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: However , clinical reports suggest that , under some circumstances , sirolimus is associated with proteinuria and acute renal dysfunction .
### Output Text:
However , clinical reports suggest that , under some circumstances , <span class="chemical">sirolimus</span> is associated with proteinuria and acute renal dysfunction . 