THE [(METHYLOXY)IMINO]METHYL MOIETY AS A BIOISOSTER OF ARYL - A NOVEL CLASS OF COMPLETELY ALIPHATIC BETA-ADRENERGIC-RECEPTOR ANTAGONISTS

Previous studies in the field of beta-adrenergic drugs had supported the hypothesis of the existence of a bioisosterism between the [(methyleneamino)oxy]methyl moiety (C=NOCH2, MAOMM) of type B beta-blocking drugs and the aryl (Ar) of type A beta-blocking agents. In the MAOMM, however, the carbon of the CH2 linked to the oximic oxygen possesses a hybridization (sp(3)) and a geometry different from those of the corresponding carbon of Ar which possesses an sp(2) hybridization. Furthermore, in the MAOMM, in its preferred conformation, the unsaturated portion (C=N) is situated in a spatial area which does not correspond exactly to the area occupied by Ar. The formal inversion of the atomic sequence C=NOCH2 of the MAOMM leads to a different type of group, the [(methyloxy)imino] methyl moiety (CH2ON=C, MOIMM), which, in the E configuration, appears to present greater steric and electronic analogies with an Ar, with respect to the MAOMM. On the basis of these observations, some completely aliphatic (E)-N-(3-amino-2-hydroxypropylidene) (alkyloxy)amino derivatives of type C (11a,b and 12a,b) were synthesized, the their beta-adrenergic properties were compared with those of the corresponding [(methyleneamino)oxy]methyl isomers of type B (19a,b and 20a,b). The similar beta-adrenergic properties of 11,12 and 19,20 evaluated in vitro both by radioligand binding assays and by functional tests on isolated preparations, are discussed on the basis of considerations regarding the spatial correspondences and electronic analogies between the MOIMM and the MAOMM.