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Current Perspectives and Methods for the Characterization of Natural Medicines
Published in Rohit Dutt, Anil K. Sharma, Raj K. Keservani, Vandana Garg, Promising Drug Molecules of Natural Origin, 2020
Muthusamy Ramesh, Arunachalam Muthuraman, Nallapilai Paramakrishnan, Balasubramanyam I. Vishwanathan
UV spectroscopy is another type of spectroscopy. The basic principles of UV spectroscopy are absorption of light and make the changes of the incident after passing to samples. It lies between the wavelength of 200–400 nm and visible spectroscopy lie at the wavelength of 400–800 nm. The instrument used for obtaining the spectrum is UV-Vis spectrophotometer. Ethyl alcohol and hexane are the solvents widely used to prepare the sample for UV-Vis spectroscopy. UV-Vis spectrum assists to characterize the aromatic group of compounds and conjugated dienes in qualitative analysis. In quantitative analysis, UV-Vis spectroscopy also helps to determine the molar concentration of constituents present in a given sample. In addition, it is also used to detect impurities, isomers, and molecular weight (Perkampus, 2013). UV-Vis spectroscopy was employed to characterize diarylheptanoids in association with other spectral techniques (Alberti et al., 2018). Diarylheptanoids have a specific absorption range, i.e., 250–290 nm. Acetonitrile was used as a solvent to get the UV-Vis spectrum. Further, a wider absorption band observed for curcumin, i.e., 410–430 nm. Keto-enol tautomerism of curcumin was characterized from the intra- and intermolecular hydrogen bonding. UV-Vis spectroscopy method is also used for the quantification of the curcuminoid content of Curcuma Longa extract (Alberti et al., 2018). The UV-Visible spectroscopy-based characterized phytoconstituents and marine compounds are listed in Table 2.2.
Curcumin and Neglected Infectious Diseases
Published in Venkatesan Jayaprakash, Daniele Castagnolo, Yusuf Özkay, Medicinal Chemistry of Neglected and Tropical Diseases, 2019
Francesca Mazzacuva, Agostino Cilibrizzi
The β-diketone function in the structure is responsible for the intramolecular hydrogen atom transfer leading to the typical keto/enol tautomers (Figure 4A). The two tautomeric forms have been reported to generate various cis and trans conformations in solution (Figure 4B) (Wright 2002, Kolev et al. 2005, Cornago et al. 2008). The relative abundance of specific keto and enol isomers can change on the basis of different temperatures, pH and polarity of the medium (or solvent). (A) Keto-enol tautomerism of curcumin (1); (B) representative cis-trans conformations for the keto-enol tautomeric forms.
Chemical Causes of Cancer
Published in Peter G. Shields, Cancer Risk Assessment, 2005
Gary M. Williams, Alan M. Jeffrey
DNA is also continuously modified by endogenous processes (258), including methylation of cytosine at position 5 by DNMT (16). The base-sugar bonds in DNA are susceptible to hydrolysis resulting in loss of bases at a rate of about 104 per cell per day creating apurinic/apyrimidinic sites (Fig. 4) (259). Deamination of 5-methylcytosine to thymine (Fig. 4) is a frequent reaction while deamination of cytosine to uracil is less frequent. Nitric oxide can deaminate 5-methylcytosine to produce thymine (260), which represents a greater challenge for DNA repair pathways (261). Keto/enol tautomerism may be responsible for some G→A point mutations (262). Oxygen metabolism generates reactive oxygen species such as hydroxyl radicals and singlet oxygen that produce in oxidation of dGTP and bases in DNA (263). The oxidation of deoxyguanine residues in DNA to 7,8-dihy-dro-8-oxodeoxyguanine (8-oxodG) (Fig. 5) has been reported to occur in up to 1 in 103 residues (264), although there is considerable uncertainty about precise levels due to artifacts in DNA preparation. A variety of other oxidized bases have also been found (198). Peroxidation of unsaturated fatty acids leads to formation of α,β-unsaturated aldehydes which produce cyclic adducts with a propano ring moiety in DNA (Fig. 5) (196,265). These are all premutagenic lesions as detailed below. Additionally, cytosine is methylated by DNMT using S-adenosylmethionine as the methyl donor (16). Methylene tetrahydrofolate reductase (MTHFR) plays a central role in converting folate to methyl donors and polymorphisms in MTHFR reduce DNA methylation (266). Chemicals, such as 5-azacytidine, can modify methyla-tion patterns (266,267).
