. . "In a more specific aspect, R3 of Structural Formula (VI) is hydrogen.In certain aspects, the compound of any of structures (I)-(VI) is a free base.Compounds of the invention, including novel compounds of the invention, can also be used in the methods described herein.Sirtuin-modulating compounds of the invention advantageously modulate the level and/or activity of a sirtuin protein, particularly t" . .