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: We studied a 37 - year - old man who developed persistent segmental dystonia within 2 months after starting sulpiride therapy .
### Output Text:
We studied a 37 - year - old man who developed persistent segmental dystonia within 2 months after starting <span class="chemical">sulpiride</span> therapy . 