Synthesis of 1-Amino-3-oxo-2,7-naphthyridines via Smiles Rearrangement: A New Approach in the Field of Chemistry of Heterocyclic Compounds

In this paper we describe an efficient method for the synthesis of new heterocyclic systems: furo[2,3-c]-2,7-naphthyridines 6, as well as a new method for the preparation of 1,3-diamino-2,7-naphthyridines 11. For the first time, a Smiles rearrangement was carried out in the 2,7-naphthyridine series, thus gaining the opportunity to synthesize 1-amino-3-oxo-2,7-naphthyridines 4, which are the starting compounds for obtaining furo[2,3-c]-2,7-naphthyridines. The cyclization of alkoxyacetamides 9 proceeds via two different processes: the expected formation of furo[2,3-c]-2,7-naphthyridines 10 and the ‘unexpected’ formation of 1,3-diamino-2,7-naphthyridines 11 (via a Smiles type rearrangement).

Pd(II)-Catalyzed Synthesis of Furo[2,3-b]pyridines from β-Ketodinitriles and Alkynes via Cyclization and N-H/C Annulation

A Pd(II)-catalyzed synthesis of furopyridines has been developed from β-ketodinitriles and alkynes via an unusual N-H/C annulation. The participation of both the nitrile groups and the concurrent construction of furan and pyridine rings through the formation of C-C, C═C, C-O, C-N, and C═N bonds are the important features. The synthetic applicability is further demonstrated through a series of postsynthetic alterations.

Synthesis and Structure-Activity Relationships of Imidazopyridine/Pyrimidine- and Furopyridine-Based Anti-infective Agents against Trypanosomiases

Neglected tropical diseases remain among the most critical public health concerns in Africa and South America. The drug treatments for these diseases are limited, which invariably leads to fatal cases. Hence, there is an urgent need for new antitrypanosomal drugs. To address this issue, a large number of diverse heterocyclic compounds were prepared. Straightforward synthetic approaches tolerated pre-functionalized structures, giving rise to a structurally diverse set of analogs. We report on a set of 57 heterocyclic compounds with selective activity potential against kinetoplastid parasites. In general, 29 and 19 compounds of the total set could be defined as active against Trypanosoma cruzi and T. brucei brucei, respectively (antitrypanosomal activities <10 μM). The present work discusses the structure-activity relationships of new fused-ring scaffolds based on imidazopyridine/pyrimidine and furopyridine cores. This library of compounds shows significant potential for anti-trypanosomiases drug discovery.

Synthesis and Evaluation of Antimicrobial Activity and Molecular Docking of New N-1,3-thiazol-2-ylacetamides of Condensed Pyrido[3',2':4,5] furo(thieno)[3,2-d]pyrimidines

Background:

From the literature it is known that many derivatives of fused thienopyrimidines and furopyrimidines possess broad spectrum of biological activity.

Objectives:

The current studies describe the synthesis and evaluation of antimicrobial activity of some new N-1,3-thiazol-2-ylacetamides of pyrido[3',2':4,5]furo(thieno)[3,2-d]pyrimidines.

Methods:

By cyclocondensation of ethyl 1-aminofuro(thieno)[2,3-b]pyridine-2-carboxylates 1with formamide were converted to the pyrido[3',2':4,5]furo(thieno)[3,2-d]pyrimidin-7(8)-ones 2.Alkylation of compound 2 with 2-chloro-N-1,3-thiazol-2-ylacetamide led to the aimed N-1,3-thiazol-2-ylaceta-mides of pyrido[3',2':4,5]furo(thieno)[3,2-d]pyrimidines 3. Starting from compound 2 the relevant S-alkylated derivatives of pyrido[3',2':4,5]furo(thieno)[3,2-d]pyrimidines 6 were also synthesized.

Results:

All the compounds showed antibacterial activity to non-resistant strains. Compounds 3a-3m showed antibacterial activity with MIC/MBC at 0.08-2.31 mg/mL/0.11-3.75 mg/mL .The two most active compounds, 3j and 6b, appeared to be more active towards MRSA than the reference drugs. Half of the tested compounds appeared to be equipotent/more potent than ketoconazole and more potent than bifonazole. The docking analysis provided useful information about the interactions occurring between the tested compounds and the different enzymes.

