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: Levobupivacaine , the pure S ( - ) enantiomer of bupivacaine , was developed to improve the cardiac safety profile of bupivacaine .
### Output Text:
<span class="chemical">Levobupivacaine</span> , the pure S ( - ) enantiomer of <span class="chemical">bupivacaine</span> , was developed to improve the cardiac safety profile of <span class="chemical">bupivacaine</span> . 