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: Both PREGS and its ( - ) enantiomer blocked the effects of scopolamine .
### Output Text:
Both <span class="chemical">PREGS</span> and its ( - ) enantiomer blocked the effects of <span class="chemical">scopolamine</span> . 