5-Amino-2-phenylpyrimidin-6-ones, some of their desamino derivatives, and miscellaneous derivatives were synthesized and biologically evaluated on both in vitro activity and oral activity in an acute hemorrhagic assay. These compounds contained an alpha-keto-1,3,4-oxadiazole moiety to bind covalently to the Ser-195 hydroxy group of human neutrophil elastase (HNE). Among those tested, compounds 11a-c,e,i-l(F), 11d,e,k(H), 21d,e,k(F), and 21d,e(H) showed a good oral profile. RS-Mixture 3(H) was selected for clinical evaluation based on its oral potency, duration of action, enzyme selectivity, safety profile, and ease of synthesis. Structure-activity relationships (SARs) are discussed.

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ABSTRACT-To develop a model of chronic experimental asthma in guinea pigs, the animal was forced to inhale the mist of a low dose of ovalbumin (OA) adsorbed on fine Al(OH)3 for sensitization once every 4 weeks. The animal was challenged by inhalation with the mist of OA on day 14 after the respective sensitizations. Either the first or the second antigen challenge markedly induced an early asthmatic response (EAR), whereas there was hardly any late asthmatic response (LAR). At the 3rd challenge, LAR also emerged with some severity. These dual responses were consistently observed until the 10th challenge. On the other hand, repeated inhalation/challenge, once every 2 weeks, with OA alone at the same dose tended to lead to the desensitization of the EAR. In addition, LAR was hardly observed throughout the experiments. In both groups, Ti and IgE levels in the serum were elevated by the repetitive antigen inhalations, yet no obvious relationship between these antibody levels and the intensity of either EAR or LAR was recognized. The present results indicate that the asthmatic model with reproducible EAR and LAR developed in this study appears to be very beneficial for the investigation of bronchial asthma and for the assessment of anti-asthma drugs.

CysLT2 receptors were expressed in lung specimens isolated from asthma subjects. Activation of CysLT2 receptors may contribute to antigen-induced bronchoconstriction in certain asthma population.