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: Four compounds known to increase QT interval and cause TDP were investigated : terfenadine , terodiline , cisapride and E4031 .
### Output Text:
Four compounds known to increase QT interval and cause TDP were investigated : <span class="chemical">terfenadine</span> , <span class="chemical">terodiline</span> , <span class="chemical">cisapride</span> and <span class="chemical">E4031</span> . 