The Effects of Trifluoromethylated Derivatives on Prostaglandin E2 and Thromboxane A2 Production in Human Leukemic U937 Macrophages.

BACKGROUND: A convenient approach to modulation of the inflammation has an influence on the production of inflammatory mediators - icosanoids, generated in arachidonic acid (AA) metabolism. The common therapeutic activity of non-steroidal anti-inflammatory drugs (NSAID), such as aspirin, includes inhibition of two crucial enzymes of AA metabolism - cyclooxygenase- 1 and -2 (COX-1/2), with certain risk for gastrointestinal and renal intolerance. Ever since the enrolment of COX-2, particularly overabundance of its main products prostaglandin E2 (PGE2) and thromboxane A2 (TXA2) in numerous pathological processes was recognized, it became a significant therapeutic target. OBJECTIVE: The aim of this study was to examine the effects of synthesized organo-fluorine compounds on PGE2 and TXA2 production in the inflammation process. METHODS: Trifluoromethyl compounds were synthesized from N-benzyl trifluoromethyl aldimine, commercially available 2-methyl or 2-phenyl α-bromo esters (ß-lactams trans-1 and trans-2 and trifluoromethyl ß-amino ester, respectively) and methyl 2-isocyanoacetate (2-imidazoline trans-4). The reactions proceeded with high geometric selectivity, furnishing the desired products in good yields. The influence of newly synthesized compounds on PGE2 and TXA2 production in human leukemic U937 macrophages on both enzyme activity and gene expression levels was observed. RESULTS: Among the tested trifluoromethyl compounds, methyl trans-1-benzyl-5-(trifluoromethyl)- 4,5-dihydro-1H-imidazole-4-carboxylate (trans-4) can be distinguished as the most powerful antiinflammatory agent, probably due to its trifluoromethyl-imidazoline moiety. CONCLUSION: Some further structural modifications in tested compounds and particularly in the synthesis of different trifluoromethyl imidazolines could contribute to the development of new COX-2 inhibitors and potent anti-inflammatory agents.

Aza-Henry Reactions on C-Alkyl Substituted Aldimines.

The reactivity of C-CH3 substituted N-protected aldimines in aza-Henry addition reactions was compared with that of the analogous trifluoromethylated compounds. C-Alkyl aldimines easily reacted with nitro alkanes under solvent-free conditions and in the absence of catalyst, despite being worse electrophiles than C-CF3 aldimines, they gave the aza-Henry addition only when ZrCl4 was added. The presence of a bulky group on the imine carbon deeply influenced the reactivity.

Ethyl Nitroacetate in Aza-Henry Addition on Trifluoromethyl Aldimines: A Solvent-Free Procedure To Obtain Chiral Trifluoromethyl α,ß-Diamino Esters.

A self-catalyzed aza-Henry addition of ethyl nitroacetate on N-alkyl trifluoromethyl aldimines was reported to synthesize ß-amino α-nitro trifluoromethyl esters, precursors of α,ß-diamino acid derivatives. In the presence of a resident chiral center on the imine nitrogen, the use of a suitable Lewis acid leads to a good stereofacial control, always resulting from a nucleophilic unlike attack. By starting from optically pure N-protected trifluoromethyl aldimines or directly from N-α-amino ester trifluoromethyl aldimines, small ψ[CH(CF3)NH]-peptidomimetic backbones can be achieved in which a new primary amine function represents a possible center for synthetic extension. Finally, a very interesting, and never observed before, palladium-catalyzed syn ß-elimination occurred, leading to the selective nitro group reduction reaction on the syn-α-amino ester functionalized aza-Henry adducts and obtaining more stable optically pure trifluoromethyl conjugated imines.

New Synthesis of Trifluoromethyl Aldimines Containing L-α-Amino Ester Moieties and Their Use in Mannich-Type Reactions.

L-α-amino esters were considered valuable chiral starting materials in the condensation reaction with trifluoroacetaldehyde (fluoral) ethyl hemiacetal to obtain new functionalized trifluoromethyl aldimines. Starting from these latter compounds, isovaleraldehyde was used in proline-catalyzed Mannich-type addition reactions to give trifluoromethyl syn- or anti-γ-amino alcohols bearing the L-α-amino ester function, simply by changing the reaction temperature.

Stereoselective ZrCl4-Catalyzed Mannich-type Reaction of ß-Keto Esters with Chiral Trifluoromethyl Aldimines.

