Solution-phase parallel synthesis of substituted chalcones and their antiparasitary activity against Giardia lamblia

Investigation of the Potential Targets behind the Promising and Highly Selective Antileishmanial Action of Synthetic Flavonoid Derivatives

Leishmaniases are among the neglected tropical diseases that still cause devastating health, social, and economic consequences to more than 350 million people worldwide. Despite efforts to combat these vector-borne diseases, their incidence does not decrease. Meanwhile, current antileishmanial drugs are old and highly toxic, and safer presentations are unaffordable to the most severely affected human populations. In a previous study by our research group, we synthesized 17 flavonoid derivatives that demonstrated impressive inhibition capacity against rCPB2.8, rCPB3, and rH84Y. These cysteine proteases are highly expressed in the amastigote stage, the target form of the parasite. However, although these compounds have been already described in the literature, until now, the amastigote effect of any of these molecules has not been proven. In this work, we aimed to deeply analyze the antileishmanial action of this set of synthetic flavonoid derivatives by correlating their ability to inhibit cysteine proteases with the action against the parasite. Among all the synthesized flavonoid derivatives, 11 of them showed high activity against amastigotes of Leishmania amazonensis, also providing safety to mammalian host cells. Furthermore, the high production of nitric oxide by infected cells treated with the most active cysteine protease B (CPB) inhibitors confirms a potential immunomodulatory response of macrophages. Besides, considering flavonoids as multitarget drugs, we also investigated other potential antileishmanial mechanisms. The most active compounds were selected to investigate another potential biological pathway behind their antileishmanial action using flow cytometry analysis. The results confirmed an oxidative stress after 48 h of treatment. These data represent an important step toward the validation of CPB as an antileishmanial target, as well as aiding in new drug discovery studies based on this protease.

Synthesis, Docking Studies and Evaluation of Chalcones as Anti-Helicobacter pylori and antitumoral Agents

Helicobacter pylori colonizes the gastric epithelium of 50 % of world population and it is the main etiological agent of human chronic gastritis, peptic ulcer, and gastric cancer. In this study, we synthesized and characterized a series of 14 chalcones and evaluated their anti-H. pylori, NO inhibition (in vitro and in silico), and AGS cells cytotoxic effects. Compounds 3b and 3h showed MIC of 8 μg/mL. We observed structure-activity relationships, mainly related to the influence of methoxy substituent at C-2 (3b) and the nitro group at C-4 (3h) in chalcone scaffold. The fourteen chalcones inhibited the NO production in LPS-stimulated macrophages and showed potential for interaction on the active site of the iNOS enzyme. Finally, 3b and 3h showed the highest selectivity to the AGS cell lines. Thus, ours results suggest 3b and 3h as potential candidates for design of new and effective agents against H. pylori and related diseases.

Flavonoid Derivatives as New Potent Inhibitors of Cysteine Proteases: An Important Step toward the Design of New Compounds for the Treatment of Leishmaniasis

Leishmaniasis is a neglected tropical disease, affecting more than 350 million people globally. However, there is currently no vaccine available against human leishmaniasis, and current treatment is hampered by high cost, side-effects, and painful administration routes. It has become a United Nations goal to end leishmaniasis epidemics by 2030, and multitarget drug strategy emerges as a promising alternative. Among the multitarget compounds, flavonoids are a renowned class of natural products, and a structurally diverse library can be prepared through organic synthesis, which can be tested for biological effectiveness. In this study, we synthesised 17 flavonoid analogues using a scalable, easy-to-reproduce, and inexpensive method. All synthesised compounds presented an impressive inhibition capacity against rCPB2.8, rCPB3, and rH84Y enzymes, which are highly expressed in the amastigote stage, the target form of the parasite. Compounds 3c, f12a, and f12b were found to be effective against all isoforms. Furthermore, their intermolecular interactions were also investigated through a molecular modelling study. These compounds were highly potent against the parasite and demonstrated low cytotoxic action against mammalian cells. These results are pioneering, representing an advance in the investigation of the mechanisms behind the antileishmanial action of flavonoid derivatives. Moreover, compounds have been shown to be promising leads for the design of other cysteine protease inhibitors for the treatment of leishmaniasis diseases.

