Bioactive 2-pyridone-containing heterocycle syntheses using multicomponent reactions

2-Pyridone-containing heterocycles are considered privileged scaffolds in drug discovery due to their behavior as hydrogen bond donors and/or acceptors and nonpeptidic mimics, and remarkable physicochemical properties such as metabolic stability, solubility in water, and lipophilicity. This review provides a comprehensive overview of multicomponent reactions (MCRs) for the synthesis of 2-pyridone-containing heterocycles. In particular, it covers the articles published from 1999 to date related to anticancer, antibacterial, antifungal, anti-inflammatory, α-glucosidase inhibitor, and cardiotonic activities of 2-pyridone-containing heterocycles obtained exclusively by an MCR. The discussion focuses on bioactivity data, synthetic approaches, plausible reaction mechanisms, and molecular docking simulations to facilitate comparison and underscore the applications of the 2-pyridone motif in drug discovery and medicinal chemistry. We also present our conclusions and outlook for the future.

Recent Applications of the Multicomponent Synthesis for Bioactive Pyrazole Derivatives

Pyrazole and its derivatives are considered a privileged N-heterocycle with immense therapeutic potential. Over the last few decades, the pot, atom, and step economy (PASE) synthesis of pyrazole derivatives by multicomponent reactions (MCRs) has gained increasing popularity in pharmaceutical and medicinal chemistry. The present review summarizes the recent developments of multicomponent reactions for the synthesis of biologically active molecules containing the pyrazole moiety. Particularly, it covers the articles published from 2015 to date related to antibacterial, anticancer, antifungal, antioxidant, α-glucosidase and α-amylase inhibitory, anti-inflammatory, antimycobacterial, antimalarial, and miscellaneous activities of pyrazole derivatives obtained exclusively via an MCR. The reported analytical and activity data, plausible synthetic mechanisms, and molecular docking simulations are organized in concise tables, schemes, and figures to facilitate comparison and underscore the key points of this review. We hope that this review will be helpful in the quest for developing more biologically active molecules and marketed drugs containing the pyrazole moiety.

3-(tert-Butyl)-N-(4-methoxybenzyl)-1-methyl-1H-pyrazol-5-amine

We reported an efficient one-pot two-step synthesis of 3-(tert-butyl)-N-(4-methoxybenzyl)-1-methyl-1H-pyrazol-5-amine 3 in good yield by a solvent-free condensation/reduction reaction sequence starting from 3-(tert-butyl)-1-methyl-1H-pyrazol-5-amine 1 and p-methoxybenzaldehyde 2. The one-pot reductive amination proceeded by the formation in situ of the N-(5-pyrazolyl)imine 4 as key synthetic intermediate of other valuable pyrazole derivatives. This methodology is distinguished by its operational easiness, short reaction time, isolation and purification of the aldimine intermediate is not required. The structure of the synthesized N-heterocyclic amine 3 was fully characterized by FTIR-ATR, 1D and 2D NMR experiments, EIMS, and elemental analysis.

Synthesis of Biologically Active Molecules through Multicomponent Reactions

Focusing on the literature progress since 2002, the present review explores the highly significant role that multicomponent reactions (MCRs) have played as a very important tool for expedite synthesis of a vast number of organic molecules, but also, highlights the fact that many of such molecules are biologically active or at least have been submitted to any biological screen. The selected papers covered in this review must meet two mandatory requirements: (1) the reported products should be obtained via a multicomponent reaction; (2) the reported products should be biologically actives or at least tested for any biological property. Given the diversity of synthetic approaches utilized in MCRs, the highly diverse nature of the biological activities evaluated for the synthesized compounds, and considering their huge structural variability, much of the reported data are organized into concise schemes and tables to facilitate comparison, and to underscore the key points of this review.

