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: Sirolimus is a novel immunosuppressant with potent antiproliferative actions through its ability to inhibit the raptor - containing mammalian target of rapamycin protein kinase .
### Output Text:
<span class="chemical">Sirolimus</span> is a novel immunosuppressant with potent antiproliferative actions through its ability to inhibit the raptor - containing mammalian target of <span class="chemical">rapamycin</span> protein kinase . 