamic acids through β-lactone intermediates. The synthetic sequence did not require the purification of the β-lactone intermediates although they were found to be stable and readily purified in most cases.
October 4, 2017: Tetrahedron Letters
Pravin C Patil, Frederick A Luzzio, Jarrid M Ronnebaum
The interchangeability of the isoindolinone group as a nitrogen protecting group for amino acid intermediates is demonstrated by the preparation of several natural and unnatural α-amino acid derivatives using a two-carbon N -isoindolinone (phthalimidine) scaffold. Using a selective benzylic oxidation, the N -isoindolinone group is then converted to the N -phthaloyl group for convenient removal (65-98%). For preparation of the isoindolinone products which were to be the substrates for benzylic oxidation, a range of side chains were installed on the isoindolinone-protected glycine equivalent on deprotonation to demonstrate the utility of the N -protected isoindolinone synthon (51-93%)...
September 20, 2017: Tetrahedron Letters
Gregory W O'Neil, Elizabeth J Cummins
Diallylsilanes can be made to rearrange upon treatment with I2. Of the silanes tested, diallyldiphenylsilane showed the greatest propensity to undergo this intramolecular carbocation allylation process. After etherification of the initially formed iodosilane, the products from this transformation represent useful synthetic intermediates, suitable for alkylation and cross-metathesis/annulation reactions.
August 30, 2017: Tetrahedron Letters
Samantha E Shockley, J Caleb Hethcox, Brian M Stoltz
Rapid access to enantioenriched spirocycles possessing a 1,4-dicarbonyl moiety spanning an all-carbon quaternary stereogenic spirocenter was achieved using a masked bromomethyl vinyl ketone reagent. The developed protocol entails an enantioselective palladium-catalyzed allylic alkylation reaction followed by a one-pot unmasking/RCM sequence that provides access to the spirocyclic compounds in good yields and selectivities.
August 23, 2017: Tetrahedron Letters
Arun K Ghosh, Anindya Sarkar
An enantioselective synthesis of ( 3 a S , 4S , 7 a R )-hexahydro-4 H -furo[2,3- b ]pyran-4-ol, a high-affinity nonpeptide ligand for a variety of potent HIV-1 protease inhibitors is described. The key steps involved a highly enantioselective enzymatic desymmetrization of meso -diacetate, an efficient transacetalization, and a highly diastereoselective reduction of a ketone. This route is amenable to large-scale synthesis using readily available starting materials.
August 16, 2017: Tetrahedron Letters
Shaban Darwish, Keykavous Parang, John Marshall, Dennis J Goebel, Rakesh Tiwari
CN2097 (R7Cs-sCYK[KTE(β-Ala)]V) is a rationally designed peptidomimetic that shows effectiveness in preclinical models for the treatment of neurological disorders, such as Angelman syndrome, traumatic brain injury (TBI) and stroke. Because of its therapeutic activity for the treatment of human CNS disorders, there was an urgent need to develop an efficient strategy for large-scale synthesis of CN2097. The synthesis of CN2097 was accomplished using Fmoc/tBu solid phase chemistry in multiple steps. Two different peptide fragments (activated polyarginine peptide Npys-sCR7 and CYK[KTE(β-Ala)]V) were synthesized, followed by solution phase coupling in water...
August 2, 2017: Tetrahedron Letters
Patrick Shelton, Toby J Ligon, Jennifer M Dell Née Meyer, Loagan Yarbrough, James R Vyvyan
Cananodine is a guaipyridine alkaloid with activity against liver cancer. Cananodine was synthesized using a remarkable intramolecular opening of a trisubstituted epoxide as the key step in construction of the seven-membered carbocycle of the target. The epoxide opening strategy allows all four stereoisomers of cananodine to be prepared.
August 2017: Tetrahedron Letters
Lissa S Tsutsumi, Ghee T Tan, Dianqing Sun
Solid-phase synthesis of antibacterial cyclohexapeptides including wollamides A, B and desotamide B has been developed. Briefly, the protected linear hexapeptides were assembled on 2-chlorotrityl chloride resin using standard Fmoc chemistry and diisopropylcarbodiimide/hydroxybenzotriazole coupling reagents, cleaved off-resin with hexafluoroisopropanol/dichloromethane to keep side-chain protecting groups intact, and cyclized in solution. Final global removal of all protecting groups using a cocktail of trifluoroacetic acid/triisopropylsilane/dichloromethane afforded the desired cyclic hexapeptides, which were characterized by (1)H, (13)C NMR, and HRMS...
July 5, 2017: Tetrahedron Letters
Chunshun Li, Ariel M Sarotti, James Turkson, Shugeng Cao
A new secondary metabolite verbenanone (1) with a unique (4aS,8aS)-octahydro-5H-chromen-5-one moiety has been obtained from the endophytic fungus FT431, which was isolated from the native Hawaiian plant Verbena sp. The structure of compound 1 was characterized based on NMR and MS spectroscopic analysis. The absolute configuration (AC) of compound 1 was determined by Mosher acids. Compound 1 was tested against A2780 and A2780cisR, but it was inactive.
June 7, 2017: Tetrahedron Letters
Serhan Turkyilmaz, Craig S Wilcox
Sorting tags are oligomeric structures that can be used as protecting groups or chiral auxiliaries enabling solution-phase mixture syntheses of multiple tagged compounds in one pot and allowing for facile and predictable chromatographic separation of products at the end of synthetic sequences. Perfluorinated hydrocarbon and oligomeric ethylene glycol (OEG) derivatives are known classes of sorting tags. Herein we describe the preparation of OEGylated chiral oxazolidinones and their use in asymmetric solution-phase mixture aldol reactions...
May 24, 2017: Tetrahedron Letters
Kristen M McGraw, Greggory T Kent, Joseph R Gonzalez, Ihsan Erden, Weiming Wu
The interaction of various 1,2-dibromides with NEt3 under various conditions (THF and DMF, respectively) at different temperatures was investigated. Our results from these reactions show that substrate dependent dehydrobrominations compete with reductive debrominations. A comprehensive discussion of these competitive pathways is offered.
May 17, 2017: Tetrahedron Letters
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