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: Moreover , enantioselectivity was demonstrated by the ability of natural PREGS to be an order of magnitude more effective than its synthetic enantiomer in reversing scopolamine - induced amnesia .
### Output Text:
Moreover , enantioselectivity was demonstrated by the ability of natural <span class="chemical">PREGS</span> to be an order of magnitude more effective than its synthetic enantiomer in reversing <span class="chemical">scopolamine</span> - induced amnesia . 