Synthesis and anticholinesterase activity of new bispyridinium compounds.

Synthesis of new bis(1-methylpyridinium) compounds containing a 1,4-diacetylbenzene linkage between the pyridinium moieties from commercially available 2-, 3-, and 4-picoline precursors was accomplished via metallation, reaction of the picolyllithium with 1,4-dicyanobenzene, and subsequent quaternization of the resulting bispyridyl compounds. Acetylcholinesterase inhibitory activity was determined colorimetrically with purified electric eel enzyme. Examination of structure-activity relationships indicated that the 3-substituted pyridinium compound is the most potent isomer, followed by the 2-substituted isomer, and that the 4-substituted analogue is the least active.

A novel tertiary pyridostigmine derivative [3-(N,N-dimethylcarbamyloxy)-1-methyl-delta 3-tetrahydropyridine]: anticholinesterase properties and efficacy against soman.

In an effort to develop an effective centrally acting pretreatment compound against organophosphorus poisons, the tertiary pyridostigmine (Pyr) derivative 3-(N,N-dimethyl-carbamyloxy)-1-methyl-delta 3-tetrahydropyridine (THP) was synthesized and studied for its anticholinesterase properties, as well as its efficacy against soman intoxication in guinea pigs. Injection of THP (262 micrograms/kg, im) into adult male guinea pigs caused inhibition of blood (30%) and brain (25%) acetylcholinesterase (AChE), showing that THP penetrates the blood-brain barrier. Pyr (131 micrograms/kg, im) caused AChE inhibition in the blood (59%), but not in the brain. The inhibitory potencies of THP and Pyr were compared by determining their IC50 values for in vitro inhibition of both AChE (brain, erythrocyte) and pseudo-cholinesterase (plasma) in three mammalian species (guinea pig, rat, rabbit). THP, although effective in inhibiting both types of cholinesterase, was in general less potent than Pyr. Pretreatment of guinea pigs with THP (262 micrograms/kg, im) plus Pyr (131 micrograms/kg, im), 30 min prior to subcutaneous soman challenge, with no antimuscarinic or oxime treatment, protected 60% of the animals against 2 X LD50 of soman. Neither THP nor Pyr alone was effective. The protective pretreatment regimen did not prevent convulsions, but shortened the recovery time in surviving animals (median recovery time 1.6 hr, compared to 24 hr in control and other groups of animals pretreated with THP or Pyr alone). A combination of THP and Pyr thus appears to provide a means of evaluating the relative importance of selective peripheral plus central vs peripheral AChE protection against soman.

Inhibition of acetylcholinesterase from electric eel by (-)-and (+)-physostigmine and related compounds.

Unnatural (+)-physostigmine (2) inhibited acetylcholinesterase (AChE) from electric eel considerably less than natural (-)-physostigmine (1), but 2 may because of its possible lower toxicity still be an interesting anticholinesterase agent. (-)-Eseroline (3), a major metabolite of (-)-physostigmine (1) and a potent narcotic analgetic, and its unnatural (+)-antipode (4), were both poor inhibitors of the enzyme. (-)-Dihydrosecophysostigmine (5), a ring-open analog of (-)-physostigmine was less, but (-)-N-methylphysostigmine (6) much more potent than the natural alkaloid. The availability of compounds related to (-)- and (+)-physostigmine by improved chemical synthesis suggests that further structural variation may well lead to other biologically interesting AChE inhibitors.