Dudley E. McMackins

A novel series of orally active antiplatelet agents

A novel series of orally active fibrinogen receptor antagonists has been discovered through structural modification of our lead intravenous (iv) antiplatelet agent, 5-(4-amidinophenyl)pentanoyl-Asp-Phe 1 (SC-52012). The Asp-Phe amide bond was removed through truncation to a 3-substituted beta-amino acid aspartate mimetic which resulted in a tripeptide mimetic inhibitor of lower molecular weight (from 482 to the 330-390 g mol-1). The zwitterionic nature of the inhibitor was masked through the preparation of an ethyl ester prodrug. A lead compound from this series, 5-(4-amidinophenyl)pentanoyl-3-(3-pyridyl)propanoic acid 19a, was found to be a potent inhibitor of canine platelet aggregation in vitro (collagen, platelet rich plasma, PRP, IC50 = 270 nM). In further canine studies, oral administration of different ester pro-drugs of 19a at 10 mg kg-1 resulted in the following oral systemic activities: pivaloyloxymethyl ester derivative 19p (5.1 +/- 1.5% OSA), cyclohexyl ester derivative 19c (9.2 +/- 1.9% OSA), and ethyl ester derivative 19e (9.9 +/- 2.3% OSA).

Design of orally active, non-peptide fibrinogen receptor antagonists. An evolutionary process from the RGD sequence to novel anti-platelet aggregation agents

The evolutionary process from the Arg-Gly-Asp-Phe (RGDF) tetrapeptide to potent orally active anti-platelet agents is presented. The RGD sequence is an important component in the recognition of fibrinogen by its platelet receptor GP IIb-IIIa (integrin alpha IIb beta 3). This work concentrates on the replacement of the Arg-Gly dipeptidyl fragment by an acylated aminobenzamidine. The C-terminal fragment has been replaced by a variety of beta-amino acids, expanding on a previously reported paradigm. The lead compounds showed good potency in an in vitro platelet aggregation assay (dog PRP/ADP). The affinity for the fibrinogen receptor was confirmed in several cases by the ability to inhibit 125I fibrinogen binding to activated human platelets. The ethyl ester prodrug form was tested by oral administration to dogs and monitoring of the anti-platelet effect on ex vivo collagen induced platelet aggregation. From the structural studies reported, the 4-[[(aminoiminomethyl)phenyl]amino]-4-oxobutanoic acid (5) was the best surrogate for the Arg-Gly dipeptide. Several conformationally restricted analogues are also reported which are compatible with the hypothesis of RGD binding to the alpha IIb beta 3 in a turn-extended-turn conformation. The structure-activity relationships described also underline the importance of the beta-amino acid substitution for potency. In particular, the absolute configuration at the beta-carbon was crucial for high affinity. The best acid/ester pairs reported in this study had high potency (acid PRP/ADP IC50 approximately 50 nM) and showed good oral activity in dogs at 5 mg/kg per os (ethyl ester).

Electrogenemtion of Mn(III) in an undivided cell

The electrochemical oxidation of manganous ion to manganic ion in acetic acid may be efficiently carried out in a parallel plate undivided cell. Reduction of manganic ion to manganous ion at the cathode is a relatively inefficient reaction, allowing the formation of solutions of manganic ion as high as 0.05 mol dm−3, at greater than 80% current efficiency. The effects of the major variables have been evaluated.