title: Facile synthesis and stereochemical investigation of Mannich base derivatives: evaluation of antioxidant property and antituberculostic potency.
abstract: A mini-library of diversely substituted 2,4-diaryl-3-azabicyco[3.3.1]nonan-9-one O-methyloximes and their N-methyl analogs were synthesized by a non-laborious, modified and an optimized Mannich condensation in good yields. Both the ring N-methylation and oxime O-methylation were employed by various methods; of them, the usage of (t)BuOK was found to be the superior in terms of good yield in short time. Stereochemistry of all the synthesized compounds was unambiguously established by their NMR spectral ((1)H, (13)C, (1)H-(1)H COSY, (1)H-(13)C one and multiple bond COSY and NOESY) as well as single-crystal XRD studies. Irrespective of the nature and position of the substituents, all the synthesized oxime ethers of the bicyclic Mannich bases as well as their N-methyl analogs adopted the twin-chair conformation with equatorial orientations of all the substituents. All the synthesized oxime ethers were evaluated for their antioxidant property by DPPH radical scavenging method. According to the structure-activity correlations, compound 4y was found to be a lead molecule with the IC(50) of 0.187 mg/mL. Thus, the present study exploits the scope of finding more active analogs by further optimization with the incorporation of more electron enriched alkoxy/amino and/or phenolic groups on the heterocycle as well as oxime ether pharmacophore. Most of the synthesized molecules were screened for their antituberculostic potency against Mycobacterium tuberculosis H(37)Rv by zone of inhibition method. Of them, 4w/5d and 4x showed very promising inhibition zones of 21 and 23 mm, respectively, which leads to the optimization of 4x by introducing various substituents on the O-benzyl moiety to enhance the antituberculostic potency.
authors.affiliation: Department of Image Science and Engineering, Pukyong National University, Busan-608 737, Republic of Korea.
authors.forename: Paramasivam
authors.initials: P
authors.lastname: Parthiban
authors.forename: Viswalingam
authors.initials: V
authors.lastname: Subalakshmi
authors.forename: Krishnamurthy
authors.initials: K
authors.lastname: Balasubramanian
authors.forename: Md Nurul
authors.initials: MN
authors.lastname: Islam
authors.forename: Jae Sue
authors.initials: JS
authors.lastname: Choi
authors.forename: Yeon Tae
authors.initials: YT
authors.lastname: Jeong
mesh_terms: D000900:Anti-Bacterial Agents / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D000975:Antioxidants / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D001643:Bridged Bicyclo Compounds / Q000737:chemistry; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008352:Mannich Bases / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D008968:Molecular Conformation; D009169:Mycobacterium tuberculosis / Q000187:drug effects; D010091:Oximes / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D000900:Anti-Bacterial Agents; D000975:Antioxidants; D001643:Bridged Bicyclo Compounds; D008352:Mannich Bases; D010091:Oximes