Herkinorin

Herkinorin is an opioid analgesic that is an analogue of the natural product Salvinorin A. It was discovered in 2005 during structure-activity relationship studies into neoclerodane diterpenes, the family of chemical compounds of which Salvinorin A is a member.

Unlike Salvinorin A which is a selective κ-opioid agonist with no significant μ-opioid receptor affinity, herkinorin is a μ-opioid agonist with more than 100x higher μ-opioid affinity and 50x lower κ-opioid affinity compared to Salvinorin A. Herkinorin is a semi-synthetic compound made from Salvinorin B, which is made from Salvinorin A, which is extracted from the plant Salvia divinorum.

Presumably herkinorin produces similar effects to other μ-opioid agonists, such as analgesia and sedation, along with side effects such as nausea, itching, vomiting and respiratory depression which may be harmful or fatal. However unlike most μ-opioid agonists, herkinorin does not promote the recruitment of β-arrestin-2 to the intracellular domain of the μ-opioid receptor, and so does not induce receptor internalisation. This means that herkinorin may not produce tolerance and dependence in the same way as other opioids, although some development of tolerance through other mechanisms has been observed.