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: Dyskinetic patients tended to have a greater OPSE than nondyskinetic ( Dunnett , P = 0 . 06 ) .
### Output Text:
Dyskinetic patients tended to have a greater OPSE than nondyskinetic ( Dunnett , P = 0 . 06 ) . 