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 31 - year - old man with rheumatoid arthritis , who had previously been treated with sulindac , fenoprofen calcium , high dose salicylates and gold salts , developed renal papillary necrosis ( RPN ) 4 months after institution of naproxen therapy .
### Output Text:
A 31 - year - old man with rheumatoid arthritis , who had previously been treated with <span class="chemical">sulindac</span> , <span class="chemical">fenoprofen calcium</span> , high dose <span class="chemical">salicylates</span> and <span class="chemical">gold</span> salts , developed renal papillary necrosis ( RPN ) 4 months after institution of <span class="chemical">naproxen</span> therapy . 