Recent Trends in the Petasis Reaction: A Review of Novel Catalytic Synthetic Approaches with Applications of the Petasis Reaction

The Petasis reaction, also called the Petasis Borono-Mannich reaction, is a multicomponent reaction that couples a carbonyl derivative, an amine and boronic acids to yield substituted amines. The reaction proceeds efficiently in the presence or absence of a specific catalyst and solvent. By employing this reaction, a diverse range of chiral derivatives can easily be obtained, including α-amino acids. A broad substrate scope, high yields, distinct functional group tolerance and the availability of diverse catalytic systems constitute key features of this reaction. In this review article, attention has been drawn toward the recently reported methodologies for executing the Petasis reaction to produce structurally simple to complex aryl/allyl amino scaffolds.

Development of diphenylmethylpiperazine hybrids of chloroquinoline and triazolopyrimidine using Petasis reaction as new cysteine proteases inhibitors for malaria therapeutics

Malaria is a widespread infectious disease, causing nearly 247 million cases in 2021. The absence of a broadly effective vaccine and rapidly decreasing effectiveness of most of the currently used antimalarials are the major challenges to malaria eradication efforts. To design and develop novel antimalarials, we synthesized a series of 4,7-dichloroquinoline and methyltriazolopyrimidine analogues using a multi-component Petasis reaction. The synthesized molecules (11-31) were screened for in-vitro antimalarial activity against drug-sensitive and drug-resistant strains of Plasmodium falciparum with an IC₅₀ value of 0.53 μM. The selected compounds were screened to evaluate in-vitro and in-silico enzyme inhibition efficacy against two cysteine proteases, PfFP2 and PfFP3. The compounds 15 and 17 inhibited PfFP2 with an IC₅₀ = 3.5 and 4.8 μM, respectively and PfFP3 with an IC₅₀ = 4.9 and 4.7 μM, respectively. Compounds 15 and 17 were found equipotent against the Pf3D7 strain with an IC₅₀ value of 0.74 μM, whereas both were displayed IC₅₀ values of 1.05 μM and 1.24 μM for the PfW2 strain, respectively. Investigation of effect of compounds on parasite development demonstrated that compounds were able to arrest the growth of the parasites at trophozoite stage. The selected compounds were screened for in-vitro cytotoxicity against mammalian lines and human red-blood-cell (RBC), which demonstrated no significant cytotoxicity associated with the molecules. In addition, in silico ADME prediction and physiochemical properties supported the drug-likeness of the synthesized molecules. Thus, the results highlighted the diphenylmethylpiperazine group cast on 4,7-dichloroquinoline and methyltriazolopyrimidine using Petasis reaction may serve as models for the development of new antimalarial agents.

Palladium-catalyzed enantioselective three-component synthesis of α-arylglycine derivatives from glyoxylic acid, sulfonamides and aryltrifluoroborates

A palladium-catalyzed enantioselective three-component reaction of glyoxylic acid, sulfonamides and aryltrifluoroborates is described. This process provides modular access to the important α-arylglycine motif in moderate to good yields and enantioselectivies. The formed α-arylglycine products constitute useful building blocks for the synthesis of peptides or arylglycine-containing natural products.

Multicomponent Petasis reaction for the identification of pyrazine based multi-target directed anti-Alzheimer's agents: In-silico design, synthesis, and characterization

