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: Extensive literature search revealed multiple cases of coronary artery vasospasm secondary to zolmitriptan , but none of the cases were associated with TS .
### Output Text:
Extensive literature search revealed multiple cases of coronary artery vasospasm secondary to <span class="chemical">zolmitriptan</span> , but none of the cases were associated with TS . 