The synthesis and biological activity of novel CD-ring modified analogues of 22-oxa-1α, 25- dihydroxyvitamin D3, lacking the D-ring and featuring a connection between C-18 and C-21 (spiro [5.5] undecane CF-ring analogues), is described. The central ring system is conveniently synthesised from an achiral intermediate. The analogues have marginal binding affinity for the nVDR and possess low to moderate genomic activity.