Multi-target directed ligands (MTDLs) have recently attracted significant interest due to their exceptional effectiveness against multi-factorial Alzheimer's disease. The present work described the development of pyrazine-based MTDLs using multicomponent Petasis reaction for the dual inhibition of tau-aggregation and human acetylcholinesterase (hAChE). The molecular structure of synthesized ligands was validated by ¹H & ¹³C NMR and mass spectrometry. The screened compounds were shown to have a strong inhibitory effect at 10 μM concentration against tau-oligomerization and hAChE, but only moderate inhibitory activity against Aβ₄₂. Among all the compounds, the half-maximal inhibitory concentration (IC₅₀) for 21 and 24 against hAChE were 0.71 μM and 1.09 μM, respectively, while they displayed half-maximal effective concentrations (EC₅₀) values of 2.21 μM and 2.71 μM for cellular tau-oligomerization, respectively. Additionally, an MTT experiment using tau-expressing SH-SY5Y neuroblastoma cells revealed that 21 was more neuroprotective than the FDA-approved medication donepezil. Furthermore, an MD simulation study was performed to investigate the dynamics and stability of AChE-21 and AChE-24 complexes in an aqueous environment. The MM-PBSA calculations were performed to evaluate the binding of 21 and 24 with AChE, and the relative binding energy was calculated as -870.578 and -875.697 kJ mol^-1, respectively. As a result, the study offered insight into the design of new MTDLs and highlighted 21 as a potential roadblock to the development of anti-AD medications.

The Chelate Effect Rationalizes Observed Rate Acceleration and Enantioselectivity in BINOL-Catalyzed Petasis Reactions

Density functional theory (DFT) calculations afforded insight into the origin of the experimentally observed reaction rate acceleration (≥500 fold) and enantioselectivity (≥99 % ee) of 1,1'-bi-2-naphthol- (BINOL-) catalyzed three-component Petasis reactions . BINOL accelerates the rate determining step by forming a B^IV chelate, which involves the loss of water from the hemiaminal moiety to generate an iminium intermediate. Subsequent vinyl group transfer from B^IV to the iminium carbon affords the enantiomerically enriched product and a cyclic trigonal B(III)BINOL complex, which rapidly releases the BINOL allowing it to re-enter the catalytic cycle. In the transition state of the vinyl transfer step, C-H-O hydrogen bonding between the iminium C-H and O of (R)-BINOL directs the vinyl group addition to the Re-face of the iminium carbon. This mechanism explains both the rate acceleration and high enantioselectivity of the stereo determining step.

Identification, in-vitro anti-plasmodial assessment and docking studies of series of tetrahydrobenzothieno[2,3-d]pyrimidine-acetamide molecular hybrids as potential antimalarial agents

Malaria is the most lethal parasitic infections in the world. To address the emergence of drug resistance to current antimalarials, here we report the design and synthesis of new series of tetrahydrobenzothieno[2,3-d]pyrimidine-acetamide hybrids by using multicomponent Petasis reaction as the key step and evaluated in vitro for their antimalarial effectiveness. The structure of all the compounds were confirmed by NMR Spectroscopy and mass spectrometry. Most of the compounds showed potent antimalarial activity against both CQ-sensitive (3D7) and CQ-resistant (W2) strains. A8, A5, and A4 are the most potent compounds that showed excellent anti-plasmodial activity against CQ-resistant strain in the nanomolar range with IC₅₀ values 55.7 nM, 60.8 nM, and 68.0 nM respectively. To assess the parasite selectivity, the in vitro cytotoxicity of selected compounds (A3-A6, A8) was tested against HPL1D cells, demonstrating low cytotoxicity with high selectivity indices. Furthermore, these compounds were also evaluated on two additional human cancerous cell lines (A549 and MDA-MB-231), confirming their anticancer effectiveness. The in vitro hemolysis assay also showed the non-toxicity of these compounds on normal uninfected human RBCs. The interaction of these hybrids was also investigated by the molecular docking studies in the binding site of wild type Pf-DHFR-TS and quadruple mutant Pf-DHFR-TS. The in silico ADMET profiling also revealed promising physicochemical and pharmacokinetic parameters for the most active hybrids, which provide strong vision for further development of potential antimalarials.

