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: Everolimus , a derivative of sirolimus , seems to mediate antileukemia effects .
### Output Text:
<span class="chemical">Everolimus</span> , a derivative of <span class="chemical">sirolimus</span> , seems to mediate antileukemia effects . 