This invention relates to certain unsaturated fatty acid derivatives of therapeutically active 1,3-dioxolane nucleoside analogues and to pharmaceutical formulations containing them. The said derivatives are referred to as “Compounds of formula I” herein. Compounds of formula I can be used in the treatment of a cancerous disease. Treatment of both solid tumours and haematological cancers such as leukaemias, lymphomas and multiple myelomas are included.