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: Helodermin produced hypotension in a dose - dependent manner with approximately similar potency and duration to VIP .
### Output Text:
<span class="chemical">Helodermin</span> produced hypotension in a dose - dependent manner with approximately similar potency and duration to VIP . 