A method for the synthesis of fluorinated ß'-amino ß-dicarbonyl compounds using a Zr-catalyzed Mannich-type reaction has been developed, starting from N-protected trifluoromethyl aldimines and cyclic or acyclic ß-keto esters bearing different ester residues. The in situ generated metallic complex reacted with optically pure trifluoromethyl aldimine derived from (R)-α-methylbenzylamine, giving a highly diastereoselective asymmetric Mannich-type addition with formation of a chiral quaternary center. The absolute configuration at the new chiral centers was assigned through two-dimensional nuclear Overhauser effect spectroscopic analysis coupled with computational studies.

Trifluoromethyl-modified dipeptides by ZrCl4-promoted aza-Henry reactions.

Chiral (R)-1-phenylethylamine was successfully employed in a tandem aza-Henry addition-reduction reaction to give chiral ß-nitro α-trifluoromethyl amines. A subsequent coupling reaction with N-Boc-protected amino acids leads to obtain optically pure CF3-modified dipeptides carrying two different N-protecting groups. These peptidomimetic units are characterized by the presence of the [CH(CF3)NH] group as mimetic of the natural [CONH] peptidic bond and can be used for the synthesis of more complex CF3-modified peptides after selective deprotection of one of the two amine functions. 2D NMR spectral analyses were employed to determine the absolute configurations of all newly synthesized chiral compounds.

Selective amination reactions of α-nitro aryl and heteroaryl enoates.

Highly functionalized tetrasubstituted alkenes were obtained by an unexpected amination reaction promoted by ethyl nosyloxycarbamate on various α-nitro aryl and heteroaryl enoates. A nitrene is likely the aminating species responsible for the observed insertion reaction leading to (E)-ß-amino α-nitro enoates as the major products, regardless of the substrate configuration. The compounds, bearing two nitrogenous functional groups in different oxidation states, can be regarded as interesting synthons. In contrast, aziridination was observed for α-nitro alkyl enoates or ß-nitro allylic alcohols.

Synthesis of gem-diamino acid derivatives by a Hofmann rearrangement.

Starting from commercially available N-protected L-α-amino acids, N,N'-protected gem-diaminic units were obtained by a two-step methodology. A Hofmann reaction performed using a primary alcohol as the solvent to trap the isocyanate intermediate represents the key step of the new synthetic procedure. Then, the methodology was applied to α-carbamoyl α'-carboxyl aziridines, also functionalized with L-α-amino esters and stable gem-diaminic units characterized by an aziridine ring and by a retro-peptide modification were obtained. The use of the latter units in the retro-peptide chemistry allows to obtain modified peptides containing an aziridine ring able to behave as an electrophilic site and as a biomimetic structural analog of proline.

Fluorinated ß-nitro amines by a selective ZrCl4-catalyzed aza-Henry reaction of (E)-trifluoromethyl aldimines.

ZrCl(4) was found to be an ideal catalyst to promote aza-Henry reactions between trifluoromethyl aldimines and some nitro alkanes giving new fluorinated ß-nitro amines. The reaction is strongly influenced by the CF(3) group, the yield by the alkyl chain of the nitro compound, while the stereochemical outcome seems to be unaffected, the anti isomer being always the major product.

Stereoselective synthesis and ROESY 1H NMR study of bidiaziridines.

The bisaziridination reaction of symmetric (E-s-trans-E)-α-diimines using ethyl nosyloxycarbamate as aminating agent yields symmetrically functionalized bidiaziridines, under mild conditions. The reactions take place with very high stereoselectivity giving only bidiaziridines with total retention of the starting α-diimine configuration, as determined by NMR measurements. Moreover, only a single pure diastereomer, derived from attack of the aza-anion on the opposite faces of conjugate system was obtained, starting from chiral substrates. ROESY analyses clearly show that all nitrogens have a stable pyramidal conformation, and the absolute configurations of new chiral centers were assigned.

Domino reactions for the synthesis of various α-substituted nitro alkenes.

Efficient one-pot methods for the synthesis of variously functionalised conjugated nitro alkenes have been reported. Despite the utility in different fields of these compounds, only a few multi-step syntheses have been reported in the literature, giving the target compounds in low overall yields. α-Nitro acrylates or cinnamates, α-nitro α,ß-unsaturated ketones and, most importantly, aromatic and heteroaromatic (E)- 2-nitro allylic alcohols, compounds characterised by a well-known anticancer activity, were obtained in high yields and high diastereomeric purity by a domino condensation-dehydration process.

Short malonyl dehydro peptides as potential scaffolds for peptidomimetics by an efficient Knoevenagel reaction.

