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: Recently , a number of commercial lots of heparin products were found to be contaminated with an oversulfated chondroitin sulfate ( OSCS ) derivative that could elicit a hypotensive response in pigs following a single high - dose infusion .
### Output Text:
Recently , a number of commercial lots of <span class="chemical">heparin</span> products were found to be contaminated with an oversulfated <span class="chemical">chondroitin sulfate</span> ( OSCS ) derivative that could elicit a hypotensive response in pigs following a single high - dose infusion . 