It was previously reported that 6β-aminomorphinan derivatives show high affinity for opiate receptors. Novel 6β-heteroarylamidomorphinanes were designed based on the MOR selective antagonist NAP. The 6β-aminomorphinanes were prepared by stereoselective Mitsunobu reaction and subsequently acylated with nicotinic acid and isonicotinic acid chloride hydrochlorides. The receptor binding and efficacy were determined in vitro and the analgesic activity was studied in vivo. The in vitro studies revealed moderate selectivity for the MOR. At least two compounds in this series exhibited a long-lasting analgesic response when administered subcutaneously and intracerebroventricularly. When the substances were given intracerebroventricularly to mice, they showed analgesic potency comparable to morphine.