AbstractUsing a highly stereoselective Evans aldol reaction for the introduction of the stereogenic center at C‐25, we describe an efficient synthesis of the orthogonally diprotected (25S)‐26‐hydroxycholesterol 11. In a few synthetic steps, this crucial intermediate 11 has been converted into the four (25S)‐cholesten‐26‐oic acids 1–4, which have been obtained in 12–15 steps and 19–53 % overall yield based on commercially available 3β‐hydroxychol‐5‐en‐24‐oic acid (5). Our biological studies of the compounds 1–4 reveal that (25S)‐Δ7‐dafachronic acid (1) represents the most active steroidal ligand for the hormonal receptor DAF‐12 in Caenorhabditis elegans. Moreover, the saturated (25S)‐dafachronic acid (3) represents a new ligand for this receptor and the (25S)‐steroidal acids are more active as compared to their corresponding (25R)‐counterparts.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)