Synthesis ofN,N-Bis(dialkoxyphosphinoylmethyl)- andN,N-Bis(diphenylphosphinoylmethyl)-β- and γ-amino acid Derivatives by the Microwave-Assisted Double Kabachnik-Fields Reaction

Microwave-Assisted Synthesis of Aminophosphonic Derivatives and Their Antifungal Evaluation against Lomentospora prolificans

Lomentospora prolificans is a pathogenic and multidrug-resistant fungus that can infect both immunocompetent and immunocompromised patients, with mortality rates up to 87%. The World Health Organization (WHO) included this fungal species in its first list of 19 priority fungal pathogens, which focused on fungal pathogens that can cause invasive acute and subacute systemic fungal infections. Therefore, there is a growing interest in finding new therapeutic alternatives. In this work, the synthesis of twelve α-aminophosphonates by the microwave-assisted Kabachnik-Fields reaction and twelve α-aminophosphonic acids by a monohydrolysis reaction is reported. All compounds were evaluated by the agar diffusion method as a preliminary screening in comparison with voriconazole, showing inhibition halos for compounds 7, 11, 13, 22 and 27. The five active compounds in the preliminary tests were evaluated against five strains of L. prolificans following protocol M38-A2 from CLSI. The results showed that these compounds exhibit antifungal activity in the concentration range of 900->900 μg/mL. Cytotoxicity against healthy COS-7 cells was also evaluated by the MTT assay, and it was shown that compound 22 was the least cytotoxic, with a viability of 67.91%, comparable to the viability exhibited by voriconazole (68.55%). Docking studies showed that the possible mechanism of action of the active compounds could be through the inhibition of the enzyme lanosterol-14-alpha-demethylase in an allosteric hydrophobic cavity.

New N-acyl- as well as N-phosphonoylmethyl- and N-phosphinoylmethyl-α-amino-benzylphosphonates by acylation and a tandem Kabachnik-Fields protocol

Diethyl α-benzylamino- and α-amino-benzylphosphonates obtained by the Kabachnik-Fields reaction were useful intermediates in the synthesis of other derivatives. Acylation of α-aminophosphonates with acyl chlorides led to the corresponding N-acyl species existing under a dynamic equilibrium of two conformers. Judging from the broad NMR signals, the sterically most crowded N-benzoyl-N-benzyl derivative suffered a hindered rotation around the N-C axis to the acyl carbon atom at 26 °C. Low temperature NMR measurements at -10 °C showed the presence of two distinct rotamers that were characterized. The other acylated α-amino-benzylphosphonates prepared revealed a less hindered rotation. Single crystal X-ray diffraction of the NH-propionyl species showed a dimer, in which the two molecules were held together by rare intermolecular PO⋯HN bonds. On the other hand, substituted α-benzylamino-benzylphosphonates prepared by phospha-Mannich reactions were employed, as a new approach, in a second Kabachnik-Fields condensation by reaction with formaldehyde and dialkyl phosphites or secondary phosphine oxides to afford novel N-phosphonoylmethyl- and N-phosphinoylmethyl-α-amino-benzylphosphonates. The structure of the new products was confirmed by two-dimensional NMR spectroscopy. A symmetrical bis derivative was prepared in a diastereoselective manner. A related tris(phosphonoylmethyl)amine species was also synthesized.

Synthesis of α-Aminophosphonates and Related Derivatives; the Last Decade of the Kabachnik-Fields Reaction

The Kabachnik-Fields reaction, comprising the condensation of an amine, oxo compound and a P-reagent (generally a >P(O)H species or trialkyl phosphite), still attracts interest due to the challenging synthetic procedures and the potential biological activity of the resulting α-aminophosphonic derivatives. Following the success of the first part (Molecules 2012, 17, 12821), here we summarize the synthetic developments in this field accumulated in the last decade. The procedures compiled include catalytic accomplishments as well as catalyst-free and/or solvent-free "greener" protocols. The products embrace α-aminophosphonates, α-aminophosphinates, and α-aminophosphine oxides along with different bis derivatives from the double phospha-Mannich approach. The newer developments of the aza-Pudovik reactions are also included.

