Structure-guided optimization was used to design new analogues of 1alpha,25-dihydroxyvitamin D(3) bearing the main side chain at C12 and a shorter second hydroxylated chain at C17. The new compounds 5a-c were efficiently synthesized from ketone 9 (which is readily accessible from the Inhoffen-Lythgoe diol) with overall yields of 15%, 6%, and 3% for 5a, 5b, and 5c, respectively. The triene system was introduced by the Pd-catalyzed tandem cyclization-Suzuki coupling method. The new analogues were assayed against human colon and breast cancer cell lines and in mice. All new vitamin D(3) analogues bound less strongly to the VDR than 1alpha,25-dihydroxyvitamin D(3) but had similar antiproliferative, pro-differentiating, and transcriptional activity as the native hormone. In vivo, the three analogues had markedly low calcemic effects.