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: Furthermore , KF17837 may be a useful drug in the treatment of parkinsonism .
### Output Text:
Furthermore , <span class="chemical">KF17837</span> may be a useful drug in the treatment of parkinsonism . 