On the structural intricacies of a metabolic precursor: Direct spectroscopic detection of water-induced conformational reshaping of mevalonolactone.

We use high-resolution rotational spectroscopy to investigate the structural intricacies of the lactone form of mevalonic acid, precursor of the mevalonate pathway. By combining microwave spectroscopy with supersonic expansions and quantum-chemical calculations, we determine the two most stable conformations of the precursor. Complementary micro-solvation studies reveal that aggregation of the first water molecule induces a substantial structural rearrangement comprising a hydroxy rotation and an endocyclic core torsion to create a favourable geometry to accommodate the water molecule. We discuss the conformational aspects of the precursor in isolation and under micro-hydrated conditions.