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The design of potent and selective non-peptide antagonists of endothelin-1 (ET-1) and its related isopeptides are important tools defining the role of ET in human diseases. In this report we will describe the detailed structure-activity relationship (SAR) studies that led to the discovery of a potent series of butenolide ETA selective antagonists. Starting from a micromolar screening hit, PD012527, use of Topliss decision tree analysis led to the discovery of the nanomolar ET(A) selective antagonist PD155080. Further structural modifications around the butenolide ring led directly to the subnanomolar ETA selective antagonist PD156707, IC50's = 0.3 (ET(A)) and 780 nM (ET(B)). This series of compounds exhibited functional activity exemplified by PD156707. This derivative inhibited the ETA receptor mediated release of arachidonic acid from rabbit renal artery vascular smooth muscle cells with an IC50 = 1.1 nM and also inhibited the ET-1 induced contraction of rabbit femoral artery rings (ETA mediated) with a pA2 = 7.6. PD156707 also displayed in vivo functional activity inhibiting the hemodynamic responses due to exogenous administration of ET-1 in rats in a dose dependent fashion. Evidence for the pH dependence of the open and closed tautomerization forms of PD156707 was demonstrated by an NMR study. X-ray crystallographic analysis of the closed butenolide form of PD156707 shows the benzylic group located on the same side of the butenolide ring as the gamma-hydroxyl and the remaining two phenyl groups on the butenolide ring essentially orthogonal to the butenolide ring. Pharmacokinetic parameters for PD156707 in dogs are also presented.

Screening of a compound library against endothelin receptors (ETA and ETB) revealed PD 102566 (compound 1) as an ETA selective antagonist. Synthesis and structure-activity relationships (SAR) of a series of analogs are described.

A new type of dihydroquinazoline-based inhibitor of acetylcholinesterase (AChE) is described. These compounds were designed to interact with the catalytic site of AChE in a manner similar to the known inhibitor tacrine. In a manner analogous to the potency enhancement obtained by addition of chlorine atoms to the tacrine molecule, a 3-chloro derivative of the parent hexahydroazepino[2,1-b]quinazoline structure was found to be about 8 times more potent as an AChE inhibitor than the unsubstituted compound.

Screening of a compound library against endothelin receptors (ETA and ETB) revealed PD 102566 (compound 1) as an ETA selective antagonist. Synthesis and structure-activity relationships (SAR) of a series of analogs are described.