Struktur und Wirkung des Muscarins,des Muscarons und ihrer Stereoisomeren

Summary All synthetic isomers of (+)-muscarine, the racemic forms of epi-muscarine, allo-muscarine, and epiallo-muscarine are at least 100 times less potent on blood pressure of cats and isolated frog hearts than the natural alkaloid. Only muscarones are more potent and exhibit strong nicotinic action on the frog rectus and in blocking ganglionic and neuro-muscular transmission in the cat. They closely resemble acetylcholine in their structure and action.The activity of the isomers depends on the position of the constituents on the tetrahydrofurane ring. Steric hindrance of the hydroxy or carbonylgroup and of etheroxygen plays an important part in the contact with the cholinergic receptor. As nor-muscarine without the quarternary nitrogen is inactive, at least 3 different points of contact have to be considered. This is stressed by the fact that muscarine is highly stereospecific in its action, whereas muscarone is not.