In Melting Points We Trust: A Review on the Misguiding Characterization of Multicomponent Reactions Adducts and Intermediates

We discuss herein the problems associated with using melting points to characterize multicomponent reactions’ (MCRs) products and intermediates. Although surprising, it is not rare to find articles in which these MCRs final adducts (or their intermediates) are characterized solely by comparing melting points with those available from other reports. A brief survey among specialized articles highlights serious and obvious problems with this practice since, for instance, cases are found in which as many as 25 quite contrasting melting points have been attributed to the very same MCR adduct. Indeed, it seems logical to assume that the inherent non-confirmatory nature of melting points could be vastly misleading as a protocol for structural confirmation, but still many publications (also in the Q1 and Q2 quartiles) insist on using it. This procedure contradicts best practices in organic synthesis, and articles fraught with limitations and misleading conclusions have been published in the MCRs field. The drawbacks inherent to this practice are indeed serious and have misguided MCRs advances. We therefore suggest some precautions aimed at avoiding future confusions.

Design and synthesis of novel quinazolinone–chalcone hybrids as potential apoptotic candidates targeting caspase-3 and PARP-1: in vitro, molecular docking, and SAR studies

Novel quinazolinone–chalcone hybrids as potential apoptotic candidates targeting caspase-3 and PARP-1.

Chemoselective and metal-free reduction of α,β-unsaturated ketones by in situ produced benzeneselenol from O-(tert-butyl) Se-phenyl selenocarbonate

The carbon–carbon double bond of arylidene acetones and chalcones can be selectively reduced with benzeneselenol generated in situ by reacting O-(tert-butyl) Se-phenyl selenocarbonate with hydrochloric acid in ethanol. This mild, metal-free and experimentally simple reduction procedure displays considerable functional-group compatibility, products are obtained in good to excellent yields, and the use of toxic Se/CO mixture and NaSeH, or the smelly and air-sensitive benzeneselenol, is avoided.

The carbon–carbon double bond of arylidene acetones and chalcones can be selectively reduced with benzeneselenol generated in situ by reacting O-(tert-butyl) Se-phenyl selenocarbonate with hydrochloric acid in ethanol.

Synthesis, characterization and application of copper oxide chitosan nanocomposite for green regioselective synthesis of [1,2,3]triazoles

Chitosan copper (II) oxide nanocomposite was synthesized, characterized and used to synthesize [1,2,3]triazoles. Nanocomposite was characterized by using FTIR, XRD, FESEM, and EDS techniques, which reflected rough morphology. The powerful catalytic activity of hybrid nanocomposite was utilized to synthesize chalcones (3a-p) in relatively high yields (82%-98%) and multicomponent regio-selective cycloaddition of chalones, aryl halides (4), and sodium azide to afford the expected N-2-aryl[1,2,3]triazoles (5a-h) (80%-95% yield) rather than N-1-aryl[1,2,3]-triazoles (6a-h). The performance of nanomaterial was optimized by several variables. The capability of the nanocomposite was compared with previous work and the nanocomposite was found more efficient, economic and reproducible. The hybrid nanocomposite could be easily isolated form the reaction mixture and recycled four times without any significant loss of its catalytic activity. The reported catalyst is an inexpensive for good yields of the triazoles and may be used at industrial production for the reported compounds.

Synthesis and biological evaluation of a library of hybrid derivatives as inhibitors of influenza virus PA-PB1 interaction

The limited treatment options against influenza virus along with the growing public health concerns regarding the continuous emergence of drug-resistant viruses make essential the development of new anti-flu agents with novel mechanisms of action. One of the most attractive targets is the interaction between two subunits of the RNA-dependent RNA polymerase, PA and PB1. Herein we report the rational design of hybrid compounds starting from a 3-cyano-4,6-diphenylpyridine scaffold recently identified as disruptor of PA-PB1 interactions. Guided by the previously reported SAR data, a library of amino acid derivatives was synthesized. The biological evaluation led to the identification of new PA-PB1 inhibitors, that do not show appreciable toxicity. Molecular modeling shed further lights on the inhibition mechanism of these compounds.

