Synthesis of Imidazo[1,2-a]pyridine C-Nucleosides with an Unexpected Site of Ribosylation

Palladium-catalyzed C3-selective C–H oxidative carbonylation of imidazo[1,2-a]pyridines with CO and alcohols: a way to access esters

A palladium-catalyzed C3-selective C–H oxidative carbonylation for the synthesis of various esters from imidazo[1,2-a]pyridines and CO with high efficiency and high atom economy has been developed.

Highly Regioselective, Acid-Catalyzed, Three-Component Cascade Reaction for the Synthesis of 2-aminopyridine-Decorated Imidazo[1,2- a]pyridine

A highly regioselective acid-catalyzed three-component reaction of 2-aminopyridine and 3-phenylpropiolaldehyde for the construction of imidazo[1,2- a]pyridine has been developed. This strategy provides a broad range of substrates and represents an efficient approach to give various 2-aminopyridine-decorated imidazo[1,2- a]pyridine in good yields.

Regioselective synthesis of naphthoquinone/naphthoquinol-carbohydrate hybrids by [4 + 2] anionic annulations and studies on their cytotoxicity

An efficient and regioselective synthetic route to naphthoquinone/naphthoquinol-carbohydrate hybrids has been developed. It is based upon anionic annulation of 3-nucleofugalphthalides with an acrylate appended sugar moiety. In each of the annulations studied, the arene-carbohydrate hybrids were obtained in good to excellent yields. The in vitro cytotoxic activity of the synthetic naphthoquinone/naphthonol-carbohydrate hybrids were evaluated against the human cervical cancer cell line (HeLa), and a few of them were found to exhibit potent anticancer activity against the cell line.

Solvent- and catalyst-free synthesis of imidazo[1,2-a]pyridines under microwave irradiation

A facile solvent- and catalyst-free method for the synthesis of a series of imidazo[1,2-a]pyridines in good to excellent yields by the condensation of 2-aminopyridines with α-bromoketones under microwave irradiation has been developed. The important features of this method are that it is reasonably fast, very clean, high yielding, simple workup and environmentally benign.

Microwave-assisted synthesis of novel 2,3-disubstituted imidazo[1,2-a]pyridines via one-pot three component reactions

An expeditious one-pot, metal-free, three-component reaction of arylglyoxals, cyclic 1,3-dicarbonyls and 2-aminopyridines in the presence of molecular iodine under microwave irradiation is reported.

One-pot synthesis of 2-phenylimidazo[1,2-α]pyridines from acetophenone, [Bmim]Br(3) and 2-aminopyridine under solvent-free conditions

One-pot synthesis of 2-phenylimidazo[1,2-α]pyridines from acetophenone, [Bmim]Br₃ and 2-aminopyridine under solvent-free conditions in the presence of Na₂CO₃, gave the corresponding 2-phenylimidazo[1,2-α]pyridines in excellent yields ranging from 72% to 89%.

Emerging approaches for the syntheses of bicyclic imidazo[1,2-x]-heterocycles

Imidazo-[1,2-x]heterocycles are versatile building blocks for use in both a 'drug hunters' quest to discover new leads and a chemical biologists search for effective molecular tools in 'cell perturbation' studies. At the front end of the drug discovery flow chart, the last 5-10 years have witnessed the discovery of new high-throughput methodologies which very quickly have enabled access to virtual libraries of these chemo-types in the realm of 10(7) derivatives. Interestingly, these often neglected cores in patent cooperation treaty (PCT) applications appear in several highly effective marketed drugs, completing the medicinal chemists search for clinical success. Such rigid chemo-types, all containing a bridgehead nitrogen atom, are thus poised for an ever increasing impact on the discovery and development of new molecular therapeutics. The following mini-review will briefly cover therapeutic utility, chemical methodologies and automation developed to enable preparation of arrays of these chemo-types in a high-throughput manner. Synthetic emphasis is placed on a 3-component-3-center isocyanide based multi-component reaction (IMCR), which spans solution, solid phase, flourous and microwave assisted organic synthesis.

