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: To elucidate the epidemiology of the syndrome , a case - control study was performed , comparing 62 of the case patients who had been reported to the spontaneous reporting system to 185 suprofen - exposed control subjects who did not have the syndrome .
### Output Text:
To elucidate the epidemiology of the syndrome , a case - control study was performed , comparing 62 of the case patients who had been reported to the spontaneous reporting system to 185 <span class="chemical">suprofen</span> - exposed control subjects who did not have the syndrome . 