10.1021/ol0157813
The study presents a novel strategy for synthesizing polypeptides using recombinant proteins, which are nonprotected peptides, in conjunction with S-alkyl peptide thioesters as building blocks. The method involves oxidizing the N-terminal serine of a peptide to form an Nr-glyoxyloyl peptide, which then undergoes reductive amination with 4,5-dimethoxy-2-(triphenylmethylthio)benzylamine to attach a thiol linker. This results in an Nr-4,5-dimethoxy-2-mercaptobenzyl glycyl peptide, which can be condensed with a peptide thioester to form a peptide bond. The innovative aspect of this approach is the use of the 4,5-dimethoxy-2-mercaptobenzyl (Dmmb) group as a linker, which can be removed under acidic conditions, allowing for the synthesis of peptides with native peptide bonds. The study demonstrates this method using a model sequence and shows the successful preparation of a thiol linker-attached peptide for condensation with peptide thioesters, providing a useful method for peptide synthesis in a neutral aqueous environment without the need for protecting groups.
10.1248/cpb.c16-00744
The study focuses on the development and application of acid-catalyzed allylating reagents based on triazine chemistry, specifically 2,4,6-tris(allyloxy)-1,3,5-triazine (TriAT-allyl) and its substituted derivatives. These reagents were used to synthesize allyl ethers and esters from various alcohols and carboxylic acids in the presence of a catalytic amount of trifluoromethanesulfonic acid (TfOH). The purpose of these chemicals is to provide a practical, high-yielding procedure for allylation, which is a method of introducing allyl groups into organic compounds. The allyl group is significant for protecting hydroxy and carboxy groups and can be used as monomer units in macromolecules. The study also explores the reaction mechanisms and the selectivity of the reactions, providing insights into the intermediates involved in the allylation process. The new reagents demonstrated remarkable reactivity, stability, and atom economy, addressing some of the drawbacks of conventional allylation methods such as poor stability, toxicity, and high cost.
10.1021/jo301607a
The research focuses on the development of a convenient synthesis method for 1,2,3-thiadiazoles and 1,2,3-selenadiazoles, which are important heterocyclic compounds with broad pharmacological properties, including anticancer, antibacterial, and antifungal activities. The study utilizes an ionic liquid as a novel soluble support, offering a simple and efficient approach to synthesize these compounds. The methodology involves the synthesis of ionic liquid-supported sulfonyl hydrazine, which is then reacted with various ketones and 1,2-diketones to form ionic liquid-supported hydrazones. These hydrazones are subsequently converted to 1,2,3-thiadiazoles in the presence of thionyl chloride, while 1,2,3-selenadiazoles are obtained by reacting the hydrazones with selenium dioxide in acetonitrile. The research concludes that this approach offers several advantages, such as ease of workup, simple reaction conditions, and high purity of the products. The chemicals used in the process include 1-methylimidazole, 1,4-butane sultone, trifluoromethane sulfonic acid (TfOH), thionyl chloride, hydrazine hydrate, and various ketones and 1,2-diketones, as well as selenium dioxide for the synthesis of selenadiazoles.
10.1021/ic010669m
The research focuses on the reagent-specific protonations of five-coordinate nitrosyl complexes, specifically trans-Re(CO)2(NO)(PR3)2 (where R is Ph or Cy), to yield either neutral nitroxyl complexes cis,trans-ReCl(CO)2(NHdO)(PR3)2 or cationic hydride complexes [trans,trans-ReH(CO)2(NO)(PPh3)2+][SO3CF3-]. The purpose of this study was to understand the factors contributing to stable nitroxyl complexes and to compare the properties of charge-neutral and cationic derivatives. The key chemicals used in the process include hydrochloric acid (HCl), triflic acid (HOSO2CF3), and various Br?nsted bases to probe the stability and reactivity of the synthesized complexes. The conclusions drawn from the research indicate that coordinated nitroxyl acts as both a σ-donor and π-acceptor ligand, and that metal coordination significantly enhances the stability of the N-H bond in HNdO by approximately 14-16 kcal/mol compared to the free molecule. The study also highlighted the acid-dependent nature of protonation reactions and provided insights into the mechanisms of nitrosyl ligand protonations.
