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: Polymyositis / dermatomyositis can develop as one of the autoimmune complications of D - penicillamine treatment , but its exact pathogenesis remains unclear .
### Output Text:
Polymyositis / dermatomyositis can develop as one of the autoimmune complications of <span class="chemical">D - penicillamine</span> treatment , but its exact pathogenesis remains unclear . 