Enantioselective Henry Addition of Methyl 4-Nitrobutyrate to Aldehydes. Chiral Building Blocks for 2-Pyrrolidinones and Other Derivatives

Chemoenzymatic synthesis of 2,6-disubstituted tetrahydropyrans with high σ1 receptor affinity, antitumor and analgesic activity

1,3-Dioxanes 1 and cyclohexanes 2 bearing a phenyl ring and an aminoethyl moiety in 1,3-relationship to each other represent highly potent σ1 receptor antagonists. In order to increase the chemical stability of the acetalic 1,3-dioxanes 1 and the polarity of the cyclohexanes 2, tetrahydropyran derivatives 3 equipped with the same substituents were designed, synthesized and pharmacologically evaluated. The key step of the synthesis was a lipase-catalyzed enantioselective acetylation of the alcohol (R)-5 leading finally to enantiomerically pure test compounds 3a-g. With respect to σ1 receptor affinity and selectivity over a broad range of related (σ2, PCP binding site) and further targets, the enantiomeric benzylamines 3a and cyclohexylmethylamines 3b represent the most promising drug candidates of this series. However, the eudismic ratio for σ1 binding is only in the range of 2.5-3.3. Classical molecular dynamics (MD) simulations confirmed the same binding pose for both the tetrahydropyran 3 and cyclohexane derivatives 2 at the σ1 receptor, according to which: i) the protonated amino moiety of (2S,6R)-3a engages the same key polar interactions with Glu172 (ionic) and Phe107 (π-cation), ii) the lipophilic parts of (2S,6R)-3a are hosted in three hydrophobic regions of the σ1 receptor, and iii) the O-atom of the tetrahydropyran derivatives 3 does not show a relevant interaction with the σ1 receptor. Further in silico evidences obtained by the application of free energy perturbation and steered MD techniques fully supported the experimentally observed difference in receptor/ligand affinities. Tetrahydropyrans 3 require a lower dissociative force peak than cyclohexane analogs 2. Enantiomeric benzylamines 3a and cyclohexylmethylamines 3b were able to inhibit the growth of the androgen negative human prostate cancer cell line DU145. The cyclohexylmethylamine (2S,6R)-3b showed the highest σ1 affinity (Ki(σ1) = 0.95 nM) and the highest analgesic activity in vivo (67%).

Solvent-Dependent Enantiodivergence in anti-Selective Catalytic Asymmetric Nitroaldol Reactions

anti-Selective catalytic asymmetric nitroaldol reactions of α-keto esters promoted by a heterogeneous Nd/Na heterobimetallic catalyst exhibited a significant, unexpected disparity in enantioselection that was solvent-dependent. This phenomenon exclusively occurred when the stereogenic center of a diamide ligand had the smallest substituent (Me group, derived from l-Ala), which behaved uniquely in comparison with other structurally similar ligands to provide antipodal products under otherwise identical conditions.

TBHP promoted demethylation of α-amino carbonyl compounds: a concise approach to substituted γ-lactams

A novel tert-butyl hydroperoxide (TBHP) promoted CH₂-extrusion reaction of α-amino carbonyl compounds has been developed, which is driven by a demethylenation process to give various ring contraction products γ-lactams under radical conditions.

Stereoselective Catalytic Synthesis of Active Pharmaceutical Ingredients in Homemade 3D-Printed Mesoreactors

3D-printed flow reactors were designed, fabricated from different materials (PLA, HIPS, nylon), and used for a catalytic stereoselective Henry reaction. The use of readily prepared and tunable 3D-printed reactors enabled the rapid screening of devices with different sizes, shapes, and channel dimensions, aimed at the identification of the best-performing reactor setup. The optimized process afforded the products in high yields, moderate diastereoselectivity, and up to 90 % ee. The method was applied to the continuous-flow synthesis of biologically active chiral 1,2-amino alcohols (norephedrine, metaraminol, and methoxamine) through a two-step sequence combining the nitroaldol reaction with a hydrogenation. To highlight potential industrial applications of this method, a multistep continuous synthesis of norephedrine has been realized. The product was isolated without any intermediate purifications or solvent switches.

A new series of bipyridine based chiral organocatalysts for enantioselective Henry reaction

We report the design and synthesis of a new series of binaphthol based chiral organocatalysts which can act as metal-free organocatalysts in the enantioselective Henry reaction with very good yield and ee.

Self-assembled asymmetric catalyst engaged in a continuous-flow platform: an anti-selective catalytic asymmetric nitroaldol reaction

An anti-selective catalytic asymmetric nitroaldol reaction was manifested in a continuous-flow platform. The requisite Nd/Na heterogeneous catalyst was readily prepared by self-assembly of an amide-based chiral ligand, NdO1/5(O(i)Pr)13/5, NaHMDS, and a multiwalled carbon nanotube without covalent linkage. A stainless-steel column filled with the Nd/Na catalyst was incorporated in a flow system to promote the nitroaldol reaction with high stereoselectivity. The flow system with the heterogeneous catalyst obviated the quenching operation, and the cooling system was minimized.

Pyridylalkylamine ligands and their palladium complexes: structure and reactivity revisited by NMR

Pyridylmethylamines or pma are versatile platforms for different catalytic transformations. Five pma-ligands and their respective Pd complexes have been studied by liquid state NMR. By comparing (1)H, (13)C and (15)N chemical shifts for each pma/pma-Pd couple, a general trend for the metallacycle atoms concerns variations of the electronic distribution at the pendant arm, especially at the nitrogen atom of the ligand. Moreover, the increase of the chemical shift of the pendant arm nitrogen atom from primary to tertiary amine is also related to the increase of crowding within the complex. This statement is in good agreement with X-ray data collected for several complexes. Catalytic results for the Suzuki-Miyaura reaction involving the pma-Pd complexes showed within this series that a sterically crowded and electron-rich ligand in the metallacycle was essential to reach the coupling product with a good selectivity. In this context, NMR study of chemical shifts of all active nuclei especially in the metallacycle could give a trend of reactivity in the studied family of pma-Pd complexes.

Recent progress towards transition metal-catalyzed synthesis of γ-lactams

The scope of transition metal-catalyzed synthesis of functionalized γ-lactams has broadened tremendously in the last decade (see the picture). These metal-catalyzed processes are reviewed by highlighting their specificity and applicability, and the mechanistic rationale is presented where possible.

(2S,5R)-2-Methylaminomethyl-1-methyl-5-phenylpyrrolidine, a chiral diamine ligand for copper(ii)-catalysed Henry reactions with superb enantiocontrol

Copper(ii)-complexes of a cis-2-aminomethyl-5-phenylpyrrolidine catalyse enantioselective Henry reactions with extraordinarily high stereocontrol.

Enantioselective bromolactonization of cis-1,2-disubstituted olefinic acids using an amino-thiocarbamate catalyst

A facile, highly regio- and enantioselective amino-thiocarbamate-catalyzed bromolactonization of cis-1,2-disubstituted olefinic acids has been developed. The use of the enantio-enriched lactones in the synthesis of chiral synthetic intermediates is also demonstrated.