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: Anginal episodes were rare : only one patient had angina ( during 5 - FU infusion ) .
### Output Text:
Anginal episodes were rare : only one patient had angina ( during <span class="chemical">5 - FU</span> infusion ) . 