1alpha,25-dihydroxyvitamin D(3) (1alpha,25 (OH)(2)D(3)) is a naturally occuring organic compound showing strong calcemic activity and anti-proliferative/differentiation-inducing activity. 1alpha,25 (OH)(2)D(3) is expected to be a therapeutic agent for metabolic bone diseases and cancer treatment. To enhance its selectivity, specificity, and safety as a therapeutic agent, it is required to separate its calcium-regulating activity from its non-calcium-regulating activity. For this reason, a variety of vitamin D analogues have been developed. The analogues with modification of A-ring are promising candidates for this purpose.