Total synthesis of calditol: structural clarification of this typical component of Archaea order Sulfolobales.

The original structure of calditol--that is, an open-chain branched nonitol--has recently been questioned by various research groups and cyclopentane-based structures have been proposed. To unambiguously clear up this confusion, four isomeric cyclopentane candidates 26-29 have been synthesized. Of these, compound 27 was found to be fully identical to the natural product present in Sulfolobus solfataricus (A.T.C.C. 49155). The synthesis of 27 uses a samarium-diiodide-induced pinacolization reaction of the ketoaldehyde 15 as the critical step.