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 studies have focused on the intracellular formation of CB 3717 polyglutamates .
### Output Text:
Recent preclinical studies have focused on the intracellular formation of <span class="chemical">CB 3717</span> polyglutamates . 