New approach to paricalcitol synthesis

Paricalcitol, an analog of vitamin D, is used as a drug for the prevention and treatment of secondary hyperparathyroidism. In this paper, a new strategy for the synthesis of paricalcitol is described. This approach includes three main improvements: one-pot regioselective ozonization cleavage of the side-chain and methylene at C-19, free-radical reduction removal of the OH group formed at C-19, and side-chain assembly using a Wittig reaction. These are all new strategies for the synthesis of 19-nor-vitamin D2 compounds.