Medicinal chemistry of muscarinic agonists for the treatment of dementia disorders.

Alzheimer disease (AD) is a neurodegenerative disorder lacking an effective therapy. The etiology is controversial and among different drug strategies, the cholinergic approach has gained great interest owing to biochemical and pharmacological evidence of the crucial role of acetylcholine in cognitive functions. Several attempts exploiting the boosting of the cholinergic system are currently under way. Inhibitors of the acetylcholinesterase enzyme sustain the availability of the natural transmitter by limiting its removal from the synapse. In a different approach, exogenous agonists may substitute acetylcholine itself. In this way the issue of the extensive cholinergic cell loss occurring in AD and leading to a reduction of cholinergic functions, could be advantageously bypassed. Moreover the discovery of different muscarinic receptor subtypes, most notably the M1 subtype as that involved in the postsynaptic transmission, has offered new opportunities to face the problem in a very specific way. In this line of research, we have now identified BIMC 182 as a new functionally selective M1 agonist. Whereas its affinity for the different receptor subtypes is almost similar (radioreceptor binding), its functional selectivity is pointed out by specific "in vitro" models. BIMC 182 behaves as a full agonist at M1 (rat superior cervical ganglion, pD2 4.8) and as a partial agonist at M2 and M3 sites (g.p. heart pD2 = 5.4 and g.p. ileum pD2 = 4.5). The agonist profile is further confirmed in hm1 transfected CHO cells where the compound stimulates PI turnover. BIMC 182 penetrates well the brain as shown by the increase in the energy of the low frequency band (theta waves) in the cortical EEG of rabbits (3 mg/kg i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis and biological evaluation of new antimuscarinic compounds with amidine basic centers. A useful bioisosteric replacement of classical cationic heads.

Amidines (guanidine, formamidine, and acetamidine) were introduced as substitutes for the cationic heads present in atropine, scopolamine, and corresponding quaternary derivatives. Amidine systems are intermediate in structure between tertiary amines and quaternary compounds, at least as regards ionization and electronic properties, but differ from the latter in shape (planar not tetrahedral). They have additional binding opportunities on account of their hydrogen-bond-forming capacity. The effect of the introduction of these cationic heads on the affinity for different muscarinic acetyl choline receptor (m-AcChR) subtypes was investigated in vitro, in binding displacement studies, and in functional tests on isolated organs. All new compounds (3a,b-5a,b) showed high affinity for the m-AcChR considered, comparable or slightly inferior to that of the parent drugs (1a-e). The new amidine derivatives proved effective as spasmolytic agents, with little tendency to cause central effects. However, no separation was achieved of spasmolytic and other untoward effects, like inhibition of salivation. Thus, amidine moieties are effective bioisosteric substitutes for conventional cationic heads present in antimuscarinic agents. Their unusual physical-chemical properties make them useful tools when modulation of pharmacokinetic or pharmacodynamic effects is required.

N-(fluoroethyl)(imidazolylphenyl)formamidines. The issue of the active species of mifentidine.

Three N-fluoroethyl-substituted (imidazolylphenyl)formamidine derivatives, namely, 2-fluoroethyl (3b), 2,2-difluoroethyl (3c), and 2,2,2-trifluoroethyl (3d), were prepared to test the effect of fluorine substitution on basicity and, then, on H2-antagonist affinity in comparison with the unsubstituted N-ethyl derivative (3a), taken as a model of mifentidine. Imidazolylphenyl isothiocyanate (1), obtained by reaction of 4-(aminophenyl)imidazole with carbon disulfide and ethyl chloroformate, was condensed with the requisite 2-fluoro-substituted ethylamines to give the intermediate thioureas (2b-d). Desulfurization of these thioureas by Raney nickel furnished the desired formamidines (3b-d). Increasing fluorine substitution was found to decrease basicity of the formamidino group substantially (3a, pKa = 8.65; 3b, pKa = 8.12; 3c, pKa = 6.60; 3d, pKa = 6.14), while having a modest effect on the imidazole portion. Affinity at the H2 receptors, evaluated from antagonism of histamine-stimulated chronotropic response on guinea pig atria, increased following fluorine substitution (3a, KB = 177; 3b, KB = 61; 3c, KB = 21; 3d, KB = 7.6). It is concluded that H2-receptor antagonist affinity in the mifentidine series is mostly dependent on the availability of the neutral species. These data support the hypothesis that mifentidine, like cimetidine, acts through the neutral species.

Synthesis and analgesic activity of N-substituted 6,7-benzomorphans.

Some new N-substituted 6,7-benzomorphans were prepared and tested for analgetic activity. The compounds (I) and (II), which proved the most active in a preliminary screening, were submitted to a more detailed investigation, and their ED50 was determined in mice by the phenylquinone, hot-plate and tail-pinch tests. Studies of acute toxicity and physical dependence capacity were also performed.