Microwaves as "Co-Catalysts" or as Substitute for Catalysts in Organophosphorus Chemistry

The purpose of this review is to summarize the importance of microwave (MW) irradiation as a kind of catalyst in organophosphorus chemistry. Slow or reluctant reactions, such as the Diels-Alder cycloaddition or an inverse-Wittig type reaction, may be performed efficiently under MW irradiation. The direct esterification of phosphinic and phosphonic acids, which is practically impossible on conventional heating, may be realized under MW conditions. Ionic liquid additives may promote further esterifications. The opposite reaction, the hydrolysis of P-esters, has also relevance among the MW-assisted transformations. A typical case is when the catalysts are substituted by MWs, which is exemplified by the reduction of phosphine oxides, and by the Kabachnik-Fields condensation affording α-aminophosphonic derivatives. Finally, the Hirao P-C coupling reaction may serve as an example, when the catalyst may be simplified under MW conditions. All of the examples discussed fulfill the expectations of green chemistry.

Microwave-Assisted Kabachnik⁻Fields Reaction with Amino Alcohols as the Amine Component

In this paper, the microwave (MW)-assisted catalyst-free and mostly solvent-free Kabachnik-Fields reaction of amino alcohols, paraformaldehyde, and various >P(O)H reagents (dialkyl phosphites, ethyl phenyl-H-phosphinate, and secondary phosphine oxides) is reported. The synthesis of N-2-hydroxyethyl-α-aminophosphonate derivatives was optimized in respect of the temperature, the reaction time, and the molar ratio of the starting materials. A few by-products were also identified. N,N-Bis(phosphinoylmethyl)amines containing a hydroxyethyl group were also prepared by the double Kabachnik-Fields reaction of ethanolamine with an excess of paraformaldehyde and secondary phosphine oxides. The crystal structure of a 2-hydroxyethyl-α-aminophosphine oxide and a bis(phosphinoylmethyl)ethanolamine was studied by X-ray analysis.

Microwave-assisted synthesis of N,N-bis(phosphinoylmethyl)amines and N,N,N-tris(phosphinoylmethyl)amines bearing different substituents on the phosphorus atoms

A family of N,N-bis(phosphinoylmethyl)amines bearing different substituents on the phosphorus atoms was synthesized by the microwave-assisted and catalyst-free Kabachnik-Fields reaction of (aminomethyl)phosphine oxides with paraformaldehyde and diphenylphosphine oxide. The three-component condensation of N,N-bis(phosphinoylmethyl)amine, paraformaldehyde and a secondary phosphine oxide affording N,N,N-tris(phosphinoylmethyl)amine derivatives was also elaborated. This method is a novel approach for the synthesis of the target products.

Microwave irradiation and catalysis in organophosphorus reactions

The usual advantage of microwave (MW) assistance is making organic reactions faster and more efficient. In this article we present reaction types from organophosphorus chemistry, when MW-assisted transformations (e.g. the direct esterification and alkylating esterification of phosphinic acids) may be promoted by suitable catalysts, or vice versa, when a catalytic reaction is enhanced by MW irradiation (e.g. the Arbuzov reaction of aryl halides), and when catalysts may be omitted or simplified under MW irradiation as shown by the alkylation of active methylene containing P=O substrates/the Kabachnik–Fields reaction/deoxygenation of phosphine oxides, and the Hirao reaction, respectively.

Milestones in microwave-assisted organophosphorus chemistry

Our recent results in the field of microwave (MW)-assisted organophosphorus syntheses, especially regarding esterifications, condensations, substitutions and additions are surveyed. Beside making organic chemical reactions more efficient, it was possible to perform transformations that are reluctant on conventional heating. Another option is to substitute catalysts, or to simplify catalyst systems under MW conditions. It is also the purpose of this paper to elucidate the scope and limitations of the MW tool, to interpret the MW effects, and to model the distribution of the local overheatings and their beneficial effect. All these considerations are possible on the basis of the enthalpy of activations determined by us utilizing the Arrhenius equation and the pseudo first order kinetic equation.