Synthesis, reactions, and preliminary evaluations of enaminone esters

An assessment study of known pyrazolopyrimidines: Chemical methodology and cellular activity

Heterocyclic compounds with nitrogen atom play a key role in the normal life cycle of a cell. Pyrazolopyrimidine is a privileged class of nitrogen containing fused heterocyclic compound contributing to a major portion of all lead molecules in medicinal chemistry. The thumbprint of pyrazolopyrimidine as a pharmacophore is always noticeable due to its analogy with the adenine base in DNA. Pyrazolopyrimidines are divided into five types [I, II, III, IV, V] based on the mechanism of action on the specific target conferring a wide scope of research which has accelerated the interest of researchers to investigate its biological profile. In 1956, the anti-cancer activity of pyrazolopyrimidine was evaluated for the first time with appreciable results. Since then, medicinal chemists centered their work on various methods of synthesis and evaluating the biological profile of pyrazolopyrimidine isomers. This report consists of novel methodologies followed to synthesize pyrazolopyrimidine isomers along with a note on their biological significance. To the best of our knowledge, this review article will be first of its kind to encompass different synthetic procedures along with anti-cancer, kinase inhibition, phosphodiesterase inhibition and receptor blocking activity of pyrazolopyrimidine moieties. IC₅₀ values of potent compounds are added wherever necessary to understand the suitability of pyrazolopyrimidine skeletons for a specific biological activity.

Microwave-assisted synthesis of some new pyrazolopyridines and their antioxidant, antitumor and antimicrobial activities

The chemical behavior of 4-(dimethylaminomethylene)-1-phenyl-3-(pyridin-3-yl)-1H-pyrazol-5(4H)-one (enaminone) (2) toward some active methylene reagents has been reported to give pyrazolopyridine derivatives. All the reactions were carried out by conventional heating and microwave irradiation technique. The antioxidant activity of the prepared compounds was studied using 1,1-phenyl-2-picrylhydrazyl (DPPH) assay. Compounds (4c) and (4d) showed the highest activity. The antitumor activity against liver and breast cell lines was tested. Compounds (6), (9) and (11) showed the highest activity for liver cell line while compounds (6) and (9) showed the highest activity for breast cell line. Compounds (4a-d) were screened for their antibacterial activity against Gram-positive, Gram-negative bacteria and antifungal activity.

Ultraviolet spectroscopy of anticonvulsant enaminones

The ultraviolet (UV) spectra of selected enaminones were determined in acidic, alkaline and neutral media and compared to their anticonvulsant activities. The wavelength of maximum absorption and molar absorptivity were compared with the anticonvulsant activity of the selected secondary and tertiary enaminones, and general inferences were made. The UV spectra of the enaminones had hypsochromic shifts in acidic media in comparison with neutral media. Generally, a small hypsochromic shift occurred in alkaline media when compared to the neutral solutions of the enaminones. The tertiary enaminones absorbed UV light at longer wavelength than the secondary enaminones in acidic, neutral and alkaline media. In particular, the tertiary enaminones displayed absorption at the higher end and secondary enaminones towards the lower end of the UV wavelength range 292-315nm in aqueous media. Tertiary enaminones (30-33) which were devoid of the NH proton were found to be uniformly inactive in a mouse model of electroshock seizures, while some secondary enaminones (1, 5-8, 12, 16, 18, 20, 23-25, 28 and 29) had anticonvulsant activity. Thus the NH group of secondary enaminones is very important for anticonvulsant activity, and this agrees with an already established trend in proton NMR spectroscopy. In addition, the para-substitution on the phenyl group in some enaminones result in higher molar absorptivity (epsilon) values that enhance anticonvulsant activity. These results indicate that the anticonvulsant activity of enaminones is not due to electronic effect alone, but is probably due to a combination of factors including electronic and steric effects, lipophilicity, and hydrogen bonding.

Stability study of the anticonvulsant enaminone (E118) using HPLC and LC-MS

The stability of the new chemical synthetic enaminone derivative (E118) was investigated using a stability-indicating high-performance liquid chromatography (HPLC) procedure. The examined samples were analyzed using a chiral HSA column and a mobile phase (pH 7.5) containing n-octanoic acid (5 mM), isopropyl alcohol and 100 mM disodium hydrogen phosphate solution (1:9 v/v) at a flow rate of 1 ml min(-1). The developed method was specific, accurate and reproducible. The HPLC chromatograms exhibited well-resolved peaks of E118 and the degradation products at retention times <5 min. The stability of E118 was performed in 0.1 M hydrochloric acid, 0.1 M sodium hydroxide, water/ethanol (1:1) and phosphate buffer (pH approximately 7.5) solutions. E118 was found to undergo fast hydrolysis in 0.1 M hydrochloric acid solution. The decomposition of E118 followed first order kinetics under the experimental conditions. The results confirmed that protonation of the enaminone system in the molecule enhanced the hydrolysis of E118 at degradation rate constant of 0.049 min(-1) and degradation half-life of 14.1 min at 25 degrees C. However, E118 was significantly stable in 0.1 M sodium hydroxide, physiological phosphate buffer (pH 7.5) and ethanol/water (1:1) solutions. The degradation rate constants and degradation half-lives were in the ranges 0.0023-0.0086 h(-1) and 80.6-150.6 h, respectively. Analysis of the acid-induced degraded solution of E118 by liquid chromatography-mass spectrometry (LC-MS) revealed at least two degradation products of E118 at m/z 213.1 and 113.1, respectively.

Nuclear magnetic resonance studies of anticonvulsant enaminones

1H nuclear magnetic resonance (NMR) spectra of enaminones were determined and compared to the anticonvulsant activity of the compounds. Although the precise employment of the NMR data to predict anticonvulsant activity of the enaminones could not be established, general inferences were made. The NMR data confirmed that the enaminones existed predominantly in the amino tautomer, and no evidence was found for the imino tautomer. The ketamine form of the enaminones was supported by the observed spin-spin splittings of the NH with the alpha-protons on certain enaminones. The NH of secondary enaminones was very important in conferring anticonvulsant activity to the enaminones. The peak for the NH proton which could be seen between delta (ppm) 4.50 and 9.70 was present in all of the active enaminones. The tertiary enaminones, which were devoid of the NH proton, were uniformly inactive. It appeared that a combination of steric and electronic effects, lipophilicity, and hydrogen bonding were necessary for the anticonvulsant activity of the enaminones. The cyclic enaminones existed in the trans-S-trans fixed conformation, and the NMR data supported our hypothesis that enantioselectivity is retained in synthesizing enaminones from cyclic, diasteriomeric 1,3-diketones. In addition, the AB system and many unique features were observed in some enaminones. The para, meta, and ortho substituted patterns were observed for monosubstituted phenyl protons, and the NMR patterns for di- and trisubstituted phenyl groups were elucidated.