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: Pemoline has not been commonly associated in the literature as a cause of acute movement disorders .
### Output Text:
<span class="chemical">Pemoline</span> has not been commonly associated in the literature as a cause of acute movement disorders . 