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: Pentoxifylline ( Trental ) does not inhibit dipyridamole - induced coronary hyperemia : implications for dipyridamole - thallium - 201 myocardial imaging .
### Output Text:
<span class="chemical">Pentoxifylline</span> ( <span class="chemical">Trental</span> ) does not inhibit <span class="chemical">dipyridamole</span> - induced coronary hyperemia : implications for <span class="chemical">dipyridamole</span> - <span class="chemical">thallium</span> - 201 myocardial imaging . 