6895
N - alkylation of the pyridazinone ring markedly enhances potency against PDE4 but suppresses PDE3 inhibition .
 Chemical: N; Chemical: pyridazinone
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: N; Chemical: pyridazinone