Design, synthesis and molecular docking of novel diarylcyclohexenone and diarylindazole derivatives as tubulin polymerization inhibitors

New target compounds were designed as inhibitors of tubulin polymerization relying on using two types of ring B models (cyclohexenone and indazole) to replace the central ring in colchicine. Different functional groups (R¹) were attached to manipulate their physicochemical properties and/or their biological activity. The designed compounds were assessed for their antitumor activity on HCT-116 and MCF-7 cancer cell lines. Compounds 4b, 5e and 5f exhibited comparable or higher potency than colchicine against colon HCT-116 and MCF-7 tumor cells. The mechanism of the antitumor activity was investigated through evaluating the tubulin inhibition potential of the active compounds. Compounds 4b, 5e and 5f showed percentage inhibition of tubulin in both cell line homogenates ranging from 79.72% to 89.31%. Cell cycle analysis of compounds 4b, 5e and 5f revealed cell cycle arrest at G₂/M phase. Molecular docking revealed the binding mode of these new compounds into the colchicine binding site of tubulin.

Biotechnological methods for chalcone reduction using whole cells of Lactobacillus, Rhodococcus and Rhodotorula strains as a way to produce new derivatives

Microbial strains of the genera Dietzia, Micrococcus, Pseudomonas, Rhodococcus, Gordonia, Streptomyces, Pseudomonas, Bacillus, Penicillium, Rhodotorula and Lactobacillus were screened for the ability to convert chalcones. Synthesis of chalcones was performed by the Claisen-Schmidt reaction. There were three groups of chalcones obtained as the products, which included the derivatives containing 4-substituted chalcone, 2'-hydroxychalcone and 4'-methoxychalcone. The B ring of the chalcones was substituted in the para position with different groups, such as halide, hydroxyl, nitro, methyl, ethyl and ethoxy one. The structure-activity relationship of the tested chalcones in biotransformation processes was studied. It has been proven that Gram-positive bacterial strains Rhodococcus and Lactobacillus catalyzed reduction of C=C bond in the chalcones to give respective dihydrochalcones. The strain Rhodotorula rubra AM 82 transformed chalcones into dihydrochalcones and respective secondary alcohols. These results suggest that the probiotic strain of Lactobacillus can be used for biotransformations of chalcones, which has not been described before. The structure of new metabolites 14a and 15b were established as 4-ethoxy-4'-methoxydihydrochalcone and 3-(4-bromophenyl)-1-(4'-O-methylphenyl)-2-propan-1-ol, respectively, which was confirmed by (1)H NMR and (13)C NMR analysis.

Antimicrobial Activity of Xanthohumol and Its Selected Structural Analogues

The objective of this study was to evaluate the antimicrobial activity of structural analogues of xanthohumol 1, a flavonoid compound found in hops (Humulus lupulus). The agar-diffusion method using filter paper disks was applied. Biological tests performed for selected strains of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, fungi (Alternaria sp.), and yeasts (Rhodotorula rubra, Candida albicans) revealed that compounds with at least one hydroxyl group—all of them have it at the C-4 position—demonstrated good activity. Our research showed that the strain S. aureus was more sensitive to chalcones than to the isomers in which the heterocyclic ring C is closed (flavanones). The strain R. rubra was moderately sensitive to only one compound: 4-hydroxy-4’-methoxychalcone 8. Loss of the hydroxyl group in the B-ring of 4’-methoxychalcones or its replacement by a halogen atom (−Cl, −Br), nitro group (−NO₂), ethoxy group (−OCH₂CH₃), or aliphatic substituent (−CH₃, −CH₂CH₃) resulted in the loss of antimicrobial activity towards both R. rubra yeast and S. aureus bacteria. Xanthohumol 1, naringenin 5, and chalconaringenin 7 inhibited growth of S. aureus, whereas 4-hydroxy-4′-methoxychalcone 8 was active towards two strains: S. aureus and R. rubra.

Parasitic diarrheal disease: drug development and targets

Diarrhea is the manifestation of gastrointestinal infection and is one of the major causes of mortality and morbidity specifically among the children of less than 5 years age worldwide. Moreover, in recent years there has been a rise in the number of reports of intestinal infections continuously in the industrialized world. These are largely related to waterborne and food borne outbreaks. These occur by the pathogenesis of both prokaryotic and eukaryotic organisms like bacteria and parasites. The parasitic intestinal infection has remained mostly unexplored and under assessed in terms of therapeutic development. The lack of new drugs and the risk of resistance have led us to carry out this review on drug development for parasitic diarrheal diseases. The major focus has been depicted on commercially available drugs, currently synthesized active heterocyclic compounds and unique drug targets, that are vital for the existence and growth of the parasites and can be further exploited for the search of therapeutically active anti-parasitic agents.

