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: 5 - Fluorouracil cardiotoxicity induced by alpha - fluoro - beta - alanine .
### Output Text:
<span class="chemical">5 - Fluorouracil</span> cardiotoxicity induced by <span class="chemical">alpha - fluoro - beta - alanine</span> . 