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: CAA but not acrolein inhibited the cysteine proteases caspase - 3 , caspase - 8 and cathepsin B .
### Output Text:
<span class="chemical">CAA</span> but not <span class="chemical">acrolein</span> inhibited the <span class="chemical">cysteine</span> proteases caspase - 3 , caspase - 8 and cathepsin B . 