3-Formylpyrazolo[1,5- a]pyrimidines as Key Intermediates for the Preparation of Functional Fluorophores

A one-pot route for the regioselective synthesis of 3-formylpyrazolo[1,5- a]pyrimidines 4a-k in good yields through a microwave-assisted process is provided. The synthesis proceeds via a cyclocondensation reaction between β-enaminones 1 with NH-3-aminopyrazoles 2, followed by formylation with an iminium salt moiety (Vilsmeyer-Haack reagent). These N-heteroaryl aldehydes 4 were successfully used as strategic intermediates for the preparation of novel functional fluorophores with yields up to 98%. The structures of the products obtained and regioselectivity of the reactions were determined on the basis of NMR measurements and X-ray diffraction analysis. Since pyrazolo[1,5- a]pyrimidines (PPs) 3 have shown an important fluorescence, photophysical properties of four 2-methylderivatives substituted at position 7 with different acceptor (A) or donor (D) groups were investigated. The compounds evaluated exhibited large Stokes shift in different solvents, but only the substituted p-methoxyphenyl (4-An) showed a strong fluorescence intensity with quantum yields up to 44% due to its greater ICT. Therefore, hybrid systems based on pyrazolo[1,5- a]pyrimidines could be used as fluorescent probes to detect biologically or environmentally relevant species.

Design of Two Alternative Routes for the Synthesis of Naftifine and Analogues as Potential Antifungal Agents

Two practical and efficient approaches have been implemented as alternative procedures for the synthesis of naftifine and novel diversely substituted analogues 16 and 20 in good to excellent yields, mediated by Mannich-type reactions as the key step of the processes. In these approaches, the γ-aminoalcohols 15 and 19 were obtained as the key intermediates and their subsequent dehydration catalyzed either by Brønsted acids like H₂SO₄ and HCl or Lewis acid like AlCl₃, respectively, led to naftifine, along with the target allylamines 16 and 20. The antifungal assay results showed that intermediates 18 (bearing both a β-aminoketo- and N-methyl functionalities in their structures) and products 20 were the most active. Particularly, structures 18b, 18c, and the allylamine 20c showed the lowest MIC values, in the 0.5-7.8 µg/mL range, against the dermatophytes Trichophyton rubrum and Trichophyton mentagrophytes. Interesting enough, compound 18b bearing a 4-Br as the substituent of the phenyl ring, also displayed high activity against Candida albicans and Cryptococcus neoformans with MIC₈₀ = 7.8 µg/mL, being fungicide rather than fungistatic with a relevant MFC value = 15.6 µg/mL against C. neoformans.

A series of (E)-5-(arylideneamino)-1-tert-butyl-1H-pyrrole-3-carbonitriles and their reduction products to secondary amines: syntheses and X-ray structural studies

An efficent access to a series of N-(pyrrol-2-yl)amines, namely (E)-1-tert-butyl-5-[(4-chlorobenzylidene)amino]-1H-pyrrole-3-carbonitrile, C16H16ClN3, (7a), (E)-1-tert-butyl-5-[(2,4-dichlorobenzylidene)amino]-1H-pyrrole-3-carbonitrile, C16H15Cl2N3, (7b), (E)-1-tert-butyl-5-[(pyridin-4-ylmethylene)amino]-1H-pyrrole-3-carbonitrile, C15H16N4, (7c), 1-tert-butyl-5-[(4-chlorobenzyl)amino]-1H-pyrrole-3-carbonitrile, C16H18ClN3, (8a), and 1-tert-butyl-5-[(2,4-dichlorobenzyl)amino]-1H-pyrrole-3-carbonitrile, C16H17Cl2N3, (8b), by a two-step synthesis sequence (solvent-free condensation and reduction) starting from 5-amino-1-tert-butyl-1H-pyrrole-3-carbonitrile is described. The syntheses proceed via isolated N-(pyrrol-2-yl)imines, which are also key synthetic intermediates of other valuable compounds. The crystal structures of the reduced compounds showed a reduction in the symmetry compared with the corresponding precursors, viz. Pbcm to P\overline{1} from compound (7a) to (8a) and P21/c to P\overline{1} from compound (7b) to (8b), probably due to a severe change in the molecular conformations, resulting in the loss of planarity observed in the nonreduced compounds. In all of the crystals, the supramolecular assembly is controlled mainly by strong (N,C)—H...N hydrogen bonds. However, in the case of (7a)–(7c), C—H...Cl interactions are strong enough to help in the three-dimensional architecture, as observed in Hirshfeld surface maps.