Activities of wogonin analogs and other flavones against Flavobacterium columnare

In our on-going pursuit to discover natural products and natural product-based compounds to control the bacterial species Flavobacterium columnare, which causes columnaris disease in channel catfish (Ictalurus punctatus), we synthesized flavone and chalcone analogs, and evaluated these compounds, along with flavonoids from natural sources, for their antibacterial activities against two isolates of F. columnare (ALM-00-173 and BioMed) using a rapid bioassay. The flavonoids chrysin (1a), 5,7-dihydroxy-4'-methoxyflavone (11), isorhamnetin (26), luteolin (27), and biochanin A (29), and chalcone derivative 8b showed strong antibacterial activities against F. columnare ALM-00-173 based on minimum inhibition concentration (MIC) results. Flavonoids 1a, 8, 11, 13 (5,4'-dihydroxy-7-methoxyflavone), 26, and 29 exhibited strong antibacterial activities against F. columnare BioMed based upon MIC results. The 24-h 50% inhibition concentration (IC50 ) results revealed that 27 and 29 were the most active compounds against F. columnare ALM-00-173 (IC50 of 7.5 and 8.5 mg/l, resp.), while 26 and 29 were the most toxic compound against F. columnare BioMed (IC50 of 9.2 and 3.5 mg/l, resp.). These IC50 results were lower than those obtained for wogonin against F. columnare ALM-00-173 and F. columnare BioMed (28.4 and 5.4 mg/l, resp.). However, based on MIC results, none of the compounds evaluated in this study were as active as wogonin (MIC 0.3 mg/l for each F. columnare isolate). Further modification of the wogonin structure to enhance antibacterial is of interest.

Structural and spectral investigations of the recently synthesized chalcone (E)-3-mesityl-1-(naphthalen-2-yl) prop-2-en-1-one, a potential chemotherapeutic agent

BACKGROUND

Chalcones (1,3-diaryl-2-propen-1-ones, represent an important subgroup of the polyphenolic family, which have shown a wide spectrum of medical and industrial application. Due to their redundancy in plants and ease of preparation, this category of molecules has inspired considerable attention for potential therapeutic uses. They are also effective in vivo as anti-tumor promoting, cell proliferating inhibitors and chemo preventing agents.

RESULTS

Synthesis and molecular structure investigation of (E)-3-mesityl-1-(naphthalen-2-yl) prop-2-en-1-one (3) is reported. The structure of the title compound 3 is confirmed by X-ray crystallography. The optimized molecular structure of the studied compound is calculated using DFT B3LYP/6-311G (d,p) method. The calculated geometric parameters are in good agreement with the experimental data obtained from our reported X-ay structure. The calculated IR fundamental bands were assigned and compared with the experimental data. The electronic spectra of the studied compound have been calculated using the time dependant density functional theory (TD-DFT). The longest wavelength band is due to H → L (79 %) electronic transition which belongs to π-π* excitation. The (1)H- and (13)C-NMR chemical shifts were calculated using gauge independent atomic orbitals (GIAO) method, which showed good correlations with the experimental data (R(2) = 0.9911-0.9965). The natural bond orbital (NBO) calculations were performed to predict the natural atomic charges at different atomic sites. The molecular electrostatic potential (MEP) was used to visualize the charge distribution on the molecule. Molecular docking results suggest that the compound might exhibit inhibitory activity against GPb and may act as potential anti-diabetic compound.

CONCLUSIONS

(E)-3-Mesityl-1-(naphthalen-2-yl) prop-2-en-1-one single crystal is grown and characterized by single crystal X-ray diffraction, FT-IR, UV-vis, DFT and optimized geometrical parameters are close to the experimental bond lengths and angles. Molecular stability was successfully analyzed using NBO and electron delocalization is confirmed by MEP. Prediction of Activity Spectra Analysis of the title compound, predicts anti-diabetic activity with probability to have an active value of 0.348. Graphical Abstract(E)-3-Mesityl-1-(naphthalen-2-yl) prop-2-en-1-one: a crystal structure and computational studies.

