In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: In addition , NIK - 247 and tacrine , but not E - 2020 , strongly inhibited butyrylcholinestrase ( BuChE ) in human serum .
### Output Text:
In addition , <span class="chemical">NIK - 247</span> and <span class="chemical">tacrine</span> , but not <span class="chemical">E - 2020</span> , strongly inhibited butyrylcholinestrase ( BuChE ) in human serum . 