Microwave-assisted combinatorial synthesis of polysubstituent imidazo[1,2-a]quinoline, pyrimido[1,2-a]quinoline and quinolino[1,2-a]quinazoline derivatives

A series of unusual fused heterocyclic compound derivatives, consisting of a pyridine and a imidazole or pyrimidine core, with a bridgehead nitrogen, were successfully synthesized by a microwave-assisted, three-component domino reaction of aldehydes, enaminones, and malononnitrile. In this one-pot reaction, up to five new bonds were formed accompanied by generating the lactam group. This method has the advantages of short synthetic route, operational simplicity, increased safety for small-scale high-speed synthesis, and minimal environment impact.

Synthesis of Polysubstituted Imidazo[1,2-a]pyridines via Microwave-Assisted One-Pot Cyclization/Suzuki Coupling/Palladium-Catalyzed Heteroarylation

A new and efficient method for the synthesis of 2,3,6-trisubstituted imidazo[1,2-a]pyridine derivatives using a microwave-assisted one-pot, two-step Suzuki/heteroarylation or one-pot, three-step cyclization/Suzuki/heteroarylation was developed. Polysubstituted compounds are obtained in good yield from 2-amino-5-halogenopyridines, 2-halogenocarbonyl derivatives, boronic acids, and heteroaryl bromides.

Glyoxylic Acid and MP-Glyoxylate: Efficient Formaldehyde Equivalents in the 3-CC of 2-Aminoazines, Aldehydes, and Isonitriles

[reaction: see text] Glyoxylic acid, either in solution or immobilized on MP-carbonate (MP-glyoxylate), participates in an uncatalyzed 3-CC with 2-aminoazines and isonitriles to afford novel 2-unsubstituted-3-amino-imidazoheterocycles. MP-glyoxylate serves as a particularly efficient and experimentally convenient formaldehyde equivalent and readily liberates products through decarboxylation/self-release from the resin. These examples furthermore constitute the first application in which MP-CO3 serves as a solid support for transformations involving carboxylic acids.

The synthesis of 4-deazaformycin A

The preparation of 4-deazaformycin A has been achieved. The synthesis features the condensation of a suitably substituted, lithiated 4-picoline with 2,3,5-tri-O-benzyl-d-ribonolactone, dehydration of the resulting hemiacetal, and ionic hydrogenation, followed by manipulation of the protecting groups and subsequent ring closure with the formation of 7-amino-3-(beta-d-ribofuranosyl)pyrazolo[3,4-c]pyridine.

Synthesis and antiviral activity of novel erythrofuranosyl imidazo[1,2-a]pyridine C-nucleosides constructed via palladium coupling of iodoimidazo[1,2-a]pyridines and dihydrofuran

2,5,6-Trichloro-1-(beta-d-ribofuranosyl)benzimidazole (TCRB) and certain analogues have shown significant activity against human cytomegalovirus. The metabolic instability of the glycosidic linkage in TCRB prompted us to synthesize the structurally similar imidazo[1,2-a]pyridine erythrofuranosyl C-nucleosides. As an approach to the synthesis of polychlorinated imidazo[1,2-a]pyridine C-3-erythrofuranosides, a palladium-based methodology for coupling 2,3-dihydrofuran with chlorinated 3-iodoimidazo[1,2-a]pyridines was developed and optimized to give 80-90% yields of 2,6-dichloro- and 2,6,7-trichloro-3-(2,3-dideoxy-2,3-didehydro-d/l-erythrofuranosyl)imidazo[1,2-a]pyridine. Dihydroxylation of these didehydro derivatives with osmium tetroxide or with AD-mix alpha gave a mixture of erythrofuranosyl C-nucleosides that were separated by standard and then chiral chromatography. When screened for anti-HCMV and HSV-1 activity, the alpha-d anomer of 2,6,7-trichloro-3-(erythrofuranosyl)imidazo[1,2-a]pyridine proved to be the most active member of the series, while the beta-anomers all proved to be inactive.

Stereoselective C-glycoside formation by a rhodium(I)-catalyzed 1,4-addition of arylboronic acids to acetylated enones derived from glycals

[reaction: see text] A new method for the formation of C-glycosides has been developed employing a cationic rhodium(I)-catalyzed 1,4-addition of arylboronic acids to enones derived from glycals. The reaction is stereoselective for the alpha-anomer and is highly dependent on the nature of the rhodium catalyst.