The Gemini analogs are the last significant contribution to the family of vitamin D derivatives in
medicine, for the treatment of cancer. The first Gemini analog was characterized by two symmetric side
chains at C-20. Following numerous modifications, the most active analog bears a C-23-triple bond, C-26, 27- hexafluoro
substituents on one side chain and a terminal trideuteromethylhydroxy group on the other side chain. This progression was
possible due to improvements in the synthetic methods for the preparation of these derivatives, which allowed for increasing
molecular complexity and complete diastereoselective control at C-20 and the substituted sidechains.