The paper presents the synthesis of some natural diterpenoids of ent-kauranic structure, starting from ent-kaur-16-en-19-oic acid, a natural diterpenoid readily available from the dried wastes of sunflower (Helianthus annuus L.). The reported ent-16α,17-dihydroxykauran-19-oic, ent-16α-hydroxy-17-acetoxykauran-19-oic and ent-16α,17-diacetoxykauran-19-oic acids have been previously isolated from different plant sources and showed diverse biological activities, including anti-HIV, anti-cancer and anti-Alzheimer properties. Their chemical synthesis has not been disclosed so far. Additional cytotoxicity studies of the obtained compounds revealed a remarkable cell proliferative effect of parent ent-kaur-16-en-19-oic acid and two of its synthetic derivatives, which is in line with recent pioneering studies in this area.