Synthesis and structure-toxicity relationships of three new stable analogues of acetyl-seco-hemicholinium-3

Abstract

In order to develop and study inhibitors of neuromuscular function which act presynaptically, three stable analogues of acetyl-seco-hemicholinum-3 (AcHC-3,2) were prepared. These analogues have 2-ethoxyethyltrimethylammonium, 4-oxopentyltrimethylammonium, and n-pentyltrimethylammonium moieties substituted for the 2-acetylethyltrimethylammonium (acetylcholine) moieties of AcHC-3 (2) to form the ether 2, ketone 4, and alkane 5 analoggues of AcHC-3 (2). Although AcHC-3 (2) has been shown to undergo deesterification rapidly in basic solutions and slowly at pH 7.4, it has been found to be stable in H2O or D2O under slightly acidic conditions. All of the analogues are stable for extended time under both slightly acidic conditions and at pH 7.4 in H2O or D3O. It has been found that 2 reacts with acetylcholinesterase and butyrylcholinesterase within seconds in H2O at pH7.4. However, deesterification of 2 with subsequent cyclization to the hemiacetal form of hemicholinium-3 (HC-3, 1) is prevented at pH 7.4, possibly by an irreversible binding of 2 to the enzyme. The analogues 3-5, however, do not react under identical conditions. Mouse toxicity studies (LD50) indicate that 2 is approximately as toxic as HC-3 (1), whereas 3, 4, and 5 are 14.2, 23.8, and 43.1 times less toxic, respectively. The toxic effects of 3-5, like 1 and 2, are antagonized by choline but not by neostigmine in mice. Structure-activity relationships of 2-5 are discussed.

Effect of sulfur substitution for the noncarbonyl oxygen in hemicholinium-3 and acetyl-seco-hemicholinium-3. Synthesis, biological activity, and structure-toxicity relations. 2

“…Both HC-3 (1) and AcHC-3 (3) have an LD50 of 0.13 mg/kg. 4 The other two compounds of interest, i.e., thio-AcHC-3 (12) and thio-seco-HC-3 (11), were equally toxic and 226 times less toxic, respectively.…”

“…12 Substitution of the acyloxy oxygen of acetylcholine with either S or Se, however, leads to the trans conformation for the -NCCBgrouping in the acetylcholine derivatives 8a and 8b (a, B = S; b, B = Se).13-15 Although the depolarizing abilities of 8a and 8b are greatly altered in various pharmacological preparations,16-18 the molecules' roles as substrates of acetylcholinesterase are not altered.19 Similar conformational differences exist for choline (9)20 and thiocholine (10).21 These conformational differences should also carry over to HC-3 (1) and AcHC-3 (3) and their acyloxy sulfur-substituted analogues. Thus, as a logical continuation of our interest in both the configurational and conformational structure-activity relationships of cholinergic compounds, an extensive investigation of thio-seco-hemicholinium-3 (11) and acetylthio-secohemicholinium-3 (12) annd their relationships to HC-3 (1) and AcHC-3 (3) was initiated. Herein we describe the synthesis, chemistry, and preliminary biological activity of 11 and 12 and compare them to the parent compounds acetylase inhibition is in progress and will be reported subsequently.…”

“…reuptake of neuronaUy released catecholamines.4 AcHC-3 (3) slowly undergoes hydrolysis with subsequent cyclization to form HC-3 (1) in water at pH 7.4. Thus it was thought possible that a portion of the pharmacological action of 3 could derive from HC-3 (1) produced in solution.…”

“…reuptake of neuronaUy released catecholamines.4 AcHC-3 (3) slowly undergoes hydrolysis with subsequent cyclization to form HC-3 (1) in water at pH 7.4. Thus it was thought possible that a portion of the pharmacological action of 3 could derive from HC-3 (1) produced in solution. Therefore, three stable seco analogues of AcHC-3 (3)-the ether 4a, the ketone 4b, and the alkane 4c-were synthesized1 **and were found to be 10-40 times less toxic than HC-3 (1) or AcHC-3 (3).…”

“…Thus it was thought possible that a portion of the pharmacological action of 3 could derive from HC-3 (1) produced in solution. Therefore, three stable seco analogues of AcHC-3 (3)-the ether 4a, the ketone 4b, and the alkane 4c-were synthesized1 **and were found to be 10-40 times less toxic than HC-3 (1) or AcHC-3 (3). Each was also found to have some HC-3-like activity, i.e., slowly developing neuromuscular blockade which could be reversed by choline.…”