Experimental and Theoretical Studies of Bromination of Diethyl 2,4,6-Trimethyl-1,4-dihydropyridine-3,5-dicarboxylate

Development of Self-Assembling bis-1,4-Dihydropyridines: Detailed Studies of Bromination of Four Methyl Groups and Bromine Nucleophilic Substitution

One of the most important steps in the synthesis of 1,4-dihydropyridine (1,4-DHP) amphiphiles is the bromination of methyl groups in positions 2 and 6 of the entire ring. However, up to now, only N-bromosuccinimide was mainly used for bromination 1,4-DHPs. In this work, the synthesis of bis-1,4-DHP derivatives with ethyl and dodecyl ester groups attached to 1,4-DHP ring at positions 3 and 5 was performed by Hantzsch synthesis. The experimental studies were carried out to find out the best conditions and the agent for the tetra bromination of bis-1,4-DHP methyl groups at positions 2 and 6. Four different brominating agents were screened. The use of pyridinium bromide-perbromide in ethyl acetate was found to be optimal for the bromination of methyl groups. The bromination reaction was followed by the synthesis of cationic pyridine moiety containing amphiphilic bis-1,4-DHP derivatives. By nucleophilic substitution of bromine with various substituted pyridines, 12 new amphiphilic bis-1,4-DHP derivatives were obtained. Evaluation of self-assembling properties of tetracationic bis-1,4-dihydropyridine derivatives by dynamic light scattering (DLS) measurements was also performed.

Highly Efficient Electrocarboxylation Method to Synthesize Novel Acid Derivatives of 1,4-Dihydropyridines and to Study Their Antimicrobial Activity

1,4-Dihydropyridines (1,4-DHPs) hold a top-notch position in the pharmaceutical world due to a broader spectrum of applications, whereas the carboxylic moiety has been an integral part of the physiological world, effective food preservatives, and antimicrobial agents. Seeking the enormous potential and applications of these two classes, we worked to combine these to synthesize 2,2'-[3,5-bis(ethoxycarbonyl)-4-phenyl-1,4-dihydropyridine-2,6-diyl]diacetic acid the novel dicarboxylic derivatives of 1,4-DHP (9a-k) achieved via the electro-carboxylation of tetrasubstituted-1,4-dihydropyridines (8a-k) derivatives using Mg-Pt electrodes in an undivided cell. The targeted compounds were established by ¹H, ¹³C NMR, IR, and ESI-MS. Further, the synthesized compounds show excellent resistance against various microbes and the activity increased 2-3 folds after the introduction of acid groups. Compound 9b (against E. coli, S. aureus, B. subtilis, A. niger, and P. glabrum), 9d (against E. coli, K. pneumonia, S. aureus, A. janus, and F. oxysporum), 9f (against E. coli and P. fluorescens), and 9k (against F. oxysporum and P. glabrum) were found to be highly active at 4 μg/mL with reference to standard amoxicillin and fluconazole. Further, the present synthetic protocol would open new gates for other researchers to develop new molecules by bioisosteres of these substrates.

Intramolecular hydrogen bonds in 1,4-dihydropyridine derivatives

1,4-Dihydropyridine (1,4-DHP) derivatives have been synthesized and characterized by 1H, 13C, 15N nuclear magnetic resonance (NMR) spectroscopy, secondary proton/deuterium 13C isotope shifts, variable temperature 1H NMR experiments and quantum-chemical calculation. The intramolecular hydrogen bonds NH⋯O=C and CH⋯O=C in these compounds were established by NMR and quantum-chemical studies The downfield shift of the NH proton, accompanied by the upfield shift of the 15N nuclear magnetic resonance signals, the shift to the higher wavenumbers of the NH stretching vibration in the infrared spectra and the increase of the 1J(15N,1H) values may indicate the shortening of the N-H bond length upon intramolecular NH⋯O=C hydrogen bond formation.