Introduction
The presence of natural products in animals, plants, and minerals plays a vital role in the field of medicinal chemistry; therefore, researchers from antiquity are working on the extraction, isolation, identification, biological activities, and many properties of these natural organic products. Conventional medicines depend on phytochemical-rich plant extracts to cure many diseases because medicines obtained from natural sources are less toxic and have fewer side effects than synthetic medicines [1]. For the remedy of many health issues, to remove pain and discomfort, such as fragrance and flavor in food, everyone depends on the plant kingdom for their needs, and medicinal plants play a vital role in developing countries. Medicinal plants are the best source for the discovery of new compounds that lead to new drugs [2]. Medicinal plants of the Moraceae family are known for their versatile applications in many fields such as agriculture, cosmetics, food, and pharmaceuticals. One example of the family Moraceae is Morus alba (mulberry), which is the most commonly used medicinal plant in Asia, especially in China. Mulberry is highly produced in China and grows throughout many regions such as Asia, Africa, America, Europe, and India. The leaves of mulberry are only known for sericulture. But the leaves are not used in sericulture but can be used as medicines as well [3]. Mulberry is a rich source of many bioactive compounds such as flavonoids, amino acids, vitamins, polysaccharides, and steroids, which are used for the treatment of many infections and internal diseases. Among these components, flavonoids have attracted more attention in recent studies because of their anti-inflammatory, anti-aging, and anti-hyperglycemic activities. [4,5]. Flavonoids belong to the polyphenolic family and incorporate at least 6000 molecules, primarily divided into phlobaphenes, aurones, isoflavonoids, flavones, flavonols, and anthocyanins [6]. Flavonoid compounds commonly found in mulberry are kuwanon (flavons), sangenon (flavanols), rutin (flavons), quercetin (flavonols), and catechins (flavanols).
Plants have an amazing tendency to identify changes in the environment, and then the rapid response to increases the opportunity and lowers the risk. The basic need to respond to these changes is the integration of growth, development, and metabolism, which leads to the evolution of many other mechanisms to regulate cellular functions. One of the mechanisms is glycosylation, which involves a large multigene family of glycosyltransferases (GTs). Glycosyltransferases can identify lipophilic small molecules, including hormones and secondary metabolites, as well as biotic and abiotic toxins in the environment [7,8]. Glycosylation of flavonoids increases their solubility and stability in plants. Flavonoids exist mainly in their glycosylated forms in plants. The final step in the biosynthesis of these glycosides is glycosylation, which plays a variety of roles in plant metabolism. Glycosyltransferases (GTFs) establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar (also known as a glycosyl donor) to a nucleophilic glycosyl acceptor molecule, the nucleophile of which can be oxygen-, carbon-, nitrogen-, or sulfur-based. GTFs play an important role in glycosylation, and it is important to understand the chemistry of these enzymes in mulberry leaves.