An Efficient Synthesis of Deoxyrhapontigenin-3- O-β- d -glucuronide, a Brain-Targeted Derivative of Dietary Resveratrol, and Its Precursor 4′- O-Me-Resveratrol

Bioactive dietary polyphenols have health benefits against a variety of disorders, but some benefits of polyphenols may be not directly related to them but rather to their metabolites. Recently, we have identified the brain-available phenol glucuronide metabolite deoxyrhapontigenin-3-O-β-d-glucuronide (5) in perfused rat brains following subacute treatment with the stilbene resveratrol (1). However, the role of such a metabolite in the neuroprotective activity of resveratrol (1) is not understood, in part due to the noncommercial availability of 5 for performing biological evaluation in animal models of Alzheimer's disease or other neurological disorders. Here, we describe a concise chemical synthesis of deoxyrhapontigenin-3-O-β-d-glucuronide (5) and its precursor 4-O-Me-resveratrol (2), accomplished in four and six steps with 74 and 21% overall yields, respectively, starting from commercially available 3,5-dihydroxybenzaldehyde. Pivotal reactions employed in the synthesis include the palladium-catalyzed C-C coupling between 3,5-di-tert-butyldiphenylsilyloxystyrene and p-iodoanisole in the presence of tributylamine and the acid-catalyzed glucuronidation between the trichloroacetimidate-activated glucuronic acid and 4-O-Me-resveratrol.