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: Flestolol is metabolized by plasma esterases and has an elimination half - life of approximately 6 . 5 minutes .
### Output Text:
<span class="chemical">Flestolol</span> is metabolized by plasma esterases and has an elimination half - life of approximately 6 . 5 minutes . 