Regioselective Diversification of a Cardiac Glycoside, Lanatoside C, by Organocatalysis

Acylation of lanatoside C in the presence of organocatalyst 5 gave the C(4′′′′)-O-acylate in up to 90% regioselectivity (catalyst-controlled regioselectivity). Various functionalized acyl groups can be introduced at the C(4′′′′)-OH by a mixed anhydride method in the presence of 5 or the related organocatalyst. On the other hand, DMAP-catalyzed acylation of lanatoside C gave the C(3′′′′)-O-acylate in up to 97% regioselectivity (substrate-controlled regioselectivity). Thus, diverse regioselective introduction of acyl groups among eight free hydroxy groups of lanatoside C was achieved.