This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Autonomic nervous system, Subject name: Pharmacology
[{'content': 'Neostigmine does not able to cross blood brain barrier because of its \nSelect and explain. \nA. Primary structure, B. Secondary structure, C. Teiary structure, D. Quaternary structure', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Refer kDT 6/e p 101 Quaternary ammonium compounds are water soluble and thus cannot cross blood brain barrier. New Stickman is a quaernary derivative whereas physostigmine is a teiary amine', 'role': 'assistant'}]