The invention provides a compound of formula (I)wherein R1-R4 represent different meanings, and pharmaceutically acceptable salts thereof. The invention also provides synthetic procedures for preparing the compounds of formula (I), pharmaceutical compositions comprising them, their use as medicaments, their use as therapeutic active substances for the treatment of conditions mediated by agonizing the orexin 2 receptor, and their use as therapeutic active substances for the treatment of narcolepsy, excessive daytime sleepiness, nighttime insomnia, depression, sleep apnea and jet lag, for promoting wakefulness and emergence from anesthesia, and for preventing diet-induced obesity.
