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: Celecoxib ( CE ) is a novel drug , with high selectivity and affinity for COX - 2 enzyme .
### Output Text:
<span class="chemical">Celecoxib</span> ( <span class="chemical">CE</span> ) is a novel drug , with high selectivity and affinity for COX - 2 enzyme . 