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: On the antiarrhythmic activity of one N - substituted piperazine derivative of trans - 2 - amino - 3 - hydroxy - 1 , 2 , 3 , 4 - tetrahydroanaphthalene .
### Output Text:
On the antiarrhythmic activity of one N - substituted <span class="chemical">piperazine</span> derivative of <span class="chemical">trans - 2 - amino - 3 - hydroxy - 1 , 2 , 3 , 4 - tetrahydroanaphthalene</span> . 