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Tetrahedron Letters

Matthew J Palframan, Krishna K Bandi, James G C Hamilton, Gerald Pattenden
A new sex-aggregation pheromone, sobralene, produced by the sand fly Lutzomyia longipalpis from Sobral (Ceará State, Brazil) is shown to have the novel 6,12-membered ring-fused diterpene structure 3. It is proposed that sobralene is a likely shunt metabolite of the taxadiene synthase-catalysed cyclisation of geranygeranyl diphosphate.
May 16, 2018: Tetrahedron Letters
Kayleigh L Brocklesby, Jennifer S Waby, Christopher Cawthorne, Graham Smith
Fluorine substitution is an established tool in medicinal chemistry to favourably alter the molecular properties of a lead compound of interest. However, gaps still exist in the library of synthetic methods for accessing certain fluorine-substituted motifs. One such area is the fluoromethyl group, particularly when required in a fluoroalkylating capacity. The cold fluorination of methylene ditosylate is under evaluated in the literature, often proceeding with low yields or harsh conditions. This report describes a novel microwave method for the rapid nucleophilic fluorination of methylene ditosylate using inexpensive reagents in good isolated yield (65%)...
April 25, 2018: Tetrahedron Letters
Neha Malik, Iredia D Iyamu, Karl A Scheidt, Gary E Schiltz
Development of drugs for new and persistent diseases will increasingly rely on the expansion of accessible chemical space to allow exploration of novel molecular targets. Here we report the synthesis of a library of novel fused heterobicyclic small molecules based on the 1,4-diazepine and 2,4-pyrrolidinedione scaffolds. Key chemical transformations included a Mannich-type condensation and chemoselective N-acylation reactions. Screening shows anti-cancer activity of several library compounds which suggests translational potential of this novel chemical scaffold...
April 11, 2018: Tetrahedron Letters
Eric R Samuels, Irina Sevrioukova
Modified amino acids are useful synthetic components in both chemistry and biology. Here we describe a simple, scalable two-step procedure to generate α-thio aromatic acids from aromatic amino acids with yields of up to 96%. Diazotization and α-lactone mediated bromination efficiently form the α-bromo acid with retention of configuration. Thiol substitution with mild reagents such as sodium hydrosulfide or sodium trithiocarbonate provides the inverted, free α-thio acid. The mildly acidic soft nucleophile can then be utilized in many synthetic applications...
March 21, 2018: Tetrahedron Letters
Shuneize Slater, Pradeep B Lasonkar, Saqlain Haider, Moneerah J Alqahtani, Amar G Chittiboyina, Ikhlas A Khan
Novel, functionalized octahydrochromene derivatives were synthesized in a single step via the Prins reaction. Enantiomerically pure (+)-isopulegol was reacted with benzaldehyde to stereoselectively yield the corresponding octahydro-2 H -chromen-4-ol derivative containing five stereocenters. A total of 10 compounds were synthesized by altering the enantiomer of isopulegol and the substituted benzaldehyde, and the resulting enantiopure octahydrochromenes were screened in vitro against the cannabinoid receptor isoforms CB1 and CB2...
February 28, 2018: Tetrahedron Letters
Jeffrey W McDonald, John E Miller, Minjee Kim, Sadanandan E Velu
Murrayaquinones A-D is a group of four bioactive carbazole-1,4-dione natural products isolated from the root bark of the plant Murraya eucrestifolia hayata. Murrayaquinone is synthesized in five steps starting from the commercially available 2,4,5-trimethoxybenzaldehyde with an overall yield of 45%. The novelty of this murrayaquinone synthesis is in the use of a Mn(OAc)3 mediated oxidative radical reaction of a N-benzylaminoquinone derivative with 2-cyclohexen-1-one for the late-stage indole ring construction...
February 7, 2018: 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
Liza Shrestha, Hardik J Patel, Yanlong Kang, Sahil Sharma, Gabriela Chiosis, Tony Taldone
A copper-mediated synthesis of diaryl sulfides utilizing Cu(I)-thiophene-2-carboxylate (CuTC) is described. We demonstrate the use of CuTC as a soluble, non-basic catalyst in the coupling of aryl iodides and aryl thiols in the synthesis of synthetically advanced diaryl sulfides. This method allows for the successful coupling of challenging substrates including ortho -substituted and heteroaryl iodides and thiols. Additionally, most of the aryl iodide substrates used here contain the privileged piperazine scaffold bound to a pyrimidine, pyridine, or phenyl ring and thus this method allows for the elaboration of complex piperazine scaffolds into molecules of biological interest...
November 29, 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
Apsara K Herath, Manoj R Bhandari, Delphine Gout, Muhammed Yousufuddin, Carl J Lovely
The utility of the thio acid-azide coupling reaction to afford amides is explored in imidazole-containing substrates for application in the total synthesis of examples of oroidin alkaloids. Good yields of the expected amides are obtained in both monomeric and dimeric substrates. Bis azides react preferentially at the 2-azido position but hydrosulfenylation and reduction interfere. 2-Thiophenyl and 2-oxo groups were evaluated as 2-amino surrogates, the thioether delivered the expected amide, whereas 2-imidazolone gave a mixture of the expected amide and the hydrosulfenylation product...
October 11, 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
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