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: Recent preclinical and clinical studies with the thymidylate synthase inhibitor N10 - propargyl - 5 , 8 - dideazafolic acid ( CB 3717 ) .
### Output Text:
Recent preclinical and clinical studies with the thymidylate synthase inhibitor <span class="chemical">N10 - propargyl - 5 , 8 - dideazafolic acid</span> ( <span class="chemical">CB 3717</span> ) . 