10.1055/s-2001-16083
The research investigates the cationic electrocyclization of a-benzoyldiphenylmethanols in the presence of superacids, specifically trifluoromethanesulfonic acid (TFSA), to produce fluorenes, phenanthrols, and benzofurans. The purpose of this study is to explore the effects of substituents on the benzene rings of these compounds and their influence on the regioselectivity of the electrocyclization reactions. The researchers found that electron-rich benzene rings preferentially participate in the electrocyclization reactions, leading to the formation of different products based on the substituents. For instance, methyl and fluorine substitutions on the benzene rings altered the ratio of fluorene to phenanthrol formation, while a methoxy group led to the exclusive formation of benzofuran. The study concludes that the substituents significantly influence the reaction pathways and product distribution, providing valuable insights into the synthetic potential of cationic electrocyclizations.
10.1021/jo9023039
The research focuses on the application of (1R)-(t)-camphor and acetone-derived R0-hydroxy enones as dienophiles in asymmetric Diels-Alder reactions, which are catalyzed by both Lewis and Br?nsted acids. The study explores the potential and limitations of these enones in addressing challenging diene-dienophile combinations, such as less reactive dienes and β-substituted acrylates. The experiments involve the synthesis of various R0-hydroxy enones and their subsequent reactions with different dienes under uncatalyzed conditions, as well as in the presence of Lewis acid catalysts like Cu(OTf)2 and Br?nsted acids like triflic acid (TfOH). The analyses used to characterize the products and monitor the reactions include techniques such as TLC, column chromatography, NMR spectroscopy, and IR spectroscopy. The research also delves into mechanistic studies through kinetic measurements and quantum calculations to rationalize the observed stereochemical outcomes and reactivity profiles. Additionally, the practicality of the methodology is demonstrated through applications in natural product synthesis, such as the synthesis of (-)-nicolaioidesin C, where a Br?nsted acid-catalyzed Diels-Alder reaction is a key step.
10.1021/ja068637r
The research focuses on the development of chiral oxazaborolidine-aluminum bromide complexes as effective catalysts for enantioselective Diels-Alder reactions. The study investigates the protonation of oxazaborolidine with triflic acid to form a chiral oxazaborolidinium cation, which is then complexed with aluminum bromide (AlBr3) to create a highly efficient catalyst (complex 3). Various experiments were conducted using cyclopentadiene and diverse dienophiles, demonstrating that only 4 mol % of catalyst 3 yielded excellent reaction yields and enantioselectivity. The effectiveness of the catalyst was analyzed through 1H NMR spectroscopy, optical rotation, and HPLC or GC analysis with chiral columns, confirming that the catalyst significantly outperformed previous catalysts in terms of efficiency and recovery for larger-scale syntheses.
10.1039/b922166b
The research focuses on the synthesis and application of azaphosphiridine complexes, specifically exploring novel access to these complexes and their first applications in Br?nsted acid-induced ring expansion reactions. The study utilizes reactants such as 2H-azaphosphirene complex 1, N-methyl C-aryl imines 2a-e, and transient Li/Cl phosphinidenoid complex 5, which are subjected to thermal group transfer reactions or reactions with dichloro(organo)phosphane complex 4. The experiments involve the synthesis of azaphosphiridine complexes 3a-e and their subsequent reactions with trifluoromethane sulfonic acid and dimethyl cyanamide, leading to the formation of 1,3,4-diazaphosphol-2-ene complexes 8a,d. The analysis of the products and intermediates is conducted using a variety of techniques including multinuclear NMR spectroscopy, IR and UV/Vis spectroscopy, mass spectrometry (MS), and single-crystal X-ray crystallography for complexes 3b-d, 8a, and 8d. Additionally, DFT studies are presented to provide insights into the reaction mechanisms and compliance constants of the model complex of 6a.
C
