An efficient chemoenzymatic approach to enantiomerically pure 4-[2-(difluoromethoxy)phenyl] substituted 1,4-dihydropyridine-3,5-dicarboxylates

Recent Approaches to Chiral 1,4-Dihydropyridines and their Fused Analogues

The purpose of this review is to highlight recent developments in the synthesis of chiral 1,4-dihydropyridines and their fused analogues. 1,4-Dihydropyridines are among the most active calcium antagonists that are used for the treatment of hypertension. Enantiomers of unsymmetrical 1,4-dihydropyridines often show different biological activities and may have even an opposite action profile. Hantzsch synthesis usually produces racemic mixtures of unsymmetrical 1,4-dihydropyridines. Therefore, the development of stereoselective synthesis of 1,4-dihydropyridines is one of the priorities of medicinal chemistry. Over the years, numerous methodologies have been developed for the production of enantiopure 1,4-dihydropyridines, such as stereoselective synthesis using chiral auxiliaries and chiral cyclocondensation partners, chromatographical methods, resolution of diastereomeric 1,4-dihydropyridine salts, enzyme catalysed kinetic resolution, or asymmetrisation of ester groups of 1,4-dihydropyridines. These approaches have been studied in detail and are relatively well established. The catalytic asymmetric approach holds the greatest promise in delivering the most practical and widely applicable methods. Substantial progress has been made toward the development of enantioselective organocatalytic methods for the construction of the chiral dihydropyridines. However, most of them do not provide a convenient way to pharmacologically important 1,4-dihydropyridine-3,5-dicarboxylates. Organocatalytic enantioselective desymmetrisation of prochiral 1,4-dihydropyridine-3,5-dicarbaldehydes also has great promise in the synthesis of pharmacologically important 1,4-dihydropyridine-3,5-dicarboxylates.

Structure–activity relationship study of 1,4-dihydropyridine derivatives blocking N-type calcium channels

Cilnidipine is a 1,4-dihydropyridine derived L/N-type calcium channel dual blocker possessing neuroprotective and analgesic effects which are related to its N-type calcium channel inhibitory activity. In order to find specific N-type calcium channel blockers with the least effects on cardiovascular system, we performed structure-activity relationship study on APJ2708, which is a derivative of cilnidipine, and found a promising N-type calcium channel blocker 21b possessing analgesic effect in vivo with a 1600-fold lower activity against L-type calcium channels than that of cilnidipine.

New Resolution of 2-Formyl-1,4-DHP Derivatives Using CIDR Methodology. Facile Access to New Chiral Tricyclic Thiolactam

(R)- and (S)-alpha-phenylethylamine (alpha-PEA: 7) have been used separately to resolve successfully a racemate 2-formyl-1,4-DHP derivative 4. The process was based on the difference of the solubility of both Schiff bases (6) since one of them crystallized out from the solution. These imines obtained by condensation of (R)-alpha-PEA (7) or (S)-alpha-PEA (7) with aldehyde (rac-4) were separated and analyzed by X-ray diffraction, and their exposition to an hydrochloric hydrolysis conditions led to the enantiopure (4R)-4 or (4S)-4 in excellent yields. Separate condensation of other chiral (8 and 13) and racemic (18) amino thiols as auxiliary with rac-4, (4S)-4, or (4R)-4 is accompanied by an in situ crystallization-induced dynamic resolution, whereby one distereomer of thiazole template selectively precipitates and can be isolated by simple filtration in 76-82% yield with dr > 99. The thiazole species isolated from this process resulted from an amino aldehyde condensation followed by a spontaneous thiol-imine cycloaddition. Finally, the racemate (+/-)-(4R,2'R)-19 and the diastereomerically pure homologous (4S,2'R)-23 and (4R,2'S)-20 (obtained in good yields (79-82%) from 2-aminoethanethiol (18) and 2-formyl-1,4-DHP derivative rac-4, (4S)-4, or (4R)-4, respectively) were converted conveniently in a one-pot procedure into newly tricyclic thiolactams in the DHP series in racemic ((+/-)-(6R,9bR)-21, 72% yield)) and enantiopure ((6S,9bR)-24, 71% yield); (6R,9bS)-24, 70% yield) forms.