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: The mechanism for this reaction is believed to be increased levels of vasoactive catecholamines due to interference of their physiologic inactivation by Imipramine .
### Output Text:
The mechanism for this reaction is believed to be increased levels of vasoactive <span class="chemical">catecholamines</span> due to interference of their physiologic inactivation by <span class="chemical">Imipramine</span> . 