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: More recently , proteinuria has been reported as a consequence of sirolimus therapy , although the mechanism has remained unclear .
### Output Text:
More recently , proteinuria has been reported as a consequence of <span class="chemical">sirolimus</span> therapy , although the mechanism has remained unclear . 