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: OBJECTIVE : To report 2 cases of ticlopidine - induced cholestatic hepatitis , investigate its mechanism , and compare the observed main characteristics with those of the published cases .
### Output Text:
OBJECTIVE : To report 2 cases of <span class="chemical">ticlopidine</span> - induced cholestatic hepatitis , investigate its mechanism , and compare the observed main characteristics with those of the published cases . 