The cloning of multiple serotonin (5-HT) receptors has improved understanding of their structural similarities and differences. Rat 5-HT1B and human 5-HT1DP receptors are species homologs, with 5-HT1D receptors functioning similarly to rodent 5-HT1B autoreceptors in humans. Sumatriptan, a 5-HT1D ligand used for migraine, has limited selectivity for 5-HT1D versus 5-HT1A receptors, reducing its pharmacological utility and potentially mediating side effects. While sumatriptan's efficacy has spurred development of newer 5-HT1D agents, existing compounds still lack sufficient selectivity. Observing a possible hydrophobic binding region at the 5-position of serotonin for 5-HT1D receptors and structural differences between 5-HT1D and 5-HT1A receptors, we hypothesized that incorporating a hydrophobic substituent at the 5-position could enhance selectivity. We report the synthesis, radioligand binding, and functional data for 5-(nonyloxy)tryptamine (NOT; 4), a novel 5-HT1DP agonist. Synthesis of 4 involved N-protection of 5-(benzyloxy)tryptamine as its N-acetyl derivative, hydrogenolysis to remove the benzyl group, O-alkylation with n-nonyl bromide, and amide hydrolysis, yielding 4. Radioligand binding assays showed 4 binds human 5-HT1DP receptors with ~5-fold higher affinity than sumatriptan (Ki = 1.2 vs. 5.5 nM) and exhibits 260-fold selectivity for 5-HT1DP versus 5-HT1A receptors—the highest reported to date. It also has ~10-fold selectivity for 5-HT1DP versus 5-HT1Da receptors and retains high selectivity over other 5-HT receptor subtypes. Functional assays evaluating effects on forskolin-stimulated cAMP production demonstrated 4 is a 5-HT1D full agonist (ED50 = 68 ± 19 nM) with no antagonist properties. At concentrations up to 1 μM, 4 lacks 5-HT1A agonist or antagonist activity. In summary, 5-(nonyloxy)tryptamine (4) is a novel high-affinity 5-HT1DP-selective agonist with a hydrophobic 5-position substituent. It binds human 5-HT1DP receptors with higher affinity and displays greater 5-HT1DP versus 5-HT1A selectivity than sumatriptan, behaves as a full 5-HT1D agonist, and lacks 5-HT1A activity, representing a valuable pharmacological tool.