The crystal and molecular structure of (R)-sirtinol-C₂₆H₂₂N₂O₂-a chemo-sensitive enhancer and ligand in metal complexes with important bio-inorganic applications

Sirtinol is a known inhibitor of sirtuin proteins-a family of deacetylases involved in the physiology of aging. Its crystalline structure has never been determined except when bound to Fe(III) where it participates in the seven-fold coordination of the metal or to Cu(II) where it acts as a bidentate or tridentate ligand. Herein, we describe the structure of this important molecule, as follows: (a) the prevalent form of the keto-enol tautomerism in the solid state, and (b) in solution. Do they match? If not, how? The crystals of (R)-sirtinol are characterized by a large number of π-πbonded interactions linking molecules in infinite ribbons, which, in turn, are linked by additional π-πinteractions of a variety of types, and by hydrogen bonds. In the latter case, we confirm by NMR that the X-ray determined position of an important H atom is on a N atom rather than on an O, which is how the molecule is usually depicted.