Structure-activity relationships among N-arachidonylethanolamine (anandamide) head group analogues for the anandamide transporter

Two putative endocannabinoids, N-arachidonylethanolamine (AEA) and 2-arachi donylglycerol, are inactivated by removal from the extracellular environmen t by a process that has the features of protein-mediated facilitated diffus ion. We have synthesized and studied 22 N-linked analogues of arachidonylam ide for the purpose of increasing our understanding of the structural requi rements for the binding of ligands to the AEA transporter. We have also det ermined the affinities of these analogues for both the CB1 cannabinoid rece ptor and fatty acid amide hydrolase (FAAH). We have identified several stru ctural features that enhance binding to the AEA transporter in cerebellar g ranule cells. We have confirmed the findings of others that replacing the e thanolamine head group with 4-hydroxybenzyl results in a high-affinity liga nd for the transporter. However, we find that the same molecule is also a c ompetitive inhibitor of FAAH. Similarly, replacement of the ethanolamine of AEA with 9-pyridinyl also results in a high-affinity inhibitor of both the transporter and FAAH. We conclude that the structural requirements for lig and binding to the CB1 receptor and binding to the transporter are very dif ferent; however, the transporter and FAAH share most, but not all, structur al requirements.