Enantioselective α-Aminophosphonate Functionalization of Indole Ring through an Organocatalyzed Friedel–Crafts Reaction

The Last Decade of Optically Active α-Aminophosphonates

α-Aminophosphonates and related compounds are important due to their real and potential biological activity. α-Aminophosphonates may be prepared by the Kabachnik-Fields condensation of oxo compounds, amines and dialkyl phosphites, or by the aza-Pudovik addition of the same P-reagents to imines. In this review, the methods that allow for the synthesis of α-aminophosphonates with optical activity are surveyed. On the one hand, optically active catalysts or ligands may induce enantioselectivity during the Kabachnik-Fields reaction. On the other hand, asymmetric catalysis during the aza-Pudovik reaction, or hydrogenations of iminophosphonates, may prove to be a useful tool. Lastly yet importantly, it is possible to start from optically active reagents that may be associated with diastereoselectivity. The "green" aspects of the different syntheses are also considered.

Aromatic C-H bond functionalization through organocatalyzed asymmetric intermolecular aza-Friedel-Crafts reaction: a recent update

The aza-Friedel-Crafts reaction allows an efficient coupling of electron-rich aromatic systems with imines for the facile incorporation of aminoalkyl groups into the aromatic ring. This reaction has a great scope of forming aza-stereocenters which can be tuned by different asymmetric catalysts. This review assembles recent advances in asymmetric aza-Friedel-Crafts reactions mediated by organocatalysts. The mechanistic interpretation with the origin of stereoselectivity is also explained.

Synthesis of Tetrasubstituted Phosphorus Analogs of Aspartic Acid as Antiproliferative Agents

An efficient general method for the synthesis of a wide family of α-aminophosphonate analogs of aspartic acid bearing tetrasubstituted carbons is reported through an aza-Reformatsky reaction of α-iminophosphonates, generated from α-aminophosphonates, in an umpolung process. In addition, the α-aminophosphonate substrates showed in vitro cytotoxicity, inhibiting the growth of carcinoma human tumor cell lines A549 (carcinomic human alveolar basal epithelial cell) and SKOV3 (human ovarian carcinoma). In view of the possibilities in the diversity of the substituents that offer the synthetic methodology, an extensive profile structure-activity is presented, measuring IC₅₀ values up to 0.34 µM in the A549 and 9.8 µM in SKOV3 cell lines.

Diethyl(benzamido(diisopropoxyphosphoryl)methyl) phosphonate

Bisphosphonates are widely used in medicine and related areas, mainly for the treatment of bone diseases, such as osteoporosis. However, their synthesis is usually performed under harsh reaction conditions. In order to overcome this limitation, the present work illustrates a new synthetic route to access the title α-aminobisphosphonate in milder reaction conditions using α-phosphorylated imines as key intermediates.

Hydroxy- and Amino-Phosphonates and -Bisphosphonates: Synthetic Methods and Their Biological Applications

Phosphonates and bisphosphonates are stable analogs of phosphates and pyrophosphates that are characterized by one and two carbon–phosphorus bonds, respectively. Among the various phosphonates and bisphosphonates, hydroxy and amino substitutes are of interest as effective in medicinal and industrial chemistry. For example, hydroxy bisphosphonates have proven to be effective for the prevention of bone loss, especially in osteoporotic disease. On the other hand, different substitutions on the carbon atom connected to phosphorus have led to the synthesis of many different hydroxy- and amino-phosphonates and -bisphosphonates, each with its distinct physical, chemical, biological, therapeutic, and toxicological characteristics. Dialkyl or aryl esters of phosphonate and bisphosphonate compounds undergo the hydrolysis process readily and gave valuable materials with wide applications in pharmaceutical and agriculture. This review aims to demonstrate the ongoing preparation of various classes of hydroxy- and amino-phosphonates and -bisphosphonates. Furthermore, the current review summarizes and comprehensively describes articles on the biological applications of hydroxyl- and amino-phosphonates and -bisphosphonates from 2015 until today.

Enantioselective Synthesis of 2-Indolyl Methanamine Derivatives Through Disulfonimides-Catalyzed Friedel–Crafts C2-Alkylation of 3-Substituted Indoles with Imines

An asymmetric Friedel-Crafts C2-alkylation between 3-substituted indoles and imines catalyzed by chiral BINOL-derived disulfonimides (DSIs) has been developed. This reaction tolerated a wide range of 3-substituted indoles and imines, affording...

An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

Since 2004, chiral phosphoric acids (CPAs) have emerged as highyl efficient organocatalysts, providing excellent results in a wide reaction scope. In this review, the applications of CPA for enantioselective additions to CO and CN bonds are covered.

Transition-Metal-Free Addition of Dialkyl Phosphites to Phthalazin-2-ium Bromide: Synthesis of α-Aminophosphonate Analogues

α-Aminophosphonate analogues containing a phthalazine skeleton were efficiently obtained by a new transition-metal-free addition of dialkyl phosphites to phthalazin-2-ium bromide under mild conditions. A mechanistic study using isotope labeling and radical inhibition experiment revealed that the present transformation passes through a nucleophilic addition of dialkyl phosphates, rather than an insertion of P-H to carbenes.

Recent Advances in Selected Asymmetric Reactions Promoted by Chiral Catalysts: Cyclopropanations, Friedel–Crafts, Mannich, Michael and Other Zinc-Mediated Processes—An Update

The main purpose of this review article is to present selected asymmetric synthesis reactions in which chemical and stereochemical outcomes are dependent on the use of an appropriate chiral catalyst. Optically pure or enantiomerically enriched products of such transformations may find further applications in various fields. Among an extremely wide variety of asymmetric reactions catalyzed by chiral systems, we are interested in: asymmetric cyclopropanation, Friedel–Crafts reaction, Mannich and Michael reaction, and other stereoselective processes conducted in the presence of zinc ions. This paper describes the achievements of the above-mentioned asymmetric transformations in the last three years. The choice of reactions is related to the research that has been carried out in our laboratory for many years.

