DESIGN, SYNTHESIS, AND BIOLOGICAL-ACTIVITY OF METHOCTRAMINE-RELATED TETRAAMINES BEARING AN 1-DIHYDRO-6H-PYRIDO[2,3-B][1,4]BENZODIAZEPIN-6-ONE MOIETY - STRUCTURAL REQUIREMENTS FOR OPTIMUM OCCUPANCY OF MUSCARINIC RECEPTOR SUBTYPES AS REVEALED BY SYMMETRICAL AND UNSYMMETRICAL POLYAMINES

Tetraamines 5-13 and diamines 14-17 as well as monoamine 18 were synth esized, and their biological profiles at muscarinic receptor subtypes were assessed by functional experiments in isolated guinea pig left at rium (M(2)) and ileum (M(3)) and by binding assays in rat cortex (M(1) ), heart (M(2)), and submaxillary gland (M(3)) homogenates and NG 108- 15 cells (M(4)) An appropriate number and type of substituents on the terminal nitrogens of a tetraamine backbone afforded compounds, such a s tripitramine (8) and dipitramine (6), which are endowed with differe nt affinity and selectivity profiles. Tripitramine, a nonsymmetrical t etraamine, resulted in the most potent and the most selective Mt musca rinic receptor antagonist so far available (pA(2) = 9.75 +/- 0.02; pK( i) = 9.54 +/- 0.08). However, it failed to discriminate between M(1) a nd M(4) muscarinic receptor subtypes (selectivity ratio: M(2)/M(3) 160 0-2200; M(2)/M(1), 81; M(2)/M(4), 41; M(1)/M(3), 28; M(4)/M(3), 55; M( 4)/M(1), 2). Dipitramine, another nonsymmetrical tetraamine bearing tw o substituents on the same terminal nitrogen, displayed the highest af finity for M(1) muscarinic receptors (pK(i) = 8.60 +/- 0.15) and was a ble to differentiate, unlike 8, all four muscarinic receptor subtypes investigated (selectivity ratio: M(1)/M(2), 5; M(1)/M(3), 2700; M(1)/M (4), 76; M(2)/M(3), 260-520; M(2)/M(4), 15; M(4)/M(3), 35). The result s are discussed in terms of a possible mode of interaction of tetraami nes with muscarinic receptor subtypes.