Antimycobacterial and anti-inflammatory activities of substituted chalcones focusing on an anti-tuberculosis dual treatment approach

Tuberculosis (TB) remains a serious public health problem aggravated by the emergence of M. tuberculosis (Mtb) strains resistant to multiple drugs (MDR). Delay in TB treatment, common in the MDR-TB cases, can lead to deleterious life-threatening inflammation in susceptible hyper-reactive individuals, encouraging the discovery of new anti-Mtb drugs and the use of adjunctive therapy based on anti-inflammatory interventions. In this study, a series of forty synthetic chalcones was evaluated in vitro for their anti-inflammatory and antimycobacterial properties and in silico for pharmacokinetic parameters. Seven compounds strongly inhibited NO and PGE₂ production by LPS-stimulated macrophages through the specific inhibition of iNOS and COX-2 expression, respectively, with compounds 4 and 5 standing out in this respect. Four of the seven most active compounds were able to inhibit production of TNF-α and IL-1β. Chalcones that were not toxic to cultured macrophages were tested for antimycobacterial activity. Eight compounds were able to inhibit growth of the M. bovis BCG and Mtb H37Rv strains in bacterial cultures and in infected macrophages. Four of them, including compounds 4 and 5, were active against a hypervirulent clinical Mtb isolate as well. In silico analysis of ADMET properties showed that the evaluated chalcones displayed satisfactory pharmacokinetic parameters. In conclusion, the obtained data demonstrate that at least two of the studied chalcones, compounds 4 and 5, are promising antimycobacterial and anti-inflammatory agents, especially focusing on an anti-tuberculosis dual treatment approach.

N-bromosuccinimide/cerium Ammonium Nitrate: An Efficient Reagent for Stereo-controlled Deamination of Ketoaziridines

An efficient and novel method for the deamination of trans-1-alkyl (H or benzoyl)-2-aroyl aziridines in a completely stereo-controlled reaction in the presence of N-bromosuccinimide/cerium (IV) ammonium nitrate is described. In comparison with the previous reported work, this reaction reveals a substituent-reactivity relationship and important role for the substituent on C1 and C2 in determining whether deamination or oxidation reaction takes place.

Synthesis and cytotoxic evaluation of alkoxylated chalcones

A series of chalcones a1–20 bearing a 4-OMe groups on the A-ring were initially synthesized and their anticancer activities towards HepG2 cells evaluated. Subsequently, a series of chalcones b1–42 bearing methoxy groups at the 2' and 6'-positions of the B-ring were synthesized and their anticancer activities towards five human cancer cell lines (HepG2, HeLa, MCF-7, A549 and SW1990) and two non-tumoral human cell lines evaluated. The results showed that six compounds (b6, b8, b11, b16, b18, b22, b23 and b29) displayed promising activities, with compounds b22 and b29 in particular showing higher levels of activity than etoposide against all five cancer cell lines. Compound b29 showed a promising SI value compared with both HMLE and L02 (2.1–6.5 fold in HMLE and > 33 > 103.1 fold in L02, respectively).

O(2)-dependent efficacy of novel piperidine- and piperazine-based chalcones against the human parasite Giardia intestinalis

Giardia intestinalis is the most frequent protozoan agent of intestinal diseases worldwide. Though commonly regarded as an anaerobic pathogen, it preferentially colonizes the fairly oxygen-rich mucosa of the proximal small intestine. Therefore, when testing new potential antigiardial drugs, O2 should be taken into account, since it also reduces the efficacy of metronidazole, the gold standard drug against giardiasis. In this study, 46 novel chalcones were synthesized by microwave-assisted Claisen-Schmidt condensation, purified, characterized by high-resolution mass spectrometry, (1)H and (13)C nuclear magnetic resonance, and infrared spectroscopy, and tested for their toxicity against G. intestinalis under standard anaerobic conditions. As a novel approach, compounds showing antigiardial activity under anaerobiosis were also assayed under microaerobic conditions, and their selectivity against parasitic cells was assessed in a counterscreen on human epithelial colorectal adenocarcinoma cells. Among the tested compounds, three [30(a), 31(e), and 33] were more effective in the presence of O2 than under anaerobic conditions and killed the parasite 2 to 4 times more efficiently than metronidazole under anaerobiosis. Two of them [30(a) and 31(e)] proved to be selective against parasitic cells, thus representing potential candidates for the design of novel antigiardial drugs. This study highlights the importance of testing new potential antigiardial agents not only under anaerobic conditions but also at low, more physiological O2 concentrations.

