“Mammalian ω3- and ω6-PUFAs are synthesized from essential fatty acids (EFAs) or supplied by the diet. PUFAs are constitutive elements of membrane-architecture and precursors of lipid signaling molecules. EFAs and long chain PUFAs are precursors in the synthesis of endocannabinoid-ligands of the Gi/o-protein coupled cannabinoid receptors 1 and 2 in the endocannabinoid-system, which critically regulates energy homeostasis, as metabolic signaling system in hypothalamic neuronal circuits, and behavioral parameters. We utilized the auxotrophic fatty acid desaturase 2 deficient (fads2-/-) mouse, deficient in long chain PUFA-synthesis, to follow the age dependent dynamics of the PUFA pattern in the CNS-phospholipidome in unbiased dietary studies of three cohorts on sustained long chain PUFA-free, ω6-arachidonic and ω3-docosahexaenoic acid supplemented diets and their impact on the precursor pool of CB1 ligands. We discovered the transformation of eicosa-all cis-5,11,14-trienoic acid, uncommon in mammalian lipidomes, into two novel endocannabinoids, 20:35,11,14-ethanolamide and 2-20:35,11,14-glycerol, acting as ligands of CB1 in HEK293-cells. Labeling experiments excluded a Δ8-desaturase activity and proved the position-specificity of FADS2. The fads2 -/- mutant might serve as an unbiased model in vivo in the development of novel CB1-agonists and antagonists.”