Dynamic combinatorial chemistry as a rapid method for discovering sequence-selective RNA-binding compounds.

The ever-growing number of RNA species that are recognized as having a role in human disease is driving a demand for novel molecular probes and therapeutics. Producing sequence-selective RNA-binding molecules remains a substantial challenge, however. One approach that has been successful in producing molecules with high affinity and specificity for disease-relevant RNAs is the use of dynamic combinatorial chemistry, a fragment-based method in which fragments combine reversibly in the presence of the target. We describe methods for the design, synthesis, and screening of dynamic combinatorial libraries targeting RNA.

7-Step Flow Synthesis of the HIV Integrase Inhibitor Dolutegravir.

Dolutegravir (DTG), an important active pharmaceutical ingredient (API) used in combination therapy for the treatment of HIV, has been synthesized in continuous flow. By adapting the reported GlaxoSmithKline process chemistry batch route for Cabotegravir, DTG was produced in 4.5 h in sequential flow operations from commercially available materials. Key features of the synthesis include rapid manufacturing time for pyridone formation, one-step direct amidation of a functionalized pyridone, and telescoping of multiple steps to avoid isolation of intermediates and enable for greater throughput.

Fast and Facile Synthesis of 4-Nitrophenyl 2-Azidoethylcarbamate Derivatives from N-Fmoc-Protected α-Amino Acids as Activated Building Blocks for Urea Moiety-Containing Compound Library.

A fast and facile synthesis of a series of 4-nitrophenyl 2-azidoethylcarbamate derivatives as activated urea building blocks was developed. The N-Fmoc-protected 2-aminoethyl mesylates derived from various commercially available N-Fmoc-protected α-amino acids, including those having functionalized side chains with acid-labile protective groups, were directly transformed into 4-nitrophenyl 2-azidoethylcarbamate derivatives in 1 h via a one-pot two-step reaction. These urea building blocks were utilized for the preparation of a series of urea moiety-containing mitoxantrone-amino acid conjugates in 75-92% yields and parallel solution-phase synthesis of a urea compound library consisted of 30 members in 38-70% total yields.

Facile synthesis of 1,3-thiazolidin-4-ones as antitubercular agents.

We have developed, highly efficient, one-pot, solvent-free, [Et3NH][HSO4] catalyzed multicomponent reaction protocol for the synthesis of 1,3-thiazolidin-4-ones in excellent yields. For the first time, the 1,3-thiazolidin-4-ones were evaluated in vitro for their antimycobacterial activity against Mycobacterium tuberculosis dormant MTB H37Ra and Mycobacterium bovis BCG strains. Among the synthesized basic 1,3-thiazolidin-4-ones, particularly the compounds 4c, 4d, 4e, 4f, 4h, 4i and 4j displays promising antitubercular activity along with no significant cytotoxicity against the cell lines MCF-7, A549 and HCT-116.

An Efficient and Facile Method for the Synthesis of Benzimidazoisoquinoline Derivatives via a Multicomponent Reaction.

Two series of benzimidazoisoquinoline and fused benzimidazoisoquinoline-benzimidazole derivatives have been synthesized using an efficient one-pot procedure. This process involves an intramolecular nucleophilic substitution reaction and provides facile access to two series of complexes and potentially interesting biologically active scaffolds.

Price-Focused Analysis of Commercially Available Building Blocks for Combinatorial Library Synthesis.

Combinatorial libraries are synthesized by combining smaller reagents (building blocks), the price of which is an important component of the total costs associated with the synthetic exercise. A significant portion of commercially available reagents are too expensive for large scale work. In this study, 13 commonly used reagent classes in combinatorial library synthesis (primary and secondary amines, carboxylic acids, alcohols, ketones, aldehydes, boronic acids, acyl halides, sulfonyl chlorides, isocyanates, isothiocyanates, azides and chloroformates) were analyzed with respect to the cost, physicochemical properties (molecular weight and calculated logP), chemical diversity, and 3D-likeness using a large data set. The results define the chemical space accessible under a constraint of limited financial resources.

A combinatorial chemistry method for fast screening of perovskite-based NO oxidation catalyst.

