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: GYKI - 41 900 has a negligible cardiodepressant activity ; it is not cardioselective .
### Output Text:
<span class="chemical">GYKI - 41 900</span> has a negligible cardiodepressant activity ; it is not cardioselective . 