[{"from": "human", "value": "What can you tell me about this molecule? [C][N+1][Branch2][Ring2][Branch2][C][C][C@][C@@H1][C][=Branch1][C][=O][C][C][C@][Ring1][#Branch1][Branch2][Ring1][#Branch1][C@H1][Ring1][O][C][C][=C][Ring1][O][C][=Branch1][=Branch2][=C][Branch1][Branch1][C][=C][Ring1][=Branch1][O][O][Ring1][S][O][C][C][C][C][Ring1][Ring1].[Br-1]"}, {"from": "gpt", "value": "The molecule is a methyl derivative of noroxymorphone with selective, opioid-receptor antagonistic activity. Methylnaltrexone displaces opioids from peripheral opioid receptors in the gastrointestinal tract, the bladder, and the skin, resulting in decreases in opioid-related constipation, urinary retention, and pruritis, respectively. Methylnaltrexone does not cross the blood-brain barrier and does not affect the centrally-mediated analgesic effect of opioids."}]