Non-symmetric disubstituted malonamides rAA-mGly-AA', obtained from Meldrum's acid, were considered as methylene active compounds and a Knoevenagel condensation methodology was developed involving piperidine and activated 4 A molecular sieves as catalysts. The reaction is efficient, broad in scope, and easy to perform and allows access to E/Z mixtures of short malonyl dehydro peptides (MDHPs) rAA-m Delta(2)AA''-AA', partially modified retro peptides characterized by an interesting combination of retro and dehydro modifications in the same structure.

An unexpected highly stereoselective bisaziridination of (E,E)-1,4-dialkyl-2,3-dinitrobutadienes followed by a nitro group driven ring enlargement.

(+/-)-2,2'-Dinitro-2,2'-biaziridines were obtained by a direct aza-MIRC (Michael initiated ring closure) reaction on (E,E)-1,4-dialkyl-2,3-dinitro-l,3-butadienes under very mild conditions. The reactions occur with high stereoselectivity as shown by the enantioselective HPLC analyses performed on the crude mixtures. Ring enlargement to 3,3'-bi(1,2,4-oxadiazole) derivatives was easily obtained by a simple treatment with sodium iodide in DMSO, with an unforeseen regioselective aziridine C-C cleavage.

Facile and highly stereoselective one-pot synthesis of either (E)- or (Z)-nitro alkenes.

Aliphatic aldehydes were reacted with nitro alkanes in the presence of catalytic amounts of piperidine over 4 A molecular sieves. Simply by changing reaction conditions (solvent and temperature) it is possible to control the stereochemical outcome of the reactions, obtaining pure (E)- and (Z)-nitro alkenes in high to excellent yields. The role of molecular sieves on the stereochemical control seems crucial in addition to that of piperidine, especially for the synthesis of the Z isomer.

Solution-phase synthesis of 2-cyano and 2-amido aziridinyl peptides.

Starting from a library of 2-l-α-amino acyl (E)-acrylonitriles, different short 2-cyano and 2-amido aziridinyl peptides, potential protease inhibitors, were obtained under parallel solution-phase conditions. The transformations include careful selection of conditions for aziridine deprotection and cyano group partial hydrolysis.

Parallel solution-phase synthesis of acrylonitrile scaffolds carrying L-alpha-amino acidic or D-glycosyl residues.

A practical and straightforward protocol for the preparation of a solution-phase library of acrylonitrile scaffolds is reported. Target compounds were obtained in high yield, stereoselectivity, and purity by two simple and practical steps from cyanoacetic acid. Moreover, our study proposes a synthetic approach starting from the constructed library to obtain three-membered heterocycles.

Amination of CF3-enones with nosyloxycarbamates.

CF3-enones showed a different reactivity in amination reactions with nosyloxycarbamates. 4-Oxazolines or vinyl carbamates were obtained as unique products depending on the nature of double-bond substituents and on the choice of carbamates and bases. Starting from trans-trifluoroacetyl olefins carrying a heterocyclic residue or the p-methoxyphenyl group on the double bond, a rare loss of CF3CO was observed when the aminations were performed under heterogeneous conditions using CaO as the base.

Unexpected and expeditious entry into trifluoromethyl aziridines from substituted beta-dicarbonyl compounds.

[Reaction: see text]. One-pot aziridinations were obtained starting from substituted 2,2,2-trifluoroethyl beta-dicarbonyl compounds with nosyloxycarbamates in the presence of an excess of CaO as base. The unexpected ring closure reaction takes place at room temperature, leading to the N-protected alpha-trifluoromethyl aziridines with good yields. The reaction pathway seems to be influenced by the choice of the base.

Aziridines versus vinyl carbamates from the direct amination of electron-withdrawing group-substituted trifluoromethyl enoates.

Aza-MIRC (Michael-initiated ring closure) and C-H insertion products were obtained in the reactions of trifluoromethylated olefins with different nosyloxycarbamates by changing base and solvent. Aza-Michael addition products were not isolated. The presence and the position of the trifluoromethyl group allow control of the outcome of the reactions.

Aza-Michael addition of nosyloxycarbamates to 2-(trifluoromethyl)acrylates.

[reaction: see text] The amination of 2-(trifluoromethyl)acrylates, performed by nosyloxycarbamates, gives two different aminated products, the derivatives of alpha-trifluoromethyl beta-amino esters or the aziridines, in high yields by changing the reaction conditions. The aza-Michael addition product was isolated for the first time in this kind of reaction. This finding confirms the aza-MIRC mechanism we previously proposed. Asymmetric induction was also pursued.