Synthesis, radio-synthesis and in vitro evaluation of terminally fluorinated derivatives of HU-210 and HU-211 as novel candidate PET tracers.

We report the synthesis of terminally fluorinated HU-210 and HU-211 analogues (HU-210F and HU-211F, respectively) and their biological evaluation as ligands of cannabinoid receptors (CB1 and CB2) and N-methyl d-aspartate receptor (NMDAR). [18F]-labelled HU-210F was radiosynthesised from the bromo-substituted precursor. In vitro assays showed that both HU-210F and HU-211F retain the potent pharmacological profile of HU-210 and HU-211, suggesting that [18F]-radiolabelled HU-210F and HU-211F could have potential as PET tracers for in vivo imaging.

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.

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.