Crystal structure of (±)-3-[(benzo[d][1,3]dioxol-5-yl)meth-yl]-2-(3,4,5-tri-meth-oxy-phen-yl)-1,3-thia-zolidin-4-one

In the title thia-zolidine-4-one derivative, C20H21NO6S, the central thia-zolidine ring is essentially planar (r.m.s. deviation for all non-H atoms = 0.0287 Å) and forms a dihedral angle of 88.25 (5)° with the meth-oxy-substituted benzene ring and 74.21 (4)° with the 1,3-benzodioxole ring. The heterocyclic ring (with two O atoms) fused to benzene ring adopts an envelope conformation with the non-ring-junction C atom as the flap. In the crystal, the mol-ecules are linked into chains along [001] through weak C-H⋯O inter-actions, forming R (4) 4(28) edge-fused rings.

Progress of the synthesis of condensed pyrazole derivatives (from 2010 to mid-2013)

Condensed pyrazole derivatives are important heterocyclic compounds due to their excellent biological activities and have been widely applied in pharmaceutical and agromedical fields. In recent years, numerous condensed pyrazole derivatives have been synthesized and advanced to clinic studies with various biological activities. In this review, we summarized the reported synthesis methods of condensed pyrazole derivatives from 2010 until now. All compounds are divided into three parts according to the rings connected to pyrazole-ring, i.e. [5, 5], [5,F 6], and [5, 7]-condensed pyrazole derivatives. The biological activities and applications in pharmaceutical fields are briefly introduced to offer an orientation for the design and synthesis of condensed pyrazole derivatives with good biological activities.

3-(Di-phenyl-amino)-isobenzo-furan-1(3H)-one

In the title isobenzo­furan­one derivative, C₂₀H₁₅NO₂, the planar fused-ring system (r.m.s. deviation for the 10 fitted atoms = 0.031 Å) forms dihedral angles of 63.58 (6) and 63.17 (8)° with the N-bound phenyl rings; the dihedral angle between the planes of these phenyl rings is 85.92 (7)°. In the crystal, mol­ecules are linked by weak C—H⋯O inter­actions, involving both O atoms, forming helical supra­molecular chains along [001].

(±)-3-(5-Amino-3-methyl-1-phenyl-1H-pyrazol-4-yl)-2-benzo-furan-1(3H)-one

In the title compound, C18H15N3O2, the benzo-furan ring system is essentially planar, the rings making a dihedral angle of 0.57 (9)°. The phenyl, furan and benzene rings subtend dihedral angles of 47.07 (10), 85.76 (7) and 86.04 (7)°, respectively, with the pyrazole ring. In the crystal, mol-ecules are linked by weak N-H⋯N, N-H⋯O and C-H⋯O inter-actions, generating edge-fused R 4 (4)(20), and R 1 (2)(7) rings linked into sheets which are parallel to (010).

Dibenzylammonium hydrogen maleate and a redetermination at 120 K of bis(dibenzylamino)methane

In dibenzylammonium hydrogen maleate [or dibenzylammonium (2Z)-3-carboxyprop-2-enoate], C14H16N+·C4H3O4−, (I), the anion contains a fairly short and nearly linear O—H...O hydrogen bond, with an O...·O distance of 2.4603 (16) Å, but with the H atom clearly offset from the mid-point of the O...O vector. The counter-ions in (I) are linked by two N—H...O hydrogen bonds to formC22(6) chains and these chains are weakly linked into sheets by a C—H...O hydrogen bond. Bis(dibenzylamino)methane, C29H30N2, (II), crystallizes with two independent molecules lying across twofold rotation axes in the space groupC2/c, and the molecules are conformationally chiral; there are no direction-specific intermolecular interactions in the crystal structure of (II).

Efficient catalyst-free four-component synthesis of novel γ-aminoethers mediated by a Mannich type reaction

Herein, it is provided an efficient and one-pot procedure for the synthesis of novel and diversely substituted γ-aminoethers in good yields through a four-component process by treatment of benzylamines with polyformaldehyde and activated alkenes in aliphatic alcohols acting both as solvent and as etherificant agents. Reactions proceeded via a Mannich-type reaction, where the formation of iminium ions and aminals was identified as the key intermediates to obtain the target products.