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: The corresponding epimers with the 3 - hydroxy group in the beta - position were also effective but less potent ( ED50 values , 33 . 8 - 63 . 5 , i . p . ) .
### Output Text:
The corresponding epimers with the 3 - hydroxy group in the beta - position were also effective but less potent ( ED50 values , 33 . 8 - 63 . 5 , i . p . ) . 