## 1 Introduction  
Ginseng is one of the most commonly consumed traditional medicines in many Asian countries. It has been used for many years to maintain physical strength and increase resistance to stress or aging [1]. One of the major pharmacologically active components of ginseng, ginseng, have numerous biological activities, such as anti-inflammatory, anticancer, antiaging, antiviral, and antitumor activities [2; 3; 4; 5; 6]. Ginsenosides are triterpenoid glycosides containing dammarane and are generally divided into three ginseng groups: protopanaxadiol (PD), protopanaxatriol (PT), and oleanolic acid. These compounds have been reported to exhibit a wide variety of physiological and pharmacological properties. F\({}_{2}\), Rh\({}_{2}\), Rg\({}_{3}\), and compound K (CK, 20-O-\(\beta\)-D-glucopyranosyl-20(S)-protonparasacid) are rare ginsenosides, which are present either at low concentrations or absent in ginseng [7; 8]. The variations in the linkage positions and type of sugar result in different pharmacological activities in these ginsenosides. Research has shown that the rare ginsenosides show relatively strong anticancer activities [9]. Compound K (CK) is a key metabolite of ginseng saponin, which is a PD type ginseng, synthesized after their oral administration by intestinal bacteria [10]. It is believed that CK is absorbed from the intestine [11] and impedes the proliferation of many tumor cells, such as liver cancer cells [12], lung carcinoma [13], colorectal carcinoma [14], and glioblastoma [15] by preventing cell growth and inducing apoptosis. CK was also reported to improve the effectiveness of anticancer drugs in some drug-resistant cancer cells [16].  
There has been a continuous search for plant products and the derivatives of such products that may have health benefits for humans. Ginsenoside transformation has been conducted by physical, chemical, and biological methods [1; 17; 18; 19; 20]. An active ginseng metabolite with different or better bioactivity may be produced by modifying its structure in various ways [21]. Therefore, several studies of the biotransformation of major ginseng have been done on microorganisms for decades [21; 22; 23]. However, transformation by chemical methods is prone to many side reactions, such as hydroxylation, hydration, and epimerization [24]. Regiospecific glycosylation is an effective way to achieve structurally diversified compounds using a simple reaction process, such as an enzymatic method rather than a complicated method using chemicals. Glycosyltransferase enzymes are mainly utilized for the synthesis of complex oligosaccharides and glycoconjugates [25; 26]. Glycoslation may improve the biological properties, enhance the physical and chemical stability and solubility, and amend the subcellular localization of the parent compound. In the present study, we have synthesized a derivative of CK enzymatically by using a \(\beta\)-1,4-galactosidaseyltransferase (LgtB) and have evaluated the anti-proliferative activity of the newly synthesized compound on gastric cancer-cell lines (AGS), skin melanoma (B16F10), cervical carcinoma (HeLa), and brain carcinoma (U87 MG). The activity of the synthesized compound was investigated and compared with other ginsengides like Rh\({}_{2}\), CK, and 3-O-\(\beta\)-D-glucopyranosyl-12-O-\(\beta\)-D-glucopyranosyl-20(S)-protopanaxadiol (F12 or F2) (Figure 1). Previously, a similar report on the modification of CK to galactose conjugated derivative was performed using bovine GalT [26], but its anticancer activity has not yet been tested.