Raghavachary Raghunathan

Synthesis of novel spiropyrrolizidines as potent antimicrobial agents for human and plant pathogens

A series of novel dispirooxindolopyrrolizidine derivatives have been synthesized through 1,3-dipolar cycloaddition reaction of azomethine ylide generated from proline and isatin with the dipolarophile (E)-2-arylidine-1-keto carbazoles. The synthesized cycloadducts were evaluated for antimicrobial activities. Compounds 7d and 7e showed relatively good antibacterial and antifungal activities.

Synthesis and antimicrobial activity of highly functionalised novel β-lactam grafted spiropyrrolidines and pyrrolizidines.

A facile and one-pot synthesis of a series of novel spiropyrrolidines/pyrrolizidines with β-lactam substituent has been accomplished through 1,3-dipolar cycloaddition reaction of alkenyl esters derived from β-lactam aldehyde as dipolarophile with the dipole azomethine ylide derived from 1,2- and 1,3-diketones and secondary amino acids. The synthesized compounds were evaluated for antimicrobial activities and found to exhibit relatively good antibacterial activity at lower concentration against four human bacterial pathogens.

Regioselective synthesis and antimicrobial screening of novel ketocarbazolodispiropyrrolidine derivatives

A series of novel dispiropyrrolidine derivatives have been synthesized through 1,3-dipolar cycloaddition reaction of azomethine ylide generated from sarcosin and di/tri ketone with the dipolarophile (E)-2-arylidine-1-keto-carbazoles. The cycloadducts ketocarbazalo spiro N-methyl pyrrolidines showed the most interesting antimicrobial activity at lower concentration.

An efficient synthesis of highly functionalized novel chromeno[4,3-b]pyrroles and indolizino[6,7-b]indoles as potent antimicrobial and antioxidant agents

A facile and efficient synthesis of novel chromeno[4,3-b]pyrroles has been accomplished by intramolecular 1,3-dipolar cycloaddition which on subsequent Pictet-Spengler cyclisation in presence of p-toluenesulfonic acid yielded indolizino[6,7-b]indoles. The synthesized chromenopyrroles and indolizinoindoles were evaluated for their antimicrobial and antioxidant activities. Compounds 7b, 7e, 7a and 7d exhibited respectively, good antibacterial and antifungal activities against tested pathogens when compared to reference control.

Synthesis of novel β-lactam fused spiroisoxazolidine chromanones and tetralones as potent antimicrobial agent for human and plant pathogens.

Synthesis of novel beta-lactam fused spiroisoxazolidine chromanones and tetralones ring systems has been achieved by intermolecular 1,3-dipolar cycloaddition reaction of bicyclic nitrone with unusual dipolarophiles, arylidene chromanones/tetralones under different reaction conditions. The synthesized compounds were evaluated for antimicrobial activities. It was observed that two of the synthesized compounds exhibited relatively good antibacterial and antifungal activities.

Synthesis of spiropyrazoline [5.3′] 4′-chromanones

Synthesis of a series of novel 1,3-diphenyl-4-aryl spiropyrazolines [5.3′] 4′-chromanones has been accomplished in good yields by regioselective 1,3-dipolar cycloaddition of diphenylnitrilimine to 3-arylidene-4-chromanones. X-ray crystal structure analysis of one of the products 4a confirms the structure and the regiochemistry of cycloaddition.

Stereoselective synthesis of hexahydro-3-methyl-1-arylchromeno[3,4-b]pyrrole and its annulated heterocycles as potent antimicrobial agents for human pathogens.

Synthesis of a series of novel hexahydrochromenopyrrole analogues has been accomplished through an intramolecular 1,3-dipolar cycloaddition (1,3-DC reaction) of azomethine ylides, generated by the aldehyde induced decarboxylation of secondary amino acids. These compounds were screened for antibacterial and antifungal activities against six human pathogenic bacteria and three human pathogenic fungi and found to have good antimicrobial properties against most of the microorganisms.

Spectral Analysis of Naturally Occurring Methylxanthines (Theophylline, Theobromine and Caffeine) Binding with DNA

Nucleic acids exist in a dynamic equilibrium with a number of molecules that constantly interact with them and regulate the cellular activities. The inherent nature of the structure and conformational integrity of these macromolecules can lead to altered biological activity through proper targeting of nucleic acids binding ligands or drug molecules. We studied the interaction of naturally occurring methylxanthines such as theophylline, theobromine and caffeine with DNA, using UV absorption and Fourier transform infrared (FTIR) spectroscopic methods, and especially monitored their binding affinity in the presence of Mg2+ and during helix-coil transitions of DNA by temperature (Tm) or pH melting profiles. The study indicates that all these molecules effectively bind to DNA in a dose dependent manner. The overall binding constants of DNA-theophylline = 3.5×103 M−1, DNA-theobromine = 1.1×103 M−1, and DNA-Caffeine = 3.8×103 M−1. On the other hand Tm/pH melting profiles showed 24–35% of enhanced binding activity of methylxanthines during helix-coil transitions of DNA rather than to its native double helical structure. The FTIR analysis divulged that theophylline, theobromine and caffeine interact with all the base pairs of DNA (A-T; G-C) and phosphate group through hydrogen bond (H-bond) interaction. In the presence of Mg2+, methylxanthines altered the structure of DNA from B to A-family. However, the B-family structure of DNA remained unaltered in DNA-methylxanthines complexes or in the absence of Mg2+. The spectral analyses indicated the order of binding affinity as “caffeine≥theophylline>theobromine” to the native double helical DNA, and “theophylline≥theobromine>caffeine to the denatured form of DNA and in the presence of divalent metal ions.

Microwave-Assisted K-10 Montmorillonite Clay–Mediated Knoevenagel Hetero-Diels–Alder Reactions: A Novel Protocol for the Synthesis of Polycyclic Pyrano[2,3,4-kl]xanthene Derivatives

Abstract The intramolecular hetero-Diels–Alder reactions of 2-(cyclohex-2-enyloxy)benzaldehyde by Knoevenagel condensation with symmetrical 1,3-diones under three different conditions afforded the pyrano[2,3,4-kl]xanthene derivatives in a stereoselective manner in good yield. The structure of one of the products was unambiguously established by x-ray analysis.

TiO2-Mediated, One-Pot, Four-Component 1,3-Dipolar Cycloaddition Reaction: A Facile Synthesis of Dispiro-pyrrolidine Ring Systems

Abstract An expedient regioselective synthesis of dispiroindenoquinoxaline pyrrolidine derivatives mediated by TiO2 in a one-pot, four-component 1,3-dipolar cycloaddition reaction is described.