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: Whether proteinuria was due to sirolimus or only a consequence of calcineurin inhibitors withdrawal remained unsolved until high range proteinuria has been observed during sirolimus therapy in islet transplantation and in patients who received sirolimus de novo .
### Output Text:
Whether proteinuria was due to <span class="chemical">sirolimus</span> or only a consequence of calcineurin inhibitors withdrawal remained unsolved until high range proteinuria has been observed during <span class="chemical">sirolimus</span> therapy in islet transplantation and in patients who received <span class="chemical">sirolimus</span> de novo . 