Regio- and stereoselective synthesis of spirooxindole 1′-nitro pyrrolizidines with five concurrent stereocenters under aqueous medium and their bioprospection using the zebrafish (Danio rerio) embryo model
A highly regio- and stereoselective method has been developed and expanded for the synthesis of a 20-membered library of spirooxindole 1′-nitro pyrrolizidines via 1,3-dipolar cycloaddition of azomethine ylides, generated in situ by a decarboxylative route from a common set of diverse isatins and L-proline derivatives, with substituted β-nitrostyrenes under aqueous medium. Among various reaction conditions, water proved to be necessary for the interaction of the reagents as well as heating the reaction at 90 °C for one hour, during which time the desired products were obtained in good yields and with excellent regio- and stereoselectivities. We subsequently applied in silico drug discovery computational methods to (i) identify the ADME properties, based on Lipinski's rule, (ii) screen the toxicological profile, and (iii) predict the penetration through the blood brain barrier (BBB) of the synthesized compounds. Next, the LC50 values of all these spirocyclic oxindoles were determined in zebrafish embryos cultured individually in buffer solutions of each compound and, finally, the phenotypes induced by these molecules in the zebrafish embryos at concentrations below their LC50 were analyzed at 48, 72 and 96 hours post fertilization.