A new strategy for isoflavone C-glycoside synthesis: The total synthesis of puerarin

Given that C-glucosylisoflavones often possess promising biological activities, the development of an efficient synthetic method for this type of molecules is useful for drug discovery. Accordingly, a highly efficient five-step strategy was developed for the total synthesis of puerarin, an isoflavone C-glycoside. An alkyl substituent 4-CH3OC6H4CH2CH2 with an electron-donating group on the aromatic ring was used to enhance the reactivity of phenol and the regioselectivity of O-C rearrangement of phenol glycoside. Thus, coupling of the ethylbenzene derivative of a phenol 1c with glycosyl trifluoroacetimidate 2 resulted in C-glycoside 3c in a 46.2% yield, which was easily de-tert-butylated with trifluoroacetic acid and oxidized with 2,3-dicyano-5,6-dichlorobenzoquinone to produce deoxybenzoin 5. The ring closure reaction of 5 followed by deprotection gave puerarin. This new synthetic strategy is also suitable for the total synthesis of other C-glucosylisoflavones.