Investigation of NPB Analogs That Target Phosphorylation of BAD-Ser99 in Human Mammary Carcinoma Cells

The design and development of a small molecule named NPB [3-{(4(2,3-dichlorophenyl)piperazin-1-yl}{2-hydroxyphenyl)methyl}-N-cyclopentylbenzamide], which specifically inhibited the phosphorylation of BAD at Ser99 in human carcinoma cells has been previously reported. Herein, the synthesis, characterization, and effect on cancer cell viability of NPB analogs, and the single-crystal X-ray crystallographic studies of an example compound (4r), which was grown via slow-solvent evaporation technique is reported. Screening for loss of viability in mammary carcinoma cells revealed that compounds such as 2[(4(2,3-dichlorophenyl)piperazin-1-yl][naphthalen-1-yl]methyl)phenol (4e), 5[(4(2,3-dichlorophenyl)piperazin-1-yl][2-hydroxyphenyl)methyl)uran-2-carbaldehyde (4f), 3[(2-hydroxyphenyl][4(p-tolyl)piperazin-1-yl)methyl)benzaldehyde (4i), and NPB inhibited the viability of MCF-7 cells with IC₅₀ values of 5.90, 3.11, 7.68, and 6.5 µM, respectively. The loss of cell viability was enhanced by the NPB analogs synthesized by adding newer rings such as naphthalene and furan-2-carbaldehyde in place of N-cyclopentyl-benzamide of NPB. Furthermore, these compounds decreased Ser99 phosphorylation of hBAD. Additional in silico density functional theory calculations suggested possibilities for other analogs of NPB that may be more suitable for further development.

Multicomponent Petasis Reaction for the Synthesis of Functionalized 2-Aminothiophenes and Thienodiazepines

Multicomponent Petasis reaction has been widely applied for the synthesis of functionalized amine building blocks and biologically active compounds. Employing primary aromatic amines that are not typical reactive substrates contributes to expand the application scope of the Petasis reaction. In this study, we demonstrated the synthesis of functionalized 2-aminothiophenes using Gewald-reaction-derived 2-aminothiophenes as the amine substrates, whose low reactivity in the Petasis reaction was overcome using hexafluoro-2-propanol as the solvent in a mild condition. The obtained Petasis products are amenable for further transformations owing to the presence of multiple functional handles. A following intramolecular cyclization of selected Petasis products afforded substituted tricyclic heterocycles that incorporate a pharmaceutically interesting thienodiazepine moiety.

Brønsted Acid-Catalyzed General Petasis Allylation and Isoprenylation of Unactivated Ketones

Brønsted acid-catalyzed general Petasis allylation and isoprenylation of unactivated ketones were developed by using o-hydroxyaniline and the corresponding pinacolyl boronic esters. This robust methodology provided access to a broad variety of quaternary homoallylic amines and dienyl amines in high yields, proved to be applicable to a gram-scale synthesis, and allowed the synthesis of a potentially bioactive quaternary homoallylic aminodiol.

Translation of the copper/bipyridine-promoted Petasis reaction to solid phase-coupled DNA for encoded library synthesis

The Petasis three-component reaction gives rise to diverse substituted α-aryl glycines from readily available amines, boronic acids and glyoxalic acid. Thus, this reaction is highly attractive for DNA-encoded small molecule screening library synthesis. The Petasis reaction is for instance promoted by a potentially DNA damaging copper(I)/bipyridine reagent system in dry organic solvents. We found that solid phase-coupled DNA strands tolerated this reagent system at elevated temperature allowing for synthesis of diverse substituted DNA-tagged α-aryl glycines from DNA-conjugated secondary amines.

Synthesis, antimycobacterial and antifungal evaluation of some new 1-ethyl-5-(hetero)aryl-6-styryl-1,6-dihydropyrazine-2,3-dicarbonitriles

The Petasis reaction of 6-hydroxy adducts of 1-alkyl-2,3-dicyano-5-arylpyrazinium salts with trans-styrylboronic acids proved to proceed smoothly at room temperature to give the corresponding 5-(hetero)aryl-6-styryl substituted 1,6-dihydropyrazine derivatives. Also it has been found that C(6) unsubstituted 1,6-dihydro- or 1,4,5,6-tetrahydropyrazine derivatives can be easy prepared in high yields from the corresponding pyrazinium salts by reduction with triethylsilane. All synthesized compounds were screened in vitro for their antifungal activities against seven pathogenic fungal strains and antimycobacterial activities against Mycobacterium tuberculosis H37Rv, avium, terrae and multi-drug-resistant strains isolated from tuberculosis patients in the Ural region (Russia).