Structural elaboration of phenylethylamine to spiro[9,10-dihydroanthracene]-9,3'-pyrrolidine (SpAMDA) produces an agent with unexpectedly high affinity (K(i)=4 nM) at 5-HT(2A) receptors. It was shown that SpAMDA acts as a 5-HT(2A) receptor antagonist. The structure and molecular geometry of SpAMDA are not consistent with existing pharmacophore features, and a novel 5-HT(2A) antagonist pharmacophore model is proposed for the binding of aminomethyl-9,10-dihydroanthracene analogs. Thus, SpAMDA may be a structurally novel parent of a new class of 5-HT(2A) receptor antagonists that binds to the receptor in a unique fashion that is distinct from the binding topology of existing 5-HT(2A) receptor antagonists.