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: WR - 2721 or amifostine initially was developed to protect military personnel in the event of nuclear war .
### Output Text:
<span class="chemical">WR - 2721</span> or <span class="chemical">amifostine</span> initially was developed to protect military personnel in the event of nuclear war . 