Synthesis and biological activity of 22-oxa CD-ring modified analogues of 1alpha,25-dihydroxyvitamin D3: spiro[5.5]undecane CF-ring analogues.

The synthesis and biological activity of novel CD-ring modified analogues of 22-oxa-1alpha,25-dihydroxyvitamin D(3), 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.