New water-soluble pilocarpine derivatives with enhanced and sustained muscarinic activity

The synthesis of an homologous series of new water-soluble derivatives of pilocarpine is described. The new compounds, referred to as soft quaternary salts, are water soluble by virtue of a cationic ammonium head and their lipophilicity can be modulated by manipulating the size and the nature of the substituent in the inactive portion of the molecule. The miotic activity of the compounds was evaluated after administration to normotensive New Zealand White rabbits. Changes in pupil size indicated a substantial cholinergic effect on the iridal sphincter musculature. The best candidate, compound 20, which has a 16-carbon side chain, was evaluated for reduction of the intraocular pressure in genetically glaucomatous Beagles. Compound 20 is superior to pilocarpine in both tests, with a potency 10 to 20 times that of the parent compound and a longer duration of action. It is suggested that the new compounds are prodrug forms of pilocarpine which greatly enhance the corneal bioavailability of the parent compound.