Anthocyanins, are water-soluble plant pigments found in almost all members of the plant kingdom providing colors for most of plant tissues (leaves, stems, roots, flowers and fruits) [1–3]. Rich anthocyanins sources used as potential edible colorants involve colored fruits such as berries, cherries, and many dark-colored vegetables such as black currant, red onion, red radish as well as Hibiscus calyces .
Anthocyanins have different types according to composition, and chemical structures. These types and their concentration are varying not only between different species, but also among the fruits . The structure of anthocyanins have basic common skeleton composed of anthocyanidin and glycoside. The anthocyanidin (aglycone) is a polyhydroxy or a polymethoxy derivative of 2-phenyl-benzopyryliurn or flavylium salt [1, 2]. The common structure of anthocyanins is illustrated in Fig. 1.
There are six major anthocyanidins, mentioned in the caption of Fig. 1, to which 90% of all identified anthocyanins based on i.e. cyanidin, delphinidin, pelargonidin, peonidin, petudinin, and malvidin [1–3].
Hibiscus sabdariffa L., Roselle –or Karkade, is an annual , or perennial herb or sub-shrub , grows in tropical and subtropical regions [4–6]. Sudan is one of its largest exporters in the world. It grows there in various parts particularly the western [4, 6, 7].
In many countries roselle is considered as traditional medicinal in the treatment of many diseases like; relieving pain and coughs also treating liver disease, fever hypercholesterolemia, hypertension, antispasmodic and antimicrobial agent etc … . The calyx containing the attractive entities of the plant that responsible of its color, flavor and aroma [4, 6, 8], however, other plant parts are also used [4, 7],
The anthocyanins pigment can be used as natural edible dye in industries . Anthocyanins-rich foods in general are recommended to use by nutritionists due to their antioxidants effects and ability to inhibit some enzymes for instance; xanthine oxidase, lipoxygenases, and nicotine amide adenine dinucleotide phosphate (NADPH) oxidase [1, 11]. Roselle extracts are used to the treatment of hyperlipidemia, inflammatory diseases, cancer, and reduction of the incidence of liver lesions . Anthocyanins plant extracts are always mixtures of different anthocyanins and colorless flavonoids . The red color of Roselle calyces was attributed to the presence of dephinidin-3-sambubioside, cyanidin-3-sambubioside, delphinidin-3-glucoside and cyanidin-3-glucoside anthocyanins [6, 7, 14]. A study on Sudanese Roselle determined delphinidin-3-sambubioside to be the major anthocyanin responsible for the reddish violet color .
The characterization of anthocyanins is usually done by the chromatographic spectrophotometric and capillary electrophoresis (CE) methods . Recently; the most common used technique for characterization of anthocyanins is high performance liquid chromatography (HPLC), usually hyphenated with mass spectrometry (LC–MS) .
Nowadays modern techniques allow identification of several anthocyanin types. However; non-availability and high cost of pure anthocyanin standards present a problem specifically when using UV/Vis spectroscopy or HPLC techniques .
Recently, modern techniques are unitized to identify pelargonidin chloride, pelargonidin-3-glucoside and petunidin-3-glucoside as well as other anthocyanins from Sudan Roselle [14, 15].
The ability of anthocyanins to inhibit xanthine oxidase (XO) [1, 11] withdrew our attention to the use of Roselle as traditional medicinal drink to reduce the human blood pressure in Sudan. Xanthine oxidase is a highly versatile enzyme, widely distributed within the different kingdom animalea species . It catalyzes the hydroxylation of hypoxanthine to xanthine and xanthine to uric acid, accompanying with the production of; reactive oxygen species ROS [16, 17]. The increase of the activity of the enzyme leads to the accumulation of uric acid and ROS leading to the infection by several diseases, mainly hyperuraecimia and gout with other associated chronic diseases such as; hypertension, metabolic syndrome, cardiovascular diseases, diabetes, obesity, cancer and hyperlipidemia [16.17,18].
Enzyme inhibition will be carried out herein via docking study. Any pharmacologically active compound acts through interaction with targets like proteins and nucleic acids . The most recent drug to treat the hyperuricemia is topiroxostat .
The objective of the current research is to identify anthocyanins in two different Sudan Roselle samples i.e., red and white, special attention paid to study the ability of the anthocyanins to inhibit xanthine oxidase enzyme and explore most promising drug related to different diseases. In particular, the binding energies obtained from our identified anthocyanins will be compared with that obtained from topiroxostat.