PAF-induced in vitro platelet-aggregation and in vivo hypotension tests. Several of these compounds exhibited more potent activity than the structurally related 2-[N-acetyl-N-[[[[2-methoxy-3-[(octadecylcarbamoyl) oxy]propoxy]carbonyl]amino]methyl]-1-ethylpyridinium chloride (CV-6209, 3) in the in vitro assay, whereas all showed less potency in the in vivo test. The role of both the substituent nature