Optimization and Effect of Substituents on the Transformation of 3-(Substituted acetoxy)azetidin-2-ones to Chiral 3-Hydroxyazetidin-2-ones, Molecular Docking and Enantiomeric Excess Determination

Abstract

: The enantioselective synthesis of chiral cis-3-hydroxyazetidin-2-ones mediated by Porcine Pancreatic Lipase (PPL) via hydrolysis of cis-3-(chloro acetoxy) azetidin-2-ones in the presence of a phosphate buffer (0.1M, pH = 7.2) in acetonitrile at a temperature range of 25-35 °C was optimized. Under the optimized reaction conditions, the influence of various electron withdrawing/donating/neutral groups on ester functionality of cis-3-(substituted acetoxy)azetidin-2- ones towards hydrolysis was extensively studied, and the bromoacetoxy, propanyloxy, and formyloxy groups provided moderate to good yields of 90%, 91%, and 81%, respectively. Moreover, the chiral cis-3-hydroxyazetidin-2-ones underwent acetylation, and their enantiomeric excess was assessed using the 1H NMR technique, employing chiral shift reagents. To gain insights into the active sites of the biocatalyst, molecular docking studies of compounds 5(a-i) with pancreatic lipase (PDB ID: 1LBS) were carried out. Additionally, the proposed interaction of substituents with the biocatalyst established the absolute stereochemistry of the target chiral cis-3-hydroxyazetidin-2-ones using Seebach's model in comparison to Jone's models. objective: With an aim to explore the general applicability and to ascertain whether 3-substituted acetoxyazetidin-2-ones would give a similar series of optically active compounds, we envisaged the comprehensive studies on the enantioselective synthesis of chiral cis-3-hydroxyazetidin-2-ones from synthesized cis-3-substitutedacetoxyazetidin-2-ones. We here describe extended PPL hydrolysis studies, wherein, the influence of replacement of the hydrogen of the acetate functionality with halide (-Cl, -Br), alkyl (-CH3), aryl (-C6H5) and aralkyl (-CH2C6H5) groups is discussed. Also, the effects of substitution of methyl group of acetate with hydrogen (-H) and aryl (-C6H5) groups upon PPL hydrolysis is investigated. Further the binding mode of cis-3-(substituted acetoxy)azetidin-2-ones with pancreatic lipase (PDB ID: 1LBS) and assessment of the impact of structural modifications has been carried out using molecular docking studies.