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: Although suprofen has been associated with the development of acute renal failure in greater than 100 subjects , the mechanism of damage remains unclear .
### Output Text:
Although <span class="chemical">suprofen</span> has been associated with the development of acute renal failure in greater than 100 subjects , the mechanism of damage remains unclear . 