A fast parallel screening method based on combinatorial chemistry (combichem) has been developed and applied in the screening tests of perovskite-based oxide (PBO) catalysts for NO oxidation to hit a promising PBO formulation for the oxidation of NO to NO2. This new method involves three consecutive steps: oxidation of NO to NO2 over a PBO catalyst, adsorption of NOx onto the PBO and K2O/Al2O3, and colorimetric assay of the NOx adsorbed thereon. The combichem experimental data have been used for determining the oxidation activity of NO over PBO catalysts as well as three critical parameters, such as the adsorption efficiency of K2O/Al2O3 for NO2 (α) and NO (ß), and the time-average fraction of NO included in the NOx feed stream (ξ). The results demonstrated that the amounts of NO2 produced over PBO catalysts by the combichem method under transient conditions correlate well with those from a conventional packed-bed reactor under steady-state conditions. Among the PBO formulations examined, La0.5Ag0.5MnO3 has been identified as the best chemical formulation for oxidation of NO to NO2 by the present combichem method and also confirmed by the conventional packed-bed reactor tests. The superior efficiency of the combichem method for high-throughput catalyst screening test validated in this study is particularly suitable for saving the time and resources required in developing a new formulation of PBO catalyst whose chemical composition may have an enormous number of possible variations.

Rapid two-step synthesis of benzimidazo[1',2':1,5]pyrrolo[2,3-c]isoquinolines by a three-component coupling reaction.

A two-step, three-component coupling reaction on ionic liquid supported 2-cyanomethylbenzimidazoles, methyl 2-formylbenzoate, and isocyanides under microwave activation is explored. Knoevenagel condensation of 2-cyanomethylbenzimidazole with methyl-2-formylbenzoate in the presence of piperidine catalyst is followed by [4+1] cycloaddition with an isocyanide in the next step. Consequent intramolecular δ-lactam formation allows rapid construction of novel aza-pentacycles, benzimidazo[1',2':1,5]pyrrolo[2,3-c]isoquinolines.

Ugi-based approaches to quinoxaline libraries.

An expedient and concise Ugi-based unified approach for the rapid assembly of quinoxaline frameworks has been developed. This convergent and versatile method uses readily available commercial reagents, does not require advanced intermediates, and exhibits excellent bond-forming efficiency, thus exemplifying the operationally simple synthesis of quinoxaline libraries.

Efficient and novel one-pot synthesis of polycycles bearing cyclols by FeCl3-promoted [2 + 2] cycloaddition: application to cannabicyclol, cannabicyclovarin, and ranhuadujuanine A.

Simple and facile synthetic routes for the preparation of biologically interesting cyclol bearing polycycles were developed using FeCl3-promoted [2 + 2] cycloaddition from readily available benzopyrans possessing a variety of substituents. As examples of this methodology, one-step syntheses of cannabicyclol, cannabicyclovarin, and ranhuadujuanine A were accomplished in good yield.

A multicomponent synthetic strategy for two-carbon-tethered 1,3-oxathiole-indole pairs.

An efficient methodology for the multicomponent synthesis of new and highly functionalized heterocycles containing 1,3-oxathiole and indole units which are connected through an sp(2)-C(2) bridge has been developed. This domino reaction enables successful assembly of three new sigma bonds including a C-S bond and a C-O bond in a one-pot operation. Features of this strategy include mild conditions, convenient one-pot operation, and high stereo- and regioselectivity.

One-pot, three-component synthesis of 7-azaindole derivatives from N-substituted 2-amino-4-cyanopyrroles, various aldehydes, and active methylene compounds.

An efficient and practical route to 7-azaindole framework has been developed by one-pot, three-component cyclocondensation of N-substituted 2-amino-4-cyanopyrroles, various aldehydes, and active methylene compounds in ethanol or acetic acid at reflux. Reactions involving tetronic acid, indane-1,3-dione, dimedone, and 5-phenylcyclohexane-1,3-dione gave carbocyclic fused 7-azaindoles, whereas Meldrum's acid, benzoylacetonitrile, and malononitrile resulted in the highly substituted 7-azaindole derivatives, making this strategy very useful in diversity-oriented synthesis (DOS).

A simple and effective approach to the synthesis of isoquinoline derivatives under solvent-free conditions.

