Synthesis and enantioselectivity of the enantiomers of PG9 and SM21, new potent analgesic and cognition-enhancing drugs

Hybridized and isosteric analogues of N1-acetyl-N4-dimethyl-piperazinium iodide (ADMP) and N1-phenyl-N4-dimethyl-piperazinium iodide (DMPP) with central nicotinic action

A series of piperazine derivatives, obtained by hybridization of N1-acetyl-N4-dimethyl-piperazinium iodide (1, ADMP) and N1-phenyl-N4-dimethyl-piperazinium iodide (3, DMPP) or of the corresponding tertiary bases (2, 4) with arecoline (5) and arecolone (6) or by isosteric substitution of the phenyl ring of DMPP, has been synthesized. Hybridization afforded compounds that, both as tertiary bases and as iodomethylates, have no affinity for the nicotinic receptor. On the contrary, isosteric substitution gave compounds that maintain affinity for the receptor; among them, two tertiary bases (37, 38), show affinity in the nanomolar range for the nicotinic receptor. The pharmacological profile of these isomeric compounds is quite interesting as they present differences in their peripheral and central effects, suggesting that they interact with different subtypes of the nicotinic receptor.

Further structure-activity relationships in the series of tropanyl esters endowed with potent antinociceptive activity

Several analogs of the alpha-tropanyl esters of 2-(4-chlorophenoxy)butyric acid (SM21) and 2-phenylthiobutyric acid (SM32), endowed with potent antinociceptive and cognition enhancing activity, were synthesized, aimed at obtaining more potent and safe drug candidates. Variation of the acyl moiety (4-11), as well as the conformational restriction of atropine to give the alpha-tropanyl ester of 2,3-dihydrobenzofurane-3-carboxylic acid (18), practically abolished activity. In the case of 18, the antimuscarinic activity was also severely affected by the conformation restrain. On the contrary, conformational restriction of phenoxybutyric and phenylthiobutyric acid derivatives to give the alpha-tropanyl ester of 2,3-dihydro-benzofurane-2-carboxylic acid and 2,3-dihydro-benzothiophene-2-carboxylic acid (12-17), afforded potent analgesic drugs that unfortunately were too toxic to be reliable drug candidates. A series of related esters of benzofurane-3-carboxylic acid (20-27) and benzothiophene-3-carboxylic acid (28) were also studied and found to be potent but toxic analgesics.

Chiral synthesis and pharmacological evaluation of the enantiomers of SM32, a new analgesic and cognition-enhancing agent

The enantiomers of 3-alpha-tropyl 2-(phenylthio)butyrate (SM32, 1) were prepared by chiral synthesis and tested for analgesic, cognition-enhancing, and ACh-releasing properties. They show enantioselectivity in some of the tests, the eutomer being related in configuration to R-(+)-hyoscyamine.