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: The men were randomly assigned to bupropion SR ( 150 mg twice daily , 117 ) or placebo ( twice daily , 117 ) for 12 weeks .
### Output Text:
The men were randomly assigned to <span class="chemical">bupropion</span> SR ( 150 mg twice daily , 117 ) or placebo ( twice daily , 117 ) for 12 weeks . 