Stereo-controlled Deamination of Ketoaziridines Using Ph3P/I2

PPh3/I2 is an efficient reagent for the stereo-controlled deamination of non-activated aziridines, N–H and N-alkyl aziridines, using. The method works gives the corresponding trans-alkenes from both cis and trans-aziridines. A plausible mechanism is proposed for the ring opening and deamination of keto-aziridines in the presence of Ph3P/I2.

New eco-friendly animal bone meal catalysts for preparation of chalcones and aza-Michael adducts

Abstract

Two efficient reactions were successfully carried out using Animal Bone Meal (ABM) and potassium fluoride or sodium nitrate doped ABMs as new heterogeneous catalysts under very mild conditions. After preparation and characterization of the catalysts, we first report their use in a simple and convenient synthesis of various chalcones by Claisen–Schmidt condensation and then in an aza-Michael addition involving several synthesized chalcones with aromatic amines. All the reactions were carried out at room temperature in methanol; the chalcone synthesis was also achieved in water environment under microwave irradiation. Doping ABM enhances the rate and yield at each reaction. Catalytic activities are discussed and the ability to re-use the ABM is demonstrated.

Results

For Claisen–Schmidt the use of ABM alone, yields never exceeded 17%. In each entry, KF/ABM and NaNO₃/ABM (79-97%) gave higher yields than using ABM alone under thermic condition. Also the reaction proceeded under microwave irradiation in good yields (72-94% for KF/ABM and 81-97% for NaNO₃/ABM) and high purity. For aza-Michael addition the use of ABM doped with KF or NaNO₃ increased the catalytic activity remarkably. The very high yields could be noted (84-95% for KF/ABM and 81-94% for NaNO₃/ABM).

Conclusion

The present method is an efficient and selective procedure for the synthesis of chalcones an aza-Michael adducts. The ABM and doped ABMs are a new, inexpensive and attractive solid supports which can contribute to the development of catalytic processes and reduced environmental problems.

Synthesis, biological evaluation, and molecular docking studies of resveratrol derivatives possessing chalcone moiety as potential antitubulin agents

Twenty-three resveratrol derivatives possessing chalcone moiety were synthesized and characterized, and their biological activities were also evaluated as potential antiproliferation and tubulin polymerization inhibitors. Compound C19 exhibited the most potent activity in vitro, which inhibited the growth of HepG2, B16-F10, and A549 cell lines with IC(50) values of 0.2, 0.1, and 1.4 μg/mL, respectively. Compound C19 also exhibited significant tubulin polymerization inhibitory activity (IC(50)=2.6 μg/mL). Docking simulation was performed to position compound C19 into the tubulin-colchicine binding site to determine the probable binding mode.

Microwave assisted solvent free synthesis of 1,3-diphenylpropenones

BACKGROUND

1,3-Diphenylpropenones (chalcones) are well known for their diverse array of bioactivities. Hydroxyl group substituted chalcones are the main precursor in the synthesis of flavonoids. Till date various methods have been developed for the synthesis of these very interesting molecules. Continuing our efforts for the development of simple, eco-friendly and cost-effective methodologies, we report here a solvent free condensation of aryl ketones and aldehydes using iodine impregnated alumina under microwave activation. This new protocol has been applied to a variety of substituted aryl carbonyls with excellent yield of substituted 1,3-diphenylpropenones.

RESULTS

Differently substituted chalcones were synthesized using iodine impregnated neutral alumina as catalyst in 79-95% yield in less than 2 minutes time under microwave activation without using any solvent. The reaction was studied under different catalytic conditions and it was found that molecular iodine supported over neutral alumina gives the best yield. The otherwise difficult single step condensation of hydroxy substituted aryl carbonyls is an attractive feature of this protocol to obtain polyhydroxychalcones in excellent yields. In order to find out the general applicability of this new endeavor it was successfully applied for the synthesis of 15 different chalcones including highly bioactive prenylated hydroxychalcone xanthohumol.

CONCLUSION

A new, simple and solvent free method was developed for the synthesis of substituted chalcones in environmentally benign way. The mild reaction conditions, easy work-up, clean reaction profiles render this approach as an interesting alternative to the existing methods.