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: RESULTS : None of the drugs enhanced LES , whereas mCPP increased percentage FPS and yohimbine increased absolute FPS values .
### Output Text:
RESULTS : None of the drugs enhanced LES , whereas <span class="chemical">mCPP</span> increased percentage FPS and <span class="chemical">yohimbine</span> increased absolute FPS values . 