Straightforward synthesis of cyclic and bicyclic peptides

Cyclic peptide architectures can be easily synthesized from cysteine-containing peptides with appending maleimides, free or protected, through an intramolecular Michael-type reaction. After peptide assembly, the peptide can cyclize either during the trifluoroacetic acid treatment, if the maleimide is not protected, or upon deprotection of the maleimide. The combination of free and protected maleimide moieties and two orthogonally protected cysteines gives access to structurally different bicyclic peptides with isolated or fused cycles.

Macrocyclizations for medicinal chemistry: synthesis of druglike macrocycles by high-concentration Ullmann coupling

Conditions have been identified for the efficient Ullmann macrocyclization of phenol and imidazole nucleophiles with aryl iodides at high reaction concentrations of up to 100 mM and using 5-10 mol % loading of an inexpensive copper catalyst. A range of substitution patterns and ring sizes are tolerated, and the method has been exemplified by the synthesis of a set of druglike macrocycles.

Metal-free arylation of oxygen nucleophiles with diaryliodonium salts

Phenols and carboxylic acids are efficiently arylated with diaryliodonium salts. The reaction conditions are mild, metal free, and avoid the use of halogenated solvents, additives, and excess reagents. The products are obtained in good-to-excellent yields after short reaction times. Steric hindrance is very well tolerated, both in the nucleophile and diaryliodonium salt. The scope includes ortho- and halo-substituted products, which are difficult to obtain by metal-catalyzed protocols. Many functional groups are tolerated, including carbonyl groups, heteroatoms, and alkenes. Unsymmetric salts can be chemoselectively utilized to obtain products with hitherto unreported levels of steric congestion. The arylation has been extended to sulfonic acids, which can be converted to sulfonate esters by two different approaches. With recent advances in efficient synthetic procedures for diaryliodonium salts the reagents are now inexpensive and readily available. The iodoarene byproduct formed from the iodonium reagent can be recovered quantitatively and used to regenerate the diaryliodonium salt, which improves the atom economy.

Tunable Ether Production via Coupling of Aldehydes or Aldehyde/Alcohol over Hydrogen-Modified Gold Catalysts at Low Temperatures

Ethers are an important group of organic compounds that are primarily prepared via homogeneous catalysis, which can lead to operational and environmental issues. Here we demonstrate the production of ethers via heterogeneous catalysis over H adatom-covered gold at temperatures lower than 250 K. Symmetrical ethers can be formed via a self-coupling reaction of corresponding aldehydes; for example, homocoupling of acetaldehyde and propionaldehyde yields diethyl ether and di-n-propyl ether, respectively. In addition, coupling reactions between alcohols and aldehydes, with different carbon chain lengths, are observed via the production of the corresponding unsymmetrical ethers. A reaction mechanism is proposed, suggesting that an alcohol-like intermediate via partial hydrogenation of aldehydes on the surface plays a key role in these reactions. These surface chemical reactions suggest possible heterogeneous routes to low-temperature production of ethers.

Microwave-assisted synthesis of macrocycles via intramolecular and/or bimolecular Ullmann coupling

Microwave-assisted synthesis of macrocyclic diaryl ethers via intramolecular and/or bimolecular Ullmann coupling is described. Using the optimized conditions, a panel of macrocycles, with different substitution patterns, ring sizes, and linkers, has been successfully synthesized using microwave irradiation. To the best of our knowledge, this work represents the first examples of the microwave-assisted synthesis of macrocyclic diaryl ethers via intramolecular and/or bimolecular Ullmann coupling.

Structure-Activity Relationship for Thiirane-Based Gelatinase Inhibitors

An extensive structure-activity relationship study with the template of 2-(4-phenoxyphenylsulfonylmethyl)thiirane (1), a potent and highly selective inhibitor for human gelatinases, is reported herein. Syntheses of 65 new analogs, each in multistep processes, allowed for exploration of key structural components of the molecular template. This study reveals that the presence of the sulfonylmethylthiirane and the phenoxyphenyl group were important for gelatinase inhibition. However, para- and some meta-substitutions of the terminal phenyl ring enhanced inhibitory activity, and led to improve metabolic stability. This agrees with the result from metabolism studies with compound 1 that the primary route of biotransformation is oxidation, mainly at the para position of the phenyl ring and alpha position of the sulfonyl group in the aliphatic side chain.

A new and useful method for the macrocyclization of linear peptides

A new and useful procedure for the macrocyclization of linear peptides is described. The natural amino acid side chains of tyrosine (phenol), lysine (alkylamine), and histidine (imidazole) react in an intramolecular fashion with a pendent pyridine-N-oxide-carboxamide, which is selectively activated by the phosphonium salt, PyBroP. The reaction is mild, rapid, and efficient with a potentially large substrate scope. Multiple examples are provided with full characterization and analyses, including a novel aza-variant of the C-O-D ring system of vancomycin.

A new biarylphosphine ligand for the Pd-catalyzed synthesis of diaryl ethers under mild conditions

A new bulky biarylphosphine ligand (L8) has been developed that allows the Pd-catalyzed C-O cross-coupling of a wide range of aryl halides and phenols under milder conditions than previously possible. A direct correlation between the size of the ligand substituents in the 2', 4', and 6' positions of the nonphosphine containing ring and the reactivity of the derived catalyst system was observed. Specifically, the rate of coupling increased with the size of these substituents.