An efficient synthesis of dialkyl pyrrolo[2,1-a]isoquinoline-2,3-dicarboxylates, pyrrolo[1,2-a]quinoline-1,2- dicarboxylates and indolizines is described via one-pot reactions of isoquinoline, quinoline or pyridine and phenacyl bromids with dialkyl acetylenedicarboxylates or diaryloylacetylene under solvent-free conditions at 50°C. The mild reaction conditions and high yields of the products exhibit the good synthetic advantage of these methods.

Efficient one-pot, three-component synthesis of a library of pyrrolo[1,2-c]pyrimidine derivatives.

Herein is reported a simple and efficient one-pot three-component synthesis of pyrrolo[1,2-c]pyrimidine derivatives starting from various substituted pyrimidines, 2-bromoacetophenones, and electron deficient alkynes in epoxides acting both as reaction medium and HBr scavanger. This method proved to be very lucrative and avoids formation of ylide inactivation products. The synthesis represents an environmentally benign alternative to classical methods. The new library of compounds was briefly characterized regarding the improved Lipinski rule to asses the potential drug-likeness of the compounds. The majority of compounds are statisfing the Lipinski rule.

Expedient synthesis of a 72-membered isoxazolino-ß-ketoamide library by a 2·3-component reaction.

An efficient 2·3-component reaction (2·3CR; a 2-component reaction followed, in one pot, by a3-component reaction) is presented for the synthesis of isoxazolino-ß-ketoamides. This 2·3CR proceeds by (i) a Meldrum's acid-generated acyl ketene, which is trapped by an amine to form a ß-ketoamide intermediate in a 2CR followed, in one pot, by (ii) a Mannich reaction followed by elimination of dimethyl amine·HCl to generate an α,ß-unsaturated ß-ketoamide dipolarophile that reacts in a nitrile oxide 1,3-dipolar cycloaddition reaction. This one-pot 2·3CR process delivers the targeted isoxazolino-ß-ketoamide product. A total of 72 compounds are presented, all of which have been submitted to the NIH Molecular Libraries Small Molecule Repository for high-throughput biological screening.

A rapid and facile method for the general synthesis of 3-aryl substituted 4,5,6,7-tetrahydro[1,2,3]triazolo[1,5-a]pyrazines and their ring fused analogues.

We report a general and facile method that provides rapid entry into 3-aryl substituted 4,5,6,7-tetrahydro[1,2,3]triazolo[1,5-a]pyrazines and their ring fused analogues in one-pot under palladium-copper catalysis. The methodology utilises simple and easily available substrates of broad range. The applicability of this reaction for the synthesis of optically active products has been demonstrated. A plausible reaction mechanism has also been proposed.

Solid-phase peptide synthesis using microwave irradiation.

Since the advent of solid-phase peptide synthesis (SPPS) in the late 1950s, numerous advancements in the underlying chemistry (i.e., orthogonal protection strategy, coupling reagents, and solid support matrices) have greatly improved the efficiency of the technique. More recently, application of microwave radiation to SPPS has been found to reduce reaction time and/or increase the initial purity of synthetic peptide products. In this protocol, conditions are described to accomplish rapid peptide coupling and 9-fluorenylmethoxycarbonyl (Fmoc) removal reactions under temperature-controlled conditions in either a manual or automated synthesis format using a microwave reactor. These microwave-assisted peptide synthesis procedures have been used to rapidly prepare a "difficult" peptide sequence from the acyl carrier protein, ACP(65-74), in less than 3 h and the reduced, linear precursor to human hepcidin, in high initial purity.

3D polymer scaffold arrays.

We have developed a combinatorial platform for fabricating tissue scaffold arrays that can be used for screening cell-material interactions. Traditional research involves preparing samples one at a time for characterization and testing. Combinatorial and high-throughput (CHT) methods lower the cost of research by reducing the amount of time and material required for experiments by combining many samples into miniaturized specimens. In order to help accelerate biomaterials research, many new CHT methods have been developed for screening cell-material interactions where materials are presented to cells as a 2D film or surface. However, biomaterials are frequently used to fabricate 3D scaffolds, cells exist in vivo in a 3D environment and cells cultured in a 3D environment in vitro typically behave more physiologically than those cultured on a 2D surface. Thus, we have developed a platform for fabricating tissue scaffold libraries where biomaterials can be presented to cells in a 3D format.