Regarding its structure, quinuclidine is unusual in that the methylene hydrogen atoms are eclipsed within each of the three ethylene linkages. Furthermore, the cyclohexane rings, of which there are three, adopt the boat conformations, not the usual chair conformations.[1]
Quinuclidine is a relatively strong organic base with pKa of the conjugate acid of 11.3.[2] The basicity of other quinuclidines have been evaluated:
3-hydroxy- quinuclidine (9.9), 3-acetoxyquinuclidine (9.3), 3-chloroquinuclidine (8.9), DABCO (8.7), and 3-quinuclidone (7.2).[3]
It forms adducts with a variety of Lewis acids. Because of its compact structure, quinuclidine binds to trimethylborane more tightly than does triethylamine.[4]
Quinuclidine is structurally related to DABCO, in which the other bridgehead is also nitrogen, and to tropane, which has a slightly different carbon frame. Due to this similarity, as with tropane, certain quinuclidines such as solifenacin, aclidinium bromide and 3-Quinuclidinyl benzilate possess antimuscarinic properties.
Cinchona alkaloids, e.g. quinine, feature quinuclidine substituents.[4]Aceclidine, a simple quinuclidine derivative, is a drug used for treatment of glaucoma.