Inhibitors of histone deacetylase 6 based on a novel 3-hydroxy-isoxazole zinc binding group
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2021
Pasquale Linciano, Luca Pinzi, Silvia Belluti, Ugo Chianese, Rosaria Benedetti, Davide Moi, Lucia Altucci, Silvia Franchini, Carol Imbriano, Claudia Sorbi, Giulio Rastelli
We firstly investigated the tautomeric preference of compound 13 in water solvent by means of quantum-chemical calculations, performed with Jaguar of the Schrödinger suite 2020–1, with default settings7,8. Indeed, five-membered heteroaromatic rings, such as 3-hydroxy-isoxazole, could undergo keto–enol tautomerism in water9,10. Results of the quantum-chemical calculations indicated that the enol form is 0.5 kcal/mol more stable than the keto tautomer, which is likely to be favoured by aromaticity. This result is in line with previous in silico and experimental studies on the tautomeric equilibria of 3-hydroxy-substituted isoxazoles10, suggesting that the 3-hydroxy tautomer is preferentially present in solution. Therefore, all in silico calculations were conducted with the enol form of the ligands.
Bovine serum albumin nanoparticles improve the antitumour activity of curcumin in a murine melanoma model
Published in Journal of Microencapsulation, 2018
Luciana Erzinger Alves de Camargo, Daniel Brustolin Ludwig, Tania Toyomi Tominaga, Bruna Carletto, Giovani Marino Favero, Rubiana Mara Mainardes, Najeh Maissar Khalil
Curcumin is the major polyphenol pigment from the turmeric Curcuma longa L., and it has been widely used as a spice ( Goel et al.2008, Akbik et al.2014). It is a bis-α, β-unsaturated β-diketone, identified as [1,7-bis (4-hydroxy-3-methoxyphenyl)-1,6-heptadi-ene-3, 5-dione]. Curcumin exhibits keto–enol tautomerism, and presents in keto form in acid–neutral solutions and in enol form in basic solutions (Sharma et al.2005). Curcumin has poor aqueous solubility and it is unstable in physiological to basic pH (Goel et al.2008) and under visible light, where it degrades into ferulic acid and vanillin (Sharma et al.2005). Due to its low solubility, curcumin has low oral bioavailability (Kim et al.2011, Khalil et al.2013). Therefore, curcumin is detectable in low nanomolar concentrations in plasma (Sharma et al.2005), hindering its therapeutic activity. A great amount is unmetabolised excreted in faeces, whereas its conjugated metabolites are excreted in urine.
Design, synthesis and α-glucosidase inhibition study of novel embelin derivatives
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2020
Xiaole Chen, Min Gao, Rongchao Jian, Weiqian David Hong, Xiaowen Tang, Yuling Li, Denggao Zhao, Kun Zhang, Wenhua Chen, Xi Zheng, Zhaojun Sheng, Panpan Wu
All final compounds were characterised by 1H-NMR, 13C-NMR, and HRMS. It is noteworthy that there is an interesting phenomenon in the 13C-NMR spectra of compounds 4d∼17d. Taking 5d as an example (Figure 2), six different carbons exist in the para-benzoquinone ring. However, there are only two carbon signals at >90 ppm, which belong to the carbons in the 3/6-position. This may be due to keto-enol tautomerism of para-benzoquinone (Figure 3). This rapid transfer between two tautomers makes it difficult to record the corresponding carbon signals. Once one of the hydroxyl groups is methylated, the 13C-NMR signals of the core structure return to be normal.