Polymer-assisted solution-phase (PASP) library synthesis of alpha-ketoamides

De Novo Synthesis of α-Ketoamides via Pd/TBD Synergistic Catalysis

Precisely controlling the product selectivity of a reaction is an important objective in organic synthesis. α-Ketoamides are vital intermediates in chemical transformations and privileged motifs in numerous drugs, natural products, and biologically active molecules. The selective synthesis of α-ketoamides from feedstock chemicals in a safe and operationally simple manner under mild conditions is a long-standing catalysis challenge. Herein, an unprecedented TBD-switched Pd-catalyzed double isocyanide insertion reaction for assembling ketoamides in aqueous DMSO from (hetero)aryl halides and pseudohalides under mild conditions is reported. The effectiveness and utility of this protocol are demonstrated by its diverse substrate scope (93 examples), the ability to late-stage modify pharmaceuticals, scalability to large-scale synthesis, and the synthesis of pharmaceutically active molecules. Mechanistic studies indicate that TBD is a key ligand that modulates the Pd-catalyzed double isocyanide insertion process, thereby selectively providing the desired α-ketoamides in a unique manner. In addition, the imidoylpalladium(II) complex and α-ketoimine amide are successfully isolated and determined by X-ray analysis, confirming that they are probable intermediates in the catalytic pathway.

Immobilized Carbodiimide Assisted Flow Combinatorial Protocol to Facilitate Amide Coupling and Lactamization

Through a screen of over one hundred and 30 permutations of reaction temperatures, solvents, carbodiimide resins, and carbodiimide molar equivalences, in the presence, absence, or combination of diisopropylamine and benzotriazole additives, a convenient and first reported carbodiimide polymer-assisted flow approach to effect amide coupling and lactamization was developed. The protocol entails injecting a single solution (1:9 dimethylformamide: dichloromethane) containing a carboxylic acid and an amine or linear peptide sequence into a continuous stream of dichloromethane. The protocol remained viable in the absence of base, did not require carboxylate preactivation which, and in concert with minimal workup requirements, enabled the isolation of products in high yields. Compared to the utilization of untethered carbodiimide reagents, the flow procedure was also observed to provide a degree of racemization safety.

Immobilized coupling reagents: synthesis of amides/peptides

The primary idea of using immobilized reagents in organic synthetic chemistry is to simplify the downstream process, product workup and isolation, and therefore avoiding time-consuming and expensive chromatographic separations, which are intrinsic to every synthetic process. Numerous polymer-bounded reagents are commercially available and applicable to almost all kinds of synthetic chemistry conversions. Herein, we have covered all known supported-coupling reagents and bases which have had a great impact in amide/peptide bond formation. These coupling reagents have been used for the activation of a carboxyl moiety; thus generating an active acylating species that is ready to couple with an amine nucleophile liberating the amide/peptide and polymeric support which can be regenerated for reuse. This also addresses a large variety of anchored coupling reagents, additives, and bases that have only been employed in amide/peptide syntheses during the last six decades.

A very large diversity space of synthetically accessible compounds for use with drug design programs

We have constructed a very large virtual diversity space containing more than 10(13) chemical compounds. The diversity space is built from about 400 combinatorial libraries, which have been expanded by choosing sizeable collections of suitable R-groups that can be attached to each link point of their scaffolds. These R-group collections have been created by selecting reagents that have drug-like properties from catalogs of available chemicals. As members of known combinatorial libraries, the compounds in the diversity space are in general synthetically accessible and useful as potential drug leads. Hence, the diversity space can be used as a vast source of compounds by a de novo drug design program. For example, we have used such a program to generate inhibitors of HIV integrase enzyme that exhibited activity in the micromolar range.

Microwave-Assisted Synthesis Utilizing Supported Reagents: A Rapid and Efficient Acylation Procedure

[reaction: see text] The application of microwave heating to a polymer-assisted solution-phase (PASP) synthesis technique has been utilized to develop a rapid and efficient protocol for the solution-phase synthesis of amides from either amine or carboxylic acid cores.

Parallel solution-phase synthesis of mechanism-based cysteine protease inhibitors

[reaction--see text] A seven-step parallel solution-phase synthesis has been developed for access to ketone-containing mechanism-based cysteine protease inhibitors. The use of liquid-liquid extractions, volatile or solid-supported reagents, and resin-bound scavengers eliminates the need for intermediate column chromatographic purification during this synthesis sequence.

Solutions for library encoding to create collections of discrete compounds

The ability to design, produce, analyze, and manage high quality combinatorial libraries depends on the encoding strategy applied. Several recent advances in encoding technology have extended the range of library design parameters. Enhancements of established techniques have made them more robust and versatile, while additional new and creative encoding concepts have been introduced. With better options now available, combinatorial chemists can more easily select an encoding technique to match resources, library design, and compound management criteria.