Synthesis and Structure-Activity Relationship Study of Antidiabetic Penta-O-galloyl-D-glucopyranose and Its Analogues Yulin Ren, †,| Klaus Himmeldirk, ‡,| and Xiaozhuo Chen †,‡,§, * Edison Biotechnology Institute, Department of Chemistry & Biochemistry, and Department of Biomedical Sciences, Molecular and Cellular Biology Program, Ohio UniVersity, Athens, Ohio 45701 ReceiVed January 25, 2006 The rapid increase of obesity-associated diabetes has created urgent demands for more effective antidiabetic therapies and pharmaceuticals that are able to address the problems of hyperglycemia and weight gain simultaneously. Our previous studies indicated that the R- and -anomers of penta-O-galloyl-D-glucopyranose (PGG), 2 and 3, act as insulin mimetics that bind to and activate the insulin receptor, stimulate glucose transport in adipocytes, and reduce blood glucose and insulin levels in diabetic and obese animals. In addition, they inhibit differentiation of preadipocytes into adipocytes. These activities suggest that 2 and 3 may reduce blood glucose without increasing adiposity. To investigate the structure-activity relationship of 2 and 3, four series of novel compounds were prepared and their glucose transport stimulatory activities were measured using a radioactive glucose uptake bioassay. The assay results indicate that both the glucose and the galloyl groups are critical to the activity of 2 and 3. It appears that the glucose core provides an optimal scaffold to present the galloyl groups with the correct spatial orientation to induce activity. Moreover, the galloyl groups linked to the 1, 2, 3, and 4 positions of glucose are essential, while the galloyl group connected to the 6 position of 2 is unnecessary for the induction of activity. The discovery that two related novel compounds, 6-deoxytetra-O-galloyl-R-D-glucopyranose (43) and tetra-O-galloyl-R-D-xylopyranose (59), also possess glucose transport stimulatory activity suggests that 2 may be further modified around position 6 to modulate and enhance its efficacy. To test this hypothesis, we developed a new synthetic method that allows for the stereoselective preparation of derivatives of 2 that are modified on C-6. We found that 6-chloro-6- deoxy-1,2,3,4-tetra-O-galloyl-R-D-glucopyranose (80) exhibits a significantly higher glucose transport stimulatory activity than 2. Its activity is comparable to that of insulin. Introduction Diabetes mellitus, which is classified into type I diabetes (T1D) and type II diabetes (T2D), has become a serious health problem worldwide, particularly in developed countries. 1,2 Increasing attention has been focused on the elucidation of the disease mechanisms in order to develop new and more effective therapies. 3,4 T1D is an autoimmune disease characterized by a decrease in pancreatic secretion of insulin, while T2D is a result of insulin resistance and decreased insulin action. 1,5 The deficiency in insulin signaling in both types of diabetes leads to hyperglycemia. 1,5,6 Visceral adiposity is associated with significantly increased risks for T2D, 7,8 and up to 90% of the T2D patients in the United States are either overweight or obese. Therefore, reducing adiposity, a major contributor to obesity, is beneficial for the prevention and treatment of T2D. Most current T2D drugs are both hypoglycemic and weight-gain-promoting, alleviating one problem (hyperglycemia) while aggravating another (weight gain). 4 Developing innovative antidiabetic therapeutics that simultaneously combat both hyperglycemia and overweight is highly desirable. 9-11 Current treatments of diabetes are focused on reducing the blood glucose level with the help of insulin and other hypogly- cemic agents. Mechanistic studies have shown that the transport of blood glucose into cells is largely induced and regulated by the circulating insulin through interaction with the insulin receptors (IR) located primarily in the plasma membrane of adipocytes and muscle cells. 12,13 IR is a heterotetrameric protein consisting of two R- and two -subunits. 12,13 The two extra- cellular R-subunits form the insulin binding domain, 13,14 and the two -subunits, covalently linked to the R-subunits and to each other by disulfide bonds, function as both the transmem- brane and intracellular tyrosine kinase domains of IR. 12-14 The binding of insulin to the extracellular insulin binding site triggers a conformation change of the IR. 12-14 This induces the intra- cellular tyrosine kinase activity of the -subunits, resulting sequentially in autophosphorylation of the tyrosine residues of the -subunits, activation of intracellular protein factors PI-3K, Akt, and GLUT4, and finally transport of glucose into the target cells. 15 All protein factors involved in this insulin-mediated signaling pathway, including IR, can be potential pharmaceutical targets for diabetes treatment. 4,16 IR has been a prime target for the development of antidiabetes pharmaceutics. 16-18 However, a high-resolution crystal structure of IR has not been established, and consequently the detailed information on insulin-IR binding is unavailable. Increased IR- mediated signaling is needed for the control of the blood glucose level in both types of diabetes. 19 Insulin has been the most frequently used antidiabetic agent that targets IR. However, insulin is a polypeptide that has to be invasively introduced (injected). Furthermore, it promotes adiposity and weight gain. Therefore, the discovery and development of nonpeptidyl, nonadiposity-promoting insulin supplements or replacements are highly desirable. 19-21 * To whom correspondence should be addressed. Address: Edison Biotechnology Institute, 109 Konneker Research Laboratories, The Ridges, Ohio University, Athens, Ohio 45701. Phone: 740-593-9699. Fax:740-593- 4795. E-mail: chenx@ohiou.edu. † Edison Biotechnology Institute. | Both authors contributed equally to this work. ‡ Department of Chemistry and Biochemistry. § Department of Biomedical Sciences, Molecular and Cellular Biology Program. 2829 J. Med. Chem. 2006, 49, 2829-2837 10.1021/jm060087k CCC: $33.50 © 2006 American Chemical Society Published on Web 04/08/2006