Conclusion:

Gram-negative and Gram-positive bacteria and fungi showed different response towards tested compounds, indicating that different substituents may lead to different modes of action or that the metabolism of some bacteria/fungi was better able to overcome the effect of the compounds or adapt to it.

Concise, gram-scale synthesis of furo[2,3-b]pyridines with functional handles for chemoselective cross-coupling

A concise 4-step synthesis of furo[2,3-b]pyridines, with handles in the 3- and 5-positions for palladium mediated cross-coupling reactions, is described. The synthetic route has been optimized, with only one step requiring purification by column chromatography. The route is amenable to scale-up, and was successfully executed on a multi-gram scale. Furopyridines are of growing interest in medicinal chemistry, and this route should enable easy access to the core for structure-activity relationship (SAR) studies.

Gold-Catalyzed Oxidative Cascade Cyclization of 1,3-Diynamides: Polycyclic N-Heterocycle Synthesis via Construction of a Furopyridinyl Core

A facile and practical approach to construct a furopyridinyl motif through a gold-catalyzed cascade cyclization of easily accessible diynamides is described. This strategy offers a straightforward approach to furo[2,3-c]isoquinoline and 6H-furo[3',2':5,6]pyrido[3,4-b]indole derivatives. The reaction could build up four new bonds and two additional heteroaromatic rings via a single operation. The heterocyclic products show promising blue luminous performance with fluorescence quantum yields up to 75%.

Exploiting the furo[2,3-b]pyridine core against multidrug-resistant Mycobacterium tuberculosis

Identification of new antibiotics suitable for the treatment of tuberculosis is required. In addition to selectivity, it is necessary to find new antibiotics that are effective when the tuberculous mycobacteria are resistant to the available therapies. The furo[2,3-b]pyridine core offers potential for this application. Herein, we have described the screening of our in-house library of furopyridines against Mycobacterium tuberculosis and identified a promising selective bioactive compound against different drug-resistant strains of this mycobacteria. The library of compounds was prepared by a CH amination reaction using mild and metal-free conditions, increasing the available information about the reactivity of furo[2,3-b]pyridine core through this reaction.

Synthesis and characterization of new 4-aryl-2-(2-oxopropoxy)-6-(2,5-dichlorothiophene)nicotinonitrile and their furo[2,3-b]pyridine derivatives: Assessment of antioxidant and biological activity

A new series of furo[2,3-b]pyridine derivatives bearing aryl substituents were synthesized in two steps, where, the cyano-(2H)-pyridones (1a-l) were converted to the corresponding nicotinonitriles (2a-l), followed by the Thorpe-Ziegler ring cyclization to the furo[2,3-b]pyridine derivatives (3a-l). All new compounds were characterized by 1D-NMR experiments (1H and 13C) and 2D-NMR experiments (COSY, HMBC and HSQC), as well as ESI-MS and HR-ESI-MS data. The new compounds were screened for their antioxidant activities by 2,2-diphenyl-1-picryl-hydrazylhydrate (DPPH) free radical assay. The highest radical scavenging effect was observed for nicotinonitriles 2d, 2h and 2l and furo[2,3-b]pyridines 3b, 3f and 3j by methanolic solvent at 4.0 mg/mL concentration. Remarkably, all nicotinonitriles and furo[2,3-b]pyridine exhibited a significant radical scavenging activity after 24 and 48 hours compared with 0.5 hour.

Charting the Chemical Reactivity Space of 2,3-Substituted Furo[2,3-b]pyridines Synthesized via the Heterocyclization of Pyridine-N-oxide Derivatives

A concise strategy for the synthesis of 2,3-substituted furo[2,3-b]pyridines is described. Mild, metal-free conditions were successfully applied to produce a range of 2-(alkyl or aryl)-3-ethylcarboxylate-furo[2,3-b]pyridines in yields of 50-91%. Then, the chemical reactivity of this heterocyclic framework was explored to develop straightforward methods for its functionalization. The pyridine moiety reactivity was successfully explored by C-H amination and borylation reactions, although C-H fluorination and radical C-H arylation processes were not as efficient. In addition, while the furopyridine core proved stable under basic conditions, the ring-opening reaction of the furan moiety with hydrazine generated a valuable new pyridine-dihydropyrazolone scaffold.