A Multicomponent Protocol for the Synthesis of Highly Functionalized γ-Lactam Derivatives and Their Applications as Antiproliferative Agents

An efficient synthetic methodology for the preparation of 3-amino 1,5-dihydro-2H-pyrrol-2-ones through a multicomponent reaction of amines, aldehydes, and pyruvate derivatives is reported. In addition, the densely substituted lactam substrates show in vitro cytotoxicity, inhibiting the growth of carcinoma human tumor cell lines HEK293 (human embryonic kidney), MCF7 (human breast adenocarcinoma), HTB81 (human prostate carcinoma), HeLa (human epithelioid cervix carcinoma), RKO (human colon epithelial carcinoma), SKOV3 (human ovarian carcinoma), and A549 (carcinomic human alveolar basal epithelial cell). Given the possibilities in the diversity of the substituents that offer the multicomponent synthetic methodology, an extensive structure-activity profile is presented. In addition, both enantiomers of phosphonate-derived γ-lactam have been synthesized and isolated and a study of the cytotoxic activity of the racemic substrate vs. its two enantiomers is also presented. Cell morphology analysis and flow cytometry assays indicate that the main pathway by which our compounds induce cytotoxicity is based on the activation of the intracellular apoptotic mechanism.

Fiaud's Acid, a novel organocatalyst for diastereoselective bis α-aminophosphonates synthesis with in-vitro biological evaluation of antifungal, antioxidant and enzymes inhibition potential

(S, S)-1-hydroxy-1-oxo-2-c,5-t-diphenylphospholane or Fiaud's acid is used as a novel and effective chiral organocatalyst for bis α-aminophosphonates synthesis with excellent diastereoselectivity and yields within short reaction time. All synthesized bis α-aminophosphonates revealed a good to excellent antifungal capacity, where the six compounds 4a, 4b, 4e, 4h, 4k and 4l are the best fungicide inhibiting the growth of Fusarium oxysporumandBotrytis cinereaby 65% to 84% with IC₅₀ values <0.02 mg/mL. Similarly, these six products exhibited a strong antioxidant effect, whereas a low inhibition activity was obtained with both AChE and BChE. Furthermore, they displayed a very weak inhibitory activity against tyrosinase except for the compound4l.These findings suggest a possible use of these compounds as synthetic pesticides with less hazardous effects with antioxidant, and anti-tyrosinase properties.

Synthesis of Non-canonical Amino Acids and Peptide Containing Them for Establishment of the Template for Drug Discovery

Non-canonical amino acid derivatives are an attractive scaffold for novel drug candidates. Among the methods used to prepare this motif, the asymmetric Mannich-type reaction of α-imino carboxylic acid derivatives is a preeminent strategy because a wide variety of non-canonical amino acids can be accessed by changing only the nucleophile. Preparing the common substrate is difficult, however, which makes this method problematic. We developed a convenient method for synthesizing common substrates using MnO₂-mediated oxidation of stable precursors. Peptides bearing non-canonical amino acids are another attractive synthetic target. We propose a new approach for synthesizing non-canonical amino acid-containing peptides by directly applying various organic reactions to peptidic substrates. Using hydrophobic anchor-supported peptides, we directly applied ring-closing metathesis and asymmetric Friedel-Crafts reactions to peptidic substrates. We also developed a novel recyclable organocatalyst according to the nature of the hydrophobic anchor tagged compound.

Asymmetric Synthesis of α-Amino Phosphonic Acids using Stable Imino Phosphonate as a Universal Precursor

A practical method for synthesizing chiral α-amino phosphonic acid derivatives was developed. Readily available and stable N-o-nitrophenylsulfenyl (Nps) imino phosphonate was utilized as a substrate for a highly enantioselective Friedel-Crafts-type addition of indole or pyrrole nucleophiles catalyzed by chiral phosphoric acid. The resulting adduct was easily converted into N-9-fluorenylmethyloxycarbonyl (Fmoc) amino phosphonic acid, which is useful for synthesizing peptides containing an amino phosphonic acid.

A Brønsted Acid-Catalyzed Multicomponent Reaction for the Synthesis of Highly Functionalized γ-Lactam Derivatives

Brønsted acids catalyze a multicomponent reaction of benzaldehyde with amines and diethyl acetylenedicarboxylate to afford highly functionalized γ-lactam derivatives. The reaction consists of a Mannich reaction of an enamine to an imine, both generated in situ, promoted by a phosphoric acid catalyst and a subsequent intramolecular cyclization. The hydrolysis of the cyclic enamine substrate can provide enol derivatives and, moreover, a second attack of the amine on the carboxylate can afford amide derivatives. An optimization of the reaction conditions is presented in order to obtain selectively cyclic enamines that can afford the enol species after selective hydrolysis.

Total Synthesis and Antibacterial Activity Evaluation of Griseofamine A and 16- epi-Griseofamine A

The first total synthesis of griseofamine A and its diastereomer, 16- epi-griseofamine A, is described over seven steps with yields of 23% and 7%, respectively. Their antibacterial activities are also disclosed for the first time. Griseofamine A exhibited in vitro activities against a panel of drug-resistant Gram-positive bacteria with minimum inhibitory concentration (MIC) values of 8-16 μg/mL. Notably, 16- epi-griseofamine A was 2-3 times more potent than griseofamine A with MIC values of 2-8 μg/mL.