J. Dineshkumar, P. Parthiban
2018
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Abstract
January March 2018 17 JCPS Volume 11 Issue 1 Impact on NMR spectra by ortho substitution of 2, 6-bis (polymethoxyphenyl) piperidin-4-ones J. Dineshkumar, P. Parthiban* Department of Chemistry, CRD, PRIST University, Thanjavur-613403, India *Corresponding author: E-Mail: parthiban.crd@prist.ac.in ABSTRACT Synthesis of new molecules with bio-potent piperidine/piperidone skeleton and their stereochemical investigation are important in the field of medicinal chemistry due to the presence of piperidine/piperidone skeleton as a building block in numerous naturally occurring alkaloids and biologically active compounds. Since the stereochemistry of any molecules plays vital role in eliciting their biological response, it is very important to ascertain the configuration and conformation of the molecules that obtained for the biological screening. Hence, it was planned to synthesis some polyfunctionalized piperidin-4-ones as new bio-active molecules to establish their stereochemistry. Particularly, the synthesis has been targeted to polyfunctionalized 2,6-bis(polymethoxyphenyl)piperidin-4-ones in view of the fact that the methoxy groups are responsible for various biological actions including antioxidant property. Thus, the target molecules 3,5-dimethyl-2,6-bis(3,4-dimethoxyphenyl)piperidin-4-one (1) and 3,5-dimethyl-2,6bis(2,5-dimethoxyphenyl)piperidin-4-one (2) were achieved as single isomer by modified Mannich condensations. Identification and characterization of the synthesized molecules were made by analytical (TLC, melting point, elemental analyses) and spectral (IR and NMR) studies. The NMR spectral studies, particularly, the proton NMR spectral data were very useful to determine the configuration and conformation of the new molecules 1 and 2. Accordingly, both of them exist in chair conformation with equatorial orientations of methyl groups on the active methylene centers (C-3 and C-5) and polymethoxyphenyl groups on both sides of the secondary amine (C-2 and C-6). Another interesting observation from the proton NMR is, the ortho substitution on 1 (i.e., molecule 2) cause a significant deshielding on benzylic (H-2a/H-6a) and ortho protons, and a minor deshielding on methinic protons (H-3a/H-5a), whereas, all the above three signals appear as broad singlet due to the restricted rotation by the interaction of ortho methoxy groups with the methyl groups at C-3 and C-5.