Atropine. Molecular model of the tropane alkaloid drug atropine (C17.H23.N.O3). This naturally occurring alkaloid is extracted from plants like deadly nightshade to produce an anti-cholinergic drug (one that blocks the action of the neurotransmitter acetylcholine). Atropine dilates the pupils, increases heart rate, and reduces salivation. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue) and oxygen (red) Illustration.