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: Reduced cardiotoxicity of doxorubicin given in the form of N - ( 2 - hydroxypropyl ) methacrylamide conjugates : and experimental study in the rat .
### Output Text:
Reduced cardiotoxicity of <span class="chemical">doxorubicin</span> given in the form of <span class="chemical">N - ( 2 - hydroxypropyl ) methacrylamide</span> conjugates : and experimental study in the rat . 