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: Several recent studies have stressed the renal sparing features of sulindac , owing to its lack of interference with renal prostacyclin synthesis .
### Output Text:
Several recent studies have stressed the renal sparing features of <span class="chemical">sulindac</span> , owing to its lack of interference with renal <span class="chemical">prostacyclin</span> synthesis . 