The hydroxamic acid functionally can be incorporated into simple molecules to produce potent inhibitors of 5-lipoxygenase. The ability of many of these hydroxamates to inhibit leukotriene synthesis in vivo has been measured directly with a rat peritoneal anaphylaxis model. Despite their potent enzyme inhibitory activity in vitro, many orally dosed hydroxamic acids only weakly inhibited leukotriene synthesis in vivo. This discrepancy is attributable at least in part to the rapid metabolism of hydroxamates to the corresponding carboxylic acids, which are inactive against the enzyme. A study of the structural features that affect this metabolism revealed that 2-arylpropionohydroxamic acids are relatively resistant to metabolic hydrolysis. Several members of this class of hydroxamates are described that are orally active inhibitors of leukotriene synthesis.
Cyclic heptapeptide 1, which contains an Arg-Gly-Asp sequence, has good affinity for the platelet receptor GPIIb-IIIa and was chosen for study by 1H NMR techniques. The key RGD sequence of this molecule was found to reside in a conformationally defined type II' Gly-Asp beta-turn, and this information was used in the design of simple non-peptide RGD mimics. Disubstituted isoquinolones, bearing an acidic side chain at position 2 and a basic side chain at position 6, were prepared and were found to have modest affinity for GPIIb-IIIa. Systematic modification of the basic residue contained in these molecules yielded compounds with high affinity for GPIIb-IIIa.
The nature of the carbonyl and nitrogen substituents of hydroxamic acids has a major influence on the biological profile of these compounds. Hydroxamates with small groups such as methyl appended to the carbonyl and relatively large nitrogen substituents generally have longer duration in vivo, produce greater plasma concentrations, and often are more potent inhibitors of in vivo leukotriene biosynthesis than hydroxamic acids with the opposite arrangement. The structure-activity relationships that describe in vitro 5-lipoxygenase inhibitory activity and in vivo leukotriene biosynthesis inhibitory potency for a group of these hydroxamic acids were investigated. While most of the compounds examined were potent in vitro inhibitors of 5-lipoxygenase, their in vivo potencies varied widely. This discrepancy was usually attributable to differences in bioavailability. Substitution patterns are described that produce potent, orally active inhibitors of leukotriene biosynthesis.
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