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: Because folinic acid was unlikely to be associated with this condition , neurotoxicity due to high - dose 5 - fluorouracil was highly suspected .
### Output Text:
Because <span class="chemical">folinic acid</span> was unlikely to be associated with this condition , neurotoxicity due to high - dose <span class="chemical">5 - fluorouracil</span> was highly suspected . 