4-P-PDOT is an antagonist of the melatonin 2 (MT2) receptor (pKi = 8.37) that displays 60-fold selectivity for MT2 over MT1.[1],[2] 4-P-PDOT is used in cells, explants, and animals to elucidate the role of MT2 in melatonin-mediated signaling.[3],[4]

Reference:
[1]. Browning, C., Beresford, I., Fraser, N., et al. Pharmacological characterization of human recombinant melatonin mt1 and MT2 receptors. Br. J. Pharmacol. 129(5), 877-886 (2000).
[2]. Dubocovich, M.L., Masana, M.I., Iacob, S., et al. Melatonin receptor antagonists that differentiate between the human Mel1a and Mel1b recombinant subtypes are used to assess the pharmacological profile of the rabbit retina ML1 presynaptic heteroreceptor. Naunyn-Schmiedeberg's Arch. Pharmacol. 355(3), 365-375 (1997).
[3]. Juszczak, M., Wolak, M., Bojanowska, E., et al. The role of melatonin membrane receptors in melatonin-dependent oxytocin secretion from the rat hypothalamo-neurohypophysial system - an in vitro and in vivo approach. Endokrynol. Pol. 67(5), 507-514 (2016).
[4]. Shin, E.-J., Chung, Y.-H., TLe, H.-L.T., et al. Melatonin attenuates memory impairment induced by Klotho gene deficiency via interactive signaling between MT2 receptor, ERK, and Nrf2-related antioxidant potential. Int. J. Neuropsychopharmacol. 18(6), (2015).