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: Four patients with rheumatoid arthritis developed heavy proteinuria after five to 12 months of treatment with D - penicillamine .
### Output Text:
Four patients with rheumatoid arthritis developed heavy proteinuria after five to 12 months of treatment with <span class="chemical">D - penicillamine</span> . 