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: Pharmacology of ACC - 9653 ( phenytoin prodrug ) .
### Output Text:
Pharmacology of <span class="chemical">ACC - 9653</span> ( <span class="chemical">phenytoin</span> prodrug ) . 