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: A patient who received antithymocyte globulin therapy for aplastic anemia due to D - penicillamine therapy is described .
### Output Text:
A patient who received <span class="chemical">antithymocyte globulin</span> therapy for aplastic anemia due to <span class="chemical">D - penicillamine</span> therapy is described . 