CoMFA analysis of the human beta(1)-adrenoceptor binding affinity of a series of phenoxypropanolamines

A series of 36 phenoxypropanolamines was examined to determine the structure--activity relationships of beta-adrenoceptor (beta-AR) antagonists for the human beta(1)-AR. The binding affinities of all the compounds were determined for human beta(1)-ARs expressed in Chinese hamster ovary cells and the antagonist potency for rat atrial beta(1)-ARs was determined for 32 of these compounds for comparative purposes. The compounds, based upon a phenoxypropanolamine core structure with various meta-, ortho-, para- and amine-substituents, displayed binding affinities (pK(i)) for the human beta(1)-AR ranging from 5.49 to 9.35. Antagonist potencies (pA(2)) in the rat ranged from 5.52 to 9.56 and correlated with the human binding affinities (r(2)=0.86). Twenty-six compounds were used as the training set for comparative molecular field analysis (CoMFA) of antagonist binding affinity at the human beta(1)-AR and also of antagonist potency for rat atrial beta(1)-ARs. The CoMFA models were derived using both the CoMFA electrostatic and steric field parameters. The initial human beta(1)-AR model (n=26, q(2)=0.59, ONC=6, SE(CV)=0.70, r(2)=0.98, SE(non-CV)=0.16, F(6,19)=148) predicted the binding affinities of seven out of ten test compounds, not included in the training set, with residual pK(i) values less-than-or-equal0.50. The final human beta(1)-AR model (n=36, q(2)=0.66, ONC=5, SE(CV)=0.61, r(2)=0.95, SE(non-CV)=0.24, F(5,30)=107), consisting of the training set plus the test set of compounds, may prove useful in the design of new phenoxypropanolamine type beta(1)-AR antagonists. The initial rat beta(1)-AR model (n=26, q(2)=0.42, ONC=6, SE(CV)=0.76, r(2)=0.94, SE(non-CV)=0.25, F(6,19)=47) predicted the affinities of five out of six test compounds with residual pA(2) values less-than-or-equal0.50. The final rat beta(1)-AR model (i.e. training set plus test set of compounds) (n=32, q(2)=0.38, ONC=5, SE(CV)=0.69, r(2)=0.93, SE(non-CV)=0.24, F(5,26)=67) in particular has a low q(2) value, indicating that, at least for the rat, the biologically active phenoxypropanolamine conformation may be quite different to the low energy extended conformation chosen for this CoMFA study.