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: Compared to healthy controls a lower DR5 frequency was observed in patients with RA except for the Tiopronin related nephritis group .
### Output Text:
Compared to healthy controls a lower DR5 frequency was observed in patients with RA except for the <span class="chemical">Tiopronin</span> related nephritis group . 