Dept. of Pharmaceutical Chemistry
Introduction of D-amino acids and N-methylation of amino acids like tyrosine, valine, alanine etc enhanced antimicrobial activity. Condensation of heterocyclic moieties viz nicotinic acid, thiazole, coumarin, quinoline, furan, imidazole etc. with amino acids and peptides resulted in compounds with potent biological activities. Many of the heterocyclic found to exhibit antifungal, antibacterial, cytotoxic, antineoplastic, insecticidal, anti-inflammatory, tyrosinase inhibitory and melanin production inhibitory activities. Imidazole has been drawn as promising structural units in the field of medicinal chemistry. The new threonine derivatives compounds are characterized by using IR, H1NMR and mass spectroscopy.
Key words: Threonine, Tyrosine, Valine, Alanine, Benzoic Acid, Imidazole.
A great number of drugs are heterocyclic compounds, mostly are of synthetic origin, few have obtained from natural resources which include alkaloids, xanthines, cardiac glycosides, vitamins and several antibiotics. Heterocyclic derivatives having two nitrogen atoms oriented in, 1-3 position are endowed with wide spectrum of biological activities. Number of organo-sulphur and nitrogen containing compounds are present in living and non living system. Nitroimidazole derivatives were developed not only because of their novelty to structure but also because of novelty to action.The N-methylated peptide antibiotics are found to possess enhanced activity ascompared to the un methylated forms.Therefore, an attempt is made to synthesize a new bioactive series of 5-nitroimidazole derivatives of amino acids and peptides. Biological activity studies performed on these synthetic compounds proved to give good results.
1.Synthesis of N-methyl amino acids methyl ester
Amino acids were converted into the corresponding methyl ester hydrochloride using thionyl chloride and methanol. The amino end was then protected by introducing Boc-group using ditertiary butylpyrocarbonate and triethylamine to get Boc-L-amino methyl ester. N-methylation of this compound was done by treating with methyl iodide and sodium hydride (Benoition method) to get Boc-(N-Me) amino methyl ester.
2. Preparation of 4-[2-(5-nitro)imidzolyl] benzoic acid
A mixture of p-amino benzoic acid (34.25 gms, 250 mmol), dilute hydrochloric acid (15%, 120ml) and water (150ml) was heated to get a clear solution. The solution was cooled to RT and diazotized by the addition of sodium nitrite solution (30%, 48ml). The diazonium salt solution was filtered and to the filtrate, dilutes HCl (100ml) and nitroimidazole (250 mmol) and aqueous cupric chloride (5gms in 20ml of water) were added with stirring. Stirring was continued for 6 hrs and kept overnight in the refrigerator. The separated solid was collected by filtration and washed with water. The crude compound was crystallized from acetone to obtain pure of4[2-(5-nitro)imidazolyl]benzoic acid.
3.Preparation of 4-[2′-(5′-nitro) imidazolyl]benzoyl(N-Me)-aminoacid
To the (N-Me) amino acid methylester(7.0 mmol.) THF (20ml), added 4-[2′-(5′-nitro) imidazolyl] benzoic acid acid (1.631gms, 7.0 mmol.), DIPC, Et3N (2.8ml) and stirred at room temp.for 24hr. The reaction mixture was filtered and the filtrate was concentrated under reduced pressure, residue was dissolved in CHCl3, washed with 10% NaHCO3 (10ml) and 5% HCl (10ml), dried over anhydrous Na2SO4 and evaporated under vacuum to get the title compounds. The crude product was recrystallized from CHCl3 and n–hexane
4. Preliminary Analysis of the sample
Thin-layer chromatography (TLC) was commonly used in the qualitative description of the complexity and composition of chemical mixtures.
Application of sample on TLC plates:
The sample was applied to the chromatogram by repeated “spotting” above 1-2 cm from one end of the plate with a capillary tube. The most important precaution was not to apply spots below the level of the top of the solvent system in developing chamber
Developing solvent systems:
Development chamber was used for developing chromatogram. Chloroform: Methanol: Water 5:3:2 was the solvent system used for running TLC of these compounds.
Visualization of chromatogram:
After developing, the TLC plates were dried and then exposed to iodine vapours in a chamber, since chromalograms of many synthetic products were frequently observed by iodine vapors. Rf value was noted down. Purity of all the synthesized compounds including intermediates was checked by TLC on silica gel G plates. All compounds have shown only single spot indicating the completion of the reaction and thepurity of the product obtained.
RESULTS & DISCUSSION :
The synthesized new amino acid derivatives further studied for characterization of IR, NMR and Mass spectra’s.To study the structural-activity relationship and to optimize the structure.
1HNMR (300 MHz. CDCl3) δ in ppm :
δ 7.6(1H, m, – NH), δ 7.4 (1H, m, Aromatic-H) δ 7.2 (2H, m, Aromatic-H), δ 6.9 (2H, m, Aromatic-H) δ 4.8 (1H, m, α-H), δ3.8 (1H, s, COCH3) δ2.9 (1H, s, -N-CH3) δ1.4 (2H, d, β-CH2), δ1.2 (1H, m, γ -H), δ0.95 (6H, d, CH3 group) of threonine
IR (CHCl3) in cm-1 :
Peak at3565 .22 corresponds to NH and Aromatic C-H stretching
Peak at 2818.14 corresponds to Aliphatic C-H stretching
Peak at1604.27 corresponds to Aliphatic C-H stretching
Peak at 1450.75corresponds to C=O (carbonyl) stretching
Peak at 1354.43corresponds to C=O (amide) stretching
Peak at1220.13 corresponds to N-H bending
Peak at1102.11 corresponds to C-H bending.
The new 4-[2′-(5′-nitro) imidazolyl] benzoyl (N-Me) amino acid derivatives was synthesized and characterized by IR, NMR and Mass spectral data. By this studies find the structure-activity relationship and to optimize the structure. The synthesized amino acid derivative i.e., 4-[2′-(5′-Nitro) imidazolyl] benzoyl N-Me) threonine was confirmed by physicochemical and spectral analysis.